Elan Library Reference

# Value data Types

## Integer

An integer is a whole number, i.e. one that has no fractional part. It may be represented in decimal, hexadecimal or binary:

100 (decimal), 0x64 (hexadecimal) and 0b1100100 all have the same value.

Its type is `IntintintIntegerint`.

name of Type | examples of defining a literal value
--- | ---
`IntintintIntegerint` | `+constant maxNumbername? set to 10literal value or data structure?1+maxNumbername? = 10literal value or data structure? # constant1+const Int maxNumbername? = 10literal value or data structure?;1+Const maxNumbername? = 10literal value or data structure?1 public class Global { +final Int maxNumbername? = 10literal value or data structure?; // constant1 }`
`IntintintIntegerint` | `variable flagsname? set to 0b1100100value or expression?0flagsname? = 0b1100100value or expression? # variable definition0var flagsname? = 0b1100100value or expression?;0Dim flagsname? = &B1100100value or expression? ' variable definition0var flagsname? = 0b1100100value or expression?;0`

### Function dot methods on an `IntintintIntegerint`

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
asBinary | (none) | `StringstrstringStringString` | string of binary digits representing the argument's integer value
equals | `IntintintIntegerint` | `BooleanboolboolBooleanbool` | true if integer and argument values are equal – false otherwise
notEqualTo | `IntintintIntegerint` | `BooleanboolboolBooleanbool` | true if integer and argument values are unequal – false otherwise
toString | (none) | `StringstrstringStringString` | a string of decimal digits representing the argument's integer value

#### Notes

- A literal integer or a named value of type `IntintintIntegerint` may always be passed into a function or procedure that is expecting a `FloatfloatdoubleDoubledouble`.
- The `IntintintIntegerint` type is intended to represent whole numbers in the range:
- - Maximum: 253 − 1 (which is 9,007,199,254,740,991)
  - Minimum value: −(253 − 1)
- If you go greater than the limit given above, the number will be accurate to approximately 17 decimal digits. Larger numbers will be rounded with zeros at the end, unless they are larger than around 270, when they will automatically be shown in exponential (scientific) format, as shown in the example.

#### Example of large numbers

● This code calculates 2 raised to the power of 50 through 72, and its output is shown below:

+main 1 +for n item? in range(50, 73)source? 2 variable np name? set to pow(2, n).floor()value or expression?3 call printTab procedureName?(n.toString().length(), $"{n}"arguments?)4 call printTab procedureName?(30 - np.toString().length(), $"{np}\n"arguments?)5 end for end main
+def main() -> None: 1 +for n item? in range(50, 73)source?: 2 np name? = pow(2, n).floor()value or expression? # variable definition 3 printTab procedureName?(n.toString().length(), f"{n}"arguments?) # call procedure 4 printTab procedureName?(30 - np.toString().length(), f"{np}\n"arguments?) # call procedure 5 main()
+static void main() { 1 +foreach (n item? in range(50, 73)source?) { 2 var np name? = pow(2, n).floor()value or expression?;3 printTab procedureName?(n.toString().length(), $"{n}"arguments?); // call procedure 4 printTab procedureName?(30 - np.toString().length(), $"{np}\n"arguments?); // call procedure 5 } // foreach } // main
+Sub main() 1 +For Each n item? In range(50, 73)source? 2 Dim np name? = pow(2, n).floor()value or expression? ' variable definition 3 printTab procedureName?(n.toString().length(), $"{n}"arguments?) ' call procedure 4 printTab procedureName?(30 - np.toString().length(), $"{np}\n"arguments?) ' call procedure 5 Next n End Sub
public class Global {
+static void main() { 1 +foreach (n item? in range(50, 73)source?) { 2 var np name? = pow(2, n).floor()value or expression?;3 printTab procedureName?(n.toString().length(), String.format("%", n)arguments?); // call procedure 4 printTab procedureName?(30 - np.toString().length(), String.format("%\n", np)arguments?); // call procedure 5 } // foreach } // main
}

## Floating point

A floating point number is a decimal number (also known as a Real number) that may have both integer and fractional parts.

It may be written using exponential (scientific) notation, e.g. 120.0 can be written as 1.20e2, and 0.012 as 1.20e-2

Its type is `FloatfloatdoubleDoubledouble`.

name of Type | examples of defining a literal value
--- | ---
`FloatfloatdoubleDoubledouble` | `+constant phiname? set to 1.618033988749895literal value or data structure?1+phiname? = 1.618033988749895literal value or data structure? # constant1+const Float phiname? = 1.618033988749895literal value or data structure?;1+Const phiname? = 1.618033988749895literal value or data structure?1 public class Global { +final Float phiname? = 1.618033988749895literal value or data structure?; // constant1 }`
`FloatfloatdoubleDoubledouble` | `variable readingname? set to 1.1e-10value or expression?0readingname? = 1.1e-10value or expression? # variable definition0var readingname? = 1.1e-10value or expression?;0Dim readingname? = 1.1e-10value or expression? ' variable definition0var readingname? = 1.1e-10value or expression?;0`

### Function dot methods on a `FloatfloatdoubleDoubledouble`

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
ceiling | (none) | `IntintintIntegerint` | the first integral value larger than or equal to the argument's floating point value
equals | `FloatfloatdoubleDoubledouble` | `BooleanboolboolBooleanbool` | true if floating point number and argument values are equal – false otherwise
floor | (none) | `IntintintIntegerint` | the first integral value smaller than or equal to the argument's floating point value
isInfinite | (none) | `BooleanboolboolBooleanbool` | true if value would be infinite, e.g. after division by zero – false otherwise
isNaN | (none) | `BooleanboolboolBooleanbool` | true if value is 'NaN', i.e. Not a Number, e.g. 0/0 – false otherwise
notEqualTo | `FloatfloatdoubleDoubledouble` | `BooleanboolboolBooleanbool` | true if floating point number and argument values are unequal – false otherwise
round | `IntintintIntegerint` | `FloatfloatdoubleDoubledouble` | the value rounded (up or down as appropriate) to the number of decimal places specified in the argument
toString | (none) | `StringstrstringStringString` | a string representing the argument's floating point value

#### Notes

- The limits on floating point numbers are:
  - Maximum value: just over 1.0 × 10308
  - Minimum value: approximately 5.0 × 10-324
- A variable that has been defined as being of type `FloatfloatdoubleDoubledouble` may not be passed as an argument into a method that requires an `IntintintIntegerint`, nor as an index into a `ListlistListListList` even if the variable contains no fractional part. It may, however, be converted into an `IntintintIntegerint` before passing, using the function floor or ceiling.
- If you wish to define a variable to be of type `FloatfloatdoubleDoubledouble`, but initialise it with an integer value, then add .0 on the end of the whole number, as in:
  `variable hourname? set to 3.0value or expression?0hourname? = 3.0value or expression? # variable definition0var hourname? = 3.0value or expression?;0Dim hourname? = 3.0value or expression? ' variable definition0var hourname? = 3.0value or expression?;0`
- Any variable or expression that evaluates to an `IntintintIntegerint` may always be used where a `FloatfloatdoubleDoubledouble` is expected.

#### Examples of standalone dot methods on a `FloatfloatdoubleDoubledouble`

● Test assertions using dot methods on a `FloatfloatdoubleDoubledouble`:

+test test_floor test_name? 1 variable p name? set to pi value or expression?2 variable mp name? set to -pi value or expression?3 assert p.floor()actual (computed) value? is 3 expected value? not run 4 assert mp.floor()actual (computed) value? is -4 expected value? not run 5 assert p.ceiling()actual (computed) value? is 4 expected value? not run 6 assert mp.ceiling()actual (computed) value? is -3 expected value? not run 7 assert p.round(3)actual (computed) value? is 3.142 expected value? not run 8 assert mp.round(2)actual (computed) value? is -3.14 expected value? not run 9 assert sqrt(-p).isNaN()actual (computed) value? is true expected value? not run 10 variable q name? set to divAsInt(1, 0).floor()value or expression?11 assert q.isInfinite()actual (computed) value? is true expected value? not run 12 end test
+def test_floor test_name?(self) -> None: 1 p name? = pi value or expression? # variable definition 2 mp name? = -pi value or expression? # variable definition 3 self.assertEqual(p.floor()actual (computed) value?, 3 expected value?) not run 4 self.assertEqual(mp.floor()actual (computed) value?, -4 expected value?) not run 5 self.assertEqual(p.ceiling()actual (computed) value?, 4 expected value?) not run 6 self.assertEqual(mp.ceiling()actual (computed) value?, -3 expected value?) not run 7 self.assertEqual(p.round(3)actual (computed) value?, 3.142 expected value?) not run 8 self.assertEqual(mp.round(2)actual (computed) value?, -3.14 expected value?) not run 9 self.assertEqual(sqrt(-p).isNaN()actual (computed) value?, True expected value?) not run 10 q name? = divAsInt(1, 0).floor()value or expression? # variable definition 11 self.assertEqual(q.isInfinite()actual (computed) value?, True expected value?) not run 12
+[TestMethod] static void test_floor test_name?() { 1 var p name? = pi value or expression?;2 var mp name? = -pi value or expression?;3 Assert.AreEqual(3 expected value?, p.floor()actual (computed) value?); not run 4 Assert.AreEqual(-4 expected value?, mp.floor()actual (computed) value?); not run 5 Assert.AreEqual(4 expected value?, p.ceiling()actual (computed) value?); not run 6 Assert.AreEqual(-3 expected value?, mp.ceiling()actual (computed) value?); not run 7 Assert.AreEqual(3.142 expected value?, p.round(3)actual (computed) value?); not run 8 Assert.AreEqual(-3.14 expected value?, mp.round(2)actual (computed) value?); not run 9 Assert.AreEqual(true expected value?, sqrt(-p).isNaN()actual (computed) value?); not run 10 var q name? = divAsInt(1, 0).floor()value or expression?;11 Assert.AreEqual(true expected value?, q.isInfinite()actual (computed) value?); not run 12 } // test
+<TestMethod> Sub test_floor test_name?() 1 Dim p name? = pi value or expression? ' variable definition 2 Dim mp name? = -pi value or expression? ' variable definition 3 Assert.AreEqual(3 expected value?, p.floor()actual (computed) value?) not run 4 Assert.AreEqual(-4 expected value?, mp.floor()actual (computed) value?) not run 5 Assert.AreEqual(4 expected value?, p.ceiling()actual (computed) value?) not run 6 Assert.AreEqual(-3 expected value?, mp.ceiling()actual (computed) value?) not run 7 Assert.AreEqual(3.142 expected value?, p.round(3)actual (computed) value?) not run 8 Assert.AreEqual(-3.14 expected value?, mp.round(2)actual (computed) value?) not run 9 Assert.AreEqual(True expected value?, sqrt(-p).isNaN()actual (computed) value?) not run 10 Dim q name? = divAsInt(1, 0).floor()value or expression? ' variable definition 11 Assert.AreEqual(True expected value?, q.isInfinite()actual (computed) value?) not run 12 End Sub
public class Global {
+@Test static void test_floor test_name?() { 1 var p name? = pi value or expression?;2 var mp name? = -pi value or expression?;3 assertEquals(3 expected value?, p.floor()actual (computed) value?); not run 4 assertEquals(-4 expected value?, mp.floor()actual (computed) value?); not run 5 assertEquals(4 expected value?, p.ceiling()actual (computed) value?); not run 6 assertEquals(-3 expected value?, mp.ceiling()actual (computed) value?); not run 7 assertEquals(3.142 expected value?, p.round(3)actual (computed) value?); not run 8 assertEquals(-3.14 expected value?, mp.round(2)actual (computed) value?); not run 9 assertEquals(true expected value?, sqrt(-p).isNaN()actual (computed) value?); not run 10 var q name? = divAsInt(1, 0).floor()value or expression?;11 assertEquals(true expected value?, q.isInfinite()actual (computed) value?); not run 12 } // test
}

## Boolean

A Boolean value is either true or false.

The words true and false must be written in lower case.

name of Type | examples of defining a literal value
--- | ---
`BooleanboolboolBooleanbool` | `variable donename? set to truevalue or expression?0donename? = Truevalue or expression? # variable definition0var donename? = truevalue or expression?;0Dim donename? = Truevalue or expression? ' variable definition0var donename? = truevalue or expression?;0`

### Function dot methods on a `BooleanboolboolBooleanbool`

function dot methods | argument Types | return Type | returns
--- | --- | --- | ---
equals | `BooleanboolboolBooleanbool` | `BooleanboolboolBooleanbool` | true if the truth value and argument are equal – false otherwise
notEqualTo | `BooleanboolboolBooleanbool` | `BooleanboolboolBooleanbool` | true if the truth value and argument are unequal – false otherwise
toString | (none) | `StringstrstringStringString` | String "true" if true, "false" if false

# Reference data Types

## String

A `StringstrstringStringString` represents text, i.e. a sequence of zero or more characters.

name of Type | examples of defining a literal value | details
--- | --- | ---
`StringstrstringStringString` | `+constant titlename? set to "Ulysses"literal value or data structure?1+titlename? = "Ulysses"literal value or data structure? # constant1+const String titlename? = "Ulysses"literal value or data structure?;1+Const titlename? = "Ulysses"literal value or data structure?1 public class Global { +final String titlename? = "Ulysses"literal value or data structure?; // constant1 }` | delimited by double quotes
`StringstrstringStringString` | `variable quotename? set to "'Hello', she said"value or expression?0quotename? = "'Hello', she said"value or expression? # variable definition0var quotename? = "'Hello', she said"value or expression?;0Dim quotename? = "'Hello', she said"value or expression? ' variable definition0var quotename? = "'Hello', she said"value or expression?;0` | ' may be used in a string delimited by "
`StringstrstringStringString` | `variable emptyStringname? set to ""value or expression?0emptyStringname? = ""value or expression? # variable definition0var emptyStringname? = ""value or expression?;0Dim emptyStringname? = ""value or expression? ' variable definition0var emptyStringname? = ""value or expression?;0` | a zero-length, or 'empty', string

### Character sets

When typing from the keyboard into a literal string all the basic ASCII characters (0x20 to 0x7e) and '£' can be input.

You cannot use Alt+numeric-keypad to enter accented letters or other special characters in the extended ASCII range (0x80 to 0xff).

You can, however, copy any text from outside Elan and paste it into a string, whether ASCII, extended ASCII or UTF-8 encoded.

To insert a character from the full range, you use its Unicode (codepoint) value, in decimal or hexadecimal, by means of function unicode :

print($"Spanish introduces a question with {unicode(191)}"arguments?)0 print(f"Spanish introduces a question with {unicode(191)}"arguments?)0 Console.WriteLine($"Spanish introduces a question with {unicode(191)}"arguments?); // print 0 Console.WriteLine($"Spanish introduces a question with {unicode(191)}"arguments?) ' print 0 System.out.println(String.format("Spanish introduces a question with %", unicode(191))arguments?); // print 0 | ⟶ | Spanish introduces a question with ¿
print($"This is an up arrow: {unicode(0x2191)}"arguments?)0 print(f"This is an up arrow: {unicode(0x2191)}"arguments?)0 Console.WriteLine($"This is an up arrow: {unicode(0x2191)}"arguments?); // print 0 Console.WriteLine($"This is an up arrow: {unicode(&H2191)}"arguments?) ' print 0 System.out.println(String.format("This is an up arrow: %", unicode(0x2191))arguments?); // print 0 | ⟶ | This is an up arrow: ↑

These examples 'interpolate' the output of function unicode by using a $ before the string and curly braces within it (see Interpolated fields ).

### Manipulating strings

Strings can be built from other strings by concatenation using the plus operator, for example:

`print("Hello " + "world"arguments?)0print("Hello " + "world"arguments?)0Console.WriteLine("Hello " + "world"arguments?); // print0Console.WriteLine("Hello " + "world"arguments?) ' print0System.out.println("Hello " + "world"arguments?); // print0` | ⟶ | Hello world

A newline may be inserted within a string with \n:

`print("Hello\nworld"arguments?)0print("Hello\nworld"arguments?)0Console.WriteLine("Hello\nworld"arguments?); // print0Console.WriteLine("Hello\nworld"arguments?) ' print0System.out.println("Hello\nworld"arguments?); // print0` | ⟶ | Hello world

When editing and you leave the field, the newline will be implicitly applied in your code.

As in most languages, strings are immutable. When you apply any operation or function with the intent of modifying an existing `StringstrstringStringString`, the existing `StringstrstringStringString` is never changed. Instead, the operation or function will return a new `StringstrstringStringString` that is based on the original, but with the specified differences.

You can loop through a `StringstrstringStringString` picking each of its characters sequentially using the for loop .

### Function dot methods on a String

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
asRegExp | (none) | `RegExpRegExpRegExpRegExpRegExp` | a new string that is a a converted to a regular expression: no check is made of whether the result is a valid regular expression
asUnicode | (none) | `IntintintIntegerint` | the Unicode value of the first character of the string (To convert a Unicode value into a string, use function unicode )
contains | (none) | `BooleanboolboolBooleanbool` | true if the string contains the substring specified as the argument – false otherwise
equals | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if the string and argument are equal – false otherwise
notEqualTo | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if the string and argument are unequal – false otherwise
indexOf | `StringstrstringStringString` | `IntintintIntegerint` | index of the first instance of the argument (substring) within the string If it is not present, -1 is returned
isAfter | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if alphabetic comparison finds the string comes strictly 'after' the argument string – false otherwise
isAfterOrSameAs | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if alphabetic comparison finds the string comes 'after' or equals the argument string – false otherwise
isBefore | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if alphabetic comparison finds the string comes strictly 'before' the argument string – false otherwise
isBeforeOrSameAs | `StringstrstringStringString` | `BooleanboolboolBooleanbool` | true if alphabetic comparison finds the string comes 'before' or equals the argument string – false otherwise
length | (none) | `IntintintIntegerint` | the number of characters in the string
lowerCase | (none) | `StringstrstringStringString` | a new string with the original rendered in lower case
matchesRegExp | `RegExpRegExpRegExpRegExpRegExp` | `BooleanboolboolBooleanbool` | true if the string matches the regular expression – false otherwise
replace | `StringstrstringStringString`, `StringstrstringStringString` | `StringstrstringStringString` | a new string with all occurrences of the first argument string replaced by the second argument string
split | `StringstrstringStringString` | List<of String> list[str] List<string> List(Of String) List<String> | a `ListlistListListList` of the substrings found between occurrences of the argument string if the argument is the empty string then the list is of all the individual characters
subString | `IntintintIntegerint`, `IntintintIntegerint` | `StringstrstringStringString` | a new string that is the substring specified by the two positive integers (m,n) where m indexes the first character of the substring required (counting from 0) and n indexes the character after the last character required (exclusive index) if m ≥ n the result is the empty string
toString | (none) | `StringstrstringStringString` | the string itself
trim | (none) | `StringstrstringStringString` | a new string with leading and trailing spaces removed
upperCase | (none) | `StringstrstringStringString` | a new string with the original rendered in upper case

### Interpolated fields in strings

Strings support interpolation, that is you can insert the values of variables or simple expressions within the string by enclosing them in curly braces and prefixing the string with a $:

If `aaaaa` and `bbbbb` have values 3 and 17:

print($"{a} times {b} equals {a*b}"arguments?)0 print(f"{a} times {b} equals {a*b}"arguments?)0 Console.WriteLine($"{a} times {b} equals {a*b}"arguments?); // print 0 Console.WriteLine($"{a} times {b} equals {a*b}"arguments?) ' print 0 System.out.println(String.format("% times % equals %", a, b, a*b)arguments?); // print 0 | ⟶ | 3 times 17 equals 51

If `velocityvelocityvelocityvelocityvelocity` and `fuelfuelfuelfuelfuel` have values 3.0 and 50.4:

reassign message variableName? to $"LANDED SAFELY AT SPEED {(velocity*100).floor()} FUEL {fuel.floor()}"value or expression?0 message variableName? = f"LANDED SAFELY AT SPEED {(velocity*100).floor()} FUEL {fuel.floor()}"value or expression? # reassign variable 0 message variableName? = $"LANDED SAFELY AT SPEED {(velocity*100).floor()} FUEL {fuel.floor()}"value or expression?; // reassign variable 0 message variableName? = $"LANDED SAFELY AT SPEED {(velocity*100).floor()} FUEL {fuel.floor()}"value or expression? ' reassign variable 0 message variableName? = String.format("LANDED SAFELY AT SPEED % FUEL %", (velocity*100).floor(), fuel.floor())value or expression?; // reassign variable 0 print(message arguments?)0 print(message arguments?)0 Console.WriteLine(message arguments?); // print 0 Console.WriteLine(message arguments?) ' print 0 System.out.println(message arguments?); // print 0 | ⟶ | LANDED SAFELY AT SPEED 300 FUEL 50

And for the area of a circle:

+main 1 variable r name? set to 2.0 value or expression?2 print($"area = {(pi*r*r).round(2)}"arguments?)3 end main +def main() -> None: 1 r name? = 2.0 value or expression? # variable definition 2 print(f"area = {(pi*r*r).round(2)}"arguments?)3 main() +static void main() { 1 var r name? = 2.0 value or expression?;2 Console.WriteLine($"area = {(pi*r*r).round(2)}"arguments?); // print 3 } // main +Sub main() 1 Dim r name? = 2.0 value or expression? ' variable definition 2 Console.WriteLine($"area = {(pi*r*r).round(2)}"arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var r name? = 2.0 value or expression?;2 System.out.println(String.format("area = %", (pi*r*r).round(2))arguments?); // print 3 } // main } | ⟶ | area = 12.57

## Standard data structures

Elan has two mutable data structure Types `ListlistListListList` and `DictionaryDictionaryDictionaryDictionaryDictionary`, and three immutable data structure Types `HashSetHashSetHashSetHashSetHashSet`, `StackStackStackStackStack` and `QueueQueueQueueQueueQueue`.

The contents of these structures are referred to as items (or sometimes elements).

The values of items in a mutable structure may be changed directly by calling the various procedure dot methods defined for each structure Type.

The values of items in an immutable structure cannot be changed directly, and so have no procedure dot methods defined for them: rather, the methods called on them create new copies of the structures containing specified changes.

Since procedure methods may be called only from within the main routine or a procedure, it is also possible to make changes via function dot methods, which return a copy of the data structure with specified changes: that is why all such methods have names starting 'with'.

Immutable data structures are intended specifically to facilitate the Functional Programming paradigm, but some are also useful within other programming paradigms.

All six contain values (and keys in the case of a `DictionaryDictionaryDictionaryDictionaryDictionary`) of only a single Type, that type being specified either explicitly (as in <of `IntintintIntegerint`>), or implicitly if the structure is created using a literal definition.

This table summarises the creation and reference to these structures. Details of their methods follow.

| List | Dictionary | HashSet | Stack | Queue
--- | --- | --- | --- | --- | ---
mutability | Mutable | Mutable | Immutable | Immutable | Immutable
Type form | `ListlistListListList`<of Type> Type of item can be any, including `ListlistListListList` for 'jagged' data | `DictionaryDictionaryDictionaryDictionaryDictionary`<of keyType, valueType> keyType is `IntintintIntegerint`, `FloatfloatdoubleDoubledouble`, `StringstrstringStringString` or `BooleanboolboolBooleanbool` valueType may be any Type | `HashSetHashSetHashSetHashSetHashSet`<of Type> Type of item must be immutable | `StackStackStackStackStack`<of Type> Type of item must be immutable | `QueueQueueQueueQueueQueue`<of Type> Type of item must be immutable
size | Dynamic | Dynamic | Dynamic | Dynamic | Dynamic
literal definition | `[2, 3, 5, 7, 11][2, 3, 5, 7, 11][2, 3, 5, 7, 11]{2, 3, 5, 7, 11}[2, 3, 5, 7, 11]` | `["a":3, "b":5]["a":3, "b":5]["a":3, "b":5]["a":3, "b":5]["a":3, "b":5]` | Only as converted from a literal `ListlistListListList` e.g. `["a", "b", "c"].asSet()["a", "b", "c"].asSet()["a", "b", "c"].asSet(){"a", "b", "c"}.asSet()["a", "b", "c"].asSet()` | Not available | Not available
create empty | new `ListlistListListList`<of Type>() | new `DictionaryDictionaryDictionaryDictionaryDictionary`<of keyType, valueType>() | new `HashSetHashSetHashSetHashSetHashSet`<of Type>() | new `StackStackStackStackStack`<of Type>() | new `QueueQueueQueueQueueQueue`<of Type>()
create initialised | `createList(number, value)createList(number, value)createList(number, value)createList(number, value)createList(number, value)` `createListOfLists(cols, rows, value)createListOfLists(cols, rows, value)createListOfLists(cols, rows, value)createListOfLists(cols, rows, value)createListOfLists(cols, rows, value)` | Not available | Not available | Not available | Not available
read by index | `li[2]li[2]li[2]li[2]li[2]` | `d["b"]d["b"]d["b"]d["b"]d["b"]` | not available | not available | not available
read by index range | `li.subList(3, 5)li.subList(3, 5)li.subList(3, 5)li.subList(3, 5)li.subList(3, 5)` lower bound is inclusive from 0 upper bound is exclusive | not available | not available | not available | not available
procedure methods to mutate contents | see Procedure methods on a List  | see Procedure methods on a Dictionary  | not available | not available | not available
function dot methods | see Function dot methods on a List  | see Function dot methods on a Dictionary  | see Function dot methods on a Set  | see Function dot methods on a Stack  | see Function dot methods on a Queue 

## List

The `ListlistListListList` type defines a data structure containing n items of any single Type, including basic value Types, structure Types such as `ListlistListListList`, and user-defined Types such as a Class.

Items in a List of n items are indexed from 0 to n-1.

To create a List, use either of:

- Method createList  to define its length and the initial value (and implicitly the Type) of its items:
  `variable aListname? set to createList(10, "no one")value or expression?0aListname? = createList(10, "no one")value or expression? # variable definition0var aListname? = createList(10, "no one")value or expression?;0Dim aListname? = createList(10, "no one")value or expression? ' variable definition0var aListname? = createList(10, "no one")value or expression?;0`
- Define an empty List of the required type, and use the procedure methods listed below to populate it:
  variable aList name? set to new List<of String>()value or expression?0
  aList name? = list[str]()value or expression? # variable definition 0
  var aList name? = new List<string>()value or expression?;0
  Dim aList name? = New List(Of String)()value or expression? ' variable definition 0
  var aList name? = new List<String>()value or expression?;0
  `call aList.initialiseprocedureName?(10, "no one"arguments?)0aList.initialiseprocedureName?(10, "no one"arguments?) # call procedure0aList.initialiseprocedureName?(10, "no one"arguments?); // call procedure0aList.initialiseprocedureName?(10, "no one"arguments?) ' call procedure0aList.initialiseprocedureName?(10, "no one"arguments?); // call procedure0`
  `call aList.appendprocedureName?("4"arguments?)0aList.appendprocedureName?("4"arguments?) # call procedure0aList.appendprocedureName?("4"arguments?); // call procedure0aList.appendprocedureName?("4"arguments?) ' call procedure0aList.appendprocedureName?("4"arguments?); // call procedure0`

The item at index ix in List aList can then be changed using a reassign variable instruction and a valid index value in square brackets:

- `reassign aList[ix]variableName? to "Smith"value or expression?0aList[ix]variableName? = "Smith"value or expression? # reassign variable0aList[ix]variableName? = "Smith"value or expression?; // reassign variable0aList[ix]variableName? = "Smith"value or expression? ' reassign variable0aList[ix]variableName? = "Smith"value or expression?; // reassign variable0`

A List's size can be dynamically changed using the procedure methods listed below.

### Deconstructing a List

A `ListlistListListList` may be split (deconstructed) into new named values using indexes and the methods head, tail  and subList :

- To extract the first item in a List:
  `variable headItemname? set to myList[0]value or expression?0headItemname? = myList[0]value or expression? # variable definition0var headItemname? = myList[0]value or expression?;0Dim headItemname? = myList[0]value or expression? ' variable definition0var headItemname? = myList[0]value or expression?;0`
  or
  `reassign heatItemvariableName? to myList.head()value or expression?0heatItemvariableName? = myList.head()value or expression? # reassign variable0heatItemvariableName? = myList.head()value or expression?; // reassign variable0heatItemvariableName? = myList.head()value or expression? ' reassign variable0heatItemvariableName? = myList.head()value or expression?; // reassign variable0`
- To form a new List of all but the first item in a List:
  `variable tailListname? set to myList.tail()value or expression?0tailListname? = myList.tail()value or expression? # variable definition0var tailListname? = myList.tail()value or expression?;0Dim tailListname? = myList.tail()value or expression? ' variable definition0var tailListname? = myList.tail()value or expression?;0`
  If the original list contains only one item, the new List will be the empty List.
- To get some other portion of a List, use the method subList:
  `reassign shortListvariableName? to myList.subList(1, 5)value or expression?0shortListvariableName? = myList.subList(1, 5)value or expression? # reassign variable0shortListvariableName? = myList.subList(1, 5)value or expression?; // reassign variable0shortListvariableName? = myList.subList(1, 5)value or expression? ' reassign variable0shortListvariableName? = myList.subList(1, 5)value or expression?; // reassign variable0`

In all these cases the items indexed must exist, else a runtime error will stop the program.

### Lists of lists

#### Two dimensional arrays

Understood as a grid, a 2D array is a List of 'columns' each of which is a List of 'row' items, i.e. it is a List of Lists in which the column number is the x coordinate, and the row number is the y coordinate.

To create a 2D array that holds a value of a single type in every cell, you define such a List of Lists thus:

- Use method createListOfLists  to set the size of, and initial value in, every x,y position:
  `variable array2Dname? set to createListOfLists(cols, rows, value)value or expression?0array2Dname? = createListOfLists(cols, rows, value)value or expression? # variable definition0var array2Dname? = createListOfLists(cols, rows, value)value or expression?;0Dim array2Dname? = createListOfLists(cols, rows, value)value or expression? ' variable definition0var array2Dname? = createListOfLists(cols, rows, value)value or expression?;0`
- For the special case of Block graphics , use 40 columns and 30 rows or (more simply):
  `variable gridname? set to createBlockGraphics(value)value or expression?0gridname? = createBlockGraphics(value)value or expression? # variable definition0var gridname? = createBlockGraphics(value)value or expression?;0Dim gridname? = createBlockGraphics(value)value or expression? ' variable definition0var gridname? = createBlockGraphics(value)value or expression?;0`

The item at index ix,iy in a 2D array can be accessed and changed using its two coordinates in square brackets:

- `variable valuename? set to array2D[ix][iy]value or expression?0valuename? = array2D[ix][iy]value or expression? # variable definition0var valuename? = array2D[ix][iy]value or expression?;0Dim valuename? = array2D[ix][iy]value or expression? ' variable definition0var valuename? = array2D[ix][iy]value or expression?;0`
- `reassign array2D[ix][iy]variableName? to 7value or expression?0array2D[ix][iy]variableName? = 7value or expression? # reassign variable0array2D[ix][iy]variableName? = 7value or expression?; // reassign variable0array2D[ix][iy]variableName? = 7value or expression? ' reassign variable0array2D[ix][iy]variableName? = 7value or expression?; // reassign variable0`

#### Higher dimensional arrays

For a 3D array, you can, for example, define:

- `variable array3Dname? set to new List<of List<of List<of Float>>>()value or expression?0array3Dname? = list[list[list[float]]]()value or expression? # variable definition0var array3Dname? = new List<List<List<double>>>()value or expression?;0Dim array3Dname? = New List(Of List(Of List(Of Double)))()value or expression? ' variable definition0var array3Dname? = new List<List<List<double>>>()value or expression?;0`

and refer to a cell using three indexes in square brackets.

### Procedure methods on a `ListlistListListList`

Where an argument provides a new value for an item in a List, that value must be of the same type as defined for the List's items.

procedure method | arguments | action
--- | --- | ---
append | value of `ListlistListListList` item's Type | the item is added to the end of the List
appendList | `ListlistListListList` | the argument List is added to the end of the List
initialise | `IntintintIntegerint`, value of `ListlistListListList` item's Type | specify the number (> 0) of items in the List, and an initial value for every item. May be called at any time to redefine the List's size and initial values.
insert | `IntintintIntegerint`, value of `ListlistListListList` item's Type | the item is inserted at the index given. If the index is negative it is counted from the end If the index is greater than the list's length, the item is inserted at the end
prepend | value of `ListlistListListList` item's Type | the item is is added to the start of the List
prependList | `ListlistListListList` | the argument List is added to the start of the List
removeAll | value of `ListlistListListList` item's Type | delete all items equal to the given item
removeAt | `IntintintIntegerint` | delete the item at the argument index
removeFirst | value of `ListlistListListList` item's Type | delete the first item equal to the given value

### Function dot methods on a `ListlistListListList`

function dot method | arguments | return Type | returns
--- | --- | --- | ---
asSet | (none) | `HashSetHashSetHashSetHashSetHashSet` | a new Set containing all the unique items in the List
contains | value | `BooleanboolboolBooleanbool` | true if the List contains the specified item – false otherwise
equals | `ListlistListListList` | `BooleanboolboolBooleanbool` | true if list and argument are identical – false otherwise
filter | `lambdalambdalambdalambdalambda` | `ListlistListListList` | a new List obtained from applying a lambda to the input List see filter  in HoFs 
head | (none) | `ListlistListListList` item's Type | the first item of the List (i.e. index = 0, which must exist)
indexOf | value of `ListlistListListList` item's Type | `IntintintIntegerint` | the index of the first occurrence of the argument value in the List, or -1 if no match is found
join | `List<of String>list[str]List<string>List(Of String)List<String>` | `StringstrstringStringString` | a single String that joins all the items in the list, with the specified String (which can be empty) inserted between the items
length | (none) | `IntintintIntegerint` | the number of items in the List
map | `lambdalambdalambdalambdalambda` | `ListlistListListList` | a new List obtained from applying a lambda to the input List see map  in HoFs 
maxBy | `lambdalambdalambdalambdalambda` | `ListlistListListList` item's Type | the list item corresponding to the maximum of the values returned by a lambda see maxBy  in HoFs 
minBy | `lambdalambdalambdalambdalambda` | `ListlistListListList` item's Type | the list item corresponding to the minimum of the values returned by a lambda see minBy  in HoFs 
notEqualTo | `ListlistListListList` | `BooleanboolboolBooleanbool` | true if list and argument differ l – false otherwise
orderBy | `lambdalambdalambdalambdalambda` | `ListlistListListList` | a new list with the items ordered according to the value returned by a lambda
reduce | item of `ListlistListListList` item's Type, `lambdalambdalambdalambdalambda` | return type of lambda | the final value obtained by applying a lambda cumulatively to each item in the input List taking account of the first argument as an initial (and default return) value see reduce  in HoFs 
subList | `IntintintIntegerint`, `IntintintIntegerint` | `ListlistListListList` | a new list that contains the items specified by the two positive integers (m,n) where m indexes the first item of the list required (counting from 0) and n indexes the item after the last item required (exclusive index) if m ≥ n the result is the empty list
tail | (none) | `ListlistListListList` item's Type | all items except the first item in the List (i.e. index = 1..n, which must exist)
toString | (none) | `StringstrstringStringString` | a String that is a comma+space-separated list of the List's items, enclosed in square brackets
withAppend | item of `ListlistListListList` item's Type | `ListlistListListList` | a new List lengthened with the item added after the end
withAppendList | `ListlistListListList` of same Type | `ListlistListListList` | a new List lengthened by appending the given List
withInsert | `IntintintIntegerint`, value of `ListlistListListList` item's Type | `ListlistListListList` | a new List with the item inserted after the item at the given index position
withPrepend | value of `ListlistListListList` item's Type | `ListlistListListList` | a new List lengthened with the item added before the beginning
withPrependList | `ListlistListListList` of same Type | `ListlistListListList` | a new List lengthened by prepending the given List
withRemoveAll | value of `ListlistListListList` item's Type | `ListlistListListList` | a new List with items equal to the given item removed
withRemoveAt | `IntintintIntegerint` | `ListlistListListList` | a new List with the item at the given index removed
withRemoveFirst | value of `ListlistListListList` item's Type | `ListlistListListList` | a new List with the first item equal to the given item removed
withSet | `IntintintIntegerint`, value of `ListlistListListList` item's Type | `ListlistListListList` | a new List with the item replacing that at the given index

## Dictionary

A `DictionaryDictionaryDictionaryDictionaryDictionary` is like a List whose items are pairs but, instead of having a numeric index, each item has a key plus an associated value, i.e. a Dictionary is a set of key:value pairs.

The key's type must be one of `IntintintIntegerint`, `FloatfloatdoubleDoubledouble`, `StringstrstringStringString` or `BooleanboolboolBooleanbool`. The values may be of any Type. The Types of both keys and values are fixed when the Dictionary is created.

You refer to a dictionary item using one of its (unique) keys:

+main 1 variable di1 name? set to ["alpha":1, "beta":2, "gamma":3]value or expression?2 print(di1["beta"]arguments?)3 variable di2 name? set to [1:"alpha", 2:"beta", 3:"gamma"]value or expression?4 print(di2[3]arguments?)5 end main +def main() -> None: 1 di1 name? = ["alpha":1, "beta":2, "gamma":3]value or expression? # variable definition 2 print(di1["beta"]arguments?)3 di2 name? = [1:"alpha", 2:"beta", 3:"gamma"]value or expression? # variable definition 4 print(di2[3]arguments?)5 main() +static void main() { 1 var di1 name? = ["alpha":1, "beta":2, "gamma":3]value or expression?;2 Console.WriteLine(di1["beta"]arguments?); // print 3 var di2 name? = [1:"alpha", 2:"beta", 3:"gamma"]value or expression?;4 Console.WriteLine(di2[3]arguments?); // print 5 } // main +Sub main() 1 Dim di1 name? = ["alpha":1, "beta":2, "gamma":3]value or expression? ' variable definition 2 Console.WriteLine(di1["beta"]arguments?) ' print 3 Dim di2 name? = [1:"alpha", 2:"beta", 3:"gamma"]value or expression? ' variable definition 4 Console.WriteLine(di2[3]arguments?) ' print 5 End Sub public class Global { +static void main() { 1 var di1 name? = ["alpha":1, "beta":2, "gamma":3]value or expression?;2 System.out.println(di1["beta"]arguments?); // print 3 var di2 name? = [1:"alpha", 2:"beta", 3:"gamma"]value or expression?;4 System.out.println(di2[3]arguments?); // print 5 } // main } | ⟶ ⟶ | 2 gamma

### Procedure method on a `DictionaryDictionaryDictionaryDictionaryDictionary`

procedure method | argument Types | action
--- | --- | ---
removeAt | key's Type | delete the key:pair at the given key (if it exists)

### Function dot methods on a `DictionaryDictionaryDictionaryDictionaryDictionary`

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
equals | `DictionaryDictionaryDictionaryDictionaryDictionary` | `BooleanboolboolBooleanbool` | true if dictionary and argument are identical – false otherwise
hasKey | item of Dictionary key's Type | `BooleanboolboolBooleanbool` | true if the Dictionary contains the given key – false otherwise
keys | (none) | `ListlistListListList` | a List containing the keys
notEqualTo | `DictionaryDictionaryDictionaryDictionaryDictionary` | `BooleanboolboolBooleanbool` | true if dictionary and argument differ – false otherwise
toString | (none) | `StringstrstringStringString` | a string that is a comma+space-separated list of the Dictionary's key:value pairs, enclosed in square brackets
values | (none) | `ListlistListListList` | a List containing the values
withSet | item of Dictionary key's Type, item of Dictionary value's Type | `DictionaryDictionaryDictionaryDictionaryDictionary` | a new Dictionary with the value replacing what was at the specified key
withRemoveAt | item of Dictionary key's Type | `DictionaryDictionaryDictionaryDictionaryDictionary` | a new Dictionary with the key:value pair removed from the specified key

## HashSet

A `HashSetHashSetHashSetHashSetHashSet` (also referred to merely as a Set) is a standard data structure containing Set members, that works somewhat like a `ListlistListListList` with two important differences:

- The value of a `HashSetHashSetHashSetHashSetHashSet` member may appear only once: if a member being added to a Set has the same value as an existing member in the Set then the Set remains the same as before.
- The values in a `HashSetHashSetHashSetHashSetHashSet` are not indexed: two Sets with the same contents but defined in a different sequence, can still be compared correctly with methods equals and notEqualTo.
- There are no methods that modify an existing Set, but several (e.g. add and remove) return a new `HashSetHashSetHashSetHashSetHashSet` that is based on the original Set or Sets with specified differences.

This enables a Set to work like a mathematical set so that it is possible to perform standard set operations such as union and intersection.

When creating a `HashSetHashSetHashSetHashSetHashSet`, the type of its members must be specified in the form `HashSet<of String>HashSet[str]HashSet<string>HashSet(Of String)HashSet<String>`

You can add members: either individually with add, or many with addFromList. And you can create a new `HashSetHashSetHashSetHashSetHashSet` from an existing `ListlistListListList` by calling asSet on it.

Example of creating a Set from a literal List and changing its content:

variable st name? set to new HashSet<of Int>()value or expression?0 st name? = HashSet[int]()value or expression? # variable definition 0 var st name? = new HashSet<int>()value or expression?;0 Dim st name? = New HashSet(Of Integer)()value or expression? ' variable definition 0 var st name? = new HashSet<int>()value or expression?;0 | ⟶ | 3
reassign st variableName? to st.add(7)value or expression?0 st variableName? = st.add(7)value or expression? # reassign variable 0 st variableName? = st.add(7)value or expression?; // reassign variable 0 st variableName? = st.add(7)value or expression? ' reassign variable 0 st variableName? = st.add(7)value or expression?; // reassign variable 0 | ⟶ | 3
reassign st variableName? to st.remove(3)value or expression?0 st variableName? = st.remove(3)value or expression? # reassign variable 0 st variableName? = st.remove(3)value or expression?; // reassign variable 0 st variableName? = st.remove(3)value or expression? ' reassign variable 0 st variableName? = st.remove(3)value or expression?; // reassign variable 0 | ⟶ | 2
reassign st variableName? to st.remove(3)value or expression?0 st variableName? = st.remove(3)value or expression? # reassign variable 0 st variableName? = st.remove(3)value or expression?; // reassign variable 0 st variableName? = st.remove(3)value or expression? ' reassign variable 0 st variableName? = st.remove(3)value or expression?; // reassign variable 0 | ⟶ | 2
`print(starguments?)0print(starguments?)0Console.WriteLine(starguments?); // print0Console.WriteLine(starguments?) ' print0System.out.println(starguments?); // print0` | ⟶ | [5, 7]

### Function dot methods on a `HashSetHashSetHashSetHashSetHashSet`

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
add | value (of `HashSetHashSetHashSetHashSetHashSet` members' Type) | `HashSetHashSetHashSetHashSetHashSet` | a new Set extended with the item, provided it differs from all of the Set's current members
addFromList | `ListlistListListList` | `HashSetHashSetHashSetHashSetHashSet` | a new Set extended with those items from the List that are not already in the Set
asList | (none) | `ListlistListListList` | a List containing the Set's members as List items
contains | value (of `HashSetHashSetHashSetHashSetHashSet` members' Type) | `BooleanboolboolBooleanbool` | true if the Set contains the item – false otherwise
difference | `HashSetHashSetHashSetHashSetHashSet` | `HashSetHashSetHashSetHashSetHashSet` | a Set containing those members of the Set that do not occur in the argument Set
equals | `HashSetHashSetHashSetHashSetHashSet` | `BooleanboolboolBooleanbool` | true if Set and argument Set contain identical values – false otherwise
notEqualTo | `HashSetHashSetHashSetHashSetHashSet` | `BooleanboolboolBooleanbool` | true if Set and argument Set differ in their values – false otherwise
intersection | `HashSetHashSetHashSetHashSetHashSet` | `HashSetHashSetHashSetHashSetHashSet` | a HashSet containing those members common to both the Set and the argument Set
isDisjointFrom | `HashSetHashSetHashSetHashSetHashSet` | `BooleanboolboolBooleanbool` | true if the Set has no items in common with the argument Set – false otherwise
isSubsetOf | `HashSetHashSetHashSetHashSetHashSet` | `BooleanboolboolBooleanbool` | true if all the Set's items are also in the argument Set – false otherwise
isSupersetOf | `HashSetHashSetHashSetHashSetHashSet` | `BooleanboolboolBooleanbool` | true if the Set contains all the items that are in the argument Set – false otherwise
length | (none) | `IntintintIntegerint` | the number of members of the Set
remove | value (of `HashSetHashSetHashSetHashSetHashSet` members' Type) | `HashSetHashSetHashSetHashSetHashSet` | a new Set with the argument item removed (if present)
toString | (none) | `StringstrstringStringString` | a string that is a comma+space-separated list of the Set's members, enclosed in brackets
union | `HashSetHashSetHashSetHashSetHashSet` | `HashSetHashSetHashSetHashSetHashSet` | a Set containing all the unique members of the Set and the argument Set (i.e. no duplicates)

## Stack and Queue

- `StackStackStackStackStack` and `QueueQueueQueueQueueQueue` are similar data structures except that `StackStackStackStackStack` is 'LIFO' (last in, first out), while `QueueQueueQueueQueueQueue` is FIFO (first in, first out). The names of the methods for adding and removing items are different, but there are also common methods.
- Both a `StackStackStackStackStack` and a `QueueQueueQueueQueueQueue` are defined with the type of the items that they can contain, similarly to how `ListlistListListList` has a specified item Type, though with different syntax. The type is specified in the form shown below e.g. `Stack<of String>Stack[str]Stack<string>Stack(Of String)Stack<String>`, `Queue<of Int>Queue[int]Queue<int>Queue(Of Integer)Queue<int>`.
- Both `StackStackStackStackStack`and`QueueQueueQueueQueueQueue` are dynamically extensible, like a `ListlistListListList`. There is no need (or means) to specify a size limit as they can continue to expand (eventually until the computer's memory limit is reached).
- The same syntax is used to specify the type if you want to pass a `StackStackStackStackStack` or `QueueQueueQueueQueueQueue` into a function, or specify it as the return Type.
- `StackStackStackStackStack` and `QueueQueueQueueQueueQueue` have two methods in common: length and peek. peek returns the next item to be removed, without actually removing it.
- The methods for adding and removing an item are different for `StackStackStackStackStack` and `QueueQueueQueueQueueQueue`, as shown here:

### Function dot methods on a `StackStackStackStackStack`

function dot method | argument Types | return Types | returns
--- | --- | --- | ---
equals | `StackStackStackStackStack` | `BooleanboolboolBooleanbool` | true if stack and argument are identical – false otherwise
notEqualTo | `StackStackStackStackStack` | `BooleanboolboolBooleanbool` | true if stack and argument differ – false otherwise
push | value (of `StackStackStackStackStack` item's Type) | `StackStackStackStackStack` | the Stack with the value added to its top
pop | (none) | `StackStackStackStackStack` item, `StackStackStackStackStack` | the topmost item of the Stack, and the Stack with the item removed
peek | (none) | `StackStackStackStackStack` item | the topmost item on the Stack (without altering the Stack)
length | (none) | `IntintintIntegerint` | the number of items in the Stack
toString | (none) | `StringstrstringStringString` | a String that is a comma+space-separated list of the Stack's items, enclosed in square brackets, the last item pushed being the first in the String

### Function dot methods on a `QueueQueueQueueQueueQueue`

function dot method | argument Types | return Types | returns
--- | --- | --- | ---
equals | `QueueQueueQueueQueueQueue` | `BooleanboolboolBooleanbool` | true if queue and argument are identical – false otherwise
notEqualTo | `QueueQueueQueueQueueQueue` | `BooleanboolboolBooleanbool` | true if queue and argument differ – false otherwise
enqueue | value (of `QueueQueueQueueQueueQueue` item's Type) | `QueueQueueQueueQueueQueue` | the Queue with the item added to the end of the Queue
dequeue | (none) | `QueueQueueQueueQueueQueue` item, `QueueQueueQueueQueueQueue` | the next item in the Queue, and the Queue with the item removed
peek | (none) | `QueueQueueQueueQueueQueue` item | the next item in the Queue (without altering the Queue)
length | (none) | `IntintintIntegerint` | the number of items in the Queue
toString | (none) | `StringstrstringStringString` | a String that is a comma+space-separated list of the Queue's items, enclosed in square brackets, the first item enqueued being the first in the String

#### Examples using `StackStackStackStackStack` and `QueueQueueQueueQueueQueue`

● Results of push and pop on strings in a `StackStackStackStackStack`:

+main 1 variable sk name? set to new Stack<of String>()value or expression?2 print(sk.length()arguments?)3 reassign sk variableName? to sk.push("apple")value or expression?4 reassign sk variableName? to sk.push("banana")value or expression?5 reassign sk variableName? to sk.push("cherry")value or expression?6 print(sk.length()arguments?)7 print(sk arguments?)8 print(sk.peek()arguments?)9 print(sk.pop()arguments?)10 print(sk arguments?)11 print(sk.pop().item_0 arguments?)12 print(sk arguments?)13 reassign sk variableName? to sk.pop().item_1 value or expression?14 print(sk arguments?)15 end main +def main() -> None: 1 sk name? = Stack[str]()value or expression? # variable definition 2 print(sk.length()arguments?)3 sk variableName? = sk.push("apple")value or expression? # reassign variable 4 sk variableName? = sk.push("banana")value or expression? # reassign variable 5 sk variableName? = sk.push("cherry")value or expression? # reassign variable 6 print(sk.length()arguments?)7 print(sk arguments?)8 print(sk.peek()arguments?)9 print(sk.pop()arguments?)10 print(sk arguments?)11 print(sk.pop().item_0 arguments?)12 print(sk arguments?)13 sk variableName? = sk.pop().item_1 value or expression? # reassign variable 14 print(sk arguments?)15 main() +static void main() { 1 var sk name? = new Stack<string>()value or expression?;2 Console.WriteLine(sk.length()arguments?); // print 3 sk variableName? = sk.push("apple")value or expression?; // reassign variable 4 sk variableName? = sk.push("banana")value or expression?; // reassign variable 5 sk variableName? = sk.push("cherry")value or expression?; // reassign variable 6 Console.WriteLine(sk.length()arguments?); // print 7 Console.WriteLine(sk arguments?); // print 8 Console.WriteLine(sk.peek()arguments?); // print 9 Console.WriteLine(sk.pop()arguments?); // print 10 Console.WriteLine(sk arguments?); // print 11 Console.WriteLine(sk.pop().item_0 arguments?); // print 12 Console.WriteLine(sk arguments?); // print 13 sk variableName? = sk.pop().item_1 value or expression?; // reassign variable 14 Console.WriteLine(sk arguments?); // print 15 } // main +Sub main() 1 Dim sk name? = New Stack(Of String)()value or expression? ' variable definition 2 Console.WriteLine(sk.length()arguments?) ' print 3 sk variableName? = sk.push("apple")value or expression? ' reassign variable 4 sk variableName? = sk.push("banana")value or expression? ' reassign variable 5 sk variableName? = sk.push("cherry")value or expression? ' reassign variable 6 Console.WriteLine(sk.length()arguments?) ' print 7 Console.WriteLine(sk arguments?) ' print 8 Console.WriteLine(sk.peek()arguments?) ' print 9 Console.WriteLine(sk.pop()arguments?) ' print 10 Console.WriteLine(sk arguments?) ' print 11 Console.WriteLine(sk.pop().item_0 arguments?) ' print 12 Console.WriteLine(sk arguments?) ' print 13 sk variableName? = sk.pop().item_1 value or expression? ' reassign variable 14 Console.WriteLine(sk arguments?) ' print 15 End Sub public class Global { +static void main() { 1 var sk name? = new Stack<String>()value or expression?;2 System.out.println(sk.length()arguments?); // print 3 sk variableName? = sk.push("apple")value or expression?; // reassign variable 4 sk variableName? = sk.push("banana")value or expression?; // reassign variable 5 sk variableName? = sk.push("cherry")value or expression?; // reassign variable 6 System.out.println(sk.length()arguments?); // print 7 System.out.println(sk arguments?); // print 8 System.out.println(sk.peek()arguments?); // print 9 System.out.println(sk.pop()arguments?); // print 10 System.out.println(sk arguments?); // print 11 System.out.println(sk.pop().item_0 arguments?); // print 12 System.out.println(sk arguments?); // print 13 sk variableName? = sk.pop().item_1 value or expression?; // reassign variable 14 System.out.println(sk arguments?); // print 15 } // main } | ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ | 0 3 [cherry, banana, apple] cherry (cherry, [banana, apple]) [cherry, banana, apple] cherry [cherry, banana, apple] [banana, apple]

● Results of enqueue and dequeue on strings in a `QueueQueueQueueQueueQueue`:

+main 1 variable qu name? set to new Queue<of String>()value or expression?2 print(qu.length()arguments?)3 reassign qu variableName? to qu.enqueue("apple")value or expression?4 reassign qu variableName? to qu.enqueue("banana")value or expression?5 reassign qu variableName? to qu.enqueue("cherry")value or expression?6 print(qu.length()arguments?)7 print(qu arguments?)8 print(qu.peek()arguments?)9 print(qu.dequeue()arguments?)10 print(qu arguments?)11 print(qu.dequeue().item_0 arguments?)12 print(qu arguments?)13 reassign qu variableName? to qu.dequeue().item_1 value or expression?14 print(qu arguments?)15 end main +def main() -> None: 1 qu name? = Queue[str]()value or expression? # variable definition 2 print(qu.length()arguments?)3 qu variableName? = qu.enqueue("apple")value or expression? # reassign variable 4 qu variableName? = qu.enqueue("banana")value or expression? # reassign variable 5 qu variableName? = qu.enqueue("cherry")value or expression? # reassign variable 6 print(qu.length()arguments?)7 print(qu arguments?)8 print(qu.peek()arguments?)9 print(qu.dequeue()arguments?)10 print(qu arguments?)11 print(qu.dequeue().item_0 arguments?)12 print(qu arguments?)13 qu variableName? = qu.dequeue().item_1 value or expression? # reassign variable 14 print(qu arguments?)15 main() +static void main() { 1 var qu name? = new Queue<string>()value or expression?;2 Console.WriteLine(qu.length()arguments?); // print 3 qu variableName? = qu.enqueue("apple")value or expression?; // reassign variable 4 qu variableName? = qu.enqueue("banana")value or expression?; // reassign variable 5 qu variableName? = qu.enqueue("cherry")value or expression?; // reassign variable 6 Console.WriteLine(qu.length()arguments?); // print 7 Console.WriteLine(qu arguments?); // print 8 Console.WriteLine(qu.peek()arguments?); // print 9 Console.WriteLine(qu.dequeue()arguments?); // print 10 Console.WriteLine(qu arguments?); // print 11 Console.WriteLine(qu.dequeue().item_0 arguments?); // print 12 Console.WriteLine(qu arguments?); // print 13 qu variableName? = qu.dequeue().item_1 value or expression?; // reassign variable 14 Console.WriteLine(qu arguments?); // print 15 } // main +Sub main() 1 Dim qu name? = New Queue(Of String)()value or expression? ' variable definition 2 Console.WriteLine(qu.length()arguments?) ' print 3 qu variableName? = qu.enqueue("apple")value or expression? ' reassign variable 4 qu variableName? = qu.enqueue("banana")value or expression? ' reassign variable 5 qu variableName? = qu.enqueue("cherry")value or expression? ' reassign variable 6 Console.WriteLine(qu.length()arguments?) ' print 7 Console.WriteLine(qu arguments?) ' print 8 Console.WriteLine(qu.peek()arguments?) ' print 9 Console.WriteLine(qu.dequeue()arguments?) ' print 10 Console.WriteLine(qu arguments?) ' print 11 Console.WriteLine(qu.dequeue().item_0 arguments?) ' print 12 Console.WriteLine(qu arguments?) ' print 13 qu variableName? = qu.dequeue().item_1 value or expression? ' reassign variable 14 Console.WriteLine(qu arguments?) ' print 15 End Sub public class Global { +static void main() { 1 var qu name? = new Queue<String>()value or expression?;2 System.out.println(qu.length()arguments?); // print 3 qu variableName? = qu.enqueue("apple")value or expression?; // reassign variable 4 qu variableName? = qu.enqueue("banana")value or expression?; // reassign variable 5 qu variableName? = qu.enqueue("cherry")value or expression?; // reassign variable 6 System.out.println(qu.length()arguments?); // print 7 System.out.println(qu arguments?); // print 8 System.out.println(qu.peek()arguments?); // print 9 System.out.println(qu.dequeue()arguments?); // print 10 System.out.println(qu arguments?); // print 11 System.out.println(qu.dequeue().item_0 arguments?); // print 12 System.out.println(qu arguments?); // print 13 qu variableName? = qu.dequeue().item_1 value or expression?; // reassign variable 14 System.out.println(qu arguments?); // print 15 } // main } | ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ ⟶ | 0 3 [apple, banana, cherry] apple (apple, [banana, cherry]) [apple, banana, cherry] apple [apple, banana, cherry] [banana, cherry]

## Tuple

A Tuple is not a value or data structure Type. Rather, it is a small collection of values of differing Types held together and referenced by a single identifier.

It may be considered a lightweight alternative to defining a Class for some specific purpose.

The items in a Tuple may be literal or named values.

Tuples are referred to as 2-Tuples, 3-Tuples, etc. according to the number of values they hold.

An item within a Tuple may be another Tuple, giving nested Tuples.

A function may return a Tuple.

A Tuple differs from a List in that:

- A Tuple may hold items of different Types.
- A Tuple is immutable: you may read, but not modify, the values it contains. Once defined, Tuples are effectively read-only.
  Nor, unlike a `ListlistListListList`, can you copy a Tuple from an existing one with specified differences except by referencing each of its items (see below).

Common uses include:

- Holding a pair of x,y coordinates (each of type `FloatfloatdoubleDoubledouble`) as a single unit.
- Allowing a function to pass back a result comprised of both a message in a `StringstrstringStringString` and a `BooleanboolboolBooleanbool` indicating whether the operation was successful.
- Returning both an updated copy of a data structure and the value of an item from it, e.g. from method pop on a Stack .

### Defining a Tuple

A new Tuple is defined by a list of items separated by commas and enclosed in round brackets:

`variable pointname? set to (3, 4)value or expression?0pointname? = (3, 4)value or expression? # variable definition0var pointname? = (3, 4)value or expression?;0Dim pointname? = (3, 4)value or expression? ' variable definition0var pointname? = (3, 4)value or expression?;0` `variable tname? set to (3, "apple", true)value or expression?0tname? = (3, "apple", True)value or expression? # variable definition0var tname? = (3, "apple", true)value or expression?;0Dim tname? = (3, "apple", True)value or expression? ' variable definition0var tname? = (3, "apple", true)value or expression?;0`

### Accessing items in a Tuple

The items in a Tuple may be individually addressed by a dot reference and its special properties item_N, thus:

+main 1 variable t name? set to (3, "apple", true)value or expression?2 print(t arguments?)3 print(t.item_0 arguments?)4 print(t.item_1 arguments?)5 print(t.item_2 arguments?)6 end main +def main() -> None: 1 t name? = (3, "apple", True)value or expression? # variable definition 2 print(t arguments?)3 print(t.item_0 arguments?)4 print(t.item_1 arguments?)5 print(t.item_2 arguments?)6 main() +static void main() { 1 var t name? = (3, "apple", true)value or expression?;2 Console.WriteLine(t arguments?); // print 3 Console.WriteLine(t.item_0 arguments?); // print 4 Console.WriteLine(t.item_1 arguments?); // print 5 Console.WriteLine(t.item_2 arguments?); // print 6 } // main +Sub main() 1 Dim t name? = (3, "apple", True)value or expression? ' variable definition 2 Console.WriteLine(t arguments?) ' print 3 Console.WriteLine(t.item_0 arguments?) ' print 4 Console.WriteLine(t.item_1 arguments?) ' print 5 Console.WriteLine(t.item_2 arguments?) ' print 6 End Sub public class Global { +static void main() { 1 var t name? = (3, "apple", true)value or expression?;2 System.out.println(t arguments?); // print 3 System.out.println(t.item_0 arguments?); // print 4 System.out.println(t.item_1 arguments?); // print 5 System.out.println(t.item_2 arguments?); // print 6 } // main } | ⟶ ⟶ ⟶ ⟶ | (3, apple, true) 3 apple true

And where p1 and p2 represent points each with 2-Tuples containing two `FloatfloatdoubleDoubledouble` values, this function returns the distance between them:

+function distanceBetween name?(p1 as (Float, Float), p2 as (Float, Float)parameter definitions?) returns Float Type? 1 return sqrt(pow(p2.item_0 - p1.item_0, 2) + pow(p2.item_1 - p1.item_1, 2))value or expression?2 end function
+def distanceBetween name?(p1: tuple[float, float], p2: tuple[float, float]parameter definitions?) -> float Type?: # function 1 return sqrt(pow(p2.item_0 - p1.item_0, 2) + pow(p2.item_1 - p1.item_1, 2))value or expression?2
+static double Type? distanceBetween name?((double, double) p1, (double, double) p2 parameter definitions?) { // function 1 return sqrt(pow(p2.item_0 - p1.item_0, 2) + pow(p2.item_1 - p1.item_1, 2))value or expression?;2 } // function
+Function distanceBetween name?(p1 As (Double, Double), p2 As (Double, Double)parameter definitions?) As Double Type? 1 Return sqrt(pow(p2.item_0 - p1.item_0, 2) + pow(p2.item_1 - p1.item_1, 2))value or expression?2 End Function
public class Global {
+static double Type? distanceBetween name?((double, double) p1, (double, double) p2 parameter definitions?) { // function 1 return sqrt(pow(p2.item_0 - p1.item_0, 2) + pow(p2.item_1 - p1.item_1, 2))value or expression?;2 } // function
}

Note that the appropriate item_Ns will be listed in the Editor's drop-down menu options for the referenced Tuple.

### Function dot methods on a Tuple

function dot methods | argument Types | return Type | returns
--- | --- | --- | ---
equals | Tuple | `BooleanboolboolBooleanbool` | true if the Types, item values and order all equal those of the argument, – false otherwise
notEqualTo | Tuple | `BooleanboolboolBooleanbool` | true if any of the Types, item values and order differ from those of the argument, – false otherwise
toString | (none) | `StringstrstringStringString` | String containing Tuple's items surrounded by brackets

# Graphic Types

## Block graphics

Block graphics provides a simple way to create low resolution graphics, ideal for simple but engaging games for example.

The graphics are defined and displayed on a grid that is 40 blocks wide by 30 blocks high.

Each block is be rendered as a solid colour.

An example of block graphics to produce a rapidly changing pattern of coloured blocks:

+main 1 variable grid name? set to createBlockGraphics(white)value or expression?2 +while true condition? 3 variable x name? set to randint(0, 39)value or expression?4 variable y name? set to randint(0, 29)value or expression?5 variable colour name? set to randint(0, white - 1)value or expression?6 reassign grid[x][y]variableName? to colour value or expression?7 call displayBlocks procedureName?(grid arguments?)8 end while end main
+def main() -> None: 1 grid name? = createBlockGraphics(white)value or expression? # variable definition 2 +while True condition?: 3 x name? = randint(0, 39)value or expression? # variable definition 4 y name? = randint(0, 29)value or expression? # variable definition 5 colour name? = randint(0, white - 1)value or expression? # variable definition 6 grid[x][y]variableName? = colour value or expression? # reassign variable 7 displayBlocks procedureName?(grid arguments?) # call procedure 8 main()
+static void main() { 1 var grid name? = createBlockGraphics(white)value or expression?;2 +while (true condition?) { 3 var x name? = randint(0, 39)value or expression?;4 var y name? = randint(0, 29)value or expression?;5 var colour name? = randint(0, white - 1)value or expression?;6 grid[x][y]variableName? = colour value or expression?; // reassign variable 7 displayBlocks procedureName?(grid arguments?); // call procedure 8 } // while } // main
+Sub main() 1 Dim grid name? = createBlockGraphics(white)value or expression? ' variable definition 2 +While True condition? 3 Dim x name? = randint(0, 39)value or expression? ' variable definition 4 Dim y name? = randint(0, 29)value or expression? ' variable definition 5 Dim colour name? = randint(0, white - 1)value or expression? ' variable definition 6 grid[x][y]variableName? = colour value or expression? ' reassign variable 7 displayBlocks procedureName?(grid arguments?) ' call procedure 8 End While End Sub
public class Global {
+static void main() { 1 var grid name? = createBlockGraphics(white)value or expression?;2 +while (true condition?) { 3 var x name? = randint(0, 39)value or expression?;4 var y name? = randint(0, 29)value or expression?;5 var colour name? = randint(0, white - 1)value or expression?;6 grid[x][y]variableName? = colour value or expression?; // reassign variable 7 displayBlocks procedureName?(grid arguments?); // call procedure 8 } // while } // main
}

#### Notes

- The definition of the grid is made using the system method createBlockGraphics which initialises a `ListlistListListList`<of `ListlistListListList`<of `IntintintIntegerint`>> structure containing 40 columns × 30 rows.
- Each cell of the grid is referenced by integers x,y where x is in [0..39] and y is in [0..29].
- x,y is 0,0 at the top left cell of the grid, positive x to the right, positive y downwards.
- You may create multiple such structures holding different patterns of blocks, and switch between them just by passing the required one as the argument to method displayBlocks.
- Any `ListlistListListList`<of `ListlistListListList`<of `IntintintIntegerint`>> structure of the same 40 × 30 dimensions can be the argument to method displayBlocks.
- A colour is specified as an `IntintintIntegerint`, as described under Colours .

## Turtle graphics

Turtle graphics are implemented with output to the IDE's display pane, i.e. the 'paper' on which the turtle draws.

The area is 200 turtle units wide by 150 turtle units high, and both integer and floating point values of turtle units can be used. If a turtle is placed or moved outside the 200 × 150 area boundary, it will not cause an error, but the turtle and any lines drawn outside the boundary will not be visible.

The origin for turtle units (0,0) is at the centre of the area: positive x rightwards, positive y upwards. So the top left corner of the display is at (-100,75).

A new turtle's default starting position is at (0,0) facing upwards (heading is 0), from where a move will be in the y direction.

You can move and turn a turtle, causing lines to be drawn, whether or not the turtle is showing.

### Procedure methods on a Turtle

procedure method | argument Types | action
--- | --- | ---
clearAndReset | (none) | clears the turtle display and moves the turtle to its starting position and heading
hide | (none) | makes the turtle invisible in the display
move | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | moves the turtle the specified number of turtle units in the direction of its heading or, if negative, in the opposite direction
moveTo | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble`, `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | moves the turtle to the specified x,y position, drawing its path if its pen is down
penColour | `IntintintIntegerint` | changes the colour  of its path in the display to the literal or named value specified
penDown | (none) | makes the turtle's subsequent moves leave a trace of its path in the display
penUp | (none) | makes the turtle's subsequent moves leave no trace of its path in the display
penWidth | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | changes the width of the line tracing the turtle's path in the display default (and minimum) is 1
placeAt | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble`, `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | places or repositions the turtle at the x,y position specified without drawing a path
show | (none) | makes the turtle visible in the display as a green blob marked with a black radius that indicates its heading
turn | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | turns the turtle through the specified number of degrees clockwise or, if negative, anticlockwise
turnToHeading | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | turns the turtle to face in the direction specified in degrees where 0 is upward and increasing values go clockwise from there

### Properties of a Turtle

The current location and heading of the turtle may be read using the properties x, y, and heading.

Property |
--- | ---
name | Type | description | default
heading | `FloatfloatdoubleDoubledouble` | the direction in which the turtle is pointing in degrees clockwise from North | 0.0 degrees, i.e. upward in the display
x, y | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` | the x,y coordinates of the turtle's current position | 0.0, 0.0

#### Examples using turtle graphics

● To draw a square:

+main 1 variable t name? set to new Turtle()value or expression?2 call t.placeAt procedureName?(-75, 50 arguments?)3 call t.show procedureName?(arguments?)4 +for i item? in range(1, 5)source? 5 call t.turn procedureName?(90 arguments?)6 call t.move procedureName?(80 arguments?)7 call sleep procedureName?(0.5 arguments?)8 end for end main
+def main() -> None: 1 t name? = Turtle()value or expression? # variable definition 2 t.placeAt procedureName?(-75, 50 arguments?) # call procedure 3 t.show procedureName?(arguments?) # call procedure 4 +for i item? in range(1, 5)source?: 5 t.turn procedureName?(90 arguments?) # call procedure 6 t.move procedureName?(80 arguments?) # call procedure 7 sleep procedureName?(0.5 arguments?) # call procedure 8 main()
+static void main() { 1 var t name? = new Turtle()value or expression?;2 t.placeAt procedureName?(-75, 50 arguments?); // call procedure 3 t.show procedureName?(arguments?); // call procedure 4 +foreach (i item? in range(1, 5)source?) { 5 t.turn procedureName?(90 arguments?); // call procedure 6 t.move procedureName?(80 arguments?); // call procedure 7 sleep procedureName?(0.5 arguments?); // call procedure 8 } // foreach } // main
+Sub main() 1 Dim t name? = New Turtle()value or expression? ' variable definition 2 t.placeAt procedureName?(-75, 50 arguments?) ' call procedure 3 t.show procedureName?(arguments?) ' call procedure 4 +For Each i item? In range(1, 5)source? 5 t.turn procedureName?(90 arguments?) ' call procedure 6 t.move procedureName?(80 arguments?) ' call procedure 7 sleep procedureName?(0.5 arguments?) ' call procedure 8 Next i End Sub
public class Global {
+static void main() { 1 var t name? = new Turtle()value or expression?;2 t.placeAt procedureName?(-75, 50 arguments?); // call procedure 3 t.show procedureName?(arguments?); // call procedure 4 +foreach (i item? in range(1, 5)source?) { 5 t.turn procedureName?(90 arguments?); // call procedure 6 t.move procedureName?(80 arguments?); // call procedure 7 sleep procedureName?(0.5 arguments?); // call procedure 8 } // foreach } // main
}

● To draw a fractal snowflake, using a procedure and recursion:

+main 1 variable t name? set to new Turtle()value or expression?2 call t.placeAt procedureName?(-50, 30 arguments?)3 call t.turn procedureName?(90 arguments?)4 call t.show procedureName?(arguments?)5 +for i item? in range(1, 4)source? 6 call drawSide procedureName?(side, t arguments?)7 call t.turn procedureName?(120 arguments?)8 end for end main +constant side name? set to 100 literal value or data structure?9 +procedure drawSide name?(length as Float, t as Turtle parameter definitions?) 10 +if (length > 1)condition? then 11 variable third name? set to length/3 value or expression?12 call drawSide procedureName?(third, t arguments?)13 call t.turn procedureName?(-60 arguments?)14 call drawSide procedureName?(third, t arguments?)15 call t.turn procedureName?(120 arguments?)16 call drawSide procedureName?(third, t arguments?)17 call t.turn procedureName?(-60 arguments?)18 call drawSide procedureName?(third, t arguments?)19 else 20 call t.move procedureName?(length arguments?)21 end if end procedure
+def main() -> None: 1 t name? = Turtle()value or expression? # variable definition 2 t.placeAt procedureName?(-50, 30 arguments?) # call procedure 3 t.turn procedureName?(90 arguments?) # call procedure 4 t.show procedureName?(arguments?) # call procedure 5 +for i item? in range(1, 4)source?: 6 drawSide procedureName?(side, t arguments?) # call procedure 7 t.turn procedureName?(120 arguments?) # call procedure 8 +side name? = 100 literal value or data structure? # constant 9 +def drawSide name?(length: float, t: Turtle parameter definitions?) -> None: # procedure 10 +if (length > 1)condition?: 11 third name? = length/3 value or expression? # variable definition 12 drawSide procedureName?(third, t arguments?) # call procedure 13 t.turn procedureName?(-60 arguments?) # call procedure 14 drawSide procedureName?(third, t arguments?) # call procedure 15 t.turn procedureName?(120 arguments?) # call procedure 16 drawSide procedureName?(third, t arguments?) # call procedure 17 t.turn procedureName?(-60 arguments?) # call procedure 18 drawSide procedureName?(third, t arguments?) # call procedure 19 else:20 t.move procedureName?(length arguments?) # call procedure 21 main()
+static void main() { 1 var t name? = new Turtle()value or expression?;2 t.placeAt procedureName?(-50, 30 arguments?); // call procedure 3 t.turn procedureName?(90 arguments?); // call procedure 4 t.show procedureName?(arguments?); // call procedure 5 +foreach (i item? in range(1, 4)source?) { 6 drawSide procedureName?(side, t arguments?); // call procedure 7 t.turn procedureName?(120 arguments?); // call procedure 8 } // foreach } // main +const Int side name? = 100 literal value or data structure?;9 +static void drawSide name?(double length, Turtle t parameter definitions?) { // procedure 10 +if ((length > 1)condition?) { 11 var third name? = length/3 value or expression?;12 drawSide procedureName?(third, t arguments?); // call procedure 13 t.turn procedureName?(-60 arguments?); // call procedure 14 drawSide procedureName?(third, t arguments?); // call procedure 15 t.turn procedureName?(120 arguments?); // call procedure 16 drawSide procedureName?(third, t arguments?); // call procedure 17 t.turn procedureName?(-60 arguments?); // call procedure 18 drawSide procedureName?(third, t arguments?); // call procedure 19 } else {20 t.move procedureName?(length arguments?); // call procedure 21 } // if } // procedure
+Sub main() 1 Dim t name? = New Turtle()value or expression? ' variable definition 2 t.placeAt procedureName?(-50, 30 arguments?) ' call procedure 3 t.turn procedureName?(90 arguments?) ' call procedure 4 t.show procedureName?(arguments?) ' call procedure 5 +For Each i item? In range(1, 4)source? 6 drawSide procedureName?(side, t arguments?) ' call procedure 7 t.turn procedureName?(120 arguments?) ' call procedure 8 Next i End Sub +Const side name? = 100 literal value or data structure?9 +Sub drawSide name?(length As Double, t As Turtle parameter definitions?) ' procedure 10 +If (length > 1)condition? Then 11 Dim third name? = length/3 value or expression? ' variable definition 12 drawSide procedureName?(third, t arguments?) ' call procedure 13 t.turn procedureName?(-60 arguments?) ' call procedure 14 drawSide procedureName?(third, t arguments?) ' call procedure 15 t.turn procedureName?(120 arguments?) ' call procedure 16 drawSide procedureName?(third, t arguments?) ' call procedure 17 t.turn procedureName?(-60 arguments?) ' call procedure 18 drawSide procedureName?(third, t arguments?) ' call procedure 19 Else 20 t.move procedureName?(length arguments?) ' call procedure 21 End If End Sub
public class Global {
+static void main() { 1 var t name? = new Turtle()value or expression?;2 t.placeAt procedureName?(-50, 30 arguments?); // call procedure 3 t.turn procedureName?(90 arguments?); // call procedure 4 t.show procedureName?(arguments?); // call procedure 5 +foreach (i item? in range(1, 4)source?) { 6 drawSide procedureName?(side, t arguments?); // call procedure 7 t.turn procedureName?(120 arguments?); // call procedure 8 } // foreach } // main +final Int side name? = 100 literal value or data structure?; // constant 9 +static void drawSide name?(double length, Turtle t parameter definitions?) { // procedure 10 +if ((length > 1)condition?) { 11 var third name? = length/3 value or expression?;12 drawSide procedureName?(third, t arguments?); // call procedure 13 t.turn procedureName?(-60 arguments?); // call procedure 14 drawSide procedureName?(third, t arguments?); // call procedure 15 t.turn procedureName?(120 arguments?); // call procedure 16 drawSide procedureName?(third, t arguments?); // call procedure 17 t.turn procedureName?(-60 arguments?); // call procedure 18 drawSide procedureName?(third, t arguments?); // call procedure 19 } else {20 t.move procedureName?(length arguments?); // call procedure 21 } // if } // procedure
}

## Vector graphics

Vector graphics are implemented using the SVG (Scalable Vector Graphics) Html tag <svg>, and are output to the display pane in the user interface.

The area is 100 units wide by 75 units high, and both integer and floating point values of the units can be used.

The origin of the units (0,0) is at the top left corner of the display: positive x rightwards, positive y downwards. So for example the centre of the display is at (50, 37.5).

The names of the shapes broadly correspond to the names of SVG tags:

- `CircleVGCircleVGCircleVGCircleVGCircleVG` for <circle../>
- `ImageVGImageVGImageVGImageVGImageVG` for <image../>
- `LineVGLineVGLineVGLineVGLineVG` for <line../>
- `RectangleVGRectangleVGRectangleVGRectangleVGRectangleVG` for <rect../>

The properties of these shapes are named to reflect the attributes used in the SVG tags but some names differ. For example, SVG's `stroke - widthstroke - widthstroke - widthstroke - widthstroke - width` is assigned with property strokeWidth, to make it a valid identifier . Also `strokestrokestrokestrokestroke` and `fillfillfillfillfill` are set by the properties strokeColour and fillColour.

In addition, graphics may be displayed from any valid string of SVG tags, as described in `RawVGRawVGRawVGRawVGRawVG` .

### Defining Vector graphic shapes

A set of SVG shapes is defined in either a `List<of VectorGraphic>list[VectorGraphic]List<VectorGraphic>List(Of VectorGraphic)List<VectorGraphic>` or a `ListlistListListList` of any specific type of `VectorGraphicVectorGraphicVectorGraphicVectorGraphicVectorGraphic` (e.g. `List<of CircleVG>list[CircleVG]List<CircleVG>List(Of CircleVG)List<CircleVG>`) by using the `ListlistListListList` append method.

`VectorGraphicVectorGraphicVectorGraphicVectorGraphicVectorGraphic` is the abstract superclass of all ..VG shapes. You use it when you want to define a `ListlistListListList` holding different types of shape.

Adding a shape returns a new instance of the list which must be assigned to a new or existing variable.

The constructors for the VG Types require arguments defining the attributes of the relevant SVG tags, so defaults are supplied from the Class properties, as shown in the table below.

To change the value of property 'p..', call the setP.. procedure method on the vector graphic or, in a function, use the withP.. dot method on the vector graphic, in either case specifying new values in the arguments.

The fillColour and strokeColour properties may be specified as described under Colours . Only fillColour can be specified as transparent.

Note that the height and width properties of an image are also dependent on the dimensions of the original graphic file.

### Displaying Vector graphic shapes

As with Block  graphics, the assembled list of shapes is not displayed until call procedure displayVectorGraphics with the list as its argument, thus allowing you to make multiple changes before display.

And as with using SVG in Html, the shapes are drawn in the order in which they are added to the `VectorGraphicVectorGraphicVectorGraphicVectorGraphicVectorGraphic` instance. Later shapes are positioned in front of earlier ones.

### Function dot methods on Vector graphic shapes

function dot method | on Type | argument Types | return Type | returns
--- | --- | --- | --- | ---
asHtml | `ImageVGImageVGImageVGImageVGImageVG` | none | `StringstrstringStringString` | string containing the Html <img> tag filled with the image's URL and attribute values
asSVG | `CircleVGCircleVGCircleVGCircleVGCircleVG` | none | `StringstrstringStringString` | string containing the SVG <circle> tag filled with the circle's attribute values
asSVG | `ImageVGImageVGImageVGImageVGImageVG` | none | `StringstrstringStringString` | string containing the SVG <image> tag filled with the image's URL and attribute values
asSVG | `LineVGLineVGLineVGLineVGLineVG` | none | `StringstrstringStringString` | string containing the SVG <line> tag filled with the line's attribute values
asSVG | `RectangleVGRectangleVGRectangleVGRectangleVGRectangleVG` | none | `StringstrstringStringString` | string containing the SVG <rectangle> tag filled with the rectangle's attribute values

### Properties of Vector graphic shapes

This table lists the properties of the Vector graphic shapes and their default values, together with the procedure and function methods provided to alter their values in a given instance.

Property | Vector graphic shape | Property | Method
--- | --- | --- | ---
name | Type | CircleVG | ImageVG | LineVG | RectangleVG | description | default | procedure | function
alt | `StringstrstringStringString` |  | ✔ |  |  | alternate textual description (for accessibility) | empty string | setAlt | withAlt
centreX | `FloatfloatdoubleDoubledouble` | ✔ |  |  |  | horizontal position of circle centre | 50 | setCentreX | withCentreX
centreY | `FloatfloatdoubleDoubledouble` | ✔ |  |  |  | vertical position of circle centre | 37.5 | setCentreY | withCentreY
fillColour | `IntintintIntegerint` | ✔ |  |  | ✔ | colour to fill the shape | yellow | setFillColour | withFillColour
height | `FloatfloatdoubleDoubledouble` |  | ✔ |  | ✔ | height to render the shape or the image | Image: 13.2 Rectangle: 20 | setHeight | withHeight
radius | `FloatfloatdoubleDoubledouble` | ✔ |  |  |  | radius of circle | 10 | setRadius | withRadius
strokeColour | `IntintintIntegerint` | ✔ |  | ✔ | ✔ | colour of the strokes in the shape | black | setStrokeColour | withStrokeColour
strokeWidth | `IntintintIntegerint` | ✔ |  | ✔ | ✔ | width of the strokes in the shape | 1 | setStrokeWidth | withStrokeWidth
title | `FloatfloatdoubleDoubledouble` |  | ✔ |  |  | title text | empty string | setTitle | withTitle
width | `FloatfloatdoubleDoubledouble` |  | ✔ |  | ✔ | width to render the shape or the image | Image: 13.2 Rectangle: 40 | setWidth | withWidth
x, y | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` |  | ✔ ✔ |  | ✔ ✔ | image's x,y position from top left | Image: 0, 0 Rectangle: 10, 10 | setX, setY | withX, withY
x1, y1 | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` |  |  | ✔ ✔ |  | line's starting x,y position from top left | 10, 10 | setX1, setY1 | withX1, withY1
x2, y2 | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` |  |  | ✔ ✔ |  | line's ending x,y position from top left | 70, 40 | setX2, setY2 | withX2, withY2

#### Examples using simple SVG graphics

● To draw a circle with a coloured circumference:

+main 1 variable vg name? set to new List<of VectorGraphic>()value or expression?2 variable circ name? set to new CircleVG()value or expression?3 call circ.setCentreX procedureName?(20 arguments?)4 call circ.setCentreY procedureName?(20 arguments?)5 call circ.setRadius procedureName?(5 arguments?)6 call circ.setFillColour procedureName?(green arguments?)7 call circ.setStrokeColour procedureName?(red arguments?)8 call circ.setStrokeWidth procedureName?(2 arguments?)9 call vg.append procedureName?(circ arguments?)10 call displayVectorGraphics procedureName?(vg arguments?)11 end main
+def main() -> None: 1 vg name? = list[VectorGraphic]()value or expression? # variable definition 2 circ name? = CircleVG()value or expression? # variable definition 3 circ.setCentreX procedureName?(20 arguments?) # call procedure 4 circ.setCentreY procedureName?(20 arguments?) # call procedure 5 circ.setRadius procedureName?(5 arguments?) # call procedure 6 circ.setFillColour procedureName?(green arguments?) # call procedure 7 circ.setStrokeColour procedureName?(red arguments?) # call procedure 8 circ.setStrokeWidth procedureName?(2 arguments?) # call procedure 9 vg.append procedureName?(circ arguments?) # call procedure 10 displayVectorGraphics procedureName?(vg arguments?) # call procedure 11 main()
+static void main() { 1 var vg name? = new List<VectorGraphic>()value or expression?;2 var circ name? = new CircleVG()value or expression?;3 circ.setCentreX procedureName?(20 arguments?); // call procedure 4 circ.setCentreY procedureName?(20 arguments?); // call procedure 5 circ.setRadius procedureName?(5 arguments?); // call procedure 6 circ.setFillColour procedureName?(green arguments?); // call procedure 7 circ.setStrokeColour procedureName?(red arguments?); // call procedure 8 circ.setStrokeWidth procedureName?(2 arguments?); // call procedure 9 vg.append procedureName?(circ arguments?); // call procedure 10 displayVectorGraphics procedureName?(vg arguments?); // call procedure 11 } // main
+Sub main() 1 Dim vg name? = New List(Of VectorGraphic)()value or expression? ' variable definition 2 Dim circ name? = New CircleVG()value or expression? ' variable definition 3 circ.setCentreX procedureName?(20 arguments?) ' call procedure 4 circ.setCentreY procedureName?(20 arguments?) ' call procedure 5 circ.setRadius procedureName?(5 arguments?) ' call procedure 6 circ.setFillColour procedureName?(green arguments?) ' call procedure 7 circ.setStrokeColour procedureName?(red arguments?) ' call procedure 8 circ.setStrokeWidth procedureName?(2 arguments?) ' call procedure 9 vg.append procedureName?(circ arguments?) ' call procedure 10 displayVectorGraphics procedureName?(vg arguments?) ' call procedure 11 End Sub
public class Global {
+static void main() { 1 var vg name? = new List<VectorGraphic>()value or expression?;2 var circ name? = new CircleVG()value or expression?;3 circ.setCentreX procedureName?(20 arguments?); // call procedure 4 circ.setCentreY procedureName?(20 arguments?); // call procedure 5 circ.setRadius procedureName?(5 arguments?); // call procedure 6 circ.setFillColour procedureName?(green arguments?); // call procedure 7 circ.setStrokeColour procedureName?(red arguments?); // call procedure 8 circ.setStrokeWidth procedureName?(2 arguments?); // call procedure 9 vg.append procedureName?(circ arguments?); // call procedure 10 displayVectorGraphics procedureName?(vg arguments?); // call procedure 11 } // main
}

● To draw a circle that changes between red and green every second:

+main 1 variable vg name? set to new List<of VectorGraphic>()value or expression?2 variable circ name? set to new CircleVG()value or expression?3 call circ.setCentreX procedureName?(50 arguments?)4 call circ.setCentreY procedureName?(37.5 arguments?)5 call circ.setRadius procedureName?(30 arguments?)6 call circ.setFillColour procedureName?(green arguments?)7 call vg.append procedureName?(circ arguments?)8 +while true condition? 9 call displayVectorGraphics procedureName?(vg arguments?)10 call sleep procedureName?(1 arguments?)11 call circ.setFillColour procedureName?(red arguments?)12 call displayVectorGraphics procedureName?(vg arguments?)13 call sleep procedureName?(1 arguments?)14 call circ.setFillColour procedureName?(green arguments?)15 end while call displayVectorGraphics procedureName?(vg arguments?)16 end main
+def main() -> None: 1 vg name? = list[VectorGraphic]()value or expression? # variable definition 2 circ name? = CircleVG()value or expression? # variable definition 3 circ.setCentreX procedureName?(50 arguments?) # call procedure 4 circ.setCentreY procedureName?(37.5 arguments?) # call procedure 5 circ.setRadius procedureName?(30 arguments?) # call procedure 6 circ.setFillColour procedureName?(green arguments?) # call procedure 7 vg.append procedureName?(circ arguments?) # call procedure 8 +while True condition?: 9 displayVectorGraphics procedureName?(vg arguments?) # call procedure 10 sleep procedureName?(1 arguments?) # call procedure 11 circ.setFillColour procedureName?(red arguments?) # call procedure 12 displayVectorGraphics procedureName?(vg arguments?) # call procedure 13 sleep procedureName?(1 arguments?) # call procedure 14 circ.setFillColour procedureName?(green arguments?) # call procedure 15 displayVectorGraphics procedureName?(vg arguments?) # call procedure 16 main()
+static void main() { 1 var vg name? = new List<VectorGraphic>()value or expression?;2 var circ name? = new CircleVG()value or expression?;3 circ.setCentreX procedureName?(50 arguments?); // call procedure 4 circ.setCentreY procedureName?(37.5 arguments?); // call procedure 5 circ.setRadius procedureName?(30 arguments?); // call procedure 6 circ.setFillColour procedureName?(green arguments?); // call procedure 7 vg.append procedureName?(circ arguments?); // call procedure 8 +while (true condition?) { 9 displayVectorGraphics procedureName?(vg arguments?); // call procedure 10 sleep procedureName?(1 arguments?); // call procedure 11 circ.setFillColour procedureName?(red arguments?); // call procedure 12 displayVectorGraphics procedureName?(vg arguments?); // call procedure 13 sleep procedureName?(1 arguments?); // call procedure 14 circ.setFillColour procedureName?(green arguments?); // call procedure 15 } // while displayVectorGraphics procedureName?(vg arguments?); // call procedure 16 } // main
+Sub main() 1 Dim vg name? = New List(Of VectorGraphic)()value or expression? ' variable definition 2 Dim circ name? = New CircleVG()value or expression? ' variable definition 3 circ.setCentreX procedureName?(50 arguments?) ' call procedure 4 circ.setCentreY procedureName?(37.5 arguments?) ' call procedure 5 circ.setRadius procedureName?(30 arguments?) ' call procedure 6 circ.setFillColour procedureName?(green arguments?) ' call procedure 7 vg.append procedureName?(circ arguments?) ' call procedure 8 +While True condition? 9 displayVectorGraphics procedureName?(vg arguments?) ' call procedure 10 sleep procedureName?(1 arguments?) ' call procedure 11 circ.setFillColour procedureName?(red arguments?) ' call procedure 12 displayVectorGraphics procedureName?(vg arguments?) ' call procedure 13 sleep procedureName?(1 arguments?) ' call procedure 14 circ.setFillColour procedureName?(green arguments?) ' call procedure 15 End While displayVectorGraphics procedureName?(vg arguments?) ' call procedure 16 End Sub
public class Global {
+static void main() { 1 var vg name? = new List<VectorGraphic>()value or expression?;2 var circ name? = new CircleVG()value or expression?;3 circ.setCentreX procedureName?(50 arguments?); // call procedure 4 circ.setCentreY procedureName?(37.5 arguments?); // call procedure 5 circ.setRadius procedureName?(30 arguments?); // call procedure 6 circ.setFillColour procedureName?(green arguments?); // call procedure 7 vg.append procedureName?(circ arguments?); // call procedure 8 +while (true condition?) { 9 displayVectorGraphics procedureName?(vg arguments?); // call procedure 10 sleep procedureName?(1 arguments?); // call procedure 11 circ.setFillColour procedureName?(red arguments?); // call procedure 12 displayVectorGraphics procedureName?(vg arguments?); // call procedure 13 sleep procedureName?(1 arguments?); // call procedure 14 circ.setFillColour procedureName?(green arguments?); // call procedure 15 } // while displayVectorGraphics procedureName?(vg arguments?); // call procedure 16 } // main
}

### `RawVGRawVGRawVGRawVGRawVG`

Strings containing raw SVG tags may be assembled and plotted directly using Class `RawVGRawVGRawVGRawVGRawVG`. By this means features such as simple SVG animation can be defined.

- The raw SVG content should be enclosed in double quotes within which the SVG attribute values must be enclosed in single quotes.
- To include interpolated  values, you precede the string with a $.
- The raw SVG may define multiple shapes.
- Multiple instances of `RawVGRawVGRawVGRawVGRawVG` may be added to the collection to be displayed, along with instances of other SVG Types; hence the need for list-defining square brackets in the parameter of method displayVectorGraphics.
- Method withContent is used to specify the property of Class `RawVGRawVGRawVGRawVGRawVG` that must contain the SVG string.
- The example is of a simple animation in which the repetition defined in the SVG continues after the program has stopped, so you would then use the Clear button to blank the display.

#### Example using `RawVGRawVGRawVGRawVGRawVG`

● To display a repeating movement of a circle:

+main 1 variable movingCircle name? set to "<circle cx='50' cy='50' r='50' style='fill:red;'>\n<animate attributeName='cx' begin='0s' dur='2s' from='50' to='90%' repeatCount='indefinite' /></circle>"value or expression?2 variable raw name? set to (new RawVG()).withContent(movingCircle)value or expression?3 call displayVectorGraphics procedureName?([raw]arguments?)4 end main
+def main() -> None: 1 movingCircle name? = "<circle cx='50' cy='50' r='50' style='fill:red;'>\n<animate attributeName='cx' begin='0s' dur='2s' from='50' to='90%' repeatCount='indefinite' /></circle>"value or expression? # variable definition 2 raw name? = (RawVG()).withContent(movingCircle)value or expression? # variable definition 3 displayVectorGraphics procedureName?([raw]arguments?) # call procedure 4 main()
+static void main() { 1 var movingCircle name? = "<circle cx='50' cy='50' r='50' style='fill:red;'>\n<animate attributeName='cx' begin='0s' dur='2s' from='50' to='90%' repeatCount='indefinite' /></circle>"value or expression?;2 var raw name? = (new RawVG()).withContent(movingCircle)value or expression?;3 displayVectorGraphics procedureName?([raw]arguments?); // call procedure 4 } // main
+Sub main() 1 Dim movingCircle name? = "<circle cx='50' cy='50' r='50' style='fill:red;'>\n<animate attributeName='cx' begin='0s' dur='2s' from='50' to='90%' repeatCount='indefinite' /></circle>"value or expression? ' variable definition 2 Dim raw name? = (New RawVG()).withContent(movingCircle)value or expression? ' variable definition 3 displayVectorGraphics procedureName?({raw}arguments?) ' call procedure 4 End Sub
public class Global {
+static void main() { 1 var movingCircle name? = "<circle cx='50' cy='50' r='50' style='fill:red;'>\n<animate attributeName='cx' begin='0s' dur='2s' from='50' to='90%' repeatCount='indefinite' /></circle>"value or expression?;2 var raw name? = (new RawVG()).withContent(movingCircle)value or expression?;3 displayVectorGraphics procedureName?([raw]arguments?); // call procedure 4 } // main
}

## Combining graphic outputs

Program outputs, whether text or graphical, can be combined in the display. In particular, Block graphics and text or Html printing can share the display along with either Vector graphics or Turtle graphics (but not both).

If you want to share the display in this way, remember that both text and Html print outputs appear sequentially down the display (which can be scrolled), whereas the graphic outputs are positioned in the display using their own absolute coordinate systems.

The order in which the outputs are displayed (and therefore overwrite) is:

1. Block graphics
2. Vector or Turtle graphics
3. Printed text or Html

So some care is needed to manage the layout in the display.

Note that, while vector graphics are being drawn, printed text that exceeds the height of the display does not scroll until the graphic completes.

# Other Types

## Random

### Generating random numbers within a function

It is not possible to use the system methods  random or randint within a function because they create unseen side effects. You may use those system methods outside the function and pass the resulting random number (as an `IntintintIntegerint` or a `FloatfloatdoubleDoubledouble`) as an argument into a function.

It is, however, possible to create and use random numbers within a function, but it requires a different approach and is a little more complex. You use the special type `RandomRandomRandomRandomRandom`. (Note the upper case `RRRRR` required for a type name).

You start by getting a seed random number in your main or in a procedure using method initialiseFromClock:

`variable rndname? set to new Random()value or expression?0rndname? = Random()value or expression? # variable definition0var rndname? = new Random()value or expression?;0Dim rndname? = New Random()value or expression? ' variable definition0var rndname? = new Random()value or expression?;0`
`call rnd.initialiseFromClockprocedureName?(arguments?)0rnd.initialiseFromClockprocedureName?(arguments?) # call procedure0rnd.initialiseFromClockprocedureName?(arguments?); // call procedure0rnd.initialiseFromClockprocedureName?(arguments?) ' call procedure0rnd.initialiseFromClockprocedureName?(arguments?); // call procedure0`

Then, in a function, apply dot method asFloat or asInt as appropriate to the `RandomRandomRandomRandomRandom` passed in, and dot method nextGen to obtain a new instance of `RandomRandomRandomRandomRandom` for generating the next random number.

Avoid applying nextGen more than once on the same `RandomRandomRandomRandomRandom` instance, because it will return the same values.

If the initialiseFromClock call is absent, the program will still generate a sequence of random values, but the sequence will be exactly the same each time you run the program. Initialising from the clock ensures that you get a different sequence each run. Using `RandomRandomRandomRandomRandom` without so initialising, however, can be extremely useful for testing purposes since the results are repeatable.

### Function method for random seed

procedure method | argument Type | action
--- | --- | ---
initialiseFromClock | (none) | uses the system clock to provide a seed from which to generate fresh random values

### Function dot methods on a `RandomRandomRandomRandomRandom`

function dot method | argument Types | return Type | returns
--- | --- | --- | ---
asFloat | (none) | `FloatfloatdoubleDoubledouble` | random `FloatfloatdoubleDoubledouble` value in the range (0.0, 1.0)
asInt | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | random `IntintintIntegerint` value in the range of the arguments
nextGen | (none) | `new codenew codenew codenew code public class Global { new code }` | `RandomRandomRandomRandomRandom` | a new instance of `RandomRandomRandomRandomRandom` for subsequent use

#### Example using `RandomRandomRandomRandomRandom`

● To roll a dice 20 times in a function that returns a 2-tuple of random value and a new instance of `RandomRandomRandomRandomRandom`:

+main 1 variable rnd name? set to new Random()value or expression?2 call rnd.initialiseFromClock procedureName?(arguments?)3 +for i item? in range(1, 20)source? 4 print(randomThrow(rnd).item_0 arguments?)5 reassign rnd variableName? to randomThrow(rnd).item_1 value or expression?6 end for end main +function randomThrow name?(rnd as Random parameter definitions?) returns (Int, Random)Type? 7 return (rnd.asInt(1, 6), rnd.nextGen())value or expression?8 end function
+def main() -> None: 1 rnd name? = Random()value or expression? # variable definition 2 rnd.initialiseFromClock procedureName?(arguments?) # call procedure 3 +for i item? in range(1, 20)source?: 4 print(randomThrow(rnd).item_0 arguments?)5 rnd variableName? = randomThrow(rnd).item_1 value or expression? # reassign variable 6 +def randomThrow name?(rnd: Random parameter definitions?) -> tuple[int, Random]Type?: # function 7 return (rnd.asInt(1, 6), rnd.nextGen())value or expression?8 main()
+static void main() { 1 var rnd name? = new Random()value or expression?;2 rnd.initialiseFromClock procedureName?(arguments?); // call procedure 3 +foreach (i item? in range(1, 20)source?) { 4 Console.WriteLine(randomThrow(rnd).item_0 arguments?); // print 5 rnd variableName? = randomThrow(rnd).item_1 value or expression?; // reassign variable 6 } // foreach } // main +static (int, Random)Type? randomThrow name?(Random rnd parameter definitions?) { // function 7 return (rnd.asInt(1, 6), rnd.nextGen())value or expression?;8 } // function
+Sub main() 1 Dim rnd name? = New Random()value or expression? ' variable definition 2 rnd.initialiseFromClock procedureName?(arguments?) ' call procedure 3 +For Each i item? In range(1, 20)source? 4 Console.WriteLine(randomThrow(rnd).item_0 arguments?) ' print 5 rnd variableName? = randomThrow(rnd).item_1 value or expression? ' reassign variable 6 Next i End Sub +Function randomThrow name?(rnd As Random parameter definitions?) As (Integer, Random)Type? 7 Return (rnd.asInt(1, 6), rnd.nextGen())value or expression?8 End Function
public class Global {
+static void main() { 1 var rnd name? = new Random()value or expression?;2 rnd.initialiseFromClock procedureName?(arguments?); // call procedure 3 +foreach (i item? in range(1, 20)source?) { 4 System.out.println(randomThrow(rnd).item_0 arguments?); // print 5 rnd variableName? = randomThrow(rnd).item_1 value or expression?; // reassign variable 6 } // foreach } // main +static (int, Random)Type? randomThrow name?(Random rnd parameter definitions?) { // function 7 return (rnd.asInt(1, 6), rnd.nextGen())value or expression?;8 } // function
}

# Input/output

This section covers a variety of input and output facilities:

- Keyboard input 
- Text file input/output 
- Rendering Html in the display 
- Displaying images from URLs 
- Sound 

## Keyboard input

soliciting and retrieving keyboard input requires using these system methods:

system method | argument Types | return Types | action
--- | --- | --- | ---
getKey | (none) | `StringstrstringStringString` | returns the last character last pressed on the keyboard during program execution
getKeyWithModifier | (none) | 2-Tuple: (`StringstrstringStringString`, `StringstrstringStringString`) | returns the last key combination pressed on the keyboard: the key pressed and the modifier key's name (if also pressed)
getNumericKey | (none) | `StringstrstringStringString` | returns either the numeric key last pressed or, if the last pressed key was not numeric, then `"-1""-1""-1""-1""-1"`
input | `StringstrstringStringString` | `StringstrstringStringString` | prints the string as a prompt, and returns the typed input when Enter is pressed, similar to the input instruction.
inputStringWithLimits | `StringstrstringStringString`, `IntintintIntegerint`, `IntintintIntegerint` | `StringstrstringStringString` | prints the string as a prompt and returns the typed input when Enter is pressed provided the length of the response is within the minimum and maximum limits specified. If it is not, the prompt is repeated with the relevant limit displayed
inputStringFromOptions | `StringstrstringStringString`, `ListlistListListList`<of `StringstrstringStringString`> | `StringstrstringStringString` | prints the string as a prompt and returns the typed input when Enter is pressed provided it is one of the options in the list. If it is not, the prompt is repeated with the options displayed
inputInt | `StringstrstringStringString` | `IntintintIntegerint` | prints the string as a prompt and returns the value of the typed input when Enter is pressed provided that it is an integer. If it is not, the prompt is repeated with an error message
inputIntBetween | `StringstrstringStringString`, `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | prints the string as a prompt and returns the value of the typed input when Enter is pressed provided that it is an integer with a value in the (inclusive) range. The first range value must be less than or equal to the second
inputFloat | `StringstrstringStringString` | `FloatfloatdoubleDoubledouble` | prints the string as a prompt and returns the value of the typed input when Enter is pressed provided that it is a number. If it is not, the prompt is repeated with an error message
inputFloatBetween | `StringstrstringStringString`, `IntintintIntegerint`, `IntintintIntegerint` | `FloatfloatdoubleDoubledouble` | prints the string as a prompt and returns the value of the typed input when Enter is pressed provided that it is a number with a value in the (inclusive) range. The first range value must be less than or equal to the second
waitForKey | (none) | `StringstrstringStringString` | pauses execution of the program until a key is pressed on the keyboard, and returns either a character or the name of a non-character key

### Reading keys 'on the fly'

In some applications – especially in games, for example – you want the program to react to a key pressed by the user, but without holding up the program to wait for value to be input.

Whether your application makes use of graphics, or uses the display just for text, reading keystrokes 'on the fly' is done via one of the three methods shown here:

+main 1 variable key1 name? set to getKey()value or expression?2 variable key2 name? set to getNumericKey()value or expression?3 variable km name? set to getKeyWithModifier()value or expression?4 variable keyCap name? set to km.item_0 value or expression?5 variable keyMod name? set to km.item_1 value or expression?6 end main
+def main() -> None: 1 key1 name? = getKey()value or expression? # variable definition 2 key2 name? = getNumericKey()value or expression? # variable definition 3 km name? = getKeyWithModifier()value or expression? # variable definition 4 keyCap name? = km.item_0 value or expression? # variable definition 5 keyMod name? = km.item_1 value or expression? # variable definition 6 main()
+static void main() { 1 var key1 name? = getKey()value or expression?;2 var key2 name? = getNumericKey()value or expression?;3 var km name? = getKeyWithModifier()value or expression?;4 var keyCap name? = km.item_0 value or expression?;5 var keyMod name? = km.item_1 value or expression?;6 } // main
+Sub main() 1 Dim key1 name? = getKey()value or expression? ' variable definition 2 Dim key2 name? = getNumericKey()value or expression? ' variable definition 3 Dim km name? = getKeyWithModifier()value or expression? ' variable definition 4 Dim keyCap name? = km.item_0 value or expression? ' variable definition 5 Dim keyMod name? = km.item_1 value or expression? ' variable definition 6 End Sub
public class Global {
+static void main() { 1 var key1 name? = getKey()value or expression?;2 var key2 name? = getNumericKey()value or expression?;3 var km name? = getKeyWithModifier()value or expression?;4 var keyCap name? = km.item_0 value or expression?;5 var keyMod name? = km.item_1 value or expression?;6 } // main
}

- When any of these functions (except waitForKey) is called, the system does not wait for a response, but immediately returns a `StringstrstringStringString` or Tuple.
- getKey returns a string containing the keyboard character last pressed, possibly shifted, e.g. "z" or "@".
- getNumericKey returns a string containing either a digit ("0".."9") or, if the last key pressed was not numeric, then "-1". A digit will be returned if the key pressed was either from the main keyboard, or from the numeric keypad when NumLock is on.
- getKeyWithModifier returns a 2-Tuple of two strings: the key last pressed and the name of one modifier key `"Shift""Shift""Shift""Shift""Shift"`, `"Ctrl""Ctrl""Ctrl""Ctrl""Ctrl"` or `"Alt""Alt""Alt""Alt""Alt"` if simultaneously pressed. If no modifier had been pressed, the Tuple's second item will be the empty string. Note that a few such modified keys will be acted on by the browser and may not then be passed to your program.
- Non-printable keys will also be returned as strings, e.g. `"Home""Home""Home""Home""Home"`, `"End""End""End""End""End"`, `"Delete""Delete""Delete""Delete""Delete"`, `"Tab""Tab""Tab""Tab""Tab"`, `"Backspace""Backspace""Backspace""Backspace""Backspace"`, `"Enter""Enter""Enter""Enter""Enter"`, `"Escape""Escape""Escape""Escape""Escape"`, `"ArrowUp""ArrowUp""ArrowUp""ArrowUp""ArrowUp"` etc., function key `"Fn""Fn""Fn""Fn""Fn"`, `"AltGraph""AltGraph""AltGraph""AltGraph""AltGraph"`, `"Meta""Meta""Meta""Meta""Meta"`, `"ContextMenu""ContextMenu""ContextMenu""ContextMenu""ContextMenu"`, as well as most others.
- Pressing just control keys Shift, Ctrl (⌘ Command under macOS) or Alt keys will not be detected by getKey.
- If no key has been pressed (since the last time the method was called), it will return the empty string.
- All these methods are system methods because they have a dependency on the system and so may be used only within a procedure or in main.
- Use the procedure method clearKeyBuffer if you want to enforce that the user cannot get too far ahead of the program by hitting keys in rapid succession.
- Method waitForKey waits for a key to be pressed, and returns it.
- Procedure methodpressAnyKeyToContinue gives an optional prompt and is used when you don't need to know which key was pressed. Its argument is a Boolean value:
  if true, the prompt "Press any key to continue" appears,
  if false, no prompt appears.

+main 1 call pressAnyKeyToContinue procedureName?(?)2 print("OK, press A or B"arguments?)3 variable key name? set to waitForKey()value or expression?4 print($"That was {key}"arguments?)5 end main
+def main() -> None: 1 pressAnyKeyToContinue procedureName?(?) # call procedure 2 print("OK, press A or B"arguments?)3 key name? = waitForKey()value or expression? # variable definition 4 print(f"That was {key}"arguments?)5 main()
+static void main() { 1 pressAnyKeyToContinue procedureName?(?); // call procedure 2 Console.WriteLine("OK, press A or B"arguments?); // print 3 var key name? = waitForKey()value or expression?;4 Console.WriteLine($"That was {key}"arguments?); // print 5 } // main
+Sub main() 1 pressAnyKeyToContinue procedureName?(?) ' call procedure 2 Console.WriteLine("OK, press A or B"arguments?) ' print 3 Dim key name? = waitForKey()value or expression? ' variable definition 4 Console.WriteLine($"That was {key}"arguments?) ' print 5 End Sub
public class Global {
+static void main() { 1 pressAnyKeyToContinue procedureName?(?); // call procedure 2 System.out.println("OK, press A or B"arguments?); // print 3 var key name? = waitForKey()value or expression?;4 System.out.println(String.format("That was %", key)arguments?); // print 5 } // main
}

## Text file input/output

Reading or writing a text file requires that you open (for reading) or create (for writing) a file using these system methods:

system method | argument Types | return Class | action
--- | --- | --- | ---
createFileForWriting | `StringstrstringStringString` | `TextFileWriterTextFileWriterTextFileWriterTextFileWriterTextFileWriter` | sets up a buffer for the data to be output, and specifies a filename (or the empty string) with or without the default filetype of .txt, and returns a file handle see Writing text files 
openFileForReading | (none) | `TextFileReaderTextFileReaderTextFileReaderTextFileReaderTextFileReader` | opens a file system dialog to choose the filename of filetype .txt to be read, and returns a file handle see Reading text files 

### Writing text files

The `TextFileWriterTextFileWriterTextFileWriterTextFileWriterTextFileWriter` Class is used to write textual data to a file.

An instance is created by the system method createFileForWriting.

The available procedure methods are:

procedure method | argument Type | action
--- | --- | ---
writeLine | `StringstrstringStringString` | writes the string to the buffer
writeWholeFile | `StringstrstringStringString` | writes the string to the buffer and then outputs the buffer to the file system
saveAndClose | none | writes the buffer to the file system

These methods may be used to write a whole file in one go:

+main 1 variable file name? set to createFileForWriting("myFile.txt")value or expression?2 call file.writeWholeFile procedureName?("Text line 1\nText line 2"arguments?)3 end main
+def main() -> None: 1 file name? = createFileForWriting("myFile.txt")value or expression? # variable definition 2 file.writeWholeFile procedureName?("Text line 1\nText line 2"arguments?) # call procedure 3 main()
+static void main() { 1 var file name? = createFileForWriting("myFile.txt")value or expression?;2 file.writeWholeFile procedureName?("Text line 1\nText line 2"arguments?); // call procedure 3 } // main
+Sub main() 1 Dim file name? = createFileForWriting("myFile.txt")value or expression? ' variable definition 2 file.writeWholeFile procedureName?("Text line 1\nText line 2"arguments?) ' call procedure 3 End Sub
public class Global {
+static void main() { 1 var file name? = createFileForWriting("myFile.txt")value or expression?;2 file.writeWholeFile procedureName?("Text line 1\nText line 2"arguments?); // call procedure 3 } // main
}

#### Notes

- `writeLinewriteLinewriteLinewriteLinewriteLine` adds the string it is passed onto the end of any data previously written, with a newline character (\n) automatically appended.
- When execution reaches `saveAndClosesaveAndClosesaveAndClosesaveAndClosesaveAndClose` you will be presented with a dialog to confirm (or edit) the given filename and location where it is to be saved. It is not therefore strictly necessary to specify a filename when creating the file, since it can be specified by the user in the dialog so, in that case, you might put the empty string `""""""""""` into the parameter of `createFileForWritingcreateFileForWritingcreateFileForWritingcreateFileForWritingcreateFileForWriting`.
- `writeWholeFilewriteWholeFilewriteWholeFilewriteWholeFilewriteWholeFile` puts the string it is given into the file and then automatically saves the file, so the user will be presented with the same dialog as if `saveAndClosesaveAndClosesaveAndClosesaveAndClosesaveAndClose` had been called.
- Calling any method on a file that has already been closed (by calling either `saveAndClosesaveAndClosesaveAndClosesaveAndClosesaveAndClose` or by `writeWholeFilewriteWholeFilewriteWholeFilewriteWholeFilewriteWholeFile`) will result in a runtime error.
- If the user were to click Cancel in the save dialogue, then the program will exit with an error. To guard against this possibility (it might mean the loss of important data), you should perform the save and close within a try instruction like this (where `CustomErrorCustomErrorCustomErrorCustomErrorCustomError` is a Class provided by Elan for this purpose):
  main
  main
  main
  main
  main
  or you could make the code offer the user options: to save again, or to continue without saving.

### Reading text files

The `TextFileReaderTextFileReaderTextFileReaderTextFileReaderTextFileReader` Class is used to read text data from a file with type extension .txt.

An instance is created by the system method openFileForReading.

The available procedure methods are:

procedure method | argument Type | action
--- | --- | ---
readLine | (none) | reads the next substring from the file that is terminated with a newline
readWholeFile | (none) | reads the whole file and closes the file
endOfFile | (none) | returns true after the last line has been read – otherwise false
close | (none) | closes the file

These methods may be used to read a whole file in one go:

+main 1 variable file name? set to openFileForReading()value or expression?2 variable text name? set to file.readWholeFile()value or expression?3 print(text arguments?)4 end main
+def main() -> None: 1 file name? = openFileForReading()value or expression? # variable definition 2 text name? = file.readWholeFile()value or expression? # variable definition 3 print(text arguments?)4 main()
+static void main() { 1 var file name? = openFileForReading()value or expression?;2 var text name? = file.readWholeFile()value or expression?;3 Console.WriteLine(text arguments?); // print 4 } // main
+Sub main() 1 Dim file name? = openFileForReading()value or expression? ' variable definition 2 Dim text name? = file.readWholeFile()value or expression? ' variable definition 3 Console.WriteLine(text arguments?) ' print 4 End Sub
public class Global {
+static void main() { 1 var file name? = openFileForReading()value or expression?;2 var text name? = file.readWholeFile()value or expression?;3 System.out.println(text arguments?); // print 4 } // main
}

#### Notes

- `openFileForReadingopenFileForReadingopenFileForReadingopenFileForReadingopenFileForReading` will present the user with a dialog to select the file.
- `readWholeFilereadWholeFilereadWholeFilereadWholeFilereadWholeFile` returns a `StringstrstringStringString` containing every character in the file, without any trimming. It automatically closes the file after the read.
- `readLinereadLinereadLinereadLinereadLine` reads as far as the next newline character (\n) and then automatically trims the line to remove any spaces and/or carriage-returns (which some file systems insert after the newline automatically) from the resulting line returned as a `StringstrstringStringString`. If this behaviour is not desired, you can use `readWholeFilereadWholeFilereadWholeFilereadWholeFilereadWholeFile`, which does no trimming, and then parse the resulting `StringstrstringStringString` into separate lines.
- Calling `file.closefile.closefile.closefile.closefile.close` after reading line by line is strongly recommended to avoid any risk of leaving the file locked. It is not necessary to call it after using `readWholeFilereadWholeFilereadWholeFilereadWholeFilereadWholeFile` because that method automatically closes the file.
- Calling any method on a file that is already closed will result in a runtime error.

## Rendering Html in the display

If you embed Html code in a string and then attempt to print it, you will see the string displayed literally: the Html tags will not be recognised. This is for security reasons. However, it is possible to display formatted Html in the display. The following code:

call displayHtml procedureName?("<h1 style='color: blue;'>A heading</h1><p>some text</p>"arguments?)0
displayHtml procedureName?("<h1 style='color: blue;'>A heading</h1><p>some text</p>"arguments?) # call procedure 0
displayHtml procedureName?("<h1 style='color: blue;'>A heading</h1><p>some text</p>"arguments?); // call procedure 0
displayHtml procedureName?("<h1 style='color: blue;'>A heading</h1><p>some text</p>"arguments?) ' call procedure 0
displayHtml procedureName?("<h1 style='color: blue;'>A heading</h1><p>some text</p>"arguments?); // call procedure 0

will produce:

This Html forms another 'layer' in the IDE's display pane. Any plain text that you print (using call procedure print() or any of the print procedures) will be overlaid on top of this.

You can clear just the Html layer in the display using the procedure clearHtml .

For specifying style or other attributes within Html tags, the attribute values should be enclosed in single quotation marks ' as shown above. Html will recognise single or double quotation marks, but entering double quotation marks would terminate the Elan string. Alternatively, you could use the constant quotes within curly braces as an interpolated field .

### Using an embedded CSS stylesheet

You can also specify a <style> tag at the start of your Html string, to apply to the whole Html being displayed. In this case you would put the style definition into a named value as a literal but enclosed in single quotes, for example:

+main 1 variable style name? set to "<style> h1 { color: Red; font-size: 24pt; } p { font-family: Serif; } </style>"value or expression?2 call displayHtml procedureName?($"{style}<h1>New heading</h1><p>some new text</p>"arguments?)3 end main
+def main() -> None: 1 style name? = "<style> h1 { color: Red; font-size: 24pt; } p { font-family: Serif; } </style>"value or expression? # variable definition 2 displayHtml procedureName?(f"{style}<h1>New heading</h1><p>some new text</p>"arguments?) # call procedure 3 main()
+static void main() { 1 var style name? = "<style> h1 { color: Red; font-size: 24pt; } p { font-family: Serif; } </style>"value or expression?;2 displayHtml procedureName?($"{style}<h1>New heading</h1><p>some new text</p>"arguments?); // call procedure 3 } // main
+Sub main() 1 Dim style name? = "<style> h1 { color: Red; font-size: 24pt; } p { font-family: Serif; } </style>"value or expression? ' variable definition 2 displayHtml procedureName?($"{style}<h1>New heading</h1><p>some new text</p>"arguments?) ' call procedure 3 End Sub
public class Global {
+static void main() { 1 var style name? = "<style> h1 { color: Red; font-size: 24pt; } p { font-family: Serif; } </style>"value or expression?;2 displayHtml procedureName?(String.format("%<h1>New heading</h1><p>some new text</p>", style)arguments?); // call procedure 3 } // main
}

will produce:

## Displaying images from URLs

An image that can be retrieved with an http or https URL may be sent to the display, though note that other URI schemes, such as in file://host/path to access an image from your local file system, are not supported. Here are two techniques:

- put the Html <img> tag into a string and then call the displayHtml method on it, thus:
  +main 1 variable pic name? set to "<img src='https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_%2828225976491%29.jpg' width='400' height='200' title='shark' alt='shark'>"value or expression?2 call displayHtml procedureName?(pic arguments?)3 end main
  +def main() -> None: 1 pic name? = "<img src='https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_%2828225976491%29.jpg' width='400' height='200' title='shark' alt='shark'>"value or expression? # variable definition 2 displayHtml procedureName?(pic arguments?) # call procedure 3 main()
  +static void main() { 1 var pic name? = "<img src='https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_%2828225976491%29.jpg' width='400' height='200' title='shark' alt='shark'>"value or expression?;2 displayHtml procedureName?(pic arguments?); // call procedure 3 } // main
  +Sub main() 1 Dim pic name? = "<img src='https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_%2828225976491%29.jpg' width='400' height='200' title='shark' alt='shark'>"value or expression? ' variable definition 2 displayHtml procedureName?(pic arguments?) ' call procedure 3 End Sub
  public class Global {
  +static void main() { 1 var pic name? = "<img src='https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_%2828225976491%29.jpg' width='400' height='200' title='shark' alt='shark'>"value or expression?;2 displayHtml procedureName?(pic arguments?); // call procedure 3 } // main
  }

  The usual <img> tag attributes are respected, though `altaltaltaltalt` does not give the expected tooltip when hovering over the image, and `titletitletitletitletitle` is only a descriptive comment.

- put the URL into a Vector Graphics `ImageVGImageVGImageVGImageVGImageVG` definition, set properties by calling vector graphic procedures , then call the method displayVectorGraphics on it, thus:
  +main 1 variable sharkUrl name? set to "https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_(28225976491).jpg"value or expression?2 variable sharkVG name? set to new ImageVG(sharkUrl)value or expression?3 call sharkVG.setWidth procedureName?(400 arguments?)4 call sharkVG.setHeight procedureName?(200 arguments?)5 call sharkVG.setAlt procedureName?("Shark"arguments?)6 call displayVectorGraphics procedureName?([sharkVG]arguments?)7 end main
  +def main() -> None: 1 sharkUrl name? = "https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_(28225976491).jpg"value or expression? # variable definition 2 sharkVG name? = ImageVG(sharkUrl)value or expression? # variable definition 3 sharkVG.setWidth procedureName?(400 arguments?) # call procedure 4 sharkVG.setHeight procedureName?(200 arguments?) # call procedure 5 sharkVG.setAlt procedureName?("Shark"arguments?) # call procedure 6 displayVectorGraphics procedureName?([sharkVG]arguments?) # call procedure 7 main()
  +static void main() { 1 var sharkUrl name? = "https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_(28225976491).jpg"value or expression?;2 var sharkVG name? = new ImageVG(sharkUrl)value or expression?;3 sharkVG.setWidth procedureName?(400 arguments?); // call procedure 4 sharkVG.setHeight procedureName?(200 arguments?); // call procedure 5 sharkVG.setAlt procedureName?("Shark"arguments?); // call procedure 6 displayVectorGraphics procedureName?([sharkVG]arguments?); // call procedure 7 } // main
  +Sub main() 1 Dim sharkUrl name? = "https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_(28225976491).jpg"value or expression? ' variable definition 2 Dim sharkVG name? = New ImageVG(sharkUrl)value or expression? ' variable definition 3 sharkVG.setWidth procedureName?(400 arguments?) ' call procedure 4 sharkVG.setHeight procedureName?(200 arguments?) ' call procedure 5 sharkVG.setAlt procedureName?("Shark"arguments?) ' call procedure 6 displayVectorGraphics procedureName?({sharkVG}arguments?) ' call procedure 7 End Sub
  public class Global {
  +static void main() { 1 var sharkUrl name? = "https://upload.wikimedia.org/wikipedia/commons/0/08/Corl0207_(28225976491).jpg"value or expression?;2 var sharkVG name? = new ImageVG(sharkUrl)value or expression?;3 sharkVG.setWidth procedureName?(400 arguments?); // call procedure 4 sharkVG.setHeight procedureName?(200 arguments?); // call procedure 5 sharkVG.setAlt procedureName?("Shark"arguments?); // call procedure 6 displayVectorGraphics procedureName?([sharkVG]arguments?); // call procedure 7 } // main
  }

## Sound

The tone procedure allows the generation of a simple tone. It requires three arguments to be provided:

- the duration of the generated tone specified in milliseconds (`IntintintIntegerint`)
- the frequency of the generated tone in Hertz (`IntintintIntegerint`)
- the volume of the tone (`FloatfloatdoubleDoubledouble`)

Note that the volume parameter is only relative in that the actual volume will be modified by the various sound settings on the output device, and may even be muted.

#### Example using tone

● An example that plays a C major scale first ascending then descending:

+main 1 variable scale name? set to [262, 294, 330, 349, 392, 440, 494, 523]value or expression?2 variable scaleL name? set to scale.length()value or expression?3 variable quaver name? set to 250 value or expression?4 variable volume name? set to 1.5 value or expression?5 +for i item? in range(0, scaleL)source? 6 call tone procedureName?(quaver, scale[i], volume arguments?)7 end for call sleep procedureName?(1 arguments?)8 +for i item? in range(0, scaleL)source? 9 call tone procedureName?(quaver, scale[scaleL - 1 - i], volume arguments?)10 end for end main
+def main() -> None: 1 scale name? = [262, 294, 330, 349, 392, 440, 494, 523]value or expression? # variable definition 2 scaleL name? = scale.length()value or expression? # variable definition 3 quaver name? = 250 value or expression? # variable definition 4 volume name? = 1.5 value or expression? # variable definition 5 +for i item? in range(0, scaleL)source?: 6 tone procedureName?(quaver, scale[i], volume arguments?) # call procedure 7 sleep procedureName?(1 arguments?) # call procedure 8 +for i item? in range(0, scaleL)source?: 9 tone procedureName?(quaver, scale[scaleL - 1 - i], volume arguments?) # call procedure 10 main()
+static void main() { 1 var scale name? = [262, 294, 330, 349, 392, 440, 494, 523]value or expression?;2 var scaleL name? = scale.length()value or expression?;3 var quaver name? = 250 value or expression?;4 var volume name? = 1.5 value or expression?;5 +foreach (i item? in range(0, scaleL)source?) { 6 tone procedureName?(quaver, scale[i], volume arguments?); // call procedure 7 } // foreach sleep procedureName?(1 arguments?); // call procedure 8 +foreach (i item? in range(0, scaleL)source?) { 9 tone procedureName?(quaver, scale[scaleL - 1 - i], volume arguments?); // call procedure 10 } // foreach } // main
+Sub main() 1 Dim scale name? = {262, 294, 330, 349, 392, 440, 494, 523}value or expression? ' variable definition 2 Dim scaleL name? = scale.length()value or expression? ' variable definition 3 Dim quaver name? = 250 value or expression? ' variable definition 4 Dim volume name? = 1.5 value or expression? ' variable definition 5 +For Each i item? In range(0, scaleL)source? 6 tone procedureName?(quaver, scale[i], volume arguments?) ' call procedure 7 Next i sleep procedureName?(1 arguments?) ' call procedure 8 +For Each i item? In range(0, scaleL)source? 9 tone procedureName?(quaver, scale[scaleL - 1 - i], volume arguments?) ' call procedure 10 Next i End Sub
public class Global {
+static void main() { 1 var scale name? = [262, 294, 330, 349, 392, 440, 494, 523]value or expression?;2 var scaleL name? = scale.length()value or expression?;3 var quaver name? = 250 value or expression?;4 var volume name? = 1.5 value or expression?;5 +foreach (i item? in range(0, scaleL)source?) { 6 tone procedureName?(quaver, scale[i], volume arguments?); // call procedure 7 } // foreach sleep procedureName?(1 arguments?); // call procedure 8 +foreach (i item? in range(0, scaleL)source?) { 9 tone procedureName?(quaver, scale[scaleL - 1 - i], volume arguments?); // call procedure 10 } // foreach } // main
}

# Common methods

## Common dot methods

Click on a type to go to the Type's function dot methods, or on  to go to the specific method on that Type.

Dot method | Value Type | Reference Type | Tuple
--- | --- | --- | ---
| `IntintintIntegerint`  | `FloatfloatdoubleDoubledouble`  | `BooleanboolboolBooleanbool`  | `StringstrstringStringString`  | `ListlistListListList`  | `DictionaryDictionaryDictionaryDictionaryDictionary`  | `HashSetHashSetHashSetHashSetHashSet`  | `StackStackStackStackStack`  | `QueueQueueQueueQueueQueue`  |
ceiling |   note 2. |   |  |  |  |  |  |  |  |
contains |  |  |  |   |   |   note 4. |   |  |  |
equals |   |   |   |   |   |   |   |   |   |  
floor |   note 2. |   |  |  |  |  |  |  |  |
indexOf |  |  |  |   |   |  |  |  |  |
isInfinite |   note 2. |   |  |  |  |  |  |  |  |
isNan |   note 2. |   |  |  |  |  |  |  |  |
length |  |  |  |   |   |   note 3. |   |   |   |
notEqualTo |   |   |   |   |   |   |   |   |   |  
peek |  |  |  |  |  |  |  |   |   |
round |   note 2. |   |  |  |  |  |  |  |  |
toString note 1. |   |   |   |   |   |   |   |   |   |  
withSet |  |  |  |  |   |   |  |  |  |
withRemoveAt |  |  |  |  |   |   |  |  |  |

#### Notes

1. The method toString is so widely applicable because it enables you to print all variables and data structures to the IDE's display pane for debugging purposes.
2. methods ceiling, floor, isInfinite, isNaN and round are designed for use on `FloatfloatdoubleDoubledouble` values, but they can accept `IntintintIntegerint` values without raising an error.
3. The length of a `DictionaryDictionaryDictionaryDictionaryDictionary` can be found by applying method length to the list returned by method keys on the dictionary:

   `print(di.keys().length()arguments?)0print(di.keys().length()arguments?)0Console.WriteLine(di.keys().length()arguments?); // print0Console.WriteLine(di.keys().length()arguments?) ' print0System.out.println(di.keys().length()arguments?); // print0` | ⟶ | 15

4. Checking whether an item is contained in a `DictionaryDictionaryDictionaryDictionaryDictionary` can be done by applying method contains to the list returned by methods keys and values on the dictionary:

   `call printprocedureName?(di.keys().contains("widget")arguments?)0printprocedureName?(di.keys().contains("widget")arguments?)0printprocedureName?(di.keys().contains("widget")arguments?);0printprocedureName?(di.keys().contains("widget")arguments?)0printprocedureName?(di.keys().contains("widget")arguments?);0` | ⟶ | true or false
   `call printprocedureName?(di.values().contains(42)arguments?)0printprocedureName?(di.values().contains(42)arguments?)0printprocedureName?(di.values().contains(42)arguments?);0printprocedureName?(di.values().contains(42)arguments?)0printprocedureName?(di.values().contains(42)arguments?);0` | ⟶ | true or false

# Library procedures

All procedures are accessed via a `callcallcallcallcall`  statement.

## Standalone procedures

procedure | input argument Types | output argument Types | action
--- | --- | --- | ---
clearPrintedText | (none) | (none) | clears the IDE's display pane
clearBlocks | (none) | (none) | clears the block graphics layer of the IDE's display pane
clearVectorGraphics | (none) | (none) | clears the vector graphics layer of the IDE's display pane
clearHtml | (none) | (none) | clears the Html layer of the IDE's display pane
clearAllDisplays | (none) | (none) | clears display pane as well as the blocks, vector graphics and Html layers
clearKeyBuffer | (none) | (none) | clears the IDE's keyboard input
pressAnyKeyToContinue | `BooleanboolboolBooleanbool` | (none) | pauses execution of the program until a keyboard key is pressed if the argument is true 'Press any key to continue' is first displayed, if false nothing is displayed
printNoLine | `StringstrstringStringString` | (none) | prints the string to the display without appending a newline so a following call will output on the same line. You can put your own \n newlines in the argument string
printTab | `IntintintIntegerint`, `StringstrstringStringString` | (none) | prints the string to the display starting at the tab position given (from 0) without appending a newline
sleep | `IntintintIntegerint` | (none) | pauses the execution of the program for the specified number of seconds, e.g. for a game `sleep(1.5)sleep(1.5)sleep(1.5)sleep(1.5)sleep(1.5)` delays execution for 1.5 seconds
sleep_ms | `IntintintIntegerint` | (none) | pauses the execution of the program for the specified number of milliseconds, e.g. `sleep(100)sleep(100)sleep(100)sleep(100)sleep(100)` delays execution for one tenth of a second

#### Examples using print and printTab

● Procedure print sends text strings to the display pane:

+main 1 print("Hello"arguments?)2 variable a name? set to 3 value or expression?3 variable b name? set to 4 value or expression?4 print(a*b arguments?)5 print($"{a} times {b}) equals {a*b}"arguments?)6 variable t name? set to (true, 42)value or expression?7 print(t.item_0 arguments?)8 print(t.item_1 arguments?)9 end main +def main() -> None: 1 print("Hello"arguments?)2 a name? = 3 value or expression? # variable definition 3 b name? = 4 value or expression? # variable definition 4 print(a*b arguments?)5 print(f"{a} times {b}) equals {a*b}"arguments?)6 t name? = (True, 42)value or expression? # variable definition 7 print(t.item_0 arguments?)8 print(t.item_1 arguments?)9 main() +static void main() { 1 Console.WriteLine("Hello"arguments?); // print 2 var a name? = 3 value or expression?;3 var b name? = 4 value or expression?;4 Console.WriteLine(a*b arguments?); // print 5 Console.WriteLine($"{a} times {b}) equals {a*b}"arguments?); // print 6 var t name? = (true, 42)value or expression?;7 Console.WriteLine(t.item_0 arguments?); // print 8 Console.WriteLine(t.item_1 arguments?); // print 9 } // main +Sub main() 1 Console.WriteLine("Hello"arguments?) ' print 2 Dim a name? = 3 value or expression? ' variable definition 3 Dim b name? = 4 value or expression? ' variable definition 4 Console.WriteLine(a*b arguments?) ' print 5 Console.WriteLine($"{a} times {b}) equals {a*b}"arguments?) ' print 6 Dim t name? = (True, 42)value or expression? ' variable definition 7 Console.WriteLine(t.item_0 arguments?) ' print 8 Console.WriteLine(t.item_1 arguments?) ' print 9 End Sub public class Global { +static void main() { 1 System.out.println("Hello"arguments?); // print 2 var a name? = 3 value or expression?;3 var b name? = 4 value or expression?;4 System.out.println(a*b arguments?); // print 5 System.out.println(String.format("% times %) equals %", a, b, a*b)arguments?); // print 6 var t name? = (true, 42)value or expression?;7 System.out.println(t.item_0 arguments?); // print 8 System.out.println(t.item_1 arguments?); // print 9 } // main } | ⟶ ⟶ ⟶ ⟶ ⟶ | Hello 12 3 times 4 equals 12 [using interpolated strings ] [defining a 2-Tuple ] true 42

● Procedure printTab helps in the layout of information printed to the display, e.g. when printing columns of data:

+main 1 call printTab procedureName?(0, "Number"arguments?)2 call printTab procedureName?(10, "Square"arguments?)3 call printTab procedureName?(20, "Cube\n"arguments?)4 +for i item? in range(1, 11)source? 5 call printTab procedureName?(0, i.toString()arguments?)6 call printTab procedureName?(10, $"{pow(i, 2)}"arguments?)7 call printTab procedureName?(20, $"{pow(i, 3)}\n"arguments?)8 end for end main
+def main() -> None: 1 printTab procedureName?(0, "Number"arguments?) # call procedure 2 printTab procedureName?(10, "Square"arguments?) # call procedure 3 printTab procedureName?(20, "Cube\n"arguments?) # call procedure 4 +for i item? in range(1, 11)source?: 5 printTab procedureName?(0, i.toString()arguments?) # call procedure 6 printTab procedureName?(10, f"{pow(i, 2)}"arguments?) # call procedure 7 printTab procedureName?(20, f"{pow(i, 3)}\n"arguments?) # call procedure 8 main()
+static void main() { 1 printTab procedureName?(0, "Number"arguments?); // call procedure 2 printTab procedureName?(10, "Square"arguments?); // call procedure 3 printTab procedureName?(20, "Cube\n"arguments?); // call procedure 4 +foreach (i item? in range(1, 11)source?) { 5 printTab procedureName?(0, i.toString()arguments?); // call procedure 6 printTab procedureName?(10, $"{pow(i, 2)}"arguments?); // call procedure 7 printTab procedureName?(20, $"{pow(i, 3)}\n"arguments?); // call procedure 8 } // foreach } // main
+Sub main() 1 printTab procedureName?(0, "Number"arguments?) ' call procedure 2 printTab procedureName?(10, "Square"arguments?) ' call procedure 3 printTab procedureName?(20, "Cube\n"arguments?) ' call procedure 4 +For Each i item? In range(1, 11)source? 5 printTab procedureName?(0, i.toString()arguments?) ' call procedure 6 printTab procedureName?(10, $"{pow(i, 2)}"arguments?) ' call procedure 7 printTab procedureName?(20, $"{pow(i, 3)}\n"arguments?) ' call procedure 8 Next i End Sub
public class Global {
+static void main() { 1 printTab procedureName?(0, "Number"arguments?); // call procedure 2 printTab procedureName?(10, "Square"arguments?); // call procedure 3 printTab procedureName?(20, "Cube\n"arguments?); // call procedure 4 +foreach (i item? in range(1, 11)source?) { 5 printTab procedureName?(0, i.toString()arguments?); // call procedure 6 printTab procedureName?(10, String.format("%", pow(i, 2))arguments?); // call procedure 7 printTab procedureName?(20, String.format("%\n", pow(i, 3))arguments?); // call procedure 8 } // foreach } // main
}

● For numeric output, it is preferable to right-align the columns, e.g. when listing powers of 9:

main
main
main
main
main

## Type instance procedures

Procedures applicable to standard Reference Types are linked from:

- Procedure methods on a `ListlistListListList` 
- Procedure methods on a `DictionaryDictionaryDictionaryDictionaryDictionary` 
- Procedure methods on a `TurtleTurtleTurtleTurtleTurtle` 

User-defined Classes may have procedures that can be applied to their Class instances.

# Library methods

These methods may be referenced from within a function.

## Standalone functions

Standalone library functions always return a value and are therefore used in contexts that expect a value, such as in the right-hand side of a variable definition declaration or a reassign variable, either on their own or within a more complex expression.

Standalone library functions require at least one argument to be passed (in round brackets), corresponding to the parameters defined for that function.

system method | argument Types | return Types | returns
--- | --- | --- | ---
parseAsFloat | `StringstrstringStringString` | `BooleanboolboolBooleanbool`, `FloatfloatdoubleDoubledouble` | a 2-Tuple in which the first item is true if the parse was successful, – false otherwise and, if true, the second item is the `FloatfloatdoubleDoubledouble` value, otherwise zero
parseAsInt | `StringstrstringStringString` | `BooleanboolboolBooleanbool`, `IntintintIntegerint` | a 2-Tuple in which the first item is true if the parse was successful, – false otherwise and, if true, the second item is the `IntintintIntegerint` value, otherwise zero
unicode | `IntintintIntegerint` | `StringstrstringStringString` | a string containing the one character defined at the given Unicode code point

#### Examples using standalone functions

● Deconstructing the 2-Tuple returned by parseAsInt:

`variable successname? set to parseAsInt(s).item_0value or expression?0successname? = parseAsInt(s).item_0value or expression? # variable definition0var successname? = parseAsInt(s).item_0value or expression?;0Dim successname? = parseAsInt(s).item_0value or expression? ' variable definition0var successname? = parseAsInt(s).item_0value or expression?;0` `variable valuename? set to parseAsInt(s).item_1value or expression?0valuename? = parseAsInt(s).item_1value or expression? # variable definition0var valuename? = parseAsInt(s).item_1value or expression?;0Dim valuename? = parseAsInt(s).item_1value or expression? ' variable definition0var valuename? = parseAsInt(s).item_1value or expression?;0`

Always check the `BooleanboolboolBooleanbool` (success) before using the returned value (value) in case the latter is zero only because the parse was unsuccessful.

● Test assertions that use methods parseAsInt and parseAsFloat:

+test test_parse test_name? 1 assert parseAsInt("31")actual (computed) value? is (true, 31)expected value? not run 2 assert parseAsInt("0")actual (computed) value? is (true, 0)expected value? not run 3 assert parseAsInt("thirty one")actual (computed) value? is (false, 0)expected value? not run 4 assert parseAsInt("3.1")actual (computed) value? is (false, 0)expected value? not run 5 assert parseAsFloat("31")actual (computed) value? is (true, 31)expected value? not run 6 assert parseAsFloat("0")actual (computed) value? is (true, 0)expected value? not run 7 assert parseAsFloat("3.1")actual (computed) value? is (true, 3.1)expected value? not run 8 end test
+def test_parse test_name?(self) -> None: 1 self.assertEqual(parseAsInt("31")actual (computed) value?, (True, 31)expected value?) not run 2 self.assertEqual(parseAsInt("0")actual (computed) value?, (True, 0)expected value?) not run 3 self.assertEqual(parseAsInt("thirty one")actual (computed) value?, (False, 0)expected value?) not run 4 self.assertEqual(parseAsInt("3.1")actual (computed) value?, (False, 0)expected value?) not run 5 self.assertEqual(parseAsFloat("31")actual (computed) value?, (True, 31)expected value?) not run 6 self.assertEqual(parseAsFloat("0")actual (computed) value?, (True, 0)expected value?) not run 7 self.assertEqual(parseAsFloat("3.1")actual (computed) value?, (True, 3.1)expected value?) not run 8
+[TestMethod] static void test_parse test_name?() { 1 Assert.AreEqual((true, 31)expected value?, parseAsInt("31")actual (computed) value?); not run 2 Assert.AreEqual((true, 0)expected value?, parseAsInt("0")actual (computed) value?); not run 3 Assert.AreEqual((false, 0)expected value?, parseAsInt("thirty one")actual (computed) value?); not run 4 Assert.AreEqual((false, 0)expected value?, parseAsInt("3.1")actual (computed) value?); not run 5 Assert.AreEqual((true, 31)expected value?, parseAsFloat("31")actual (computed) value?); not run 6 Assert.AreEqual((true, 0)expected value?, parseAsFloat("0")actual (computed) value?); not run 7 Assert.AreEqual((true, 3.1)expected value?, parseAsFloat("3.1")actual (computed) value?); not run 8 } // test
+<TestMethod> Sub test_parse test_name?() 1 Assert.AreEqual((True, 31)expected value?, parseAsInt("31")actual (computed) value?) not run 2 Assert.AreEqual((True, 0)expected value?, parseAsInt("0")actual (computed) value?) not run 3 Assert.AreEqual((False, 0)expected value?, parseAsInt("thirty one")actual (computed) value?) not run 4 Assert.AreEqual((False, 0)expected value?, parseAsInt("3.1")actual (computed) value?) not run 5 Assert.AreEqual((True, 31)expected value?, parseAsFloat("31")actual (computed) value?) not run 6 Assert.AreEqual((True, 0)expected value?, parseAsFloat("0")actual (computed) value?) not run 7 Assert.AreEqual((True, 3.1)expected value?, parseAsFloat("3.1")actual (computed) value?) not run 8 End Sub
public class Global {
+@Test static void test_parse test_name?() { 1 assertEquals((true, 31)expected value?, parseAsInt("31")actual (computed) value?); not run 2 assertEquals((true, 0)expected value?, parseAsInt("0")actual (computed) value?); not run 3 assertEquals((false, 0)expected value?, parseAsInt("thirty one")actual (computed) value?); not run 4 assertEquals((false, 0)expected value?, parseAsInt("3.1")actual (computed) value?); not run 5 assertEquals((true, 31)expected value?, parseAsFloat("31")actual (computed) value?); not run 6 assertEquals((true, 0)expected value?, parseAsFloat("0")actual (computed) value?); not run 7 assertEquals((true, 3.1)expected value?, parseAsFloat("3.1")actual (computed) value?); not run 8 } // test
}

##### Notes

- Any string that parses as an `IntintintIntegerint` will also parse as a `FloatfloatdoubleDoubledouble`.
- When validating user input,it may be easier to use the various input methods .

● Using method unicode:

`print(unicode(0x2665)arguments?)0print(unicode(0x2665)arguments?)0Console.WriteLine(unicode(0x2665)arguments?); // print0Console.WriteLine(unicode(&H2665)arguments?) ' print0System.out.println(unicode(0x2665)arguments?); // print0` | ⟶ | ♥

## Maths functions

All the maths functions expect `FloatfloatdoubleDoubledouble` arguments, but `IntintintIntegerint` arguments are accepted. They all return a value of type `FloatfloatdoubleDoubledouble`, except for divAsInt which returns an `IntintintIntegerint`.

function | argument Type | input unit | returns | output unit
--- | --- | --- | --- | ---
abs | `FloatfloatdoubleDoubledouble` |  | absolute value of the input |
acos | `FloatfloatdoubleDoubledouble` |  | arccosine of the input | radians
asin | `FloatfloatdoubleDoubledouble` |  | arcsine of the input | radians
atan | `FloatfloatdoubleDoubledouble` |  | arctangent of the input | radians
cos | `FloatfloatdoubleDoubledouble` | radians | cosine of the input |
divAsFloat | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` |  | first input value divided by second input value |
divAsInt | `FloatfloatdoubleDoubledouble`, `FloatfloatdoubleDoubledouble` |  | first input value divided by second input value and result rounded down to integer |
exp | `FloatfloatdoubleDoubledouble` |  | 𝑒𝑥 where 𝑥 is the argument and 𝑒 is Euler's number 2.718281828459045.. the base of natural logarithms |
logE | `FloatfloatdoubleDoubledouble` |  | natural logarithm of the input |
log10 | `FloatfloatdoubleDoubledouble` |  | base-10 logarithm of the input |
log2 | `FloatfloatdoubleDoubledouble` |  | base-2 logarithm of the input |
sin | `FloatfloatdoubleDoubledouble` | radians | sine of the input |
sqrt | `FloatfloatdoubleDoubledouble` |  | positive square root of the input |
tan | `FloatfloatdoubleDoubledouble` | radians | tangent of the input |
radians | `FloatfloatdoubleDoubledouble` | degrees | converts input from degrees to radians | radians
degrees | `FloatfloatdoubleDoubledouble` | radians | converts input from radians to degrees | degrees

Examples of some maths functions and constants being tested:

+test test_maths test_name? 1 assert pi actual (computed) value? is 3.141592653589793 expected value? not run 2 assert abs(-3.7)actual (computed) value? is 3.7 expected value? not run 3 assert pow(2, 10)actual (computed) value? is 1024 expected value? not run 4 assert sqrt(2).round(3)actual (computed) value? is 1.414 expected value? not run 5 assert asin(0.5).round(3)actual (computed) value? is 0.524 expected value? not run 6 assert acos(0.5).round(3)actual (computed) value? is 1.047 expected value? not run 7 assert atan(1).round(2)actual (computed) value? is 0.79 expected value? not run 8 assert sin(pi/6).round(2)actual (computed) value? is 0.5 expected value? not run 9 assert cos(pi/4).round(3)actual (computed) value? is 0.707 expected value? not run 10 assert tan(pi/4).round(2)actual (computed) value? is 1 expected value? not run 11 assert exp(2).round(3)actual (computed) value? is 7.389 expected value? not run 12 assert logE(7.389).round(2)actual (computed) value? is 2 expected value? not run 13 assert log10(1000)actual (computed) value? is 3 expected value? not run 14 assert log2(65536)actual (computed) value? is 16 expected value? not run 15 assert log2(0x10000)actual (computed) value? is 16 expected value? not run 16 end test
+def test_maths test_name?(self) -> None: 1 self.assertEqual(pi actual (computed) value?, 3.141592653589793 expected value?) not run 2 self.assertEqual(abs(-3.7)actual (computed) value?, 3.7 expected value?) not run 3 self.assertEqual(pow(2, 10)actual (computed) value?, 1024 expected value?) not run 4 self.assertEqual(sqrt(2).round(3)actual (computed) value?, 1.414 expected value?) not run 5 self.assertEqual(asin(0.5).round(3)actual (computed) value?, 0.524 expected value?) not run 6 self.assertEqual(acos(0.5).round(3)actual (computed) value?, 1.047 expected value?) not run 7 self.assertEqual(atan(1).round(2)actual (computed) value?, 0.79 expected value?) not run 8 self.assertEqual(sin(pi/6).round(2)actual (computed) value?, 0.5 expected value?) not run 9 self.assertEqual(cos(pi/4).round(3)actual (computed) value?, 0.707 expected value?) not run 10 self.assertEqual(tan(pi/4).round(2)actual (computed) value?, 1 expected value?) not run 11 self.assertEqual(exp(2).round(3)actual (computed) value?, 7.389 expected value?) not run 12 self.assertEqual(logE(7.389).round(2)actual (computed) value?, 2 expected value?) not run 13 self.assertEqual(log10(1000)actual (computed) value?, 3 expected value?) not run 14 self.assertEqual(log2(65536)actual (computed) value?, 16 expected value?) not run 15 self.assertEqual(log2(0x10000)actual (computed) value?, 16 expected value?) not run 16
+[TestMethod] static void test_maths test_name?() { 1 Assert.AreEqual(3.141592653589793 expected value?, pi actual (computed) value?); not run 2 Assert.AreEqual(3.7 expected value?, abs(-3.7)actual (computed) value?); not run 3 Assert.AreEqual(1024 expected value?, pow(2, 10)actual (computed) value?); not run 4 Assert.AreEqual(1.414 expected value?, sqrt(2).round(3)actual (computed) value?); not run 5 Assert.AreEqual(0.524 expected value?, asin(0.5).round(3)actual (computed) value?); not run 6 Assert.AreEqual(1.047 expected value?, acos(0.5).round(3)actual (computed) value?); not run 7 Assert.AreEqual(0.79 expected value?, atan(1).round(2)actual (computed) value?); not run 8 Assert.AreEqual(0.5 expected value?, sin(pi/6).round(2)actual (computed) value?); not run 9 Assert.AreEqual(0.707 expected value?, cos(pi/4).round(3)actual (computed) value?); not run 10 Assert.AreEqual(1 expected value?, tan(pi/4).round(2)actual (computed) value?); not run 11 Assert.AreEqual(7.389 expected value?, exp(2).round(3)actual (computed) value?); not run 12 Assert.AreEqual(2 expected value?, logE(7.389).round(2)actual (computed) value?); not run 13 Assert.AreEqual(3 expected value?, log10(1000)actual (computed) value?); not run 14 Assert.AreEqual(16 expected value?, log2(65536)actual (computed) value?); not run 15 Assert.AreEqual(16 expected value?, log2(0x10000)actual (computed) value?); not run 16 } // test
+<TestMethod> Sub test_maths test_name?() 1 Assert.AreEqual(3.141592653589793 expected value?, pi actual (computed) value?) not run 2 Assert.AreEqual(3.7 expected value?, abs(-3.7)actual (computed) value?) not run 3 Assert.AreEqual(1024 expected value?, pow(2, 10)actual (computed) value?) not run 4 Assert.AreEqual(1.414 expected value?, sqrt(2).round(3)actual (computed) value?) not run 5 Assert.AreEqual(0.524 expected value?, asin(0.5).round(3)actual (computed) value?) not run 6 Assert.AreEqual(1.047 expected value?, acos(0.5).round(3)actual (computed) value?) not run 7 Assert.AreEqual(0.79 expected value?, atan(1).round(2)actual (computed) value?) not run 8 Assert.AreEqual(0.5 expected value?, sin(pi/6).round(2)actual (computed) value?) not run 9 Assert.AreEqual(0.707 expected value?, cos(pi/4).round(3)actual (computed) value?) not run 10 Assert.AreEqual(1 expected value?, tan(pi/4).round(2)actual (computed) value?) not run 11 Assert.AreEqual(7.389 expected value?, exp(2).round(3)actual (computed) value?) not run 12 Assert.AreEqual(2 expected value?, logE(7.389).round(2)actual (computed) value?) not run 13 Assert.AreEqual(3 expected value?, log10(1000)actual (computed) value?) not run 14 Assert.AreEqual(16 expected value?, log2(65536)actual (computed) value?) not run 15 Assert.AreEqual(16 expected value?, log2(&H10000)actual (computed) value?) not run 16 End Sub
public class Global {
+@Test static void test_maths test_name?() { 1 assertEquals(3.141592653589793 expected value?, pi actual (computed) value?); not run 2 assertEquals(3.7 expected value?, abs(-3.7)actual (computed) value?); not run 3 assertEquals(1024 expected value?, pow(2, 10)actual (computed) value?); not run 4 assertEquals(1.414 expected value?, sqrt(2).round(3)actual (computed) value?); not run 5 assertEquals(0.524 expected value?, asin(0.5).round(3)actual (computed) value?); not run 6 assertEquals(1.047 expected value?, acos(0.5).round(3)actual (computed) value?); not run 7 assertEquals(0.79 expected value?, atan(1).round(2)actual (computed) value?); not run 8 assertEquals(0.5 expected value?, sin(pi/6).round(2)actual (computed) value?); not run 9 assertEquals(0.707 expected value?, cos(pi/4).round(3)actual (computed) value?); not run 10 assertEquals(1 expected value?, tan(pi/4).round(2)actual (computed) value?); not run 11 assertEquals(7.389 expected value?, exp(2).round(3)actual (computed) value?); not run 12 assertEquals(2 expected value?, logE(7.389).round(2)actual (computed) value?); not run 13 assertEquals(3 expected value?, log10(1000)actual (computed) value?); not run 14 assertEquals(16 expected value?, log2(65536)actual (computed) value?); not run 15 assertEquals(16 expected value?, log2(0x10000)actual (computed) value?); not run 16 } // test
}

## Bitwise functions

These functions take in an integer value, and manipulate the bit representation of that value.

function | argument Types | return Type | returns
--- | --- | --- | ---
bitAnd | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | integer whose binary representation is the bitwise AND of the inputs
bitOr | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | integer whose binary representation is the bitwise OR of the inputs
bitNot | `IntintintIntegerint` | `IntintintIntegerint` | integer whose binary representation is the bitwise complement of the input
bitXor | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | integer whose binary representation is the bitwise XOR of the inputs
bitShiftL | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | integer bit shifted to the left by the value of the second argument, i.e. multiplied by 2 to the power of the second argument
bitShiftR | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | integer bit shifted to the right by the value of the second argument, i.e. divided by 2 to the power of the second argument

#### Examples of the bitwise functions being tested

● Examples of the bitwise functions being tested

+test test_bitwise test_name? 1 variable a name? set to 13 value or expression?2 assert a actual (computed) value? is 0xd expected value? not run 3 assert a actual (computed) value? is 0b1101 expected value? not run 4 assert a.asBinary()actual (computed) value? is "1101"expected value? not run 5 variable b name? set to 30 value or expression?6 assert b actual (computed) value? is 0b11110 expected value? not run 7 assert bitAnd(a, b)actual (computed) value? is 0b1100 expected value? not run 8 variable aob name? set to bitOr(a, b)value or expression?9 assert aob actual (computed) value? is 0b11111 expected value? not run 10 variable axb name? set to bitXor(a, b)value or expression?11 assert axb actual (computed) value? is 0b10011 expected value? not run 12 variable nota name? set to bitNot(a)value or expression?13 assert nota actual (computed) value? is -14 expected value? not run 14 variable aL name? set to bitShiftL(a, 2)value or expression?15 assert aL actual (computed) value? is 0b110100 expected value? not run 16 assert bitShiftR(a, 2)actual (computed) value? is 0b11 expected value? not run 17 end test
+def test_bitwise test_name?(self) -> None: 1 a name? = 13 value or expression? # variable definition 2 self.assertEqual(a actual (computed) value?, 0xd expected value?) not run 3 self.assertEqual(a actual (computed) value?, 0b1101 expected value?) not run 4 self.assertEqual(a.asBinary()actual (computed) value?, "1101"expected value?) not run 5 b name? = 30 value or expression? # variable definition 6 self.assertEqual(b actual (computed) value?, 0b11110 expected value?) not run 7 self.assertEqual(bitAnd(a, b)actual (computed) value?, 0b1100 expected value?) not run 8 aob name? = bitOr(a, b)value or expression? # variable definition 9 self.assertEqual(aob actual (computed) value?, 0b11111 expected value?) not run 10 axb name? = bitXor(a, b)value or expression? # variable definition 11 self.assertEqual(axb actual (computed) value?, 0b10011 expected value?) not run 12 nota name? = bitNot(a)value or expression? # variable definition 13 self.assertEqual(nota actual (computed) value?, -14 expected value?) not run 14 aL name? = bitShiftL(a, 2)value or expression? # variable definition 15 self.assertEqual(aL actual (computed) value?, 0b110100 expected value?) not run 16 self.assertEqual(bitShiftR(a, 2)actual (computed) value?, 0b11 expected value?) not run 17
+[TestMethod] static void test_bitwise test_name?() { 1 var a name? = 13 value or expression?;2 Assert.AreEqual(0xd expected value?, a actual (computed) value?); not run 3 Assert.AreEqual(0b1101 expected value?, a actual (computed) value?); not run 4 Assert.AreEqual("1101"expected value?, a.asBinary()actual (computed) value?); not run 5 var b name? = 30 value or expression?;6 Assert.AreEqual(0b11110 expected value?, b actual (computed) value?); not run 7 Assert.AreEqual(0b1100 expected value?, bitAnd(a, b)actual (computed) value?); not run 8 var aob name? = bitOr(a, b)value or expression?;9 Assert.AreEqual(0b11111 expected value?, aob actual (computed) value?); not run 10 var axb name? = bitXor(a, b)value or expression?;11 Assert.AreEqual(0b10011 expected value?, axb actual (computed) value?); not run 12 var nota name? = bitNot(a)value or expression?;13 Assert.AreEqual(-14 expected value?, nota actual (computed) value?); not run 14 var aL name? = bitShiftL(a, 2)value or expression?;15 Assert.AreEqual(0b110100 expected value?, aL actual (computed) value?); not run 16 Assert.AreEqual(0b11 expected value?, bitShiftR(a, 2)actual (computed) value?); not run 17 } // test
+<TestMethod> Sub test_bitwise test_name?() 1 Dim a name? = 13 value or expression? ' variable definition 2 Assert.AreEqual(&Hd expected value?, a actual (computed) value?) not run 3 Assert.AreEqual(&B1101 expected value?, a actual (computed) value?) not run 4 Assert.AreEqual("1101"expected value?, a.asBinary()actual (computed) value?) not run 5 Dim b name? = 30 value or expression? ' variable definition 6 Assert.AreEqual(&B11110 expected value?, b actual (computed) value?) not run 7 Assert.AreEqual(&B1100 expected value?, bitAnd(a, b)actual (computed) value?) not run 8 Dim aob name? = bitOr(a, b)value or expression? ' variable definition 9 Assert.AreEqual(&B11111 expected value?, aob actual (computed) value?) not run 10 Dim axb name? = bitXor(a, b)value or expression? ' variable definition 11 Assert.AreEqual(&B10011 expected value?, axb actual (computed) value?) not run 12 Dim nota name? = bitNot(a)value or expression? ' variable definition 13 Assert.AreEqual(-14 expected value?, nota actual (computed) value?) not run 14 Dim aL name? = bitShiftL(a, 2)value or expression? ' variable definition 15 Assert.AreEqual(&B110100 expected value?, aL actual (computed) value?) not run 16 Assert.AreEqual(&B11 expected value?, bitShiftR(a, 2)actual (computed) value?) not run 17 End Sub
public class Global {
+@Test static void test_bitwise test_name?() { 1 var a name? = 13 value or expression?;2 assertEquals(0xd expected value?, a actual (computed) value?); not run 3 assertEquals(0b1101 expected value?, a actual (computed) value?); not run 4 assertEquals("1101"expected value?, a.asBinary()actual (computed) value?); not run 5 var b name? = 30 value or expression?;6 assertEquals(0b11110 expected value?, b actual (computed) value?); not run 7 assertEquals(0b1100 expected value?, bitAnd(a, b)actual (computed) value?); not run 8 var aob name? = bitOr(a, b)value or expression?;9 assertEquals(0b11111 expected value?, aob actual (computed) value?); not run 10 var axb name? = bitXor(a, b)value or expression?;11 assertEquals(0b10011 expected value?, axb actual (computed) value?); not run 12 var nota name? = bitNot(a)value or expression?;13 assertEquals(-14 expected value?, nota actual (computed) value?); not run 14 var aL name? = bitShiftL(a, 2)value or expression?;15 assertEquals(0b110100 expected value?, aL actual (computed) value?); not run 16 assertEquals(0b11 expected value?, bitShiftR(a, 2)actual (computed) value?); not run 17 } // test
}

The result of bitNot(a) being `-14-14-14-14-14` , when a is `1313131313`, might be a surprise. But this is because the bitwise functions assume that the arguments are represented as 32-bit signed binary integers. So 13 is represented as
`0000000000000000000000000000110100000000000000000000000000001101000000000000000000000000000011010000000000000000000000000000110100000000000000000000000000001101`, and applying bitNot gives
`1111111111111111111111111111001011111111111111111111111111110010111111111111111111111111111100101111111111111111111111111111001011111111111111111111111111110010`which is the value `-14-14-14-14-14`in signed two's complement format,
the left-most bit being the sign (`00000` positive, `11111` negative).

#### Single bit operations

● A reminder of single bit operations.
As noted in the example tests above, these methods act on 32-bit signed integers rather than on values of only one or a few bits, so the effect of bitNot is not just the simple bit reversal shown here:

| p,q
--- | ---
| 0,0 | 0,1 | 1,0 | 1,1
`bitAnd(p, q)bitAnd(p, q)bitAnd(p, q)bitAnd(p, q)bitAnd(p, q)` | 0 | 0 | 0 | 1
`bitOr(p, q)bitOr(p, q)bitOr(p, q)bitOr(p, q)bitOr(p, q)` | 0 | 1 | 1 | 1
`bitNot(p)bitNot(p)bitNot(p)bitNot(p)bitNot(p)` | 1 | 1 | 0 | 0
`bitXor(p, q)bitXor(p, q)bitXor(p, q)bitXor(p, q)bitXor(p, q)` | 0 | 1 | 1 | 0

## RegExp functions

Elan's regular expressions are modelled on those of JavaScript, including the syntax for literal regular expressions. See, for example this Guide to Regular Expressions .

More functions for using regular expressions will be added in a future release of Elan. For now:

The method matchesRegExp is applied to a `StringstrstringStringString` using dot syntax  and requires a `RegExpRegExpRegExpRegExpRegExp` parameter specified as a literal or as variable. It returns a `BooleanboolboolBooleanbool`. For example:

+test test_matchesRegExp test_name? 1 variable s1 name? set to "hello"value or expression?2 variable s2 name? set to "World"value or expression?3 variable r name? set to /^[a-z]*$/value or expression?4 assert s1.matchesRegExp(r)actual (computed) value? is true expected value? not run 5 assert s2.matchesRegExp(r)actual (computed) value? is false expected value? not run 6 end test
+def test_matchesRegExp test_name?(self) -> None: 1 s1 name? = "hello"value or expression? # variable definition 2 s2 name? = "World"value or expression? # variable definition 3 r name? = /^[a-z]*$/value or expression? # variable definition 4 self.assertEqual(s1.matchesRegExp(r)actual (computed) value?, True expected value?) not run 5 self.assertEqual(s2.matchesRegExp(r)actual (computed) value?, False expected value?) not run 6
+[TestMethod] static void test_matchesRegExp test_name?() { 1 var s1 name? = "hello"value or expression?;2 var s2 name? = "World"value or expression?;3 var r name? = /^[a-z]*$/value or expression?;4 Assert.AreEqual(true expected value?, s1.matchesRegExp(r)actual (computed) value?); not run 5 Assert.AreEqual(false expected value?, s2.matchesRegExp(r)actual (computed) value?); not run 6 } // test
+<TestMethod> Sub test_matchesRegExp test_name?() 1 Dim s1 name? = "hello"value or expression? ' variable definition 2 Dim s2 name? = "World"value or expression? ' variable definition 3 Dim r name? = /^[a-z]*$/value or expression? ' variable definition 4 Assert.AreEqual(True expected value?, s1.matchesRegExp(r)actual (computed) value?) not run 5 Assert.AreEqual(False expected value?, s2.matchesRegExp(r)actual (computed) value?) not run 6 End Sub
public class Global {
+@Test static void test_matchesRegExp test_name?() { 1 var s1 name? = "hello"value or expression?;2 var s2 name? = "World"value or expression?;3 var r name? = /^[a-z]*$/value or expression?;4 assertEquals(true expected value?, s1.matchesRegExp(r)actual (computed) value?); not run 5 assertEquals(false expected value?, s2.matchesRegExp(r)actual (computed) value?); not run 6 } // test
}

You can convert a valid string without `/..//..//..//..//../` delimiters to a `RegExpRegExpRegExpRegExpRegExp` using function asRegExp:

+test test_matchesRegExp test_name? 1 variable s1 name? set to "hello"value or expression?2 variable s2 name? set to "World"value or expression?3 variable r name? set to "^[a-z]*$".asRegExp()value or expression?4 assert s1.matchesRegExp(r)actual (computed) value? is true expected value? not run 5 assert s2.matchesRegExp(r)actual (computed) value? is false expected value? not run 6 end test
+def test_matchesRegExp test_name?(self) -> None: 1 s1 name? = "hello"value or expression? # variable definition 2 s2 name? = "World"value or expression? # variable definition 3 r name? = "^[a-z]*$".asRegExp()value or expression? # variable definition 4 self.assertEqual(s1.matchesRegExp(r)actual (computed) value?, True expected value?) not run 5 self.assertEqual(s2.matchesRegExp(r)actual (computed) value?, False expected value?) not run 6
+[TestMethod] static void test_matchesRegExp test_name?() { 1 var s1 name? = "hello"value or expression?;2 var s2 name? = "World"value or expression?;3 var r name? = "^[a-z]*$".asRegExp()value or expression?;4 Assert.AreEqual(true expected value?, s1.matchesRegExp(r)actual (computed) value?); not run 5 Assert.AreEqual(false expected value?, s2.matchesRegExp(r)actual (computed) value?); not run 6 } // test
+<TestMethod> Sub test_matchesRegExp test_name?() 1 Dim s1 name? = "hello"value or expression? ' variable definition 2 Dim s2 name? = "World"value or expression? ' variable definition 3 Dim r name? = "^[a-z]*$".asRegExp()value or expression? ' variable definition 4 Assert.AreEqual(True expected value?, s1.matchesRegExp(r)actual (computed) value?) not run 5 Assert.AreEqual(False expected value?, s2.matchesRegExp(r)actual (computed) value?) not run 6 End Sub
public class Global {
+@Test static void test_matchesRegExp test_name?() { 1 var s1 name? = "hello"value or expression?;2 var s2 name? = "World"value or expression?;3 var r name? = "^[a-z]*$".asRegExp()value or expression?;4 assertEquals(true expected value?, s1.matchesRegExp(r)actual (computed) value?); not run 5 assertEquals(false expected value?, s2.matchesRegExp(r)actual (computed) value?); not run 6 } // test
}

Although it is recommended that literal regular expressions are written with `/..//..//..//..//../` delimiters, the ability to convert a `stringstringstringstringstring` allows you to input a regular expression into a running program.

# System methods

System methods appear to work like functions, because:

- they may require one or more arguments to be provided
- they always return a value
- they can be used in expressions

They are not, however, pure functions because:

- they may have a dependency on data that is not provided in an argument
- they may generate side effects, such as changing the screen display or writing to a file

Because of these properties, system methods may be used only within the main routine or a procedure. They may not be used inside a function that you have defined, because to do so would prevent the function from being pure.

You cannot write a system method yourself.

## Input/output

- Keyboard input 
- Text file input/output 

## Clock and random numbers

Methods random and randint cannot be used in a function because of their dependence on external factors, i.e. they are subject to side effects.
To obtain random numbers within a function, use type `RandomRandomRandomRandomRandom` .

system method | argument Types | return Types | returns
--- | --- | --- | ---
clock | (none) | `IntintintIntegerint` | the current value (in milliseconds) of a system clock. Useful for measuring elapsed time by comparing the values returned by two calls
random | (none) | `FloatfloatdoubleDoubledouble` | a random number in the range [0..1]
randint | `IntintintIntegerint`, `IntintintIntegerint` | `IntintintIntegerint` | a random number in the (inclusive) range between the two arguments

## System functions

These methods are pure functions and so may be referenced in your functions as well as in procedures:

system method | argument Types | return Types | returns
--- | --- | --- | ---
copy | named value of any Type | same type as argument | a copy of the named value
createList | `IntintintIntegerint`, value of `ListlistListListList` item's Type | `ListlistListListList`<of item's Type> | a List containing the specified number of items each initialised to the value in the second argument
createListOfLists | `IntintintIntegerint`, `IntintintIntegerint`, value of `ListlistListListList` item's Type | `ListlistListListList`<of `ListlistListListList`<of item's Type>> | a List of length the first argument containing that number of Lists each initialised to a List of length the second argument with each item therein initialised to the value in the third argument
max | `ListlistListListList`<of `IntintintIntegerint`> or `ListlistListListList`<of `FloatfloatdoubleDoubledouble`> | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | the maximum value found in the List
min | `ListlistListListList`<of `IntintintIntegerint`> or `ListlistListListList`<of `FloatfloatdoubleDoubledouble`> | `IntintintIntegerint` or `FloatfloatdoubleDoubledouble` | the minimum value found in the List
range | `IntintintIntegerint`, `IntintintIntegerint` | `ListlistListListList` | a List containing the integers from the first argument to one less than the second argument. If the second argument is not greater than the first, then the empty List is returned
rangeInSteps | `IntintintIntegerint`, `IntintintIntegerint`, `IntintintIntegerint` | `ListlistListListList` | a List containing the integers from the first argument to one less than the second argument in increments specified by the third argument. If the third argument is negative, the second argument must be less than the first, and the integers returned will run from the first to one more than the second

#### Examples using range or rangeInSteps

● Print every second item in a List:

+main 1 variable numbers name? set to ["zero", "one", "two", "three", "four", "five", "six"]value or expression?2 +for n item? in rangeInSteps(0, numbers.length() + 1, 2)source? 3 print(numbers[n]arguments?)4 end for end main
+def main() -> None: 1 numbers name? = ["zero", "one", "two", "three", "four", "five", "six"]value or expression? # variable definition 2 +for n item? in rangeInSteps(0, numbers.length() + 1, 2)source?: 3 print(numbers[n]arguments?)4 main()
+static void main() { 1 var numbers name? = ["zero", "one", "two", "three", "four", "five", "six"]value or expression?;2 +foreach (n item? in rangeInSteps(0, numbers.length() + 1, 2)source?) { 3 Console.WriteLine(numbers[n]arguments?); // print 4 } // foreach } // main
+Sub main() 1 Dim numbers name? = {"zero", "one", "two", "three", "four", "five", "six"}value or expression? ' variable definition 2 +For Each n item? In rangeInSteps(0, numbers.length() + 1, 2)source? 3 Console.WriteLine(numbers[n]arguments?) ' print 4 Next n End Sub
public class Global {
+static void main() { 1 var numbers name? = ["zero", "one", "two", "three", "four", "five", "six"]value or expression?;2 +foreach (n item? in rangeInSteps(0, numbers.length() + 1, 2)source?) { 3 System.out.println(numbers[n]arguments?); // print 4 } // foreach } // main
}

● Using the Higher-order Function filter  to print the prime numbers less than a given limit:

+main 1 print(primesFromList(range(2, 100))arguments?)2 end main +function primesFromList name?(li as List<of Int>parameter definitions?) returns List<of Int>Type? 3 # returns primes from the list assuming it starts with a prime (e.g. 2)comment? return if(li.length() is 0, li, [li.head()].withAppendList(primesFromList(li.tail().filter(lambda n as Int => (n mod li.head()) > 0))))value or expression?4 end function
+def main() -> None: 1 print(primesFromList(range(2, 100))arguments?)2 +def primesFromList name?(li: list[int]parameter definitions?) -> list[int]Type?: # function 3 # returns primes from the list assuming it starts with a prime (e.g. 2)comment? return if(li.length() == 0, li, [li.head()].withAppendList(primesFromList(li.tail().filter(lambda n: int: (n % li.head()) > 0))))value or expression?4 main()
+static void main() { 1 Console.WriteLine(primesFromList(range(2, 100))arguments?); // print 2 } // main +static List<int>Type? primesFromList name?(List<int> li parameter definitions?) { // function 3 // returns primes from the list assuming it starts with a prime (e.g. 2)comment? return if(li.length() == 0, li, [li.head()].withAppendList(primesFromList(li.tail().filter(int n => (n % li.head()) > 0))))value or expression?;4 } // function
+Sub main() 1 Console.WriteLine(primesFromList(range(2, 100))arguments?) ' print 2 End Sub +Function primesFromList name?(li As List(Of Integer)parameter definitions?) As List(Of Integer)Type? 3 ' returns primes from the list assuming it starts with a prime (e.g. 2)comment? Return if(li.length() = 0, li, {li.head()}.withAppendList(primesFromList(li.tail().filter(Function (n As Integer) (n Mod li.head()) > 0))))value or expression?4 End Function
public class Global {
+static void main() { 1 System.out.println(primesFromList(range(2, 100))arguments?); // print 2 } // main +static List<int>Type? primesFromList name?(List<int> li parameter definitions?) { // function 3 // returns primes from the list assuming it starts with a prime (e.g. 2)comment? return if(li.length() == 0, li, [li.head()].withAppendList(primesFromList(li.tail().filter((int n) -> (n % li.head()) > 0))))value or expression?;4 } // function
}

# Higher-order Functions (HoFs)

A higher-order Function (HoF) is one that takes in a reference to another function as a parameter. (Strictly speaking, a HoF may also be a function that returns another function, but Elan does not currently support that pattern.)

## Standard HoFs

The standard library contains several HoFs that are widely recognised and used within Functional Programming, namely filter , map  and reduce , and also provides maxBy , minBy  and orderBy .

You cannot define your own Higher-order Functions.

## Library functions that process Lists

These dot methods may be called on any `ListlistListListList` or `StringstrstringStringString`. As Higher-order Functions they take either a lambda or a function reference as one of their arguments.

These are not yet fully documented but, for readers familiar with HoFs from another programming language, some examples are shown below.

### filter

You give a `ListlistListListList` to the Higher-order Function filter in order to return a new `ListlistListListList` containing a subset of items. The subset is chosen by a lambda function that tests list item values and returns a Boolean to specify filtering in or out.

#### Example using filter

● Example from demo program `pathfinder.elanpathfinder.elanpathfinder.elanpathfinder.elanpathfinder.elan` in which filter applies the `lambdalambdalambdalambdalambda` to the nodes (of Class `NodeNodeNodeNodeNode`) to find one that contains p (of Class `PointPointPointPointPoint`):

+function getNodeFor name?(p as Point parameter definitions?) returns Node Type? 1 variable matches name? set to this.nodes.filter(lambda n as Node => n.point.equals(p))value or expression?2 return if(matches.length() is 1, matches.head(), emptyNode())value or expression?3 end function
+def getNodeFor name?(p: Point parameter definitions?) -> Node Type?: # function 1 matches name? = self.nodes.filter(lambda n: Node: n.point.equals(p))value or expression? # variable definition 2 return if(matches.length() == 1, matches.head(), emptyNode())value or expression?3
+static Node Type? getNodeFor name?(Point p parameter definitions?) { // function 1 var matches name? = this.nodes.filter(Node n => n.point.equals(p))value or expression?;2 return if(matches.length() == 1, matches.head(), emptyNode())value or expression?;3 } // function
+Function getNodeFor name?(p As Point parameter definitions?) As Node Type? 1 Dim matches name? = Me.nodes.filter(Function (n As Node) n.point.equals(p))value or expression? ' variable definition 2 Return if(matches.length() = 1, matches.head(), emptyNode())value or expression?3 End Function
public class Global {
+static Node Type? getNodeFor name?(Point p parameter definitions?) { // function 1 var matches name? = this.nodes.filter((Node n) -> n.point.equals(p))value or expression?;2 return if(matches.length() == 1, matches.head(), emptyNode())value or expression?;3 } // function
}

### map

The function map is used to apply a function to every item in a `ListlistListListList`, and return a new List. The function to be applied is usually specified as a `lambdalambdalambdalambdalambda` having a single argument of the type of the list's items, as in these examples:

#### Examples using map

● To cube each integer value in a list:

+main 1 variable li name? set to [1, 2, 3, 4, 5]value or expression?2 print(li.map(lambda n as Int => pow(n, 3))arguments?)3 end main +def main() -> None: 1 li name? = [1, 2, 3, 4, 5]value or expression? # variable definition 2 print(li.map(lambda n: int: pow(n, 3))arguments?)3 main() +static void main() { 1 var li name? = [1, 2, 3, 4, 5]value or expression?;2 Console.WriteLine(li.map(int n => pow(n, 3))arguments?); // print 3 } // main +Sub main() 1 Dim li name? = {1, 2, 3, 4, 5}value or expression? ' variable definition 2 Console.WriteLine(li.map(Function (n As Integer) pow(n, 3))arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var li name? = [1, 2, 3, 4, 5]value or expression?;2 System.out.println(li.map((int n) -> pow(n, 3))arguments?); // print 3 } // main } | ⟶ | [1, 8, 27, 125]

● To change each string in a list to upper case:

+main 1 variable names name? set to ["Tom", "Dick", "Harriet"]value or expression?2 print(names.map(lambda s as String => s.upperCase())arguments?)3 end main +def main() -> None: 1 names name? = ["Tom", "Dick", "Harriet"]value or expression? # variable definition 2 print(names.map(lambda s: str: s.upperCase())arguments?)3 main() +static void main() { 1 var names name? = ["Tom", "Dick", "Harriet"]value or expression?;2 Console.WriteLine(names.map(string s => s.upperCase())arguments?); // print 3 } // main +Sub main() 1 Dim names name? = {"Tom", "Dick", "Harriet"}value or expression? ' variable definition 2 Console.WriteLine(names.map(Function (s As String) s.upperCase())arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var names name? = ["Tom", "Dick", "Harriet"]value or expression?;2 System.out.println(names.map((String s) -> s.upperCase())arguments?); // print 3 } // main } | ⟶ | [TOM, DICK, HARRIET]

● To reverse each string in the list of names using the function reverse (from the example of the for  loop):

`print(names.map(lambda s as String => reverse(s))arguments?)0print(names.map(lambda s: str: reverse(s))arguments?)0Console.WriteLine(names.map(string s => reverse(s))arguments?); // print0Console.WriteLine(names.map(Function (s As String) reverse(s))arguments?) ' print0System.out.println(names.map((String s) -> reverse(s))arguments?); // print0` | ⟶ | [moT, kciD, teirraH]

● And this example from demo program `maze - generator.elanmaze - generator.elanmaze - generator.elanmaze - generator.elanmaze - generator.elan`:

`variable nname? set to p.neighbouringPoints().map(lambda p as Point => getValue(p, g))value or expression?0nname? = p.neighbouringPoints().map(lambda p: Point: getValue(p, g))value or expression? # variable definition0var nname? = p.neighbouringPoints().map(Point p => getValue(p, g))value or expression?;0Dim nname? = p.neighbouringPoints().map(Function (p As Point) getValue(p, g))value or expression? ' variable definition0var nname? = p.neighbouringPoints().map((Point p) -> getValue(p, g))value or expression?;0`

### reduce

The function reduce is used to combine the items in a list in some way to produce a single result. This result may be of the same type as the items in the list, for example to:

- Find the sum or sum-of-squares of a list of numeric values.
- Concatenate, or combine in some other way, the items from a List of Strings.

The result may, however, be of a different type than the items in the list, and may even be a data structure, for example to:

- Generate a 3-Tuple  of the sum, sum-of-squares, and count of numerical items.
- Generate a dictionary of all the unique words in a list, with the number of times each word appears in the input List

Method reduce requires two arguments:

1. The initial, or 'seed', value, of the type that you wish to be returned by the function specified in the second argument.. For example, if you were finding the sum of a list of type `FloatfloatdoubleDoubledouble`, the initial seed value would typically be 0.0. If you were creating a dictionary of words, the initial seed value would be an empty Dictionary of the correct Types.
2. The function or lambda to be applied, which itself requires two arguments:
   1. The accumulating value, which is therefore of the same type as the initial seed value. (This will be the return value of the function or `lambdalambdalambdalambdalambda`).
   2. The item to which the function is applied, which is therefore of the same Type as the items in the input list.

In other words, the specified function or `lambdalambdalambdalambdalambda` is applied to each item of the input List in turn, in each case passing in the current value of the result. The function makes use of both to generate a new value for the result, replacing the current one for application to the next item. This is best understood by looking at the examples.

#### Examples using reduce

● To reduce the floating point values in a `ListlistListListList` to their sum:

+main 1 variable n name? set to [0.1, 2, 2.5, 0.3, 5.75, 0.29]value or expression?2 print(n.reduce(0.0, lambda sum as Float, m as Float => (sum + m).round(2))arguments?)3 end main +def main() -> None: 1 n name? = [0.1, 2, 2.5, 0.3, 5.75, 0.29]value or expression? # variable definition 2 print(n.reduce(0.0, lambda sum: float, m: float: (sum + m).round(2))arguments?)3 main() +static void main() { 1 var n name? = [0.1, 2, 2.5, 0.3, 5.75, 0.29]value or expression?;2 Console.WriteLine(n.reduce(0.0, double sum, double m => (sum + m).round(2))arguments?); // print 3 } // main +Sub main() 1 Dim n name? = {0.1, 2, 2.5, 0.3, 5.75, 0.29}value or expression? ' variable definition 2 Console.WriteLine(n.reduce(0.0, Function (sum As Double, m As Double) (sum + m).round(2))arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var n name? = [0.1, 2, 2.5, 0.3, 5.75, 0.29]value or expression?;2 System.out.println(n.reduce(0.0, (double sum, double m) -> (sum + m).round(2))arguments?); // print 3 } // main } | ⟶ | 10.94

##### Notes

- You usually need to round floating point values when outputting them.
- The inclusion of an integer in a `ListlistListListList` of floats is valid provided it is not the first value.

● To reverse the order of items in a `ListlistListListList`:

+main 1 variable n name? set to [2, 3, 5, 7, 11, 13]value or expression?2 variable nR name? set to new List<of Int>()value or expression?3 variable eL name? set to new List<of Int>()value or expression?4 print(n.reduce(eL, lambda nR as List<of Int>, m as Int => nR.withPrepend(m))arguments?)5 end main +def main() -> None: 1 n name? = [2, 3, 5, 7, 11, 13]value or expression? # variable definition 2 nR name? = list[int]()value or expression? # variable definition 3 eL name? = list[int]()value or expression? # variable definition 4 print(n.reduce(eL, lambda nR: list[int], m: int: nR.withPrepend(m))arguments?)5 main() +static void main() { 1 var n name? = [2, 3, 5, 7, 11, 13]value or expression?;2 var nR name? = new List<int>()value or expression?;3 var eL name? = new List<int>()value or expression?;4 Console.WriteLine(n.reduce(eL, List<int> nR, int m => nR.withPrepend(m))arguments?); // print 5 } // main +Sub main() 1 Dim n name? = {2, 3, 5, 7, 11, 13}value or expression? ' variable definition 2 Dim nR name? = New List(Of Integer)()value or expression? ' variable definition 3 Dim eL name? = New List(Of Integer)()value or expression? ' variable definition 4 Console.WriteLine(n.reduce(eL, Function (nR As List(Of Integer), m As Integer) nR.withPrepend(m))arguments?) ' print 5 End Sub public class Global { +static void main() { 1 var n name? = [2, 3, 5, 7, 11, 13]value or expression?;2 var nR name? = new List<int>()value or expression?;3 var eL name? = new List<int>()value or expression?;4 System.out.println(n.reduce(eL, (List<int> nR, int m) -> nR.withPrepend(m))arguments?); // print 5 } // main } | ⟶ | [13, 11, 7, 5, 3, 2]

● To reverse the order of the words in a `StringstrstringStringString`, use reduce on a `ListlistListListList` of words (created by split and then reassembled by join):

+main 1 variable s name? set to "'Twas brillig and the slithy toves"value or expression?2 variable sR name? set to ""value or expression?3 variable eL name? set to new List<of String>()value or expression?4 reassign sR variableName? to s.split(" ").reduce(eL, lambda sR as List<of String>, word as String => sR.withPrepend(word)).join(" ")value or expression?5 print(sR arguments?)6 end main +def main() -> None: 1 s name? = "'Twas brillig and the slithy toves"value or expression? # variable definition 2 sR name? = ""value or expression? # variable definition 3 eL name? = list[str]()value or expression? # variable definition 4 sR variableName? = s.split(" ").reduce(eL, lambda sR: list[str], word: str: sR.withPrepend(word)).join(" ")value or expression? # reassign variable 5 print(sR arguments?)6 main() +static void main() { 1 var s name? = "'Twas brillig and the slithy toves"value or expression?;2 var sR name? = ""value or expression?;3 var eL name? = new List<string>()value or expression?;4 sR variableName? = s.split(" ").reduce(eL, List<string> sR, string word => sR.withPrepend(word)).join(" ")value or expression?; // reassign variable 5 Console.WriteLine(sR arguments?); // print 6 } // main +Sub main() 1 Dim s name? = "'Twas brillig and the slithy toves"value or expression? ' variable definition 2 Dim sR name? = ""value or expression? ' variable definition 3 Dim eL name? = New List(Of String)()value or expression? ' variable definition 4 sR variableName? = s.split(" ").reduce(eL, Function (sR As List(Of String), word As String) sR.withPrepend(word)).join(" ")value or expression? ' reassign variable 5 Console.WriteLine(sR arguments?) ' print 6 End Sub public class Global { +static void main() { 1 var s name? = "'Twas brillig and the slithy toves"value or expression?;2 var sR name? = ""value or expression?;3 var eL name? = new List<String>()value or expression?;4 sR variableName? = s.split(" ").reduce(eL, (List<String> sR, String word) -> sR.withPrepend(word)).join(" ")value or expression?; // reassign variable 5 System.out.println(sR arguments?); // print 6 } // main } | ⟶ | toves slithy the and brillig 'Twas

##### Note

- In these two examples on Lists, an empty List has to be defined for use as the first argument of reduce.

### maxBy and minBy

maxBy and minBy are dot methods on a `ListlistListListList`. They take a function as an argument, and return the list item corresponding to the maximum or minimum of the values returned by the function.

For simply finding the maximum or minimum value in a `ListlistListListList`, you can use max , min .

#### Examples using maxBy and minBy

● To find in a list the integer that has the highest last digit:

+main 1 variable a name? set to [33, 4, 0, 92, 89, 55, 102]value or expression?2 print(a.maxBy(lambda x as Int => x mod 10)arguments?)3 end main +def main() -> None: 1 a name? = [33, 4, 0, 92, 89, 55, 102]value or expression? # variable definition 2 print(a.maxBy(lambda x: int: x % 10)arguments?)3 main() +static void main() { 1 var a name? = [33, 4, 0, 92, 89, 55, 102]value or expression?;2 Console.WriteLine(a.maxBy(int x => x % 10)arguments?); // print 3 } // main +Sub main() 1 Dim a name? = {33, 4, 0, 92, 89, 55, 102}value or expression? ' variable definition 2 Console.WriteLine(a.maxBy(Function (x As Integer) x Mod 10)arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var a name? = [33, 4, 0, 92, 89, 55, 102]value or expression?;2 System.out.println(a.maxBy((int x) -> x % 10)arguments?); // print 3 } // main } | ⟶ | 89

● To find in a list the the shortest string:

+main 1 variable fruit name? set to ["apple", "orange", "pear"]value or expression?2 print(fruit.minBy(lambda x as String => x.length())arguments?)3 end main +def main() -> None: 1 fruit name? = ["apple", "orange", "pear"]value or expression? # variable definition 2 print(fruit.minBy(lambda x: str: x.length())arguments?)3 main() +static void main() { 1 var fruit name? = ["apple", "orange", "pear"]value or expression?;2 Console.WriteLine(fruit.minBy(string x => x.length())arguments?); // print 3 } // main +Sub main() 1 Dim fruit name? = {"apple", "orange", "pear"}value or expression? ' variable definition 2 Console.WriteLine(fruit.minBy(Function (x As String) x.length())arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var fruit name? = ["apple", "orange", "pear"]value or expression?;2 System.out.println(fruit.minBy((String x) -> x.length())arguments?); // print 3 } // main } | ⟶ | pear

### orderBy

orderBy takes a `lambdalambdalambdalambdalambda` that has two arguments of the same type as that of the `ListlistListListList` items to be re-ordered and compares them, returning a Boolean value that distinguishes between less than (or greater than) for numerics and before (or after) for strings.

#### Examples using orderBy

● To reorder integers in a `ListlistListListList`, using > for ascending (you would use < for descending):

variable numbers name? set to [27, 2, 3, 5, 7, 31, 37, 11, 23, 13, 19, 23]value or expression?0 numbers name? = [27, 2, 3, 5, 7, 31, 37, 11, 23, 13, 19, 23]value or expression? # variable definition 0 var numbers name? = [27, 2, 3, 5, 7, 31, 37, 11, 23, 13, 19, 23]value or expression?;0 Dim numbers name? = {27, 2, 3, 5, 7, 31, 37, 11, 23, 13, 19, 23}value or expression? ' variable definition 0 var numbers name? = [27, 2, 3, 5, 7, 31, 37, 11, 23, 13, 19, 23]value or expression?;0 | ⟶ | [2, 3, 5, 7, 11, 13, 19, 23, 23, 27, 31, 37]

● To reorder strings in a `ListlistListListList`, using method isBefore for descending (you would use isAfter for ascending):

+main 1 variable names name? set to ["Simon", "Pauline", "Jason", "Zelda", "Edith", "Lance", "Alice", "Paul"]value or expression?2 print(names.orderBy(lambda x as String, y as String => x.isBefore(y))arguments?)3 end main +def main() -> None: 1 names name? = ["Simon", "Pauline", "Jason", "Zelda", "Edith", "Lance", "Alice", "Paul"]value or expression? # variable definition 2 print(names.orderBy(lambda x: str, y: str: x.isBefore(y))arguments?)3 main() +static void main() { 1 var names name? = ["Simon", "Pauline", "Jason", "Zelda", "Edith", "Lance", "Alice", "Paul"]value or expression?;2 Console.WriteLine(names.orderBy(string x, string y => x.isBefore(y))arguments?); // print 3 } // main +Sub main() 1 Dim names name? = {"Simon", "Pauline", "Jason", "Zelda", "Edith", "Lance", "Alice", "Paul"}value or expression? ' variable definition 2 Console.WriteLine(names.orderBy(Function (x As String, y As String) x.isBefore(y))arguments?) ' print 3 End Sub public class Global { +static void main() { 1 var names name? = ["Simon", "Pauline", "Jason", "Zelda", "Edith", "Lance", "Alice", "Paul"]value or expression?;2 System.out.println(names.orderBy((String x, String y) -> x.isBefore(y))arguments?); // print 3 } // main } | ⟶ | [Zelda, Simon, Pauline, Paul, Lance, Jason, Edith, Alice]

## Passing a function as a reference

To use a Higher-order Function (HoF), you have to pass in a reference to a function. This can be either a `lambdalambdalambdalambdalambda`  or the name of a function. It is also possible to use references to functions not in the context of HoFs.

On most occasions when you write the name of an existing function elsewhere in code your intent is to evaluate the function and, to do so, you write the name of the function followed by round brackets containing such arguments as are required by the function. When passing a function, its name is not followed by round brackets (or arguments), as in this example:

+class Pupil Name? inheritance?1 property mathsPercent name? as Int Type?2 +constructor(parameter definitions?) 3 new code end constructor +function toString name?(parameter definitions?) returns String Type? 4 return "undefined"value or expression?5 end function end class +main 6 variable allPupils name? set to new List<of Pupil>()value or expression?7 variable passes name? set to allPupils.filter(passedMathsTest)value or expression?8 end main +function passedMathsTest name?(p as Pupil parameter definitions?) returns Boolean Type? 9 return p.mathsPercent > 35 value or expression?10 end function
+class Pupil Name? inheritance? # concrete class 1 mathsPercent name?: int Type? # property 2 +def __init__(self: Pupil) -> None: 3 new code +def toString name?(self: Pupil) -> str Type?: # function method 4 return "undefined"value or expression?5 +def main() -> None: 6 allPupils name? = list[Pupil]()value or expression? # variable definition 7 passes name? = allPupils.filter(passedMathsTest)value or expression? # variable definition 8 +def passedMathsTest name?(p: Pupil parameter definitions?) -> bool Type?: # function 9 return p.mathsPercent > 35 value or expression?10 main()
+class Pupil Name? inheritance? {1 public int Type? mathsPercent name? {get; private set;} // property 2 +public Pupil(parameter definitions?) { 3 new code } // constructor +public string Type? toString name?(parameter definitions?) { // function method 4 return "undefined"value or expression?;5 } // function method } // class +static void main() { 6 var allPupils name? = new List<Pupil>()value or expression?;7 var passes name? = allPupils.filter(passedMathsTest)value or expression?;8 } // main +static bool Type? passedMathsTest name?(Pupil p parameter definitions?) { // function 9 return p.mathsPercent > 35 value or expression?;10 } // function
+Class Pupil Name? inheritance?1 Property mathsPercent name? As Integer Type?2 +Sub New(parameter definitions?) 3 new code End Sub +Function toString name?(parameter definitions?) As String Type? 4 Return "undefined"value or expression?5 End Function End Class +Sub main() 6 Dim allPupils name? = New List(Of Pupil)()value or expression? ' variable definition 7 Dim passes name? = allPupils.filter(passedMathsTest)value or expression? ' variable definition 8 End Sub +Function passedMathsTest name?(p As Pupil parameter definitions?) As Boolean Type? 9 Return p.mathsPercent > 35 value or expression?10 End Function
public class Global {
+class Pupil Name? inheritance? {1 public int Type? mathsPercent name?; // property 2 +public Pupil(parameter definitions?) { 3 new code } // constructor +public String Type? toString name?(parameter definitions?) { // function method 4 return "undefined"value or expression?;5 } // function method } // class +static void main() { 6 var allPupils name? = new List<Pupil>()value or expression?;7 var passes name? = allPupils.filter(passedMathsTest)value or expression?;8 } // main +static bool Type? passedMathsTest name?(Pupil p parameter definitions?) { // function 9 return p.mathsPercent > 35 value or expression?;10 } // function
}

# System constants

System constants are unlike values that you define in your program constant , in that they are mutable named values, though it would be poor practice to change them.

## String constants

These constants are of use when the characters { } and " are required within a string.

name | Type | value
--- | --- | ---
openBrace | `StringstrstringStringString` | {
closeBrace | `StringstrstringStringString` | }
quotes | `StringstrstringStringString` | "

## Maths constant

name | Type | value
--- | --- | ---
pi | `FloatfloatdoubleDoubledouble` | 𝜋 = 3.141592653589793..

## Boolean constants

name | Type | value
--- | --- | ---
true | `BooleanboolboolBooleanbool` | `trueTruetrueTruetrue` 
false | `BooleanboolboolBooleanbool` | `falseFalsefalseFalsefalse` 

## Colour constants

colour |  | decimal | decimal | hexadecimal
--- | --- | --- | --- | ---
name |  | integer | R G B | 0xrrggbb
black | ◼ | 0 | 0 0 0 | `0x0000000x0000000x000000&H0000000x000000`
white | ◼ | 16777215 | 255 255 255 | `0xffffff0xffffff0xffffff&Hffffff0xffffff`
red | ◼ | 16711680 | 255 0 0 | `0xff00000xff00000xff0000&Hff00000xff0000`
green | ◼ | 32768 | 0 128 0 | `0x0080000x0080000x008000&H0080000x008000`
blue | ◼ | 255 | 0 0 255 | `0x0000ff0x0000ff0x0000ff&H0000ff0x0000ff`
yellow | ◼ | 16776960 | 255 255 0 | `0xffff000xffff000xffff00&Hffff000xffff00`
brown | ◼ | 10824234 | 165 42 42 | `0xa52a2a0xa52a2a0xa52a2a&Ha52a2a0xa52a2a`
grey | ◼ | 8421504 | 128 128 128 | `0x8080800x8080800x808080&H8080800x808080`
transparent | ◻ | -1 | n/a | n/a

A colour is specified as an `IntintintIntegerint` value using one of these methods:

- the limited colours defined as library constants as in the above table.
- an integer in the decimal range 0 (black) to 224-1 (white).
- a six digit hexadecimal value in the range 0x000000 – 0xffffff using the same 'RGB' format as used in Html style, for example 0xff0000 for red.
- transparent is used only for filling vector graphics  shapes.

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