syntax.md

Syntax

Line Endings

All expressions end with a semicolon ;.

Core Data Types

Data Type	Examples
Number	1, 2, 3, 10, 13, 100, 1234567890, 1.1, 2.5, 3.14159
String	"Hello, world!", "1234567890"
Boolean	true, false
List	(), (1,), (1, "hello, world!"), (1, "hello, world!", true)

Operators

Prefix Operators and Operations

Operator Symbol	Right Type	Result Type	Result Description
-	Number	Number	Make number negative.
-	List	List	Reverse list.
+	Number	Number	Absolute value. Make number positive.
not	Boolean	Boolean	Not operator. Return opposite boolean value (true becomes false and false becomes true).
**	List	List	Create a new 1-element list, where the first and only element is the given list (list of lists).

Infix Operators and Operations

Left Type	Operator Symbol	Right Type	Result Type	Result Description
Identifier	=	Any	Any	Assign right value to variable on right. Return value of variable.
Any	==	Any	Boolean	Return true if both values are equal; false otherwise.
Any	!=	Any	Boolean	Return false if both values are equal; true otherwise.
Number	+	Number	Number	Add right number to left number.
String	+	String	String	Combine both strings into one new string.
List	+	List	List	Combine both lists into one new list.
Number	-	Number	Number	Subtract right number from left number.
List	-	List	List	Filter lists by value. Return a new list where values in the right list are removed from the left list.
Number	*	Number	Number	Multiply left number by right number.
Number	/	Number	Number	Divide left number by right number.
List	@	Number	Any	Get the value in the list at the given index position (e.g., index == 0 is the first element, index == 1 is the second element, index == 2 is the second element, etc.). Negative indices are supported as well, so index == -1 gets the last element, index == -2 gets the second-to-last element, etc. The range of valid indices is -len(self.values) <= index < len(self.values).
Number	>	Number	Boolean	Return true if the left value is greater than the right value; false otherwise.
Number	>=	Number	Boolean	Return true if the left value is greater than or equal to the right value; false otherwise.
Number	<	Number	Boolean	Return true if the left value is less than the right value; false otherwise.
Number	<=	Number	Boolean	Return true if the left value is less than or equal to the right value; false otherwise.
Number	%	Number	Number	Modulus. Divide the left value by the right value and return the remainder as a whole number.
Boolean	and	Boolean	Boolean	Return true if left and right are true; false otherwise.
Boolean	or	Boolean	Boolean	Return true if left is true or right is true; false if both left and right are false.
List	<-	Any	List	Append the value on the right to the end of the list on the left. Return a new list.
Function	<-	List	Any	Call function on left with parameters on right.

Postfix Operators and Operations

Left Type	Operator Symbol	Result Type	Result Description
Number	--	Number	Decrement number by 1. Return a new number.
Number	++	Number	Increment number by 1. Return a new number.
Number	!	Number	Factorial. Iteratively multiply values from 1 to left.

Expressions

Variable Assignment and Reassignment

number = 10;
float = 3.14;
string = "hello, world!";
boolean = true;
list = (1, 2, 3, 4);
function = func a, b: a + b;

Math Expressions

1 + 1;
1 + 2 + 3 + 4;
5 - 3;
6 * 4;
10 / 2;
3 + (10 - 9 - 8);
-3;
-(5 + 4 + 3 + 2 + 1);
+6;

Functions

Boomerang has first-class functions, meaning they are treated like any other type of data (number, boolean, string, etc.). They are defined by being assigned to variables.

The syntax for functions is very similar to lambda expressions in Python, except Boomerang uses func instead of lambda, starting with the func keyword, followed by a comma-separated list parameters, a colon, and an expression. Be aware that functions only have one expression for the body, and the result of that expression is returned by the function. Below are some examples:

add = func a, b: a + b;

negative = func n: -n;

greeting = func: print <- ("hello, world!",);

Use the Send (<-) operator to call functions:

add <- (1, 2);
negative <- (1,);
greeting <- ();

When Expressions

When expressions are a hybrid of if-else and switch statements in other languages. Unlike many other languages, though, when expressions are expressions and return a value.

Below is an example of the if-else implementation:

a = 5;
when:
   a == 1: "1"
   a == 2: "2"
   a == 3: "3"
   a == 4: "4"
   else: "0";

For the switch implementation, an expression comes after when and each case starts with the is keyword.

a = 3;
when a:
   is 1: "1"
   is 2: "2"
   is 3: "3"
   is 4: "4"
   else: "0";

Note the else at the end of both. This handles the default case (when none of the above cases match or return true) and is required.

For Loops

For loops act like map in other languages. They return a new list where the expression is evaluated for each element in the original list. However, unlike map, the expression does not have to be applied to each element; any expression, including one that does not use the element variable, can be used.

Below are some examples:

for i in (1, 2, 3): i + 1;  # Returns: (2, 3, 4)
for i in range <- (10,): i % 2 == 0;  # Returns: (true, false, true, false, true, false, true, false, true, false)
for i in (1, 2, 3): "hello";  # Returns ("hello", "hello", "hello"). This ignores "i" entirely and returns its own thing

For loops also support a filtering mechanism with an optional conditional expression. With this expression, values are only returned in the new list if the conditional expression returns true. Below are some examples:

list = (0, 1, 2, 3, 4, 5, 6);
list = for n in list if n % 2 == 0: n;  # Returns `(0, 2, 4, 6)`