Functions and Lambdas

Sun supports both named functions and anonymous lambda expressions.

Named Functions

Functions are defined using the function keyword. They are hoisted and available throughout their scope:

function add(a: i32, b: i32) i32 {
    return a + b;
}

function main() i32 {
    println_i32(add(3, 4));  // 7
    return 0;
}

Lambdas

Lambdas are anonymous functions created with the lambda keyword. They must be assigned to a variable or used immediately:

function main() i32 {
    var square = lambda (x: i32) i32 { return x * x; };
    println_i32(square(5));  // 25
    return 0;
}

Semantic Differences

Aspect	`function`	`lambda`
Name	Required, becomes the function's identity	Anonymous (empty name internally)
Declaration	Top-level or nested statement	Expression (must assign to variable)
First-class	No—cannot be assigned or passed	Yes—can be assigned, passed, returned
Recursion	Can call itself by name	Must reference the variable it's assigned to
Hoisting	Available throughout scope	Only after assignment

When to use which:

Use function for named, top-level operations called directly
Use lambda for callbacks, higher-order function arguments, or when you need to store/pass functions

First-Class Lambdas

Only lambdas are first-class values—they can be assigned to variables, passed as arguments, and returned from functions:

// Assign a lambda to a variable
var double = lambda (x: i32) i32 { return x * 2; };
println_i32(double(5));  // 10

// Pass a lambda as an argument
function apply(fn: (i32) i32, x: i32) i32 {
    return fn(x);
}
println_i32(apply(double, 3));  // 6

// Return a lambda from a function
function makeAdder(n: i32) (i32) i32 {
    return lambda (x: i32) i32 { return x + n; };
}
var add5 = makeAdder(5);
println_i32(add5(10));  // 15

Builtin Types Control Flow