Introduction

A function is a sequence of propositions (let expressions, or expressions) always returning a value.

It may take type parameters, or call parameters. The value returned by the last proposition is the return value of the function.

NB: The only form of early return possible is by throwing an exception.

Type checking happens at the function boundaries:

• when a function is called, its call parameters are type-checked
• when the function returns, its return value is type-checked

Examples

Simple pure function:

func adder(a: number, b: number) -> number {
  a + b;
}

Simple pure generic function:

func swap<T, U>(a: T, b: U) -> (U, T) {
  (b, a);
}

Function with side effects:

effect log(msg: string) -> @ok;

func task() -> @ok {
  @ok := perform log("hello");
  @ok := perform log("world");
}

Early return with exceptions:

import std::math;

func task(a: number) -> @ok {
  cond {
    a >= 0 => {
      std::math::sqrt(a);
    },
    else => {
      throw (@error, "no complex numbers here");
    },
  };
}