Version: 1.1.0

Closure declarations

A closure declaration is a nested function plus the names it captures.

Essentials

• The capture is the set of outer names the body uses.
• Explicit capture lists document copies and moves.
• A closure has the same parameter and argument syntax as a function.
• Returning a closure extends the lifetime of what it captured, or the program does not compile.

Example

def adder(base: Int) -> fn(Int) -> Int:
    fn inner(n: Int) -> Int:
        return n + base
    return inner

Keep in mind

If the capture list is longer than the body, the closure should be a struct with a method.