Slide 15 of 37

First-class functions

A bare reference, and map

func double(n: Int): Int { return n * 2 }

proc main(): void {
	f := double
	echo "{f(21)} {map([1, 2, 3], double)}"
}

Partial application

func add(a: Int, b: Int): Int { return a + b }

proc main(): void {
	addFive := add(5, _)   // _ becomes the parameter
	echo addFive(10)
}

A callable is a value: a bare name on its own (f := takes) or a partial application with _ holes (handler(_, db)), each hole becoming a parameter in order. A func value may be used where a proc is expected, never the reverse. Three things cannot become values: a generic callable, one with a mutex parameter, and one with a statically-sized parameter beyond a single immutable binding.

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