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Functions on functions, creating functions from simpler inputs.

(Most commonly used when programming in functional style using higher-order functions.)

Function compose

func compose<A, B, C>(f : B -> C, g : A -> B) : A -> C

Import from the base library to use this module.

import { compose; const; identity } = "mo:base/Func";
import Text = "mo:base/Text";
import Char = "mo:base/Char";

The composition of two functions f and g is a function that applies g and then f.


let textFromNat32 = compose(Text.fromChar, Char.fromNat32);
assert textFromNat32(65) == "A";

Function identity

func identity<A>(x : A) : A

The identity function returns its argument. Example:

assert identity(10) == 10;
assert identity(true) == true;

Function const

func const<A, B>(x : A) : B -> A

The const function is a curried function that accepts an argument x, and then returns a function that discards its argument and always returns the x.


assert const<Nat, Text>(10)("hello") == 10;
assert const(true)(20) == true;