1 unstable release
0.1.0 | Mar 20, 2023 |
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#2546 in Rust patterns
10KB
91 lines
currycompose
A crate providing a trait for performing currying (and non-currying) function-composition in rust.
A can be composed with B if A implements FnOnce and takes one or more argument, while B implements FnOnce and returns something of the same type as the first argument of A.
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For instance (A, B) -> Y can be composed with (C) -> A, yiedling (B, C) -> Y (currying).
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Composing (A, B) -> Y with (C) -> A then with (D) -> B yields (C, D) -> Y (currying twice).
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While of course (A) -> Y composed with (B) -> A, yields (B) -> Y as expected (non-currying composition).
Currying functions which implement FnMut or Fn will yield something also implementing FnMut/Fn if both operands do.
lib.rs
:
https://en.wikipedia.org/wiki/Function_composition
A crate providing a trait for performing currying (and non-currying) function-composition in rust.
Non-currying composition: h(x) = g ∘ f = g(f(x))
Currying composition: h(..., x) = g ∘ f = g(f(x), ...)
When currying, arguments of the function being curried with (f) is moved to the end of the argument-list
Both operands must implement FnOnce. If both implement FnMut or Fn, the resulting composition will also implement these traits.
g must also have one or more argument, where the first argument type equals the return type of f.
#![feature(generic_const_exprs)]
use currycompose::*;
// g ∘ f
// where
// g :: f32 -> f32
// f :: u8 -> f32
// g ∘ f :: u8 -> f32
let g = |x: f32| x*x;
let f = |x: u8| x as f32;
let gf = g.compose(f);
let x = 1;
assert_eq!(gf(x), g(f(x)));
// g ∘ f
// where
// g :: f32 -> f32 -> f32
// f :: u8 -> f32
// g ∘ f :: f32 -> u8 -> f32
let g = |x: f32, y: f32| x + y;
let f = gf;
let gf = g.compose(f);
let x = 1;
let y = 1.0;
// note here the argument x has been shifted to the end of the args in gf
assert_eq!(gf(y, x), g(f(x), y));
// g ∘ f ∘ f
// where
// g :: f32 -> f32 -> f32
// f :: u8 -> f32
// g ∘ f ∘ f :: u8 -> u8 -> f32
let gff = gf.compose(f);
let x = 1;
let y = 1;
assert_eq!(gff(x, y), g(f(x), f(y)));
Dependencies
~1.5MB
~36K SLoC