g33k57
6/14/2019 - 8:15 PM
Common combinators in JavaScript
Common combinators in JavaScript
const I = x => x;
const K = x => y => x;
const A = f => x => f(x);
const T = x => f => f(x);
const W = f => x => f(x)(x);
const C = f => y => x => f(x)(y);
const B = f => g => x => f(g(x));
const S = f => g => x => f(x)(g(x));
const P = f => g => x => y => f(g(x))(g(y));
const Y = f => (g => g(g))(g => f(x => g(g)(x)));| Name | # | Haskell | Ramda | Sanctuary | Signature |
|---|---|---|---|---|---|
| identity | I | id | identity | I | a → a |
| constant | K | const | always | K | a → b → a |
| apply¹ | A | ($) | call | (a → b) → a → b | |
| thrush | T | (&) | applyTo | T | a → (a → b) → b |
| duplication | W | join² | unnest² | join² | (a → a → b) → a → b |
| flip | C | flip | flip | flip | (a → b → c) → b → a → c |
| compose | B | (.), fmap² | map² | compose, map² | (b → c) → (a → b) → a → c |
| substitution | S | ap² | ap² | ap² | (a → b → c) → (a → b) → a → c |
| psi | P | on | on | (b → b → c) → (a → b) → a → a → c | |
| fix-point³ | Y | fix | (a → a) → a |
¹) The A-combinator can be implemented as an alias of the I-combinator. Its implementation in Haskell exists because the infix nature gives it some utility. Its implementation in Ramda exists because it is overloaded with additional functionality.
²) Algebras like ap have different implementations for different types.
They work like Function combinators only for Function inputs.
³) In JavaScript and other non-lazy languages, it is impossible to implement the Y-combinator. Instead a variant known as the applicative or strict fix-point combinator is implemented. This variant is sometimes rererred to as the Z-combinator.