premap

import { premap } from "https://github.gh-proxy.cn/raw.githubusercontent.com/baetheus/fun/main/fn.ts";

Map over the input of a function, turning D => A and L => D into L => A.

@example

import { premap, pipe } from "./fn.ts";

const equalsZero = (n: number): boolean => n === 0;
const strLength = (s: string): number => s.length;

const isEmpty = pipe(
  equalsZero,
  premap(strLength),
);

const result1 = isEmpty(""); // true
const result2 = isEmpty("Hello"); // false

function premap<L, D>(fld: (l: L) => D): <A>(ta: Fn<D, A>) => Fn<L, A>;

premap<L, D>(fld: (l: L) => D): <A>(ta: Fn<D, A>) => Fn<L, A>

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§Type Parameters

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§Parameters

fld: (l: L) => D

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§Return Type

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