fmap-null-undefined v1.0.1

fmap-null-undefined

Strongly typed, curried functions inspired by Haskell's fmap (for Maybe).

Installation

npm install --save fmap-null-undefined

Usage

Given a function of type A => B, fmap creates a function of type A | null | undefined => B | null | undefined. Use fmap_null or fmap_undefined if you want a more specific type (e.g. A | null => B | null).

import { fmap, fmap_null, fmap_undefined } from "fmap-null-undefined";

const show = (x: number): string => x.toString();

fmap(show)(5) === "5";
fmap(show)(null) === null;
fmap(show)(undefined) === undefined;

fmap_null(show)(5) === "5";
fmap_null(show)(null) === null;
fmap_null(show)(undefined); // type error

fmap_undefined(show)(5) === "5";
fmap_undefined(show)(undefined) === undefined;
fmap_undefined(show)(null); // type error

Partial Application

The functions are curried to simplify partial application.

const fmapShow = fmap(show);

fmapShow(5) === "5";

[ 5, null, undefined, 10 ].map(fmapShow); // [ "5", null, undefined, "10" ]

TypeScript

The package is primarily intended for use with TypeScript. Declarations are included.