pragmatic-fp-ts/deno_lib/Monad.ts

Opinionated functional programming library with easy use in mind

import { either } from "./Either.ts";
import { chain, Chain, Either, Maybe } from "./main.ts";
import { maybe } from "./Maybe.ts";
import { Monad } from "./types.ts";

// "map"
function bind<A, B>(
  f: (_: A) => B
): <M extends Monad<A>>(
  _: M
) => M extends Maybe<A> ? Maybe<B> : M extends Chain<any> ? Chain<B> : Either<B, any>;

function bind<A, B>(f: (_: A) => B) {
  return (m: Monad<any>) => m._(f);
}

// "bind"
function bindM<A, B>(f: (_: A) => Maybe<B>): (_: Maybe<A>) => Maybe<B>;
function bindM<A, B>(f: (_: A) => Either<B>): (_: Either<A>) => Either<B>;
function bindM<A, B>(f: (_: A) => Chain<B>): (_: Chain<A>) => Chain<B>;
function bindM(f: (_: any) => any) {
  return (m: Monad<any>) => lift(m._(f)) as any;
}

const of = (m: any) => (v: any) =>
  (m.isJust && m.isJust(m)) || (m.isNothing && m.isNothing())
    ? maybe(v)
    : (m.isLeft && m.isLeft()) || (m.isRight && m.isRight())
    ? either(v)
    : chain(v);

function lift<A>(_: Maybe<Monad<A>>): Maybe<A>;
function lift<A>(_: Either<Monad<A>>): Either<A>;
function lift<A>(_: Chain<Monad<A>>): Chain<A>;
function lift(m: any) {
  return of(m)(m.getValueOr(undefined)) as any;
}

export { bind, bindM, lift };