@jsoldi/hkt/dist/classes/monad.js

Higher kinded types for typescript and a few utility monads.

import { functor } from "./functor.js";
import { monadTrans } from "./transformer.js";
import { id } from "../core/utils.js";
import { pipe as _pipe } from "../core/utils.js";
const is_monad = Symbol("is_monad");
function _monad(base) {
    if (is_monad in base)
        return base;
    return _pipe(base, base => ({
        ...functor({
            map: (fa, f) => base.bind(fa, a => base.unit(f(a))),
            ...base
        }),
        ...base
    }), base => {
        const lift2 = (f) => (fa, fb) => base.bind(fa, a => base.bind(fb, b => base.unit(f(a, b))));
        const lift3 = (f) => (fa, fb, fc) => base.bind(fa, a => base.bind(fb, b => base.bind(fc, c => base.unit(f(a, b, c)))));
        const flatMap = (f) => (fa) => base.bind(fa, f);
        const flat = (ffa) => base.bind(ffa, id);
        const _kleisli = (...fs) => fs.reduceRight((acc, f) => (...arg) => base.bind(f(...arg), a => acc(...[a, ...arg])), base.unit);
        const _pipe = (head, ...tail) => base.bind(head, _kleisli(...tail));
        const _chain = (...fs) => flatMap(_kleisli(...fs));
        const runFree = (t) => {
            if (t.right) {
                return base.bind(t.value, runFree);
            }
            else {
                return base.unit(t.value);
            }
        };
        return {
            [is_monad]: true,
            lift2,
            lift3,
            flatMap,
            flat,
            fish: _kleisli,
            chain: _chain,
            pipe: _pipe,
            runFree,
            ...base
        };
    });
}
_monad.trivial = {
    ..._monad({
        unit: a => a,
        bind: (fa, f) => f(fa),
        map: (fa, f) => f(fa),
    }),
    transform: (inner) => monadTrans({ ...inner, lift: id, wrap: inner.unit })
};
/** The monad factory, providing a set of functions for working with monads. */
export const monad = _monad;
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