@jsoldi/hkt/dist/types/lazy.js

Higher kinded types for typescript and a few utility monads.

import { monad } from "../classes/monad.js";
import { monadTrans } from "../classes/transformer.js";
import { id, memo, pipe } from "../core/utils.js";
/** The lazy monad, providing a set of functions for working with lazy values. */
export const lazy = (() => {
    return pipe(monad({
        unit: a => () => a,
        bind: (fa, f) => () => f(fa())(),
        map: (fa, f) => () => f(fa()),
    }), base => {
        const run = (fa) => fa();
        const runFree = (t) => () => {
            while (t.right)
                t = t.value();
            return t.value;
        };
        const transformOver = (m) => {
            const unit = (a) => () => m.unit(a);
            const bind = (fma, f) => () => m.bind(fma(), a => f(a)());
            const map = (fa, f) => () => m.map(fa(), f);
            const lift = (ma) => () => ma;
            const wrap = (fa) => () => m.unit(fa());
            return {
                ...monadTrans({ unit, bind, map, lift, wrap }),
                drop: run,
            };
        };
        const transformUnder = (m) => {
            const unit = (a) => m.unit(() => a);
            const bind = (ma, f) => m.bind(ma, a => f(a()));
            const map = (ma, f) => m.map(ma, a => () => f(a()));
            const lift = (ma) => m.map(ma, a => () => a);
            const wrap = (fa) => m.unit(() => fa());
            const drop = (ma) => m.map(ma, a => a());
            return {
                ...monadTrans({ unit, bind, map, lift, wrap }),
                drop,
            };
        };
        return {
            ...base,
            runFree,
            run,
            memo,
            lazy: id,
            transformOver,
            transformUnder,
        };
    });
})();
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