@jsoldi/hkt/dist/types/free/functorFree.js

Higher kinded types for typescript and a few utility monads.

import { either } from "../either.js";
import { monad } from "../../classes/monad.js";
/** Creates a free monad from a functor. */
export function functorFree(freeBase) {
    const unit = (a) => either.left(a);
    const suspend = (f) => either.right(f);
    const delay = (fa) => suspend(freeBase.map(fa, unit));
    const foldFree = (pure, impure) => function go(ta) {
        if (ta.right) {
            return impure(freeBase.map(ta.value, go));
        }
        else {
            return pure(ta.value);
        }
    };
    const bind = (fa, f) => foldFree(f, either.right)(fa);
    const mapFreeFrom = (transform) => function go(ft) {
        if (ft.right) {
            return either.right(freeBase.map(transform(ft.value), go));
        }
        else {
            return unit(ft.value);
        }
    };
    const mapFreeTo = (transform) => foldFree(either.left, ftag => either.right(transform(ftag)));
    return {
        ...monad({ unit, bind }),
        freeBase,
        suspend,
        delay,
        foldFree,
        mapFreeFrom,
        mapFreeTo
    };
}
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