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

Higher kinded types for typescript and a few utility monads.

import { functor } from "./functor.js";
import { num } from "../types/primitive.js";
import { chain, pipe } from "../core/utils.js";
const is_fold = Symbol('is_fold');
/** Creates an `IFold` from an `IFoldBase`. */
export function fold(base) {
    if (is_fold in base)
        return base;
    return pipe(base, base => ({
        ...functor(base),
        ...base
    }), base => {
        const toArray = (fa) => base.foldl((acc, a) => [...acc, a])([])(fa);
        const _fold = m => base.foldl(m.append)(m.empty());
        const reduce = (acc, f) => base.foldl(f)(acc);
        const length = fa => base.foldl((acc, _) => acc + 1)(0)(fa);
        const sum = _fold(num.sum);
        const all = (p) => (fa) => base.foldl((acc, a) => acc && !!p(a))(true)(fa);
        const any = (p) => (fa) => base.foldl((acc, a) => acc || !!p(a))(false)(fa);
        const avg = chain(base.foldl(([sum, count], n) => [sum + n, count + 1])([0, 0]), base.scalar.fmap(([sum, count]) => sum / count));
        return {
            [is_fold]: true,
            toArray,
            fold: _fold,
            reduce,
            length,
            sum,
            avg,
            any,
            all,
            ...base,
        };
    });
}
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