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

Higher kinded types for typescript and a few utility monads.

import { curry, pipe } from "../core/utils.js";
const is_monoid = Symbol("is_monoid");
/** Creates an `IMonoid` from an `IMonoidBase`. */
function _monoid(base) {
    if (is_monoid in base)
        return base;
    return pipe(base, base => {
        const mappend = curry(base.append);
        const concat = (fas) => fas.reduce(base.append, base.empty());
        return {
            mappend,
            concat,
            ...base
        };
    }, base => {
        const when = (b) => (fa) => b ? fa : base.empty();
        const join = (separator) => (fas) => {
            if (fas.length === 0)
                return base.empty();
            const [head, ...tail] = fas;
            return tail.reduce((acc, a) => base.append(base.append(acc, separator), a), head);
        };
        const dual = () => _monoid({
            empty: base.empty,
            append: (a, b) => base.append(b, a),
        });
        const liftMonoid = (m) => {
            return monoid({
                empty: () => m.unit(base.empty()),
                append: m.lift2(base.append)
            });
        };
        return {
            [is_monoid]: true,
            when,
            join,
            dual,
            liftMonoid,
            ...base,
        };
    });
}
_monoid.concrete = (empty, append) => _monoid({
    empty: () => empty,
    append: (a, b) => append(a, b)
});
/** The monoid factory, providing functions for working with monoids. */
export const monoid = _monoid;
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