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

Higher kinded types for typescript and a few utility monads.

import { monad } from "./monad.js";
import { monoid } from "./monoid.js";
import { pipe } from "../core/utils.js";
import { semiring } from "./semiring.js";
const is_monadPlus = Symbol("is_monadPlus");
/** Creates a `IMonadPlus` from an instance of `IMonadBase` and `IMonoidBase`. */
export function _monadPlus(base) {
    if (is_monadPlus in base)
        return base;
    return pipe(base, base => ({
        ...monoid(base),
        ...monad(base),
        ...base
    }), base => {
        const guard = (b) => b ? base.unit(null) : base.empty();
        const from = (as) => as.reduce((acc, a) => base.append(acc, base.unit(a)), base.empty());
        const _semiring = (mult) => semiring({ sum: base, mult: mult.liftMonoid(base) });
        const filter = (f) => (fa) => base.bind(fa, a => f(a) ? base.unit(a) : base.empty());
        const some = (fa) => base.bind(fa, a => base.map(base.append(some(fa), base.unit([])), as => [a, ...as]));
        const many = (fa) => base.append(some(fa), base.unit([]));
        return {
            [is_monadPlus]: true,
            guard,
            from,
            semiring: _semiring,
            filter,
            some,
            many,
            ...base,
        };
    });
}
_monadPlus.const = (t) => _monadPlus({
    unit: () => t,
    bind: () => t,
    map: () => t,
    flatMap: () => () => t,
    flat: () => t,
    empty: () => t,
    append: () => t,
});
_monadPlus.void = _monadPlus.const(undefined);
_monadPlus.null = _monadPlus.const(null);
/** The monad plus factory. */
export const monadPlus = _monadPlus;
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