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

Higher kinded types for typescript and a few utility monads.

import { monad } from "../classes/monad.js";
import { monadTrans } from "../classes/transformer.js";
/** Creates a state monad with a fixed state type. */
function stateOf() {
    const unit = (a) => s => [a, s];
    const bind = (fa, f) => s => {
        const [a, t] = fa(s);
        return f(a)(t);
    };
    const of = () => stateOf();
    const get = s => [s, s];
    const put = (s) => _ => [null, s];
    const transform = (inner) => {
        const unit = (a) => s => inner.unit([a, s]);
        const bind = (fa, f) => s => inner.bind(fa(s), ([a, t]) => f(a)(t));
        const lift = (ma) => s => inner.map(ma, a => [a, s]);
        const wrap = fa => s => inner.unit(fa(s));
        return monadTrans({ unit, bind, lift, wrap });
    };
    return {
        ...monad({ unit, bind }),
        of,
        get,
        put,
        transform
    };
}
/** The `state` module, providing a set of functions for working with state functions. The environment type is fixed to `any`. To change the environment type, call the `of` function. */
export const state = stateOf();
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