Hanshi

Hanshi is a functional programming library designed with minimal boilerplate, pattern compliance, and native TypeScript/JavaScript support in mind. For those who are less concerned with these aspects, hanshi offers simple monadic operations on some native types like Array and Promise, "FP black magic" as some may refer, as well as various convenient utilities.

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Usage

import {
    warp as warpPromise,
    fmap as fmapPromise,
    lift as liftPromise
} from '@hanshi/promise-typeclass';

// import { PromiseTypeclass as pt } from 'hanshi'; // or import as a namespace and refer as `pt.warp`.

// const { warp: warpPromise, fmap: fmapPromise, lift: liftPromise } = pt; // or destruct and rename.

const waitedValue = <T>(v: T, t: number): Promise<T> =>
    new Promise((resolve) => setTimeout(() => resolve(v), t));

const terminalWithPromise = (a: number): Promise<number> =>
    new Promise((resolve) => setTimeout(() => resolve(a + 5), 500));

const waited1sNumber10 = warpPromise(waitedValue(5, 500), terminalWithPromise); // For any function that returns a promise, warp(or `>>=` in `haskell) can `partial apply` a promise as if it's normal(awaited), and **return as usual**.

function display<T>(n: T) {
    console.log('value', n);
}

fmapPromise(display, waited1sNumber10); // For any function(terminated with a promise or not), `fmap` can apply a promise instead of the normal(awaited), but **returns a Promise of the value as result**.

// The function `display` does not return anything, so technically it now returns a Promise<void>.

// The side effect of promises are also retained by `fmap`. For instance this `display` invocation will wait for 1 second in the scheduler.

const terminalWithPromise2 = (a: number, b: string): Promise<number> =>
    new Promise((resolve) => setTimeout(() => resolve(b.length + a), 2000));

const waited4sNumber20 = warpPromise(
    waitedValue(10, 1000),
    warpPromise(waitedValue('abcdefghji', 1000), terminalWithPromise2)
); // Due to the fact that `monad` has associativity, `warp` operation works in a reverse order from `partial application`.

fmapPromise(display, waited4sNumber20); // This `display` invocation will wait for 4 seconds in the scheduler, since all the side effects are retained.

const noneTerminal = (name: string, value: object): string =>
    name + JSON.stringify(value);

const liftedNoneTerminal = liftPromise(noneTerminal); // `Lift` takes a function and returns a version of it that all parameters and the return value are promises.

fmapPromise(
    display,
    liftedNoneTerminal(
        waitedValue('waited name', 1500),
        waitedValue({ sample: 1 }, 1500)
    )
); // This `display` invocation will wait for 3 seconds in the scheduler, since all the side effects are retained.