nozzlegear/railway

Functional helpers including `Async` and `Result` to help enable things like "railway-oriented" programming. Heavily inspired by F#

railway's Issues

Async.Bind should bind both promises and Asyncs

function toLowerCaseAsync(str: string) {
    return Promise.resolve(str.toLowerCase());
}

const value: string = pipe(Promise.resolve("HELLO"))
    .chain(Async.ofPromise)
    .chain(Async.bind(toLowerCaseAsync))
    .value();

console.log(value) // "hello"

Currently if you want to use a promise in the middle of an Async chain you have to add Async.ofPromise to the chain:

function toLowerCaseAsync(str: string) {
    return Promise.resolve(str.toLowerCase());
}

const value: string = pipe(Promise.resolve("HELLO"))
    .chain(Async.ofPromise)
    .chain(Async.bind(arg => Async.ofPromise(toLowerCaseAsync(arg))))
    .value();

console.log(value) // "hello"

Result should allow errors of any type

Not all Result use-cases need an actual Error object to represent the error. Sometimes you might just want to return a string. The Result monad should be refactored to accept two generic times: one for the result and one for the error. It should use an underlying union type to determine what is a result and what is an error.

// A function that returns a Result containing either the parsed number, or an error message.
function parseNumber(str: string): Result<number, string> {
    const parsed = parseInt(str):

    if (isNaN(parsed)) {
        return Result.ofError("Parsed string was not a number!");
    }

    return Result.ofValue(parsed);
}