Lambda: A simple functional TypeScript library

README.md

Lambda

This is just meant to be a small proof of concept functional programming libray for TypeScript which handles working with Releasables, Maps, Maybes, and Results.

lambda.ts

export interface Releasable {
    release();
}

export interface Handle<T> extends Releasable {
    value(): T;
}

export interface Map<T> {
    [key: string]: T;
}

export interface Set extends Map<boolean> {}

export type Maybe<T> = T | void;
export type Either<T, U> = T | U;
export type Result<T> = Either<Error, T>;

export namespace maybe {
    export function isNone<T>(adt: Maybe<T>): adt is void {
        return adt === undefined || adt === null;
    }

    export function isValue<T>(adt: Maybe<T>): adt is T {
        return !isNone(adt);
    }

    export function map<T, U>(adt: Maybe<T>, callback: (value: T) => U): Maybe<U> {
        if (isNone(adt)) {
            return adt;
        } else {
            return callback(adt);
        }
    }
}

export namespace result {
    export function isError<T>(adt: Result<T>): adt is Error {
        return adt instanceof Error;
    }

    export function isValue<T>(adt: Result<T>): adt is T {
        return !isError(adt);
    }

    export function map<T, U>(adt: Result<T>, callback: (value: T) => U): Result<U> {
        if (isError(adt)) {
            return adt;
        } else {
            return callback(adt);
        }
    }
}