@raini/pipes

@raini/pipes

@raini/pipes is a set of monoids called Pipelines. Pipelines are lazy and do not get invoked until they are forked with process method.

A Pipeline is a Monoid and can be concatenated with other Pipelines with concat which allows joining separate pieces of composed functions.

Features

• Composition of functions via pipe
• Helper pipe methods, e.g. pipeTap or extendPipe
• Implements Semigroup (holds associativity) with p.concat
• Implements Monoid (holds right identity and left identity) with P.concat
• PromisePipeline allows abstracting from using Promises in composed functions - promisePipeline.process returns the only Promise to work with
• Can be used both in Node and in browsers (JS transpiled to ES5)

Installation

npm i -S @raini/pipes

Usage

PromisePipeline

import { PromisePipeline } from "@raini/pipes";
import * as rl from "readline";

const addSpaceIfMissing = (q: string): string => (q.endsWith(" ") ? q : q.concat(" "));
const toObject = (q: string) => ({ q });
const createReadLine = () => ({ rl: rl.createInterface(process.stdin, process.stdout) });
const askQuestionAsync = ({ rl, q }) => new Promise((res) => rl.question(q, (a: string) => res(a)));
const applyGreenColor = (x: string) => `\x1b[32m${x}\x1b[0m`;
const log = console.log;
const exit = () => process.exit(0);

PromisePipeline.of(addSpaceIfMissing)
  .pipe(toObject)
  .pipeExtend(createReadLine) // Extend argument object with return value
  .pipe(askQuestionAsync)
  .pipe(applyGreenColor)
  .pipeTap(log) // Execute function on the argument and return the argument
  .process(() => "What is the answer to life, the universe and everything?")
  .then(exit);

SyncPipeline

import { SyncPipeline } from "@raini/pipes";

const isOdd = (num: number) => num % 2 == 0;
const negate = <T>(f: (x: T) => any) => (x: T) => !f(x);
const filterOutOddNumbers = (nums: number[]) => nums.filter(negate(isOdd));
const multiplyBy2 = (num: number) => num * 2;
const multiplyItemsBy2 = (nums: number[]) => nums.map(multiplyBy2);
const log = console.log;

const result = SyncPipeline.of(filterOutOddNumbers)
  .pipeTap(log) // [ 1, 3, 5 ]
  .pipe(multiplyItemsBy2)
  .process(() => [1, 2, 3, 4, 5]);

log(result); // [ 2, 6, 10 ]

// A fun thing using pipeExtend (instead of pipe) for multiplying items by 2

const result2 = SyncPipeline.of(filterOutOddNumbers)
  .pipeTap(log) // [ 1, 3, 5 ]
  .pipeExtend(multiplyItemsBy2)
  .process(() => [1, 2, 3, 4, 5]);

log(result2); // [ 1, 3, 5, 2, 6, 10 ]