100% type-safe pipe() and compose() functions written in TS

According to Wikipedia, "Function composition is an act or mechanism to combine simple functions to build more complicated ones. Like the usual composition of functions in mathematics, the result of each function is passed as the argument of the next, and the result of the last one is the result of the whole".

Piping is basically the same idea, but in reverse order, where the functions are provided in a more natural order (i.e. the same order as they are actually invoked).

This package provides a simple way to transform functions into their piped or composed versions using Higher-Order Functions (HOFs) called pipe() and compose(), respectively, while keeping the original functions signatures, making sure that, for each function in the sequence:

• pipe(): the type of the output (result) of the previous function will always match the type of the input of the next function. The type of the parameter of the piped function will always match the type of its first function's parameter and the final result will have the type of its last function.
• compose(): the type of the input of the previous function will always match the type of the output (result) of the next function. The type of the parameter of the composed function will always match the type of its last function's parameter and the final result will have the type of its first function.

Features

• 100% type-safe
• Supports functions that have up to 30 parameters
• Fully compatible with JavaScript
• Very small (both functions have under 250 bytes gzipped after bundling)
• No external dependencies

Installation

Install from npm using your favorite package manager:

npm install @cdandrea/piping-ts

yarn add @cdandrea/piping-ts

pnpm install @cdandrea/piping-ts

Usage

Pipe:

Simply supply the functions to be piped as parameters of the pipe() HOF.

Basic example:

import { pipe } from '@cdandrea/piping-ts'

const isEven = (n: number): boolean => n % 2 === 0
const asString = (b: boolean): string => b.toString()
const asArray = (s: string): string[] => [s]

const f = pipe(isEven, asString, asArray)

// f's signature will be: `(a1: number) => string[]`
//
// Notice how `f` expects a `number` as input, which is the same
// type expected by its first function parameter, `isEven`, and
// returns a `string[]` as the result, which is the result of
// its last function parameter, `asArray`.

console.log(f(10)) // Prints ["true"]

More elaborate example, using pipe() and curry():

import { curry } from '@cdandrea/currying-ts'
import { pipe } from '@cdandrea/piping-ts'

const prop = curry((prop: string, obj: Record<string, number>) => obj[prop])
const add = curry((a: number, b: number) => b + a)
const modulo = curry((a: number, b: number) => b % a)
const amtAdd1Mod7 = pipe(prop('amount'), add(1), modulo(7))

console.log(amtAdd1Mod7({ amount: 17 })) // Prints 4
console.log(amtAdd1Mod7({ amount: 987 })) // Prints 1
console.log(amtAdd1Mod7({ amount: 68 })) // Prints 6

Notice that the piped function returned by pipe() gets fully typed.

Compose:

Simply supply the functions to be composed as parameters of the compose() HOF:

import { curry } from '@cdandrea/currying-ts'
import { compose } from '@cdandrea/piping-ts'

const prop = curry((prop: string, obj: Record<string, number>) => obj[prop])
const add = curry((a: number, b: number) => b + a)
const modulo = curry((a: number, b: number) => b % a)
const amtAdd1Mod7 = compose(modulo(7), add(1), prop('amount'))

console.log(amtAdd1Mod7({ amount: 17 })) // Prints 4
console.log(amtAdd1Mod7({ amount: 987 })) // Prints 1
console.log(amtAdd1Mod7({ amount: 68 })) // Prints 6