fp-loop v0.2.3

fp-loop

A JavaScript functional module to simulate loops.

FP-Loop is a module that merges the traditional way of looping with functional programming concepts. This module defines a curried function that simulates an imperative loop behavior by using recursion. Its general purpose is to create immutable lists without side-effects.

Download

NPM

npm install fp-loop

Build

git clone http://gitub.com/ahlechandre/fp-loop

Function applications

loop

The loop is a curried function that takes five arguments.

loop(init)(condition)(end)(callback)(list)

arguments

The condition, end and cabllback are curried functions that takes two arguments.

condition(index)(list)

end(index)(list)

callback(index)(list)

Usage

First of all, import the module:

import loop from 'fp-loop'

// or

const loop = require('fp-loop')

Basic example:

const listInitial = [] // Initial empty list.
const li = 
  loop(1)(
    index => list => (index <= 3) // Will stop after 3 recursive calls.
  )(
    index => list => (index + 1) // Increases index by 1.
  )(
    index => list => index * 10 // Setting list items as indexes times 10.
  )(listInitial)

console.log(li) // [10, 20, 30]

Currying benefits:

const listInitial = [] // Initial empty list.

const listFrom1 = loop(1)

// Something...

const listFrom1To3 = listFrom1(
    index => list => (index <= 3) // Will stop after 3 recursive calls.
  )

// Something...

const listFrom1To3By1 = listFrom1To3(
    index => list => (index + 1) // Increases index by 1.
  )

// Something...

const listFrom1To3By1ItemTimes10 = listFrom1To3By1(
    index => list => index * 10 // Setting list items as indexes times 10.
  )

// Something...

const listFinal = listFrom1To3By1ItemTimes10(listInitial)

console.log(listFinal) // [10, 20, 30]

Creating immutable list with positive numbers:

const listInitial = []
const li = 
  loop(1)(
    index => list => (index <= 10)
  )(
    index => list => (index + 1)
  )(
    index => list => index
  )(listInitial)

console.log(li) // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Creating immutable list with negative numbers:

const listInitial = []
const list = 
  loop(-1)(
    index => list => (index >= -10)
  )(
    index => list => (index - 1)
  )(
    index => list => index
  )(listInitial)

console.log(li) // [-1, -2, -3, -4, -5, -6, -7, -8, -9, -10]

Getting initial list:

The condition predicate (explicitly) return false on the first call.

const listInitial = [1, 2, 3]
const li = 
  loop()(
    index => list => false
  )()()(listInitial)

console.log(li) // [1, 2, 3]

Infinite recursion (case 1):

The index argument will always receive the value 0 (because it's not increasing on end function) then condition predicate will always return true.

const li = 
  loop(0)(
    index => list => (index <= 10)
  )(
    index => list => index
  )(
    index => list => index
  )([])

// ...

Infinite recursion (case 2):

The condition predicate explicitly will always return true.

const li = 
  loop(0)(
    index => list => true
  )(
    index => list => index
  )(
    index => list => index
  )([])

// ...

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