crocks/logic/ifElse.js

A collection of well known Algebraic Datatypes for your utter enjoyment.

/** @license ISC License (c) copyright 2016 original and current authors */
/** @author Ian Hofmann-Hicks (evil) */

var curry = require('../core/curry')
var isFunction = require('../core/isFunction')
var isPredOrFunc = require('../core/isPredOrFunc')
var predOrFunc = require('../core/predOrFunc')

// ifElse : (a -> Boolean) | Pred -> (a -> b) -> (a -> c) -> a -> (a | c)
function ifElse(pred, f, g) {
  if(!isPredOrFunc(pred)) {
    throw new TypeError(
      'ifElse: Pred or predicate function required for first argument'
    )
  }

  if(!(isFunction(f) && isFunction(g))) {
    throw new TypeError(
      'ifElse: Functions required for second and third arguments'
    )
  }

  return function (x) { return predOrFunc(pred, x) ? f(x) : g(x); }
}

module.exports = curry(ifElse)