Merge pull request #225 from hemanth/jethrolarson-combinator

added definition for functional combinator #126

Author: hemanth

readme.md

@@ -50,6 +50,7 @@ __Table of Contents__
 * [Equational Reasoning](#equational-reasoning)
 * [Lambda](#lambda)
 * [Lambda Calculus](#lambda-calculus)
+* [Functional Combinator](#functional-combinator)
 * [Lazy evaluation](#lazy-evaluation)
 * [Monoid](#monoid)
 * [Monad](#monad)
@@ -580,6 +581,24 @@ const add1 = (a) => a + 1
 ## Lambda Calculus
 A branch of mathematics that uses functions to create a [universal model of computation](https://en.wikipedia.org/wiki/Lambda_calculus).
 
+## Functional Combinator
+A higher-order function, usually curried, which returns a new function changed in some way. Functional combinators are often used in [Point-Free Style](#point-free-style) to write especially terse programs.
+
+```js
+// The "C" combinator takes a curried two-argument function and returns one which calls the original function with the arguments reversed.
+const C = (f) => (a) => (b) => f(b)(a)
+
+const divide = (a) => (b) => a / b
+
+const divideBy = C(divide)
+
+const divBy10 = divideBy(10)
+
+divBy10(30) // => 3
+```
+
+See also [List of Functional Combinators in JavaScript](https://gist.github.com/Avaq/1f0636ec5c8d6aed2e45) which includes links to more references.
+
 ## Lazy evaluation
 
 Lazy evaluation is a call-by-need evaluation mechanism that delays the evaluation of an expression until its value is needed. In functional languages, this allows for structures like infinite lists, which would not normally be available in an imperative language where the sequencing of commands is significant.