Like the Lambda Calculus, Combinatory Logic is a mathematical notation that is powerful enough to handle set theory and issues in computability.

Combinatory logic is a notation introduced by Moses Schnfinkel and Haskell Curry to eliminate the need for variables in mathematical logic. It has more recently been used in computer science as a theoretical model of computation and also as a basis for the design of functional programming languages. It is based on combinators. A combinator is a higher-order function that uses only function application and earlier defined combinators to define a result from its arguments.

In this book, we’re going to meet some of the standard combinators, and for each one we’ll explore some of its ramifications when writing programs using the Ruby programming language. In Combinatory logic, combinators combine and alter each other, and our Ruby examples will focus on combining and altering Ruby code. From simple examples like the K Combinator and Ruby’s .tap method, we’ll work our way up to meta-programming with aspects and recursive combinators.