A calculus is a “formal system”, i.e. a set of rules to do something. The rules of the Lambda Calculus describe computation. Any language that has anonymous fun

A calculus is a “formal system”, i.e. a set of rules to do something. The rules of the Lambda Calculus describe computation. Any language that has anonymous functions which behave as closures and can be passed around freely immediately contains an encoding of the lambda calculus. Anonymous functions correspond to lambda expressions, except that in the LC functions always have exactly one argument. A program is usually said to be functional when it uses some concepts of functional programming, such as first-class functions and higher-order functions. However, a first-class function may use techniques from the imperative paradigm, such as arrays or input/output methods are not purely functional programs, therefore the first-class function needs not be purely functional. Lisp is an "impure" functional language by the current definition. However, The main article is absurd. Lisp may not be a "Pure" functional language but it is a still a functional language.