View source for Scheme (programming language)

===Scheme is a functional language===
In fact, Scheme is an ''almost'' functional language, it does still allow functions to have side-effects, but in practice it is considered to be a [[functional language]]. What does this mean? In the simplest sense, it means that programs consist of functions, objects taking zero or more inputs and producing an output according to a well-defined scheme. By contrast, languages like [[C (language)|C]], [[Pascal (language)|Pascal]] and [[FORTRAN]] are said to be [[procedural language]]s. But this description can be a bit misleading. Programs written in procedural languages "compute" by carrying out instructions specified by the programmer. By contrast, a functional program does not consist of instructions to '''do''' things, but consists of expressions that may be reduced to simpler expressions via application of a few basic rules (te terminology is due to Church)

* '''Alpha conversion''' - consistent renaming of variables
* '''Beta reduction''' - application of functions
* '''Eta conversion''' - converting expressions to functions (lambda abstraction)
* '''Delta rules''' - rules governing application of built-in functions such as addition (delta rules are not part of the lambda calculus)

In practice, though, Scheme does not make use of reductions directly, but instead proceeds by evaluation. This is made possible by other features of Scheme (notably strictness). The equivalence of the approaches is an important result.