Functional programming, also known as applicative programming, is a form of programming in which functions can be manipulated in arbitrary ways. The evaluation of expressions is emphasized, rather than the execution of commands. Using the various functions forms the expressions. Programming languages such as XML, Perl, XML and Python incorporate some functional programming-inspired features.

Another way of describing functional programming, in computer terminology, is that it is a declarative language--a language that specifies what ought to be done, rather than in what order things are to occur. This descriptive programming is different in approach from the more normal imperative programming. Instead of giving commands to the computer, objects are described. Each object is either a "primitive" object--like a number--or is created by applying some function to another object.

The declarative nature of functional programming means that the compiler, which translates source code into object code, has...