functional programming

(FP) A program in a functional language consists

of a set of (possibly {recursive}) {function} definitions and

an expression whose value is output as the program's result.

Functional languages are one kind of {declarative language}.

They are based on the {typed lambda-calculus} with constants.

There are no {side-effect}s to expression evaluation so an

expression (e.g. a function applied to certain arguments) will

always evaluate to the same value (if its evaluation

terminates). Furthermore, an expression can always be

replaced by its value without changing the overall result

({referential transparency}).

The order of evaluation of subexpressions is determined by the

language's {evaluation strategy}. In a {strict}

({call-by-value}) language this will specify that arguments

are evaluated before applying a function whereas in a

non-strict ({call-by-name}) language arguments are passed

unevaluated.

Programs written in a functional language are generally

compact and elegant, but have tended, until recently, to run

slowly and require a lot of memory.

Examples of functional languages are {Clean}, {FP}, {Haskell},

{Hope}, {LML}, {Miranda} and {SML}. Many other languages such

as {Lisp} have a subset which is {purely functional} but also

contain non-functional constructs.

See also {lazy evaluation}, {reduction}.

{Lecture notes

(ftp://ftp.cs.olemiss.edu/pub/tech-reports/umcis-1995-01.ps)}

or the same {in dvi-format

(ftp://ftp.cs.olemiss.edu/pub/tech-reports/umcis-1995-01.dvi)}.

{FAQ

(http://www.cs.nott.ac.uk/Department/Staff/gmh/faq.html)}.

{SEL-HPC Article Archive

(http://www.lpac.ac.uk/SEL-HPC/Articles/)}.

(1999-01-08)