[W/K] :: functional programming

  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 mostly based on the typed lambda-calculus with
          constants.  There are no side-effects 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 purely functional languages are Clean, FP,
          Haskell, Hope, Joy, 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/).
       
          (2003-03-25)