In [functional programming%|%functional] and semi-functional [programming language%|%languages] including [Scheme], [Javascript], [Haskell], [ML] , functions are '''[http://en.wikipedia.org/wiki/First-class_citizen%|%First Class Citizens]''' , meaning that , like any other value , they can be passed as arguments to other functions .  By definition, they do not exist in languages such as [C] , [Perl] , and [Algol] , where functions inhabit a different namespace than variables.  As with many things , [Tcl] is rather unique in this area .  [proc%|%commands] themselves can not be passed as arguments to other commands , but their names can , which provides something very similar to first-class functions .  Additionally , `[apply]` can be used to interpret a value as a function and evaluate it , providing the equivalent of [lambda] functions .

As a "fisrt-class citizen" , a function can be 

   * stored in variables
   * passed to functions
   * returned from functions

like any other value .  In other langauges , functions are usually [opaque objects], so [introspection] is not available .  In Tcl , they are simply [EIAS%|%strings]

First-class functions permit coding styles that are not available in languages without them ([C] is a good example):

   * [higher order functions], like [lmap] and other [fold]s
   * [static variables] become natural
   * [curry] becomes easy when functions are first class
   * [closures] become important with first-class functions



** See Also **

   [functional programming]:   

   [Playing Scheme]:   An exploratory implementation of first-class functions in Tcl

<<categories>> Category Concept | Category Functional Programming