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 paussed as arguments toin 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 "first-class citizen", a function can be
* stored in variables
* passed to functions
* returned from functions
like any other value. In other langauages, 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