caf

constant applicative form
CAF

   <functional programming> (CAF) A {supercombinator} which is
   not a {lambda abstraction}.  This includes truly constant
   expressions such as 12, (+ 1 2), [1, 2, 3] as well as partially
   applied functions such as (+ 4).  Note that this last example
   is equivalent under {eta abstraction} to \ x . + 4 x which is
   not a CAF.

   Since a CAF is a supercombinator, it contains no free
   variables.  Moreover, since it is not a lambda abstraction it
   contains no variables at all.  It may however contain
   identifiers which refer to other CAFs, e.g.

   	c 3 where c = (* 2).

   A CAF can always be lifted to the top level of the program.
   It can either be compiled to a piece of graph which will be
   shared by all uses or to some shared code which will overwrite
   itself with some graph the first time it is evaluated.  A CAF
   such as

   	ints = from 1  where  from n = n : from (n+1)

   can grow without bound but may only be accessible from within
   the code of one or more functions.  In order for the {garbage
   collector} to be able to reclaim such structures, we associate
   with each function a list of the CAFs to which it refers.
   When garbage collecting a reference to the function we collect
   the CAFs on its list.

   [The Implementation of Functional Programming Languages, Simon
   Peyton Jones
(http://research.microsoft.com/%7Esimonpj/papers/slpj-book-1987/PAGES/224.HTM)].

   (2006-10-12)