full laziness

    A transformation, described by
   Wadsworth in 1971, which ensures that subexpressions in a
   function body which do not depend on the function's arguments
   are only evaluated once.  E.g. each time the function

   	f x = x + sqrt 4

   is applied, (sqrt 4) will be evaluated.  Since (sqrt 4) does
   not depend on x, we could transform this to:

   	f x = x + sqrt4
   	sqrt4 = sqrt 4

   We have replaced the dynamically created (sqrt 4) with a
   single shared constant which, in a graph reduction system,
   will be evaluated the first time it is needed and then updated
   with its value.

   See also fully lazy lambda lifting, let floating.

   (1994-11-09)