lambda lifting

   A program transformation to remove free variables.  An
   expression containing a free variable is replaced by a
   function applied to that variable.  E.g.

   	f x = g 3  where g y = y + x

   x is a free variable of g so it is added as an extra argument:

   	f x = g 3 x  where g y x = y + x

   Functions like this with no free variables are known as
   supercombinators and are traditionally given upper-case names
   beginning with "$".  This transformation tends to produce many
   supercombinators of the form f x = g x which can be eliminated
   by eta reduction and substitution.  Changing the order of
   the parameters may also allow more optimisations.  References
   to global (top-level) constants and functions are not
   transformed to function parameters though they are technically
   free variables.

   A closely related technique is closure conversion.  See also
   Full laziness.