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 3where g y = y + xx is a free variable of g so it is added as an extra argument:f x = g 3 xwhere g y x = y + xFunctions 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.