unfold/fold

A {program transformation} where a {recursive} call to a

function is {unfold}ed to an instance of the function's body

and then later an instance of the function's body is replaced

by a call. E.g.

sumdouble l ◦ sum (double l)

double l ◦ case l of

[] -> []

x:xs -> 2▫x : double xs

◦◦> (unfold double)

sumdouble l ◦ sum (case l of

[] -> []

x:xs -> 2▫x : double xs)

◦◦> (distribute over case)

sumdouble l ◦ case l of

[] -> sum []

x:xs -> sum (2▫x : double xs)

◦◦> (unfold sum)

sumdouble l ◦ case l of

[] -> 0

x:xs -> 2▫x : sum (double xs)

◦◦> (fold sumdouble)

sumdouble l ◦ case l of

[] -> 0

x:xs -> 2▫x : sumdouble xs

(1994-11-03)