Short cut fusion

Short cut fusion is an optimizer method that merges some function calls into one. E.g. map f . map g can be substituted by map (f . g) and filter p . filter q can be substituted by filter (\x -> q x && p x). It can also help to remove intermediate data structures. E.g. computing sum [1..n] does not require an explicit list structure, and the expression is actually translated into a simple loop.

See also correctness of short cut fusion.