#14224: zipWith does not inline -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Core | Version: 8.2.1 Libraries | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `zipWith` is currently defined {{{#!hs zipWith :: (a->b->c) -> [a]->[b]->[c] zipWith _f [] _bs = [] zipWith _f _as [] = [] zipWith f (a:as) (b:bs) = f a b : zipWith f as bs }}} For now (I gather that might change soon?), the fact that it's recursive means that it will never inline. But we really want it to inline when applied to a function, for the same reasons we want `map` to inline. If `f` is something like `const`, `flip const`, or a lazy constructor, it's wasteful to create a thunk to apply it. All three of those cases are common. So unless/until we start inlining recursive functions, we probably want to use {{{#!hs zipWith f = go where go [] _ = [] go _ [] = [] go (x:xs) (y:ys) = f x y : go xs ys }}} There will probably be some regressions, of course. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14224 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler