#10711: Defining mapM_ in terms of traverse_ causes substantial blow-up in ByteCodeAsm -------------------------------------+------------------------------------- Reporter: bgamari | Owner: bgamari Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: ghcirun004 Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by nomeata): BTW, here are the relevant definitions that add up to three `>>=` for one `*>`: {{{#!hs a1 *> a2 = (id <$ a1) <*> a2 (<$) = fmap . const fmap = liftM liftM f m1 = do { x1 <- m1; return (f x1) } -- here is one (<*>) = ap ap m1 m2 = do { x1 <- m1; x2 <- m2; return (x1 x2) } -- here are two }}} It seems that performance-worrying code should simply ''not'' implement `Functor` and `Applicative` via the `Monad`-derived methods. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10711#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler