#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 rwbarton): I have to say that I still don't understand exactly why {{{ a1 *> a2 == (a1 >>= (\_ -> return id)) >>= (\x2 -> a2 >>= (\x3 -> return (x2 x3))) }}} is more than a constant (say 10 times) slower than `a1 >> a2` for this `Assembler` monad. Experimentally bgamari's test program does ~n^2^ allocations and takes ~n^3^ total time in the Applicative version, while the Monad version runs in linear allocations and time. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10711#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler