#9844: Bang pattern doesn't work on a newtype constructor -------------------------------------+------------------------------------- Reporter: akio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Incorrect Blocked By: | result at runtime Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- According to the documentation, {{{f0}}} and {{{f1}}} in the following program should have the identical semantics: {{{#!hs {-# LANGUAGE BangPatterns #-} module Main where newtype N = N Int f0 :: N -> Int f0 n = case n of !(N _) -> 0 _ -> 1 f1 :: N -> Int f1 n = n `seq` case n of N _ -> 0 _ -> 1 main = do print $ f0 undefined print $ f1 undefined }}} However, ghc only compiles {{{f1}}} into a strict function: {{{ % ./bang-newtype 0 bang-newtype: Prelude.undefined }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9844 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler