#14112: bang patterns on pattern synonyms? (left vs right hand sides) -------------------------------------+------------------------------------- Reporter: carter | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
But what about pattern synonyms?
That's an excellent point, one that I had not considered. The right thing to do would probably be to `seq` on the sub-pattern thus {{{ pattern P x = Just !(Id x) }}} would give rise to a builder thus {{{ P x = let !a = Id x in Just a }}} In short, when converting from pattern to expression, let!-bind the expressions gotten from converting each banged sub-pattern. But now I grant you that the cost/benefit ratio is less attractive. I'm happy with A. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14112#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler