#12235: Wrong compilation of bang patterns -------------------------------------+------------------------------------- Reporter: osa1 | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by rwbarton): * status: new => closed * resolution: => invalid Comment: It should fail. Pattern matching is top-to-bottom, left-to-right, and according to the user's guide
Matching an expression e against a pattern !p is done by first evaluating e (to WHNF) and then matching the result against p.
So on the third line, we evaluate `i` to WHNF before checking whether the head of the list is `B`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12235#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler