#15143: Passing an IO value through several functions results in program hanging. -------------------------------------+------------------------------------- Reporter: Burtannia | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Burtannia): Replying to [comment:6 simonpj]: First of all I'm very excited that you replied to this. Your financial contracts paper was of great interest and your talk(s) on writing a good dissertation / paper were a huge help! So thank you for those. Anyway, back to the issue at hand...
Each call of `incTime` invokes its argument `o` twice.
After thinking through this for a while I think I understand what's happening. `o` is being evaluated both in `obs <- o` and with `_ -> o`? I wasn't thinking of `o` as a monadic computation and therefore I thought of `_ -> o` as just returning the input unchanged rather than evaluating it again.
{{{ incTime (do { updRef r (+ 1); return ObsTemp }) }}}
I don't understand this example. What is `updRef` and what value is `ObsTemp` wrapping? Not that it matters because I agree that the observed behaviour with `incTime` is not a bug. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15143#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler