#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 danilo2): @Burtannia, thanks for the reply! Why do you think `mr` is not strictly evaluated there? It is a strict function argument, so it have to be evaluated at least to WHNF. This is State over IO, so probably there could be some unevaluated parts, like the inner tuple (not the tuple values, because this is a strict state) in the state monad definition, but in such case I don't see (yet) how it could affect the performance and why `!r <- mr` and `!_ <- mr` behave differently – they both force evaluation of all intermediate structures of the monadic stack. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15143#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler