#14356: "Main: thread blocked indefinitely in an MVar operation" in fixIO -------------------------------------+------------------------------------- Reporter: nickkuk | Owner: (none) Type: bug | Status: new Priority: low | Milestone: Component: Runtime System | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by nickkuk: Old description:
I'm not sure whether such behavior is expected, but this program {{{#!hs import System.IO
main = fixIO (\x -> return 1) >>= print }}} prints "1"; and this {{{#!hs import System.IO
main = fixIO (\(x, _) -> return (1, print x)) >>= print . fst }}} prints "Main: thread blocked indefinitely in an MVar operation".
New description: I'm not sure whether such behavior is expected, but this program {{{#!hs import System.IO main = fixIO (\x -> return 1) >>= print }}} prints "1"; and this {{{#!hs import System.IO main = fixIO (\(x, _) -> return (1, print x)) >>= print . fst }}} prints "Main: thread blocked indefinitely in an MVar operation". This behavior can be fixed with additional ~ as alexbiehl said below. Also, this program with mdo {{{#!hs {-# LANGUAGE RecursiveDo #-} main = mdo print x x <- return 1 return () }}} prints "Main: thread blocked indefinitely in an MVar operation". -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14356#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler