#15349: fixST is a bit wrong -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: dfeuer Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Core Libraries | Version: 8.5 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): The only alternative I see for now is to use `noDuplicate#` to fix up the implementation, like maybe {{{#!hs fixST :: (a -> ST s a) -> ST s a fixST k = ST $ \ s -> let ans = liftST (noDuplicate >> k r) s STret _ r = ans in case ans of STret s' x -> (# s', x #) }}} That implementation is also available for `fixIO`, of course. I don't have a terribly good sense of how it would compare. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15349#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler