#13406: IO hack in demand analyzer can miss I/O -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If someone digs into the `IO` type, they could (with good reason, even!) decide that they want to produce something other than an unboxed pair. Here's an example, imitating `StateT st IO a` in a way that's sure to be unboxed well: {{{#!hs newtype IOState st a = IOState { unIOState :: State# RealWorld -> st -> (# State# RealWorld, st, a #) } }}} This won't trip `io_hack_reqd`, so demand analysis won't see it as I/O, and everything will be wrong. Urk. Furthermore, in the future, we may allow newtypes around unlifted types, in which case this stuff gets even messier. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13406 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler