id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
7369,Simplifier bug(?),sweirich,,"Not sure if it is really a bug.  I was playing around with the following infinite loop in GHC 7.6:

{{{

{-# LANGUAGE GADTs, KindSignatures #-}

data False

data I (c :: * -> *)

data R (c :: *) where
  R :: (a (I a) -> False) -> R (I a)

delta :: R (I R) -> False
delta = \ (R f) -> f (R f)

omega :: False
omega = delta (R delta)

main :: IO ()
main = seq omega (return ())

}}}

And I got the following result.  It's supposed to be an infinite loop, though, so maybe it is ok. GHC 7.4 just hangs on this example.

{{{
spaceman:haskell sweirich$ ghc inj4.hs
[1 of 1] Compiling Main             ( inj4.hs, inj4.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.1 for i386-apple-darwin):
	Simplifier ticks exhausted
    When trying UnfoldingDone main:Main.$WR{v reV} [gid[DataConWrapper]]
    To increase the limit, use -fsimpl-tick-factor=N (default 100)
    If you need to do this, let GHC HQ know, and what factor you needed
    To see detailed counts use -ddump-simpl-stats
    Total ticks: 5160

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
}}}",bug,closed,normal,,Compiler,7.6.1,duplicate,,,Unknown/Multiple,Unknown/Multiple,Other,Unknown,,,,