[Hugs] #37: Equal Ints are not equal

[Hugs]

#37: Equal Ints are not equal
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 Reporter:  guest    |       Owner:  nobody 
     Type:  defect   |      Status:  new    
 Priority:  blocker  |   Milestone:         
Component:  hugs     |     Version:  current
 Keywords:           |  
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Hi,

 a few days ago I wrote a program which handles my own integers. Then I
 check my own implementation against the normal Int implementation in Hugs.
 Thereby I wonder about inequality of Ints which are definitely equal.

 This is a test program I wrote after I recognized that hugs
 has probably a bug in the inequality check of Ints.


   data MInt = Zero | Succ MInt | Pred MInt deriving Show

   tn :: Int -> MInt
   tn x | x<0 = Pred (tn (x+1))
   tn 0     =  Zero
   tn (n+1) = Succ (tn n)

   ti :: MInt -> Int
   ti Zero = 0
   ti (Succ x) = 1+(ti x)
   ti (Pred x) = (ti x) -1

   testi :: (MInt -> MInt -> MInt) -> (Int -> Int -> Int) -> Int -> Int ->
 Bool
   testi f g x y = (ti (f (tn x) (tn y))) /= (g x y)

   myMul x y = tn ((ti x) * (ti y))

   test = [(x,y,ti (myMul (tn x) (tn y)),x * y)|
             x<-[-100..100],
             y<-([-100..(-1)]++[1..100]),(testi myMul (*)  x y) ]

 the list "test" should be empty in any case
 but unfortunately hugs returns this (copy of the console):

   __   __ __  __  ____   ___
 _________________________________________
   ||   || ||  || ||  || ||__      Hugs 98: Based on the Haskell 98
 standard
   ||___|| ||__|| ||__||  __||     Copyright (c) 1994-2003
   ||---||         ___||           World Wide Web: http://haskell.org/hugs
   ||   ||                         Report bugs to: hugs-bugs at haskell.org
   ||   || Version: November 2003
 _________________________________________

   Haskell 98 mode: Restart with command line option -98 to enable
 extensions

   Type :? for help
   Main> test
   [(-100,80,-8000,-8000),(-100,99,-9900,-9900),
   (-99,58,-5742,-5742),(-99,83,-8217,-8217),
   (-98,71,-6958,-6958),(-98,86,-8428,-8428),
   (-97,46,-4462,-4462),(-97,87,-8439,-8439),
   (-96,76,-7296,-7296),(-95,88,-8360,-8360),(-94,73,-6862,-6862)
   ERROR - Control stack overflow
   Main>

 I have checked this program with Hugs on different plattforms:
 Gentoo Linux x86 64-Bit and Suse Linux 32-Bit. On both plattforms
 the same bug occurs with different Ints for each run (i.e. the list
 contains different tuples). I have also checked my program with
 other Haskell implementations and there it returns an empty list
 as expected.

 Best regards,
 Stephan Swiderski (swiderski at informatik.rwth-aachen.de)

 P.S.: We have tested Sep2006 with similar results:
 __   __ __  __  ____   ___      _________________________________________
 ||   || ||  || ||  || ||__      Hugs 98: Based on the Haskell 98 standard
 ||___|| ||__|| ||__||  __||     Copyright (c) 1994-2005
 ||---||         ___||           World Wide Web: http://haskell.org/hugs
 ||   ||                         Bugs: http://hackage.haskell.org/trac/hugs
 ||   || Version: September 2006 _________________________________________

 Haskell 98 mode: Restart with command line option -98 to enable extensions

 Type :? for help
 Main> :e
 Main> test
 [(-100,90,-9000,-9000),(-98,40,-3920,-3920),(-97,63,-6111,-6111),(-97,69,-6693,-
 6693)
 ERROR - Control stack overflow

-- 
Ticket URL: <http://hackage.haskell.org/trac/hugs/ticket/37>
Hugs <http://www.haskell.org/hugs/>
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