I said:
| Sorry if this is caused by exactly the same as my last tcLookupTyVar
| report. Since I can't tell, I'll report it anyway.
| panic! (the `impossible' happened):
| tcLookupTyVar:a_r6F
|
| Please report it as a compiler bug to [EMAIL PROTECTED]
| If the instance definition for (*) at the end of this toy module
| is replaced by the definition that is commented, this all compiles
| fine. Strange, because the two implementations are equivalent modulo
| the theory {(*) = multiply}.
That is if the `a -> a -> a' in my previous posting is replaced by
`(Group a) => a -> -> a'.
It still crashes though.
| Remove the `multiply :: (Group a) => a -> a -> a' part, and it compiles without
| problems.
> module Rings( Group, Ring ) where
> import qualified Prelude( Ord(..), Eq(..), Num(..) )
> import Prelude hiding( Ord(..), Eq(..), Num(..), MonadZero( zero ) )
> class Group a where
> compare :: a -> a -> Prelude.Ordering
> fromInteger :: Integer -> a
> (+) :: a -> a -> a
> (-) :: a -> a -> a
> zero :: a
> one :: a
> zero = fromInteger 0
> one = fromInteger 1
> -- class (Group a) => Ring a where
> -- (*) :: a -> a -> a
> -- (*) a b =
> -- case (compare a zero) of
> -- EQ -> zero
> -- LT -> zero - ((*) (zero - a) b)
> -- GT -> case compare a one of
> -- EQ -> b
> -- _ -> b + ((*) (a - one) b)
> class (Group a) => Ring a where
> (*) :: a -> a -> a
> (*) a b = multiply a b
> where multiply :: (Group a) => a -> a -> a
Group a => added
> multiply a b
> = case (compare a zero) of
> EQ -> zero
> LT -> zero - (multiply (zero - a) b)
> GT -> case compare a one of
> EQ -> b
> _ -> b + (multiply (a - one) b)
________________________________________________________________
Marc van Dongen | phone: +353 21 903083
Department of Computer Science | Fax: +353 21 903113
University College Cork, Cork, Ireland | Email: [EMAIL PROTECTED]
