[ I didn't see a CC: in Marcin's reply, so I'll quote the full
mail again... ]
Marcin 'Qrczak' Kowalczyk wrote:
> Mon, 5 Jun 2000 20:26:05 +0100, Nick Williams <[EMAIL PROTECTED]> pisze:
> > data Cost = Val Integer | Infinity deriving Show
>
> deriving (Eq, Ord, Show) makes right instances in your case.
>
> > instance Ord Cost where
> > Val x < Val y = x<y
> > Infinity < Val _ = False
> > Val _ < Infinity = True
> > Infinity < Infinity = False
>
> Default implementation of (<=) uses compare and vice versa. If you
> define neither of them, both will loop forever. It's enough to
> provide either compare or (<=) in the Ord class, but not (<).
But -fwarn-missing-methods (which is on by default) should yield a
warning in that case. Perhaps it doesn't handle circular default
methods correctly? Don't know...
Cheers,
Sven
--
Sven Panne Tel.: +49/89/2178-2235
LMU, Institut fuer Informatik FAX : +49/89/2178-2211
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