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 (<).
--
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