Excerpts from Bulat Ziganshin's message of Thu May 28 15:07:02 +0200 2009:
Hello Lennart,
Thursday, May 28, 2009, 11:57:09 AM, you wrote:
-- | Generalization of the 'Bool' type. Used by the generalized 'Eq' and 'Ord'. class Boolean bool where (&&) :: bool -> bool -> bool -- ^Logical conjunction. (||) :: bool -> bool -> bool -- ^Logical disjunction.
i use another approach which imho is somewhat closer to interpretation of logical operations in dynamic languages (lua, ruby, perl):
I tend to prefer Monoid: (|||) :: (Monoid a, Eq a) => a -> a -> a a ||| b | a == mempty = b | otherwise = a (&&&) :: (Monoid a, Eq a, Monoid b) => a -> b -> b a &&& b | a == mempty = mempty | otherwise = b In particular I also like this one (however I would like another name): mapNonEmpty :: (Eq a, Monoid a, Monoid b) => (a -> b) -> a -> b mapNonEmpty f x | x == mempty = mempty | otherwise = f x Best regards, -- Nicolas Pouillard http://nicolaspouillard.fr