Am Samstag 30 Mai 2009 02:04:29 schrieb Bartosz Wójcik:
On Friday 29 May 2009 22:10:51 Bryan O'Sullivan wrote:
myFloat = try (symbol "-" >> float >>= return . negate) <|> try float <|> (integer >>= return . fromIntegral)
Any time you see ">>= return .", something is being missed. Use liftM or <$> instead, i.e. "fromIntegral <$> integer" instead of "integer >>= return . fromIntegral".
I don't undersdand what is being missed.
liftM f m1 = do { x1 <- m1; return (f x1) } so liftM fromIntegral integer will result the same. Is it then not just a convenience?
Even, desugaring the definition of liftM, we get liftM f m1 = m1 >>= return . f or, eta-reducing, liftM f= (>>= return . f) It's a matter of style and readability.
Bartek