29 May
2009
29 May
'09
6:28 p.m.
On Fri, May 29, 2009 at 8:04 PM, 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?
For some monads, fmap (or <$>) has a more efficient definition than
liftM. Otherwise, it's just a style thing.
--
Dave Menendez