Tim,
On Sun, Nov 21, 2010 at 7:27 AM, Tim Baumgartner
data Token = Number Int -- ... number :: Parser Token number = many1 digit ↠ (read >>> Number >>> return) -- = many1 digit ↠ return∘Number∘read
But I wonder what an advanced haskeller would code instead. Particularly, I'd like to get rid of the 'return'.
My understanding is that to remove the return, you can lift your pure function (Number . read) into the Parser monad using fmap or <$> from Control.Applicative: number' = Number . read <$> many1 digit A bit of Sunday morning exploration yielded that you may also like the <$$> operator, but it is not defined in the standard libraries (see discussion here: http://www.haskell.org/pipermail/libraries/2010-April/013403.html) : (<$$>) :: Functor f => f a -> (a -> b) -> f b (<$$>) = flip (<$>) infixl 4 <$$> number' = many1 digit <$$> Number . read or number' = many1 digit <$$> (read >>> Number) Patrick
Thanks in advance Tim _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners
-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada