Hello, I didn't try to understand what the function is doing, but just quickly noticed that
> reMatr a = Matr . (flip (.) unMatr) a can be written as > reMatr a = Matr . ((flip (.) unMatr) a) but that > reMatr = Matr . (flip (.) unMatr) can be written as > reMatr a = (Matr . (flip (.) unMatr)) a so because of precedence rules a different function is being applied to 'a' in the 2 versions Best Keith On Tue, Dec 22, 2009 at 9:13 AM, slemi <[email protected]> wrote: > > thanks, that's a really neat syntactic sugar :) > > however, my original question was how to make the reMatr function pointfree, > as > reMatr = Matr . (flip (.) unMatr) > is not working. any ideas/explanation why it doesnt work? > > > Kim-Ee Yeoh wrote: >> >> Here's another way of writing it: >> >> data Matrix a = Matr {unMatr :: [[a]]} | Scalar a deriving (Show, Eq) >> -- RealFrac constraint removed >> >> reMatr :: RealFrac a => ([[a]] -> [[a]]) -> (Matrix a -> Matrix a) >> reMatr f = Matr . f . unMatr -- this idiom occurs a lot, esp. with >> newtypes >> >> Affixing constraints to type constructors is typically deprecated. >> >> >> >> slemi wrote: >>> >>> i have trouble making a function pointfree: >>> >>> data RealFrac a => Matrix a = Matr [[a]] | Scalar a >>> deriving (Show, Eq) >>> >>> unMatr :: RealFrac a => Matrix a -> [[a]] >>> unMatr = (\(Matr a) -> a) >>> >>> reMatr :: RealFrac a => ([[a]] -> [[a]]) -> (Matrix a -> Matrix a) >>> reMatr a = Matr . (flip (.) unMatr) a >>> >>> this works fine, but if i leave the 'a' in the last function's definition >>> like this: >>> reMatr = Matr . (flip (.) unMatr) >>> it gives an error. can anybody tell me why? (i'm using ghci) >>> >> >> > > -- > View this message in context: > http://old.nabble.com/pointfree-trouble-tp26881661p26888978.html > Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. > > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- keithsheppard.name _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
