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)
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