[Haskell-cafe] pointfree-trouble

[slemi]

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.