Am Mittwoch, 11. März 2009 23:13 schrieb Manlio Perillo:
Hi.
I have an array (Data.Array.Vector.UArr) of Word8 elements. Elements are stored as Word8 to keep memory usage down.
Now I need to compute the sum of all the array elements; what is the best method? The sum must be of type Int.
How efficient is to simply convert to an UArr Int, using:
mapU fromIntegral v :: UArr Int ?
What about, instead, of something like:
genericSumU :: (UA e, Integral e) => UArr e -> Int genericSumU = foldU add 0
That would have to be foldlU, the type of foldU is foldU :: UA a => (a -> a -> a) -> a -> UArr a -> a while foldlU :: UA a => (b -> a -> b) -> b -> UArr a -> b
where add x y = x + fromIntegral y ?
Unfortunately the latter does not compile:
Couldn't match expected type `Int' against inferred type `e' `e' is a rigid type variable bound by the type signature for `genericSumU' at bin/process-data-1.hs:64:19 In the expression: foldU add 0 In the definition of `genericSumU': genericSumU = foldU add 0 where add x y = x + fromIntegral y
Moreover, this is not really a generic version. I would like to have:
genericSumU :: (Num i, UA e, Num e) => UArr e -> i
is this possible?
Thanks Manlio _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe