Am Dienstag 13 Oktober 2009 01:03:24 schrieb b1g3ar5:
I can't get the following to work in Leksah - but it works OK in GHC. Can anyone spot the error?
I wondered if it was becasue the libraries loaded are different - but I'm just a Haskell beginner ...
I have:
myGroupBy :: Int→ [a]→ [[a]] ^^^^^^^^^^ That "Int" isn't used in the definition of myGroupBy
perhaps you intended to write myGroupBy k = takeWhile (not . null) . unfoldr (Just . splitAt k) ?
myGroupBy = takeWhile not . null . (unfoldr (Just . (splitAt 3)))
and I am getting the error:
Couldn't match expected type `Int' against inferred type `[a]' In the second argument of `(.)', namely `(splitAt 3)' In the first argument of `unfoldr', namely `(Just . (splitAt 3))' In the second argument of `(.)', namely `(unfoldr (Just . (splitAt 3)))'
But I think that
splitAt :: Int->[a]->([a],[a])
so:
splitAt 3 :: [a]->([a], [a])
and:
Just.(splitAt 3) :: [a]->Maybe ([a], [a])
which seems OK as the first argument of unfoldr:
unfoldr :: (b-> Maybe(a,b))->b->[a]
with the a and b of unfoldr being [a] and [a].
The mention of Int in the error makes me wonder if I've got the wrong splitAt - with the arguments reversed maybe.
Any ideas?
Thanks.
N