Hi Job, thanks for replying.
Thanks for explaining this. I never really thought about the
implications of kinds on type classes, and it's all much more clear
now.
The first version, with only one parameter, almost works, except that
some instances (e.g. uvector, storablevector) have further
One clarification. That is, I could write map with the cNull/cCons
implementation already suggested, but I couldn't do:
instance Chunkable Data.StorableVector.Vector el where
...
cMap = Data.StorableVector.map
which is what I really want.
However, I just realized that I should be able to
Hello,
I'm working on some code like the following:
class Chunkable c el | c - el where
cLength :: c - Int
cHead :: c - Maybe el
I want to be able to map over this type, like this:
cMap :: Chunkable c' el' = (el - el') - c - c'
but this isn't quite right. c' shouldn't be any
What do you mean by parameterized over a different type?
will c have a kind of * - * ? I don't think it has to be for what you
want to work, but the idea of same instance will go out the window.
Do you have a small usage example?
On Wed, Feb 11, 2009 at 11:52 AM, John Lato jwl...@gmail.com
Hi Job,
Thanks for answering. What I'm trying to do is probably very simple,
and I think the biggest problem is that I don't fully understand kinds
yet.
Here's an example instance:
instance Chunkable [a] a where
cmap = map
--etc.
In the class I wrote, c has kind * (e.g. [a]), but then I
You can do this with another type class.
class (Chunkable c1 el1, Chunkable c2 el2) = ChunkMap c1 el1 c2 el2 where
cMap :: (el1 - el2) - c1 - c2
instance ChunkMap [a] a [b] b where cMap = map
If you want to assert that c1 and c2 are really related, you can add
functional dependencies to
I think what you probably want is something like this:
class Chunckable c where
cLength :: c el - Int
cHead :: c el - Maybe el
cMap :: (a - b) - c a - c b
instance Chunckable [] where
cLength [] = 0
cLength (x:xs) = 1 + cLength xs
cHead [] = Nothing
cHead (x:xs) = Just x
cMap =
