Just a quick follow-up that I meant to say in that last email. For instance, I think it would be reasonable to define tuples as instances of a HasBounds class, but that's not possible with the current definition. With my definition, I'd write:
instance HasBounds (a,b) Int where { bnds _ = (0,1) } instance HasBounds (a,b,c) Int where { bnds _ = (0,2) } etc...
On the other hand, tuples could not be considered arrays in the IArray sense unless each element of the tuple had the same time. We could have:
instance IArray (a,a) a where ...
but not
instance IArray (a,b) ...
Anyway, it's late, bed time. :) - Hal -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Sun, 24 Feb 2002, Hal Daume III wrote:
After reading your email i went to the discussion of IArray on the haskell doc page (http://www.haskell.org/ghc/docs/latest/set/sec-iarray.html) and am somewhat disturbed by it. There is the introduction of the following class:
class HasBounds a where bounds :: Ix ix => a ix e -> (ix,ix)
which is then used in:
class HasBounds a => IArray a e where array :: Ix ix => (ix,ix) -> [(ix,e)] -> a ix e (!) :: ... (//) :: ...
I'm not sure what's bothering me about this, except that this HasBounds declaration seems to be "anticipating" the IArray declaration. That the type of the bounds function assumes that for this type "a" which "has bounds", there are two associated types, the index type and the element type, seems to be reading too much into what it means to have bounds. A more reasonable (imo) definition would be:
class Ix ix => HasBounds a ix | a -> ix where bounds :: a -> (ix,ix)
that way, we would efine things like:
instance Ix ix => HasBounds (Array.Array ix) ix where ... instance Ix ix => HasBounds (UArray ix) ix where ...
I think this makes things much cleaner (arguably it makes these instance declarations a bit longer, but it makes HasBounds a class in its own right; as it is, I don't see any reason why HasBounds should be its own class and why the 'bounds' function isn't simply lumped into the IArray class).
Of course, this require dep types, which is unfortunate, but then again, anyone who is using IArrays probably isn't writing Haskell 98 anyway, and every compiler supports dep types, so... ;)
On the other hand, if using dep types is opposed, I would be in favor of getting rid of the HasBounds class and lumping the bounds function into IArray.
Of course, that's just my opinion... :)
- Hal
-- Hal Daume III
"Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume
On Fri, 22 Feb 2002, David Feuer wrote:
What is IArray? This seems rather mysterious to me.
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