[Haskell-cafe] [Newbie] Cannot derive Eq and Show. Why?

[Bulat Ziganshin]

Hello Peter,

Friday, September 8, 2006, 6:03:36 PM, you wrote:

> I am stumped again. The following code generates the error "ERROR
> file:.\Cube.hs:12 - An instance of IArray UArray a is required to derive Eq
> (Cube a b)" in Hugs. But I did specify the IArray UArray k constraint. So
> what is wrong?

> data (Ord k, IArray UArray k, IArray UArray v) =>

shortly speaking, you should either use boxed Array or switch to using
my ArrayRef library which supports polymorphic unboxed arrays

look for detailed explanations of problem to
http://www.haskell.org/pipermail/haskell-cafe/2004-July/006400.html

ArrayRef library can be found at http://haskell.org/haskellwiki/Library/ArrayRef

for use with Hugs it need to be preprocessed via one of included
MakeHugs scripts

i have added your module to the library as the shortest example of using
polymorphic unboxed arrays :)  see attached file. of course, if you
want that this file will be removed or modified, i will do



-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com
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