Hi,

I tried to use unboxed arrays for generating an antialiased texture. To make it easier to understand, here is the stripped down code that produces an error:

>import Control.Monad.ST
>import Data.Array.ST
>import Data.Array.Unboxed
>import Data.Word
>type BitMask = UArray Int Word16 -- for determining the grey value of a pixel
>type Pixels = (Int, Int, T)
>data T = N | B BitMask -- this does not work
>-- type T = Int -- this works if int the next line N is replaced by ..lets say 0
>f = newArray (0,10) N :: (ST s (STUArray s Int T))

http://hackage.haskell.org/packages/archive/array/0.2.0.0/doc/html/Data-Array-MArray.html#t%3AMArray
shows that mutable/unboxed arrays only allow simple types:
i.e.  MArray (STUArray s) Int32 (ST s)

Isn't this ugly? Imagine this would be the case in C:


struct stupidArrayElement{
 int a;
 int b; // not allowed!
}

stupidArrayElement s[10];


Wouldn't it be nice to have something like: MArray (STUArray s) e (ST s)
with e being a non-recursive data type (like data T = N | B Bitmask).
My understanding of Haskell isn't deep enough to know if I have overlooked something or if the problem is solvable without a language extension. With a language extension I guess that it is not hard to find out if an abstract data type is non-recursive. Then this type should be serializable automatically.

What do you think?
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