On Wed, Nov 11, 2009 at 5:28 PM, Tillmann Vogt wrote: 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-Arra...
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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http://www.haskell.org/mailman/listinfo/haskell-cafe Actually, there's a cool package called storable record. Could it be of
some use to you? (Perhaps you *might* be able to use it if the BitMasks are
of uniform length). Am not 100% sure though.
Isn't this ugly?
I am not sure if it is really *ugly*... and if am allowed to nit-pick,
the analogy with C is not appropriate either.
Arrays are just different. (At least thats how I console myself, when am
looking for a high performance strict array). Also, on an approximately
related issue,
I was suggested to look into data parallel arrays.