[Haskell-cafe] Array copying

2 Dec 2007


      Andrew Coppin wrote:
...
copy :: Word32 -> IOUArray Word32 Bool -> Word32 -> IO (IOUArray 
Word32 Bool)
copy p grid size = do
 let size' = size * p
 grid' <- newArray (1,size') False
mapM_
   (\n -> do
     b <- readArray grid n
     if b
       then mapM_ (\x -> writeArray grid' (n + size*x) True) [0..p-1]
       else return ()
   )
   [1..size]
return grid'
Actually, thinking about this... for most kinds of arrays (whether boxed 
or unboxed, mutable or immutable) there's probably a more efficient way 
to copy the data then this. Maybe we should add something to the various 
array APIs to allow efficient copying of arrays / large chunks of arrays?

(In the case of an unboxed array of bits, you can probably copy whole 
32-bit or 64-bit words with a few machine instructions, for example.)