[Haskell-cafe] Array copying

[Andrew Coppin]

Jules Bean wrote:
> Andrew Coppin wrote:
>> 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?
>
> Ideally we'd have the compiler generate optimal code anyway, then you 
> wouldn't need such things.
>
> So, let's hope those compiler/optimiser guys keep working hard!

True - but "copyArray x y" is surely a lot clearer than some longwinded 
mapM thing, no? ;-)