Mutable array ops (was: file operations)

[Sigbjorn Finne (Intl Vendor)]

Martin Stein <[EMAIL PROTECTED]> writes: 
> 
..
> 
> Yes, I tried to use them but missed some functions to handle 
> ByteArrays, particularly
> 1. How can I get a ByteArray? (freezing a MutableByteArray 
> seems to be a little strange)

Strange as it might be, but that's the way :)If you want to
hide the use of MutableByteArrays, you can without too much
effort:

  -- untested code.
  doubleByteArray :: [Double] -> ByteArray Int
  doubleByteArray dbls = runST $ do
      marr <- newDoubleArray (0,len)
      zipWithM_ (writeDoubleArray marr) [0..] dlbs
      unsafeFreezeByteArray marr
     where
      len = max 0 (length dbls - 1)

> 2. How can I thaw a ByteArray to get a MutableByteArray?
> 

By manually copying over the bytes - here's the version that I'll
probably add to the MutableArray interface:

\begin{code}
thawByteArray :: Ix ix => ByteArray ix -> ST s (MutableByteArray s ix)
thawByteArray (ByteArray ixs barr#) =
     {- 
        The implementation is made more complex by the
        fact that the indexes are in units of whatever
        base types that's stored in the byte array.
     -}
   case (sizeofByteArray# barr#) of 
     i# -> do
       marr <- newCharArray (0,I# i#)
       mapM_ (\ idx@(I# idx#) -> 
                 writeCharArray marr idx (C# (indexCharArray# barr# idx#)))
             [0..]
       let (MutableByteArray _ arr#) = marr
       return (MutableByteArray ixs arr#) 
\end{code}

The unsafe version of this and thawArray should be supported in the
next release too. 

--Sigbjorn