Hrm. On the C side the arrays disappear shortly after my call, so just
casting wouldn't really work. I settled for the following monstrosity
where (cast :: a -> b) is your standard unsafePerformIO/IORef based
casting function:
peekPackedCString :: CString -> IO PackedString
peekPackedCString cs = do
i <- findLength cs 0
(arr :: IOUArray Int Char) <- newArray_ (0,i)
writeToArr arr i 0 cs
(arr' :: UArray Int Char) <- unsafeFreeze arr
return (cast arr')
where
findLength ptr n = do
c <- peek ptr
if c == 0
then return n
else findLength (plusPtr ptr 1) $! n+1
writeToArr arr len pos ptr
| pos >= len = return ()
| otherwise = do
c <- peek ptr
writeArray arr pos (castCCharToChar c)
writeToArr arr len (len+1) (plusPtr ptr 1)
it's pretty fast and works only because the type of PackedString is
newtype PackedString = PS (UArray Int Char)
so the casting gives us what we want.
This does seem like something that belongs in the PackedString library
or the Foreign.C.String library, though.
- Hal
--
Hal Daume III | [EMAIL PROTECTED]
"Arrest this man, he talks in maths." | www.isi.edu/~hdaume
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> John Meacham
> Sent: Thursday, August 21, 2003 3:10 AM
> To: [EMAIL PROTECTED]
> Subject: Re: fast CString -> IO PackedString fuction
>
>
> On Wed, Aug 20, 2003 at 06:48:58PM -0700, Hal Daume wrote:
> > is there a way to go from a CString to a PackedString w/o
> going through
> > a normal String in the middle?
> > or should i write my own?
>
> If you can get a wchar_t * out of the app then that can be simply cast
> to a packedstring, this is quite speedy.
> if you use mbsrtowcs(3) and friends to do the conversion from char *
> then you get properly localized text via locale settings for free :)
> I have used this sort of thing for interfacing haskell to libraries
> where honoring locale was important in the past.
> John
>
> --
> --------------------------------------------------------------
> -------------
> John Meacham - California Institute of Technology, Alum. -
> [EMAIL PROTECTED]
> --------------------------------------------------------------
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