I suppose there are plenty of flavors for such functions, and they are
simple enough to write.
One I've been using a bit is this one:
loopM :: Monad m => a -> (a -> m (Maybe a)) -> m ()
loopM start action = loop start
where
loop i =
do result <- action i
case result of
Nothing -> return ()
Just newval -> loop newval
BTW: what is considered better? The above or this one:
loopM :: Monad m => a -> (a -> m (Maybe a)) -> m ()
loopM i action =
do result <- action i
case result of
Nothing -> return ()
Just newval -> loopM newval action
Or is there no difference at all? Sorry for the non-sequitur here.
Usage example:
streamToFile :: Storable a => [a] -> String -> IO ()
streamToFile list fname =
do let elementSize = sizeOf (head list)
let numElements = (65535 + elementSize) `div` elementSize
let bufferSize = numElements * elementSize
f <- openBinaryFile fname WriteMode
allocaArray bufferSize $ \buf ->
loopM list $ \list ->
do let (cur, next) = splitAt numElements list
pokeArray buf cur
hPutBuf f buf (length cur * elementSize)
case next of
[] -> return Nothing
otherwise -> return (Just next)
hClose f
(allows writing a lazy list to a binary file)
JCAB
On Wed, 21 Mar 2007 13:34:48 -0700, Dominic Steinitz
These sort of things come up from time to time. Why not make a proposal?
http://www.haskell.org/pipermail/haskell-cafe/2006-February/014214.html
Dominic.
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