[Haskell-cafe] runST $ unsafeIOToST $ ioWhatever

[Folsk Pratima]

How wrong is it exactly? Did not get a reply on beginners at haskell.org


import Control.Exception
import Control.Monad.ST
import Control.Monad.ST.Unsafe
import Data.Word
import Foreign.C.String
import Foreign.C.String
import Foreign.C.Types
import Foreign.Marshal
import Foreign.Ptr
import Foreign.Storable

foreign import ccall unsafe "strerror_r_portalbe.c strerror_r_portable" c_strerror_r
    :: CInt -> Ptr CChar -> CSize -> IO CInt

memSet :: Ptr a -> Word8 -> Word32 -> IO (Ptr a)
memSet ptr _ 0 = return ptr
memSet ptr byte size = do
    let voidptr = castPtr ptr :: Ptr Word8
        acts =
            map
                (\i -> pokeByteOff voidptr i byte)
                [0 .. fromIntegral (size - 1)]
    mapM_ id acts
    return ptr

strError :: Int -> String
strError errnum = runST $ unsafeIOToST ioString
  where
    baseSize :: CSize
    baseSize = 50
    ioString = run baseSize
    run :: CSize -> IO String
    run size
        | size > 100000 =
            throwIO $
            userError $
            "!!! INTERNAL strError memory leak detected, " ++
            "you can not recover !!!"
        | otherwise = do
            may <- tryIOString size
            case may of
                Just str -> return str
                Nothing -> run (size + baseSize)
    tryIOString :: CSize -> IO (Maybe String)
    tryIOString size =
        allocaBytes (fromIntegral size) $ \ptr -> do
            zeroptr <- memSet ptr 0 (fromIntegral size)
            st <- c_strerror_r (fromIntegral errnum) ptr size
            -- heuristic
            case st of
                22 -> return . return $ "Unknown error " ++ show errnum
                34 -> return Nothing
                _ -> peekCAString ptr >>= return . return

main = mapM_ (putStrLn) $ map strError [1 .. 1000]


The C file is


#define _POSIX_C_SOURCE 200112L
#include <string.h>

int strerror_r (int, char *, size_t);

int
strerror_r_portable (int e, char *c, size_t s)
{
    return strerror_r (e, c, s);
}

By default GHC picks up GNU version of strerror_r(), I want to pick up
the default portable version. I do not know how to make GHC understand
my desires.