Stefan O'Rear wrote:
On Fri, Aug 17, 2007 at 04:27:29PM -0400, Thomas Hartman wrote:
trying to compile regex-tdfa, I ran into another issue. (earlier I had a cabal problem but that's resolved.)
there's a line that won't compile, neither for ghc 6.6.1 nor 6.7
import GHC.Prim(MutableByteArray#,RealWorld,Int#,sizeofMutableByteArray#,unsafeCoerce#)
so the fresh darcs regex tdfa package won't build.
This line (line 16 below) causes this error for
ghc -e '' RunMutState.hs
for both ghc 6.1 and 6.7
There are at least two things going on here.
1. GHC-specific unboxed identifiers have a # in the name. I think this is a relic from back when the only reasonable way to namespace was to modify your compiler to add extra identifier characters, and use them in all non-portable identifiers. In any case, you have to enable the -fglasgow-exts option (or -XMagicHash in recent 6.7) to allow imports of such identifiers.
2. Explicitly importing GHC.Prim has been discouraged for as long as I can remember, and GHC HQ has finally made good on the promise to make it impossible. Code which imports it has a bug already, which can be fixed by switching to GHC.Exts. (Why? GHC.Prim is wired into the compiler, while GHC.Exts is a normal Haskell module, so by using GHC.Exts you are insulated from questions of what is primitive and what is derived but still unportable. Yes, this does change.)
Stefan
Hi, I wrote regex-tdfa, and since I don't use beyond GHC 6.6.1 I had not seen this problem emerge. The use of GHC.Prim and CPP is intimitely linked: from http://darcs.haskell.org/packages/regex-unstable/regex-tdfa/Text/Regex/TDFA/...
#ifdef __GLASGOW_HASKELL__ foreign import ccall unsafe "memcpy" memcpy :: MutableByteArray# RealWorld -> MutableByteArray# RealWorld -> Int# -> IO ()
{-# INLINE copySTU #-} copySTU :: (Show i,Ix i,MArray (STUArray s) e (ST s)) => STUArray s i e -> STUArray s i e -> ST s () copySTU (STUArray _ _ msource) (STUArray _ _ mdest) = -- do b1 <- getBounds s1 -- b2 <- getBounds s2 -- when (b1/=b2) (error ("\n\nWTF copySTU: "++show (b1,b2))) ST $ \s1# -> case sizeofMutableByteArray# msource of { n# -> case unsafeCoerce# memcpy mdest msource n# s1# of { (# s2#, () #) -> (# s2#, () #) }}
#else /* !__GLASGOW_HASKELL__ */
copySTU :: (MArray (STUArray s) e (ST s))=> STUArray s Tag e -> STUArray s Tag e -> ST s () copySTU source destination = do b@(start,stop) <- getBounds source b' <- getBounds destination -- traceCopy ("> copySTArray "++show b) $ do when (b/=b') (fail $ "Text.Regex.TDFA.RunMutState copySTUArray bounds mismatch"++show (b,b')) forM_ (range b) $ \index -> unsafeRead source index >>= unsafeWrite destination index #endif /* !__GLASGOW_HASKELL__ */
The entire point of using the ST monad is manage memory more efficiently than with (U)Array. The copySTU simply uses a "memcpy" to copy the whole source array into the destination efficiently. This lets me re-use the already allocated destination array. If there had been a high level "copyMArray" then this would not have been needed. The CPP is used to let non-GHC compilers copy element by element. The *right* solution is to patch the STUArray and/or MArray code to do this behind the scenes. So how does one get the array pointer without GHC.Prim in 6.7 ? -- Chris