- Glasgow-haskell-users

Re: unsafePtrCompare, anybody?
by cwitty＠newtonlabs.com 17 Sep '01

17 Sep '01

Leon Smith <lps(a)po.cwru.edu> writes: > However, in this situation, pointer comparison is simply an arbitrary total > order on the set of all atoms, which is all we need to implement finite maps > based on search trees. And of course, pointer comparisons are a much cheaper > operation that actual string comparison. You could just add an extra Int sequence number to your Atoms, and compare using that. Carl Witty

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Re: Converting [Word8] to CString
by Ashley Yakeley 16 Sep '01

16 Sep '01

At 2001-09-15 02:15, Marcin 'Qrczak' Kowalczyk wrote: >Fri, 14 Sep 2001 23:40:42 -0700, Ashley Yakeley <ashley(a)semantic.org> pisze: > >> I'm looking for a function that will convert a [Word8] byte-array >> to a CString (i.e. a C byte array) for the purposes of FFI. > >You can use newArray which allocates the C byte array using malloc >so it must be freed by free, and cast the resulting pointer from >Ptr Word8 to CString using castPtr. Thank you. I ended up doing this and simply using Ptr Word8 as the FFI type. Curiously, the GHC user's guide sec. 8.2.4.1 seems to suggest that Ptr types are illegal as arguments in foreign import function declarations. I think this is the source of my confusion. http://www.haskell.org/ghc/docs/latest/set/sec-primitive.html#SEC-PRIM-TYPE S -- Ashley Yakeley, Seattle WA

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Re: unsafePtrCompare, anybody?
by Marcin 'Qrczak' Kowalczyk 15 Sep '01

15 Sep '01

Sat, 15 Sep 2001 15:11:02 -0400, Leon Smith <lps(a)po.cwru.edu> pisze: > The point of all of this is that now string equality, when strings > are made into atoms, is just pointer equality, which is available > as IOExts.unsafePtrEq. > > However, in this situation, pointer comparison is simply an > arbitrary total order on the set of all atoms, which is all we need > to implement finite maps based on search trees. The physical pointer order changes with garbage collection. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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unsafePtrCompare, anybody?
by Leon Smith 15 Sep '01

15 Sep '01

I'm writing an atom table for a compiler/interpreter, and it would be really nice to use unsafePtrLT to implement tree-based finite maps. For clarification, my atom table consists of these three functions: mkAtom :: String -> IO Atom show :: Atom -> String (==) :: Atom -> Atom -> Bool such that mkAtom s >>= (return . show) == return s and mkAtom . show == return and atom == atom' <=> show atom == show atom' mkAtom looks up each string in a table stored in an global variable, and returns the atom stored in the table if it is there. Otherwise, it makes the string into an atom, inserts the atom into the table, and returns this new atom. The point of all of this is that now string equality, when strings are made into atoms, is just pointer equality, which is available as IOExts.unsafePtrEq. However, in this situation, pointer comparison is simply an arbitrary total order on the set of all atoms, which is all we need to implement finite maps based on search trees. And of course, pointer comparisons are a much cheaper operation that actual string comparison. Of course, the misuses of unsafePtrEq aren't nearly as heinous as those of unsafePtrCompare. On the other hand, it might be next to impossible to effectively use unsafePtrCompare in cases that it isn't completely safe to use, whereas there are plently of situations where unsafePtrEq is semi-safe to use. best, leon

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Re: Converting [Word8] to CString
by Marcin 'Qrczak' Kowalczyk 15 Sep '01

15 Sep '01

Fri, 14 Sep 2001 23:40:42 -0700, Ashley Yakeley <ashley(a)semantic.org> pisze: > I'm looking for a function that will convert a [Word8] byte-array > to a CString (i.e. a C byte array) for the purposes of FFI. You can use newArray which allocates the C byte array using malloc so it must be freed by free, and cast the resulting pointer from Ptr Word8 to CString using castPtr. When the array is temporary, it's better (and faster) to use withArray list_of_Word8 $ \word8Ptr -> let cstring = castPtr word8Ptr in ... > And it has to be the _same_ list of bytes that comes through on > the native side. I don't unserstand this. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Converting [Word8] to CString
by Ashley Yakeley 15 Sep '01

15 Sep '01

I'm looking for a function that will convert a [Word8] byte-array to a CString (i.e. a C byte array) for the purposes of FFI. foreign import "JVMBridge" "JVMBridge_FindClass" rawFindClass :: JavaVM -> CString -> IO JVMObjectRef; makeCString :: [Word8] -> IO CString; It has to work correctly with _any_ list of bytes. And it has to be the _same_ list of bytes that comes through on the native side. Note that we are only dealing with bytes here, this has nothing whatever to "characters", "text", "charsets", "Unicode", "encodings" or any of that nonsense. If this really can't be done, is there another type I can use? In some cases, the external function may call back into Haskell. -- Ashley Yakeley, Seattle WA

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RE: Confused by profiling
by Simon Marlow 14 Sep '01

14 Sep '01

> I am confused by the GHC profiling output. I have put some abstracts > below to illustrate my confusion. > > I compiled my code with: > HFLAGS="-Wall -package lang -prof -auto-all" hmake -ghc main > and then ran it with: > ./main -t +RTS -p < test5.hs > > Here is some of main.prof: > individual inherited > COST CENTRE MODULE entries %time %alloc > %time %alloc > > [...] > parse Parser 1 0.0 0.0 > 81.4 62.3 > p_module Parser 0 0.0 0.0 > 81.4 62.3 > <|> PC_base 69517 20.3 5.7 > 81.4 62.3 > [...] > p_aexp_list Parser 0 0.0 0.0 > 0.0 0.3 > con2tag_Token# Tokens 880 0.0 0.0 > 0.0 0.0 > pIfThing PC_base 896 0.0 0.0 > 0.0 0.0 > <$ PC 0 0.0 0.0 > 0.0 0.3 > <$> PC 0 0.0 0.0 > 0.0 0.3 > pSucceed PC_base 896 0.0 0.3 > 0.0 0.3 > <*> PC_base 896 0.0 0.0 > 0.0 0.0 > <*> PC_base 896 0.0 0.0 > 0.0 0.0 > p_aexp_tuple Parser 0 0.0 0.0 > 0.0 0.3 > [...] > > and here is the code for p_aexp_list: > > p_aexp_list :: Parser Token Aexp > p_aexp_list = (Aexp_list . get_rights) > <$ pIfThing ((==) (Special '[')) > <*> pSList False p_comma p_exp > <* pIfThing ((==) (Special ']')) > > Now basically my problem is how things under p_aexp_list can > be entered > 896 times if p_aexp_list is entered 0 times - am I reading it wrong? Hmmm. I suspect it may be to do with the fact that p_aexp_list isn't a function, it's a CAF (constant applicative form - basically a top-level expression). The "entries" field counts the number of times an SCC annotation is executed, which corresponds more to "calls" than entries. I must admit I haven't thought too hard about this. It might be helpful to see what happens to the code inside the compiler: p_aexp_list = {-# SCC "p_aexp_list" #-} ... this SCC annotation gets executed once, when p_aexp_list is first entered, and you'll probably find it elsewhere on the profile under one of the CAF entries. The first time it is entered, p_aexp_list reduces to a function closure with the SCC annotation attached to it, so subsequent enters don't actually execute the SCC they just append it to the current cost-centre-stack. Perhaps the act of appending an SCC annotation when entering a function closure should bump the entry counts for all the cost centres in the stack. That might yield more reasonable-looking figures. Cheers, Simon

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RE: problems exporting haskell functions
by Simon Marlow 14 Sep '01

14 Sep '01

Hi there, > Hello, I have tried to export haskell functions, but I > haven't been able to compile anything and obtain a executable > file. My program has two parts. > - Haskell part: > module Hex where > fh :: Int -> Int > foreign export "f" fh :: Int -> Int > fh x = 7 > > - C part: > #include <stdio.h> > #include <stdlib.h> > extern int f(int x); > > int main( ){ > int a; > a = f(5); > printf("%d\n",a); > return 0; > } When you provide your own main() function, you have to arrange to initialize GHC's runtime system. I've attached some example code, and I've added some material to the User's Guide for the next release which explain how to do this. Cheers, Simon

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