I want to be able to take a simple C program and
access a function from it in Haskell. A simple example
The attachement is a file where the Haskell program first creates the
C-source, compiles it to an shared object file, loads the object using
the dynamic linker and uses the just constructed function.
Regards,
--
-- Mirko Rahn -- Tel +49-721 608 7504 --
--- http://liinwww.ira.uka.de/~rahn/ ---
module Main where
import System.Posix.DynamicLinker as DL
import System.Process ( runInteractiveProcess , waitForProcess )
import Foreign.C ( CString , withCString )
import Foreign ( FunPtr )
import Directory ( removeFile )
-------------------------------------------------------------------------------
fun_name = "fun"
mod_contents =
unlines
[ "#include <string.h>"
, "#include <stdio.h>"
, ""
, "int " , fun_name , " ( int n , char * msg )"
, "{"
, " static int count = 1 ; "
, " int l = strlen ( msg ) ;"
, " printf ( \"[call %d] %s (%d) - %d\\n\" , count ++ , msg , l , n ) ; "
, " return ( l * n ) ; "
, "}"
]
cc = "gcc"
cc_opts = [ "-shared" ,"-fpic" ]
mod_name = "./dl.o"
mod_src = "./dl.c"
create_mod = do
writeFile mod_src mod_contents
(_,_,_,pid) <-
runInteractiveProcess cc ( cc_opts ++ [ mod_src , "-o" , mod_name ] )
Nothing Nothing
waitForProcess pid
removeFile mod_src
remove_mod = removeFile mod_name
with_mod f = create_mod >> f >> remove_mod
-------------------------------------------------------------------------------
type Fun = Int -> CString -> IO Int
foreign import ccall "dynamic" fun__ :: FunPtr Fun -> Fun
-------------------------------------------------------------------------------
use_fun f (msg,n) = withCString msg (f n)
use_once x =
DL.withDL mod_name [DL.RTLD_NOW] $ \ dl -> do
fun_ptr <- DL.dlsym dl fun_name
use_fun (fun__ fun_ptr) x
use_often xs = do
dl <- DL.dlopen mod_name [DL.RTLD_NOW]
fun_ptr <- DL.dlsym dl fun_name
res <- mapM (use_fun (fun__ fun_ptr)) xs
DL.dlclose dl
return res
inp = [("Foo",3),("Bar",4),("FooBar",2)]
main = with_mod $ do
mapM use_once inp >>= print
use_often inp >>= print
{-
[EMAIL PROTECTED]:~/dl$ ls
DL.hs
[EMAIL PROTECTED]:~/dl$ ghc --make -fffi DL.hs -o DL
[1 of 1] Compiling Main ( DL.hs, DL.o )
Linking DL ...
[EMAIL PROTECTED]:~/dl$ ./DL
[call 1] Foo (3) - 3
[call 1] Bar (3) - 4
[call 1] FooBar (6) - 2
[9,12,12]
[call 1] Foo (3) - 3
[call 2] Bar (3) - 4
[call 3] FooBar (6) - 2
[9,12,12]
[EMAIL PROTECTED]:~/dl$ ls
DL DL.hi DL.hs DL.o
-}_______________________________________________
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