How do I create C-libraries that I can load into GHCi? I am trying to do some basic FFI, and it's not working. Here's the background. I created three files, foo.h, foo.cpp, and test_foo.lhs. (source code below) Note: I am using MinGW/Msys under Windows XP. If I compile foo.cpp and then try to load test_foo into GHCi, I get an error. OTOH, if I compile test_foo with GHC, it works. I just don't understand why it works one way and not the other. What am I doing wrong? -- Ron ------------------------------ Shell commands ------------------------------ $ gcc -c foo.cpp $ ghci test_foo.lhs foo.o ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading object (static) foo.o ... done final link ... done [1 of 1] Compiling Main ( test_foo.lhs, interpreted ) During interactive linking, GHCi couldn't find the following symbol: foo This may be due to you not asking GHCi to load extra object files, [snip] $ ghc --make test_foo.lhs foo.o [1 of 1] Compiling Main ( test_foo.lhs, test_foo.o ) Linking test_foo.exe ... $ test_foo.exe Entering main y = 22 Exiting main $ ar rcs libfoo.a foo.o $ ghc --make test_foo.lhs -lfoo $ test_foo.exe Entering main y = 22 Exiting main $ ghci test_foo.lhs -lfoo ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading object (dynamic) foo ... failed. Dynamic linker error message was: addDLL: unknown error Whilst trying to load: (dynamic) foo Directories to search are: : user specified .o/.so/.DLL could not be loaded. ------------------------------ Source code ------------------------------ // foo.h extern "C" { __stdcall int foo(int x); } ------------------------------ // foo.cpp #include "foo.h" __stdcall int foo(int x) { return 3 * x + 1; } ------------------------------ test_foo.lhs
{-# OPTIONS_GHC -fglasgow-exts #-} module Main where import Foreign import Foreign.C
foreign import stdcall unsafe "foo" c_Foo :: Word32 -> IO Word32
main = do putStrLn "Entering main" let x = 7::Word32 y <- c_Foo(x) putStrLn $ "y = " ++ show y putStrLn "Exiting main"