Expose C++ API to Haskell via FFI.

acpp.cpp

#include <iostream>
#include "acpp.h"

using namespace std;

A::A(int v): _v(v) {
    std::cout << "Construct A, value: " << _v << std::endl;
}

void A::job(int arg) {
    std::cout << "Execute job in A, arg: " << arg << std::endl;
}

A::~A() {
    std::cout << "Destruct A" << std::endl;
}

acpp.h

#ifndef __ACPP_H__
#define __ACPP_H__

#ifdef __cplusplus

class A {
   public:
    A(int v);
    void job(int arg);
    ~A();

   public:
    int _v;
};

#endif // !__cplusplus

#endif  // !__ACPP_H__

acpp_capi.cpp

#include "acpp_capi.h"

APtr makeA(int a) {
    return new A(a);
}

void jobA(APtr aptr, int arg) {
    aptr->job(arg);
}

void freeA(APtr aptr) {
    delete aptr;
}

acpp_capi.h

#ifndef __ACPP_CAPI_H__
#define __ACPP_CAPI_H__

#include "acpp.h"

#ifdef __cplusplus
extern "C" {
typedef A *APtr;
#else
typedef void *APtr; // dummy type.
#endif

APtr makeA(int v);
void jobA(APtr aptr, int arg);
void freeA(APtr aptr);

#ifdef __cplusplus
}
#endif

#endif  // !__ACPP_CAPI_H__

app.hs

import Foreign.C.Types
import Foreign.Ptr

main :: IO ()
main = do
    a <- makeA 1234
    jobA a 5678
    freeA a

-- | Here @Ptr ()@ is a dummy type, means @class A *@ in C++.
foreign import ccall unsafe "acpp_capi.h makeA" makeA :: CInt -> IO (Ptr ())
foreign import ccall unsafe "acpp_capi.h jobA" jobA :: Ptr () -> CInt -> IO (Ptr ())
foreign import ccall unsafe "acpp_capi.h freeA" freeA :: Ptr () -> IO ()

Makefile

all: libacpp.dll app.exe

GHC			:= stack ghc --

%.o: %.cpp
	$(CXX) -c $< -o $@

libacpp.dll: acpp.o acpp_capi.o
	$(CXX) $^ -shared -o $@ # On Linux/Unix, -fPIC is needed.

app.exe: app.hs acpp_capi.h libacpp.dll
	$(GHC) $< -lacpp -o $@

clean:
	$(RM) -f *.o *.exe *.hi
.PNONY: clean