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copied!<p><strong>Edit:</strong> You should also see Tomer's answer below. My answer here describes the theory of what's going on, but I may have some of the details of execution incomplete, whereas his answer is a complete working example.</p> <p>As sclv indicates, compiling should be no problem. The difficulty there is likely to be linking the C++ code, and here you will have a little bit of difficulty with getting all the needed runtime libraries linked in. The problem is that Haskell programs need to be linked with the Haskell runtime libraries, and C++ programs need to be linked with the C++ runtime libraries. In the Wiki page you reference, when they do</p> <pre><code>$ ghc -optc -O test.c A.o A_stub.o -o test </code></pre> <p>to compile the C program, that actually does two steps: It compiles the C program into an object file, and then links it together. Written out, that would be something like (probably not quite right, as I don't speak GHC):</p> <pre><code>$ ghc -c -optc-O test.c -o test.o $ ghc test.o A.o A_stub.o -o test </code></pre> <p>GHC just acts like GCC (and, IIUC, functionally <em>is</em> GCC) when compiling the C program. When linking it, however, it is different from what happens if you call GCC directly, because it also magically includes the Haskell runtime libraries. G++ works the same way for C++ programs -- when it's used as a linker, it includes the C++ runtime libraries.</p> <p>So, as I mentioned, you need to compile in a way that links with both runtime libraries. If you run G++ in verbose mode to compile and link a program, like so:</p> <pre><code>$ g++ test.cpp -o test -v </code></pre> <p>it will create a long list of output about what it's doing; at the end will be a line of output where it does the linking (with the <code>collect2</code> subprogram) indicating what libraries it links to. You can compare that to the output for compiling a simple C program to see what's different for C++; on my system, it adds <code>-lstdc++</code>.</p> <p>Thus, you should be able to compile and link your mixed Haskell/C++ program like so:</p> <pre><code>$ ghc -c -XForeignFunctionInterface -O A.hs # compile Haskell object file. $ g++ -c -O test.cpp # compile C++ object file. $ ghc A.o A_stub.o test.o -lstdc++ -o test # link </code></pre> <p>There, because you've specified <code>-lstdc++</code>, it will include the C++ runtime library (assuming <code>-l</code> is the right GHC syntax; you'll need to check), and because you've linked with <code>ghc</code>, it will include the Haskell runtime library. This should result in a working program.</p> <p>Alternately, you should be able to do something similar to the <code>-v</code> output investigation with GHC, and figure out what Haskell runtime library (or libraries) it links to for Haskell support, and then add that library when linking your program with C++, just as you already do for pure C++ programs. (See Tomer's answer for details of that, since that's what he did.)</p>

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