Hi, Would it be possible to upload your full repo somewhere so people could see everything and possibly reproduce this? Thanks, toz On Mon, May 25, 2020 at 5:03 AM wrote:

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Today's Topics:

1. Linking C++ in Cabal (Leonhard Applis)

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Message: 1 Date: Sun, 24 May 2020 16:30:22 +0000 From: Leonhard Applis To: "beginners@haskell.org" Subject: [Haskell-beginners] Linking C++ in Cabal Message-ID:

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Hello,

I want to use a foreign C++ Function in a Haskell Library, and the Library in a Haskell Program. The C++ function is separate in a file and I have a header file. I made a minimal reproducing repository.

The closes I have found is this repository which wraps the c++ in c and makes a full library, needing a makefile etc. So while I think I'd get it working like that, it looks to be quite a lot to do for my simple task.

the repository structure looks as follows:

Projekt

- cpp-src

- some.cpp - some.h

- lib-src

- CPPLib.hs

- program-src

- program.hs

- project.cabal

And my (currently failing) project.cabal the following:

cabal-version: 3.0 name: cpp_lib [...] library exposed-modules: CPPLib other-extensions: ForeignFunctionInterface build-depends: base hs-source-dirs: lib-src default-language: Haskell2010 include-dirs: ./cpp-src cxx-sources: ./cpp-src/some.cpp install-includes: ./cpp-src/some.h

executable CPPApp main-is: program.hs default-language: Haskell2010 build-depends: HaskellForeignCPP, base hs-source-dirs: program-src

The some.cpp is trivial for this case lets assume its a function multiply :: Int -> Int -> Int, and both .cpp and .h are well-formed and don't have further dependencies.

The library compiles fine, but when building the executable it fails telling me

collect2: error: ld returned 1 exit status `gcc' failed in phase `Linker'. (Exit code: 1)

Can someone help me out? I find very little documentation on this topic.

I know there is Inline-CPP which would help as well, but I just very much like the idea of having a nice separate file and interface for modularity.

best Leonhard