Linking C++ in Cabal

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Linking C++ in Cabal

Leonhard Applis
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. 

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


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Re: Linking C++ in Cabal

鲍凯文
Hi,

Would it be possible to upload your full repo somewhere so people could see everything and possibly reproduce this?

Thanks,

toz

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Message: 1
Date: Sun, 24 May 2020 16:30:22 +0000
From: Leonhard Applis <[hidden email]>
To: "[hidden email]" <[hidden email]>
Subject: [Haskell-beginners] Linking C++ in Cabal
Message-ID:
        <51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@protonmail.com>

Content-Type: text/plain; charset="utf-8"

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
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Re: Linking C++ in Cabal

鲍凯文
In reply to this post by Leonhard Applis
Hi,

So I tried it out, and there're a couple of things:
- Declaring a function as `static` will hide it from anything other than the current translation unit, AFAIK, which means that you won't be able to link it to anything else; the symbol won't be visible (you can verify using `objdump`).
- For C++ functions, you need to suppress name-mangling since Haskell's FFI doesn't know about that. With your repo as is, the symbol corresponding to the `multiply` function is not...`multiply`:
```
dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o:     file format elf64-x86-64

SYMBOL TABLE:
0000000000000000 l    df *ABS* 0000000000000000 some.cpp
0000000000000000 l    d  .text 0000000000000000 .text
0000000000000000 l    d  .data 0000000000000000 .data
0000000000000000 l    d  .bss 0000000000000000 .bss
0000000000000000 l    d  .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l    d  .eh_frame 0000000000000000 .eh_frame
0000000000000000 l    d  .comment 0000000000000000 .comment
0000000000000000 g     F .text 0000000000000006 _Z8multiplyii
```
so you just need to wrap every exposed function in `extern "C"` blocks, like it's explained here: https://www.geeksforgeeks.org/extern-c-in-c/.

With `extern "C"` and removing `static`:
```
dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o:     file format elf64-x86-64

SYMBOL TABLE:
0000000000000000 l    df *ABS* 0000000000000000 some.cpp
0000000000000000 l    d  .text 0000000000000000 .text
0000000000000000 l    d  .data 0000000000000000 .data
0000000000000000 l    d  .bss 0000000000000000 .bss
0000000000000000 l    d  .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l    d  .eh_frame 0000000000000000 .eh_frame
0000000000000000 l    d  .comment 0000000000000000 .comment
0000000000000000 g     F .text 0000000000000006 multiply
```
...and everything builds fine.

Best,

toz

On Tue, May 26, 2020 at 5:03 AM <[hidden email]> wrote:
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Today's Topics:

   1. Re:  Linking C++ in Cabal - repository Link (Leonhard Applis)
   2. Re:  Linking C++ in Cabal (鲍凯文)


----------------------------------------------------------------------

Message: 1
Date: Mon, 25 May 2020 13:00:03 +0000
From: Leonhard Applis <[hidden email]>
To: "[hidden email]" <[hidden email]>
Subject: Re: [Haskell-beginners] Linking C++ in Cabal - repository
        Link
Message-ID:
        <iF7eLvkM4HniAVDyO09U-O3y48pPEAciKs5zjKAtajj8lldf1g8Tp5UHi3-HiT2GMc15GBi5JgVgkRXr4KQ8Y8p6i0CuuAU-RLh-g2t57uQ=@protonmail.com>

Content-Type: text/plain; charset="utf-8"

Ups, in my mailing list the links have disappeared.
Just in case: 


The minimal reproducing repository:

https://github.com/Twonki/HaskellForeingCPPMinimal

The repository from Aditya Siram with C and makefile:

https://github.com/deech/CPlusPlusBindings

best
Leonhard



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On Monday, May 25, 2020 2:00 PM, <[hidden email]> wrote:

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> Today's Topics:
>

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

>

> Message: 1
> Date: Sun, 24 May 2020 16:30:22 +0000
> From: Leonhard Applis [hidden email]
> To: "[hidden email]" [hidden email]
> Subject: [Haskell-beginners] Linking C++ in Cabal
> Message-ID:
> 51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@protonmail.com
>

> Content-Type: text/plain; charset="utf-8"
>

> 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
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Message: 2
Date: Mon, 25 May 2020 16:45:09 -0700
From: 鲍凯文 <[hidden email]>
To: [hidden email]
Subject: Re: [Haskell-beginners] Linking C++ in Cabal
Message-ID:
        <CAMjcG+FWPZtkM7soC34VOdSBQ+ArdWY2Bpk2Wm=[hidden email]>
Content-Type: text/plain; charset="utf-8"

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 <[hidden email]> wrote:

> Send Beginners mailing list submissions to
>         [hidden email]
>
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> or, via email, send a message with subject or body 'help' to
>         [hidden email]
>
> You can reach the person managing the list at
>         [hidden email]
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Beginners digest..."
>
>
> Today's Topics:
>
>    1.  Linking C++ in Cabal (Leonhard Applis)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 24 May 2020 16:30:22 +0000
> From: Leonhard Applis <[hidden email]>
> To: "[hidden email]" <[hidden email]>
> Subject: [Haskell-beginners] Linking C++ in Cabal
> Message-ID:
>
> <51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@
> protonmail.com>
>
> Content-Type: text/plain; charset="utf-8"
>
> 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
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>
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Re: Linking C++ in Cabal

Leonhard Applis
In reply to this post by Leonhard Applis
Thanks Toz!


Works like a charm.


Repository is updated for anyone interested.


Beginners Mailing list is the best <3


‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, May 26, 2020 10:01 PM, <[hidden email]> wrote:

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> than "Re: Contents of Beginners digest..."
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> Today's Topics:
>

> 1.  Re: Linking C++ in Cabal (鲍凯文)
>    

>

> Message: 1
> Date: Tue, 26 May 2020 13:03:13 -0700
> From: 鲍凯文 [hidden email]
> To: [hidden email]
> Subject: Re: [Haskell-beginners] Linking C++ in Cabal
> Message-ID:
> [hidden email]
> Content-Type: text/plain; charset="utf-8"
>

> Hi,
>

> So I tried it out, and there're a couple of things:
>

> -   Declaring a function as `static` will hide it from anything other than
>     the current translation unit, AFAIK, which means that you won't be able to
>     link it to anything else; the symbol won't be visible (you can verify using
>     `objdump`).
>    

> -   For C++ functions, you need to suppress name-mangling since Haskell's FFI
>     doesn't know about that. With your repo as is, the symbol corresponding to
>     the `multiply` function is not...`multiply`:
>    

>

>     dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o:
>         file format elf64-x86-64
>    

>     SYMBOL TABLE:
>     0000000000000000 l    df *ABS* 0000000000000000 some.cpp
>     0000000000000000 l    d  .text 0000000000000000 .text
>     0000000000000000 l    d  .data 0000000000000000 .data
>     0000000000000000 l    d  .bss 0000000000000000 .bss
>     0000000000000000 l    d  .note.GNU-stack 0000000000000000 .note.GNU-stack
>     0000000000000000 l    d  .eh_frame 0000000000000000 .eh_frame
>     0000000000000000 l    d  .comment 0000000000000000 .comment
>     0000000000000000 g     F .text 0000000000000006 _Z8multiplyii
>    

>

> so you just need to wrap every exposed function in `extern "C"` blocks,
> like it's explained here: https://www.geeksforgeeks.org/extern-c-in-c/.
>

> With `extern "C"` and removing `static`:
>

>     dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o:
>         file format elf64-x86-64
>    

>     SYMBOL TABLE:
>     0000000000000000 l    df *ABS* 0000000000000000 some.cpp
>     0000000000000000 l    d  .text 0000000000000000 .text
>     0000000000000000 l    d  .data 0000000000000000 .data
>     0000000000000000 l    d  .bss 0000000000000000 .bss
>     0000000000000000 l    d  .note.GNU-stack 0000000000000000 .note.GNU-stack
>     0000000000000000 l    d  .eh_frame 0000000000000000 .eh_frame
>     0000000000000000 l    d  .comment 0000000000000000 .comment
>     0000000000000000 g     F .text 0000000000000006 multiply
>    

>

> ...and everything builds fine.
>

> Best,
>

> toz
>

> On Tue, May 26, 2020 at 5:03 AM [hidden email] wrote:
>

> > Send Beginners mailing list submissions to
> > [hidden email]
> > To subscribe or unsubscribe via the World Wide Web, visit
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > or, via email, send a message with subject or body 'help' to
> > [hidden email]
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> > [hidden email]
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Beginners digest..."
> > Today's Topics:
> >

> > 1.  Re: Linking C++ in Cabal - repository Link (Leonhard Applis)
> > 2.  Re: Linking C++ in Cabal (鲍凯文)
> >

> > Message: 1
> > Date: Mon, 25 May 2020 13:00:03 +0000
> > From: Leonhard Applis [hidden email]
> > To: "[hidden email]" [hidden email]
> > Subject: Re: [Haskell-beginners] Linking C++ in Cabal - repository
> > Link
> > Message-ID:
> > <iF7eLvkM4HniAVDyO09U-O3y48pPEAciKs5zjKAtajj8lldf1g8Tp5UHi3-HiT2GMc15GBi5JgVgkRXr4KQ8Y8p6i0CuuAU-RLh-g2t57uQ=@
> > protonmail.com>
> > Content-Type: text/plain; charset="utf-8"
> > Ups, in my mailing list the links have disappeared.
> > Just in case:
> > The minimal reproducing repository:
> > https://github.com/Twonki/HaskellForeingCPPMinimal
> > The repository from Aditya Siram with C and makefile:
> > https://github.com/deech/CPlusPlusBindings
> > best
> > Leonhard
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Monday, May 25, 2020 2:00 PM, [hidden email] wrote:
> >

> > > Send Beginners mailing list submissions to
> > > [hidden email]
> >

> > > To subscribe or unsubscribe via the World Wide Web, visit
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> > > [hidden email]
> >

> > > You can reach the person managing the list at
> > > [hidden email]
> >

> > > When replying, please edit your Subject line so it is more specific
> > > than "Re: Contents of Beginners digest..."
> >

> > > Today's Topics:
> >

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

> > >

> >

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

> > 51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@
> > protonmail.com
> >

> > >

> >

> > > Content-Type: text/plain; charset="utf-8"
> >

> > > 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
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> >

> > Message: 2
> > Date: Mon, 25 May 2020 16:45:09 -0700
> > From: 鲍凯文 [hidden email]
> > To: [hidden email]
> > Subject: Re: [Haskell-beginners] Linking C++ in Cabal
> > Message-ID:
> > <CAMjcG+FWPZtkM7soC34VOdSBQ+ArdWY2Bpk2Wm=
> > [hidden email]>
> > Content-Type: text/plain; charset="utf-8"
> > 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 [hidden email] wrote:
> >

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> > > Today's Topics:
> > >

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

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

> > <51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@
> >

> > > protonmail.com>
> > > Content-Type: text/plain; charset="utf-8"
> > > 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
> > > -------------- next part --------------
> > > An HTML attachment was scrubbed...
> > > URL: <
> >

> > http://mail.haskell.org/pipermail/beginners/attachments/20200524/9019cbc0/attachment-0001.html
> >

> > > >

> > >

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> >

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> >

> > > >

> > >

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