[Haskell-cafe] FFI - Approaches to C/C++

Casey Basichis caseybasichis at gmail.com
Thu Jan 31 09:53:45 CET 2013

Hi Ertugrul,

Thank you for the detailed reply.  From what you wrote, partial FFI still
seems like the way to go.

Unfortunately Ogre isn't the only large library I'm using, so "difficult"
several times over sounds like a good way to handicap the project early on.

I'm perfectly happy to use Haskell for the strengths that will most benefit
my project.  I can always go back and try to bring the C++ specific parts
into the fold once a prototype is up and running.

As it seems there is a great deal of c/c++ to do either way, I would really
appreciate so thoughts towards my original question.

What practices in C++ are preferred by Haskell users, in the know, for the
parts of the app that will not be pure Haskell?

Should I be looking to avoid OOP?  Dependency Injection? I wont reiterate
all the facets of the first post, but it would help me immensely to zero in
on a few patterns and strategies that can minimized the damage I inflict in
c++ land.




"That used to be true, but the reason has nothing to do with the language.
 The problem was that the libraries weren't there."

What do you mean? Which packages should I be looking at?  I am on iOS like
I said, its a stage 1 GHC compiler so I don't have access to GHCI or
template haskell.

>Casey Basichis <caseybasichis at gmail.com> wrote:
>> I'm not entirely sure what you mean.
>> I'm intending on using Ogre for GUI - for which there is the Hogre
>> bindings, but after emailing the DEV about it, I didn't get the
>> impression from his advice that I should be using it for production
>> code.  Here is what he suggested:
>> "It depends, really. Hogre is good for running Ogre from within
>> Haskell, but it has its limitations. The number one thing people have
>> been struggling with is handling input with hogre - there's Hois
>> (Haskell wrapper for OIS) but it's not perfect (it misses input
>> events), and the other option is having to write some C++ glue. Hogre
>> is a solid proof of concept and you can do some demos with it, but if
>> you're e.g. writing a game it might be a bit of a struggle. In the end
>> it's about how much you value being able to write code in Haskell (or
>> how allergic to C++ you are)."
>> I'm on iOS so I imagine those difficulties are compounded.
>> I am using several other C++ libraries for which there are no existing
>> bindings and no Haskell alternative packages that are even remotely
>> close.
>> Are you suggesting it would be better to write all my own FFI bindings
>> for all the needed libraries?
>That's not what I'm suggesting.  It was just too little information to
>properly judge the difficulty of doing everything in Haskell.
>Binding to Ogre (or C++ in general) is indeed difficult.  If Hogre
>doesn't work or is too limited, your best option might be to write a C
>wrapper around the Hogre functionality you need.  Another option is to
>use SDL/OpenGL directly, which may be easier or harder depending on your
>However, if you can build the bridge between your rendering library and
>Haskell, then Haskell is certainly the better choice.
>> Everything I read suggests that Haskells strengths are in
>> transformation and that interaction is not its strong suit.
>> I am interested in your thoughts and I am open to whatever, but you
>> are the first to suggest that the mix is a bad idea.
>That used to be true, but the reason has nothing to do with the
>language.  The problem was that the libraries weren't there.  Nowadays
>you can write all sorts of interactive applications in Haskell,
>including GUIs, TUIs, games, simulations and web applications.  However,
>I've long been waiting for useful bindings to Ogre or Irrlicht, but I'm
>afraid that it's not going to happen any time soon.
>Ultimately it's your choice.  Let me summarize the possiblities:
>  * C wrapper around Ogre.  Easy integration, but need to write the
>    rendering code in C/C++.
>  * Full FFI bindings to Ogre.  Difficult integration, but you can write
>    your rendering code in Haskell.
>  * Partial FFI bindings to Ogre.  Integration may be somewhat easy, if
>    you do the initialization in Haskell and the actual rendering in
>    C/C++.  However, this again requires to write the rendering in
>    C/C++.
>  * Using SDL/OpenGL directly:  Everything available for Haskell.  May
>    be difficult, because you need to write OpenGL code.
>I hope, this helps.

Casey James Basichis
Composer - Cartoon Network
caseybasichis at gmail.com
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