[Haskell-cafe] c2hs seems to ignore the types I give it when generating foreign import declarations

Manuel M T Chakravarty chak at cse.unsw.edu.au
Sun Dec 11 20:17:18 EST 2005

Cale Gibbard:
> On 11/12/05, Manuel M T Chakravarty <chak at cse.unsw.edu.au> wrote:
> > You need to tell c2hs to what Haskell type a C pointer type maps before
> > it can generate the right signature for the import declaration.  This is
> > done using a pointer hook:
> >
> >   http://www.cse.unsw.edu.au/~chak/haskell/c2hs/docu/c2hs-3.html#ss3.10
> >
> > In your case, you would usually do
> >
> >   {#pointer *Display as Display newtype#}
> >
> > However, when you use this form, c2hs will generate the newtype
> > declaration for you that you import from `Graphics.X11.Xlib.Types' (and
> > you would have to cast between your version of `Display' and that of
> > `Xlib').
> I wanted to use the existing types so as to have compatibility with
> any other libraries which might use them. It would be a shame if every
> Haskell binding to an X library had different, incompatible versions
> of the X types, and thus they couldn't be used together.

The darcs version of c2hs

  darcs get --partial http://www.cse.unsw.edu.au/~chak/repos/c2hs/

now permits the use of a `nocode' keyword at the end of a pointer hook.
This suppresses the generation of the type declaration, so you can do

  {#pointer *Display as Display newtype nocode#}

to get what you want.

Let me know if there are any problems.


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