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

12 Dec 2005

      Cale Gibbard:
...
On 11/12/05, Manuel M T Chakravarty  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.

Manuel