[HOpenGL] Re: FFI Addendum, CVS Id 1.19

[Sven Panne]

[ This mail answers Andre's last question in the HOpenGL mailing list, so
  I'll cross-post... ]

The addendum looks fine for me, well done Manuel! But as usual, I've got a few
minor points:

   * Section 3.4 (export declarations) says:

        "If an evaluation triggered by an external invocation of an exported
         Haskell value returns with an exception, the system behaviour is
         undefined."

     So far, so good... It continues:

        "Thus, Haskell exceptions have to be caught within Haskell and
         explicitly marshalled to the foreign code."

     I understand the idea here, but what about System.exitWith and
     System.exitFailure in callbacks? GHC implements this via throwing an
     exception, but this is an implementation detail IMHO. The consequence
     of this implementation choice is a fatal error (uncaught exception)
     when exit{With,Failure} is evaluated in callbacks. So there are two
     questions:

        * Should we allow exit{With,Failure} in such circumstances?
          (My opinion: yes)

        * If the answer is no, what is the "official" way to terminate
          cleanly from callbacks? Note that in the context of HOpenGL
          the callback can't return a value due to the nature of an
          external lib (GLUT). I fear that the answer could be hs_exit(),
          but that would lead to a backwards compatibility hell...

   * The example in section 5.4.2 should use "wrapper" instead of the old f.e.d.

   * I'm still not happy with the choice of Int in the signature of
     plusPtr/minusPtr, but I'll probably surrender... :-]

Cheers,
   S.