Hello dear Schemers,

i have some trouble with Gambit-C's /c-declare-type/ special form. Better to say with the logic beyond. There are actually two flavours of it. The two argument version (called 'alias in _ptree2.scm) instructs gambit's back-end to handle the type conversions on its own. The four (resp. five) argument version (called 'c-type in _ptree2.scm) lets the user gain some control. For this there is a protocol cummunicating the raw ___SCMOBJs and the actual Ctype's locations.

For many C types one could choose to use either form. That is one would specify Gambit's conversion/construction c-macros explictly or let gambit do this. However, this does not hold true for the (nonnull-)pointer case. Here the communication protocol is insufficient. Those conversion (C-)macros need two additional arguments: The release function and the location of the type-checking chain. But the latter is not known to the programmer.

In my special case this is a problem, as follows. I am working on a GTK+ binding. Thus is need the type conversion to explicitly check whether an object belongs to a certain class or not. So i want something like:

___HIDDEN ___SCMOBJ scm_to_GtkButtonstar(___SCMOBJ src, GtkButton **dst, ___SCMOBJ typlst_gobject, int idx) { ___SCMOBJ ___err = ___FIX(___NO_ERR); GtkObject *obj1; ___BEGIN_CFUN_SCM_TO_NONNULLPOINTER(src, obj1, typlst_gobject, idx)

/* it is an GObject, as reported via Gambit's typechecking, now we need to pass over to GLibs type checking. */

*dst = CHECK_AND_CAST_GTK_BUTTON(obj1); if (*btn == NULL) { ___err = ___FIX(___UNKNOWN_ERR); }

___END_CFUN_SCM_TO_NONNULLPOINTER(src, obj1, typlst_gobject, idx) return ___err; }

But for making this work i need to get the typlst_object passed (at least) (also for the other way round).

I feel i am overlooking something obvious here. The only way (hack) out i could think of would be to construct a c-function via /c-define/ to get an appropiate (literal, constant!) list for type checking.

Any help?

Regards Tara