Object type tag bits

[Frank Cieslok <frankc@senax.iguana.priconet.de>]

Hello,

...so I tried to create my own smobs using a C++ function like this :

   SCM createInstance()
   {
       Object* obj = new Object;

       SCM smob;
       SCM_NEWCELL(smob);
       SCM_SETCAR(smob, ObjectTag);
       SCM_SETCDR(smob, obj);

       return smob;
   }

This function was registered via gh_new_procedure() and therefor callable 
by guile code. The class 'Object' is keeping references to other scheme 
objects and a mark function for garbage collection was needed to let these
objects survive garbage collection, too :

   SCM mark(SCM s)
   {
       ...
       SCM_ASSERT( (SCM_NIMP(s) && SCM_CAR(s) == ObjectTag),
                   s, SCM_ARG1, "mark" );
       ...

       return SCM_BOOL_F;
   }

The assertion always falied, because the tags did not match. When 
created by createInstance(), the new object got #x1EF7 as tag value, the 
mark function was called with a parameter tagged with #x1EFF. The CDR of
the smob was equal in both cases.

I did not completely understand the code in "libguile/tags.h". Is only a 
part of the tag used for object type information ? If so, is there a 
function returning just these valid bits for comparison with the tag 
value returned by scm_newsmob() during object registration ?

Thank you in advance,
Frank

---
Mail: frankc@senax.iguana.priconet.de
WWW : http://www.tu-bs.de/~y0000070