Bauer, Christoph [Friday 20 January 2006] :
 > Could be here a problem (CAMLparam+CAMLreturn in C-called function):
 > 
 > static value copy_tcl_array(int objc,  Tcl_Obj * const * objv)
 > {
 >   CAMLparam0 ();
 >   CAMLlocal2 (result, t);
 >   int n;
 > 
 >   result = Val_int(0);
 >   for (n = objc-1; n >= 0; --n) {
 >     t = caml_alloc_small(2,0);
 >     Field(t, 0) = alloc_tcl_obj( objv[n] );
                     ^^^^^^^^^^^^^

I guess alloc_tcl_obj creates the custom block. That's wrong because
the block t you've just allocated with caml_alloc_small is not
completely initialized yet.

Either do this (safe, higher-level way):
,----
|   t = caml_alloc (2, 0);
|   Store_field (t, 0, alloc_tcl_obj (objv[n]));
|   Store_field (t, 1, result);
`----

or that (lower-level) :
,----
|   CAMLlocal1(obj);
|   obj = alloc_tcl_obj (objv[n]);
|   t = caml_alloc_small (2, 0);
|   Field (t, 0) = obj;
|   Field (t, 1) = result;
`----

-- 
   Olivier