print attributes of variables when attribute_goals/2 is not defined

src/prolog/machine/mod.rs

@@ -187,7 +187,7 @@ impl Machine {
                 self.machine_st.attr_var_init.project_attrs_loc = self.code_repo.code.len();
                 self.code_repo.code.extend(code.into_iter());
             }
-            Err(_) => panic!("Machine::compile_special_forms() failed at PROJECT_ATTRS"),
+            Err(e) => panic!("Machine::compile_special_forms() failed at PROJECT_ATTRS: {}", e),
         }
     }
 

src/prolog/machine/project_attributes.pl

@@ -40,7 +40,7 @@ call_goals([], _).
 call_goals([AttrVar|AttrVars], Module) :-
     (   catch(Module:attribute_goals(AttrVar, Goal),
 	      error(evaluation_error((Module:attribute_goals)/2), attribute_goals/2),
-	      true),
+	      atts:'$default_attr_list'(Module, AttrVar, Goal)),
 	nonvar(Goal) -> enqueue_goal(Goal)
     ;   true
     ),