xo-expression2: scaffold variable eval in VSM

xo-expression2/include/xo/expression2/exprtype.hpp

@@ -31,8 +31,10 @@ namespace xo {
             apply,
             /** function definition **/
             lambda,
+#endif
             /** variable reference **/
             variable,
+#ifdef NOT_YET
             /** if-then-else **/
             ifexpr,
             /** sequence **/

xo-interpreter2/include/xo/interpreter2/VirtualSchematikaMachine.hpp

@@ -45,6 +45,12 @@ namespace xo {
              **/
             void _do_eval_constant_op();
 
+            /** evaluate a variable expression
+             *  Require:
+             *  - expression in @ref expr_
+             **/
+            void _do_eval_variable_op();
+
         private:
             /*
              * Some registers are preserved by evaluation:
@@ -60,8 +66,10 @@ namespace xo {
             /** program counter **/
             VsmInstr pc_ = VsmInstr::halt();
 
+#ifdef NOT_YET
             /** stack pointer **/
             Stack stack_;
+#endif
 
             /** expression register **/
             obj<AExpression> expr_;

xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp

@@ -45,6 +45,9 @@ namespace xo {
             case exprtype::constant:
                 _do_eval_constant_op();
                 break;
+            case exprtype::variable:
+                _do_eval_variable_op();
+                break;
             }
         }
 
@@ -58,6 +61,12 @@ namespace xo {
             this->pc_ = this->cont_;
         }
 
+        void
+        VirtualSchematikaMachine::_do_eval_variable_op()
+        {
+            // not implemented
+            assert(false);
+        }
     } /*namespace scm*/
 } /*namespace xo*/