diff --git a/include/xo/interpreter2/VirtualSchematikaMachine.hpp b/include/xo/interpreter2/VirtualSchematikaMachine.hpp
index a149173e..e8e58dbc 100644
--- a/include/xo/interpreter2/VirtualSchematikaMachine.hpp
+++ b/include/xo/interpreter2/VirtualSchematikaMachine.hpp
@@ -57,6 +57,12 @@ namespace xo {
              **/
             void _do_eval_variable_op();
 
+            /** evaluate an apply expression
+             *  Require:
+             * - expression in @ref expr_
+             **/
+            void _do_eval_apply_op();
+
         private:
             /*
              * Some registers are preserved by evaluation:
diff --git a/src/interpreter2/VirtualSchematikaMachine.cpp b/src/interpreter2/VirtualSchematikaMachine.cpp
index 4dccce34..b2789c26 100644
--- a/src/interpreter2/VirtualSchematikaMachine.cpp
+++ b/src/interpreter2/VirtualSchematikaMachine.cpp
@@ -51,6 +51,9 @@ namespace xo {
             case exprtype::variable:
                 _do_eval_variable_op();
                 break;
+            case exprtype::apply:
+                _do_eval_apply_op();
+                break;
             }
         }
 
@@ -77,6 +80,13 @@ namespace xo {
             // not implemented
             assert(false);
         }
+
+        void
+        VirtualSchematikaMachine::_do_eval_apply_op()
+        {
+            // not implemented
+            assert(false);
+        }
     } /*namespace scm*/
 } /*namespace xo*/