+ virtual long calleval(long x); // invoke "eval"
+};
+
+/*!
+ * \brief base class for evaluating a function: void -> void
+ * \ingroup misc
+ *
+ * This class is designed to be subclassed in Python or C++
+ * and is callable from both places. It uses SWIG's
+ * "director" feature to implement the magic.
+ * It's slow. Don't use it in a performance critical path.
+ *
+ * Override eval to define the behavior.
+ * Use calleval to invoke eval (this kludge is required to allow a
+ * python specific "shim" to be inserted.
+ */
+class gr_feval
+{
+protected: