partial implementation for recursive def rules

src/runtime/c/pgf/data.h

@@ -117,6 +117,8 @@ typedef enum {
   PGF_INSTR_PUT_FLT,
   PGF_INSTR_SET_VALUE,
   PGF_INSTR_SET_VARIABLE,
+  PGF_INSTR_PUSH_VALUE,
+  PGF_INSTR_PUSH_VARIABLE,
   PGF_INSTR_TAIL_CALL,
   PGF_INSTR_FAIL,
   PGF_INSTR_RET