diff --git a/include/xo/reader/define_xs.hpp b/include/xo/reader/define_xs.hpp
index f1e0e2c7..de1fb44d 100644
--- a/include/xo/reader/define_xs.hpp
+++ b/include/xo/reader/define_xs.hpp
@@ -44,6 +44,11 @@ namespace xo {
             virtual void on_singleassign(exprstatestack * p_stack) override;
             virtual void on_leftparen(exprstatestack * p_stack,
                                       rp<Expression> * /*p_emit_expr*/) override;
+            virtual void on_rightparen(exprstatestack * p_stack,
+                                       rp<Expression> * /*p_emit_expr*/) override;
+            virtual void on_f64(const token_type & tk,
+                                exprstatestack * p_stack,
+                                rp<Expression> * /*p_emit_expr*/) override;
 
         private:
             /**
diff --git a/include/xo/reader/exprstate.hpp b/include/xo/reader/exprstate.hpp
index 461ecddf..75a955ce 100644
--- a/include/xo/reader/exprstate.hpp
+++ b/include/xo/reader/exprstate.hpp
@@ -128,6 +128,7 @@ namespace xo {
              *  forward instructions to parent parser
              **/
             void on_input(const token_type & tk, exprstatestack * p_stack, rp<Expression> * p_emit_expr);
+
             /** update exprstate in response to a successfully-parsed subexpression **/
             virtual void on_expr(ref::brw<Expression> expr,
                                  exprstatestack * p_stack,
diff --git a/src/reader/define_xs.cpp b/src/reader/define_xs.cpp
index 4c5b3cb4..f5859c23 100644
--- a/src/reader/define_xs.cpp
+++ b/src/reader/define_xs.cpp
@@ -520,6 +520,45 @@ namespace xo {
 
             assert(false); /* inserting this during refactor...? */
         }
+
+        void
+        define_xs::on_rightparen(exprstatestack * /*p_stack*/,
+                                 rp<Expression> * /*p_emit_expr*/)
+        {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            constexpr const char * self_name = "exprstate::on_rightparen";
+
+            if (!this->admits_rightparen())
+            {
+                throw std::runtime_error(tostr(self_name,
+                                               ": unexpected rightparen ')' for parsing state",
+                                               xtag("state", *this)));
+            }
+
+            assert(false); /* inserting this during refactor..? */
+        }
+
+        void
+        define_xs::on_f64(const token_type & /*tk*/,
+                          exprstatestack * /*p_stack*/,
+                          rp<Expression> * /*p_emit_expr*/)
+        {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            constexpr const char * self_name = "exprstate::on_f64";
+
+            if (!this->admits_f64())
+            {
+                throw std::runtime_error(tostr(self_name,
+                                               ": unexpected floating-point literal for parsing state",
+                                               xtag("state", *this)));
+            }
+
+            assert(false);
+        }
     } /*namespace scm*/
 } /*namespace xo*/