diff --git a/include/xo/reader/expect_expr_xs.hpp b/include/xo/reader/expect_expr_xs.hpp
index 6e039c79..d826b5ae 100644
--- a/include/xo/reader/expect_expr_xs.hpp
+++ b/include/xo/reader/expect_expr_xs.hpp
@@ -19,6 +19,10 @@ namespace xo {
 
             static std::unique_ptr<expect_expr_xs> expect_rhs_expression();
 
+            virtual void on_f64_token(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 1a0219e6..2ac8cf67 100644
--- a/include/xo/reader/exprstate.hpp
+++ b/include/xo/reader/exprstate.hpp
@@ -96,8 +96,10 @@ namespace xo {
             virtual bool admits_leftparen() const;
             /** truee iff this parsing state admits a rightparen ')' as next token **/
             virtual bool admits_rightparen() const;
+#ifdef OBSOLETE
             /** true iff this parsing state admits a 64-bit floating point literal token **/
             virtual bool admits_f64() const;
+#endif
 
             /** update exprstate in response to incoming token @p tk,
              *  forward instructions to parent parser
diff --git a/include/xo/reader/paren_xs.hpp b/include/xo/reader/paren_xs.hpp
index 670a62c3..31e3e45c 100644
--- a/include/xo/reader/paren_xs.hpp
+++ b/include/xo/reader/paren_xs.hpp
@@ -31,16 +31,14 @@ namespace xo {
 
             static std::unique_ptr<paren_xs> lparen_0();
 
-#ifdef OBSOLETE
-            virtual bool admits_definition() const override;
-#endif
+            bool admits_f64() const;
+
             virtual bool admits_symbol() const override;
             virtual bool admits_colon() const override;
             virtual bool admits_semicolon() const override;
             virtual bool admits_singleassign() const override;
             virtual bool admits_leftparen() const override;
             virtual bool admits_rightparen() const override;
-            virtual bool admits_f64() const override;
 
             virtual void on_expr(ref::brw<Expression> expr,
                                  exprstatestack * p_stack,
diff --git a/include/xo/reader/progress_xs.hpp b/include/xo/reader/progress_xs.hpp
index 9df42717..9131b048 100644
--- a/include/xo/reader/progress_xs.hpp
+++ b/include/xo/reader/progress_xs.hpp
@@ -22,16 +22,14 @@ namespace xo {
 
             static std::unique_ptr<progress_xs> make(rp<Expression> valex);
 
-#ifdef OBSOLETE
-            virtual bool admits_definition() const override;
-#endif
+            bool admits_f64() const;
+
             virtual bool admits_symbol() const override;
             virtual bool admits_colon() const override;
             virtual bool admits_semicolon() const override;
             virtual bool admits_singleassign() const override;
             virtual bool admits_leftparen() const override;
             virtual bool admits_rightparen() const override;
-            virtual bool admits_f64() const override;
 
             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 5dc5c760..ad6c994f 100644
--- a/src/reader/define_xs.cpp
+++ b/src/reader/define_xs.cpp
@@ -425,12 +425,7 @@ namespace xo {
 
             constexpr const char * self_name = "exprstate::on_f64";
 
-            if (!this->admits_f64())
-            {
-                this->illegal_input_error(self_name, tk);
-            }
-
-            assert(false);
+            this->illegal_input_error(self_name, tk);
         }
 
         void
diff --git a/src/reader/expect_expr_xs.cpp b/src/reader/expect_expr_xs.cpp
index ddc75aa6..78a69be2 100644
--- a/src/reader/expect_expr_xs.cpp
+++ b/src/reader/expect_expr_xs.cpp
@@ -4,8 +4,12 @@
  */
 
 #include "expect_expr_xs.hpp"
+#include "progress_xs.hpp"
+#include "xo/expression/Constant.hpp"
 
 namespace xo {
+    using xo::ast::Constant;
+
     namespace scm {
 
         std::unique_ptr<expect_expr_xs>
@@ -18,6 +22,26 @@ namespace xo {
             : exprstate(exprstatetype::expect_rhs_expression)
         {}
 
+        void
+        expect_expr_xs::on_f64_token(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_token";
+
+            /* e.g.
+             *   def pi = 3.14159265;
+             *            \---tk---/
+             */
+            p_stack->push_exprstate
+                (progress_xs::make
+                 (Constant<double>::make(tk.f64_value())));
+        }
+
+
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/src/reader/exprstate.cpp b/src/reader/exprstate.cpp
index 88154353..8161f62e 100644
--- a/src/reader/exprstate.cpp
+++ b/src/reader/exprstate.cpp
@@ -257,19 +257,18 @@ namespace xo {
             return false;
         }
 
+#ifdef OBSOLETE
         bool
         exprstate::admits_f64() const {
             switch (exs_type_) {
             case exprstatetype::expect_toplevel_expression_sequence:
             case exprstatetype::defexpr:
             case exprstatetype::parenexpr:
+            case exprstatetype::expect_rhs_expression:
                 /* unreachable - redirects to define_xs */
                 assert(false);
                 return false;
 
-            case exprstatetype::expect_rhs_expression:
-                return true;
-
             case exprstatetype::expect_symbol:
             case exprstatetype::expect_type:
                 return false;
@@ -287,6 +286,7 @@ namespace xo {
 
             return false;
         }
+#endif
 
         void
         exprstate::on_def_token(const token_type & tk,
@@ -522,7 +522,7 @@ namespace xo {
 
         void
         exprstate::on_f64_token(const token_type & tk,
-                                exprstatestack * p_stack,
+                                exprstatestack * /*p_stack*/,
                                 rp<Expression> * /*p_emit_expr*/)
         {
             constexpr bool c_debug_flag = true;
@@ -530,24 +530,7 @@ namespace xo {
 
             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)));
-            }
-
-            if (this->exs_type_ == exprstatetype::expect_rhs_expression) {
-                /* e.g.
-                 *   def pi = 3.14159265;
-                 *            \---tk---/
-                 */
-                p_stack->push_exprstate
-                    (progress_xs::make
-                     (Constant<double>::make(tk.f64_value())));
-            } else {
-                assert(false);
-            }
+            this->illegal_input_error(self_name, tk);
         }
 
         void