xo-reader: simplify f64 token handling

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:
         };