xo-reader: + exprseq_xs.on_typedef() + simplie tl exprseq case

include/xo/reader/exprseq_xs.hpp

@@ -31,6 +31,10 @@ namespace xo {
 
             // ----- victory methods -----
 
+            virtual void on_typedescr(TypeDescr /*td*/,
+                                      exprstatestack * /*p_stack*/,
+                                      rp<Expression> * /*p_emit_expr*/) override;
+
         };
     } /*namespace scm*/
 } /*namespace xo*/

src/reader/exprseq_xs.cpp

@@ -47,6 +47,16 @@ namespace xo {
 
             this->illegal_input_error(c_self_name, tk);
         }
+
+        void
+        exprseq_xs::on_typedescr(TypeDescr /*td*/,
+                                 exprstatestack * /*p_stack*/,
+                                 rp<Expression> * /*p_emit_expr*/)
+        {
+            /* unreachable - typedescr should never get delivered to exprseq */
+            assert(false);
+            return;
+        }
     } /*namespace scm*/
 } /*namespace xo*/
 

src/reader/exprstate.cpp

@@ -413,7 +413,6 @@ namespace xo {
 
             switch (this->exs_type_) {
             case exprstatetype::expect_toplevel_expression_sequence:
-
             case exprstatetype::defexpr:
             case exprstatetype::parenexpr:
                 /* unreachable - redirects to define_xs */