diff --git a/include/xo/reader/parserstatemachine.hpp b/include/xo/reader/parserstatemachine.hpp
index 065513c5..0e69d44c 100644
--- a/include/xo/reader/parserstatemachine.hpp
+++ b/include/xo/reader/parserstatemachine.hpp
@@ -52,6 +52,7 @@ namespace xo {
             // ---- parsing inputs -----
 
             void on_semicolon_token(const token_type & tk);
+            void on_operator_token(const token_type & tk);
             void on_leftbrace_token(const token_type & tk);
             void on_rightbrace_token(const token_type & tk);
 
diff --git a/src/reader/expect_expr_xs.cpp b/src/reader/expect_expr_xs.cpp
index 3d238ede..1f07d131 100644
--- a/src/reader/expect_expr_xs.cpp
+++ b/src/reader/expect_expr_xs.cpp
@@ -55,10 +55,14 @@ namespace xo {
         expect_expr_xs::on_def_token(const token_type & tk,
                                      parserstatemachine * p_psm)
         {
-            if (allow_defs_)
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            if (allow_defs_) {
                 define_xs::start(p_psm);
-            else
+            } else {
                 exprstate::on_def_token(tk, p_psm);
+            }
         }
 
         void
@@ -101,6 +105,9 @@ namespace xo {
         expect_expr_xs::on_rightbrace_token(const token_type & tk,
                                             parserstatemachine * p_psm)
         {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
             if (cxl_on_rightbrace_) {
                 auto self = p_psm->pop_exprstate();
 
@@ -116,7 +123,10 @@ namespace xo {
         expect_expr_xs::on_symbol_token(const token_type & tk,
                                         parserstatemachine * p_psm)
         {
-            /* todo: treat symbol as variable name */
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            log && log(xtag("tk", tk));
 
             /* various possibilities when looking for rhs expression:
              *
diff --git a/src/reader/expect_symbol_xs.cpp b/src/reader/expect_symbol_xs.cpp
index 27a94b64..0e01924e 100644
--- a/src/reader/expect_symbol_xs.cpp
+++ b/src/reader/expect_symbol_xs.cpp
@@ -28,6 +28,11 @@ namespace xo {
         expect_symbol_xs::on_symbol_token(const token_type & tk,
                                           parserstatemachine * p_psm)
         {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            log && log(xtag("tk", tk));
+
             /* have to do pop first, before sending symbol to
              * the o.g. symbol-requester
              */
diff --git a/src/reader/exprstate.cpp b/src/reader/exprstate.cpp
index 550e20d0..77480dcb 100644
--- a/src/reader/exprstate.cpp
+++ b/src/reader/exprstate.cpp
@@ -394,9 +394,17 @@ namespace xo {
             constexpr bool c_debug_flag = true;
             scope log(XO_DEBUG(c_debug_flag));
 
+            const char * c_self_name = "exprstate::on_expr_with_semicolon";
+
             log && log(xtag("exstype", this->exs_type_),
                        xtag("expr", expr));
 
+            throw std::runtime_error
+                (tostr(c_self_name,
+                       ": unexpected expression for parsing state",
+                       xtag("expr", expr),
+                       xtag("state", *this)));
+
             assert(false);
         } /*on_expr_with_semicolon*/
 
diff --git a/src/reader/parserstatemachine.cpp b/src/reader/parserstatemachine.cpp
index 814c3a3b..373e83e3 100644
--- a/src/reader/parserstatemachine.cpp
+++ b/src/reader/parserstatemachine.cpp
@@ -100,6 +100,19 @@ namespace xo {
                 ->top_exprstate().on_semicolon_token(tk, this);
         }
 
+        void
+        parserstatemachine::on_operator_token(const token_type & tk)
+        {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
+            log && log(xtag("tk", tk),
+                       xtag("psm", *this));
+
+            this->p_stack_
+                ->top_exprstate().on_operator_token(tk, this);
+        }
+
         void
         parserstatemachine::on_leftbrace_token(const token_type & tk)
         {
diff --git a/src/reader/progress_xs.cpp b/src/reader/progress_xs.cpp
index 47bf2c04..40d857b6 100644
--- a/src/reader/progress_xs.cpp
+++ b/src/reader/progress_xs.cpp
@@ -332,6 +332,9 @@ namespace xo {
         progress_xs::on_operator_token(const token_type & tk,
                                        parserstatemachine * p_psm)
         {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag));
+
             constexpr const char * c_self_name = "progress_xs::on_operator_token";
 
             if (op_type_ == optype::invalid) {