diff --git a/include/xo/reader/exprstate.hpp b/include/xo/reader/exprstate.hpp
index d2c58d67..3e79dee4 100644
--- a/include/xo/reader/exprstate.hpp
+++ b/include/xo/reader/exprstate.hpp
@@ -171,59 +171,6 @@ namespace xo {
             x.print(os);
             return os;
         }
-
-        // ----- exprstatestack -----
-
-        /** @class exprstatestack
-         *  @brief A stack of exprstate objects
-         **/
-        class exprstatestack {
-        public:
-            exprstatestack() {}
-
-            bool empty() const { return stack_.empty(); }
-            std::size_t size() const { return stack_.size(); }
-
-            exprstate & top_exprstate();
-            void push_exprstate(std::unique_ptr<exprstate> exs);
-            std::unique_ptr<exprstate> pop_exprstate();
-
-            /** relative to top-of-stack.
-             *  0 -> top (last in),  z-1 -> bottom (first in)
-             **/
-            std::unique_ptr<exprstate> & operator[](std::size_t i) {
-                std::size_t z = stack_.size();
-
-                assert(i < z);
-
-                return stack_[z - i - 1];
-            }
-
-            const std::unique_ptr<exprstate> & operator[](std::size_t i) const {
-                std::size_t z = stack_.size();
-
-                assert(i < z);
-
-                return stack_[z - i - 1];
-            }
-
-            void print (std::ostream & os) const;
-
-        private:
-            std::vector<std::unique_ptr<exprstate>> stack_;
-        };
-
-        inline std::ostream &
-        operator<< (std::ostream & os, const exprstatestack & x) {
-            x.print(os);
-            return os;
-        }
-
-        inline std::ostream &
-        operator<< (std::ostream & os, const exprstatestack * x) {
-            x->print(os);
-            return os;
-        }
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/include/xo/reader/exprstatestack.hpp b/include/xo/reader/exprstatestack.hpp
new file mode 100644
index 00000000..c5ee0894
--- /dev/null
+++ b/include/xo/reader/exprstatestack.hpp
@@ -0,0 +1,66 @@
+/* file exprstatestack.hpp
+ *
+ * author: Roland Conybeare, Aug 2024
+ */
+
+#pragma once
+
+#include "exprstate.hpp"
+
+namespace xo {
+    namespace scm {
+        /** @class exprstatestack
+         *  @brief A stack of exprstate objects
+         **/
+        class exprstatestack {
+        public:
+            exprstatestack() {}
+
+            bool empty() const { return stack_.empty(); }
+            std::size_t size() const { return stack_.size(); }
+
+            exprstate & top_exprstate();
+            void push_exprstate(std::unique_ptr<exprstate> exs);
+            std::unique_ptr<exprstate> pop_exprstate();
+
+            /** relative to top-of-stack.
+             *  0 -> top (last in),  z-1 -> bottom (first in)
+             **/
+            std::unique_ptr<exprstate> & operator[](std::size_t i) {
+                std::size_t z = stack_.size();
+
+                assert(i < z);
+
+                return stack_[z - i - 1];
+            }
+
+            const std::unique_ptr<exprstate> & operator[](std::size_t i) const {
+                std::size_t z = stack_.size();
+
+                assert(i < z);
+
+                return stack_[z - i - 1];
+            }
+
+            void print (std::ostream & os) const;
+
+        private:
+            std::vector<std::unique_ptr<exprstate>> stack_;
+        };
+
+        inline std::ostream &
+        operator<< (std::ostream & os, const exprstatestack & x) {
+            x.print(os);
+            return os;
+        }
+
+        inline std::ostream &
+        operator<< (std::ostream & os, const exprstatestack * x) {
+            x->print(os);
+            return os;
+        }
+    } /*namespace scm*/
+} /*namespace xo*/
+
+
+/* end exprstatestack.hpp */
diff --git a/include/xo/reader/parser.hpp b/include/xo/reader/parser.hpp
index 3211fd0c..dae3091f 100644
--- a/include/xo/reader/parser.hpp
+++ b/include/xo/reader/parser.hpp
@@ -5,7 +5,7 @@
 
 #pragma once
 
-#include "exprstate.hpp"
+#include "exprstatestack.hpp"
 #include <stdexcept>
 
 namespace xo {
diff --git a/src/reader/CMakeLists.txt b/src/reader/CMakeLists.txt
index 32a4cd5a..0a2f7704 100644
--- a/src/reader/CMakeLists.txt
+++ b/src/reader/CMakeLists.txt
@@ -5,6 +5,7 @@ set(SELF_SRCS
     parser.cpp
     reader.cpp
     exprstate.cpp
+    exprstatestack.cpp
     define_xs.cpp
     progress_xs.cpp
     paren_xs.cpp
diff --git a/src/reader/define_xs.cpp b/src/reader/define_xs.cpp
index 58006125..f0e7924f 100644
--- a/src/reader/define_xs.cpp
+++ b/src/reader/define_xs.cpp
@@ -1,6 +1,7 @@
 /* @file define_xs.cpp */
 
 #include "define_xs.hpp"
+#include "exprstatestack.hpp"
 #include "parserstatemachine.hpp"
 #include "expect_symbol_xs.hpp"
 #include "expect_expr_xs.hpp"
diff --git a/src/reader/expect_expr_xs.cpp b/src/reader/expect_expr_xs.cpp
index 74afec19..3c5001ae 100644
--- a/src/reader/expect_expr_xs.cpp
+++ b/src/reader/expect_expr_xs.cpp
@@ -5,6 +5,7 @@
 
 #include "expect_expr_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "lambda_xs.hpp"
 #include "paren_xs.hpp"
 #include "progress_xs.hpp"
diff --git a/src/reader/expect_formal_arglist_xs.cpp b/src/reader/expect_formal_arglist_xs.cpp
index 3dcd2c2e..1eef0563 100644
--- a/src/reader/expect_formal_arglist_xs.cpp
+++ b/src/reader/expect_formal_arglist_xs.cpp
@@ -4,9 +4,10 @@
  */
 
 #include "expect_formal_arglist_xs.hpp"
+#include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "expect_formal_xs.hpp"
 #include "expect_symbol_xs.hpp"
-#include "parserstatemachine.hpp"
 #include "xo/expression/Variable.hpp"
 #include "xo/indentlog/print/vector.hpp"
 
diff --git a/src/reader/expect_formal_xs.cpp b/src/reader/expect_formal_xs.cpp
index 94120e79..8bdcf6b1 100644
--- a/src/reader/expect_formal_xs.cpp
+++ b/src/reader/expect_formal_xs.cpp
@@ -7,6 +7,7 @@
 #include "expect_symbol_xs.hpp"
 #include "expect_type_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "xo/expression/Variable.hpp"
 
 namespace xo {
diff --git a/src/reader/expect_symbol_xs.cpp b/src/reader/expect_symbol_xs.cpp
index bae85927..591f4ca8 100644
--- a/src/reader/expect_symbol_xs.cpp
+++ b/src/reader/expect_symbol_xs.cpp
@@ -5,6 +5,7 @@
 
 #include "expect_symbol_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 
 namespace xo {
     namespace scm {
diff --git a/src/reader/expect_type_xs.cpp b/src/reader/expect_type_xs.cpp
index 90f2932a..97365062 100644
--- a/src/reader/expect_type_xs.cpp
+++ b/src/reader/expect_type_xs.cpp
@@ -5,6 +5,7 @@
 
 #include "expect_type_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "xo/reflect/Reflect.hpp"
 
 namespace xo {
diff --git a/src/reader/exprseq_xs.cpp b/src/reader/exprseq_xs.cpp
index 44f28624..0db1a394 100644
--- a/src/reader/exprseq_xs.cpp
+++ b/src/reader/exprseq_xs.cpp
@@ -1,9 +1,10 @@
 /* @file exprseq_xs.cpp */
 
 #include "exprseq_xs.hpp"
+#include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "define_xs.hpp"
 #include "expect_symbol_xs.hpp"
-#include "parserstatemachine.hpp"
 
 namespace xo {
     namespace scm {
diff --git a/src/reader/exprstate.cpp b/src/reader/exprstate.cpp
index 1b9644b6..9a2917e0 100644
--- a/src/reader/exprstate.cpp
+++ b/src/reader/exprstate.cpp
@@ -1,6 +1,7 @@
 /* @file exprstate.cpp */
 
 #include "exprstate.hpp"
+#include "exprstatestack.hpp"
 #include "parserstatemachine.hpp"
 //#include "formal_arg.hpp"
 #include "xo/expression/Variable.hpp"
@@ -390,67 +391,6 @@ namespace xo {
                        xtag("token", tk),
                        xtag("state", *this)));
         }
-
-        // ----- exprstatestack -----
-
-        exprstate &
-        exprstatestack::top_exprstate() {
-            std::size_t z = stack_.size();
-
-            if (z == 0) {
-                throw std::runtime_error
-                    ("parser::top_exprstate: unexpected empty stack");
-            }
-
-            return *(stack_[z-1]);
-        }
-
-        void
-        exprstatestack::push_exprstate(std::unique_ptr<exprstate> exs) {
-            constexpr bool c_debug_flag = true;
-            scope log(XO_DEBUG(c_debug_flag),
-                      xtag("exs", *exs));
-
-            std::size_t z = stack_.size();
-
-            stack_.resize(z+1);
-
-            stack_[z] = std::move(exs);
-        }
-
-        std::unique_ptr<exprstate>
-        exprstatestack::pop_exprstate() {
-            constexpr bool c_debug_flag = true;
-            scope log(XO_DEBUG(c_debug_flag),
-                      xtag("top.exstype", top_exprstate().exs_type()));
-
-            std::size_t z = stack_.size();
-
-            if (z > 0) {
-                std::unique_ptr<exprstate> top = std::move(stack_[z-1]);
-
-                stack_.resize(z-1);
-
-                return top;
-            } else {
-                return nullptr;
-            }
-        }
-
-        void
-        exprstatestack::print(std::ostream & os) const {
-            os << "<exprstatestack"
-               << xtag("size", stack_.size())
-               << std::endl;
-
-            for (std::size_t i = 0, z = stack_.size(); i < z; ++i) {
-                os << "  [" << z-i-1 << "] "
-                   << stack_[i]
-                   << std::endl;
-            }
-
-            os << ">" << std::endl;
-        }
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/src/reader/exprstatestack.cpp b/src/reader/exprstatestack.cpp
new file mode 100644
index 00000000..07ca85bb
--- /dev/null
+++ b/src/reader/exprstatestack.cpp
@@ -0,0 +1,71 @@
+/* file exprstatestack.cpp
+ *
+ * author: Roland Conybeare
+ */
+
+#include "exprstatestack.hpp"
+
+namespace xo {
+    namespace scm {
+        exprstate &
+        exprstatestack::top_exprstate() {
+            std::size_t z = stack_.size();
+
+            if (z == 0) {
+                throw std::runtime_error
+                    ("parser::top_exprstate: unexpected empty stack");
+            }
+
+            return *(stack_[z-1]);
+        }
+
+        void
+        exprstatestack::push_exprstate(std::unique_ptr<exprstate> exs) {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag),
+                      xtag("exs", *exs));
+
+            std::size_t z = stack_.size();
+
+            stack_.resize(z+1);
+
+            stack_[z] = std::move(exs);
+        }
+
+        std::unique_ptr<exprstate>
+        exprstatestack::pop_exprstate() {
+            constexpr bool c_debug_flag = true;
+            scope log(XO_DEBUG(c_debug_flag),
+                      xtag("top.exstype", top_exprstate().exs_type()));
+
+            std::size_t z = stack_.size();
+
+            if (z > 0) {
+                std::unique_ptr<exprstate> top = std::move(stack_[z-1]);
+
+                stack_.resize(z-1);
+
+                return top;
+            } else {
+                return nullptr;
+            }
+        }
+
+        void
+        exprstatestack::print(std::ostream & os) const {
+            os << "<exprstatestack"
+               << xtag("size", stack_.size())
+               << std::endl;
+
+            for (std::size_t i = 0, z = stack_.size(); i < z; ++i) {
+                os << "  [" << z-i-1 << "] "
+                   << stack_[i]
+                   << std::endl;
+            }
+
+            os << ">" << std::endl;
+        }
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end exprstatestack.cpp */
diff --git a/src/reader/lambda_xs.cpp b/src/reader/lambda_xs.cpp
index fbde492a..90270b07 100644
--- a/src/reader/lambda_xs.cpp
+++ b/src/reader/lambda_xs.cpp
@@ -2,6 +2,7 @@
 
 #include "lambda_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "expect_formal_arglist_xs.hpp"
 #include "expect_expr_xs.hpp"
 #include "xo/expression/Lambda.hpp"
diff --git a/src/reader/paren_xs.cpp b/src/reader/paren_xs.cpp
index b9dde8f4..96318e4c 100644
--- a/src/reader/paren_xs.cpp
+++ b/src/reader/paren_xs.cpp
@@ -2,6 +2,7 @@
 
 #include "paren_xs.hpp"
 #include "parserstatemachine.hpp"
+#include "exprstatestack.hpp"
 #include "progress_xs.hpp"
 #include "expect_expr_xs.hpp"
 
diff --git a/src/reader/progress_xs.cpp b/src/reader/progress_xs.cpp
index 6b474db3..d1bae5c3 100644
--- a/src/reader/progress_xs.cpp
+++ b/src/reader/progress_xs.cpp
@@ -1,6 +1,7 @@
 /* @file progress_xs.cpp */
 
 #include "progress_xs.hpp"
+#include "exprstatestack.hpp"
 #include "expect_expr_xs.hpp"
 #include "parserstatemachine.hpp"
 #include "xo/expression/Apply.hpp"