diff --git a/include/xo/reader/parser.hpp b/include/xo/reader/parser.hpp
index dae3091f..30dd94ea 100644
--- a/include/xo/reader/parser.hpp
+++ b/include/xo/reader/parser.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include "exprstatestack.hpp"
+#include "envframestack.hpp"
 #include <stdexcept>
 
 namespace xo {
@@ -212,6 +213,12 @@ namespace xo {
              **/
             exprstatestack xs_stack_;
 
+            /** environment frames for lexical context.
+             *  push a frame on each nested lambda;
+             *  pop when lambda body goes out of scope
+             **/
+            envframestack env_stack_;
+
         }; /*parser*/
 
         inline std::ostream &