Add 'xo-reader/' from commit 'c46c0f1cc4'

git-subtree-dir: xo-reader
git-subtree-mainline: dacdeb2cd7
git-subtree-split: c46c0f1cc4

xo-reader/include/xo/reader/envframestack.hpp

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+/* file envframestack.hpp
+ *
+ * author: Roland Conybeare, Aug 2024
+ */
+
+#pragma once
+
+#include "envframe.hpp"
+
+namespace xo {
+    namespace scm {
+        /** @class envframestack
+         *  @brief A stack of envframe objects
+         **/
+        class envframestack {
+        public:
+            using Variable = xo::ast::Variable;
+
+        public:
+            envframestack() {}
+
+            bool empty() const { return stack_.empty(); }
+            std::size_t size() const { return stack_.size(); }
+
+            /** lookup variable in environment stack.
+             *  Visit frames in fifo order,  report first match;
+             *  nullptr if no matches.
+             **/
+            rp<Variable> lookup(const std::string & x) const;
+
+            envframe & top_envframe();
+            void push_envframe(envframe x);
+            void pop_envframe();
+
+            /** relative to top-of-stack.
+             *  0 -> top (last in),  z-1 -> bottom (first in)
+             **/
+            envframe & operator[](std::size_t i) {
+                std::size_t z = stack_.size();
+
+                assert(i < z);
+
+                return stack_[z - i - 1];
+            }
+
+            const envframe & 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<envframe> stack_;
+        };
+
+        inline std::ostream &
+        operator<< (std::ostream & os, const envframestack & x) {
+            x.print(os);
+            return os;
+        }
+
+        inline std::ostream &
+        operator<< (std::ostream & os, const envframestack * x) {
+            if (x)
+                x->print(os);
+            else
+                os << "nullptr";
+            return os;
+        }
+    } /*namespace scm*/
+} /*namespace xo*/
+
+
+/* end envframestack.hpp */