Adding Scope lookup utility class.

Scope.hpp

@@ -0,0 +1,47 @@
+#ifndef SCOPE_HPP
+#define SCOPE_HPP
+
+#include <boost/optional.hpp>
+#include <boost/range/adaptor/reversed.hpp>
+
+#include <vector>
+#include <unordered_map>
+
+
+namespace monicelli {
+
+template<class Key, class Value>
+class Scope {
+public:
+    boost::optional<Value> lookup(Key name) {
+        for (auto const& table: boost::adaptors::reverse(tables)) {
+            auto result = table.find(name);
+            if (result != table.end()) {
+                return result->second;
+            }
+        }
+
+        return boost::none;
+    }
+
+    void push(Key const& key, Value const& value) {
+        tables.back().insert({key, value});
+    }
+
+    void enter() {
+        tables.emplace_back();
+    }
+
+    void leave() {
+        if (!tables.empty()) {
+            tables.pop_back();
+        }
+    }
+
+private:
+    std::vector<std::unordered_map<Key, Value>> tables;
+};
+
+}
+
+#endif