Index: doc/proposals/interned_string.cc
===================================================================
--- doc/proposals/interned_string.cc	(revision 0efb26929e1396507033dfb87f35284ba533db90)
+++ doc/proposals/interned_string.cc	(revision 0efb26929e1396507033dfb87f35284ba533db90)
@@ -0,0 +1,8 @@
+// Copyright (c) 2015 University of Waterloo
+//
+// The contents of this file are covered under the licence agreement in 
+// the file "LICENCE" distributed with this repository.
+
+#include "interned_string.h"
+
+std::unordered_set< std::string > interned_string::canonical;
Index: doc/proposals/interned_string.h
===================================================================
--- doc/proposals/interned_string.h	(revision 0efb26929e1396507033dfb87f35284ba533db90)
+++ doc/proposals/interned_string.h	(revision 0efb26929e1396507033dfb87f35284ba533db90)
@@ -0,0 +1,57 @@
+#pragma once
+
+// Copyright (c) 2015 University of Waterloo
+//
+// The contents of this file are covered under the licence agreement in 
+// the file "LICENCE" distributed with this repository.
+
+#include <functional>
+#include <string>
+#include <unordered_set>
+#include <utility>
+
+/// Keeps canonical copies of a std::string for quicker comparisons
+class interned_string {
+	/// Shared map of canonical string representations
+	static std::unordered_set< std::string > canonical;
+
+	/// Canonical representation of empty string
+	static const std::string* empty_string() {
+		static const std::string* mt = [](){
+			return &*canonical.emplace( "" ).first;
+		}();
+		return mt;
+	}
+
+	/// Canonicalize string
+	template<typename S>
+	static const std::string* intern( S&& s ) {
+		return &*canonical.emplace( std::forward<S>(s) ).first;
+	}
+
+	/// Pointer to stored string
+	const std::string* s;
+	
+public:
+	interned_string() : s{empty_string()} {}
+	interned_string(const char* cs) : s{intern(cs)} {}
+	interned_string(const std::string& ss) : s{intern(ss)} {}
+
+	operator const std::string& () const { return *s; }
+
+	bool operator== (const interned_string& o) const { return s == o.s; }
+	bool operator!= (const interned_string& o) const { return s != o.s; }
+	bool operator< (const interned_string& o) const { return *s < *o.s; }
+};
+
+inline std::ostream& operator<< (std::ostream& out, const interned_string& s) {
+	return out << (const std::string&)s;
+}
+
+namespace std {
+	template<> struct hash<interned_string> {
+		std::size_t operator() (const interned_string& s) const {
+			return std::hash<const std::string*>{}( &(const std::string&)s );
+		}
+	};
+}