diff --git a/src/wren/string_bt.hpp b/src/wren/string_bt.hpp
new file mode 100644
index 0000000..39def96
--- /dev/null
+++ b/src/wren/string_bt.hpp
@@ -0,0 +1,128 @@
+/* Copyright 2016-2018 Michele Santullo
+ * This file is part of "duckhandy".
+ *
+ * "duckhandy" is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * "duckhandy" is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with "duckhandy".  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef id170B0E6C34D14EBA9B92A35977BDBFB3
+#define id170B0E6C34D14EBA9B92A35977BDBFB3
+
+#include <utility>
+#include <cstddef>
+#include <iostream>
+#include <stdexcept>
+
+namespace dhandy {
+	namespace bt {
+		template <std::size_t S, typename Ch=char>
+		class string;
+
+		template <std::size_t S, typename Ch>
+		std::basic_ostream<Ch>& operator<< ( std::basic_ostream<Ch>& parStream, const string<S, Ch>& parString );
+
+		namespace implem {
+			template <std::size_t S, typename Ch> constexpr bool eq (const string<S, Ch>& l, const string<S, Ch>& r);
+		} //namespace implem
+
+		template <std::size_t S, typename Ch>
+		class string {
+			friend std::ostream& operator<< <>( std::ostream& parStream, const string<S>& parString );
+			friend constexpr bool implem::eq<S, Ch> (const string<S, Ch>&, const string<S, Ch>&);
+		public:
+			using value_type = Ch;
+			constexpr string ( const value_type* parString );
+
+			constexpr std::size_t size ( void ) const { return S - 1; }
+			template <std::size_t S2>
+			constexpr string<S + S2 - 1, Ch> operator+ ( const string<S2, Ch>& parOther ) const;
+			constexpr value_type operator[] ( std::size_t parIndex ) const;
+			constexpr bool operator== (const string<S, Ch>& other) const;
+			template <std::size_t S2> constexpr bool operator== (const string<S2, Ch>&) const { return false; }
+
+			template <typename... Args>
+			constexpr string ( Args... );
+
+			constexpr const value_type (&data_arr() const)[S] { return m_data; }
+			constexpr const value_type* data() const { return m_data; }
+
+		private:
+			template <std::size_t... I>
+			constexpr string ( std::index_sequence<I...>, const value_type* parString );
+
+			const value_type m_data[S];
+		};
+
+		namespace implem {
+			template <std::size_t S, std::size_t S2, std::size_t... I>
+			constexpr string<S + S2 - 1> concat ( std::index_sequence<I...>, const string<S>& parLeft, const string<S2>& parRight ) {
+				return string<S + S2 - 1>(
+					(I < S - 1 ? parLeft[I] : (I < S + S2 - 2 ? parRight[I - (S - 1)] : '\0'))...
+				);
+			}
+
+			template <> constexpr inline bool eq (const string<1>& l, const string<1>& r) { return l[0] == r[0]; }
+			template <std::size_t S, typename Ch>
+			constexpr inline bool eq (const string<S, Ch>& l, const string<S, Ch>& r) { return l[0] == r[0] and eq(string<S-1>(l.m_data+1), string<S-1>(r.m_data+1)); }
+		} //namespace implem
+
+		template <std::size_t S, typename Ch>
+		template <std::size_t... I>
+		constexpr string<S, Ch>::string (std::index_sequence<I...>, const value_type* parString) :
+			m_data{parString[I]...}
+		{
+		}
+
+		template <std::size_t S, typename Ch>
+		inline constexpr string<S, Ch>::string (const value_type* parString) :
+			string(std::make_index_sequence<S>(), parString)
+		{
+		}
+
+		template <std::size_t S, typename Ch>
+		template <typename... Args>
+		inline constexpr string<S, Ch>::string (Args... parArgs) :
+			m_data{parArgs...}
+		{
+		}
+
+		template <std::size_t S, typename Ch>
+		template <std::size_t S2>
+		constexpr inline string<S + S2 - 1, Ch> string<S, Ch>::operator+ (const string<S2, Ch>& parOther) const {
+			return implem::concat(std::make_index_sequence<S + S2 - 1>(), string<S>(m_data), parOther);
+		}
+
+		template <std::size_t S, typename Ch>
+		inline std::ostream& operator<< (std::ostream& parStream, const string<S, Ch>& parString) {
+			parStream << parString.m_data;
+			return parStream;
+		}
+
+		template <std::size_t S, typename Ch>
+		constexpr auto string<S, Ch>::operator[] (std::size_t parIndex) const -> value_type {
+			return (parIndex < S ? m_data[parIndex] : throw std::out_of_range(""));
+		}
+
+		template <std::size_t S, typename Ch>
+		constexpr string<S, Ch> make_string (const Ch (&parData)[S]) {
+			return string<S>(parData);
+		}
+
+		template <std::size_t S, typename Ch>
+		constexpr bool string<S, Ch>::operator== (const string<S, Ch>& other) const {
+			return implem::eq(*this, other);
+		}
+	} //namespace bt
+} //namespace dhandy
+
+#endif