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+// Copyright 2012 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors
+//   may be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+/// \file examples/bindings.cpp
+/// Showcases how to define Lua functions from C++ code.
+///
+/// A major selling point of Lua is that it is very easy too hook native C and
+/// C++ functions into the runtime environment so that Lua can call them.  The
+/// purpose of this example program is to show how this is done by using Lutok.
+
+#include <cassert>
+#include <cstdlib>
+#include <iostream>
+#include <map>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+
+#include <lutok/exceptions.hpp>
+#include <lutok/operations.hpp>
+#include <lutok/state.ipp>
+
+
+/// Calculates the factorial of a given number.
+///
+/// \param i The postivie number to calculate the factorial of.
+///
+/// \return The factorial of i.
+static int
+factorial(const int i)
+{
+    assert(i >= 0);
+
+    if (i == 0)
+        return 1;
+    else
+        return i * factorial(i - 1);
+}
+
+
+/// A custom factorial function for Lua.
+///
+/// \pre stack(-1) contains the number to calculate the factorial of.
+/// \post stack(-1) contains the result of the operation.
+///
+/// \param state The Lua state from which to get the function arguments and into
+///     which to push the results.
+///
+/// \return The number of results pushed onto the stack, i.e. 1.
+///
+/// \throw std::runtime_error If the input parameters are invalid.  Note that
+///     Lutok will convert this exception to lutok::error.
+static int
+lua_factorial(lutok::state& state)
+{
+    if (!state.is_number(-1))
+        throw std::runtime_error("Argument to factorial must be an integer");
+    const int i = state.to_integer(-1);
+    if (i < 0)
+        throw std::runtime_error("Argument to factorial must be positive");
+    state.push_integer(factorial(i));
+    return 1;
+}
+
+
+/// Program's entry point.
+///
+/// \param argc Length of argv.  Must be 2.
+/// \param argv Command-line arguments to the program.  The first argument to
+///     the tool has to be a number.
+///
+/// \return A system exit code.
+int
+main(int argc, char** argv)
+{
+    if (argc != 2) {
+        std::cerr << "Usage: bindings <number>\n";
+        return EXIT_FAILURE;
+    }
+
+    // Create a new Lua session and load the print() function.
+    lutok::state state;
+    state.open_base();
+
+    // Construct a 'module' that contains an entry point to our native factorial
+    // function.  A module is just a Lua table that contains a mapping of names
+    // to functions.  Instead of creating a module by using our create_module()
+    // helper function, we could have used push_cxx_function on the state to
+    // define the function ourselves.
+    std::map< std::string, lutok::cxx_function > module;
+    module["factorial"] = lua_factorial;
+    lutok::create_module(state, "native", module);
+
+    // Use a little Lua script to call our native factorial function providing
+    // it the first argument passed to the program.  Note that this will error
+    // out in a controlled manner if the passed argument is not an integer.  The
+    // important thing to notice is that the exception comes from our own C++
+    // binding and that it has been converted to a lutok::error.
+    std::ostringstream script;
+    script << "print(native.factorial(" << argv[1] << "))";
+    try {
+        lutok::do_string(state, script.str(), 0, 0, 0);
+        return EXIT_SUCCESS;
+    } catch (const lutok::error& e) {
+        std::cerr << "ERROR: " << e.what() << '\n';
+        return EXIT_FAILURE;
+    }
+}