1 files changed, 47 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/lazy/monad.cpp b/src/boost/libs/hana/example/lazy/monad.cpp
new file mode 100644
index 000000000..f425e2810
--- /dev/null
+++ b/src/boost/libs/hana/example/lazy/monad.cpp
@@ -0,0 +1,47 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/chain.hpp>
+#include <boost/hana/eval.hpp>
+#include <boost/hana/lazy.hpp>
+
+#include <functional>
+#include <iostream>
+#include <sstream>
+namespace hana = boost::hana;
+
+
+template <typename T>
+T read_(std::istream& stream) {
+    T x;
+    stream >> x;
+    std::cout << "read " << x << " from the stream\n";
+    return x;
+}
+
+int main() {
+    std::stringstream ss;
+    int in = 123;
+
+    std::cout << "creating the monadic chain...\n";
+    auto out = hana::make_lazy(read_<int>)(std::ref(ss))
+        | [](auto x) {
+            std::cout << "performing x + 1...\n";
+            return hana::make_lazy(x + 1);
+        }
+        | [](auto x) {
+            std::cout << "performing x / 2...\n";
+            return hana::make_lazy(x / 2);
+        };
+
+    std::cout << "putting " << in << " in the stream...\n";
+    ss << in; // nothing is evaluated yet
+
+    std::cout << "evaluating the monadic chain...\n";
+    auto eout = hana::eval(out);
+
+    std::cout << "the result of the monadic chain is " << eout << "\n";
+    BOOST_HANA_RUNTIME_CHECK(eout == (in + 1) / 2);
+}