--- a/CMakeLists.txt	Thu Mar 26 10:06:28 2020 +0100
+++ b/CMakeLists.txt	Thu Mar 26 10:53:17 2020 +0100
@@ -7,6 +7,7 @@
 add_executable(describe_type src/describe_type.cc)
 add_executable(example src/example.cc)
 add_executable(fac src/fac.cc)
+add_executable(higherorder src/higherorder.cc)
 add_executable(replace_type src/replace_type.cc)
 add_executable(sequence src/sequence.cc)
 add_executable(units src/units.cc)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/higherorder.cc	Thu Mar 26 10:53:17 2020 +0100
@@ -0,0 +1,29 @@
+#include <iostream>
+#include <boost/mpl/apply.hpp>
+#include <boost/mpl/int.hpp>
+#include <boost/mpl/lambda.hpp>
+#include <boost/mpl/placeholders.hpp>
+#include <boost/mpl/plus.hpp>
+
+namespace mpl = boost::mpl;
+
+struct plus10 {
+    template<typename X>
+    struct apply {
+        typedef typename mpl::int_<10 + X::value>::type type;
+    };
+};
+
+template<typename F, typename X>
+struct apply_twice {
+    typedef typename F::template apply<X>::type once;
+    typedef typename F::template apply<once>::type type;
+};
+
+int main(void) {
+    typedef mpl::int_<3> three;
+    typedef mpl::lambda<mpl::plus<mpl::int_<11>, mpl::_1>>::type plus11;
+
+    std::cout << apply_twice<plus11, three>::type::value << std::endl;
+    return 0;
+}

--- a/src/units.cc	Thu Mar 26 10:06:28 2020 +0100
+++ b/src/units.cc	Thu Mar 26 10:53:17 2020 +0100
@@ -80,7 +80,7 @@
 
 template <typename U1, typename U2>
 struct multiply_units {
-    typedef typename mpl::transform<U1, U2, make_lambda<plus>>::type type;
+    typedef typename mpl::transform<U1, U2, plus<mpl::_1, mpl::_2>>::type type;
 };
 
 template <typename U1, typename U2>