add an example

3 files changed, 46 insertions, 0 deletions

diff --git a/README.rst b/README.rst
index c1d9088..eb1f591 100644
--- a/README.rst
+++ b/README.rst
@@ -14,6 +14,35 @@ the underlying `any` type, an exception will be thrown when the resolved value
 types do not match the types expected in the subsequent computation. See
 `test.cpp` for detailed examples.
 
+Example
+=======
+
+Calculate the factorial of n, the hard way:
+
+.. code-block:: cpp
+
+   #include "promise.hpp"
+   
+   using promise::promise_t;
+   
+   int main() {
+       promise_t root;
+       promise_t t = root;
+       for (int i = 0; i < 10; i++)
+           t = t.then([](std::pair<int, int> p) {
+               p.first *= p.second;
+               p.second++;
+               return p;
+           });
+       t.then([](std::pair<int, int> p) {
+           printf("fac(%d) = %d\n", p.second, p.first);
+       });
+       /* no actual calculation until here */
+       root.resolve(std::make_pair(1, 1));
+       return 0;
+   }
+    
+
 API
 ===
 
diff --git a/test.cpp b/test.cpp
index 3c2bfc9..7fa7f60 100644
--- a/test.cpp
+++ b/test.cpp
@@ -30,6 +30,21 @@ promise_t g(int x) {
     return promise_t([](promise_t pm) {pm.resolve(1);});
 }
 
+void test_fac() {
+    promise_t root;
+    promise_t t = root;
+    for (int i = 0; i < 10; i++)
+        t = t.then([](std::pair<int, int> p) {
+            p.first *= p.second;
+            p.second++;
+            return p;
+        });
+    t.then([](std::pair<int, int> p) {
+        printf("fac(%d) = %d\n", p.second, p.first);
+    });
+    root.resolve(std::make_pair(1, 1));
+}
+
 int main() {
     callback_t t1;
     callback_t t2;
@@ -143,4 +158,5 @@ int main() {
     t1();
     puts("calling t2: resolve the second half of promise 1 (promise 2)");
     t2();
+    test_fac();
 }
diff --git a/test_ref.txt b/test_ref.txt
index 574a8b3..40d1b22 100644
--- a/test_ref.txt
+++ b/test_ref.txt
@@ -27,3 +27,4 @@ promise 9 resolved with 101
 rejecting with value -1
 reason: -1
 reason: 0
+fac(11) = 3628800