Show causes in simple example

Author: mitsuhiko

examples/simple.rs

@@ -1,14 +1,22 @@
 #[macro_use]
 extern crate failure;
 
+use failure::Fail;
+
 #[derive(Debug, Fail)]
 #[fail(display = "my error")]
 struct MyError;
 
-fn bad_function() -> Result<(), MyError> {
-    Err(MyError)
+#[derive(Debug, Fail)]
+#[fail(display = "my wrapping error")]
+struct WrappingError(#[fail(cause)] MyError);
+
+fn bad_function() -> Result<(), WrappingError> {
+    Err(WrappingError(MyError))
 }
 
 fn main() {
-    println!("{}", bad_function().unwrap_err());
+    for cause in Fail::iter_causes(&bad_function().unwrap_err()) {
+        println!("{}", cause);
+    }
 }