diff --git a/core/src/lib.rs b/core/src/lib.rs
index aac31a71..ad78de81 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -473,3 +473,4 @@ mod test {
 }
 
 pub mod intern_set;
+pub mod util;
diff --git a/core/src/util.rs b/core/src/util.rs
new file mode 100644
index 00000000..cd2205d2
--- /dev/null
+++ b/core/src/util.rs
@@ -0,0 +1,60 @@
+
+// Copyright 2016 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+/// Side-effect chaining on `Result`.
+pub trait ResultEffect<T> {
+    /// Invoke `f` if `self` is `Ok`, returning `self`.
+    fn when_ok<F: FnOnce()>(self, f: F) -> Self;
+
+    /// Invoke `f` if `self` is `Err`, returning `self`.
+    fn when_err<F: FnOnce()>(self, f: F) -> Self;
+}
+
+impl<T, E> ResultEffect<T> for Result<T, E> {
+    fn when_ok<F: FnOnce()>(self, f: F) -> Self {
+        if self.is_ok() {
+            f();
+        }
+        self
+    }
+
+    fn when_err<F: FnOnce()>(self, f: F) -> Self {
+        if self.is_err() {
+            f();
+        }
+        self
+    }
+}
+
+/// Side-effect chaining on `Option`.
+pub trait OptionEffect<T> {
+    /// Invoke `f` if `self` is `None`, returning `self`.
+    fn when_none<F: FnOnce()>(self, f: F) -> Self;
+
+    /// Invoke `f` if `self` is `Some`, returning `self`.
+    fn when_some<F: FnOnce()>(self, f: F) -> Self;
+}
+
+impl<T> OptionEffect<T> for Option<T> {
+    fn when_none<F: FnOnce()>(self, f: F) -> Self {
+        if self.is_none() {
+            f();
+        }
+        self
+    }
+
+    fn when_some<F: FnOnce()>(self, f: F) -> Self {
+        if self.is_some() {
+            f();
+        }
+        self
+    }
+}
\ No newline at end of file