diff --git a/src/vs/base/common/functional.ts b/src/vs/base/common/functional.ts
new file mode 100644
index 00000000000..5be547ec594
--- /dev/null
+++ b/src/vs/base/common/functional.ts
@@ -0,0 +1,11 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+export function not<A>(fn: (a: A) => boolean): (a: A) => boolean;
+export function not(fn: Function): Function {
+	return (...args) => !fn(...args);
+}
\ No newline at end of file