Merge pull request #3236 from dbp/or

core: adding option::or(a,b) that returns the leftmost some() or none otherwise

src/libcore/option.rs

@@ -93,6 +93,16 @@ enum option<T> {
     match *opt { some(ref x) => f(x), none => none }
 }
 
+pure fn or<T>(+opta: option<T>, +optb: option<T>) -> option<T> {
+    /*!
+     * Returns the leftmost some() value, or none if both are none.
+     */
+    match opta {
+        some(_) => opta,
+        _ => optb
+    }
+}
+
 #[inline(always)]
 pure fn while_some<T>(+x: option<T>, blk: fn(+T) -> option<T>) {
     //! Applies a function zero or more times until the result is none.