Refactored list::tail() to be based on List<T>

src/libcollections/list.rs

@@ -61,6 +61,14 @@ impl<T> List<T> {
           Cons(ref head, _) => Some(head)
         }
     }
+
+    /// Returns all but the first element of a list
+    pub fn tail(&self) -> Option<@List<T>> {
+        match *self {
+            Nil => None,
+            Cons(_, tail) => Some(tail)
+        }
+    }
 }
 
 impl<T> Container for List<T> {
@@ -78,14 +86,6 @@ impl<T:Eq> List<T> {
     }
 }
 
-/// Returns all but the first element of a list
-pub fn tail<T>(list: @List<T>) -> @List<T> {
-    match *list {
-        Cons(_, tail) => return tail,
-        Nil => fail!("list empty")
-    }
-}
-
 /// Appends one list to another
 pub fn append<T:Clone + 'static>(list: @List<T>, other: @List<T>) -> @List<T> {
     match *list {
@@ -117,7 +117,7 @@ fn push<T:Clone>(ll: &mut @list<T>, vv: T) {
 
 #[cfg(test)]
 mod tests {
-    use list::{List, Nil, tail};
+    use list::{List, Nil};
     use list;
 
     #[test]
@@ -143,13 +143,13 @@ mod tests {
 
     #[test]
     fn test_from_vec() {
-        let list = @List::from_vec([0, 1, 2]);
+        let list = List::from_vec([0, 1, 2]);
         assert_eq!(list.head().unwrap(), &0);
 
-        let mut tail = tail(list);
+        let mut tail = list.tail().unwrap();
         assert_eq!(tail.head().unwrap(), &1);
 
-        tail = tail(tail);
+        tail = tail.tail().unwrap();
         assert_eq!(tail.head().unwrap(), &2);
     }