Implemented list::is_empty() based on Container trait

src/libcollections/list.rs

@@ -58,6 +58,9 @@ impl<T> List<T> {
 impl<T> Container for List<T> {
     /// Returns the length of a list
     fn len(&self) -> uint { self.iter().len() }
+
+    /// Returns true if the list is empty
+    fn is_empty(&self) -> bool { match *self { Nil => true, _ => false } }
 }
 
 /// Returns true if a list contains an element with the given value
@@ -69,14 +72,6 @@ pub fn has<T:Eq>(list: @List<T>, element: T) -> bool {
     return found;
 }
 
-/// Returns true if the list is empty
-pub fn is_empty<T>(list: @List<T>) -> bool {
-    match *list {
-        Nil => true,
-        _ => false
-    }
-}
-
 /// Returns all but the first element of a list
 pub fn tail<T>(list: @List<T>) -> @List<T> {
     match *list {
@@ -153,7 +148,7 @@ pub fn each<T>(list: @List<T>, f: |&T| -> bool) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use list::{List, Nil, head, is_empty, tail};
+    use list::{List, Nil, head, tail};
     use list;
 
     #[test]
@@ -168,13 +163,13 @@ mod tests {
 
     #[test]
     fn test_is_empty() {
-        let empty : @list::List<int> = @List::from_vec([]);
-        let full1 = @List::from_vec([1]);
-        let full2 = @List::from_vec(['r', 'u']);
+        let empty : list::List<int> = List::from_vec([]);
+        let full1 = List::from_vec([1]);
+        let full2 = List::from_vec(['r', 'u']);
 
-        assert!(is_empty(empty));
-        assert!(!is_empty(full1));
-        assert!(!is_empty(full2));
+        assert!(empty.is_empty());
+        assert!(!full1.is_empty());
+        assert!(!full2.is_empty());
     }
 
     #[test]

src/test/run-pass/non-boolean-pure-fns.rs

@@ -14,7 +14,7 @@
 
 extern crate collections;
 
-use collections::list::{List, Cons, Nil, head, is_empty};
+use collections::list::{List, Cons, Nil, head};
 
 fn pure_length_go<T:Clone>(ls: @List<T>, acc: uint) -> uint {
     match *ls { Nil => { acc } Cons(_, tl) => { pure_length_go(tl, acc + 1u) } }
@@ -25,7 +25,7 @@ fn pure_length<T:Clone>(ls: @List<T>) -> uint { pure_length_go(ls, 0u) }
 fn nonempty_list<T:Clone>(ls: @List<T>) -> bool { pure_length(ls) > 0u }
 
 fn safe_head<T:Clone>(ls: @List<T>) -> T {
-    assert!(!is_empty(ls));
+    assert!(!ls.is_empty());
     return head(ls);
 }