Add std::vec::foldr

src/lib/vec.rs

@@ -435,7 +435,7 @@ Function: foldl
 
 Reduce a vector from left to right
 */
-fn foldl<T, U>(p: block(U, T) -> U, z: U, v: [mutable? T]) -> U {
+fn foldl<T, U>(p: block(T, U) -> T, z: T, v: [mutable? U]) -> T {
     let accum = z;
     iter(v) { |elt|
         accum = p(accum, elt);
@@ -443,6 +443,19 @@ fn foldl<T, U>(p: block(U, T) -> U, z: U, v: [mutable? T]) -> U {
     ret accum;
 }
 
+/*
+Function: foldr
+
+Reduce a vector from right to left
+*/
+fn foldr<T, U>(p: block(T, U) -> U, z: U, v: [mutable? T]) -> U {
+    let accum = z;
+    riter(v) { |elt|
+        accum = p(elt, accum);
+    }
+    ret accum;
+}
+
 /*
 Function: any
 

src/test/stdtest/vec.rs

@@ -302,6 +302,16 @@ fn test_foldl2() {
     assert sum == -10;
 }
 
+#[test]
+fn test_foldr() {
+    fn sub(&&a: int, &&b: int) -> int {
+        a - b
+    }
+    let v = [1, 2, 3, 4];
+    let sum = vec::foldr(sub, 0, v);
+    assert sum == -2;
+}
+
 #[test]
 fn iter_empty() {
     let i = 0;