Add reverse() function to lists extension.

ext/README.md

@@ -442,6 +442,19 @@ Examples:
 	lists.range(5) -> [0, 1, 2, 3, 4]
 
 
+### Reverse
+
+**Introduced in version 2**
+
+Returns the elements of a list in reverse order.
+
+	<list(T)>.reverse() -> <list(T)>
+
+Examples:
+
+	[5, 3, 1, 2].reverse() // return [2, 1, 3, 5]
+
+
 ### Slice
 
 

ext/lists.go

@@ -52,6 +52,17 @@ var comparableTypes = []*cel.Type{
 //
 //	lists.range(5) -> [0, 1, 2, 3, 4]
 //
+// # Reverse
+//
+// Introduced in version: 2
+//
+// Returns the elements of a list in reverse order.
+//
+// 	<list(T)>.reverse() -> <list(T)>
+//
+// Examples:
+//
+// 	[5, 3, 1, 2].reverse() // return [2, 1, 3, 5]
 //
 // # Slice
 //
@@ -245,6 +256,19 @@ func (lib listsLib) CompileOptions() []cel.EnvOption {
 				}),
 			),
 		))
+		opts = append(opts, cel.Function("reverse",
+			cel.MemberOverload("list_reverse",
+				[]*cel.Type{listType}, listType,
+				cel.FunctionBinding(func(args ...ref.Val) ref.Val {
+					list := args[0].(traits.Lister)
+					result, err := reverseList(list)
+					if err != nil {
+						return types.WrapErr(err)
+					}
+					return result
+				}),
+			),
+		))
 	}
 
 	return opts
@@ -263,6 +287,16 @@ func genRange(n types.Int) (ref.Val, error) {
 	return types.DefaultTypeAdapter.NativeToValue(newList), nil
 }
 
+func reverseList(list traits.Lister) (ref.Val, error) {
+	var newList []ref.Val
+	listLength := list.Size().(types.Int)
+	for i := types.Int(0); i < listLength; i++ {
+		val := list.Get(listLength - i - 1)
+		newList = append(newList, val)
+	}
+	return types.DefaultTypeAdapter.NativeToValue(newList), nil
+}
+
 func slice(list traits.Lister, start, end types.Int) (ref.Val, error) {
 	listLength := list.Size().(types.Int)
 	if start < 0 || end < 0 {

ext/lists_test.go

@@ -43,6 +43,7 @@ func TestLists(t *testing.T) {
 		{expr: `[1,2,3,4].slice(0, 10)`, err: "cannot slice(0, 10), list is length 4"},
 		{expr: `[1,2,3,4].slice(-5, 10)`, err: "cannot slice(-5, 10), negative indexes not supported"},
 		{expr: `[1,2,3,4].slice(-5, -3)`, err: "cannot slice(-5, -3), negative indexes not supported"},
+
 		{expr: `dyn([]).flatten() == []`},
 		{expr: `dyn([1,2,3,4]).flatten() == [1,2,3,4]`},
 		{expr: `[1,[2,[3,4]]].flatten() == [1,2,[3,4]]`},