array and linked-list: at operator

types/list/linked-list-type.go

@@ -137,3 +137,16 @@ func (ls *LinkedList) HasValue(value any) (found bool) {
 	}
 	return
 }
+
+func (ls *LinkedList) Index(value any) (index int64) {
+	index = -1
+	i := int64(0)
+	for node := ls.FirstNode(); node != nil; node = node.Next() {
+		if kern.Equal(node.Data(), value) {
+			index = i
+			break
+		}
+		i++
+	}
+	return
+}