Changed to constructor functions

validators/string.ts

@@ -1,14 +1,32 @@
 import { Validator, Args } from "../mod.ts";
 
-export const isString: Validator = {
-  type: "isString",
-  check: (value: any) => {
-    if (value === null || value === undefined) return;
-    if (typeof value !== "string" && !(value instanceof String)) {
-      return {};
-    }
-  },
-  message: (value: any, args?: Args) => {
-    return `This value has to be a string.`;
-  },
-};
+export function isString(): Validator {
+  return {
+    type: "isString",
+    check: (value: any) => {
+      if (value === null || value === undefined) return;
+      if (typeof value !== "string" && !(value instanceof String)) {
+        return {};
+      }
+    },
+    message: (value: any, args?: Args) => {
+      return `This value has to be a string.`;
+    },
+  };
+}
+
+export function isURL(): Validator {
+  return {
+    type: "isURL",
+    extends: [isString()],
+    check: (value: any) => {
+      if (value === null || value === undefined) return;
+      if (value !== "http://google.com") {
+        return {};
+      }
+    },
+    message: (value: any, args?: Args) => {
+      return `This value is not a valid URL.`;
+    },
+  };
+}