Wrote functions to convert collections and maps to strings and invoked

frog/lib/collections.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-/**
- * The [Collections] class implements static methods useful when
- * writing a class that implements [Collection] and the [iterator]
- * method.
- */
-class Collections {
-  static void forEach(Iterable<Object> iterable, void f(Object o)) {
-    for (final e in iterable) {
-      f(e);
-    }
-  }
-
-  static List map(Iterable<Object> source,
-                  List<Object> destination,
-                  f(o)) {
-    for (final e in source) {
-      destination.add(f(e));
-    }
-    return destination;
-  }
-
-
-  static bool some(Iterable<Object> iterable, bool f(Object o)) {
-    for (final e in iterable) {
-      if (f(e)) return true;
-    }
-    return false;
-  }
-
-  static bool every(Iterable<Object> iterable, bool f(Object o)) {
-    for (final e in iterable) {
-      if (!f(e)) return false;
-    }
-    return true;
-  }
-
-  static List filter(Iterable<Object> source,
-                     List<Object> destination,
-                     bool f(o)) {
-    for (final e in source) {
-      if (f(e)) destination.add(e);
-    }
-    return destination;
-  }
-
-  static bool isEmpty(Iterable<Object> iterable) {
-    return !iterable.iterator().hasNext();
-  }
-}