Introduce Ordered

Author: cranst0n

packages/core/lib/src/order.dart

@@ -1,4 +1,4 @@
-import 'package:ribs_core/src/function.dart';
+import 'package:ribs_core/ribs_core.dart';
 
 /// Defines a total ordering for elements of type `A`.
 ///
@@ -12,6 +12,9 @@ abstract class Order<A> {
   static Order<A> fromComparable<A extends Comparable<dynamic>>() =>
       Order.from((A a, A b) => a.compareTo(b));
 
+  static Order<A> fromOrdered<A extends Ordered<dynamic>>() =>
+      Order.from((A a, A b) => a.compareTo(b));
+
   /// Creates a new [Order] that compares 2 elements using [f].
   factory Order.from(Function2<A, A, int> f) => _OrderF(f);
 

packages/core/lib/src/ordered.dart

@@ -0,0 +1,14 @@
+abstract class Ordered<A> implements Comparable<A> {
+  const Ordered();
+
+  @override
+  int compareTo(A other);
+
+  bool operator <(A that) => compareTo(that) < 0;
+
+  bool operator <=(A that) => compareTo(that) <= 0;
+
+  bool operator >(A that) => compareTo(that) > 0;
+
+  bool operator >=(A that) => compareTo(that) >= 0;
+}