generic: new module comparison plus general support code

1 files changed, 56 insertions, 0 deletions

diff --git a/src/clojure/contrib/generic/comparison.clj b/src/clojure/contrib/generic/comparison.clj
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+++ b/src/clojure/contrib/generic/comparison.clj
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+;; Generic interfaces for comparison operations
+
+;; by Konrad Hinsen
+;; last updated March 19, 2009
+
+;; Copyright (c) Konrad Hinsen, 2009. All rights reserved.  The use
+;; and distribution terms for this software are covered by the Eclipse
+;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
+;; which can be found in the file epl-v10.html at the root of this
+;; distribution.  By using this software in any fashion, you are
+;; agreeing to be bound by the terms of this license.  You must not
+;; remove this notice, or any other, from this software.
+
+(ns clojure.contrib.generic.comparison
+  "Generic comparison interface
+
+   NOTE: This library is VERY experimental. It WILL change significantly
+   with future release.
+
+   This library defines generic versions of = < > <= >= zero? as multimethods
+   that can be defined for any type."
+  (:refer-clojure :exclude [= < > <= >= zero?])
+  (:use [clojure.contrib.generic
+	 :only (root-type nulary-type nary-type nary-dispatch)]))
+
+;
+; zero?
+;
+(defmulti zero? type)
+
+;
+; Equality
+;
+(defmulti = nary-dispatch)
+
+(defmethod = root-type
+  [x] true)
+
+(defmethod = nary-type
+  [x y & more]
+  (if (= x y)
+    (if (next more)
+      (recur y (first more) (next more))
+      (= y (first more)))
+    false))
+
+;
+; Implementations for Clojure's built-in types
+;
+(defmethod zero? java.lang.Number
+  [x]
+  (clojure.core/zero? x))
+
+(defmethod = [Object Object]
+  [x y]
+  (clojure.core/= x y))