1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/clojure/contrib/generic/comparison.clj	Sat Aug 21 06:25:44 2010 -0400
     1.3 @@ -0,0 +1,214 @@
     1.4 +;; Generic interfaces for comparison operations
     1.5 +
     1.6 +;; by Konrad Hinsen
     1.7 +;; last updated May 25, 2010
     1.8 +
     1.9 +;; Copyright (c) Konrad Hinsen, 2009-2010. All rights reserved.  The use
    1.10 +;; and distribution terms for this software are covered by the Eclipse
    1.11 +;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
    1.12 +;; which can be found in the file epl-v10.html at the root of this
    1.13 +;; distribution.  By using this software in any fashion, you are
    1.14 +;; agreeing to be bound by the terms of this license.  You must not
    1.15 +;; remove this notice, or any other, from this software.
    1.16 +
    1.17 +(ns
    1.18 +  ^{:author "Konrad Hinsen"
    1.19 +     :doc "Generic comparison interface
    1.20 +           This library defines generic versions of = < > <= >= zero?
    1.21 +           as multimethods that can be defined for any type. Of the
    1.22 +           greater/less-than relations, types must minimally implement >."}
    1.23 +  clojure.contrib.generic.comparison
    1.24 +  (:refer-clojure :exclude [= < > <= >= zero? pos? neg? min max])
    1.25 +  (:use [clojure.contrib.generic
    1.26 +	 :only (root-type nulary-type nary-type nary-dispatch)]))
    1.27 +
    1.28 +;
    1.29 +; zero? pos? neg?
    1.30 +;
    1.31 +(defmulti zero?
    1.32 +  "Return true of x is zero."
    1.33 +  {:arglists '([x])}
    1.34 +  type)
    1.35 +
    1.36 +(defmulti pos?
    1.37 +  "Return true of x is positive."
    1.38 +  {:arglists '([x])}
    1.39 +  type)
    1.40 +
    1.41 +(defmulti neg?
    1.42 +  "Return true of x is negative."
    1.43 +  {:arglists '([x])}
    1.44 +  type)
    1.45 +
    1.46 +;
    1.47 +; Equality
    1.48 +;
    1.49 +(defmulti =
    1.50 +  "Return true if all arguments are equal. The minimal implementation for type
    1.51 +   ::my-type is the binary form with dispatch value [::my-type ::my-type]."
    1.52 +  {:arglists '([x] [x y] [x y & more])}
    1.53 +  nary-dispatch)
    1.54 +
    1.55 +(defmethod = root-type
    1.56 +  [x] true)
    1.57 +
    1.58 +(defmethod = nary-type
    1.59 +  [x y & more]
    1.60 +  (if (= x y)
    1.61 +    (if (next more)
    1.62 +      (recur y (first more) (next more))
    1.63 +      (= y (first more)))
    1.64 +    false))
    1.65 +
    1.66 +;
    1.67 +; Greater-than
    1.68 +;
    1.69 +(defmulti >
    1.70 +  "Return true if each argument is larger than the following ones.
    1.71 +   The minimal implementation for type ::my-type is the binary form
    1.72 +   with dispatch value [::my-type ::my-type]."
    1.73 +  {:arglists '([x] [x y] [x y & more])}
    1.74 +  nary-dispatch)
    1.75 +
    1.76 +(defmethod > root-type
    1.77 +  [x] true)
    1.78 +
    1.79 +(defmethod > nary-type
    1.80 +  [x y & more]
    1.81 +  (if (> x y)
    1.82 +    (if (next more)
    1.83 +      (recur y (first more) (next more))
    1.84 +      (> y (first more)))
    1.85 +    false))
    1.86 +
    1.87 +;
    1.88 +; Less-than defaults to greater-than with arguments inversed
    1.89 +;
    1.90 +(defmulti <
    1.91 +  "Return true if each argument is smaller than the following ones.
    1.92 +   The minimal implementation for type ::my-type is the binary form
    1.93 +   with dispatch value [::my-type ::my-type]. A default implementation
    1.94 +   is provided in terms of >."
    1.95 +  {:arglists '([x] [x y] [x y & more])}
    1.96 +  nary-dispatch)
    1.97 +
    1.98 +(defmethod < root-type
    1.99 +  [x] true)
   1.100 +
   1.101 +(defmethod < [root-type root-type]
   1.102 +  [x y]
   1.103 +  (> y x))
   1.104 +
   1.105 +(defmethod < nary-type
   1.106 +  [x y & more]
   1.107 +  (if (< x y)
   1.108 +    (if (next more)
   1.109 +      (recur y (first more) (next more))
   1.110 +      (< y (first more)))
   1.111 +    false))
   1.112 +
   1.113 +;
   1.114 +; Greater-or-equal defaults to (complement <)
   1.115 +;
   1.116 +(defmulti >=
   1.117 +  "Return true if each argument is larger than or equal to the following
   1.118 +   ones. The minimal implementation for type ::my-type is the binary form
   1.119 +   with dispatch value [::my-type ::my-type]. A default implementation
   1.120 +   is provided in terms of <."
   1.121 +  {:arglists '([x] [x y] [x y & more])}
   1.122 +  nary-dispatch)
   1.123 +
   1.124 +(defmethod >= root-type
   1.125 +  [x] true)
   1.126 +
   1.127 +(defmethod >= [root-type root-type]
   1.128 +  [x y]
   1.129 +  (not (< x y)))
   1.130 +
   1.131 +(defmethod >= nary-type
   1.132 +  [x y & more]
   1.133 +  (if (>= x y)
   1.134 +    (if (next more)
   1.135 +      (recur y (first more) (next more))
   1.136 +      (>= y (first more)))
   1.137 +    false))
   1.138 +
   1.139 +;
   1.140 +; Less-than defaults to (complement >)
   1.141 +;
   1.142 +(defmulti <=
   1.143 +  "Return true if each arguments is smaller than or equal to the following
   1.144 +   ones. The minimal implementation for type ::my-type is the binary form
   1.145 +   with dispatch value [::my-type ::my-type]. A default implementation
   1.146 +   is provided in terms of >."
   1.147 +  {:arglists '([x] [x y] [x y & more])}
   1.148 +  nary-dispatch)
   1.149 +
   1.150 +(defmethod <= root-type
   1.151 +  [x] true)
   1.152 +
   1.153 +(defmethod <= [root-type root-type]
   1.154 +  [x y]
   1.155 +  (not (> x y)))
   1.156 +
   1.157 +(defmethod <= nary-type
   1.158 +  [x y & more]
   1.159 +  (if (<= x y)
   1.160 +    (if (next more)
   1.161 +      (recur y (first more) (next more))
   1.162 +      (<= y (first more)))
   1.163 +    false))
   1.164 +
   1.165 +;
   1.166 +; Implementations for Clojure's built-in types
   1.167 +;
   1.168 +(defmethod zero? java.lang.Number
   1.169 +  [x]
   1.170 +  (clojure.core/zero? x))
   1.171 +
   1.172 +(defmethod pos? java.lang.Number
   1.173 +  [x]
   1.174 +  (clojure.core/pos? x))
   1.175 +
   1.176 +(defmethod neg? java.lang.Number
   1.177 +  [x]
   1.178 +  (clojure.core/neg? x))
   1.179 +
   1.180 +(defmethod = [Object Object]
   1.181 +  [x y]
   1.182 +  (clojure.core/= x y))
   1.183 +
   1.184 +(defmethod > [java.lang.Number java.lang.Number]
   1.185 +  [x y]
   1.186 +  (clojure.core/> x y))
   1.187 +
   1.188 +(defmethod < [java.lang.Number java.lang.Number]
   1.189 +  [x y]
   1.190 +  (clojure.core/< x y))
   1.191 +
   1.192 +(defmethod >= [java.lang.Number java.lang.Number]
   1.193 +  [x y]
   1.194 +  (clojure.core/>= x y))
   1.195 +
   1.196 +(defmethod <= [java.lang.Number java.lang.Number]
   1.197 +  [x y]
   1.198 +  (clojure.core/<= x y))
   1.199 +
   1.200 +;
   1.201 +; Functions defined in terms of the comparison operators
   1.202 +;
   1.203 +(defn max
   1.204 +  "Returns the greatest of its arguments. Like clojure.core/max except that
   1.205 +   is uses generic comparison functions implementable for any data type."
   1.206 +  ([x] x)
   1.207 +  ([x y] (if (> x y) x y))
   1.208 +  ([x y & more]
   1.209 +   (reduce max (max x y) more)))
   1.210 +
   1.211 +(defn min
   1.212 +  "Returns the least of its arguments. Like clojure.core/min except that
   1.213 +   is uses generic comparison functions implementable for any data type."
   1.214 +  ([x] x)
   1.215 +  ([x y] (if (< x y) x y))
   1.216 +  ([x y & more]
   1.217 +   (reduce min (min x y) more)))