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;; Generic interfaces for arithmetic operations
;; by Konrad Hinsen
;; last updated March 12, 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.arithmetic
"Generic arithmetic interface
NOTE: This library is VERY experimental. It WILL change significantly
with future release.
This library defines generic versions of + - * / as multimethods
that can be defined for any type. The minimal required implementations
for a type are binary + and * plus unary - and /. Everything else
is derived from these automatically. Explicit binary definitions
for - and / can be given for efficiency reasons."
(:refer-clojure :exclude [+ - * /]))
;
; A dispatch function that separates nulary, unary, binary, and
; higher arity calls and also selects on type for unary and binary
; calls.
;
(defn- nary-dispatch
([] ::nulary)
([x] [::unary (type x)])
([x y]
(let [tx (type x)
ty (type y)]
(cond (isa? tx ty) [::binary ty]
(isa? ty tx) [::binary tx]
; Should there be clause checking if tx and ty have
; a common ancestor? This would cover cases like
; java.lang.Integer and java.lang.Double, which have the
; common ancestor java.lang.Number.
:else [::binary tx ty])))
([x y & more] ::n-ary))
;
; We can't use [::binary :default], so we need to define a root type
; of the type hierarcy. The derivation for Object covers all classes,
; but all non-class types will need an explicit derive clause.
; Ultimately, a macro might take care of this.
;
(derive Object ::any)
;
; Addition
;
; The minimal implementation is for [::binary my-type]. It is possible
; in principle to implement [::unary my-type] as well, though this
; doesn't make any sense.
;
(defmulti + nary-dispatch)
(defmethod + ::nulary
[]
::zero)
(defmethod + [::unary ::any]
[x] x)
(defmethod + ::n-ary
[x y & more]
(if more
(recur (+ x y) (first more) (next more))
(+ x y)))
;
; Subtraction
;
; The minimal implementation is for [::unary my-type]. A default binary
; implementation is provided as (+ x (- y)), but it is possible to
; implement [::unary my-type] explicitly for efficiency reasons.
;
(defmulti - nary-dispatch)
(defmethod - ::nulary
[]
(throw (java.lang.IllegalArgumentException.
"Wrong number of arguments passed")))
(defmethod - [::binary ::any]
[x y] (+ x (- y)))
(defmethod - ::n-ary
[x y & more]
(if more
(recur (- x y) (first more) (next more))
(- x y)))
;
; Multiplication
;
; The minimal implementation is for [::binary my-type]. It is possible
; in principle to implement [::unary my-type] as well, though this
; doesn't make any sense.
;
(defmulti * nary-dispatch)
(defmethod * ::nulary
[]
::one)
(defmethod * [::unary ::any]
[x] x)
(defmethod * ::n-ary
[x y & more]
(if more
(recur (* x y) (first more) (next more))
(* x y)))
;
; Division
;
; The minimal implementation is for [::unary my-type]. A default binary
; implementation is provided as (* x (/ y)), but it is possible to
; implement [::unary my-type] explicitly for efficiency reasons.
;
(defmulti / nary-dispatch)
(defmethod / ::nulary
[]
(throw (java.lang.IllegalArgumentException.
"Wrong number of arguments passed")))
(defmethod / [::binary ::any]
[x y] (* x (/ y)))
(defmethod / ::n-ary
[x y & more]
(if more
(recur (/ x y) (first more) (next more))
(/ x y)))
;
; Minimal implementations for java.lang.Number
;
(defmethod + [::binary java.lang.Number]
[x y] (clojure.core/+ x y))
(defmethod - [::unary java.lang.Number]
[x] (clojure.core/- x))
(defmethod * [::binary java.lang.Number]
[x y] (clojure.core/* x y))
(defmethod / [::unary java.lang.Number]
[x] (clojure.core// x))
|
