From acb2b216edc7e2527d4da5c6c8dd8c5907369d41 Mon Sep 17 00:00:00 2001
From: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>
Date: Thu, 15 Nov 2012 19:33:47 -0800
Subject: [PATCH] CLJ-99: Make min-key and max-key evaluate k on each argument
 at most once

Previous versions of these functions evaluated k on most argument
twice if there were 3 or more.
---
 src/clj/clojure/core.clj                      | 20 ++++++++++++++++++--
 test/clojure/test_clojure/other_functions.clj |  9 +++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/clj/clojure/core.clj b/src/clj/clojure/core.clj
index 985532a..4bc5e26 100644
--- a/src/clj/clojure/core.clj
+++ b/src/clj/clojure/core.clj
@@ -4500,7 +4500,15 @@
   ([k x] x)
   ([k x y] (if (> (k x) (k y)) x y))
   ([k x y & more]
-   (reduce1 #(max-key k %1 %2) (max-key k x y) more)))
+   (let [kx (k x) ky (k y)
+         [v kv] (if (> kx ky) [x kx] [y ky])]
+     (loop [v v kv kv more more]
+       (if-let [w (first more)]
+         (let [kw (k w)]
+           (if (> kw kv)
+             (recur w kw (next more))
+             (recur v kv (next more))))
+         v)))))
 
 (defn min-key
   "Returns the x for which (k x), a number, is least."
@@ -4509,7 +4517,15 @@
   ([k x] x)
   ([k x y] (if (< (k x) (k y)) x y))
   ([k x y & more]
-   (reduce1 #(min-key k %1 %2) (min-key k x y) more)))
+   (let [kx (k x) ky (k y)
+         [v kv] (if (< kx ky) [x kx] [y ky])]
+     (loop [v v kv kv more more]
+       (if-let [w (first more)]
+         (let [kw (k w)]
+           (if (< kw kv)
+             (recur w kw (next more))
+             (recur v kv (next more))))
+         v)))))
 
 (defn distinct
   "Returns a lazy sequence of the elements of coll with duplicates removed"
diff --git a/test/clojure/test_clojure/other_functions.clj b/test/clojure/test_clojure/other_functions.clj
index c23e599..688224b 100644
--- a/test/clojure/test_clojure/other_functions.clj
+++ b/test/clojure/test_clojure/other_functions.clj
@@ -328,6 +328,15 @@
                  (apply (apply some-fn (repeat i (comp not boolean))) (range i))))
                  true))))
 
+
+(deftest test-max-min-key
+  (are [k coll min-item max-item] (and (= min-item (apply min-key k coll))
+                                       (= max-item (apply max-key k coll)))
+       count ["longest" "a" "xy" "foo" "bar"] "a" "longest"
+       - [5 10 15 20 25] 25 5
+       #(if (neg? %) (- %) %) [-2 -1 0 1 2 3 4] 0 4))
+
+
 ; Printing
 ; pr prn print println newline
 ; pr-str prn-str print-str println-str [with-out-str (vars.clj)]
-- 
1.8.0