accumulators: new range accumulator

2 files changed, 42 insertions, 1 deletions

diff --git a/src/clojure/contrib/accumulators.clj b/src/clojure/contrib/accumulators.clj
index 9fe140a7..65821976 100644
--- a/src/clojure/contrib/accumulators.clj
+++ b/src/clojure/contrib/accumulators.clj
@@ -1,7 +1,7 @@
 ;; Accumulators
 
 ;; by Konrad Hinsen
-;; last updated February 12, 2009
+;; last updated February 13, 2009
 
 ;; This module defines various accumulators (list, vector, map,
 ;; sum, product, counter, and combinations thereof) with a common
@@ -179,6 +179,32 @@
   "An empty minimum accumulator. Only numbers can be added.")
 
 ;
+; Numeric range accumulator
+; (combination of minimum and maximum)
+;
+(let [range-tag {::accumulator ::range}]
+  (defn- make-range
+    [min max]
+    (with-meta {:minimum min :maximum max} range-tag)))
+
+(defvar empty-range (make-range nil nil)
+  "An empty range accumulator, combining minimum and maximum.
+   Only numbers can be added.")
+
+(defmethod combine ::range
+  [& vs]
+  (let [total-min (apply min (map :minimum vs))
+	total-max (apply max (map :maximum vs))]
+    (make-range total-min total-max)))
+
+(defmethod add ::range
+  [v e]
+  (let [{min-v :minimum max-v :maximum} v
+	new-min (if (nil? min-v) e (min min-v e))
+	new-max (if (nil? max-v) e (max max-v e))]
+    (make-range new-min new-max)))
+
+;
 ; Counter accumulator
 ;
 (defvar empty-counter (with-meta {} {::accumulator ::counter})
diff --git a/src/clojure/contrib/accumulators/examples.clj b/src/clojure/contrib/accumulators/examples.clj
index a3d7b026..ee0727e9 100644
--- a/src/clojure/contrib/accumulators/examples.clj
+++ b/src/clojure/contrib/accumulators/examples.clj
@@ -53,6 +53,21 @@
       p2 (add-items empty-product [(/ 1 2)])]
   (combine p1 p2))
 
+; Maximum accumulator: combine is max
+(let [m1 (add-items empty-maximum [2 3])
+      m2 (add-items empty-maximum [(/ 1 2)])]
+  (combine m1 m2))
+
+; Minimum accumulator: combine is min
+(let [m1 (add-items empty-minimum [2 3])
+      m2 (add-items empty-minimum [(/ 1 2)])]
+  (combine m1 m2))
+
+; Range accumulator: combination of minimum and maximum
+(let [m1 (add-items empty-range [2 3])
+      m2 (add-items empty-range [(/ 1 2)])]
+  (combine m1 m2))
+
 ; String accumulator: combine is concatenation
 (combine "a" "b" "c" "def")
 (add "a" (char 44))