Improved compatibility with Clojure 1.4 and lower

Engelberg · Engelberg · commit 47ac63a098b1 · 2015-03-17T20:27:46.000-07:00
Was running into problem in earlier versions where
memoize was crashing because it was receiving
inputs that weren't comparable.
diff --git a/src/main/clojure/clojure/math/combinatorics.clj b/src/main/clojure/clojure/math/combinatorics.clj
@@ -489,7 +489,7 @@ output is nth-permutation (0-based)"
 (defn- count-combinations-unmemoized
   "We need an internal version that doesn't memoize each call to count-combinations-from-frequencies
 so that we can memoize over a series of calls."
-  [items t]
+  [items t]
   (if (all-different? items)
     (n-take-k (count items) t)
     (count-combinations-from-frequencies (frequencies items) t)))
@@ -557,12 +557,12 @@ represented by freqs"
 (defn nth-combination
   "The nth element of the sequence of t-combinations of items"
   [items t n]
-  (binding [count-combinations-from-frequencies (memoize count-combinations-from-frequencies)]
-    (assert (< n (count-combinations-unmemoized items t))
-            (format "%s is too large. Input has only %s combinations."
-                    (str n) (str (count-combinations-unmemoized items t))))
-    (if (all-different? items)
-      (nth-combination-distinct items t n)
+  (assert (< n (count-combinations items t))
+          (format "%s is too large. Input has only %s combinations."
+                  (str n) (str (count-combinations-unmemoized items t))))
+  (if (all-different? items)
+    (nth-combination-distinct items t n)
+    (binding [count-combinations-from-frequencies (memoize count-combinations-from-frequencies)]
       (let [v (vec (distinct items))
             f (frequencies items),
             indices (apply concat
@@ -573,10 +573,10 @@ represented by freqs"
 
 (defn nth-subset
   [items n]
+  (assert (< n (count-subsets items))
+          (format "%s is too large. Input has only %s subsets."
+                  (str n) (str (count-subsets items))))
   (binding [count-combinations-from-frequencies (memoize count-combinations-from-frequencies)]
-    (assert (< n (count-subsets items))
-            (format "%s is too large. Input has only %s subsets."
-                    (str n) (str (count-subsets-unmemoized items))))
     (loop [size 0,
            n n]
       (let [num-combinations (count-combinations-unmemoized items size)]
