From d16bd380faa3099b1b5f6630a4b3215e06ac6799 Mon Sep 17 00:00:00 2001
From: Christophe Grand <christophe@cgrand.net>
Date: Thu, 8 Dec 2016 12:01:49 +0100
Subject: [PATCH] x/count can now be used as a transducing context (x/count
 xform coll). /cc @iig

---
 src/net/cgrand/xforms.clj | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/net/cgrand/xforms.clj b/src/net/cgrand/xforms.clj
index 542884a..de99f69 100644
--- a/src/net/cgrand/xforms.clj
+++ b/src/net/cgrand/xforms.clj
@@ -433,12 +433,17 @@
                  (vswap! vwacc f x))
                acc))))))))
 
-(defn count [rf]
-  (let [n (java.util.concurrent.atomic.AtomicLong.)] 
-    (fn
-      ([] (rf))
-      ([acc] (rf (unreduced (rf acc (.get n)))))
-      ([acc _] (.incrementAndGet n) acc))))
+(defn count
+  "Count the number of items. Either used directly as a transducer or invoked with two args
+   as a transducing context."
+  ([rf]
+    (let [n (java.util.concurrent.atomic.AtomicLong.)]
+      (fn
+        ([] (rf))
+        ([acc] (rf (unreduced (rf acc (.get n)))))
+        ([acc _] (.incrementAndGet n) acc))))
+  ([xform coll]
+    (transduce (comp xform count) rf/last coll)))
 
 (defn multiplex
   "Returns a transducer that runs several transducers (sepcified by xforms) in parallel.