From 8e6f8399ae17753e619f0e225de2fbcecfc34cf0 Mon Sep 17 00:00:00 2001
From: Richard Newman <rnewman@twinql.com>
Date: Tue, 8 Nov 2016 12:09:13 -0800
Subject: [PATCH] Add <??, a null-safe variant of <?.

---
 src/common/datomish/pair_chan.cljc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/common/datomish/pair_chan.cljc b/src/common/datomish/pair_chan.cljc
index 0c97fe88..5d40619f 100644
--- a/src/common/datomish/pair_chan.cljc
+++ b/src/common/datomish/pair_chan.cljc
@@ -71,6 +71,13 @@
      (consume-pair (cljs.core.async/<! ~pc-chan))
      (consume-pair (clojure.core.async/<! ~pc-chan))))
 
+(defmacro <??
+  "Takes from the channel if it's non-nil."
+  [pc-chan]
+  `(let [c# ~pc-chan]
+     (when c#
+       (datomish.pair-chan/<? c#))))
+
 (defn consume-pair
   "When passed a [value nil] pair, returns value. When passed a [nil error] pair,
   throws error. See also `<?`."