From 4199011b42b3eba837b88167287b51d591e23567 Mon Sep 17 00:00:00 2001
From: Rob Rix <robrix@github.com>
Date: Mon, 23 Sep 2019 15:02:17 -0400
Subject: [PATCH] Define an Element instance for matching on the left.

---
 semantic-tags/src/Tags/Taggable/Precise.hs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/semantic-tags/src/Tags/Taggable/Precise.hs b/semantic-tags/src/Tags/Taggable/Precise.hs
index 387b10402..52e834f9e 100644
--- a/semantic-tags/src/Tags/Taggable/Precise.hs
+++ b/semantic-tags/src/Tags/Taggable/Precise.hs
@@ -143,3 +143,8 @@ instance {-# OVERLAPPABLE #-}
     reassoc (L1 (L1 l)) = L1 l
     reassoc (L1 (R1 l)) = R1 (L1 l)
     reassoc (R1 r)      = R1 (R1 r)
+
+instance {-# OVERLAPPABLE #-}
+         Element t (t :+: r) where
+  prj (L1 l) = Just l
+  prj _      = Nothing