Define an Element instance for matching on the left.

2024-11-29 11:02:26 +03:00 · 2019-09-23 15:02:17 -04:00 · 2019-09-23 15:02:17 -04:00 · 4199011b42
commit 4199011b42
parent fe76c3dca6
1 changed files with 5 additions and 0 deletions
--- 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