From ca536fabbae92f389eae422c93623047719c5a3d Mon Sep 17 00:00:00 2001
From: George Thomas <georgefsthomas@gmail.com>
Date: Wed, 29 Oct 2025 11:49:50 +0000
Subject: [PATCH] Add semigroup instance for located line trails

---
 src/Diagrams/Trail.hs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Diagrams/Trail.hs b/src/Diagrams/Trail.hs
index c65fa965..0474e2dd 100644
--- a/src/Diagrams/Trail.hs
+++ b/src/Diagrams/Trail.hs
@@ -539,6 +539,11 @@ instance (Metric v, OrderedField n, Metric u, OrderedField n')
   _Snoc = _Wrapped . _Snoc . bimapping _Unwrapped id
   {-# INLINE _Snoc #-}
 
+instance (Real n, Floating n, Metric v)
+  => Semigroup (Located (Trail' Line v n)) where
+    a@(Loc aLoc aLine) <> b@(Loc _ bLine) =
+      Loc aLoc (aLine <> lineFromOffsets [atStart b .-. atEnd a] <> bLine)
+
 --------------------------------------------------
 -- Extracting segments