From 1cdbe8166aada351d479d5b7f8463af612e70ee7 Mon Sep 17 00:00:00 2001
From: Chris Jefferson <caj21@st-andrews.ac.uk>
Date: Wed, 5 May 2021 12:41:34 +0100
Subject: [PATCH] Add better error

---
 gap/GraphBacktracking.gi | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gap/GraphBacktracking.gi b/gap/GraphBacktracking.gi
index b846b5f..b0d1cea 100644
--- a/gap/GraphBacktracking.gi
+++ b/gap/GraphBacktracking.gi
@@ -75,6 +75,9 @@ InstallMethod(ApplyFilters, [IsGBState, IsTracer, IsObject],
                 return false;
             fi;
         else
+            if not IsRecord(f) then
+                ErrorNoReturn("Refiner must be a function or record: ", filters);
+            fi;
             if IsBound(f.vertlabels) then
                 # Note that this only covers the 'basic' vertices, any extended ones
                 # are handled later in 'ShiftGraph'