From 68097681c1ce912f5b3a51769ee1dcc6332b2579 Mon Sep 17 00:00:00 2001
From: Mark Barbone <mark.l.barbone@gmail.com>
Date: Sat, 24 Apr 2021 14:48:58 -0700
Subject: [PATCH] Use =>/2 in foldl/4 so it errors when the input is not a list

---
 library/apply.pl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/library/apply.pl b/library/apply.pl
index a56a7ed0f9..d4ae787596 100644
--- a/library/apply.pl
+++ b/library/apply.pl
@@ -311,8 +311,8 @@
 foldl(Goal, List, V0, V) :-
     foldl_(List, Goal, V0, V).
 
-foldl_([], _, V, V).
-foldl_([H|T], Goal, V0, V) :-
+foldl_([], _, V0, V) => V0 = V.
+foldl_([H|T], Goal, V0, V) =>
     call(Goal, H, V0, V1),
     foldl_(T, Goal, V1, V).