From 46a70cb9022b0b2f381a218ab2a2ae30774df277 Mon Sep 17 00:00:00 2001
From: Doug Coleman <doug.coleman@gmail.com>
Date: Sun, 14 Aug 2022 13:31:49 -0500
Subject: [PATCH] ranges: Fix sum of empty range.

Fixes #2655
---
 core/ranges/ranges-tests.factor | 3 +++
 core/ranges/ranges.factor       | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/core/ranges/ranges-tests.factor b/core/ranges/ranges-tests.factor
index 6d4c6055ac..4506d3b15e 100644
--- a/core/ranges/ranges-tests.factor
+++ b/core/ranges/ranges-tests.factor
@@ -55,3 +55,6 @@ USING: arrays kernel math ranges sequences sets tools.test ;
 { t } [ -10 10 2 <range> [ sum ] [ >array sum ] bi = ] unit-test
 { t } [ 10 -10 -1 <range> [ sum ] [ >array sum ] bi = ] unit-test
 { t } [ 10 -10 -2 <range> [ sum ] [ >array sum ] bi = ] unit-test
+
+! Empty range
+{ 0 } [ 1 0 1 <range> sum ] unit-test
\ No newline at end of file
diff --git a/core/ranges/ranges.factor b/core/ranges/ranges.factor
index 25a3b21bd7..4aff21ec1f 100644
--- a/core/ranges/ranges.factor
+++ b/core/ranges/ranges.factor
@@ -32,7 +32,10 @@ M: range hashcode* tuple-hashcode ;
 
 INSTANCE: range immutable-sequence
 
-M: range sum [ length ] [ first ] [ last ] tri + * 2 / ;
+M: range sum
+    dup length
+    [ drop 0 ]
+    [ swap [ first-unsafe ] [ last-unsafe ] bi + * 2 / ] if-zero ;
 
 <PRIVATE
 
-- 
2.34.1