X-Git-Url: https://gitweb.factorcode.org/gitweb.cgi?p=factor.git;a=blobdiff_plain;f=core%2Franges%2Franges.factor;h=4aff21ec1f1ea9d2f3f8e040bb3a264a6c6b94e2;hp=25a3b21bd7f50e32ad76b57af0687bf09140b424;hb=46a70cb9022b0b2f381a218ab2a2ae30774df277;hpb=c03f79c73718c20ee2ab995bf67a51867a80ceb3

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