From 75276855aeb99b5c580d8d69dcef6f04542ba17b Mon Sep 17 00:00:00 2001
From: Slava Pestov <slava@slava-pestovs-macbook-pro.local>
Date: Sun, 14 Jun 2009 18:22:31 -0500
Subject: [PATCH] sequences: change implementation of interleave

---
 core/sequences/sequences.factor | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/core/sequences/sequences.factor b/core/sequences/sequences.factor
index 745fe2a033..c58304de44 100755
--- a/core/sequences/sequences.factor
+++ b/core/sequences/sequences.factor
@@ -508,9 +508,11 @@ PRIVATE>
     (each-index) each-integer ; inline
 
 : interleave ( seq between quot -- )
-    swap [ drop ] [ [ 2dip call ] 2curry ] 2bi
-    [ [ 0 = ] 2dip if ] 2curry
-    each-index ; inline
+    pick empty? [ 3drop ] [
+        [ [ drop first-unsafe ] dip call ]
+        [ [ rest-slice ] 2dip [ [ call ] bi@ ] 2curry each ]
+        3bi
+    ] if ; inline
 
 : map-index ( seq quot -- newseq )
     [ dup length iota ] dip 2map ; inline