03/04: Fix chunk-for-each! calling proc when there's nothing to do

[Christopher Baines]

cbaines pushed a commit to branch master
in repository data-service.

commit 5a1b6d41eb35711ef89531e0cbd73dd7223419ec
Author: Christopher Baines <mail@cbaines.net>
AuthorDate: Fri Jan 14 15:25:35 2022 +0000

    Fix chunk-for-each! calling proc when there's nothing to do
---
 guix-data-service/utils.scm | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/guix-data-service/utils.scm b/guix-data-service/utils.scm
index 14721b1..0250e42 100644
--- a/guix-data-service/utils.scm
+++ b/guix-data-service/utils.scm
@@ -195,9 +195,11 @@
            (map cdr chunks-and-rest)))
         (apply proc lsts)))
 
-  (unless (eq? 1
-               (length (delete-duplicates
-                        (map length lsts))))
-    (error "lists not equal length"))
+  (let ((list-lengths (map length lsts)))
+    (unless (eq? 1 (length (delete-duplicates list-lengths)))
+      (error "lists not equal length"))
 
-  (do-one-iteration lsts))
+    (unless (eq? 0 (first list-lengths))
+      (do-one-iteration lsts)))
+
+  #t)