From: Thomas Morgan <tlm@ziiuu.com>
Date: Thu, 12 Nov 2009 20:07:58 +0000 (+0000)
Subject: Fix `split-at-predicate' in `scm/lily-library.scm'.
X-Git-Tag: release/2.13.8-1~54
X-Git-Url: https://git.donarmstrong.com/?a=commitdiff_plain;h=caf6f697cc296afe42de14fc7296e3a27f8e1cf9;p=lilypond.git

Fix `split-at-predicate' in `scm/lily-library.scm'.

Don't make the assumption that if `(PRED previous_element element)'
is false, `(PRED element previous_element)' must be true.

Suppose we want to split `(1 2 3 5 7)' into two lists such that
the first list contains the initial consecutive integers `(1 2 3)'
and the second contains the remaining elements `(5 7)'.  We expect
`(split-at-predicate (lambda (x y) (= (- y x) 1)) '(1 2 3 5 7))'
to return `((1 2 3) . (5 7))', but in fact it returns `((1 2 3 5 7))'
because of this erroneous assumption.
---

diff --git a/scm/lily-library.scm b/scm/lily-library.scm
index 4a7973abb1..572972169f 100644
--- a/scm/lily-library.scm
+++ b/scm/lily-library.scm
@@ -362,7 +362,9 @@
   Example: (split-at-predicate < '(1 2 3 2 1)) ==> ((1 2 3) . (2 1))"
   (if (null? lst)
       (list lst)
-      (let ((i (list-index pred (cdr lst) lst)))
+      (let ((i (list-index (lambda (x y) (not (pred x y)))
+			   lst
+			   (cdr lst))))
         (if i
             (cons (take lst (1+ i)) (drop lst (1+ i)))
             (list lst)))))