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emacs-27 bf09106: Improve documentation of 'sort-subr'
From: |
Eli Zaretskii |
Subject: |
emacs-27 bf09106: Improve documentation of 'sort-subr' |
Date: |
Fri, 5 Jun 2020 04:31:02 -0400 (EDT) |
branch: emacs-27
commit bf09106256f9212d3162a4335c18fd2ef876066d
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>
Improve documentation of 'sort-subr'
* doc/lispref/text.texi (Sorting): Clarify the meaning and use of
PREDICATE argument to 'sort-subr'. (Bug#41706)
---
doc/lispref/text.texi | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index a14867e..0bbb0aa 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -2028,8 +2028,15 @@ non-@code{nil} value.
@end enumerate
The argument @var{predicate} is the function to use to compare keys.
-If keys are numbers, it defaults to @code{<}; otherwise it defaults to
-@code{string<}.
+It is called with two arguments, the keys to compare, and should
+return non-@code{nil} if the first key should come before the second
+in the sorting order. What exactly are the key arguments depends on
+what @var{startkeyfun} and @var{endkeyfun} return. If @var{predicate}
+is omitted or @code{nil}, it defaults to @code{<} if the keys are
+numbers, to @code{compare-buffer-substrings} if the keys are cons
+cells (whose @code{car} and @code{cdr} are start and end buffer
+positions of the key), and to @code{string<} otherwise (with keys
+assumed to be strings).
As an example of @code{sort-subr}, here is the complete function
definition for @code{sort-lines}:
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