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Improve documentation of 'sort-subr'

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* doc/lispref/text.texi (Sorting): Clarify the meaning and use of
PREDICATE argument to 'sort-subr'.  (Bug#41706)
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Eli Zaretskii 2020-06-05 11:30:03 +03:00
parent 73749efa13
commit bf09106256
1 changed files with 9 additions and 2 deletions
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11
doc/lispref/text.texi
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@ -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}: