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Improve documentation of 'assoc'

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* doc/lispref/lists.texi (Association Lists):
* src/fns.c (Fassoc): Document how TESTFN is called.  (Bug#50110)
This commit is contained in:
Eli Zaretskii 2021-08-18 22:07:30 +03:00
parent 91f549becd
commit 78b427648b
2 changed files with 8 additions and 5 deletions
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10
doc/lispref/lists.texi
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@ -1557,10 +1557,12 @@ of property lists and association lists.
@defun assoc key alist &optional testfn
This function returns the first association for @var{key} in
@var{alist}, comparing @var{key} against the alist elements using
@var{testfn} if it is non-@code{nil} and @code{equal} otherwise
(@pxref{Equality Predicates}). It returns @code{nil} if no
association in @var{alist} has a @sc{car} equal to @var{key}. For
example:
@var{testfn} if it is a function, and @code{equal} otherwise
(@pxref{Equality Predicates}). If @var{testfn} is a function, it is
called with two arguments: the @sc{car} of an element from @var{alist}
and @var{key}. The function returns @code{nil} if no
association in @var{alist} has a @sc{car} equal to @var{key}, as
tested by @var{testfn}. For example:
@smallexample
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))

3
src/fns.c
View file

@ -1755,7 +1755,8 @@ DEFUN ("assoc", Fassoc, Sassoc, 2, 3, 0,
doc: /* Return non-nil if KEY is equal to the car of an element of ALIST.
The value is actually the first element of ALIST whose car equals KEY.
Equality is defined by TESTFN if non-nil or by `equal' if nil. */)
Equality is defined by the function TESTFN, defaulting to `equal'.
TESTFN is called with 2 arguments: a car of an alist element and KEY. */)
(Lisp_Object key, Lisp_Object alist, Lisp_Object testfn)
{
if (eq_comparable_value (key) && NILP (testfn))