When you have a series of similar questions to ask, such as "Do you
want to save this buffer" for each buffer in turn, you should use
map-y-or-n-p to ask the collection of questions, rather than
asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at
once.
The value of list specifies the objects to ask questions about.
It should be either a list of objects or a generator function. If it is
a function, it should expect no arguments, and should return either the
next object to ask about, or nil meaning stop asking questions.
The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)
where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument
(the next object to ask about) and should return the question text. If
the value is a string, that is the question to ask the user. The
function can also return t meaning do act on this object (and
don't ask the user), or nil meaning ignore this object (and don't
ask the user).
The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)
where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is ("object"
"objects" "act on").
Each time a question is asked, the user may enter y, Y, or
SPC to act on that object; n, N, or DEL to skip
that object; ! to act on all following objects; ESC or
q to exit (skip all following objects); . (period) to act on
the current object and then exit; or C-h to get help. These are
the same answers that query-replace accepts. The keymap
query-replace-map defines their meaning for map-y-or-n-p
as well as for query-replace; see section Search and Replace.
You can use action-alist to specify additional possible answers
and what they mean. It is an alist of elements of the form
(char function help), each of which defines one
additional answer. In this element, char is a character (the
answer); function is a function of one argument (an object from
list); help is a string.
When the user responds with char, map-y-or-n-p calls
function. If it returns non-nil, the object is considered
"acted upon", and map-y-or-n-p advances to the next object in
list. If it returns nil, the prompt is repeated for the
same object.
If map-y-or-n-p is called in a command that was invoked using the
mouse--more precisely, if last-nonmenu-event (see section Information from the Command Loop) is either nil or a list--then it uses a dialog box
or pop-up menu to ask the question. In this case, it does not use
keyboard input or the echo area. You can force use of the mouse or use
of keyboard input by binding last-nonmenu-event to a suitable
value around the call.
The return value of map-y-or-n-p is the number of objects acted on.
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