Help of interactive ::
interactive is a special form.
(interactive ARGS)
Specify a way of parsing arguments for interactive use of a function.
For example, write
(defun foo (arg) "Doc string" (interactive "p") ...use arg...)
to make ARG be the prefix argument when `foo' is called as a command.
The "call" to `interactive' is actually a declaration rather than a function;
it tells `call-interactively' how to read arguments
to pass to the function.
When actually called, `interactive' just returns nil.
The argument of `interactive' is usually a string containing a code letter
followed by a prompt. (Some code letters do not use I/O to get
the argument and do not need prompts.) To prompt for multiple arguments,
give a code letter, its prompt, a newline, and another code letter, etc.
Prompts are passed to format, and may use % escapes to print the
arguments that have already been read.
If the argument is not a string, it is evaluated to get a list of
arguments to pass to the function.
Just `(interactive)' means pass no args when calling interactively.
Code letters available are:
a -- Function name: symbol with a function definition.
b -- Name of existing buffer.
B -- Name of buffer, possibly nonexistent.
c -- Character (no input method is used).
C -- Command name: symbol with interactive function definition.
d -- Value of point as number. Does not do I/O.
D -- Directory name.
e -- Parametrized event (i.e., one that's a list) that invoked this command.
If used more than once, the Nth `e' returns the Nth parameterized event.
This skips events that are integers or symbols.
f -- Existing file name.
F -- Possibly nonexistent file name.
i -- Ignored, i.e. always nil. Does not do I/O.
k -- Key sequence (downcase the last event if needed to get a definition).
K -- Key sequence to be redefined (do not downcase the last event).
m -- Value of mark as number. Does not do I/O.
M -- Any string. Inherits the current input method.
n -- Number read using minibuffer.
N -- Raw prefix arg, or if none, do like code `n'.
p -- Prefix arg converted to number. Does not do I/O.
P -- Prefix arg in raw form. Does not do I/O.
r -- Region: point and mark as 2 numeric args, smallest first. Does no I/O.
s -- Any string. Does not inherit the current input method.
S -- Any symbol.
v -- Variable name: symbol that is user-variable-p.
x -- Lisp expression read but not evaluated.
X -- Lisp expression read and evaluated.
z -- Coding system.
Z -- Coding system, nil if no prefix arg.
In addition, if the string begins with `*'
then an error is signaled if the buffer is read-only.
This happens before reading any arguments.
If the string begins with `@', then Emacs searches the key sequence
which invoked the command for its first mouse click (or any other
event which specifies a window), and selects that window before
reading any arguments. You may use both `@' and `*'; they are
processed in the order that they appear.