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interactive
This section describes how to write the interactive
form that
makes a Lisp function an interactively-callable command.
This special form declares that the function in which it appears is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares how to compute the arguments to the command when the command is called interactively.
A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect.
The interactive
form has its effect because the command loop
(actually, its subroutine call-interactively
) scans through the
function definition looking for it, before calling the function. Once
the function is called, all its body forms including the
interactive
form are executed, but at this time
interactive
simply returns nil
without even evaluating its
argument.
There are three possibilities for the argument arg-descriptor:
nil
; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
If this expression reads keyboard input (this includes using the minibuffer), keep in mind that the integer value of point or the mark before reading input may be incorrect after reading input. This is because the current buffer may be receiving subprocess output; if subprocess output arrives while the command is waiting for input, it could relocate point and the mark.
Here’s an example of what not to do:
(interactive (list (region-beginning) (region-end) (read-string "Foo: " nil 'my-history)))
Here’s how to avoid the problem, by examining point and the mark only after reading the keyboard input:
(interactive (let ((string (read-string "Foo: " nil 'my-history))) (list (region-beginning) (region-end) string)))
(interactive "bFrobnicate buffer: ")
The code letter ‘b’ says to read the name of an existing buffer, with completion. The buffer name is the sole argument passed to the command. The rest of the string is a prompt.
If there is a newline character in the string, it terminates the prompt. If the string does not end there, then the rest of the string should contain another code character and prompt, specifying another argument. You can specify any number of arguments in this way.
The prompt string can use ‘%’ to include previous argument values
(starting with the first argument) in the prompt. This is done using
format
(see Formatting Strings). For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If the first character in the string is ‘*’, then an error is signaled if the buffer is read-only.
If the first character in the string is ‘@’, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run.
If the first character in the string is ‘_’, then this command will
not cause the region to be deactivated when it completes; that is,
zmacs-region-stays
will be set to t
when the command exits
successfully.
You can use ‘*’, ‘@’, and ‘_’ together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not ‘*’, ‘@’, or ‘_’).
This function retrieves the interactive specification of function,
which may be any funcallable object. The specification will be returned
as the list of the symbol interactive
and the specs. If
function is not interactive, nil
will be returned.
Next: Interactive Codes, Previous: Defining Commands, Up: Defining Commands [Contents][Index]