Info Catalog eintr: Interactive eintr: Writing Defuns eintr: Permanent Installation

eintr: Interactive Options

 
 3.4 Different Options for ‘interactive’
 =======================================
 
 In the example, ‘multiply-by-seven’ used ‘"p"’ as the argument to
 ‘interactive’.  This argument told Emacs to interpret your typing either
 ‘C-u’ followed by a number or <META> followed by a number as a command
 to pass that number to the function as its argument.  Emacs has more
 than twenty characters predefined for use with ‘interactive’.  In almost
 every case, one of these options will enable you to pass the right
 information interactively to a function.  (Code Characters for
 ‘interactive’ (elisp)Interactive Codes.)
 
    Consider the function ‘zap-to-char’.  Its interactive expression is
 
      (interactive "p\ncZap to char: ")
 
    The first part of the argument to ‘interactive’ is ‘p’, with which
 you are already familiar.  This argument tells Emacs to interpret a
 prefix, as a number to be passed to the function.  You can specify a
 prefix either by typing ‘C-u’ followed by a number or by typing <META>
 followed by a number.  The prefix is the number of specified characters.
 Thus, if your prefix is three and the specified character is ‘x’, then
 you will delete all the text up to and including the third next ‘x’.  If
 you do not set a prefix, then you delete all the text up to and
 including the specified character, but no more.
 
    The ‘c’ tells the function the name of the character to which to
 delete.
 
    More formally, a function with two or more arguments can have
 information passed to each argument by adding parts to the string that
 follows ‘interactive’.  When you do this, the information is passed to
 each argument in the same order it is specified in the ‘interactive’
 list.  In the string, each part is separated from the next part by a
 ‘\n’, which is a newline.  For example, you can follow ‘p’ with a ‘\n’
 and an ‘cZap to char: ’.  This causes Emacs to pass the value of the
 prefix argument (if there is one) and the character.
 
    In this case, the function definition looks like the following, where
 ‘arg’ and ‘char’ are the symbols to which ‘interactive’ binds the prefix
 argument and the specified character:
 
      (defun NAME-OF-FUNCTION (arg char)
        "DOCUMENTATION..."
        (interactive "p\ncZap to char: ")
        BODY-OF-FUNCTION...)
 
 (The space after the colon in the prompt makes it look better when you
 are prompted.  The Definition of ‘copy-to-buffer’ copy-to-buffer,
 for an example.)
 
    When a function does not take arguments, ‘interactive’ does not
 require any.  Such a function contains the simple expression
 ‘(interactive)’.  The ‘mark-whole-buffer’ function is like this.
 
    Alternatively, if the special letter-codes are not right for your
 application, you can pass your own arguments to ‘interactive’ as a list.
 
    The Definition of ‘append-to-buffer’ append-to-buffer, for an
 example.  Using ‘Interactive’ (elisp)Using Interactive, for a
 more complete explanation about this technique.
 

Info Catalog eintr: Interactive eintr: Writing Defuns eintr: Permanent Installation