Info Catalog eintr: Effect of installation eintr: Install

eintr: Change a defun

 
 3.2.1 Change a Function Definition
 ----------------------------------
 
 If you want to change the code in ‘multiply-by-seven’, just rewrite it.
 To install the new version in place of the old one, evaluate the
 function definition again.  This is how you modify code in Emacs.  It is
 very simple.
 
    As an example, you can change the ‘multiply-by-seven’ function to add
 the number to itself seven times instead of multiplying the number by
 seven.  It produces the same answer, but by a different path.  At the
 same time, we will add a comment to the code; a comment is text that the
 Lisp interpreter ignores, but that a human reader may find useful or
 enlightening.  The comment is that this is the second version.
 
      (defun multiply-by-seven (number)       ; Second version.
        "Multiply NUMBER by seven."
        (+ number number number number number number number))
 
    The comment follows a semicolon, ‘;’.  In Lisp, everything on a line
 that follows a semicolon is a comment.  The end of the line is the end
 of the comment.  To stretch a comment over two or more lines, begin each
 line with a semicolon.
 
DONTPRINTYET     Beginning a ‘.emacs’ File Beginning init File, and *noteDONTPRINTYET     Beginning a ‘.emacs’ File Beginning init File, and 
 Comments (elisp)Comments, for more about comments.
 
    You can install this version of the ‘multiply-by-seven’ function by
 evaluating it in the same way you evaluated the first function: place
 the cursor after the last parenthesis and type ‘C-x C-e’.
 
    In summary, this is how you write code in Emacs Lisp: you write a
 function; install it; test it; and then make fixes or enhancements and
 install it again.
 

Info Catalog eintr: Effect of installation eintr: Install