www.delorie.com/gnu/docs/emacs-lisp-intro/emacs-lisp-intro_271.html   search  
 
Buy the book!


Programming in Emacs Lisp

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

Labelled Example Graph

Since insertions fill a buffer to the right and below point, the new graph printing function should first print the Y or vertical axis, then the body of the graph, and finally the X or horizontal axis. This sequence lays out for us the contents of the function:

  1. Set up code.

  2. Print Y axis.

  3. Print body of graph.

  4. Print X axis.

Here is an example of how a finished graph should look:

 
    10 -
                  *
                  *  *
                  *  **
                  *  ***
     5 -      *   *******
            * *** *******
            *************
          ***************
     1 - ****************
         |   |    |    |
         1   5   10   15

In this graph, both the vertical and the horizontal axes are labelled with numbers. However, in some graphs, the horizontal axis is time and would be better labelled with months, like this:

 
     5 -      *
            * ** *
            *******
          ********** **
     1 - **************
         |    ^      |
         Jan  June   Jan

Indeed, with a little thought, we can easily come up with a variety of vertical and horizontal labelling schemes. Our task could become complicated. But complications breed confusion. Rather than permit this, it is better choose a simple labelling scheme for our first effort, and to modify or replace it later.

These considerations suggest the following outline for the print-graph function:

 
(defun print-graph (numbers-list)
  "documentation..."
  (let ((height  ...
        ...))
    (print-Y-axis height ... )
    (graph-body-print numbers-list)
    (print-X-axis ... )))

We can work on each part of the print-graph function definition in turn.


  webmaster   donations   bookstore     delorie software   privacy  
  Copyright 2003   by The Free Software Foundation     Updated Jun 2003