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(emacs-lisp-intro.info)Labelled Example

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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.