Test print-graph (Programming in Emacs Lisp)

C.4.1 Testing print-graph

We can test the print-graph function with a short list of numbers:

1. Install the final versions of Y-axis-column, graph-body-print, and print-graph (in addition to the rest of the code.)
2. Copy the following expression:

   (print-graph '(3 2 5 6 7 5 3 4 6 4 3 2 1))
   

3. Switch to the *scratch* buffer and place the cursor where you want the axis labels to start.
4. Type M-: (eval-expression).
5. Yank the test expression into the minibuffer with C-y (yank).
6. Press RET to evaluate the expression.

Emacs will print a graph that looks like this:

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

On the other hand, if you pass print-graph a vertical-step value of 2, by evaluating this expression:

(print-graph '(3 2 5 6 7 5 3 4 6 4 3 2 1) 2)

The graph looks like this:

20 -
 *
 ** *
10 - **** *
 **** ***
 * *********
 ************
 2 - *************
 | | | |
 1 5 10 15

(A question: is the ‘2’ on the bottom of the vertical axis a bug or a feature? If you think it is a bug, and should be a ‘1’ instead, (or even a ‘0’), you can modify the sources.)