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(emacs-lisp-intro.info)recursive-graph-body-print

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The `recursive-graph-body-print' Function
=========================================

   The `graph-body-print' function may also be written recursively.
The recursive solution is divided into two parts: an outside `wrapper'
that uses a `let' expression to determine the values of several
variables that need only be found once, such as the maximum height of
the graph, and an inside function that is called recursively to print
the graph.

   The `wrapper' is uncomplicated:

     (defun recursive-graph-body-print (numbers-list)
       "Print a bar graph of the NUMBERS-LIST.
     The numbers-list consists of the Y-axis values."
       (let ((height (apply 'max numbers-list))
             (symbol-width (length graph-blank))
             from-position)
         (recursive-graph-body-print-internal
          numbers-list
          height
          symbol-width)))

   The recursive function is a little more difficult.  It has four
parts: the `do-again-test', the printing code, the recursive call, and
the `next-step-expression'.  The `do-again-test' is an `if' expression
that determines whether the `numbers-list' contains any remaining
elements; if it does, the function prints one column of the graph using
the printing code and calls itself again.  The function calls itself
again according to the value produced by the `next-step-expression'
which causes the call to act on a shorter version of the `numbers-list'.

     (defun recursive-graph-body-print-internal
       (numbers-list height symbol-width)
       "Print a bar graph.
     Used within recursive-graph-body-print function."
     
       (if numbers-list
           (progn
             (setq from-position (point))
             (insert-rectangle
              (column-of-graph height (car numbers-list)))
             (goto-char from-position)
             (forward-char symbol-width)
             (sit-for 0)     ; Draw graph column by column.
             (recursive-graph-body-print-internal
              (cdr numbers-list) height symbol-width))))

   After installation, this expression can be tested; here is a sample:

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

   Here is what `recursive-graph-body-print' produces:

                     *
                    **   *
                   ****  *
                   **** ***
                 * *********
                 ************
                 *************

   Either of these two functions, `graph-body-print' or
`recursive-graph-body-print', create the body of a graph.