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19/08/2009

End of the rainbow

If you use Safari, the following code may look intriguingly multi-coloured.

 (define (add-columns table-name new-column-list (value nil))
 ;; @syntax (add-columns table-name new-column-list value)
 ;; Add more columns to table (and every row in table).
 ;; You can provide a default value for them.
 ;; (add-columns 'elements '(Price Postage) 0)
     (letex ((table table-name))
         (let ((columns (first table)))
              ; mustn't duplicate columns
              (if (empty? (intersect new-column-list columns))
                  (setf table
                      (cons (append columns new-column-list)
                          (map  (fn (r) 
                                   (append r (dup value (length new-column-list)))) 
                                (rest table))))))))

Let me know if you can work out what's going on, and what you think.

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