CSC151 2007S, Class 25: Recursion with Helper Procedures

* I will continue to reserve time at the start of class for any campus 
  issues you want to discuss.
  * Remember that the vast majority of those on campus are good, 
    supportive people
  * Work to focus on the positive aspects of Mary B. James

Admin:
* Are there questions on Assignment 6?
  * Typos fixed
  * (image-colorscale image dark light)
    * Write (rgb-recolor color dark light)
    * (image-variant image rgb-recolor) NOT CORRECT
      * The second parameter to image-variant is a procedure
        of ONE PARAMETER, rgb-recolor is a procedure of THREE PARAMETERS
        ONE != THREE (except mod 2)
      * Instead of rgb-recolor, use a one-parameter variant
        * Anonymous (lambda (color) (rgb-recolor color ...))
        * Named with a let
   * What would an anonymous blue-yellow procedure look like?
     (image-variant image (lambda (color) (rgb-recolor color blue yellow)))
* It looks like we're on target to distribute the next exam tomorrow.
* Reading for Wednesday: List Recursion, Revisited.
* Thursday's Thursday Extra: John Stone on Open Document Formats.

Overview:
* Delayed evaluation in recursive procedures.
* A strategy: Carry along intermediate results.
* Using recursive helpers.
* A term: Tail recursion.
* Designing recursive procedures.
* MOSTLY LAB