CSC151.01 2015S, Class 17: Homogeneous Lists
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_Overview_

* Preliminaries.
    * Admin.
    * Upcoming Work.
    * Extra Credit.
    * Questions.
* Discuss `irgb-anti-redder`
* Lab.
* Debrief.

Preliminaries
-------------

### Admin

* Continue partners!
* Friday the 13th falls on Friday next month.  Be careful.
* *Exam 1 to be returned today*.  
    * I do not report averages or ranges or other statistics.  You know
      what your grade means, there's no reason to hear the rest.
    * I recommend that you do not discuss your grade with a classmate.
      You can ask about solutions to problems, but there is no benefit
      to discussing what grade you got.
    * **Do not post solutions anywhere.**
    * Note that if you got under 70 before TMTL, I will fill in an APR for 
      you.  The APR serves as a note to your adviser and to academic
      advising that you are having difficulty.  If you needed TMTL, then
      please talk to me and Prof. Weinman about getting an individual
      or small-group tutor.  (Also please come see me today or next week.)
    * Some cover sheets are missing.  I'll need some help identifying
      your exams.  Random numbers (easy) or code (harder) will work.
    * Notes on the exam distributed via email.  Please do not share.
* Tomorrow, you will have the choice whether or not to have a partner
  for the homework.  One set of placement cards will be "no partner".
  One will be "with partner".  I need an estimate of how many people
  want to work alone.  (This time, your eyes, rather than mine, are
  closed.)
  
### Upcoming Work

* [Homework 4](../assignments/assignment.04.html).
    * Due TONIGHT at 10:30 p.m.
* NO Lab writeup for today.
* Readings for Wednesday:
    * [The GNU Image-Manipulation Program](../readings/gimp-reading.html)
    * [Programming with GIMP Tools](../readings/gimp-tools-reading.html)

### Extra Credit Opportunities

#### Academic 

* 4:15 today, Mindset and Academics, JRC 101.
* Pioneer Diversity Council Diversity Dialogue, 8:30 p.m. 19th, Main Quad
  "Academic Athletes and Academic Students".
* Any two talks from TEDx Grinnell, February 21, 1-5 pm.  Live stream at 
  <http://tedxgrinnell.com>.

#### Peer Support (Afternoon Section)

* Men's Basketball vs. Knox, Wednesday at 7:30 p.m., New Darby
* Spring new year event, Feb. 21 5:30-7:30 in Harris

### Other Good Things

* Women's Basketball vs. Knox on Wednesday.
* Host a prospie!

### Questions

Discuss `irgb-anti-redder`
--------------------------

Write a function, that for colors not at the extremes, inverts the
`irgb-redder` operation.  Assume that I might make slight changes
to `irgb-redder` (and the rest).

* One solution: apply `irgb-bluer` then `irgb-greener` then `irgb-darker`
  twice.  We know that the first two add 32 to individual components, 
  and the last two subtract 16 for each.
        (define irgb-anti-redder (o irgb-darker irgb-darker irgb-greener irgb-bluer))
* What if we didn't know the details of each of these procedures?
* Idea: use `irgb-complement`.
        (define irgb-anti-redder-2 (o irgb-complement irgb-redder irgb-complement))
* Alternate approach: Use a lambda
        (define irgb-anti-redder-3
          (lambda (color)
            (irgb (- (irgb-red color) 32)
                  (irgb-green color)
                  (irgb-blue color))))

Lab
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Debrief
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