CSC151 2009F, Class 04: An Introduction to Scheme

Admin:
* Extra credit for attending any of the Rosenfield Human Rights 
  Symposium talks over the next few days.  (Jane Mayer at 4:15 today; 
  Michael Grodin at 8:00 tonight; Lynn Hunt in the convo slot tomorrow.)
* Extra credit for going on the Prairie Studies Farm Tour on Saturday.
* Extra credit for supporting your colleagues:
  * Attending Saturday's Women's soccer game, supporting Lauren
  * Attending Saturday's football game, as we have at least three football 
    players in this class.
  * Any other upcoming student performances / events / etc?
* My notes on assignment 1 (including my answers to all of your strange 
  questions) are now available.  [Link in Assignments page.]
  + This is an eboard.
  + There are at least six different ways to find the current assignment.
  + Correct = Check
  + Most of you have no background with programming.  That's fine.
  + A few of you have a lot of background.   We'll cope.
* I will go over the key concepts of today's readings and then give 
  you a chance to ask questions before you start lab.
* Reading for Friday: Programming the GIMP Tools.
* Syllabus change: We had a homework scheduled for this Friday.  
  Now we don't.
* Assignment 2 is now available.  It is due next Wednesday.
* If you don't finish today's lab, please work on it on your own before
  Friday's class.
* Questions?
  * Yes, we have a quiz on Friday
  * On paper
  * Two or three questions
  * Ten minutes (but you can keep working when I start talking)
  * On everything through today

Overview:
* Why use programming languages?
* Scheme basics.
* Scheme history.
* Lab.

Computer Science is the study of algorithms and data structures (whee!)
* We need a way to represent algorithms and describe data structures
* English is one option
  * But not a good one
* Computer scientists have designed tens of thousands of languages for
  describing algorithms and data structures
  * Most follow a combination of four basic models of computation
    * Imperative (like cookbooks)
    * Object-oriented (describe interacting and reactive objects)
    * Functional - Try to think in terms of functions that we build
      up into complex expressions
    * Declarative - Programs are collections of facts
* Languages have three key characteristics
  * Their model of comptuation (see above)
  * Their syntax: How you write programs in the language
  * Their semantics: How to determine the meaning of programs

* Why not use English
  * It's hard to parse
    * Time flies like an arrow
    * Fruit flies like a banana
  * It's ambiguious
    * John gave a rock to Joe.  I worry about him.

* At Grinnell, we start with Scheme.  Why?
  * Simplest syntax of almost any language: If you can match parens
    and understand a few simple rules, you can understand Scheme
  * Scheme has a simple definition
  * We find the functional paradigm a natural and important one
  * Screws with the minds of people with previous programming experience
  * An old language: Based on LISP, created in late 1950's.