CSC151.02 2003F, Class 6: An Introduction to Scheme

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* Questions on homework 1.  Does anyone need a partner?
* Any general questions or concerns about the class so far?
* Reading: Symbolic values in Scheme.
* Reading: Lists in Scheme.
* Festival of the Arts and opening of Roots of Renewal this weekend.  Extra credit for attending!
* Two weeks to "Talk Like a Pirate" day.  I may make the focus of that class (and the previous day) a Web service to generate pirate-speak.  Email me objections or suggestions.
* Everyone should get a Plan.  Email accounts@grinnellplans.com and say Sam sent you.

Topics:
* Telling Scheme to do things.
* Some key Scheme operations.
* A short history of Scheme.
* DrScheme lab.
* Scheme lab.
* Reflection (if there is time).

History and Background
* More than forty years ago, "folks" (mostly Psychologists) said "Thought is algorithmic, computer can run algorithms, hence we can simulate intelligence".
* Most computer languages focused on numeric processing.
* Thought is more symbolic.
* John McCarthy (scholar at MIT) wrote a language to support this community.  He called it "LISP".  "LIst and Symbolic Processing language".
* Incredily simple syntax: Generally easy to use 
* Included this funky "lambda" thing, which he later reported he didn't really understand.
* Amazingly enough, forty years later, people still program in LISP.
* However, LISP has some significant problems, so there are dozens of variants.
* About twenty years ago, a few folks at MIT decided to re-design LISP for education.  The result is "Scheme".
* Scheme is a pretty nice teaching langauge:
  * Easy to learn (very little syntax)
  * Symbolic processing is fun
  * Built-in lists are convenient
  * Lambdas let us consider some very complex ideas

The basics of Scheme:

* Every operation in Scheme is written in more-or-less the same way.
  * open paren
  * operation
  * arguments, separated by spaces
  * close paren
* (sqrt 5)
* (+ 2 3)

Key Scheme operations:

* sqrt
* +, -, *, /
* expt

You now know enough Scheme to start today's labs.  Any questions?

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Reflection:

Observations about the laboratory manual(s):
* The DrScheme introduction is cleverly written to show two different mechansisms for giving instructions.
* The DrScheme introduction is often written "robustly"; it predicts errors and tries to recover from them.

Questions:
* What's the difference between the top and bottom panes?
* How would you know that the answer to (sqrt 843256) was correct?
* How do you write "multiply three by seven and then add 5"?
(+ (* 3 7) 5)