CSC151.01 2006F, Class 04: Beginning Scheme

Admin:
* Homework: Read "Symbolic Values in Scheme" and "Lists in Scheme"
* Today will mix lecture, lab, and a bit of discussion.
* A note on homework 2: CITE YOUR PARTNER.
* When you don't finish a lab in class, please come back in the 
  evening to complete it.
* When you finish early, work on the extra problems.
* Speed on labs does not predict success in course.
* Second-year students: Don't forget the "Sophomore" events tomorrow.

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

/About Programming Languages/

* We do algorithms
* We express them in a formal language (aka "programming language")
* Why?
  * English can be ambiguous
    * Times flies like an arrow
    * Fruit flies like a banana
  * Therefore we need something unambiguous
    * To express things to the computer
    * To express things to each other
* In this class, we use Scheme
* Two rules for writing Scheme "sentences" (aka "expressions", "programs")
  * Parenthesize (almost) everything
  * Prefix: Put operations first
  * Perfection: If the smallest thing is incorrect, everything is wrong.  Ha ha!

/Where Does Scheme Come From (and Do We Care?)/

* Scheme evolved from LISP
  * Developed in the late 1950's at MIT to do AI research
  * Belief "knowledge is symbolic" "knowledge represented as collections"
  * Evidence that some success of LISP by accident
  * But survives today

/Reflective Questions and Comments/

* Why do you verify that an answer is correct?  What if I'm so untrustworthy
  that I've given you software that intentionally gives incorrect answers.
  What if Noyce's death led to a lack of quality control at Intel, so that
  some of the chips in these computers are flawed?
  * And yes, the latter is true.
* This will be a question we ask you regularly.
* How did you verify that the difference was correct?

* Why are the default behaviors for zero-parameter + and * different?
* Why are the default behaviors for one-parameters + and - different?
* Why are the default behaviors for one-parameters * and / different?

* Observation: The thing immediately after the parens is treated as a
  procedure.  Hence, Scheme hates
  (4)
  (-5)
  (dozen)

* Strive for readability