CSC151 2007S, Class 03: An Introduction to Scheme

Admin:
* Assignment 2 is ready and was distributed late on Saturday.
  + Originally due 10:00 a.m. Tuesday.
  + Free extension until 10:00 a.m. Wednesday.
  + Questions?
    + Circles are prefereable to squares, but squares will be accepted
* Tonight, as is the case nearly every night, there is a reading.  
  + This reading is on raster graphics.
  + It is fairly short
  + The links do not necessarily work
* I regularly offer extra credit for academic activities and activities
  in which you support classmates.
  + Thursday at 11:00: Osgood's convo
  + Thursday at 4:15: Robert Richards from UofC
  + Thursday at 4:30: John David Stone on really big numbers
  + Home cross-country meet Saturday (the only one this semester)
    + Shuttles run from ...
* Working outside these rooms
  + We'll have some instructions in about a week

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

/What is Computer Science?/

* The study of algorithms and data
* We need to express the algorithms so that the computer can understand them
* Maybe English? (French, Esperanto)
  * English, in particular, is confusing
    * Grammar and syntax are complicated
  * English tends to be ambiguous
* In order to teach the computer to understand, we'll have to teach it 
  the language, so we want a simple language
* We want to avoid ambiguity, and most "natural" languages are ambiguous
  * Time flies like an arrow
  * Fruit flies like a banana
* In response, Computer Scientists design their own languages
  * Lots and lots
  * Each with advantages and disadvantages

/Scheme - The Language we use in this course/

* Very simple syntax and model of computation
* Most computing takes the form of
  * apply functions to argumentsa
  * define our own functions
* To apply functions to arguments
  open paren
  name of the function (or just the function)
  the arguments to the function, separated by spaces
  close paren
  (+ 3 4) ; "Add three and four"
  (sqrt 10)
  (max grade1 grade2 grade3 grade4)a
* Warning! Terminology
  * function = procedure = operation
  * argument = parameter = actual

/History/

* Scheme is "old" - Based on Lisp, invented in 1958
* Scheme is a better version of Lisp
  * Resolves problems
  * Designed for teaching

/Reflection/

* Okay, quitting and restarting is a *bad* idea.  We'll work on it!
* How did you know that the square root answer was correct?
  * My calculator says so
  * The computer says so when I try to square
  * I did it by hand