CSC151.01 2007S, Class 04: Beginning Scheme

Admin:
* Due: HW 2
* Please do not address me in the generic
* How Extra Credit works:
  * At the end of the semester, Sam distributes checklist
  * Students check off appropriate boxes
  * Sam counts
* Last-minute recommendations ate my Thursday.  
  Expect responses to HW1 and HW2 over the weekend.
* There are two readings for Monday: 
  * Symbolic values in Scheme
  * Lists in Scheme
* HW3 is now ready.

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

/About programming languages/

* We are writing algorithms in this weird that doesn't look like
  English (or math or ...)
* Algorirthms for the computer (i.e., programs) are ALWAYS written
  in an artificial language
* Artificial languages can be simpler
  * Easier to make the computer understand them - Easier to translate
    them to a language the computer does understand
  * Less likely to be ambiguous
* Artificial languages can be more precise
* Term for figuring out structure of a statement (English, Computer
  language, whatever): "Parse"
  * Time flies like an arrow
  * Fruit flies like a banana
* Artificial languages let us solve these problems
* Artificial languages are also easier to teach

/Scheme: A Simple Programming Language with a Weird Syntax/
* Primary grammatical structure: "Evaluate a function on arguments"
  * Open paren (
  * Name of the function +
  * Arguments, separated by spaces 3 4
  * Close paren
  (+ 3 4)
* Implications:
  * An open paren tells Scheme "Look for a function to come next"
    ((+ 3 4))
  * When you want to apply a function, you need an open paren

/Scheme's History/
* Based on LISP, designed in 1959 as an AI language
* Improved in the 1970s into Scheme for *teaching*
  * And with a clearer set of meanings

/Lab!/

* Why is (+) 0 and (*) 1?
* What does - do?