Details for Tuesday Morning

  Syntax: page 79--80 (prepare hand-out)

  Semantics: 
   - what are values: numbers, booleans, symbols
   - primitives computing on basic values
   - functions on values: beta-value
   - the laws of conditionals

  Examples: small and big

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  THE DESIGN RECIPE FOR STRUCTS

  Data analysis and data definition: 
  A position is (cons num (cons num empty))
  If so, introduce constructors and selectors: 
    (define (make-pos x y) (cons x (cons y empty))
    (define (pos-x a-pos) (first a-pos))
    (define (pos-y a-pos) (first (rest a-pos)))

  Compare distance-to-O with and without selectors
  Apply to (cons 3 (cons 4 empty)) and (make-pos 3 4)

RECAP: evaluate in DrS

  (/ (* 12 33) 9)
  (/ 45 9)
  5  ===> EXECUTE: must see same value printed everywhere; delta: BUG

  SYMBOLS: eq? 

ASSIGNMENTS:
  - (sqrt (+ (* 4 4) (* 3 3)))
  - (define (f x y) (sqrt (+ (* x x) (* y y)))) and (f 4 3)

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RECAP: STRUCTs (use personnel record), data-driven; wage

  (define (wage hours a-pr)
    (* hours (pr-hourly-rate a-pr)))

  Introduce make-posn for screen (upside-down)
  Play with draw-solid-disk, draw-solid-rect, etc. 
  Write down series of expressions in DEF; execute
  Draw face

ASSIGNMENTS 
  - 4.3
  - 5.12--5.14