TeachScheme! 2000

 RECAP: Discuss need to think about reuse and breaking up
   problems *before* selecting a recipe. `check-guess-for-list',
   for example, treats its argument list as an atomic entity
   passed to `convert'.

  WARM UP: 
   given a list of temperatures in C, 
   determine whether they are all between 0 and 100

  LIST		  QUOTE
  [Demo in DrScheme's intermediate language]

  PROBLEM: 
   given a list of temperatures in C, 
   produce list of equivalent F temperatures

  the program produces a list, it doesn't just consume one 

  ; convert-temps : list-of-num -> list-of-num
  ; consume list of Celsius temps, produce list of equivalent Fahr
  ;    temps
  [Note: they wrote C->F in class on Monday]
   
  SORT: 
   given a list of numbers,
   produce a list of numbers with the exact same numbers, 
    but sorted in descending order
   
  DON'T FORGET: compose functions/make up helpers!!!

  AUXILIARY PROGRAMS: 
   (1) cond expressions are in-line
   (2) auxiliary programs: if they encapsulate domain knowledge
   (3) auxiliary programs: if they are required -- process arb-large data
 
  -------------------------------------------------------------------

  Structures in Lists: celestial bodies

  ;; a celestial-body is a structure
  ;;  (make-celbody name relwgt photo)
  ;; where name is a symbol, relwgt is a num, photo is a picture
  ;;  [leave picture undefined]

  define list-of-celbody

  set up template for program over celbody.  
  -- two data definitions, two templates
  -- show arrow between data definitions

  PROBLEM: LOOKUP picture of planet 
   (What happens if the lookup fails? We went with errors, but
    false would have probably been better.)