Lecture 14 Summary, CSE 341, Spring 2004

* Forward references and danger of mutating top-level bindings
  * Can mutate bindings with set! or (at top-level) define  
  * Don't do it!
  * But it's nice to see how you can program defensively against it
    * A common idiom in imperative programming: make a local copy
    * No need to actually do this on your homework (nobody does)

* Lazy evaluation
  * A more careful consideration of when code is evaluated
  * Example: why if is not a function
  * Key idiom: Thunks
  * Key idiom: Memoization
  * Key idiom: Streams
  * Notes:
    * Thunking and memoizing is equivalent only without effects
    * Some languages make lazy evaluation of function arguments the
      default!