Statistics 540: Code separate from data

Announcement

• HW issues?

lecture

get the picture?

• In the beginning:
  • code on heavy trays
  • data in lights and tubes
  • life was good, but backs were sore

• The fall from grace--the loadable program
  • makes data look just like code
  • consider the following program:
    • loop: i = i + 1
    • total = total + a[i]
    • goto loop

  • it works, but why? It is self modifying code
    • i stored here
    • loop: i = i + 1
    • total = total + a[i]
    • goto loop

  • when i overflows the i = i + 1 command polymorfs into a "goto" which jumps to the value of the instruction total=total+a[i]. Like wow!

• Fast forward: modern equivalent is a global variable
  • a = sort(b)
  • increasing or decreasing?
  • check a global maybe?
  • yikes!
  • Too ugly to even consider? Look at most operating systems code

• Solutions 1: outlaw it
  • functional programming
  • some mroe pure than others
  • remimber: lisp was the orginal functional programming language and was loved since you could write programs that wrote programs!
  • so it takes some careful control

• solution 2: ignore it
  • leads to microsoft(r) viruses
  • a word(r) file shouldn't be able to be a program!

• solution 3: control it
  • object orented programming
  • read chapters 10 and 11

Last modified: Tue Nov 6 08:52:11 2001