Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Debrief on procedures lab.
• The need for documentation.
• The Six P's - a strategy for documenting procedures.
• A few additional P's.
• Practice.

Preliminaries

Admin

• New lab partners! Take a card to figure out where you work.
• New HW partners! I'll take attendance to help you figure out your partners.
  • We'll also end five minutes early.
• Today's class will mostly involve lecture/recitation.
• Please return your flash drives so that I can supply them to the other section of the class.
• Friday's quiz: Emphasis on drawings-as-values and procedures. We may also ask you to document a bit.
• Review sessions:
  • Tonight at 8:00 p.m. in the commons (Alex or Evan)
  • Tomorrow at 10:00 a.m. (Sam)
  • Tomorrow night at 7:30 p.m. (Ajuna)
• If you forget to include your name on a lab writeup or don't fill in everything you are supposed to, feel free to resubmit.

Upcoming Work

• Lab writeup (due Friday): Document the rectangle procedure from the lab on procedures. See link on schedule or list of labs for link to submit it.
• HW 3 assigned. Due next Tuesday.
  • Bring questions on Thursday or Friday.
• Readings for Friday
  • Output in Scheme
  • Basic Image Operations

Extra Credit Opportunities

Academic

• Awesome show at the Faulconer gallery.
• Convo TODAY at noon. "Limiting Armed Drone Proliferation" by Micah Zenko, the Douglas Dillon fellow in the Center for Preventive Action at the Council on Foreign Relations and vice chair of the World Economic Forum Global Agenda Council on Terrorism.
• Any other event in the Rosenfield Drones program.
• CS Extra, Thursday, September 11: Ajuna Kyaruzi '17 on being a SysAdmin (4:30 p.m., Science 3821)
• CS Table, Friday, September 12: Robots for Autistic Children (12:10 p.m., JRC 224A) (Led by students; No faculty present) Email me if you'd like the readings.

Peer Support

• Football Games (???)
• Women's Volleyball home matches (Sat 9/13 @ 2pm and 4pm and Sun 9/14 @ 11am and 1pm in Darby.)
• Men's Tennis home matches (???)
• Women's Tennis (???)
• Anna Christie, Oct. 9-12 (SB plays Marthy)
• EB presents "Electrronic Potpourri" Friday at 5pm.

Questions

• How do I resize the workspace? (Come ask me.)

Debrief on procedures lab

What are the key concepts you learned in the reading/lab?

• We can generalize a piece of code by turning it into a procedure and replacing constant values with parameters.
• Sometimes you can write a new procedure by tweaking an previous one.
  • Make sure to cite!
• To define a procedure, one writes (define NAME (PARAMS) BODY).
• We can use previously defined procedures as we write new procedures.
• Ctrl-uparrow or Escape p give you the previous thing you typed in the interactions pane.

What were the more difficult aspects of the reading/lab?

• Parenthesis
  • An open paren usually means "About to call a procedure", so only use them in that context.
  • When you want to call a procedure, don't forget the open paren.
  • If you force DrRacket to reindent, it will show you how it understands matching parenthesis. Control-I.
• What do we mean by "body" of the procedure?
  • The part of the procedure that does the calculation of what value it should return.
• Scheme doesn't always react they way we think it should.
  • (* .75 drawing)

What else would you like to know about (with regards to proc)?

• Why do we write procedures?
  • General code is useful, and makes you more efficient.
• Will we always have to write them.
  • Yes, it's central to writing algorithms.
• Not everyone can read code, shouldn't we write documentation too?
  • Of course
• Do we have to?
  • Much of the time
• When should we cite?
  • If you copy and paste code other than on a lab, from the lab text.
  • If my name is on the top of a file that you are editing, that (usually) suffices.

The need for documentation

• We need to know what the procedures we write do, not how they operate.
• When we write our own procedures, we should explain what they do (but not how).
• Documentation helps you think carefully about the procedures you are writing.

The Six P's

• Procudure - name
• Parameters - name and type
• Purpose - Short, informal
• Produces - name the output, indicate its type
• Preconditions - Formal requirements in order for the procedure to succeed.
• Postconditions - Formal specifications of the output.

Practice

    ;;; Procedure:
    ;;;   max
    ;;; Parameters:
    ;;;   x, a number
    ;;;   y, a number
    ;;; Purpose:
    ;;;   Find the greatest value in the set (x,y),
    ;;; Produces:
    ;;;   greatest, a number
    ;;; Preconditions:
    ;;;   Neither x nor y is imaginary.
    ;;; Postconditions:
    ;;;   greatest >= x
    ;;;   greatest >= y
    ;;;   greatest is one of (x,y)

    ;;; Procedure:
    ;;;   max
    ;;; Parameters:
    ;;;   x1 ... xn, two or more real numbers
    ;;; Purpose:
    ;;;   Find the greatest value in the set [x1 ... xn]
    ;;; Produces:
    ;;;   greatest, a number
    ;;; Preconditions:
    ;;;   [No additional]
    ;;; Postconditions:
    ;;;   greatest >= xi, for any i.
    ;;;   greatest is an element of [x1 ... xn]