• Continue partners for one more day.
• No handouts!

Overview

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

Preliminaries

Admin

• We will discuss quizzes today. I will only record your quiz 2 grade if you got a 9 or 10.
• Note: You can quickly navigate a large Racket file using the (define ...) menu at the top.
• Notes on HW3:
  • Yes, you need to document the smiley procedure using the 6P format.
  • No, you don't need to document the other procedures. But it's nice if you do (or at least a short comment).
• A new format for today's class: For each topic, you'll spend two minutes talking to your partner about the issues, and then we'll talk about it together as a wohle class.

Upcoming Work

• Assignment 3.
  • Due Tuesday at 10:30 p.m.
  • Don't forget the prologue and epilogue!
• Exam 1 to be distributed on Wednesday.
• Lab writeup for lab 8 (today), due Wednesday: Document the rectangle procedure from the previous lab.
  http://bit.ly/151-2015S-lab08
• Readings for Tuesday:
  • Output in Scheme
  • Basic Image Operations

Extra Credit Opportunities

Academic

• Wednesday, February 4, 12:00 noon, JRC 101, Scholars' Convication: "The Fight for Economic Justice from the Streets of Chicago" by Virginia Parks.
• Any other event in this Rosenfield symposium.
• Friday, February 6, 12:00 noon, Science 3821, CS Table, Summer Research Opportunities for CS Students
• TEDx Grinnell, sometime in February.

Peer Support (Afternoon Section)

• Swimming, Conference Championships, February 13-14-15, The Osgood. An hour is good.
• Indoor track, next Saturday, time to be announced

Recommended Events (no EC unless mentioned above)

• #OneGrinnell, Wednesday, February 4 at 4:15 p.m.

Questions

Is there a way we can know if our lab write ups are submitted or not? I am confused if my partner in the classroom submitted the writeup or not.

You should ask your partner in the classroom.

Notes on Quizzes

Quiz 1: You all had a better process for getting people to be with matching cards. Why didn't you use it?

Quiz 2, Problem 1.

(define d0 (recolor-drawing "blue" drawing-unit-square))
(define d1 (scale-drawing 30 d0))
(define d2 (hshift-drawing 20 d1))
(recolor-drawing "red" d1)
(scale-drawing 1.5 d2)
(image-show (drawing->image (drawing-group d1 d2) 50 50))

Two minutes: Discuss with partner. Then Sam has a series of questions.

How big is the image/canvas we draw?

50x50

After the first expression, (define d0 ...), what is the value of d0?

1x1 square, blue, left boundary is 0, top boundary is 0 (mostly right)

1x1 square, blue, center is at (0,0), left boundary is -0.5 and top boundary is -0.5 (correct)

How could we be more sure?

Look it up in the reading

Try it (visual will be hard, textual will be useful)

Ask someone else (e.g., a mentor or professor)

_After the second expression, (define d1 ...), what is the value of d0?

d0 does not change, so it is still 1x1 square, blue, center at (0,0)

_After the second expression, (define d1 ...), what is the value of d1?

d1 is d0 scaled by 30. 30x30 blue square, left edge at -15, top edge at -15, right edge at 15, bottom edge at 15

_After the third expression, (define d2 ...), what is the value of d0?

Doesn't change

_After the third expression, (define d2 ...), what is the value of d1?

Doesn't change

_After the third expression, (define d2 ...), what is the value of d2?

A 30x30 square, left edge at 5, top edge at -15, right edge at 35, bottom edge at 15

_What is the value of the fourth expression, (recolor-drawing "red" d1)?

A square, centered at (0,0), 30x30, colored red

After the fourth expression, what is the value of d1?

What it was before, a square, centered at (0,0), 30x30, colored blue

What is the value of the fifth expression, (scale-drawing 1.5 d2)?

d2 was a 30x30 square, centered at (20,0), left edge at 5, top edge at -15, right edge at 35, bottom edge at 15

The value is a 45x45 square, centered at (30,0), left edge at 7.5, top edge at -22.5, right edge at 52.5, bottom edge at 22.5

General principle: You can multiple any of the edges by the scale factor.

What does the final image look like?

Debrief on procedures lab

Pair programming

The need for documentation

• People won't figure out what the vocabulary means just by looking at code.
• We need to communicate meaning.
• You can create new vocabulary - every procedure you write is a piece of vocabulary.
• You need to communicate that meaning to others.
• The most important thing to communicate: What is the goal of the procedure.
• But we want to be clear to the speaker/user/client
• The 151 model: 6 P's
  • The word/name: "Procedure"
  • Inputs: "Parameters"
    • Name, Type
  • What it does/goal: "Purpose"
  • Output/result: "Produces"
    • Name, Type
  • Requirements for it to function: Preconditions
  • Formal guarantees: Postconditions

Practice

;;; Procedure:
;;;   create-neighbor
;;; Parameters:
;;;   d, a drawing
;;; Purpose: 
;;;   Create a copy of the drawing, immediately to the right
;;; Produces:
;;;   neighbor, a drawing
;;; Preconditions:
;;;   [No additional]
;;; Postconditions:
;;;   (drawing-left neighbor) = (drawing-right d)
;;;   Neighbor is the same appearance as d - same colors, shapes, etc.
;;;   (drawing-height neighbor) = (drawing-height d)
;;;   (drawing-width neighbor) = (drawing-width d)
;;;   (drawing-top neighbor) = (drawing-top d)

max, neighbor, and more.