• Continue partners/positions for one more day.
• No handouts.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Debrief on quizzes.
• 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

• Happy too-much-snow day!
• Mentor session at 7.00
• 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 (Morning Section)

• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m. This week's theme might be Songs About Summer.
• Indoor Track and Field, Saturday Afternoon.
• Swimming, Conference Championships, February 13-14-15, The Osgood

Recommended Events (no EC unless mentioned above)

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

Questions

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?

50 by 50.

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

A 1x1 square, centered at (0,0), colored blue. Left boundary is -0.5, top boundary is -0.5, right boundary is 0.5, bottom boundary is 0.5.

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

Answer 1: I don't know.

Answer 2: d0 stays the same, we're just defining a new square which is a bigger version of d0.

Answer 3: The side length of d0 becomes 30, which means that we have A 30x30 square, centered at (0,0), colored blue. Left boundary is -15.0 top boundary is -15.0, right boundary is 15.0, bottom boundary is 15.0.

How would we figure out which is correct?

Try it!

Ask someone who might know.

Read your notes (or the reading, or the reference pages, or ...)

And our conclusion is?

Answer 2 is correct.

All of the drawing manipulation procedures create a new drawing rather than modifing the existing drawing.

(define x 2)

(square x)

x

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

A 30x30 square, centered at (0,0), colored blue. Left boundary is -15.0 top boundary is -15.0, right boundary is 15.0, bottom boundary is 15.0.

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

Whatever it was before. Blue unit square, centered at (0,0).

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

Still a blue square 30x30 centered at (0,0).

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

A blue square 30x30 centered at (20,0), left boundary at 5, top boundary at -15.

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

A red square centered at (0,0), of side length 30.

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

The same thing it was before, blue square.

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

A 45x45 blue square, centered at (30,0).

What does the final image look like?

For Problem 2 on Quiz 2, you need to know that we had procedures like drawing-left, drawing-top, drawing-width.

Question for Sam: Can we change the definition of d0?

If it's defined in the definitions pane, no.

If it's defined in the interactions pane, yes.

Debrief on procedures lab

Pair programming

The need for documentation

• To use vocabulary, we need to understand/know that vocabulary.
• When you write your own procedure, you have a responsibility to give a clear definition to your reader.
• Six basic parts to a clear definition.
  • Name of procedure. ("Procedure")
  • Inputs to procedures ("Parameters")
    • Name and give the type
  • What the procedure does ("Purpose")
  • Output ("Produces")
    • Name and give the type
  • Formal definitions of what you need for the procedure to work and what the output is.

Practice

    ;;; Procedure:
    ;;;   max
    ;;; Parameters:
    ;;;   val1, real
    ;;;   val2, real
    ;;; Purpose:
    ;;;   Find the largest of val1 and val2.
    ;;; Produces:
    ;;;   larger-of-the-two, real
    ;;; Preconditions:
    ;;; Postconditions:
    ;;;   larger-of-the-two = val1 or larger-of-the-two = val2
    ;;;   larger-of-the-two >= val1
    ;;;   larger-of-the-two >= val2

    ;;; Procedure:
    ;;;   neighbor
    ;;; Parameters:
    ;;;   drawing, a drawing
    ;;; Purpose:
    ;;;   Make a copy of drawing, immediately to the right of drawing.
    ;;; Produces:
    ;;;   greener-grass, another drawing
    ;;; Postconditions:
    ;;;   (drawing-left greener-grass) = (drawing-right drawing)
    ;;;   (drawing-width greener-grass) = (drawing-width drawing)
    ;;;   (drawing-height greener-grass) = (drawing-height drawing)
    ;;;   (drawing-top greener-grass) = (drawing-top drawing)
    ;;;   greener-grass is the same type and colors as drawing.
    ;;;