• New partners!
• Be prepared to shuffle around; we had too many cards.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Conditionals, Revisited.
• Anonymous Procedures, Revisited.
• Lab.
• Reflection.

Preliminaries

Admin

• Review session tonight at 7pm.
• I hope you had a great weekend and a great two days without me. I think I've caught up on all of the email questions I've received. If not, let me know.
• Office hours today at 3:30 p.m. Office hours Tuesday at 10:00 a.m.
  
  • http://rebelsky.youcanbook.me
  • Remember that if you invoked "There's More To Life" on the exam, you need to meet with me.

Upcoming Work

• Homework 5.
  • Due Tuesday at 10:30 p.m.
  • Note that 6P-style documentation is expected for every primary procedure you write.
• Lab writeup for today: Exercise 5, parts b-f, http://bit.ly/151-2015S-lab20
• Reading for Tuesday
  • Local Bindings

Extra Credit Opportunities

Academic

• Pioneer Diversity Council Diversity Dialogue, 8:30 p.m. 26th, Main Quad "Academic Athletes and Academic Students". Note new date!
• CS Table Friday: Art and CS

Peer Support (Afternoon Section)

• Indoor Track and Field Conference

Other Good Things

• Host a prospie.
• Neverland players this weekend

Questions

How do I copy and paste from images?

;;; Procedure:
;;;   image-copy-paste-block!
;;; Parameters:
;;;   source, an image id
;;;   source-col, an integer
;;;   source-row, an integer
;;;   target, an image id
;;;   target-col, an integer
;;;   target-row, an integer
;;;   width, an integer
;;;   height, an integer
;;; Purpose:
;;;   Copy a width-by-height block from source to target, with the 
;;;   top-left corner of each block as specified.
;;; Produces:
;;;   [Nothing; called for the side effect.]
;;; Problems:
;;;   Does not do well with improper column/row pairs (e.g., those
;;;   outside the bounds of the image).

I'm having trouble with problem 2. Any hints?

(visualize-transforms (color->irgb "pink") (list (lambda (irgb-color) irgb-color) irgb-darker (o irgb-darker irgb-darker) (o irgb-darker irgb-darker irgb-darker) (o irgb-darker irgb-darker irgb-darker irgb-darker)) 5)

Identify parameters: 1. Integer-encoded RGB color; 2. List of procs. "transformations" - given a color, produce a (potentially) new color. 3. The number of transformations.

You want to make a list of colors, and then use visualize-colors.

How do you make the list of colors? Well, given a list of the form '(t1 t2 t3 t4 t5), you want to make the list that contains the values (t1 irgb-color), (t2 irgb-color), (t3 irgb-color), (t4 irgb-color), and (t5 irgb-color). Given one list, you make another list with an appropriate call to map.

(map ______ transformations).

How do you write post-conditions for a procedure that returns a procedure?

Option 1:

;;; Produces:
;;;   proc, a procedure
;;; ...
;;; Postconditions:
;;;   proc has the form (proc param1 param2) where param1 is a
;;;   an integer and param2 is an image id.  proc computes ...

Option 2:

;;; Produces:
;;;   proc, a procedure from integers and image ids to image ids.
;;; ...
;;; Postconditions:
;;;   (proc param1 param2) has the value ...

Option 3:

;;; Produces:
;;;   proc, a procedure
;;; ...
;;; Postconditions:
;;;   proc meets the following specifications
;;;     Parameters:
;;;       param1, an integer
;;;       param2, an image id
;;;     Purpose:
;;;       ...
;;;     Produces:
;;;       image, an image id
;;;     Preconditions:
;;;       [No additional]
;;;     Postconditions:
;;;        ...

In Problem 4 on Assignment 5, does "a simple shape of your choice" mean that the user can customize a shape, or that the programmer decides what shape to use?

I was assuming that you, in implementing the procedure, would decide what the shape would be.

Conditionals, Revisited

You learned three new mechanisms for conditional evaluation: if, when, and cond. What are the similarities and differences between them? Why might you use one over another?

Many Scheme programmers consider and and or additional mechanisms for conditional evaluation. Why?

Anonymous Procedures, Revisited

The reading was intended partially as review and partially to introduce new ideas. What new things did you learn about anonymous procedures?

Lab

• Yes, you can use l-s within compose.