Held: Tuesday, 4 February 2014

Back to Outline 09 - Testing Your Procedures. On to Outline 11 - A Design Perspective.

Summary

We consider a few important procedures that get called for their effect on the system (or on a value), rather than for the value returned. These procedures have "side effects". We focus on two kinds of procedures with side effects: Procedures that display text on the screen, and procedures that work with images, including images stored in files.

Related Pages

• Reading: Output in Scheme
• Reading: Basic Image Operations
• Lab: Side Effects
• EBoard (Source) (HTML) (PDF)

Overview

• Output with display and newline.
• Using output procedures to trace code.
• More procedures for working with images.

Administrivia

• Yesterday's writeup: Just send me your unit tests.
• Today's writeup (due Friday): Exercise 4a from Side Effects
  • Email subject: CSC 151 Writeup 7: Side Effects (YOUR NAME(s) HERE)
• Wednesday's reading: Design and Color
• Extra credit:
  • Convocation, Wednesday, noon, JRC 101 (Putin and Pussy Riot)
  • CS Extras, Wednesday at 4:30 in Science 3821: AppDev
  • CS Table, Friday at noon in the Day PDR: NP Completeness

Output

• Use display to print values.
• Use newline to print a newline.

Tracing Code with Output

• By inserting appropriate calls to display and newline, we can better see what our program does.

More Image Procedures

• image-new - create a new image
• image-show - you know
• drawing->image - you know
• image-load - load an image from a file
• image-save - save an image to a file
• drawing-render! - put a drawing on an image