Extended Exercise: Drawing Simple Pictures

Wehn you evaluate (start 300 300) with the draw.ss library, DrScheme create a new, empty drawing canvas, like this one:

Evaluating a drawing expressions, such as

(draw-solid-line (make-posn 100 100) (make-posn 200 200) 'red)

If you try to evaluate drawing expressions before using start, DrScheme reports an error message that reminds you to use start.

When the canvas window appears with your images, do not close it, because there is no way to re-open a closed canvas window. Instead, you have to re-execute your program, or create a new canvas window with start.

If you use start multiple times, drawing commands affect the most recently created canvas.

To close a canvas (when you are done with it), you can click the canvas window's close box, or evaluate (stop). Clicking DrScheme's Execute button also closes canvas windows.

Exercise Notes

Exercise 6.2.1 To open Help Desk, select the Help|Help Desk menu item. On Help Desk's home page, the third major bullet has a sub-link Teachpacks that provides a menu of Teachpack documentation links.