[Newbies] tutorial: "doesNotUnderstand" instance variable

[Andrew n marshall]

I'm trying to go through the pipsqueak tutorial, but it throws a 
doesNotUnderstand error when I try to initialize the exitSides instance 
variable the first time.  The browser shows the exitSides variable (with 
nil value), so the VM knows its there.

This is my class declaration:
Object subclass: #BlankCell
    instanceVariableNames: 'activeSegments exitSides'
    classVariableNames: ''
    poolDictionaries: ''
    category: 'Laser-Game-Model'

This is my init function:
initializeExitSides
    self exitSides: Dictionary new.
    self exitSides at: #north put: #south.
    self exitSides at: #east put: #west.
    self exitSides at: #south put: #north.
    self exitSides at: #west put: #east.

And a screen shot of my error stack trace is here:
  http://www.isi.edu/~amarshal/transfers/squeak_error.png
(How do I copy it as text anyway?)


Anm