Tried:

  a := TextWindow new: 'a test'.
  a moveX:200 Y: 200.

It worked. Nice.

Tried to add a factorial instance method to the Number class:

  factorial

  "comments"

  self = 0 ifTrue: [^ 1].
  self > 0 ifTrue: [^ self * (self - 1) factorial].

Then in Workspace:

  Transcript show: 10 factorial.

prints: 10 does not understand factorial.

Anyway, it looks promising.