to rotate.left :thing
  output lput first :thing butfirst :thing
end
to rotate.right :thing
  output fput last :thing butlast :thing
end

make "text "|Hello World! |
make "right? "true

to step.animation
  label :text			; graphical
  ; type char 13  type :text	; textual
  wait 6			; 1/10 second
  if button <> 0 [make "right? not :right?]
  make "text ifelse :right? [rotate.right :text] [rotate.left :text]
end

hideturtle
until [key?] [step.animation]