Let's see if i can write something real quick.
backdrop on
sync on
text$ = "Your sentence goes here."
index = 0
max_length = len(text$) : rem number of characters in string
delay = 200 : rem delay for showing new character in milliseconds
timestamp = timer()
do
if index <= max_length
if timeStamp + delay <= timer()
inc index, 1
display$ = typewriter(text$, index)
timeStamp = timer()
endif
endif
set cursor 0,0
print display$
sync
loop
function typewriter(t$, index)
if len(t$) > index then t$ = left$(t$, index)
endfunction t$