10 LET t$="Hello world! ": LET lt=LEN t$
20 LET direction=1
30 PRINT AT 0,0;t$
40 IF direction THEN LET t$=t$(2 TO )+t$(1): GO TO 60
50 LET t$=t$(lt)+t$( TO lt-1)
60 IF INKEY$<>"" THEN LET direction=NOT direction
70 PAUSE 5: GO TO 30