       10 // REPEAT/UNTIL test program
       20 //
       30 DIM a$ OF 20
       40 REPEAT a$:+"X" UNTIL LEN(a$)=20
       50 SYS assert, a$="XXXXXXXXXXXXXXXXXXXX"
       60 REPEAT
       70   IF LEN(a$)>1 THEN a$:=a$(2:)
       80 UNTIL LEN(a$)=1
       90 SYS assert, a$="X"
      100 PRINT "Ok"
