       10 // Substring test program
       20 //
       30 a$:="abcdefghijklmnopqrstuvwxyz"
       40 //
       50 SYS assert, a$(4:8)="defgh"
       60 a$(4:8):="X"
       70 SYS assert, a$="abcX    ijklmnopqrstuvwxyz"
       80 //
       90 SYS assert, "Hallo"(1:2)="Ha"
      100 SYS assert, aap$(1:2)="aa"
      110 SYS assert, aap2$("AB")(2:3)="BA"
      120 //
      130 PRINT "Ok"
      140 //
      150 FUNC aap$
      160   RETURN "aap"
      170 ENDFUNC aap$
      180 //
      190 FUNC aap2$(a$)
      200   RETURN a$+a$
      210 ENDFUNC aap2$
