How to manage part of a STRING?

[LukeBord1]

In standard Basic, we have this example correctly working:

Code:

10 LET a$="123456789012345678901234567890xy" 20 PRINT AT 0,0; a$ 30 IF INKEY$="0" THEN LET a$=a$(32) + a$(1 TO 31) 40 GOTO 20

...but it doesn't seem to work in ZXB:

Code:

DIM test AS STRING test="123456789012345678901234567890xy" mainloop: PRINT AT 0,0; test IF INKEY="0" THEN test=test(32) + test(1 TO 31) END IF GOTO mainloop

Thoughts?