Since release 6.3 amforth has three redefinable prompt words. They are called in the outer interpreter quit:

: quit ( -- )
   lp0 lp ! sp0 sp! rp0 rp! \ setup the stacks
   [ \ switch to interpret mode
   begin \ an endless loop begins
     state @ 0= if .ready then
     refill if
       ['] interpret catch
       ?dup if
         dup -2 < if .error then
         recurse \ restarts without turnkey
   again ;

The .ready is called whenever the system signals its readyness for input. It’s default starts a new line and displays the > character. The definition is

USER_P_RDY Udefer .ready
:noname ( -- ) cr ."> " ; is .ready

After this prompt, the refill action is called when the command line has been processed. The .ok prompt word is used when the input line has been processed successfully. It’s default displays the “ok” string

USER_P_OK Udefer .ok
:noname ( -- ) ." ok " ; is .ok

The third prompt word is called whenever the systems detects an error or an unhandled exception. It default prints the exception number and the position in the input buffer where the error has been detected

USER_P_ERR Udefer .error
:noname ( n -- ) ." ?? "
   \ print the exception number in decimal
   base @ >r decimal .
   \ print the position in the input buffer
   >in @ .
   \ restore base
   r> base !
; is .error

The :nonames indicate that the default actions don’t have a name in the dictionary. The defers are stored in the USER area since all other words related to command IO are there too. Any replacement words are expected to follow the stack diagrams otherwise the system may crash.