User blog comment:ヌヌハラ/alice-tools v0.2.0/@comment-45214281-20200313112813/@comment-44256294-20200314181344

You can use the system.MsgBox function to open a dialog box with a message in it. This will require allocating an unused string number (similar to what I described above for adding messages). For example,

.STR 0x123456 "value is %d" ; assign to new string S_PUSH 0x123456            ; push string onto stack PUSH 123                   ; push value to insert into string PUSH 2                     ; 2=integer (%d), 4=string (%s) S_MOD                      ; replace "%d" with "123" CALLSYS system.MsgBox      ; show message box with string "value is 123" S_POP                      ; clean up

(I haven't tested this code, but I think I got right.)

There is also the system.Output function which prints to the console in the System 4 IDE. It *may* be possible to trick the IDE into running more recent games, but I haven't tried it (the publicly released version of the IDE is quite old). You can find the IDE in the System 4 SDK linked here.