I've just looked at the code for the debugger (which is a direct copy of the CHDK code). It seems that the exit_alt statement expects an operand. Thus:
exit_alt
fails with a parse error, but
exit_alt 0
works fine. The code doesn't seem to do anything with the operand. Here's the code in ubasic.c
static void exit_alt_statement()
{
int to;
accept(TOKENIZER_EXIT_ALT);
to = expr();
exit_alt(to);
accept_cr();
}
