<b_jonas> learn ayacc is ais523\'s yacc parser generator implementation, get it from (darcs clone http://nethack4.org/projects/ayacc) or a snapshot from "http://nethack4.org/pastebin/ayacc-2020-04.tar.gz".

#include <stdio.h>
int main(){printf("\e[1m");int a,c=0;b:a=getchar();if(a==EOF)return 0;if(!(a&128)||(a&64))printf("\e[%dm","\37! $\"#"[c]),c=c+1-6*(c>4);putchar(a);goto b;}