[ Main c;
    while (true) {
        @read_char 1 0 0 c;
        print (char) rot13(c);
    }
];

[ rot13 c;
    switch (c) 
    {
     'a' to 'm', 'A' to 'M': return c + 13;
     'n' to 'z', 'N' to 'Z': return c - 13;
     default: return c;
    }
];