(do*((w(coerce"helloworld"'list))(c(nconc w w))(x #1=(read-char nil nil)#1#))((not x))(write-char(if(eql #\ x)x(prog1(if(eql #\# x)(char-upcase #3=(car c))#3#)(setf c(cdr c))))))
Note that non-ascii characters in the above source code will be escaped (such as \x9f).