294 val fib = """

   295 write "Fib";

   296 read n;

   297 minus1 := 0;

   298 minus2 := 1;

   299 while n > 0 do {

   300 temp := minus2;

   301 minus2 := minus1 + minus2;

   302 minus1 := temp;

   303 n := n - 1

   304 };

   305 write "Result";

   306 write minus2

   307 """

   308 

   309 println(env(lexing_simp(WHILE_REGS, prog2)).filterNot{_._1 == "w"})