A calculator

                                         {my %variables}

start:          statement  /^\Z/         {$variables {'.'} = $item [1]}

statement:      variable '=' statement   {$variables {$item [1]} = $item [3]}
              | expression

expression:     term '+' expression      {$item [1] + $item [3]}
              | term '-' expression      {$item [1] - $item [3]}
              | term

term:           factor '*' term          {$item [1] * $item [3]}
              | factor '/' term          {$item [1] / $item [3]}
              | factor

factor:         number
              | variable                 {$variables {$item [1]} ||=
                                                Math::BigInt -> new (0)}
              | '+' factor               {$item [2]}
              | '-' factor               {$item [2] * -1}
              | '(' statement ')'        {$item [2]}

number:         /\d+/                    {Math::BigInt -> new ($item [1])}

variable:       /[a-z]+/i
              | '.'