    The flex-specification file used by the calculator is simple: blanks are
ignored, single characters are returned, and numeric values are returned as
either tt(Parser::INT) or tt(Parser::DOUBLE) tokens.

    The tt(flexc++) directive tt(%interactive) is provided since the
calculator is a program actively interacting with its human user.

Here is the complete tt(flexc++) specification file:
        verbinclude(-a bisonc++/scanner/lexer)
