void non_fatal_error (string) const;
void error (string) const;
void message (string) const;
void set_spot (Input const &);
void step_forward ();
void set_location (Input const &, Input const &);
void non_fatal_error (string) const;
void error (string) const;
void message (string) const;
void set_spot (Input const &);
void step_forward ();
void set_location (Input const &, Input const &);