G_PARSE(2)              Demeter Software               G_PARSE(2)



NAME
     g_parse - send the generic parse message to an object.

SYNOPSIS
     Universal* Universal:: _g__p_a_r_s_e ( char* filename )


DESCRIPTION
     _g__p_a_r_s_e parses in the text contained in  file  _f_i_l_e_n_a_m_e  and
     produces  an  object of the class of the object to which the
     message was sent. Or, if  the  text  in  _f_i_l_e_n_a_m_e  does  not
     describe  a  legal  object, then an error output is produced
     and the program is aborted.  _g__p_a_r_s_e  is  a  generic  method
     implemented  at  class  Universal  and inherited by any user
     class.


RETURN VALUES
     _g__p_a_r_s_e returns an object of the  class  of  the  object  to
     which  the  message  was sent. However, the type returned by
     _g__p_a_r_s_e is  _U_n_i_v_e_r_s_a_l*,  since  _g__p_a_r_s_e  does  not  know  in
     advance  to  what  class  the  message  is going to be sent.
     Therefore, the value returned must be cast to the  appropri-
     ate  type  before it can be assigned or used in any way. For
     example:

     Compound* iCompound = new Compound();
     iCompound = (Compound*)iCompound->g_parse("demeter-input");

     If _g__p_a_r_s_e finds an error, i.e., the input text in  _f_i_l_e_n_a_m_e
     does not represent a legal object of the class of the object
     to which the message was sent, _g__p_a_r_s_e returns the NULL con-
     stant.  Thus,  it  is  recommendable to check for the return
     value before using it.


ERROR MESSAGES
     If the input text in _f_i_l_e_n_a_m_e does  not  represent  a  legal
     object  of  the class of the object to which the message was
     sent, _g__p_a_r_s_e produces as output three error messages:


     Error     An explanation of the error, along with  the  line
               in _f_i_l_e_n_a_m_e where it occurred.

     Current token
               The token  in _f_i_l_e_n_a_m_e that caused  the  error  is
               printed along with up to the following 10 tokens.

     Production stack dump
               A listing, in reverse order, of the productions in
               the  grammar that led to the point where the error



Demeter             Last change: 8 April 1991                   1






G_PARSE(2)              Demeter Software               G_PARSE(2)



               occurred.

MODIFYING THE CONCRETE SYNTAX
     The file _c_d-_p_a_r_s_e, created by Demeter from  the  class  dic-
     tionary at generation time, contains the grammar the generic
     parser uses in parsing the text in the input file.  In  this
     file  the  user  can  modify  the  concrete syntax (constant
     strings appearing in the specifications of  productions)  to
     change  the  appearance  of input sentences. After modifying
     _c_d-_p_a_r_s_e, the user needs to rerun _g_e_n-_s_c_a_n_n_e_r and to  recom-
     pile the program to make the modification effective.


FILES
     demeter-input
     cd-parse


SEE ALSO
     gen-scanner(1), universal(2)


REFERENCES
     _U_s_e_r _M_a_n_u_a_l _f_o_r _T_h_e _C++ _D_e_m_e_t_e_r
     Walter L. Hursch
     Northeastern University, 1993

     _T_h_e _A_n_n_o_t_a_t_e_d _C++ _R_e_f_e_r_e_n_c_e _M_a_n_u_a_l
     Margaret A. Ellis and Bjarne Stroustrup
     Addison-Wesley, 1990

     _C++ _P_r_i_m_e_r
     Stanley B. Lippman
     Addison-Wesley, 1989





















Demeter             Last change: 8 April 1991                   2