G_PRINT(2)              Demeter Software               G_PRINT(2)



NAME
     g_print - sends the generic print message to an object.

SYNOPSIS
     void Universal:: _g__p_r_i_n_t ( ostream& strm = cout )


DESCRIPTION
     _g__p_r_i_n_t prints out the object to which the message  is  sent
     in  textual  form, according to the printing commands in the
     file _c_d-_p_r_i_n_t. The receiving object must be a  tree  object.
     That  is,  it  cannot  have any cycles or shared subobjects.
     _g__p_r_i_n_t is a generic method implemented at  class  Universal
     and inherited by any user class.


RETURN VALUES
     Once an object has been created or parsed in, it can be sent
     the g_print message. For example:

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

     If the _s_t_r_m argument is provided, then the output is sent to
     the ostream in the given _s_t_r_m. For example:

     Compound* iCompound = new Compound();
     iCompound = (Compound*)iCompound->g_parse("demeter-input");
     ofstream outFile( "demeter-output" );
     iCompound->g_print( outFile );
     outFile.close;

     Notice that since ofstream is a subclass of ostream  in  the
     C++  class  library, both output to the screen and to a disk
     file can be handled smoothly by _g__p_r_i_n_t.


EXAMPLE
     The file _c_d-_p_r_i_n_t, created by Demeter from  the  class  dic-
     tionary at generation time, contains the grammar the generic
     printer uses in printing the object to which the message  is
     sent.  In this file the user can add or remove printing com-
     mands to modify the layout of the  output  text.  There  are
     four printing commands that can be used:


     *l        Add new line.

     *s        Add space.

     +         Indent.  _g__p_r_i_n_t starts a new  indentation  level.



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G_PRINT(2)              Demeter Software               G_PRINT(2)



               Indentation is by three spaces.

     -         Unindent.  _g__p_r_i_n_t ends  the  current  indentation
               level.

     As an example of the effect of the printing  commands,  with
     the following contents in _c_d-_p_r_i_n_t:

     Example = <exps> Prefix_List.
     Prefix : Numerical |
              Compound.
     Numerical = <val> Real.
     Compound = "("
                Op
                <args> Prefix_List
                ")"
                <val> Real.
     Op : MulSym |
          AddSym |
          SubSym.
     MulSym = "*".
     AddSym = "+".
     SubSym = "-".
     Prefix_List ~ Prefix { Prefix }.
        *terminal_sets* Number, Ident, String, Real.

     the object with input text:

     (+ (* 3.0 4.0) 12.0 5.7) 17.7

     is printed as

     ( + ( * 3.000000 4.000000 ) 12.000000 5.700000 ) 17.700000.

     The following modification of _c_d-_p_r_i_n_t adds indentation  and
     unindentation  commands around the args part of the compound
     production. We also add new lines around the args  part  and
     before  each  repeated Prefix of a Prefix_list. The modified
     _c_d-_p_r_i_n_t is now

     Example = <exps> Prefix_List.
     Prefix : Numerical |
              Compound.
     Numerical = <val> Real.
     Compound = "("
                Op *l +
                <args> Prefix_List
                - *l ")" "value ="
                <val> Real.
     Op : MulSym |
          AddSym |
          SubSym.



Demeter             Last change: 8 April 1991                   2






G_PRINT(2)              Demeter Software               G_PRINT(2)



     MulSym = "*".
     AddSym = "+".
     SubSym = "-".
     Prefix_List ~ Prefix { *l Prefix }.
        *terminal_sets* Number, Ident, String, Real.

     and the output is

     ( +
        ( *
           3.000000
           4.000000
        ) value = 12.000000
        5.700000
     ) value = 17.700000

     Notice that we have also added the constant string "value ="
     before  the  val  part in the same production Compound. This
     addition of concrete syntax does not  require  recompilation
     and produces the improved output shown.


FILES
     cd-print


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                   3