.TH G_PARSE 2 "8 April 1991" "Demeter" "Demeter Software"
.SH NAME
g_parse \- send the generic parse message to an object.
.SH SYNOPSIS

Universal* Universal::
.I g_parse
( char* filename )

.SH DESCRIPTION

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

.SH RETURN VALUES

.I g_parse
returns an object of the class of the object to which the message was
sent. However, the type returned by
.I g_parse
is
.I Universal*,
since
.I g_parse
does not know in advance to what class the message is going to be
sent. Therefore, the value returned must be cast to the appropriate type
before it can be assigned or used in any way. For example:

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

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

.SH ERROR MESSAGES

If the input text in
.I filename
does not represent a legal object of the class of the object to which
the message was sent,
.I g_parse
produces as output three error messages:

.TP 10
Error
An explanation of the error, along with the line in
.I filename
where it occurred.
.TP
Current token
The token  in
.I filename
that caused the error is printed along with up to the
following 10 tokens.
.TP
Production stack dump
A listing, in reverse order, of the productions in the grammar that
led to the point where the error occurred.
.LP

.SH MODIFYING THE CONCRETE SYNTAX

The file
.I cd-parse,
created by Demeter from the class dictionary 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
.I cd-parse,
the user needs to rerun
.I gen-scanner
and to recompile the program to make the modification effective.

.SH FILES
demeter-input
.br
cd-parse

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

.SH REFERENCES 

.I User Manual for The C++ Demeter System
.br
Walter L. Hursch
.br
Northeastern University, 1993

.I The Annotated C++ Reference Manual
.br
Margaret A. Ellis and Bjarne Stroustrup
.br
Addison-Wesley, 1990

.I C++ Primer
.br
Stanley B. Lippman
.br
Addison-Wesley, 1989