Grammar -> Parser question

chris63@my-dejanews.com
4 Jun 1998 23:40:01 -0400

          From comp.compilers
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From: chris63@my-dejanews.com
Newsgroups: comp.compilers
Date: 4 Jun 1998 23:40:01 -0400
Organization: Deja News - The Leader in Internet Discussion
Keywords: parse, question

Suppose I have the following Grammar:


condition -> expr PLUS expr |
                            LPAREN condition RPAREN


expr -> ID |
                            LPAREN expr RPAREN


I want to hand-code a top down recursive descent parser for this grammar
using ideas from the Dragon Book (nonterminals become functions, terminals
become calls to match()). I can't use lex or yacc.


However, the LPAREN symbol is causing a problem: When I see it, I don't
know if I'm dealing with a nested condition or a nested expression.


How does one typically deal with this situation if one has to hand-code
the parser? It looks like I need some sort of lookahead and/or backtracking
mechanism so I can figure out which case I am dealing with.


sample source code demonstrating concepts appreciated. The actual grammar
is somewhat more complicated, but this is the critical area I need to address.


Regards,
Chris


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