Re: Can Pascal be parsed by LR(1) parsing algorithm?

Yacc is really a crude tool for parser construction. After much
experimentation, I got yacc to not only accept Modula-2's statements, but
to report when you forgot to put in a missing semicolon as well. I didn't
do the same for Pascal, as it was too much work. You can find complete
grammars in the Modula-2/Pascal distribution available for anonymous ftp
from gatekeeper.dec.com, file /pub/DEC/Modula-2/m2.vax.tar.Z. Here's the
relevant code for Modula-2, just to let you know the horrors of yacc
grammar c onstruction.




/* blame yacc for gross sequence syntax */
StatementSequence:
                                StatementSequence1
                                                                /**/
                | semis StatementSequence1 semis
                                                                { $$ = $2; }
                | StatementSequence1 semis
                                                                /**/
                | semis StatementSequence1
                                                                { $$ = $2; }
                | semis
                                                                { $$ = AddToStmtList(0,0); }
                | /* empty */
                                                                { $$ = AddToStmtList(0,0); }
                ;


StatementSequence1:
                                StatementSequence1 semis statement
                                                                { $$ = AddToStmtList($1,$3); }
                | StatementSequence1 { yyerror("Missing semicolon"); } statement
                                                                { $$ = AddToStmtList($1,$3); }
                | statement
                                                                { $$ = AddToStmtList(0,$1); }
                ;


semis:
                                SEMICOLON
                | semis SEMICOLON
                ;






--
- Joel McCormack (decwrl!joel, joel@decwrl.dec.com)
--

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