[antlr-interest] expression parser example Expr.g dont work
Jack Pan
Jack.Pan at Lewtan.com
Wed Jan 7 10:40:01 PST 2009
How does AntlrWorks pick the default starting rule? It is the first rule in alphabetical order, neither is the first rule in grammar file.
From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Jim Idle
Sent: Wednesday, January 07, 2009 11:31 AM
Cc: antlr-interest at antlr.org
Subject: Re: [antlr-interest] expression parser example Expr.g dont work
Mats Ekberg wrote:
I removed the NEWLINE requirement entierly and evaluates "expr" in ANTLRWorks, same result. Sorry.
The input "(1 + 2) * 3 - 4" (with a newline at the end) just recognizes "( 1 + 2" and the nothing more.
Place an EOF in the mix:
stat : expr? EOF ;
And fix your NEWLINE:
NEWLINE: '\r'? '\n' { $channel = HIDDEN; } ;
Then when you run ANTLR Works, make sure that you are choosing the stat rule as the start rule (and use the debugger, not the interpretter).
Jim
grammar Expr;
expr
: multExpr ( '+' multExpr | '-' multExpr )*
;
multExpr
: atom ('*' atom )*
;
atom
: INT
| '(' expr ')'
;
INT : '0'..'9'+ ;
NEWLINE:'\r'? '\n' ;
WS : (' '|'\t')+ {skip();} ;
ons 2009-01-07 klockan 09:55 -0500 skrev Chris Snyder:
stat: expr NEWLINE
looks like is should just be
stat: expr
The current form hits the ‘(‘ and then looks for expr which requires a NEWLINE after ‘2’ which you don’t have.
I didn’t verify this though.
C
_____
From:antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Mats Ekberg
Sent: Wednesday, January 07, 2009 1:22 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] expression parser example Expr.g dont work
I have stripped the classical expr.g example and when I run it in ANTLRWorks it dont work.
The input "(1 + 2) * 3 - 4" (with a newline at the end) just recognizes "( 1 + 2" and the nothing more.
How come?
grammar Expr;
prog: stat+ ;
stat: expr NEWLINE
| NEWLINE
;
expr
: multExpr ( '+' multExpr | '-' multExpr )*
;
multExpr
: atom ('*' atom )*
;
atom
: INT
| '(' expr ')'
;
INT : '0'..'9'+ ;
NEWLINE:'\r'? '\n' ;
WS : (' '|'\t')+ {skip();} ;
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