[antlr-interest] Fwd: Rule precedence works differently when using a predicate?

[Jim Idle]

As I said earlier you need more predicates:

But you also need to not use .+, which essentially match anything anyway
once it is triggered. Try something like this.

fragment KEY : ;

ANY
   : {!test()}?=> 'KEY')
   | ({test()}?=> . )
   ;


But once you take out .+ , then it might just work as it was anyway.

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Bart Kiers
> Sent: Thursday, October 27, 2011 10:56 AM
> To: antlr-interest at antlr.org interest
> Subject: [antlr-interest] Fwd: Rule precedence works differently when
> using a predicate?
>
> Just a little bump, in case it got buried under some of the newer
> posts.
> And in case my previous grammar wasn't entirely clear, the following
> grammar:
>
> grammar T;
>
> @lexer::members {
>   private boolean test() {
>     return true;
>   }
> }
>
> parse
>   :  KEY EOF
>   ;
>
> KEY
>   :  'key'
>   ;
>
> ANY
>   :  ({test()}?=> . )+
>   ;
>
>
> with the test class:
>
> import org.antlr.runtime.*;
>
> public class Main {
>   public static void main(String[] args) throws Exception {
>     TLexer lexer = new TLexer(new ANTLRStringStream("key"));
>     TParser parser = new TParser(new CommonTokenStream(lexer));
>     parser.parse();
>   }
> }
>
>
> Produces the following error:
>
> line 1:0 mismatched input 'key' expecting KEY
>
>
> In other words, 'key' is being tokenized as ANY instead of KEY.
> Is this expected behavior or a bug? And if it's expected behavior,
> could someone point me to the documentation (book) or wiki-link that
> explains this?
>
> Cheers & regards,
>
> Bart.
>
> -------------------
>
> From: Bart Kiers <bkiers at gmail.com>
> Date: Mon, Oct 24, 2011 at 11:46 AM
> Subject: Rule precedence works differently when using a predicate?
> To: "antlr-interest at antlr.org interest" <antlr-interest at antlr.org>
>
>
> Hi all,
>
> As I understand it, ANTLR's lexer matches rules from top to bottom in
> the .g grammar file and when two rules match the same number of
> characters, the one that is defined first has precedence over the later
> one(s).
>
> However, take the following grammar:
>
> grammar T;
>
> @lexer::members {
>   private boolean test() {
>     return true;
>   }
> }
>
> parse
>   :  (t=. {System.out.println(tokenNames[$t.type] + " :: " +
> $t.text);})* EOF
>   ;
>
> KEY
>   :  'key'
>   ;
>
> ANY
>   :  ({test()}?=> . )+
>   ;
>
>
> And the test class:"
>
> import org.antlr.runtime.*;
>
>
> public class Main {
>   public static void main(String[] args) throws Exception {
>     TLexer lexer = new TLexer(new ANTLRStringStream("key"));
>     TParser parser = new TParser(new CommonTokenStream(lexer));
>     parser.parse();
>   }
> }
>
>
> I'd expected "KEY :: key" to be printed to the console, however, "ANY
> :: key"
> is printed instead. So the last rule is matched, while the KEY rule
> also matches the same input and is defined before ANY. Why?
>
> Kind regards,
>
> Bart.
>
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