[antlr-interest] How can I avoid "mismatched input" error?

[Gabriel Petrovay]

Hi Indhu,

I was trying to simplify the example such that I still get the error and the
example is simple enough for everybody to understand the problem.

Here is the corrected grammar:

//========================================
 grammar k;
options {
output=AST;
}

rule : KEYWORD1 (KEYWORD2 Name)? ';' ;

KEYWORD1 : 'keywordA';
KEYWORD2 : 'keywordB';

Name : ('a'..'z' | 'A'..'Z')+ ;
S : ('\t' | ' ' | '\n' | '\r')+  { $channel = HIDDEN; } ;
//========================================

With this the problems you mentioned are eliminated.

As I can see your proposed solution is not scalable if I have the keywords:
keywordA, keywordB,...,keywordZ, and the Name rules: Name1, Name2,...,
NameN. Or is it?

Any solution for this?


Regards,
Gabriel


On Tue, Mar 24, 2009 at 9:29 AM, Indhu Bharathi <indhu.b at s7software.com>wrote:

>  Looks like you are trying to use keyword as identifier. AFAIK, this cannot
> be resolved in the lexer. You have to use predicates in the parser rule.
> Something like this:
>
> rule : keyKEYWORD1 (keyKEYWORD2 enc=Name)? ';' ;
>
> keyKEYWORD1
>     :    {input.LT(1).getText().equals("keyword1")}? Name ;
>
> keyKEYWORD2
>     :    {input.LT(1).getText().equals("keyword2")}? Name ;
>
>
> One more problem I see is the production "Name : Letter* ;". Lexer
> production cannot define a zero length string.
>
> Another problem is you are expecting 'keyword1' to be parsed as Name but
> production for Name doesn't allow numbers.
>
> - Indhu
>
> Gabriel Petrovay wrote:
>
> Hi all,
>
> I have the following grammar file:
>
> //========================================
> grammar k;
> options {
> output=AST;
> }
>
> rule : KEYWORD1 (KEYWORD2 enc=Name)? ';' ;
>
> KEYWORD1 : 'keyword1';
> KEYWORD2 : 'keyword2';
>
> Name : Letter* ;
> fragment Letter : 'a'..'z' | 'A'..'Z' ;
>
> S            :    ('\t' | ' ' | '\n' | '\r')+  { $channel = HIDDEN; } ;
> //========================================
>
>
> The following text is not a valid one.
>
> INPUT:
> =====
> keyword1 keyword2 keyword1 ;
>
> OUTPUT:
> =======
> line 1:18 mismatched input 'keyword1' expecting Name
> <mismatched token: [@4,18:25='keyword1',<4>,1:18], resync=keyword1 keyword2
> keyword1 ;>
>
>
> How can I make a parser to recognize this input? I want to be able to allow
> the keywords in the places where any char combination is allowed. How can I
> make this?
>
> Regards,
> Gabriel
>
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-- 
MSc Gabriel Petrovay
MCSA, MCDBA, MCAD
Mobile: +41(0)787978034
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