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

[Gabriel Petrovay]

Hi all,

I am trying to parse XQuery. It is known that XQuery is not keyword based.
For example you can have the following function declaration:

declare function declare:function($declare as element(declare)) as
element(function) {
  <function declare="declare function">{$declare/function}</function>
}

This declares a function called "function" in the namespace that has the
prefix "declare". This function takes the parameter "declare" of type XML
element having the tag name "declare", and returns also an XML element
having the tag name "function". And so forth...
:)

Can I solve this?

Thanks!
Gabriel

On Tue, Mar 24, 2009 at 10:46 AM, Indhu Bharathi <indhu.b at s7software.com>wrote:

>  I assume when you say 'keyword' you are talking about the keywords (like
> 'if', 'else'. 'type', etc) in the language you are trying to parse. Those
> must be finite and the regular approach is to have a production for each.
> Under that assumption the proposed model is certainly scalable.
>
> But I'm just getting a doubt if you are meaning something else by
> 'keyword'. Are you trying to parse a input containing name value pair where
> name and value can be anything?
>
> And what do you mean by Name1, Name2, ... NameN? I dont see any such thing
> in grammar. Is name not a plain ID (like a variable name)?
>
> Throwing some more light on what exactly you are trying to parse will be
> helpful.
>
>
> - Indhu
>
> Gabriel Petrovay wrote:
>
> 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
>
>
>


-- 
MSc Gabriel Petrovay
MCSA, MCDBA, MCAD
Mobile: +41(0)787978034
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