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Terminal Rule Error [message #899938]

Fri, 03 August 2012 01:53

Eclipse User

I meet a problem about the terminal rule. The grammar I used is following

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals hidden(CONDITIONAL_COMPILE_BEGIN)

generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"

Model:
	greetings+=Greeting*;
	
Greeting:
	'#' name=ID '!'	;

terminal INCLUDE:
	'#' ('include'|'INCLUDE') WS ID;

And the following case should be accepted by the grammer

#input!

But I got the error message as following
Multiple markers at this line
- missing EOF at 'ut'
- mismatched character 'p' expecting 'c'

I tried to find the reason. And, I found that the lexer using an DFA to predict which terminal rule should be used. When it find the letter '#' followed by the 'i', it decide to use the terminal rule "INCLUDE". But it fail to recognize the token, because the input is "#input" not "#include".

Beside using backtrack of Lexer, what can I do to solve this problem?
By the way, I need the terminal rule "INCLUDE" in that form. Because I want to treat the string "#include someName" as a token.

[Updated on: Fri, 03 August 2012 02:04] by Moderator

Re: Terminal Rule Error [message #899939 is a reply to message #899938]

Fri, 03 August 2012 02:03

Eclipse User

Hi,

your grammar is ambigous. you may want to use a datatype rule instead

INCLUDE hidden():
'#' ('include'|'INCLUDE') WS ID;

Re: Terminal Rule Error [message #899940 is a reply to message #899939]

Fri, 03 August 2012 02:07

Eclipse User

thank you for your reply.

I forget to mention that I do need the terminal rule "INCLUDE" in that form. Because I want to treat the string "#include someName" as a token.

Re: Terminal Rule Error [message #899941 is a reply to message #899940]

Fri, 03 August 2012 02:08

Eclipse User

What do you mean by:

Quote:

I want to treat the string "#include someName" as a token.

Re: Terminal Rule Error [message #899942 is a reply to message #899941]

Fri, 03 August 2012 02:12

Eclipse User

I need the Lexer recognize "#include someName" as a token.

If there is no easy way to solve this problem, I'll change it to a datatype rule. But I hope I can remain it as a terminal rule.

Re: Terminal Rule Error [message #899943 is a reply to message #899942]

Fri, 03 August 2012 02:14

Eclipse User

Still the question: why?

Re: Terminal Rule Error [message #899944 is a reply to message #899943]

Fri, 03 August 2012 02:23

Eclipse User

I have done something like preprocess in the Lexer. I know it is a little unreasonable. The "INCLUDE" is a flag that I should filter all the things behind it. In the Lexer, I change the type of the token that has been read to be "Other". All the tokens behind the "INCLUDE" will not be seen by the Parser. And to get the configure information to do this job I have ask another question as below.
http://www.eclipse.org/forums/index.php/m/893934/#msg_893934

Re: Terminal Rule Error [message #899971 is a reply to message #899938]

Fri, 03 August 2012 05:42

Eclipse User

How about:


Greeting:
	NUMBER_SIGN name=ID '!'	;

terminal INCLUDE:
	'#' ('include'|'INCLUDE') WS ID;

terminal NUMBER_SIGN:
	'#' ;

The difference is that the NUMBER_SIGN is listed after the INCLUDE. So If INCLUDE does not match it still can match NUMBER_SIGN. I have not tested it, and still often get confused with TERMINAL rules. I just have recognized that such things can make huge difference.
It has some ugly side effects as you can not use a greeting like this:

#include !

So if possible better use datatype rules.

Re: Terminal Rule Error [message #899973 is a reply to message #899938]

Fri, 03 August 2012 05:44

Eclipse User

Did you try to use something like

terminal IdWithHash: '#' ID;

and a value converter that strips the # from that token?

Regards,
Sebastian
--
Looking for professional support for Xtext, Xtend or Eclipse Modeling?
Go visit: http://xtext.itemis.com

Am 03.08.12 07:54, schrieb Kevin Sun:
> I meet a problem about the terminal rule. The grammar I used is following
>
> grammar org.xtext.example.mydsl.MyDsl with
> org.eclipse.xtext.common.Terminals hidden(CONDITIONAL_COMPILE_BEGIN)
>
> generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"
>
> Model:
> greetings+=Greeting*;
>
> Greeting:
> '#' name=ID '!' ;
>
> terminal INCLUDE:
> '#' ('include'|'INCLUDE') WS ID;
>
>
> And the following case should be accepted by the grammer
> #input!
>
> But I got the error message as following
> Multiple markers at this line
> - missing EOF at 'ut'
> - mismatched character 'p' expecting 'c'
>
> I tried to find the reason. And, I found that the lexer using an DFA to
> predict which terminal rule should be used. When it find the letter '#'
> followed by the 'i', it decide to use the terminal rule "INCLUDE". But
> it fail to recognize the token, because the input is "#input" not
> "#include".
>
> Beside using backtrack of Lexer, what can I do to solve this problem?

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