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Xtext - Recursive grammar [message #1066988]

Fri, 05 July 2013 07:00

Eclipse User

How can I use a recursive grammar?

I have the following code:

model:
defs += CFG_objects
;

CFG_objects:
statement=ID name=ID '{'
(par+=CFG_pars)*
'}' (':' comment=STRING)? ';'
;

CFG_pars:
condition=ID val=ID
('{' (pars+=CFG_pars) '}')?
(':' comment=STRING)? ';'
;

It throws me an error with this:

switch answer
{
case good : do_nothing ;
}: store answer;

What is wrong with my grammar? How can I implement a recursive grammar rule? I was expecting the above example to work.

[Updated on: Fri, 05 July 2013 07:01] by Moderator

Re: Xtext - Recursive grammar [message #1066991 is a reply to message #1066988]

Fri, 05 July 2013 07:13

Eclipse User

Hi,

you define your comments as String, but in your sample they are not. STRING requires single or double quotes.

Also, you are probably missing "+" or "*" in your list definitions (model feature defs, CFG_pars feature pars).

Alex

Re: Xtext - Recursive grammar [message #1067246 is a reply to message #1066991]

Sun, 07 July 2013 23:39

Eclipse User

Hello,

I have changed the code and my configuration. But I am still getting an error.

model:
defs += CFG_objects
;

CFG_objects:
statement=ID name=ID '{'
(pars+=CFG_pars)*
'}' (':' comment=STRING1)? ';'
;

CFG_pars:
condition=ID val=ID
('{' (pars+=CFG_pars)* '}')?
(':' comment=STRING1)? ';'
;
terminal STRING1: '"' -> '"';

switch answer
{
case good : "do nothing" ;
TYPE bad;
}: "store answer";

The error I am getting is:
ERROR:mismatched input 'TYPE' expecting '}'
ERROR:extraneous input ';' expecting RULE_ID

[Updated on: Sun, 07 July 2013 23:40] by Moderator

Re: Xtext - Recursive grammar [message #1067254 is a reply to message #1067246]

Mon, 08 July 2013 02:31

Eclipse User

Hi,

this is not the complete grammar. It does not rise the problem you claim.

Alex

Re: Xtext - Recursive grammar [message #1067327 is a reply to message #1066988]

Mon, 08 July 2013 06:15

Eclipse User

I have modified the grammar a bit.

Model:
defs += CFG_objects*
;

CFG_objects:
	statement=ID name=ID '{'
	(pars+=CFG_pars)*
	'}'  comment=CFG_comment ';'
;

CFG_pars:
	name=ID value=SPECIAL
	('{' (pars+=CFG_pars)* '}')?
	comment=CFG_comment ';'
;

CFG_comment: {CFG_comment}
	(':' comment=STRING1)?
;

SPECIAL hidden():
	STRING1 | ID | INT| HEX | DOUBLE
;

terminal STRING1: '"' -> '"';
terminal DOUBLE:  INT '.' INT;
terminal HEX: '0' ('x' | 'X')(('0'..'9') | ('a'..'f') | ('A'..'F'))+;

I noticed that the error only occur in some scenarios.

switch answer
{
case good : "do nothing" ;
TYPE BAD; <--Problem line-->
PRIO HIGH;
}: "store answer";

If I change the problem line to "type", parsing still will not work. But other keywords works fine (e.g.STATUS, Size, size).

Re: Xtext - Recursive grammar [message #1067330 is a reply to message #1067327]

Mon, 08 July 2013 06:24

Eclipse User

Hi,

this is still not the complete grammar, the example is processed without errors. My guess is that you use "TYPE" as a keyword somewhere in your real grammar. That way TYPE will not be read as ID (as your rule reqires) but as keyword token.

Alex

Re: Xtext - Recursive grammar [message #1067481 is a reply to message #1067330]

Mon, 08 July 2013 21:48

Eclipse User

OH! You are right! [Banging head on the monitor screen]
Been staring at this for a week now.

Is there a way to fix this? I do not want to specify each possible keyword. But other rules do require for the "TYPE" keyword to be there.

[Updated on: Mon, 08 July 2013 21:57] by Moderator

Re: Xtext - Recursive grammar [message #1067499 is a reply to message #1067481]

Tue, 09 July 2013 02:25

Eclipse User

See e.g. here. I'd recommend simple escaping if possible.

Alex

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