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Textblock within ParserRule [message #1479977]

Wed, 19 November 2014 22:18

Andreas Studer

Messages: 5
Registered: July 2009

Junior Member

Hello

I have the problem that I would like to get a language like this:

legend center
   This is the text
   of a legend.
endlegend

I would like to have a ParserRule like this:

Legend:
	'legend' (align=AlignEnum)?
		content=MULTILINE
	'endlegend'
;

enum AlignEnum:
	LEFT		= 'left' |
	RIGHT		= 'right' |
	CENTER		= 'center'
;

I didn't found any way to get something useful for the MULTILINE rule. Everything results in some sort of troubles (e.g. all Terminal Rules I've tried would overrule other rules according to the generator warnings, and some even result in exception stacktraces).
I also can't use the STRING terminal rule since this would mean I have to use ' or " (the target language is simply not like this and from the perspective of the language, it wouldn't make sense anyway.)
I think some sort of Data Type Rule for MULTILINE would be elegant, because then it would be part of the parsing context of the "Legend" parser rule. But I didn't found a way to build one.

Has anybody an idea how a solution could look like?

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Re: Textblock within ParserRule [message #1480438 is a reply to message #1479977]

Thu, 20 November 2014 07:16

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

Hi,

you can workaround the keyword problem by introducing a so called Datatype rule e.g.

MULTILINE: (ID | INT | 'keyword1' | 'keyword2')+

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: Textblock within ParserRule [message #1481147 is a reply to message #1480438]

Thu, 20 November 2014 20:08

Andreas Studer

Messages: 5
Registered: July 2009

Junior Member

Hello Christian

Thanks, that helped me (at least partially).

Since you've called it "workaround" I assume it's a real problem to get a freetext string between two keywords. I think it would be helpful to put that into a FAQ.

The other problem I have is a single line. Something like

title this is a title.

My solution here is simply:

terminal TITLE_TERMINAL:
	'title' !('\n'|'\r')* ('\r'? '\n')?;

However, that's also not a neat solution too because "title" should be a keyword and not part of a terminal rule. But anyhow...
I guess there is not a Datatype rule workaround that would help here.

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Re: Textblock within ParserRule [message #1481160 is a reply to message #1481147]

Thu, 20 November 2014 20:22

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

hi,

keep in mind that xtext uses a lexer and that terminals are lexed.
have a look at the grammar feature 'Hidden Terminal Symbols' (see docs)
if you split up whitespace rule into ws and newline you could get that running

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: Textblock within ParserRule [message #1486192 is a reply to message #1481160]

Mon, 24 November 2014 22:21

Andreas Studer

Messages: 5
Registered: July 2009

Junior Member

Hello Christian

I'm sorry to say, I've tried to do something with the hidden terminal symbols to get a single line string 'till the EOL after a term, but it seems as I didn't got the idea.
If I declare something like this it doesn't work:

grammar x.y.z with org.eclipse.xtext.common.Terminals
	hidden (WS, NEWLINE, SL_COMMENT, ML_COMMENT)
(...)
SingleTitle:
	'title' title=SINGLELINE;

SINGLELINE hidden (WS, SL_COMMENT, ML_COMMENT):
	(ID|INT|ANY_OTHER)+;

terminal WS:
	(' '|'\t')+;

terminal NEWLINE:
	('\r'|'\n')+;

Could you provide me an example that works?

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Re: Textblock within ParserRule [message #1486629 is a reply to message #1486192]

Tue, 25 November 2014 07:06

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

Please share a complete sample grammar + test model

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

[Updated on: Tue, 25 November 2014 07:32]

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Re: Textblock within ParserRule [message #1486759 is a reply to message #1486629]

Tue, 25 November 2014 09:11

Uli Merkel

Messages: 250
Registered: June 2013

Senior Member

Hi Andreas,

I do not see some "ANY_OTHER" specification.

And in your grammar, you have the hidden clause twice,
AFAIK you have to modify the hidden clause of the with ...

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