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Parser Rule Fragments [message #1725076]

Mon, 29 February 2016 14:43

Ronan B

Messages: 273
Registered: July 2009

Senior Member

Hi,
I was reading https://www.eclipse.org/forums/index.php/t/1072927/ and hoping to solve my unordered group issue as outlined a while back in https://www.eclipse.org/forums/index.php/t/1071359/.

It seems the Parser Rule Fragments concept introduced in Xtext 2.9 is rather restrictive in that it cannot be used in unordered groups. When I use the following fragment XText complains "Unassigned rule calls may not be used in unordered groups"

fragment X returns xyz::Element :
(( children+=Node ) | ( properties += Property ))*
;

Element returns xyz::Element:
'element'name=OptionallyQuotedName'{'
(
X
& 'des' des=(ConcatenatedString|QuotedConcatenatedString) ';'?
& X
& 'ref' ref=(ConcatenatedString|QuotedConcatenatedString) ';'?
& X
)
'}';

Also I think it is odd that the fragment must have an explicit return type matching the rule from which it is used, or have I misunderstood?

Thanks!
Ronan

[Updated on: Mon, 29 February 2016 19:38]

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Re: Parser Rule Fragments [message #1725196 is a reply to message #1725076]

Tue, 01 March 2016 14:40

Ronan B

Messages: 273
Registered: July 2009

Senior Member

Hi,
A quick follow up. I don't see any documentation of "rule fragments". Can someone provide a few samples, or even confirm my suspiction that they cannot be used in unordered groups.
Thanks!
Ronan

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Re: Parser Rule Fragments [message #1725251 is a reply to message #1725196]

Wed, 02 March 2016 07:14

Sven Efftinge

Messages: 83
Registered: January 2016
Location: Kiel

Member

Hi Ronan,
seems like it is the unassigned call to 'X' that the error is about.
Also you don't need to specify the return type, but you can if you want to have a common type for the features used in a fragment.
Sven

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Re: Parser Rule Fragments [message #1742897 is a reply to message #1725251]

Thu, 08 September 2016 13:00

Martin Westerkamp

Messages: 9
Registered: September 2016

Junior Member

I just stumbled across the same issue. It seems to be caused by the "and" operator.

Super:
	A | B;
fragment frag returns Super:
	name = ID;
A:
	frag |
	something = ID;
B:
	frag &
	something = ID;

While A works without any issues, B throws the same error "Unassigned rule calls may not be used in unordered groups".
Is there any reason behind that?

Greets,
Martin

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