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Nested Expressions / Recursion [message #1693207]

Wed, 22 April 2015 12:10

Patrick Neubauer

Messages: 8
Registered: December 2014

Junior Member

Hi,

I am wondering how to build nested expressions for key/value pairs using Xtext grammar.

The blog entry from Sven Efftige shows the idea:
http://blog.efftinge.de/2010/08/parsing-expressions-with-xtext.html

However, what I am trying to come up with is to represent instances such as:

"key1" : "value1" (
  "key11" : "value11"
  "key12" : "value12" (
    "key121" : "value121"
  )
  "key13" : "value13"
)

The Xtext grammar, which obviously is not completely correct is as follows:

Primary returns Expression:
	(STRING ':' STRING) | '(' Child ')'
;

Child returns Expression:
	Primary ({Child.left=current} '(' right=Primary)*
;

Cheers, Patrick

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Re: Nested Expressions / Recursion [message #1693209 is a reply to message #1693207]

Wed, 22 April 2015 12:21

Christian Dietrich

Messages: 14669
Registered: July 2009

Senior Member

Hi,

how shall the object tree look like

where shall the () be put too. on the same level as the pair before?
or does it ( optionally) belong to the values?

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

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Re: Nested Expressions / Recursion [message #1693210 is a reply to message #1693209]

Wed, 22 April 2015 12:29

Christian Dietrich

Messages: 14669
Registered: July 2009

Senior Member

a very naive approach works fine btw

Model:
elements+=Element+;

Element:
Pair | Pairs
;

Pair:
key=STRING ":" value=STRING
;

Pairs:
{Pairs}"(" elements+=Element* ")"
;

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

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Re: Nested Expressions / Recursion [message #1693216 is a reply to message #1693210]

Wed, 22 April 2015 12:53

Patrick Neubauer

Messages: 8
Registered: December 2014

Junior Member

Dear Christian,

Thank you very much for your fast reply!
Using your grammar I can successfully build the stated example.

Well, what I am trying to do is to come up with a construct to represent a feature map.
When transforming an XML Schema to Genmodel + Ecore and then generate an Xtext project from the Genmodel it does not create a construct for EFeatureMapEntry (original creation caused by xsd:complexType mixed="true" in the XSD).

Cheers, Patrick

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