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Recursive Grammar with EMF [message #1842471]

Mon, 21 June 2021 04:10

Eclipse User

I am trying to add some simple recursion in my rules and I am using EMF for generating the code of my models.
I tried following the recursion guide in the docs, but get an error:
"Cannot add supertype 'JdlExpression' to sealed type 'JdlBracedExpression'."
I don't want Expression to be a Supertype of BracedExpression (since it might contain multiple expressions).
Here are my rules:

JdlExpressions returns JdlExpressions:
	{JdlExpressions}
	exp+=JdlExpression*
;

JdlExpression returns JdlExpression:
	{JdlExpression}
	(=> JdlBracedExpression | ID)
;

JdlBracedExpression returns JdlBracedExpression:
	"(" exp=JdlExpressions ")"
;

My Genmodel:

<genClasses ecoreClass="cbcmodel.ecore#//JdlExpressions">
       <genFeatures createChild="true" ecoreFeature="ecore:EReference cbcmodel.ecore#//JdlExpressions/exp"/>       
    </genClasses>
    <genClasses ecoreClass="cbcmodel.ecore#//JdlExpression">
    </genClasses>
    <genClasses ecoreClass="cbcmodel.ecore#//JdlBracedExpression">
       <genFeatures createChild="true" ecoreFeature="ecore:EReference cbcmodel.ecore#//JdlExpressions/exp"/>       
    </genClasses>

Ecore:

<eClassifiers xsi:type="ecore:EClass" name="JdlExpressions">
    <eStructuralFeatures xsi:type="ecore:EReference" name="exp" upperBound="-1" eType="#//JdlExpression"
        containment="true"/>
  </eClassifiers>
  <eClassifiers xsi:type="ecore:EClass" name="JdlExpression">
  </eClassifiers>
  <eClassifiers xsi:type="ecore:EClass" name="JdlBracedExpression">
    <eStructuralFeatures xsi:type="ecore:EReference" name="exp" upperBound="1" eType="#//JdlExpressions"
        containment="true"/>
  </eClassifiers>

Re: Recursive Grammar with EMF [message #1842472 is a reply to message #1842471]

Mon, 21 June 2021 04:25

Eclipse User

your ecore looks wired. i dont see a storage for the ID.

maybe something like this will work

JdlExpression:
{JdlExpression}
ID | JdlBracedExpression
;

JdlBracedExpression returns JdlExpression:
{JdlBracedExpression} "(" exp=JdlExpressions ")"
;

Re: Recursive Grammar with EMF [message #1842473 is a reply to message #1842472]

Mon, 21 June 2021 04:34

Eclipse User

This yields "Cannot find compatible feature exp in sealed EClass JdlExpression from imported package http://www.example.org/cbcmodel: The type 'JdlExpression' does not have a feature 'exp'."

What do you mean by strange ecore? Isn't Expression just a Unassigned Rule Call and thus has no attributes? How can I fix that?

[Updated on: Mon, 21 June 2021 04:35] by Moderator

Re: Recursive Grammar with EMF [message #1842475 is a reply to message #1842473]

Mon, 21 June 2021 04:56

Eclipse User

i dont get your error.
your type hierarchy is terrible too
JdlBracedExpression does not inherit JdlExpression

how shall the hierarchy really look like?

Re: Recursive Grammar with EMF [message #1842476 is a reply to message #1842475]

Mon, 21 June 2021 05:04

Eclipse User

Ok maybe lets add another Rule and it might start making some sense.
Lets add an
JdlOperator:
"&" | "|" | "=>"

Now I want to be able to parse something like this:

(x & (x=>y) =>z)

Later I want to extend the Operations and add some rules like "foreach ... "

Re: Recursive Grammar with EMF [message #1842477 is a reply to message #1842476]

Mon, 21 June 2021 05:07

Eclipse User

maybe its better to start with a new grammar and a derived metamodel.
or you change the type hierarchy to reflect it

<eClassifiers xsi:type="ecore:EClass" name="JdlBracedExpression" eSuperTypes="#//JdlExpression">
<eStructuralFeatures xsi:type="ecore:EReference" name="exp" eType="#//JdlExpressions"
containment="true"/>
</eClassifiers>

https://www.eclipse.org/Xtext/documentation/307_special_languages.html#expressions

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