Xtext cross reference with this keyword

Question

I am currently in the process of making a new DSL with the help op Xtext. I want to be able to define rules in my grammar, where certain values can be manipulated and refer to the current object using this. However, I cannot get the syntax right for it to work.

I have taken a bit of code from the Xtext Expressions example and modified it to be able to also put a cross-reference to the cards value. How can I use the this keyword? I understood from some other SO questions that I can use my own scoping provider for this, but do not know where to start.

See some code:

// MyDSL.xtext

Game returns Game:
    'Game'
    name=STRING
    ...
    ('Cardpropertytypes' '{' cardpropertytypes+=CardPropertyType ( "," cardpropertytypes+=CardPropertyType)* '}' )?
    cards += Card*
;

Card returns Card:
    'Card'
    name=ID
    '{'
        'type' type=[CardType]
        ('cost' '{' cost+=Cost ( "," cost+=Cost)* '}' )?
        ('properties' '{' properties+=CardProperty ( "," properties+=CardProperty)* '}' )?
        ('rules' '{' rules+=CardRule ( "," rules+=CardRule)* '}' )?
        ('actions' '{' actions+=CardAction ( "," actions+=CardAction)* '}' )?
    '}';

CardRule returns CardRule:
    {CardRule}
    '{'
        ('description' description=STRING)?
        ('requirements' requirements=Addition)?
        ('action' action=Addition)?
        ('duration' duration=Duration)?
    '}';

CardProperty returns CardProperty:
  type=[CardPropertyType] (':' value=INT)?;

Addition returns Expression:
  Multiplication ({Addition.left=current} '+' right=Multiplication)*;

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

Primary returns Expression:
  Literal |
  '(' Addition ')';

Literal returns Expression: 
    {Expression}
    QualifiedName |
    NumberLiteral;

QualifiedName:
    ID ('.' ID)*;

NumberLiteral:
  value=INT;

// Card.mydsl

Cardpropertytypes {
    Toughness,
    Power,
    Flying,
    Indestructible
}
Card AdantoVanguard {
    ...
    properties {
        Toughness: 1,
        Power: 1,
        Flying
    }
    rules {
        {
            //action this.properties.Toughness + 2
            action ????
        }
    }
}

Clarification: If I have a Card model, which has properties as in the code sample above, I want to be able to say in the rules section:

this.properties.propertyName + 2

How can I achieve that?

which cross reference are you talking about? your grammar seems incomplete in that regard — Christian Dietrich

Christian Dietrich Christian Dietrich · Accepted Answer · 2017-12-18T18:35:22

in xtext cross references look like

ref=[SomeType]

which is short for

ref=[SomeType|ID]

which means that an ID will be parsed to refer to a SomeType so by replacing ID with another rule e.g.

ref=[SomeType|IDORTHIS]
...
IDORTHIS: ID | "this";

you can achieve the parsing side

for the scoping side you need to implement the scope provider

inside the scope provider

override getScope
use context and reference parameter to determine which reference is scoped
used the context to collect the elements you want to put into scope
create a new Scope e.g. using the methods inside the Scopesclass or intantiating a SimpleScope manually / EObjectDescription.create or ..... (your requirements are very vague regarding this)

Xtext cross reference with this keyword

1 Answers