is it possible to assign constant values to attributes in xtext rule? -

i have metamodel in have class range min max integer values , want define xtext dsl, in can define range 1..10, standard defaults ? , ! stand 0..1 or 1..1. looked around documentation, couldn't find way define in xtext grammar. far, have rule general case

range: min=int '..' max=int;

however, didn't find way define like

range: '?' min=0 max=1;

range: '!' min=1 max=1;

how achieve similar behavior dsl?

please note not interested in generating metamodel grammar, dsl models should adhere existing metamodel.

i dont know easy solution might able customize xtexts object creation e.g. like

model: ranges+=abstractrange*; abstractrange returns range: explicitrange | zorange | oorange; explicitrange returns range: min=int ".." max=int; zorange returns range: {range} max=zeroone; zeroone returns ecore::eint: "?"; oorange returns range: {range} max=oneone; oneone returns ecore::eint: "!"; 

and following customizations

class mydslecoreelementfactory extends defaultecoreelementfactory {      @inject extension mydslgrammaraccess      override set(eobject object, string feature, object value, string rulename, inode node) throws valueconverterexception {         if (object instanceof range) {             if (rulename == grammar.name+"."+zeroonerule.name) {                 object.max = 1                 object.min = 0                 return;             } else if (rulename == grammar.name+"."+oneonerule.name) {                 object.max = 1                 object.min = 1                 return;             }          }         super.set(object, feature, value, rulename, node)     }  } 

bound this

class mydslruntimemodule extends abstractmydslruntimemodule {      override bindiastfactory() {         mydslecoreelementfactory     }  } 

unfortunately org.eclipse.xtext.parser.iastfactory.create(eclassifier) not have second param specifies node or rule in , resist introduce subclasses ranges (in metamodel inherited one) make bit easy (override create only)