grammar org . xtext . Langa with org.eclipse.xtext.common.Terminals

generate langa "http : //www . xtext . org / Langa"

Model:
	( declarations += ConstantDeclaration)*;
	
ConstantDeclaration :
	'const' name = ID '=' val = INT;

grammar org.xtext.Langb with org.eclipse.xtext.common.Terminals

generate langb "http : // www . xtext . org / Langb"

import 'platform:/resource/org.xtext.langa/src-gen/org/xtext/Langa.ecore' as langa

Model:
	(definitions += ExpressionDefinition)*;
	
ExpressionDefinition :
	'exp' name = ID '=' exp = Expression;
	
Expression :
	Add;
	
Add returns Expression :
	TerminalExpression ({Add.left = current} '+' right = TerminalExpression)*;
	
TerminalExpression returns Expression :
	Reference | '(' Expression ')';
	
Reference :
	referred = [langa::ConstantDeclaration];

fragment = ecore.EcoreGeneratorFragment {
     			referencedGenModels = "platform:/resource/org.xtext.langa/src-gen/org/xtext/Langa.genmodel"
			}

org.eclipse.emf.mwe.core.WorkflowInterruptedException: The generated EPackage references an external EPackage, but 'referencedGenModels' hasn't been registered.
	at org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment.checkGenModelExists(EcoreGeneratorFragment.java:222)
	at org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment.proxifyExternalReferences(EcoreGeneratorFragment.java:214)
	at org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment.generate(EcoreGeneratorFragment.java:158)
	at org.eclipse.xtext.generator.CompositeGeneratorFragment.generate(CompositeGeneratorFragment.java:81)
	at org.eclipse.xtext.generator.LanguageConfig.generate(LanguageConfig.java:69)
	at org.eclipse.xtext.generator.Generator.generate(Generator.java:296)
	at org.eclipse.xtext.generator.Generator.invokeInternal(Generator.java:106)
	at org.eclipse.emf.mwe.core.lib.AbstractWorkflowComponent.invoke(AbstractWorkflowComponent.java:126)
	at org.eclipse.emf.mwe.core.lib.Mwe2Bridge.invoke(Mwe2Bridge.java:34)
	at org.eclipse.emf.mwe.core.lib.AbstractWorkflowComponent.invoke(AbstractWorkflowComponent.java:201)
	at org.eclipse.emf.mwe2.runtime.workflow.AbstractCompositeWorkflowComponent.invoke(AbstractCompositeWorkflowComponent.java:31)
	at org.eclipse.emf.mwe2.runtime.workflow.Workflow.run(Workflow.java:19)
	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Runner.run(Mwe2Runner.java:80)
	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Runner.run(Mwe2Runner.java:52)
	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Launcher.run(Mwe2Launcher.java:74)
	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Launcher.main(Mwe2Launcher.java:35)

fragment = ecore.EcoreGeneratorFragment {
    referencedGenModels = "platform:/resource/org.xtext.langa/src-gen/org/xtext/Langa.genmodel"
}

fragment = ecore.EcoreGeneratorFragment {
    // referencedGenModels = "uri to genmodel, uri to next genmodel"
}