Student
       age:String    <=== getting error here as it can't resolve String

School
      students:Student

MyEStructuralFeature returns ecore::EStructuralFeature:
	{ecore::EAttribute} name=ID ':'  (eType=[ ecore::EDataType|MyDefaultDataType] (defaultValueLiteral=MyValue)?)
	| {ecore::EReference} name=ID ':' (eType=[ecore::EClass])
;

MyEClass returns ecore::EClass:
	{ecore::EClass} name=ID (NEWLINE eStructuralFeatures+=MyEStructuralFeature)+;

MyDataType returns ecore::EDataType:
	{EBoolean} name='Boolean'
	| {EInteger} name='Integer'
	| {ENumber} name='Number'
	| {EString} name='String'
	| {UUID} name='UUID';

MyDefaultDataType:
	'Boolean' | 'Integer' | 'Number' | 'String' | 'UUID';

https://www.eclipse.org/forums/index.php/m/1424738/#msg_1424738

FPackage /*returns ecore::EPackage*/:
	(eClassifiers+=FClass
	(NEWLINE NEWLINE eClassifiers+=FClass)*)?;

FProperty returns ecore::EStructuralFeature:
	{FProperty} name=ID ':' ((multi?=ASTERISK)? ((eAttributeType=FDataType (defaultValueLiteral=FValue)?) |
	eReferenceType=[ecore::EClass]));

FClass returns ecore::EClass:
	{ecore::EClass} name=ID (NEWLINE eStructuralFeatures+=FProperty)+;

FValue:
	STRING | NUMBER | INT | BOOLEAN;

enum FDataType:
	Boolean='Boolean'
	| Integer='Integer'
	| Number='Number'
	| String='String'
	| UUID='UUID';

terminal ASTERISK:
	'*';

terminal BOOLEAN returns ecore::EBoolean:
	'true' | 'false';

terminal NUMBER returns ecore::EDouble:
	'-'? INT? '.' INT (('E' | 'e') '-'? INT)?;

terminal ID:
	'^'? ('a'..'z' | 'A'..'Z' | '_') ('a'..'z' | 'A'..'Z' | '_' | '0'..'9')*;

terminal INT returns ecore::EInt:
	('0'..'9')+;

terminal STRING returns ecore::EString:
	'"' ('\\' ('b' | 't' | 'n' | 'f' | 'r' | 'u' | '"' | "'" | '\\') | !('\\' | '"'))* '"' |
	"'" ('\\' ('b' | 't' | 'n' | 'f' | 'r' | 'u' | '"' | "'" | '\\') | !('\\' | "'"))* "'";

terminal ML_COMMENT:
	'/*'->'*/';

terminal SL_COMMENT:
	'//' !('\r' | '\n')* ('\r'? '\n')?;

terminal NEWLINE:
	('\r'? '\n');

terminal WS:
	('\t' | ' ')+;	

	override discardDerivedState(DerivedStateAwareResource resource) {
		resource.allContents.filter(typeof(FProperty)).forEach [ attr |
			(attr.eContainer as EClass).EStructuralFeatures.remove(attr)
		]
	}

	override installDerivedState(DerivedStateAwareResource resource, boolean preLinkingPhase) {
		resource.allContents.filter(FProperty).forEach [
			toEReference
		]
	}

	def EStructuralFeature toEStructuralFeature(FProperty attr) {
		if (attr.EReferenceType != null) {
			attr.toEReference
		} else {
			attr.toEAttribute
		}
	}

	def EStructuralFeature toEReference(FProperty ref) {
		val eReference = EcoreFactory::eINSTANCE.createEReference
		eReference.name = ref.name
		eReference.EType = ref.EReferenceType.eClass
		if (ref.multi)
			eReference.upperBound = -1
		var eClass = ref.eContainer as EClass
		eClass.EStructuralFeatures.remove(ref);
		eClass.EStructuralFeatures += eReference
		return eReference
	}

	def EStructuralFeature toEAttribute(FProperty attr) {
		val eAttribute = EcoreFactory::eINSTANCE.createEAttribute
		eAttribute.name = attr.name
		eAttribute.EType = attr.EAttributeType.toEDataType
		if (attr.multi)
			eAttribute.upperBound = -1
		eAttribute.defaultValueLiteral = attr.defaultValueLiteral
		var eClass = attr.eContainer as EClass
		eClass.EStructuralFeatures.remove(attr)
		eClass.EStructuralFeatures += eAttribute
		return eAttribute
	}

	def EDataType toEDataType(FDataType e) {
		switch (e) {
			case BOOLEAN:
				return EcorePackage::eINSTANCE.EBoolean
			case STRING:
				return EcorePackage::eINSTANCE.EString
			case NUMBER:
				return EcorePackage::eINSTANCE.EDouble
			case INTEGER:
				return EcorePackage::eINSTANCE.EInt
			case UUID: {
				val uuid = EcoreFactory::eINSTANCE.createEDataType
				uuid.name = e.getName
				uuid.instanceClassName = "java.util.UUID"
				return uuid
			}
		}
	}

Person 
     name:String
     parents: * Person // here it can't resolve the person ref

	def EStructuralFeature toEReference(FProperty ref) {
		val eReference = EcoreFactory::eINSTANCE.createEReference
		eReference.name = ref.name
		eReference.EType = ref.EReferenceType.eClass
		if (ref.multi)
			eReference.upperBound = -1
		var eClass = ref.eContainer as EClass
		eClass.EStructuralFeatures.remove(ref); //this part I remove the FProperty from the model
		eClass.EStructuralFeatures += eReference
		return eReference
	}

Customer
          name:String
          cutomers:* Customer

EClass : Customer     //EClass here
        name : EString    //EAttribute
        customers : Customer   //EReference