Model:
	greetings+=Greeting*;
Greeting:
	'greeting' name=ID '{'
	definitions += Definition*
'}';
Definition:
	'def' name = ValidID '(' (params+=([Greeting]))')'
(':' type=[Greeting])?
body = XBlockExpression	
;

   	 	def dispatch void infer(Greeting greeting, IJvmDeclaredTypeAcceptor acceptor, boolean isPreIndexingPhase) {
   		
   		acceptor.accept(greeting.toClass(greeting.name))[
   			for (d:greeting.definitions){
   				members += greeting.toMethod(d.name, d.type)[
   					for (p : d.params){
   						parameters += p.toParameter(p.name, p.parameterType)
   					}
   					body = d.body
   				]
   			}
   		]

BuiltInFunction:
	'op' name = ValidID '('(params+=[Greeting] (',' params+=[Greeting])*)? ')'
	(':' type=Greeting)?
	body=XBlockExpression
;

members += greeting.toMethod(....)
parameters += p.toParameter(greeting.name, greeting.name.typeRef())

op displayGreeting (Welcom) {
return false;	
}

Greeting welcome {

boolean isDisplayed = displayGreeting(Welcom);
...
...
...
op displayGreeting (Welcom) {
return false;	
}
}

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.xbase.Xbase
generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"

Greeting:
	'greeting' name = ID '{'
		methods += Method* 
		body=XExpressionInClosure
'}'
;
Method:
	 UserDefinedFunction | BuiltInFunction 
;
BuiltInFunction:
	'op' name = ValidID '('(params+=[Greeting] (',' params+=[Greeting])*)? ')'
	(':' type=Greeting)?
	body=XBlockExpression
;
UserDefinedFunction:
	'def' name = ID '('(params+=FullJvmFormalParameter (',' params+=FullJvmFormalParameter)*)? ')'
	(':' type=JvmTypeReference)?
	body=XBlockExpression
	;

def dispatch void infer(Greeting greeting, IJvmDeclaredTypeAcceptor acceptor, boolean isPreIndexingPhase) {
			acceptor.accept(greeting.toClass(greeting.name)) [
				members += greeting.toConstructor()[]
					for (m : greeting.methods) {	  		 		
   		 		switch m {
   		 			UserDefinedFunction : {
   		 				members += greeting.toMethod(m.name, m.type ?: inferredType) [
   						for (p : m.params) {
   							parameters += p.toParameter(p.name, p.parameterType)
   						}
   						body = m.body
   						]
   	   				}
   	   				BuiltInFunction	: {
   	   					members += greeting.toMethod(m.name, boolean.typeRef() ?: inferredType) [
   	   					for (p: m.params) {
   	   					parameters += p.toParameter(greeting.name, greeting.name.typeRef())
   	   					}
   	   					body = m.body
   	   					]
   	   				}			
   	   			}
   		 	}
	    			members += greeting.toMethod("display", boolean.typeRef()) [
  					body = '''
  					'''
  					]
			]
   			}

greeting welcomeGreeting {

var isGreetingDisplayed = false;

isGreetingDisplayed = displayGreeting(welcomeGreeting)  
....
....
...

[b]<----ERROR - no viable alternative at input 'op'[/b]
op displayGreeting(welcomeGreeting) {
	
	if (welcomeGreeting.isDisplayed) { 
		//do something
	} else {
		//do something
	}
	return result;
}	
}

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.xbase.Xbase

generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"
import "http://www.eclipse.org/xtext/xbase/Xbase" as xbase

Greeting:
	'greeting' name = ID '{'
		body=XBlockExpressionWithoutBraces
		methods += Method* 
'}'
;

XBlockExpressionWithoutBraces returns xbase::XExpression: 
	{xbase::XBlockExpression}
		(expressions+=XExpressionOrVarDeclaration ';'?)*
	;

Method:
	 UserDefinedFunction | BuiltInFunction 
;
BuiltInFunction:
	'op' name = ValidID '('(params+=[Greeting] (',' params+=[Greeting])*)? ')'
	(':' type=Greeting)?
	body=XBlockExpression
;
UserDefinedFunction:
	'def' name = ID '('(params+=FullJvmFormalParameter (',' params+=FullJvmFormalParameter)*)? ')'
	(':' type=JvmTypeReference)?
	body=XBlockExpression
	;

/*
 * generated by Xtext 2.9.0
 */
package org.xtext.example.mydsl.jvmmodel

import com.google.inject.Inject
import org.eclipse.xtext.xbase.jvmmodel.AbstractModelInferrer
import org.eclipse.xtext.xbase.jvmmodel.IJvmDeclaredTypeAcceptor
import org.eclipse.xtext.xbase.jvmmodel.JvmTypesBuilder
import org.xtext.example.mydsl.myDsl.BuiltInFunction
import org.xtext.example.mydsl.myDsl.Greeting
import org.xtext.example.mydsl.myDsl.UserDefinedFunction

/**
 * <p>Infers a JVM model from the source model.</p> 
 *
 * <p>The JVM model should contain all elements that would appear in the Java code 
 * which is generated from the source model. Other models link against the JVM model rather than the source model.</p>     
 */
class MyDslJvmModelInferrer extends AbstractModelInferrer {

    /**
     * convenience API to build and initialize JVM types and their members.
     */
	@Inject extension JvmTypesBuilder

	def dispatch void infer(Greeting greeting, IJvmDeclaredTypeAcceptor acceptor, boolean isPreIndexingPhase) {
			acceptor.accept(greeting.toClass(greeting.name)) [
				members += greeting.toConstructor()[]
					for (m : greeting.methods) {	  		 		
   		 		switch m {
   		 			UserDefinedFunction : {
   		 				members += greeting.toMethod(m.name, m.type ?: inferredType) [
   						for (p : m.params) {
   							parameters += p.toParameter(p.name, p.parameterType)
   						}
   						body = m.body
   						]
   	   				}
   	   				BuiltInFunction	: {
   	   					members += greeting.toMethod(m.name, boolean.typeRef() ?: inferredType) [
   	   					for (p: m.params) {
   	   					parameters += p.toParameter(greeting.name, greeting.name.typeRef())
   	   					}
   	   					body = m.body
   	   					]
   	   				}			
   	   			}
   		 	}
	    			members += greeting.toMethod("display", boolean.typeRef()) [
  					body =  greeting.body
  					]
			]
   			}
}