int a = 1;
int b = 2;
boolean sleepSuccess = doSleep(2000); // sleep two seconds
int c = 3;
int d = 4;

int a = 1;
int b = 2;
doSleep(2000, new DoSleepCallback() {
  public void onTrigger(boolean rc) {
    boolean sleepSuccess = rc;
    int c = 3;
    int d = 4;
  }
});

grammar org.qedlang.qed.QED with jbase.Jbase // Jbase inherits Xbase

...

FunctionDeclaration return XExpression:
    =>({FunctionDeclaration} type=JvmTypeReference name=ValidID '(')
   (params+=FullJvmFormalParameter (',' params+=FullJvmFormalParameter)*)?
   ')' block=XBlockExpression
;

boolean doSleep(int millis) {} // async FunctionDeclaration element stub

public static class DoSleepCallback() {
  public abstract void onTrigger(boolean rc);
}
public void doSleep(int millis, DoSleepCallback callback) {
  <perform sleep and call callback.onTrigger(<success>)>
}

override appendFeatureCall(XAbstractFeatureCall call, ITreeAppendable b) {
...
        val feature = call.feature
  ...
        if (feature instanceof JvmExecutable) {
            b.append('(')

            val arguments = call.actualArguments

            if (!arguments.isEmpty) {
      ...
                arguments.appendArguments(b, shouldBreakFirstArgument)

      // HERE IS THE PART I DON'T KNOW HOW TO DO
      <IF feature IS A FunctionDeclaration>
        <argument.appendArgument(NEW GENERATED CALLBACK PARAMETER)>
        <INSERT REST OF XBlockExpression body INSIDE CALLBACK INSTANCE>
      <ENDIF>
            }

            b.append(');')
        }
    }

def void inferExpressions(JvmDeclaredType it, FunctionDeclaration function) {
    // now let's go over the features
    for ( f : (function.block as XBlockExpression).expressions ) {
        if (f instanceof FunctionDeclaration) {
            members += f.toClass(f.fullyQualifiedName) [
                inferVariables(f)
                superTypes += typeRef(FunctionDeclarationObject)

                // let's add a default constructor
                members += f.toConstructor [
                    for (p : f.params)
                        parameters += p.toParameter(p.name, p.parameterType)
                    body = f.block
                ]
                inferExpressions(f)
            ]
        }
    }
}