public Binding lookup(String varName){
  if (varName.equals(binding.getVarName())) {
    return binding;
  }
  return parent != null ? parent.lookup(varName) : null;
}

public Binding lookup ( String varName ) { if ( varName . equals ( binding . getVarName ( ) ) ) { return binding ; } return parent != null ? parent . lookup ( varName ) : null ; }
look for a binding for given variable .
