public Declaration getDeclaration(String name) {
   for (Declaration d : declarations.getDeclarations()) {
     if (d.getName().equalsIgnoreCase(name)) {
       return d;
     }
   }
   return null;
 }
 public Expression getValue(String name) {
   Declaration declaration = getDeclaration(name);
   return (declaration != null) ? declaration.getExpression() : null;
 }