class Environment {

    public Declaration lookupVariableDeclaration(String name) {
        Declaration declaration = lookupLocalVariableDeclaration(name);
        if (declaration != null) {
            return declaration;
        } else {
            if (getParent() != null) {
                return getParent().lookupVariableDeclaration(name);
            } else {
                return null;
            }
        }
    }

      Environment();
      Environment(Environment parent);
      Environment(Environment parent, Expression inputExpression);

}