类 Option<E,T>
java.lang.Object
jaskell.parsec.common.Option<E,T>
public class Option<E,T> extends Object implements Parsec<E,Optional<T>>
Created by Mars Liu on 16/9/18.
Option accept a parsec<E, T, Status, Tran> and
return new one parsec<Optional<T>, E, Status, Tran>.
If the parser fail, Option parsec just return option.empty without Exception thrown.