jaskell.parsec.common.Option Maven / Gradle / Ivy

Go to download
package jaskell.parsec.common;

import jaskell.parsec.ParsecException;

import java.io.EOFException;
import java.util.Optional;

/**
 * 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.
 */
public class Option
    implements Parsec> {
    private final Parsec parser;

    public Option(Parsec parser) {
        this.parser = parser;
    }

    @Override
    public  Optional parse(State s)
            throws EOFException, ParsecException {
        Integer status = s.status();
        try{
            return Optional.of(parser.parse(s));
        } catch (Exception e) {
            if(status.equals(s.status())) {
                return Optional.empty();
            } else {
                throw e;
            }
        }
    }
}