//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.gdata.util.parser;
/**
* The <code>Alternative</code> parser parses either the <code>left</code> or
* <code>right</code> sub-parsers. If the <code>left</code> parser matches, the
* <code>right</code> parser is not invoked. This short-circuiting is similar
* to the way the evaluation of the logical-or (<code>||</code>) operator is
* short-circuited in C++ and Java. It is important to be aware of the
* short-circuiting in cases where the <code>right</code> parser contains a
* <code>Action</code>.
*
* The following is a complicated way of constructing a parser which matches
* letters:
*
* Parser p = Parser.alternative(Chset.LOWER, Chset.UPPER);
* p.parse("a") -> matches "a"
* p.parse("A") -> matches "A"
*
* @param <T>
* @see Parser
*
*/
public class Alternative<T> extends Parser<T> {
private Parser<? super T> left;
private Parser<? super T> right;
/**
* Class constructor.
*
* @param left The <code>Parser</code> that is matched against the parse
* buffer first.
*
* @param right The <code>Parser</code> that is matched against the parse
* buffer if the <code>left</code> parser does not match.
*/
public Alternative(Parser<? super T> left, Parser<? super T> right) {
this.left = left;
this.right = right;
}
/**
* Matches the current prefix of the buffer being parsed
* <code>buf[start,end]</code> against <code>left</code> or
* <code>right</code> sub-parsers.
*
* @see Parser#parse
*/
@Override
public int parse(char[] buf, int start, int end, T data) {
int hit = left.parse(buf, start, end, data);
if (hit != NO_MATCH) {
return hit;
}
return right.parse(buf, start, end, data);
}
};