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A general-purpose mathematical expression parser, which converts infix expression strings into postfix queues and/or syntax trees.

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/*
 * #%L
 * Parsington: the SciJava mathematical expression parser.
 * %%
 * Copyright (C) 2015 - 2016 Board of Regents of the University of
 * Wisconsin-Madison.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * #L%
 */

package org.scijava.parse;

/**
 * A mutable parse position. Similar to {@link java.text.ParsePosition}, but
 * less complex.
 *
 * @author Curtis Rueden
 */
public class Position {

	private int index;

	public int get() {
		return index;
	}

	public void set(final int index) {
		this.index = index;
	}

	public void inc() {
		inc(1);
	}

	public void inc(final int count) {
		index += count;
	}

	public char ch(final CharSequence s) {
		return ch(s, 0);
	}

	public char ch(final CharSequence s, final int offset) {
		final int i = get() + offset;
		return i < s.length() ? s.charAt(i) : '\0';
	}

	/** Throws {@link IllegalArgumentException} when syntax is incorrect. */
	public void die(final String message) {
		throw new IllegalArgumentException(messageWithDetails(message));
	}

	/** Throws {@link IllegalStateException} if something goes wrong. */
	public void assertThat(final boolean condition, final String message) {
		if (condition) return;
		fail(message);
	}

	/** Throws {@link IllegalStateException} when something is wrong. */
	public void fail(final String message) {
		throw new IllegalStateException(messageWithDetails(message));
	}

	// -- Object methods --

	@Override
	public String toString() {
		return "" + get();
	}

	// -- Helper methods --

	private String messageWithDetails(final String message) {
		return message + " at index " + get();
	}

}