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/*******************************************************************************
* Copyright (c) 2009, 2019 Mountainminds GmbH & Co. KG and Contributors
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Marc R. Hoffmann - initial API and implementation
*
*******************************************************************************/
package org.jacoco.examples.parser;
import static java.io.StreamTokenizer.TT_EOF;
import static java.io.StreamTokenizer.TT_NUMBER;
import java.io.IOException;
import java.io.StreamTokenizer;
import java.io.StringReader;
import org.jacoco.examples.expressions.Add;
import org.jacoco.examples.expressions.Const;
import org.jacoco.examples.expressions.Div;
import org.jacoco.examples.expressions.IExpression;
import org.jacoco.examples.expressions.Mul;
import org.jacoco.examples.expressions.Sub;
public class ExpressionParser {
private final StreamTokenizer tokenizer;
public ExpressionParser(final String s) throws IOException {
tokenizer = new StreamTokenizer(new StringReader(s));
tokenizer.ordinaryChar('(');
tokenizer.ordinaryChar(')');
tokenizer.ordinaryChar('+');
tokenizer.ordinaryChar('-');
tokenizer.ordinaryChar('*');
tokenizer.ordinaryChar('/');
}
public IExpression parse() throws IOException {
tokenizer.nextToken();
final IExpression e = term();
expect(TT_EOF);
return e;
}
private IExpression term() throws IOException {
IExpression e = product();
while (true) {
if (accept('+')) {
e = new Add(e, product());
} else if (accept('-')) {
e = new Sub(e, product());
} else {
return e;
}
}
}
private IExpression product() throws IOException {
IExpression e = factor();
while (true) {
if (accept('*')) {
e = new Mul(e, factor());
} else if (accept('/')) {
e = new Div(e, factor());
} else {
return e;
}
}
}
private IExpression factor() throws IOException {
final IExpression e;
if (accept('(')) {
e = term();
expect(')');
} else {
expect(TT_NUMBER);
e = new Const(tokenizer.nval);
}
return e;
}
private boolean accept(final int type) throws IOException {
if (tokenizer.ttype == type) {
tokenizer.nextToken();
return true;
}
return false;
}
private void expect(final int type) throws IOException {
if (tokenizer.ttype != type) {
throw new IOException("Invalid Syntax.");
}
tokenizer.nextToken();
}
}
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