The figure below contains a complete and working grammar file - example for a simple arithmetic language.
+These examples come from the test/src/grammar and
+ test/src/java directories. The source code has been
+ simplified in these examples in order to be easier to read. Please
+ refer to the original source code in the above directories for the
+ complete compilable versions. Also note that the corresponding C#
+ examples are found in the test/src/csharp
+ directory.
The figure below contains a complete and working example of a + grammar file for a simple arithmetic language.
To create a parser for the grammar above, the parser source
+ code must first be created. If the grammar above has been stored
+ in the file arithmetic.grammar, this can be
+ accomplished with the following command:
# java -jar lib/grammatica-.jar arithmetic.grammar --javaoutput test+ +
This will create the files ArithmeticAnalyzer.java,
+ ArithmeticConstants.java,
+ ArithmeticParser.java, and
+ ArithmeticTokenizer.java in the test
+ subdirectory. These files contain the source code for the parser.
+ In order to call the parser, the method in the figure below can
+ be inserted into another Java class.
private Node parseArithmetic(String input) {
+ Parser parser = null;
+
+ parser = new ArithmeticParser(new StringReader(input));
+ return parser.parse();
+}
+ In the case of the arithmetic language, is it also interesting
+ to analyze and evaluate the contents of the string. This can be
+ done by subclassing the ArithmeticAnalyzer class and
+ overloading the callback methods for the relevant productions. A
+ small example of this can be seen in the figure below.
class ArithmeticCalculator extends ArithmeticAnalyzer {
+
+ protected Node exitNumber(Token node) {
+ node.addValue(new Integer(node.getImage()));
+ return node;
+ }
+
+ protected Node exitExpression(Production node) {
+ ArrayList values = getChildValues(node);
+ Integer value1;
+ Integer value2;
+ String op;
+ int result;
+
+ if (values.size() == 1) {
+ result = ((Integer) values.get(0)).intValue();
+ } else {
+ value1 = (Integer) values.get(0);
+ value2 = (Integer) values.get(2);
+ op = (String) values.get(1);
+ result = operate(op, value1, value2);
+ }
+ node.addValue(new Integer(result));
+ return node;
+ }
+
+ protected Node exitExpressionTail(Production node) {
+ node.addValues(getChildValues(node));
+ return node;
+ }
+
+ protected Node exitTerm(Production node) {
+ ArrayList values = getChildValues(node);
+ Integer value1;
+ Integer value2;
+ String op;
+ int result;
+
+ if (values.size() == 1) {
+ result = ((Integer) values.get(0)).intValue();
+ } else {
+ value1 = (Integer) values.get(0);
+ value2 = (Integer) values.get(2);
+ op = (String) values.get(1);
+ result = operate(op, value1, value2);
+ }
+ node.addValue(new Integer(result));
+ return node;
+ }
+
+ protected Node exitTermTail(Production node) {
+ node.addValues(getChildValues(node));
+ return node;
+ }
+
+ protected Node exitFactor(Production node) throws ParseException {
+ int result;
+
+ if (node.getChildCount() == 1) {
+ result = getIntValue(getChildAt(node, 0), 0);
+ } else {
+ result = getIntValue(getChildAt(node, 1), 0);
+ }
+ node.addValue(new Integer(result));
+ return node;
+ }
+
+ protected Node exitAtom(Production node) {
+ node.addValues(getChildValues(node));
+ return node;
+ }
+
+