gistfile1.java

/***
 * Excerpted from "The Definitive ANTLR 4 Reference",
 * published by The Pragmatic Bookshelf.
 * Copyrights apply to this code. It may not be used to create training material, 
 * courses, books, articles, and the like. Contact us if you are in doubt.
 * We make no guarantees that this code is fit for any purpose. 
 * Visit http://www.pragmaticprogrammer.com/titles/tpantlr2 for more book information.
***/
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.ParseTree;

import java.io.FileInputStream;
import java.io.InputStream;

public class Calc {
    public static void main(String[] args) throws Exception {
        String inputFile = null;
        if ( args.length>0 ) inputFile = args[0];
        InputStream is = System.in;
        if ( inputFile!=null ) is = new FileInputStream(inputFile);
        ANTLRInputStream input = new ANTLRInputStream(is);
        LabeledExprLexer lexer = new LabeledExprLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        LabeledExprParser parser = new LabeledExprParser(tokens);
        ParseTree tree = parser.prog(); // parse

        EvalVisitor eval = new EvalVisitor();
        eval.visit(tree);
    }
}