Programming Implementation Grammar's

/** * Programming Languages: Implementation and Design. * * A Simple Compiler Adapted from Sebesta (2010) by Josh Dehlinger further modified by Adam Conover * (2012-2015) * * A simple compiler used for the simple English grammar in Section 2.2 of Adam Brooks Weber's * "Modern Programming Languages" book. Parts of this code was adapted from Robert Sebesta's * "Concepts of Programming Languages". * * This compiler assumes that the source file containing the sentences to parse is provided as the * first runtime argument. Within the source file, the compiler assumes that each sentence to parse * is provided on its own line. * * NOTE: A "real" compiler would more likely treat an entire file as a single stream of input, * rather than each line being an independent input stream. */ import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class Compiler { /** * It is assumed that the first argument provided is the name of the source file that is to be * "compiled". */ public static void main(String[] args) throws IOException { //args = new String[]{"<some hard coded path for testing>"}; //args = new String[]{"D:\\Version_Controlled\\_SVN_\\Newton\\COS420\\Java\\ParserSample\\input.txt"}; if (args.length < 1) { System.out.println("Need a filename!"); } else { // Java 7 "try-with-resource" to create the file input buffer. try (BufferedReader br = new BufferedReader(new FileReader(args[0]))) { // Create the new lexer. LexicalAnalyzer lexer = new LexicalAnalyzer(); // Start lexing and parsing. processFile(lexer, br); } } } /** * Reads each line of the input file and invokes the lexer and parser for each. */ static void processFile(LexicalAnalyzer lexer, BufferedReader br) throws IOException { String sourceLine; // Read each line in the source file to be compiled as a unique sentence // to check against the grammar. while ((sourceLine = br.readLine()) != null) { // Ignore empty lines and comments. if (sourceLine.trim().length() <= 0) { continue; } if (sourceLine.trim().startsWith("#")) { System.out.println("Comment: " + sourceLine.substring(1).trim()); continue; } // Create a new syntax analyzer over the provided lexer. SyntaxAnalyzer parser = new SyntaxAnalyzer(lexer); // Parse the given sentence against the given grammar. We assume that the // sentence, <S>, production is the start state. try { // Start the lexer... lexer.start(sourceLine); // Start the parser... parser.analyze(); // No exceptions, so we must be good! System.out.printf("The sentence '%s' follows the BNF grammar.%n", sourceLine); } catch (ParseException error) { // If a syntax error was found, print that the sentence does not follow the grammar. System.out.printf("SYNTAX ERROR while processing: '%s'%n", sourceLine); System.out.printf("ERROR MSG: %s%n", error.getErrMsg()); } System.out.println("-----------------------------------------------------------"); } } }