Programming-Language-Theory/Lexer.java at main · LePetitRenard01/Programming-Language-Theory · GitHub

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// Lexer.java
// Lexical analyzer for S

import java.io.*;

public class Lexer {
    private char ch = ' ';
    private BufferedReader input;
    private final char eolnCh = '\n';
    private final char eofCh = '\004';
    static boolean interactive = false;

    public Lexer (String fileName) { // source filename
        try {
            input = new BufferedReader (new FileReader(fileName));
        }
        catch (FileNotFoundException e) {
            System.out.println("File not found: " + fileName);
            System.exit(1);
        }
    }

    public Lexer ( ) { // from standard input
	    input = new BufferedReader (new InputStreamReader(System.in));
    }

    private char getchar() { // Return next char
        int c = 0;
        try {
            c = input.read();
            if (c == -1)
                c = eofCh;
        } catch(IOException e) { System.err.println(e);}
        return (char) c;
    }

    public Token getToken( ) { // Return next token
        do {
            if (Character.isLetter(ch)) { // ident or keyword
                String s = "";
                do {
                    s += ch;
                    ch = getchar();
                } while (Character.isLetter(ch) || Character.isDigit(ch));
                return Token.idORkeyword(s);
            }

            if (Character.isDigit(ch)) { // number
                String s = "";
                do {
                    s += ch;
                    ch = getchar();
                } while (Character.isDigit(ch));
                return Token.NUMBER.setValue(s);
            }

	        switch (ch) {
            case ' ': case '\t': case '\r':
                ch = getchar();
                break;

	        case eolnCh:
		        ch = getchar();
			    if (ch == '\r')			// for Windows
			        ch = getchar();		// for Windows
		        if (ch == eolnCh && interactive)
		            return Token.EOF;
		        break;

            case '/':  // divide
                ch = getchar();
                if (ch != '/')  return Token.DIVIDE;
                do {
                    ch = getchar();
                } while (ch != eolnCh);
                ch = getchar();
                break;

	        case '\"':  // string literal
                String s ="";
		        while ((ch = getchar()) != '\"')
		             s += ch;
                ch = getchar();
                return Token.STRLITERAL.setValue(s);
            case eofCh:
		        return Token.EOF;
            case '+': ch = getchar();
                return Token.PLUS;
            case '-': ch = getchar();
                return Token.MINUS;
            case '*': ch = getchar();
                return Token.MULTIPLY;
            case '(': ch = getchar();
                return Token.LPAREN;
            case ')': ch = getchar();
                return Token.RPAREN;
            case '{': ch = getchar();
                return Token.LBRACE;
            case '}': ch = getchar();
                return Token.RBRACE;
            case '[': ch = getchar();
                return Token.LBRACKET;
            case ']': ch = getchar();
                return Token.RBRACKET;
            case ';': ch = getchar();
                return Token.SEMICOLON;
            case ',': ch = getchar();
                return Token.COMMA;
            case '&': ch = getchar();
		        return Token.AND;
            case '|': ch = getchar();
		        return Token.OR;
            case '=': ch = getchar();
                if (ch != '=') return Token.ASSIGN;
                else {ch = getchar(); return Token.EQUAL;}
            case '<': ch = getchar();
                if (ch != '=') return Token.LT;
                else {ch = getchar(); return Token.LTEQ;}
            case '>': ch = getchar();
                if (ch != '=') return Token.GT;
                else {ch = getchar(); return Token.GTEQ;}
            case '!': ch = getchar();
                if (ch != '=') return Token.NOT;
                else {ch = getchar(); return Token.NOTEQ;}
            } // switch
        } while (true);
    } // next

    public void error (String msg) {
        System.err.println("Error: " + msg);
        // System.exit(1);
    }

    static public void main (String[] args) {
        Lexer lexer;
	    if (args.length == 0)
            lexer = new Lexer( );
	    else
            lexer = new Lexer(args[0]);

        Token tok = lexer.getToken( );
        while (tok != Token.EOF) {
            System.out.println(tok.toString());
            tok = lexer.getToken( );
        }
    } // main
}