scan.java

pl0编译器的java版本

// Things to think about adding:
// 1. A new exception to return at end of file.
// 2. A call back when a new line is read so 
//    a listing can be produced

import java.io.*;
import java.util.*;

public class Scan {
    BufferedReader in;
    String currLine;
    HashMap keywords;
    HashMap syms;
    int posnInLine;     // position in the input line of the most recently
                        // read character (the first is char 0).
    LineRead callback;

    Scan(BufferedReader br, LineRead lr) {
    	in = br;
    	callback = lr;
    	currLine = "";
    
    	keywords = new HashMap();
    	keywords.put("begin", new Integer(Symbol.beginsym));
    	keywords.put("call", new Integer(Symbol.callsym));
    	keywords.put("const", new Integer(Symbol.constsym));
    	keywords.put("do", new Integer(Symbol.dosym));
    	keywords.put("end", new Integer(Symbol.endsym));
    	keywords.put("if", new Integer(Symbol.ifsym));
    	keywords.put("odd", new Integer(Symbol.oddsym));
    	keywords.put("procedure", new Integer(Symbol.procsym));
        keywords.put("read", new Integer(Symbol.readsym));
    	keywords.put("then", new Integer(Symbol.thensym));
    	keywords.put("var", new Integer(Symbol.varsym));
    	keywords.put("while", new Integer(Symbol.whilesym));
        keywords.put("write", new Integer(Symbol.writesym));
    
    	syms = new HashMap();
    	syms.put("+", new Integer(Symbol.plus));
    	syms.put("-", new Integer(Symbol.minus));
    	syms.put("*", new Integer(Symbol.times));
    	syms.put("/", new Integer(Symbol.slash));
    	syms.put("(", new Integer(Symbol.lparen));
    	syms.put(")", new Integer(Symbol.rparen));
    	syms.put("=", new Integer(Symbol.eql));
    	syms.put(",", new Integer(Symbol.comma));
    	syms.put(".", new Integer(Symbol.period));
    	syms.put("#", new Integer(Symbol.neq));
    	syms.put(";", new Integer(Symbol.semicolon));
    }

    String ch2str(char ch) {
    	return new Character(ch).toString();
    }

    char getch() throws IOException {
	    if (currLine.length() == 0) {
	        currLine = in.readLine();
	        if (currLine == null) {
		        throw new IOException("Unexpected end of file\n");
	        }
	        if (callback != null) {
		        callback.lineRead(currLine);
	        }
	        currLine = currLine + " ";
	        posnInLine = -1; 
	    }
	
	    char ret = currLine.charAt(0);
	    currLine = currLine.substring(1);
	    posnInLine++;
	    return ret;
    }

    void ungetch(char ch) {
	    currLine = ch2str(ch) + currLine;
	    posnInLine--;
    }

    Symbol getSym() throws IOException {
	    char ch;
    	do {
	        ch = getch();
	    } while (ch==' ' || ch==10 || ch==9);

	    if (Character.isLetter(ch)) {  // Identifier or reserved word
	        String id = ch2str(ch);

	        for (;;) {
		        ch = getch();
		        if (!Character.isLetter(ch) && !Character.isDigit(ch)) {
		            ungetch(ch);
		            break;
		        }
		        id = id + ch2str(ch);
	        }

	        Integer i = (Integer) keywords.get(id);
	        if (i == null) {
		        // Not a keyword
		        return new Symbol(Symbol.ident, id);
	        }
	        // A keyword!
	        return new Symbol(i.intValue());
	    }

	    if (Character.isDigit(ch)) {   // A number
	        String num = ch2str(ch);

	        for (;;) {
		        ch = getch();
		        if (!Character.isDigit(ch)) {
		            ungetch(ch);
		            break;
		        }
		        num = num + ch2str(ch);
	        }
	    
	        int i;
	        try {
		        i = Integer.parseInt(num);
	        } catch (NumberFormatException nfe) {
		        return new Symbol(Symbol.number, true, 0);
	        }
	        return new Symbol(Symbol.number, false, i);
	    }

	    if (ch == ':') {
	        ch = getch();
	        if (ch != '=') {
		        return new Symbol(Symbol.nul);
	        }
	        return new Symbol(Symbol.becomes);
	    } else {
            if (ch == '<') {
                ch = getch();
                if (ch == '=') {
                    return new Symbol(Symbol.leq);    
                } else {
                    ungetch(ch);
                    return new Symbol(Symbol.lss);
                }
            } else {
                if (ch == '>') {
                    ch = getch();
                    if (ch == '=') {
                        return new Symbol(Symbol.geq);        
                    } else {
                        ungetch(ch); 
                        return new Symbol(Symbol.gtr); 
                    }
                }
            }
	    }
	
	    Integer i = (Integer) syms.get(ch2str(ch));
	    if (i == null) {
	        return new Symbol(Symbol.nul);
	    }
	    return new Symbol(i.intValue());
    }
    
    public int linePosn() {
	    return posnInLine;
    }
/*
    public static void main(String args[]) {
	    Scan s = new Scan(new BufferedReader(new InputStreamReader(System.in)), null);
	
	    try {
	        while (true) {
		        Symbol sym = s.getSym();
		        System.out.print(sym.symtype);
		        if (sym.symtype == Symbol.ident) {
		            System.out.print(" " + sym.id);
		        } else if (sym.symtype == Symbol.number) {
		            if (sym.overflow) {
			            System.out.print(" overflow");
		            } else {
			            System.out.print(" " + sym.num);
		            }
		        }
		        System.out.println();
	        }
	    } catch (IOException ioe) {
	    }
    }
*/
}