slpscanner.java

compiler constructor using the recursive deceiding way

/*****************************************************************/
/*                                                               */
/* This is a hand-written lexical analyser for SLP written in    */
/* Java. It implements the SLPTokeniserConstants interface which */
/* was generated by the JavaCC lexical analyser. This would not  */
/* normally be done, but it ensures compatibility between the    */
/* two different lexical analysers.                              */
/*                                                               */
/*****************************************************************/

import java.io.*;

public class SLPScanner implements SLPTokeniserConstants {

/* This implements

InputStream input_stream; /* This is where the input comes from */
char c; /* This gives the next character in the input stream */
int line = 1; /* The current line number in the input */
int i;

public SLPScanner (InputStream stream) {
  input_stream = stream;
  try {
    i = input_stream.read();
    c = (char)i;
  }
  catch (IOException e) {};
}

/* getNextToken returns the next token */
/*    recognised in the input stream   */

public Token getNextToken() {
  String s = new String("");
  Token t = new Token();

  try {

    /* Skip white space */

    while ((c == ' ') || (c== '\t') || (c == '\n') || (c == '\r') || (c == '\f')) {
      if (c == '\n')
         line++;
      i = input_stream.read();
      c = (char)i;
    } 
    t.beginLine = line;
    t.endLine = line;

    /* Check for end of input */

    if (i == -1) {
      t.kind = EOF;
      return t;
    }
    if (Character.isLetter(c)) { 

      /* identifier or reserved word encountered */

      do {
        s = s + String.valueOf(c);
        c = (char)input_stream.read();
      } while (Character.isLetter(c));
      t.image = s;
      if (s.equals("print")) 
        t.kind = PRINT;
      else 
        t.kind = ID;
      return t;
    }    
    else if (Character.isDigit(c)) {

      /* number encountered */

      do {
        s = s + String.valueOf(c);
        i = input_stream.read();
        c = (char)i;
      } while (Character.isDigit(c));
      t.image = s;
      t.kind = NUM;
      return t;  
    }
    else {
      switch(c) {
        case ',': t.kind = COMMA;
                  t.image = ",";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case ';': t.kind = SEMIC;
                  t.image = ";";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case '(': t.kind = LBR;
                  t.image = "(";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case ')': t.kind = RBR;
                  t.image = ")";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case ':': i = input_stream.read();
                  c = (char)i;
                  if (c == '=') {
                    t.kind = ASSIGN;
                    t.image = ":=";
                    i = input_stream.read();
                    c = (char)i;
                  }
                  else {
                    t.kind = OTHER;
                    t.image = "=";
                  }
                  return t; 
        case '+': t.kind = PLUS_SIGN;
                  t.image = "+";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case '-': t.kind = MINUS_SIGN;
                  t.image = "-";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case '*': t.kind = MULT_SIGN;
                  t.image = "*";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        case '/': t.kind = DIV_SIGN;
                  t.image = "/";
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
        default:  t.kind = OTHER;
                  t.image = String.valueOf(c);
                  i = input_stream.read();
                  c = (char)i;
                  return t; 
      }
    }
  }
  catch (IOException e) {
    t.kind = OTHER;
    t.image = String.valueOf(c);
    return t; 
  }
}

}