Exemplo n.º 1
0
 // Parse the input words stream into corresponding statement
 public Statement parseStatement(TokenScanner scanner) {
   String token = scanner.nextToken();
   if (token.equals("PRINT")) {
     return new PrintStmt(scanner);
   }
   if (token.equals("LET")) {
     return new LetStmt(scanner);
   }
   if (token.equals("INPUT")) {
     return new InputStmt(scanner);
   }
   if (token.equals("GOTO")) {
     return new GoToStmt(scanner);
   }
   if (token.equals("IF")) {
     return new IfStmt(scanner);
   }
   if (token.equals("END")) {
     return new EndStmt(scanner);
   }
   if (token.equals("REM")) {
     return new RemStmt(scanner);
   }
   System.out.println("Not a legal statement");
   return null;
 }
Exemplo n.º 2
0
 public Expression readT(TokenScanner scanner) {
   String token = scanner.nextToken();
   if (token.charAt(0) >= 'A' && token.charAt(0) <= 'Z'
       || token.charAt(0) >= 'a' && token.charAt(0) <= 'z') {
     return new IdentifierExp(token);
   } else if (token.charAt(0) >= '0' && token.charAt(0) <= '9') {
     return new ConstantExp(Integer.parseInt(token));
   }
   if (!token.equals("(")) {
     System.out.println("Unexpected token");
   }
   Expression exp = readE(scanner, 0);
   if (!scanner.nextToken().equals(")")) {
     System.out.println("Unbalanced parentheses");
   }
   return exp;
 }
Exemplo n.º 3
0
 public Expression readE(TokenScanner scanner, int prec) {
   Expression exp = readT(scanner);
   String token = null;
   while (true) {
     token = scanner.nextToken();
     int tprec = precedence(token);
     if (tprec <= prec) {
       break;
     }
     Expression rhs = readE(scanner, tprec);
     exp = new CompoundExp(token, exp, rhs);
   }
   if (token != null) {
     scanner.saveToken(token);
   }
   return exp;
 }