/*	CalcParser.java
	Implementes a simple expression language parser
	Uses java.io.StreamTokenizer and recursive descent parsing

	Compile:
	javac CalcParser.java

	Execute:
	java CalcParser <filename>
*/

import java.io.*;
public class CalcParser
{ private static StreamTokenizer tokens;
  private static int ahead;
  public static void main(String argv[]) throws IOException
  { FileInputStream stream = new FileInputStream(argv[0]);
    InputStreamReader reader = new InputStreamReader(stream);
    tokens = new StreamTokenizer(reader);
    tokens.ordinaryChar('.');
    tokens.ordinaryChar('-');
    tokens.ordinaryChar('/');
    get();
    expr();
    if (ahead == (int)'$')
      System.out.println("Syntax ok");
    else
      System.out.println("Syntax error");
    stream.close();
  }
  private static void get() throws IOException
  { ahead = tokens.nextToken();
  }
  private static void expr() throws IOException
  { term();
    term_tail();
  }
  private static void term_tail() throws IOException
  { if (ahead == (int)'+' || ahead == (int)'-')
    { add_op();
      term();
      term_tail();
    }
  }
  private static void term() throws IOException
  { factor();
    factor_tail();
  }
  private static void factor_tail() throws IOException
  { if (ahead == (int)'*' || ahead == (int)'/')
    { mult_op();
      factor();
      factor_tail();
    }
  }
  private static void factor() throws IOException
  { if (ahead == (int)'(')
    { get();
      expr();
      if (ahead == (int)')')
        get();
      else System.out.println("closing ) expected");
    }
    else if (ahead == (int)'-')
    { get();
      factor();
    }
    else if (ahead == tokens.TT_WORD)
      get();
    else if (ahead == tokens.TT_NUMBER)
      get();
    else System.out.println("factor expected");
  }
  private static void add_op() throws IOException
  { if (ahead == (int)'+' || ahead == (int)'-')
      get();
  }
  private static void mult_op() throws IOException
  { if (ahead == (int)'*' || ahead == (int)'/')
      get();
  }
}