calcparser.h

用于词法分析的词法分析器

/*
  $Id: CalcParser.h,v 1.1 1997/02/23 13:29:28 matt Exp $

  CalcParser class.  Implements a simple calculator parser and
  evaluator.
  
  (c) Matt Phillips, 1997.  */

/*
  Calculator grammar
  ------------------

  <expr>   ::= <term>   ( ['+' '-']       <term>   )*
  <term>   ::= <factor> ( ['/' '*' 'mod'] <factor> )*
  <factor> ::= number
  <factor> ::= '(' <expr> ')'
  <factor> ::= variable

*/

#ifndef _CalcParser_h
#define _CalcParser_h

#include <iostream.h>

#include "CalcScanner.h"

class CalcParser
{
public:

  CalcParser (istream &input_);

  // Returns the result of the expression.
  double getResult () const {return result;}

  // Returns true if expression parsed OK.
  int ok () const {return scanner.getErrors ().nItems () == 0;}

  // Returns a list of errors found during parsing.
  const ErrorMessageList &getErrors () const {return scanner.getErrors ();}

protected:

  XInputStream input;
  CalcScanner scanner;
  double result;

  double parseExpr ();
  double parseTerm ();
  double parseFactor ();
  double getVariableValue (const string &variable);
  double getNumberValue (const string &number);
};

#endif