// Integer arithmetic interpreter lexeme declaration.
//
// File:        lexeme.h
// Author:      course
// Version:     2
//
// This file declares the arithmetic interpreter lexeme
// type, or lexeme.

#ifndef _LEXEME_H_
#define _LEXEME_H_

// Constants that one may want to change:
//
// Maximum length of symbol.
//
const int MAX_SYMBOL_LENGTH = 100;

#include "avalue.h"     // Arithmetic interpreter value
			// type definition, >> operator,
			// and << operator.

// Character constants:
//
const char PLUS_SIGN            = '+';
const char MINUS_SIGN           = '-';
const char TIMES_SIGN           = '*';
const char DIVIDE_SIGN          = '/';
const char EQUAL_SIGN           = '=';
const char LEFT_PAREN           = '(';
const char RIGHT_PAREN          = ')';
const char SEMICOLON            = ';';
const char EOF_MARKER           = '.';

// Operator types:
//
enum optype { OP_PLUS, OP_MINUS, OP_TIMES, OP_DIVIDE };

// Lexeme Types:
//
enum lextype
    { LEX_SYMBOL,       LEX_NUMBER,     LEX_OP,
      LEX_ASSIGN,       LEX_EOF,        LEX_LEFT_PAREN,
      LEX_RIGHT_PAREN,                  LEX_SEMICOLON };


// Lexemes:
//
class lexeme_class;
typedef lexeme_class * lexeme;

// Lexeme_classes:
//
class lexeme_class
{
public:

    lextype     type;   // See above for lexeme types.

    char *      pname;  // Print name if LEX_SYMBOL.

    optype      op;     // Operator type if LEX_OP.

    avalue      value;  // Value if LEX_NUMBER.
	  		// Possible value if LEX_SYMBOL.

    bool        inited; // True for LEX_SYMBOL if value
	  		// has been set; else false.

    lexeme      next;   // For LEX_SYMBOL, pointer to
	  		// next symbol in symbol table.
};

// Output a lexeme to a stream: s << l where s is
// typically cout.
//
ostream& operator << (ostream& s, lexeme l);

// Input lexeme from a stream: s >> l where s is
// typically ein.
//
// Remove preceding space.  If end of stream,
// return l = NULL.   On other errors, call error.
//
istream& operator >> (istream& s, lexeme& l);


// Functions to read lexemes from ein.

// Initialize lexeme reader (i.e. initialize symbol
// table).
//
void init_lexemes(void);

// Test to see if there are no more lexemes in input
// stream ein.
//
bool end_lexemes(void);

// Get the next lexeme from the input stream ein.
//
lexeme get_lexeme(void);

// Backup over last lexeme gotten.
//
void unget_lexeme(void);

// Flush line of lexemes (e.g. after error).
//
void flush_lexemes(void);

#endif  // _LEXEME_H_