// Lexical Scanner Definitions.
//
// File:	scanner.h
// Author:	course
// Version:	1

// Types of tokens.
//
typedef enum
{
    LPAREN_TOKEN,   // the left parenthesis	(
    RPAREN_TOKEN,   // the right parenthesis	)
    RBRACKET_TOKEN, // the right bracket	]
    DOT_TOKEN,	    // the period		.
    QUOTE_TOKEN,    // the single quote mark	'
    FNQUOTE_TOKEN,  // function quote		#'
    NUMBER_TOKEN,   // number atom
    SYMBOL_TOKEN,   // symbol atom
    EOF_TOKEN,      // end of file
    ERROR_TOKEN     // signals an unrecognizable token
} token_type;

// The token structure.
//
class token
{
public:
  token_type	type;	    // Type of the token.
  object	* value;    // For symbols and fixnums,
			    // the value of the token.
};


// Functions to get the next token and backup over it.
//
token get_token (istream& s);
void backup_token();