Token.py

#!/usr/bin/env python

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class TokenTypes(object):
    """A singleton to represent all token types."""

    (EOF, SEMICOLON, EQUALS, CONFIGURATION, PRODUCTIONS, LBRACE, RBRACE, \
    	DOUBLEARROW, ARROW, ID, NUMBER, COMMA) = range(12)

    names = [ 'EOF', 'SEMICOLON', 'EQUALS', 'CONFIGURATION', 'PRODUCTIONS', 
    	'LBRACE', 'RBRACE', 'DOUBLEARROW', 'ARROW', 'ID', 'NUMBER', 'COMMA' ]
        
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#                             
class Token(object):
    """An abstract token."""
    
    def __init__(self, type, text):
        """Constructor.
           type is a numeric token type from TokenTypes
           text is the lexeme
        """
        self.type = type
        self.text = text
        
    def __str__(self):
        """Converts a token to string."""
        return "<'%s', %s>" % (self.text, TokenTypes.names[self.type])