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1
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# A general recursive descent parser
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2
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3
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import re
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4
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5
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import term
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6
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7
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class SyntaxError(Exception): pass
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8
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9
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class Parser:
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10
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def __init__(self, str_):
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11
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self._str = str_
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12
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self._pos = 0
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13
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14
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def end(self):
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15
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if not self._pos == len(self._str): self.syntax_err('End of string')
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16
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17
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def str_(self, str_, required=False):
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18
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end_pos = self._pos + len(str_)
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19
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if self._str[self._pos:end_pos] == str_:
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20
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self._pos = end_pos
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21
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return True
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22
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elif required: self.syntax_err(str_)
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23
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else: return False
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24
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25
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def re(self, pattern, required=False):
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26
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matcher = re.compile(pattern).match(self._str, self._pos)
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27
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if matcher:
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28
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self._pos = matcher.end(0)
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29
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return matcher.group(0)
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30
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elif required: self.syntax_err(pattern)
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31
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else: return None
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32
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33
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def syntax_err(self, token):
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34
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after = self._str[self._pos:]
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35
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if after == '': after += '<END>'
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36
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raise SyntaxError(self.__class__.__name__+' syntax error: '+token
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37
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+' expected in '+ term.as_style('37', self._str[:self._pos]) +after)
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