88 lines
2.8 KiB
Python
88 lines
2.8 KiB
Python
from rule import Rule, EMPTY_SYMBOL
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import re
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class RulesParser:
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TRANSFORM = r'->'
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B_TRANSFORM = r'->\|'
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NEWLINE = '\n'
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IGNORE = r'\s+'
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COMMENTS = r'//.+$'
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EMPTY = re.escape(EMPTY_SYMBOL)
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def parse(self, file: str) -> list[Rule]:
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"""
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Parsing file according to syntax, specified
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in class variables. Hardcoded for now (and forever)
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"""
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with open(file, 'r') as f:
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text = f.read()
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lines = self._get_lines(text)
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rules = list()
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for line in lines:
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rules.append(self._parse_rule(line))
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return rules
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def _parse_rule(self, line: str) -> Rule:
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"""
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tries to parse rule according to set grammar
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"""
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tokens = re.split(self.IGNORE, line)
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# we always expect 3 parts: operand, arrow, target
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arrow = tokens[1]
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is_blocking = None
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if re.fullmatch(self.TRANSFORM, arrow):
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is_blocking = False
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elif re.fullmatch(self.B_TRANSFORM, arrow):
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is_blocking = True
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else:
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raise ValueError(f"Can't recognize transform symbol. "
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f"\"{self.TRANSFORM}\" or \"{self.B_TRANSFORM}\""
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f" expected, but \"{arrow}\" encountered")
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#optimising empty symbol
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return Rule(
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operand=self._optimise_empty(tokens[0]),
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target=self._optimise_empty(tokens[2]),
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is_blocking=is_blocking
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)
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def _optimise_empty(self, string: str) -> str:
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"""
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Empty symbol has meaning only while it's the only
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symbol in the string (I hope i'm not wrong right now),
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so all empty symbols can be optimised
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Returns sting without EMPTY symbols if deleting them
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is semantically possible, returns unchanges string if
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nothing can be optimised
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NOTE: right now contains naive implementation
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"""
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string = re.sub(self.EMPTY+'+', EMPTY_SYMBOL, string)
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if re.fullmatch(self.EMPTY, string):
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return string
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return re.sub(self.EMPTY, '', string)
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def _get_lines(self, src: str) -> list[str]:
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"""
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Get cleaned lines only with rules to parse
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"""
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text = self._remove_comments(src)
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text = self._strip_lines(text)
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lines = list(filter(lambda x: x != '', text.split(self.NEWLINE)))
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return lines
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def _remove_comments(self, src: str) -> str:
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"""
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removes comments from end of lines and returns
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cleaned text
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"""
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return re.sub(self.COMMENTS, '', src, flags=re.M)
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def _strip_lines(self, src: str) -> str:
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"""
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Strips whitespaces at the end of lines
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"""
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result = re.sub(r' +$', '', src, flags=re.M)
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return result
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