113 lines
2.5 KiB
Python
113 lines
2.5 KiB
Python
import sys
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from regex import Literal, Concatenation, Alternation, Star, lit
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from nfa import NFA, prettyprint
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from parse_regex import parse, ParseError
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def to_nfa(regex):
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def new_state():
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nonlocal state_name_counter, transitions
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state_name = state_name_counter
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state_name_counter += 1
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transitions[state_name] = {}
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return state_name
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def worker(node):
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nonlocal transitions
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if type(node) == Literal:
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# text
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# (start) ---------> (end)
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start_state = new_state()
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end_state = new_state()
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transitions[start_state][end_state] = lit(node.text)
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return (start_state, end_state)
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elif type(node) == Concatenation:
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# (start) → […] → […] → […]
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start_state = new_state()
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prev_state = start_state
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for element in node.elements:
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inner_start, inner_end = worker(element)
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# (prev) → (inner_start) → […]
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transitions[prev_state][inner_start] = lit('')
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# Link next element straight to the inner end
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# state
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prev_state = inner_end
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return (start_state, prev_state)
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elif type(node) == Alternation:
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# +-> […] --+
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# | |
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# (start) --+-> […] --+-> (end)
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# | |
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# +-> […] --+
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start_state = new_state()
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end_state = new_state()
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for element in node.elements:
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inner_start, inner_end = worker(element)
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# (start) → (inner_start) → […]
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transitions[start_state][inner_start] = lit('')
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# […] → (inner_end) → (end)
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transitions[inner_end][end_state] = lit('')
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return (start_state, end_state)
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elif type(node) == Star:
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# +- […] <-+
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# | |
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# v |
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# (start) --+--> (end)
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start_state = new_state()
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end_state = new_state()
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inner_start, inner_end = worker(node.element)
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# (start) → (inner_start) → […]
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transitions[start_state][inner_start] = lit('')
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# […] → (inner_end) → (start)
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transitions[inner_end][start_state] = lit('')
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# (start) → (end)
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transitions[start_state][end_state] = lit('')
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return (start_state, end_state)
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else:
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raise ValueError('node has to be Literal, Concatenation, Alternation, or Star')
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state_name_counter = 0
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transitions = {}
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start_state, end_state = worker(regex)
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return NFA(start_state, [end_state], transitions)
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def main():
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try:
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regex = parse(input('regex> '))
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except ParseError as err:
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print('%s: Error: %s' % (sys.argv[0], str(err)), file=sys.stderr)
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else:
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nfa = to_nfa(regex)
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prettyprint(nfa)
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if __name__ == '__main__':
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main()
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