115 lines
2.5 KiB
Python
115 lines
2.5 KiB
Python
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# BNF
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# expression -> bool ( ( '|' | '&' | '^' ) bool )*
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# bool -> '0' | '1'
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def tokenize(xs):
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result = []
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for c in xs:
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if c == '0':
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result.append(0)
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elif c == '1':
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result.append(1)
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elif c in "&|^":
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result.append(c)
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else:
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raise Exception("Unexpected token, \"{}\"".format(c))
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return result
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class Parser(object):
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def __init__(self, tokens):
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self.tokens = tokens
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self.i = 0
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def prev(self):
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return self.tokens[self.i - 1]
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def curr(self):
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return self.tokens[self.i]
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def match(self, xs):
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if self.exhausted():
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return False
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if (self.curr() in xs):
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self.consume()
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return True
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return False
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def consume(self):
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result = self.curr()
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self.i += 1
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return result
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def exhausted(self):
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return self.i >= len(self.tokens)
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def recursive_descent(tokens):
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parser = Parser(tokens)
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return parse_expression(parser)
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def parse_expression(parser):
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lhs = parse_bool(parser)
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while parser.match(['|', '&', '^']):
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op = parser.prev()
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rhs = parse_expression(parser)
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lhs = [op, lhs, rhs]
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return lhs
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def parse_bool(parser):
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if parser.curr() == 0:
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parser.consume()
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return False
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elif parser.curr() == 1:
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parser.consume()
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return True
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else:
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raise Exception("Unexpected token: {}".format(parser.curr()))
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def f(expr, result):
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tokens = tokenize(expr)
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tree = recursive_descent(tokens)
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return do_f(tree, result)
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def do_f(tree, result):
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if type(tree) == bool:
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if tree == result:
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return 1
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else:
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return 0
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op, lhs, rhs = tree[0], tree[1], tree[2]
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truth_tables = {
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True: {
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'|': [
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(True, True),
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(True, False),
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(False, True),
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],
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'&': [
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(True, True),
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],
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'^': [
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(True, False),
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(False, True),
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],
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},
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False: {
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'|': [
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(False, False),
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],
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'&': [
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(False, False),
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(True, False),
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(False, True),
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],
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'^': [
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(True, True),
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(False, False),
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],
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}
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}
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return sum([do_f(lhs, x) * do_f(rhs, y) for x, y in truth_tables[result][op]])
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print(f("1^0|0|1", False))
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print(f("1|0|1|1", False))
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