32 lines
977 B
Python
32 lines
977 B
Python
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from emis_funky_funktions import *
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from ir import IRNeg, IRProp, IRTerm, IRVar, Substitutions, unify, unify_clauses
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def terms_cancel(t1: IRTerm, t2: IRTerm) -> Option[Substitutions]:
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"""
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Determine if two terms could cancel each other out, given the right substitutions
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That is, is there some set of substitutions such that t1 = ¬t2 or ¬t1 = t2?
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If negation is possible and a substitution exists, that substitution is returned.
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Otherwise, `None` is returned.
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>>> terms_cancel(IRNeg(IRVar('x1')), IRProp('Terezi'))
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Some((Terezi()/x1,))
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>>> terms_cancel(IRProp('Nepeta'), IRVar('x1'))
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Some((¬Nepeta()/x1,))
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>>> terms_cancel(IRProp('ancestor', [IRVar('x1')]), IRVar('x1')) is None
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True
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"""
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match (t1, t2):
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case (IRNeg(a), b) | (b, IRNeg(a)): #type: ignore
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return hush(unify(a, b))
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case (IRVar(_) as x, a) | (a, IRVar(_) as x): #type: ignore
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return hush(unify(x, IRNeg(a)))
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return None
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if __name__ == '__main__':
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import doctest
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doctest.testmod()
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