90 lines
2 KiB
Python
90 lines
2 KiB
Python
# mypy: allow-untyped-defs
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from contextlib import contextmanager
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from .dispatch import dispatch
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from .utils import hashable
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_global_logic_variables = set() # type: ignore[var-annotated]
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_glv = _global_logic_variables
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class Var:
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"""Logic Variable"""
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_id = 1
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def __new__(cls, *token):
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if len(token) == 0:
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token = f"_{Var._id}" # type: ignore[assignment]
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Var._id += 1
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elif len(token) == 1:
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token = token[0]
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obj = object.__new__(cls)
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obj.token = token # type: ignore[attr-defined]
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return obj
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def __str__(self):
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return "~" + str(self.token) # type: ignore[attr-defined]
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__repr__ = __str__
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def __eq__(self, other):
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return type(self) == type(other) and self.token == other.token # type: ignore[attr-defined]
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def __hash__(self):
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return hash((type(self), self.token)) # type: ignore[attr-defined]
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def var():
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return lambda *args: Var(*args)
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def vars():
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return lambda n: [var() for i in range(n)]
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@dispatch(Var)
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def isvar(v):
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return True
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isvar
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@dispatch(object) # type: ignore[no-redef]
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def isvar(o):
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return not not _glv and hashable(o) and o in _glv
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@contextmanager
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def variables(*variables):
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"""
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Context manager for logic variables
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Example:
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>>> # xdoctest: +SKIP("undefined vars")
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>>> from __future__ import with_statement
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>>> with variables(1):
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... print(isvar(1))
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True
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>>> print(isvar(1))
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False
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>>> # Normal approach
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>>> from unification import unify
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>>> x = var("x")
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>>> unify(x, 1)
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{~x: 1}
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>>> # Context Manager approach
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>>> with variables("x"):
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... print(unify("x", 1))
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{'x': 1}
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"""
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old_global_logic_variables = _global_logic_variables.copy()
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_global_logic_variables.update(set(variables))
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try:
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yield
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finally:
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_global_logic_variables.clear()
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_global_logic_variables.update(old_global_logic_variables)
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