45 lines
1.0 KiB
Python
45 lines
1.0 KiB
Python
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import enum
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class Direction(enum.Enum):
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UP = enum.auto()
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LEFT = enum.auto()
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RIGHT = enum.auto()
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class ReductionType(enum.Enum):
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# Nothing happened. This implies that
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# an expression cannot be reduced further.
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NOTHING = enum.auto()
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# We replaced a macro with an expression.
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MACRO_EXPAND = enum.auto()
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# We expanded a history reference
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HIST_EXPAND = enum.auto()
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# We turned a church numeral into an expression
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AUTOCHURCH = enum.auto()
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# We applied a function.
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# This is the only type of "formal" reduction step.
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FUNCTION_APPLY = enum.auto()
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# Pretty, short names for each reduction type.
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# These should all have the same length.
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reduction_text = {
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ReductionType.NOTHING: "N",
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ReductionType.MACRO_EXPAND: "M",
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ReductionType.HIST_EXPAND: "H",
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ReductionType.AUTOCHURCH: "C",
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ReductionType.FUNCTION_APPLY: "F",
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}
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class ReductionError(Exception):
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"""
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Raised when we encounter an error while reducing.
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These should be caught and elegantly presented to the user.
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"""
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def __init__(self, msg: str):
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self.msg = msg
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