52 lines
1.3 KiB
Python
52 lines
1.3 KiB
Python
"""A Maybe Monad. Requires Python >= 3.7 for type hints."""
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from __future__ import annotations
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from typing import Any
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from typing import Callable
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from typing import Generic
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from typing import Optional
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from typing import TypeVar
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from typing import Union
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T = TypeVar("T")
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class Maybe(Generic[T]):
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def __init__(self, value: Union[Optional[T], Maybe[T]] = None):
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if isinstance(value, Maybe):
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self.value: Optional[T] = value.value
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else:
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self.value = value
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def __rshift__(self, func: Callable[[Optional[T]], Maybe[Any]]):
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return self.bind(func)
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def bind(self, func: Callable[[Optional[T]], Maybe[Any]]) -> Maybe[Any]:
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return func(self.value)
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def __str__(self):
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return f"{self.__class__.__name__}({self.value!r})"
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def plus_one(value: Optional[int]) -> Maybe[int]:
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if value is not None:
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return Maybe[int](value + 1)
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return Maybe[int](None)
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def currency(value: Optional[int]) -> Maybe[str]:
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if value is not None:
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return Maybe[str](f"${value}.00")
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return Maybe[str](None)
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if __name__ == "__main__":
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test_cases = [1, 99, None, 4]
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for case in test_cases:
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m_int = Maybe[int](case)
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result = m_int >> plus_one >> currency
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# or..
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# result = m_int.bind(plus_one).bind(currency)
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print(f"{str(case):<4} -> {result}")
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