mirror of
https://github.com/correl/typesafe-monads.git
synced 2024-11-14 19:19:32 +00:00
33 lines
1 KiB
Python
33 lines
1 KiB
Python
from __future__ import annotations
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import functools
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from typing import Any, Callable, Generic, Iterable, List, TypeVar
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from .applicative import Applicative
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from .functor import Functor
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T = TypeVar("T")
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S = TypeVar("S")
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class Monad(Applicative[T]):
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# FIXME: Callable return type set to Any, as the proper value
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# (Monad[S]) is reported as incompatible with subclass
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# implementations due to a flaw in mypy:
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# https://github.com/python/mypy/issues/1317
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def bind(self, function: Callable[[T], Any]) -> Monad[S]: # pragma: no cover
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raise NotImplementedError
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@classmethod
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def pure(cls, value: T) -> Monad[T]:
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raise NotImplementedError
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@classmethod
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def sequence(cls, xs: Iterable[Monad[T]]) -> Monad[List[T]]:
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"""Evaluate monadic actions in sequence, collecting results."""
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def reducer(acc: Monad[List[T]], x: Monad[T]) -> Monad[List[T]]:
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return acc.bind(lambda acc_: x.map(lambda x_: acc_ + [x_]))
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return functools.reduce(reducer, xs, cls.pure([]))
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__rshift__ = bind
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