Monads/Writer monad: Difference between revisions
m
→{{header|Python}}: Complete type hints
m (Added language identifier.) |
m (→{{header|Python}}: Complete type hints) |
||
Line 1,128:
=={{header|Python}}==
<syntaxhighlight lang="python">
"""A Writer Monad. Requires Python >= 3.7 for type hints."""
from __future__ import annotations
Line 1,135 ⟶ 1,136:
import os
from typing import Callable
from typing import Generic
Line 1,144:
T = TypeVar("T")
U = TypeVar("U")
Line 1,155 ⟶ 1,156:
self.msgs = list(f"{msg}: {self.value}" for msg in msgs)
def bind(self, func: Callable[[T], Writer[
writer = func(self.value)
return Writer(writer, *self.msgs)
def __rshift__(self, func: Callable[[T], Writer[
return self.bind(func)
Line 1,169 ⟶ 1,170:
def lift(func: Callable[[T], U], msg: str) -> Callable[[
"""Return a writer monad version of the simple function `func`."""
@functools.wraps(func)
def wrapped(value: T) -> Writer[U]:
return Writer(func(value), msg)
Line 1,181 ⟶ 1,182:
if __name__ == "__main__":
square_root = lift(math.sqrt, "square root")
add_one = lift(lambda x: x + 1, "add one")▼
add_one: Callable[[Union[int, float]], Writer[Union[int, float]]] = lift(
half = lift(lambda x: x / 2, "div two")▼
)
half: Callable[[Union[int, float]], Writer[float]] = lift(
)
print(Writer(5, "initial") >> square_root >> add_one >> half)
| |||