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