async def main() -> IOResultE[Sequence[str]]:
"""
Main entrypoint for the async world.
Let's fetch 3 titles of posts asynchronously.
We use `gather` to run requests in "parallel".
"""
futures: Sequence[IOResultE[str]] = await asyncio.gather(*_show_titles(3))
return Fold.collect(futures, IOResultE.from_value(()))
def _show_titles(
number_of_posts: int,
) -> RequiresContextFutureResultE[Sequence[str], httpx.AsyncClient]:
def factory(post: _Post) -> str:
return post['title']
titles = [
# Notice how easily we compose async and sync functions:
_fetch_post(post_id).map(factory)
# TODO: try `for post_id in (2, 1, 0):` to see how errors work
for post_id in range(1, number_of_posts + 1)
]
return Fold.collect(titles, RequiresContextFutureResultE.from_value(()))
def test_fold_collect(iterable, sequence):
"""Iterable for regular types and ``Fold``."""
assert Fold.collect(iterable, sequence.from_value(())) == sequence
def test_fold_collect_recursion_limit():
"""Ensures that ``.collect`` method is recurion safe."""
limit = sys.getrecursionlimit() + 1
iterable = (IO(1) for _ in range(limit))
expected = IO((1, ) * limit)
assert Fold.collect(iterable, IO(())) == expected
def test_fold_collect_reader(iterable, sequence):
"""Ensures that ``.collect`` works for readers."""
assert Fold.collect(
iterable,
sequence.from_value(()),
)(...) == sequence(...)
