I would like to propose two new functions for the `Stream` module:
*Head Function*
@spec head(Enumerable.t) :: Stream.element
This function is the equivalent of the following code:
[element] = stream
|> Stream.take(1)
|> Enum.to_list
*Tail Function*
@spec tail(Enumerable.t) :: Enumerable.t # %Stream{...}
This function returns a new stream without the head element.
*Syntax Sugar*
It would further be awesome if the following would work:
[element1, elementN... | rest] = stream # I'm aware that this would not
work as a function head / case etc.
%Stream{} = rest
*Real Wold Example*
This capability would for example enable the following (using
https://hexdocs.pm/crontab):
def setup do
~e[*/10] # Every 10 Minutes
|> Crontab.Scheduler.get_next_run_dates() # Creating a Stream with dates
matching schedule
|> run(fn date ->
# Do something useful
end)
end
def run(schedules, callback) do
[next_date | rest] = schedules # With Syntax Sugar
next_date = Stream.head(schedules) # Without Syntax Sugar
rest = Stream.tail(schedules) # Without Syntax Sugar
next_date
|> DateTime.from_naive!("Etc/UTC")
|> DateTime.diff(DateTime.utc_now(), :millisecond)
|> min(0)
|> Process.sleep()
callback.(next_date)
run(schedules, callback)
end
*Problems*
There's some problems with this exact approach since pattern matching
doesn't work with streams. Therefore all of the above will need some work.
It should however illustrate the intention of this proposal.
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