Process.md

Module Elm.Process

Right now, this library is pretty sparse. For example, there is no public API for processes to communicate with each other. This is a really important ability, but it is also something that is extraordinarily easy to get wrong!

Id

type Id = ProcessId

A light-weight process that runs concurrently. You can use spawn to get a bunch of different tasks running in different processes. The Elm runtime will interleave their progress. So if a task is taking too long, we will pause it at an andThen and switch over to other stuff.

Note: We make a distinction between concurrency which means interleaving different sequences and parallelism which means running different sequences at the exact same time. For example, a time-sharing system is definitely concurrent, but not necessarily parallel. So even though JS runs within a single OS-level thread, Elm can still run things concurrently.

spawn

spawn :: forall x y a. Task x a -> Task y Id

Run a task in its own light-weight process. In the following example, task1 and task2 will be interleaved. If task1 makes a long HTTP request or is just taking a long time, we can hop over to task2 and do some work there.

spawn task1
  |> Task.andThen (\_ -> spawn task2)

Note: This creates a relatively restricted kind of Process because it cannot receive any messages. More flexibility for user-defined processes will come in a later release!

sleep

sleep :: forall x. Time -> Task x Unit

Block progress on the current process for a given amount of time. The JavaScript equivalent of this is setTimeout which lets you delay work until later.

kill

kill :: forall y. Id -> Task y Unit

Sometimes you spawn a process, but later decide it would be a waste to have it keep running and doing stuff. The kill function will force a process to bail on whatever task it is running. So if there is an HTTP request in flight, it will also abort the request.