Introduced Suspendable type class #710
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This PR moves `suspend` and `delay` from the `Effect` type class to a new `Suspendable` type class. There are two motivations for doing this: - Exposing `unsafeRunAsync` to any function that requires `suspend` or `delay` gives up a lot of parametricity. - Some type constructors have `Suspendable` instances but do not support value extraction. This came up in the [port of Doobie to FS2](typelevel/doobie#323 (comment)). This [came up on Gitter a while back as well](http://www.gitterforum.com/discussion/scalaz-scalaz-stream?page=143).
| @@ -108,14 +108,15 @@ val eff = Stream.eval(Task.delay { println("TASK BEING RUN!!"); 1 + 1 }) | |||
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| [`Task`](../core/shared/src/main/scala/fs2/Task.scala) is an effect type we'll see a lot in these examples. Creating a `Task` has no side effects, and `Stream.eval` doesn't do anything at the time of creation, it's just a description of what needs to happen when the stream is eventually interpreted. Notice the type of `eff` is now `Stream[Task,Int]`. | |||
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| The `eval` function works for any effect type, not just `Task`. FS2 does not care what effect type you use for your streams. You may use the included [`Task` type][Task] for effects or bring your own, just by implementing a few interfaces for your effect type ([`Catchable`][Catchable] and optionally [`Effect`][Effect] or [`Async`][Async] if you wish to use various concurrent operations discussed later). Here's the signature of `eval`: | |||
| The `eval` function works for any effect type, not just `Task`. FS2 does not care what effect type you use for your streams. You may use the included [`Task` type][Task] for effects or bring your own, just by implementing a few interfaces for your effect type ([`Catchable`][Catchable], [`Suspendable`][Suspendable], [`Effect`][Effect], and optional [`Async`][Async] if you wish to use various concurrent operations discussed later). Here's the signature of `eval`: | |||
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"optionally Async", not "optional Async"
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lgtm |
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This PR moves
suspendanddelayfrom theEffecttype class to anew
Suspendabletype class. There are two motivations for doing this:unsafeRunAsyncto any function that requiressuspendor
delaygives up a lot of parametricity.Suspendableinstances but do notsupport value extraction. This came up in the port of Doobie to
FS2.
This came up on Gitter a while back as
well.
/cc @tpolecat @guersam