functional-streams-for-scala/fs2

Compositional, streaming I/O library for Scala

Fabio Labella

@SystemFw

you can simply unNone to only take the options that are defined

Drew Boardman

@drewboardman

yeah exactly that

Fabio Labella

@SystemFw

cool so just add unNone after evalMap

Drew Boardman

@drewboardman

thanks!

it seems like i'm losing the IO context somewhere in there

when I unNone

do i need to type parametrize the evalMap?

i can wrap it in an IO.delay

val streamOfFoo: fs2.Stream[IO, Foo] =
  consumer.readFromKinesisStream[IO]("APPNAME", "KINESIS_STREAM_A")flatMap { committableRecord =>
    fs2.Stream
      .chunk(Chunk.byteBuffer(committableRecord.record.data))
      .through(io.circe.fs2.byteStreamParser[IO])
      .through(io.circe.fs2.decoder[IO, Foo])
      .evalMap(evt ⇒ IO.delay(Transformers.transform(evt)))
      .unNone

the through(io.circe.fs2.decoder[IO, Foo]) returns an fs2.Stream[IO, Foo]

Fabio Labella

@SystemFw

ah wait

I though you had a typo

Drew Boardman

@drewboardman

no typo

Fabio Labella

@SystemFw

just map(..).unNone if you don't have an IO around

Drew Boardman

@drewboardman

how am i losing IO context in the evalmap?

isnt just flatMap(o => Stream.eval(f(o))

Fabio Labella

@SystemFw

yes

it takes an A => IO[B] in your case

Drew Boardman

@drewboardman

hmm

Fabio Labella

@SystemFw

but you are passing to it an A => Option[B]

Drew Boardman

@drewboardman

you think I should keep IO.delay or the map(..).unNone?

Fabio Labella

@SystemFw

the latter

Drew Boardman

@drewboardman

I'd need to map it into an IO thoug

Fabio Labella

@SystemFw

I don't understand

does your function return A => IO[Option[B]] or A => Option[B]?

Drew Boardman

@drewboardman

second

Fabio Labella

@SystemFw

so map(...).unNone

Drew Boardman

@drewboardman

what function am i passing into the map?

oh, instead of evalMap

i see

ah, so If i want to do some effectful operation

than evalMap would be great

but since I'm doing a pure transformation, map is fine

Fabio Labella

@SystemFw

yeah

Drew Boardman

@drewboardman

i should have finished your control flow talk lmao

thanks for the help

Fabio Labella

@SystemFw

Nik Gushchin

@Dr-Nikson

@SystemFw Hello!) Thanks for the link to this channel 👍🏼

Drew Boardman

@drewboardman

is there any possibility of IO being ran by the scala runtime, like how haskell does it?

Ryan Peters

@sloshy

@drewboardman As in, it being part of the standard library? Every app being an IO? Scala is built as being an impure functional language so it would fundamentally change a lot of things and break basically everybody's code if they did that. I don't think it's ever likely.

It would have to be a new language at this point, so pure FP in scala will stay opt-in.

IMO it's also nice that we have multiple implementations of the same ideas in the ecosystem for a "runtime" for effects. Cats Effect v Monix is a good historical example where each lib has different tradeoffs and styles

bifunctor

@bifunctor

Hi folks
How to make interval streams?

Paolo Anastagi

@poliez

What do you mean with "interval" stream? You mean like "Range"?

Michael Pilquist

@mpilquist

2.0.1 released with an important memory leak fix: https://github.com/functional-streams-for-scala/fs2/releases/tag/v2.0.1

Viktor Lövgren

@vlovgr

Looks like mima isn't happy about 2.0.0 -> 2.0.1: https://travis-ci.org/ovotech/fs2-kafka/builds/587924731 (errors toward end). Can someone verify that these are safe to exclude?

Michael Pilquist

@mpilquist

Yep safe to exclude : https://github.com/functional-streams-for-scala/fs2/pull/1631#issuecomment-533806577

Viktor Lövgren

@vlovgr

Perfect, thanks!

bifunctor

@bifunctor

Could someone please explain be, what is a pipe?

Diego E. Alonso Blas

@diesalbla

@bifunctor A function from one stream to another stream in the same effect F.

type Pipe[F, - In, + Out] = Stream[F, In] => Stream[F, Out]

Nothing in that type tells you what the correspondence is between elements and effects in the input and the output stream.

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