functional-streams-for-scala/fs2

Most discussion is on Typelevel Discord: https://discord.gg/bSQBZA3Ced

Fabio Labella

@SystemFw

make sure you handle the error at the apiCall level by returning an empty Stream (and potentially logging ofc)

unless you want one api call failure to end the whole thing

Jakob Oesinghaus

@joesinghaus

@SystemFw Seems right, the main difficulty here seems to be handling of multibyte characters. I think if I can assume for simplicity that I only need to handle UTF8 or single-byte encodings, I should be good.

Martijn Hoekstra

@martijnhoekstra

given an s: Segment[O, Unit], what is the difference between Pull.segment(s) and Pull.output(s)?

Fabio Labella

@SystemFw

first: Segment is gone

anyway, the types are different

ah, sorry

your Segment is of Unit

then they are effectively the same

Martijn Hoekstra

@martijnhoekstra

https://functional-streams-for-scala.github.io/fs2/guide.html uses Segment -- what should be used instead?

Fabio Labella

@SystemFw

The guide is for 0.10 since 1.0 is still in M3

we are using Chunk only now

but you can't really do that unless you upgrade to 1.0-M3

because Chunk in 0.10 is purposefully underpowered

Michael Pilquist

@mpilquist

@SystemFw Are we going to pass Timer[F] and ContextShift[F] explicitly now?

Fabio Labella

@SystemFw

heh, that's good question

my inclination is no for Timer

as for ContextShift, I need to have a closer look at the PR

Michael Pilquist

@mpilquist

right ok, i'm working on the fs2 upgrade now

Fabio Labella

@SystemFw

wrt to how you select which ec you want to run your stuff into

right

I think the argument Daniel made about Ec being ok implicitly because there's the CPU one as a good default still applies here

my mental model for Timer is still "there's a Time[F] typeclass, the runtime gives you an implementation", e.g. IOApp

but I'm open to chaining my mind and more importantly I'm exhausted by having to think about it :joy: :joy:

Michael Pilquist

@mpilquist

oh ContextShift is okay to pass implicitly

trait ContextShift[F[_]] {
  def shift: F[Unit]
  def evalOn[A](ec: ExecutionContext)(fa: F[A]): F[A]
}

Fabio Labella

@SystemFw

ah, cool

it's defo a typeclass then in my mind

Christopher Davenport

@ChristopherDavenport

So happy to get ContextShift

Fabio Labella

@SystemFw

oh yeah, it's awesome

Thanks Pavel ;)

Calvin Lee Fernandes

@calvinlfer

hey guys, I have a question about the Pull datatype, what exactly does the R type represent? Can you think of it as some kind of Resource that you can use to produce Os?

Fabio Labella

@SystemFw

it's the return type

you can imagine it as a computation the emits some values and ~~emits~~ returns a new thing

it's actually similar to pagination ;)

which is indeed pull-based

Calvin Lee Fernandes

@calvinlfer

so there's two output types? O and R?

Fabio Labella

@SystemFw

R is not an output type, it's a return type

note that to convert a Pull to a Stream

R needs to Unit

Calvin Lee Fernandes

@calvinlfer

oh i see

Fabio Labella

@SystemFw

i.e. a Stream doesn't have the ability to terminate with a value

Calvin Lee Fernandes

@calvinlfer

so R is used to transfer some state between Pulls

but its not used in Stream

Fabio Labella

@SystemFw

Pull and Stream are two "moral" newtype over Algebra

the Stream monad instance (which is on O)

is better for control flow

the Pull monad instance (which is on R) is better for stateful combinators (so for the actual "streaming" aspect)

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