functional-streams-for-scala/fs2

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

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@slice

my goal is to make sure every pull from a Stream[F, B] is wrapped in Limiter.await[F, B]

Fabio Labella

@SystemFw

can you change so that you don't have to do that?

for example by changing builds

or is that too undesirable?

skip

@slice

i think i can, by doing def build: F[B] and def builds: Stream[F, B] = Stream.repeatEval(build)

Fabio Labella

@SystemFw

yeah, I would recommend that

skip

@slice

:+1: a good idea considering that Stream.repeatEval is done everywhere anyways, so making it just a F[B] would be better

Fabio Labella

@SystemFw

yeah

skip

@slice

-      def builds =
-        Stream.repeatEval(
-          Limiter.await[F, B](source.builds.head.compile.last.map(_.get)),
-        )
+      def build = Limiter.await[F, B](source.build, priority)

so much cleaner!

Gavin Bisesi

@Daenyth

^ this is why you want to use the simplest effect you can :)

F[A] > A => F[B] > A => Stream[F, B] > Pipe[F, A, B]

skip

@slice

ah :) that makes a lot of sense!

Billzabob

@Billzabob

Am I missunderstanding or isn’t that the opposite of the whole “Constraints liberate, liberties constrain” thing? I thought you’re supposed to try and keep things specific and in the “unexploded” form for as long as you can.

Christopher Davenport

@ChristopherDavenport

Thats waht he said.

Constrain yourself more.

F[A] is strictly less powerful than Stream[F, A]

Billzabob

@Billzabob

So you would want to keep it as Stream[F, A] as long as possible and only .compile as late as possible then right? Ok, I guess I was just missunderstanding what the > meant is that list.

Christopher Davenport

@ChristopherDavenport

If you are in Stream, then you don't drop down.

But if you are F[A] dont needlessly escalate to Stream[F, A]

Adam Rosien

@arosien

"do this more" > "do this less" in that description

Bob Glamm

@glammr1

^^ one of the earliest lessons I learned by trying Scala FP is exactly that

"why am I using A => F[B] here when a simple F[B] would do"

Adam Rosien

@arosien

if you apply that literally, you get tagless-final style :)

Billzabob

@Billzabob

@ChristopherDavenport Ah ok that makes sense :) Thanks

Bob Glamm

@glammr1

@arosien yes, it was on that path of discovery

Christopher Davenport

@ChristopherDavenport

Then it all becomes kleisli.

Adam Rosien

@arosien

i'm still getting there...

Bob Glamm

@glammr1

You know Kleisli pops up a lot more than I would have expected when I write FP

Adam Rosien

@arosien

a SUPER example is scala-steward, the ENTIRE app is just tagless-final traits + mixing them all together at the top layer: https://github.com/fthomas/scala-steward/tree/master/modules/core/src/main/scala/org/scalasteward/core

oh and any of @ChristopherDavenport's libraries too

he basically takes an idea for a library, writes out the algebra, writes an impl or 2, then is done

:jazz-hands:

Christopher Davenport

@ChristopherDavenport

Thats the idea, that and minimizing allocations for the small wins in FP.

Adam Rosien

@arosien

but scala-steward is a great example of the tagless-final discipline in a big-ish app

Bob Glamm

@glammr1

That's Liskov's process for writing applications

"I think of a language that enables me to solve the problem at hand then write the interpreter for the language"

Adam Rosien

@arosien

yeah, we're all just catching up :)

Christopher Davenport

@ChristopherDavenport

^^ This is final tagless

A laguage where it all just writes like butter.

In the french style of cooking.

Bob Glamm

@glammr1

I've seen glimmerings of that in my exploration

"wow, this code reads how I would write it up in my software design docs and requirements"

Adam Rosien

@arosien

but there's also the step of integrating that language into the main program, so it pays to have a very composable return type, like F

Christopher Davenport

@ChristopherDavenport

As @arosien states, that app is a great example.

Adam Rosien

@arosien

i randomly wondered how he implemented that bot, and was totally surprised!

Bob Glamm

@glammr1

How much benefit is there to going all the way to data constructors & free algebras for implementation? I seem to recall that some of the libraries use that instead of direct final tagless impls

Christopher Davenport

@ChristopherDavenport

Don't go free in scala unless you have a real use case why you should at the moment.

Most libraries using free are exploring rewriting in tagless.

Adam Rosien

@arosien

you can go tagless-final => free with an interpreter :)

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