scalaz/scalaz

Scalaz: Functional programming for Scala | IRC: irc://irc.freenode.net/scalaz | Discord: https://discord.gg/eYZhcW | Channel logs http://ircbrowse.net/scalaz | Latest stable release: 7.2.26 | http://github.com/scalaz/scalaz | https://scalaz.github.io/scalaz/#scaladoc Wokest message of the day: Well, I personally think that he's solving the problem of typeclasses not being horrible in Scala - @oleg-py

Emily Pillmore

@emilypi

I'm not a maintainer, do I can't so anything. I'll see if I can get ahold of Tony

Wiem Zine El Abidine

@wi101

Alright, otherwise we can make a new repository in zio

Afsal Thaj

@afsalthaj

@wi101 :+1: That will be good.

Emily Pillmore

@emilypi

*so

@wi101 that'd probably be the most expedient way. Sorry for the inconvenience

Wiem Zine El Abidine

@wi101

@emilypi alright, no problem

Thanks

Steven Fines

@sfines

anyone around?

Emily Pillmore

@emilypi

Sup

realfiretiger

@realfiretiger

@realfiretiger
is there anything wrong about using val (where I don't need generics of course) instead of def?
so instead of

def doStuff(par1: String, par2: Int): Int

I always do

val doStuff: (String, Int) => Int

or is there a standard about this?

OlegYch

@OlegYch

you are giving up parameter names but otherwise it might be preferable, even if not commonly accepted

realfiretiger

@realfiretiger

@OlegYch thanks

OlegYch

@OlegYch

personally i wouldn't recommend it

enzief

@enzief

@realfiretiger you'll allocate one more object for the lambda at runtime for val doStuff: (String, Int) => Int
and two lambdas for val doStuff: String => Int => Int

toxicafunk

@toxicafunk

I don't think val doStuff: String => Int => Int works though

enzief

@enzief

what do you mean?

scala> val x: Int => Int => Int = a => a + _
x: Int => (Int => Int) = $$Lambda$18428/0x0000000803207040@f39ce67

Alexander Konovalov

@alexknvl

! type Id[a >: Id[] <: Id[]] = a

! 1 + 1

multibot1

@multibot1

^

error: illegal cyclic reference involving type a

Int = 2

toxicafunk

@toxicafunk

@enzief indeed it works... now I have to figure out what I was thinking about when I said the contrary

Jim Collins

@jim-collins

Hi what is the benefit of having an invariant immutable IList?

Georgi Krastev

@joroKr21

IList is simpler than std lib List and truly immutable (List is mutable under the hood). And it doesn't suffer from the a huge traits hierarchy. Unpopular opinion in this room but I think invarience has no benefit and even worse type inference. Anothe disadvantage is the lack of interop.

Jim Collins

@jim-collins

Thanks @joroKr21 it is why it is invariant I was wondering about.

cosmin33

@cosmin33

! scala.util.Properties.versionMsg

multibot1

@multibot1

Cameron Joannidis

@camjo

Hey is most chat on discord now? Link in the description doesn’t seem to work

Justin Heyes-Jones

@justinhj

Scalaz chat is here but there's not much of it

Salar Rahmanian

@softinio

@camjo ZIO has moved to discord fully ... no idea about scalaz

Justin Heyes-Jones

@justinhj

Is there a Monoid instance for Tags.Max? Having trouble...

import scalaz._, Scalaz._
@ (Tags.Max(10) |+| Tags.Max(20)) 
cmd11.sc:1: value |+| is not a member of Int @@ scalaz.Tags.Max

Justin Heyes-Jones

@justinhj

I was wondering if it would be unlawful but this implementation seems fair enough

implicit val intMaxInstance = Monoid.instance[Int @@ Tags.Max]({
    case (a : (Int @@ Tags.Max),b : (Int @@ Tags.Max)) =>
    val m : Int = Math.max(a.asInstanceOf[Int], b.asInstanceOf[Int])
    Tags.Max(m)
}, Tags.Max(Int.MinValue))

beezee

@beezee

what law are you worried that violates? looks 100 % iso to max monoid on plain int to me

Dimitar Georgiev

@dimitarg

My colleague was trying to write a function def something(f: A => F[B]): F[A => B]

We established that function cannot exist, because it proposes that any applicative is a monad:

trait Nope[F[_]] {
  def applicative: Applicative[F]
  def nope[A, B](f: A => F[B]): F[A => B]
  def flatMap[A, B](f: A => F[B])(x: F[A]): F[B] =
    applicative.ap(nope(f))(x)
}

But before we established it cannot exist, I searched for it, and found

assemble :: forall b f . (Finite a, Applicative f) => (a -> f b) -> f (a -> b)

Could somebody please walk me through what that type is, and what it says?

(Assuming as usual little is off topic in this channel and that WTF questions are okay)

Harrison Houghton

@hrhino

So, Finite is the class of all types having a finite number of elements, it appears.

That function just evaluates a -> f b for all possible as, getting an f [(a,b)], and then turns the [(a, b)] into a function a -> b by viewing the list of pairs as a relation.

So it's very limited: you can't do it unless you know all possible as, and the resulting applicative effect is just the combination of all possible effects resulting from a -> f b.

Justin Heyes-Jones

@justinhj

@beezee I was curious why there is an implementation of monoid for numbers tagged with multiplication but not for max, so I started to suspect it wasn't lawful, but I guess not

Barry Zhong

@zhongdj

what happened to scalaz.github.io? It's so incomplete.

https://scalaz.github.io/7/typeclass/

Dimitar Georgiev

@dimitarg

@hrhino thank you!
I can't understand how we go from a relation to a function. Forget elements?

Harrison Houghton

@hrhino

A function is just a binary relation a R b such that each element of a is related to exactly one b

So this depends on that list always being such a relation, which isn't a trivial fact but is also not hard to show.

Practically speaking, you do so with a: A => pairs.find(_._1 == a)

Barry Zhong

@zhongdj

is scalaz still active?

Dimitar Georgiev

@dimitarg

@hrhino right, I got thrown off somehow. thanks for the patient explanation.
Finite a implies an equality notion, and surely allValues :: [a] is going to give me back all distinct values.
(I guess I was thinking about injectivity and confused it with function-ness. Flipped the arrows somehow)

@zhongdj this channel, not so much. What do you mean by "active"?

Philip Schwarz

@philip_schwarz_twitter

@zhongdj https://twitter.com/scalazlog

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