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Michael Ahlers
@michaelahlers
The section right before it.
bblfish
@bblfish:matrix.org
[m]
I know. My own library banana-rdf is having trouble moving to Scala3 because of the removal of type projections. https://github.com/lampepfl/dotty-feature-requests/issues/14#issuecomment-815928271
bblfish
@bblfish:matrix.org
[m]
Though that covers a lot more, not just strings...
Adam Rosien
@arosien
@bblfish:matrix.org there's https://github.com/typelevel/case-insensitive, which i think might be useful for headers, since @rossabaker wrote it
but i can't remember the RFC anymore
Ross A. Baker
@rossabaker
case-insensitive was written for http4s, and used in its modeled headers, but can represent characters that are illegal in headers.
bblfish
@bblfish:matrix.org
[m]
Ah yes, I saw that one be used by http4s :-)
Ross A. Baker
@rossabaker
I've thought about tightening those headers down to make illegal states unrepresentable, but haven't figured it out without making the library unusable.
Refined is probably the closest.
A lot of things you can handle by storing Plain Old Strings and encoding/decoding them. Unfortunately, there's no standard way to encode several codepoints into an HTTP header. You're dealing with a restricted alphabet.
Even ASCII doesn't get you out of the mess, because most (all?) control characters are forbidden.
You could use something like Literally to validate literals. It's a macro soution, but works on Scala 2 and Scala 3.
But anytime you're accepting things from the wire, or doing anything dynamic, that error type is going to be a big nuisance for limited benefit, and we don't like to throw.
Alexander Van Hecke
@alexandervanhecke
is there a way to let cats-parse consume an fs2.Stream[F, Byte] or an InputStream instead of a String?
I have a zip file full of files I need to parse in one go, I first read all the files to Strings and concatenate those before passing it to my parser. doing it directly from stream would be nice
Ross A. Baker
@rossabaker
I think the answer is no: incremental parsing is a lot more complicated, and I don't remember cats-parse supporting it. But there's a dedicated cats-parse Gitter, where perhaps there's better news.
bblfish
@bblfish:matrix.org
[m]
What I am doing (provisionally) is to create a case class FsString private (chars: Seq[Char]) which can only be built by cats.parse or by a constructor in the object that does the verification of the content first. That should give me enough type safety for the moment. (Good to know about Literally).
bernardopinto
@bernardopinto

Hi tere,
I'm exploring how cats does type conversion, in this specific case, Either => EitherOps conversion.
I've tracked up to EitherSyntax that implements an implicit def catsSyntaxEither converting an Either => EitherOps.
However I don't get where/how the conversion is summoned. I would expect some implicit class to allow infix notation to do
something like Right().bimap(leftChannel, rightChannel).
either syntax

Would appreciate any help :)

Rob Norris
@tpolecat
The conversion is typically in scope via the import of cats.syntax.all._
@ cats.syntax.all.catsSyntaxEither(Right()) 
res3: cats.syntax.EitherOps[Nothing, Unit] = cats.syntax.EitherOps@f29f2af0
Maybe I don't understand your question.
Luis Miguel Mejía Suárez
@BalmungSan
@bernardopinto do you know that an implicit class is just sugar syntax for a class and an implicit def (implicit conversion)?
That is why they can not be top-level and why libraries like cats don't use them but rather just have normal class and the conversions in some traits that are shared.
Does that answer your question? Or did I misunderstood it?
Adam Rosien
@arosien

What I am doing (provisionally) is to create a case class FsString private (chars: Seq[Char]) which can only be built by cats.parse or by a constructor in the object that does the verification of the content first. That should give me enough type safety for the moment. (Good to know about Literally).

@bblfish:matrix.org you may know already, but refined automates that stuff. there may be other "newtype"-like support that removes the tagged type approach of refined

bblfish
@bblfish:matrix.org
[m]
bernardopinto
@bernardopinto
@BalmungSan I actually didn't know that.
But in cats.syntax.either the final class EitherOps does not extends EitherSyntax. And in EitherSyntax is where catsSyntaxEither (Either => EitherOps) lives. So I'm not sure how that connection happens.
Also @tpolecat how does cats gets from a Right(value): Either[E, A] => Bifunctor[Either] just by importing import cats.syntax.either._ and calling Right(value).bimap(ec, vc)?
I have an example here: https://github.com/bernardopinto/ammonite-scripts/blob/master/BifunctorStudy.sc
Luis Miguel Mejía Suárez
@BalmungSan

@bernardopinto
Ok, let's try to go step by step in more or less the way the compiler does.

Given:

import cats.syntax.all._
val either: Either[E, A] = Right(value)
either.bimap(ec, vc)

The compiler sees a call to bimap on a value of type Either[E, A], the type Either[E, A] doesn't have such a method so the compiler tries to search for implicit conversion from Either[E, A] into anything that has a bimap method with the correct signature; remember it has a limited scope from where it searches.

In this case, it will eventually search in the lexical scope, i.e., in whatever is imported.
The line import cats.syntax.all._ imports an implicit conversion from Either into EitherOps which does has such bimap method.
But, how does that import provided that extension?

You can see that conversion defined here inside the EitherSyntax trait.
Then here we can see that the AllSyntax trait extends the EitherSyntax one.
And finally here you can see that the all object extends the AllSyntax trait; thus having inside it the implicit conversion.
Which is ultimately put in scope with the import

bernardopinto
@bernardopinto
@BalmungSan alright got it thanks :)
I was not familiar with regular use of type conversions like this. But it makes sense now, goes back to what you said about having an implicit def and a case class.
Luis Miguel Mejía Suárez
@BalmungSan
@bernardopinto note is not a case class, is a value class. You do not want the class that contains the extension methods to really exists.
bernardopinto
@bernardopinto
@BalmungSan true, mental typo. Thanks for the help :)
Luis Miguel Mejía Suárez
@BalmungSan
You are welcome :)
Adam Rosien
@arosien
i usually think of it like:
case class Foo(s: String)

implicit class FooOps(foo: Foo) extends AnyVal {
  def hello(): String = s"Hello $foo.s!"
}
val foo = Foo("Luis")

- foo.hello() // the compiler replaces this code with the following
+ new FooOps(foo).hello() // since FooOps is a value class, no FooOps actually gets instantiated
Adam Rosien
@arosien
but, as always, @BalmungSan :thumbsup:
Luis Miguel Mejía Suárez
@BalmungSan
:grimacing:
Adam Rosien
@arosien
scala 3 will lower the conceptual overhead of this stuff
Eugene Apollonsky
@chessman

hi! rookie's question. I have a List[ValidatedNec[Error, Any]] and I want to collect left parts as Option[NonEmptyChain[Error]]. I came up with

    List(Error("a").invalidNec[String], Error("b").invalidNec[Any]).map(_.fold(Some(_), _ => None)).combineAll

but it looks ugly. is there a better way to do it?

daenyth
@daenyth:matrix.org
[m]
mmm
Luis Miguel Mejía Suárez
@BalmungSan
list.sequence.swap.toOption ?
You may even avoid the List[Validated] in the first place if you can use parTraverse but you would need to show more code for that.
Adam Rosien
@arosien
separate
def separate[G[_, _], A, B](fgab: F[G[A, B]])(implicit FM: Monad[F], G: Bifoldable[G]): (F[A], F[B])
Separate the inner foldable values into the "lefts" and "rights"
Example:
scala> import cats.implicits._
scala> val l: List[Either[String, Int]] = List(Right(1), Left("error"))
scala> Alternative[List].separate(l)
res0: (List[String], List[Int]) = (List(error),List(1))
Eugene Apollonsky
@chessman
thanks, looks good
bblfish
@bblfish:matrix.org
[m]
I see there is initial work on fthomas/refined#921.
Adam Rosien
@arosien
noel and i presented about various options for refinements, etc., for a larger view on the subject: https://www.youtube.com/watch?v=w7FuQiSi48w
but yes, refined is quite amazing
bblfish
@bblfish:matrix.org
[m]
Oh thanks.
I am actually starting to wonder if refinement is not actually extremely useful when working with data. So RFC8941 defines a bunch of types for HTTP headers. But each header will only use a subset of some of those types. So eg. a Signing HTTP Messages header will have a SfDict, but restricted to certain types of lists, and certain types of attributes. So it would be interesting if one could keep the underlying data structure but after testing it that it matches some criteria, refine it without changing the structure. Then one could use the underlying data structures without always needing to copy them to new structures.
Adam Rosien
@arosien
yes!
bblfish
@bblfish:matrix.org
[m]
now I understand what sealed abstract case classes are about :-)
2 replies