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
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?
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.
as, and the resulting applicative effect is just the combination of all possible effects resulting from a -> f b.
a: A => pairs.find(_._1 == a)
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)
Hi guys, i am struggling with:
val foo = List(Validation.failure("bar"), Validation.success(8), Validation.success(10))
foo.sequenceThe error says
<console>:19: error: could not find implicit value for parameter ev: scalaz.Validation[String,Int] === G[B]I am trying to get List[Int] or List[String] (depends on existence of Failure). My questions are:
- What does the error says? (After some digging I think it should say there is no
Traversableinstance forValidationinstead) - Is there any reasonable way to get the expected result?
Hi! I'm trying to migrate pureconfig to scalaz 7.3 (pureconfig/pureconfig#752) but I'm getting an error about a missing instance of Unapply:
<console>:42: error: Implicit not found: scalaz.Unapply[scalaz.Applicative, Unit]. Unable to unapply type `Unit` into a type constructor of kind `M[_]` that is classified by the type class `scalaz.Applicative`. Check that the type class is defined by compiling `implicitly[scalaz.Applicative[type constructor]]` and review the implicits in object Unapply, which only cover common type 'shapes.'
List(validConf, invalidConf, anotherInvalidConf).traverseU { c =>
^I couldn't find any migration guide or release notes for scalaz 7.3. Do I have to import something now?
def f[F[_]](implicit E: MonadError[F, String], implicit T: MonadTell[F, Vector[String]]) = ...import scalaz._
import Scalaz._
type W[A] = Writer[Vector[String], A]
type T[A] = EitherT[W, String, A]
f[T].run.run
libraryDependencies += "org.scalaz" %% "scalaz-base" % "1804fbf6-SNAPSHOT"
