Scalaz provides type classes and purely functional data structures for Scala
Questions tagged [scalaz7]
102 questions
1
vote
1 answer
scalaz.syntax.monad._ brokes applicative syntax
I have some code which uses either applicative and monad syntax. The code looks like this:
import scalaz._
import scalaz.syntax.applicative._
import scalaz.syntax.std.boolean._
import scalaz.syntax.traverse._
//import…
Aitor ATuin
- 15
- 1
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1
vote
1 answer
When using an EitherT[StateWithSomeFixedStateType, T, U], how do you do some state manipulation when a left is returned?
Say you have an EitherT that looks something like this:
type StateListOfString[+T] = State[List[String], T]
type MyEitherT = EitherT[StateListOfString, Int, Boolean]
If you have a for-comprehension that could return a left:
my computation = for {
…
James Moore
- 8,636
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1
vote
1 answer
global, default implicits in scalaz (scalaz7)
When I code using Scalaz I often encounter problems, that there is no implicit in scope. I think there should be some default implicits somwhere in vast package scalaz, but either I don't know where or there are not any.
Suppose we want to show any…
pawel.panasewicz
- 1,831
- 16
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0
votes
1 answer
Unwrapping the value of an Identity monad
I have been playing a little bit with scalaz and I am stuck on a seemingly trivial issue. I was playing around with the Reader and Kliesli monads and found myself with something like this:
val gr = Reader { (_: Int) + 1 }
val a = gr(1)
That…
Luis Sisamon
- 101
- 7
0
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1 answer
Lifting a function which takes implicit parameter using functor (Scalaz7)
Just started learning Scalaz. Here is my code
trait Monoid[A] {
def mappend(a1: A, a2: A): A
def mzero: A
}
object Monoid {
implicit val IntMonoid: Monoid[Int] = new Monoid[Int] {
def mappend(a1: Int, a2: Int): Int = a1 + a2
…
xeonzion
- 35
- 8
0
votes
1 answer
Scala multiple generic parameter data structure typeclass instance
I'm using Scalaz as I'm loving a lot of aspects from Haskell's type class setup in the standard libraries. But exactly this is my current problem. I have a generic data structure with two generic parameters:
case class Parser[T,A](f: T => (T,A))
In…
bash0r
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- 17
0
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1 answer
Scalaz.NonEmptyList vs Scala.List?
Can someone explain why should I use Scalaz's NonEmptyList over Scala's List?
In a immutable application it does not make much sense to create an empty List
So should I always use NonEmptyList in an immutable application ?
Why else would I use…
user794783
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0
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1 answer
Scalaz Writer Monad and filterM
I am working my way through learning scalaz and Learn You A Haskell For Greater Good and wonder how to translate the filterM example from LYAHFGG to Scala.
fst $ runWriter $ filterM keepSmall [9,1,5,2,10,3]
with keepSmall defined as
keepSmall :: Int…
mjaskowski
- 1,479
- 1
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- 16
0
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1 answer
Create a OptionT[Future, A] from a lower-kinded type
I'm pretty new to scalaz, and I'm trying to figure out to convert various types to monad transformers.
I'm stuck on trying to convert a Int to a OptionT[Future, Int], or even to EitherT[Future, String, Int].
I found a bunch of tutorials/SO answers…
dcastro
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0
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0 answers
Memory efficient stream traversal using the scalaz Traverse typeclass
I'm trying to traverse/sequence a large stream (e.g. scala.collection.immutable.Stream) using Scalaz' (version 7.1.2) Traverse typeclass, but I'm constantly running into a java.lang.OutOfMemoryError: GC overhead limit exceeded issue.
My traversal…
Martin Studer
- 2,213
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0
votes
1 answer
Testing if the static types of 2 definitions are equal
Let's say I come up with a combinator:
def optional[M[_]: Applicative, A, B](fn: Kleisli[M, A, B]) =
Kleisli[M, Option[A], Option[B]] {
case Some(t) => fn(t).map(_.some)
case None => Applicative[M].point(none[B])
}
This combinator maps…
Erik Kaplun
- 37,128
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0
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1 answer
underscore in expression
What does the underscore mean in below snipped. This is fragment of scalaz7 library:
trait Apply[F[_]] extends Functor[F] { self =>
//...
def ap[A, B](fa: => F[A])(f: => F[A => B]): F[B]
//...
def apF[A, B](f: => F[A => B]): F[A] => F[B] =…
pawel.panasewicz
- 1,831
- 16
- 27