Scalaz provides type classes and purely functional data structures for Scala
Questions tagged [scalaz7]
102 questions
5
votes
2 answers
scalaz 7 equivalent of `<|*|>` from scalaz 6
In Nick Partridge's presentation on deriving scalaz, based on an older version of scalaz, he introduces validations using a function:
def even(x: Int): Validation[NonEmptyList[String], Int] =
if (x % 2 == 0) x.success else { s"not even:…
Joe Kearney
- 7,397
- 6
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5
votes
1 answer
How to use a Monad Transformer when Disjunction is the outermost container?
val vLInts = (1 to 10).toList.right[String]
for {
i <- ListT(vLints)
_ = println(i)
} yield i
//error: no type parameters for method apply:(underlying: M[List[A]])scalaz.ListT[M,A] in object ListT exist so that it can be applied to arguments…
jordan3
- 877
- 5
- 13
5
votes
0 answers
Implicit conversion from Traversable to Foldable in Scalaz 7
Where is the implicit conversion from a scala.collection.Traversable[A] to a scalaz.Foldable[A] defined in Scalaz 7.x? The standard import
import scalaz._
import Scalaz._
does not include it.
There used to be an implicit def…
David B.
- 5,700
- 5
- 31
- 52
5
votes
2 answers
Scalaz Tree to JSON
I'm currently trying to use the Tree class to build a tree-strucuture from a database query. Afterwards I want to convert it to a json object (with playframework api).
Some examples or a bit more documentation for the Tree class would be awesome. I…
Muki
- 3,513
- 3
- 27
- 50
5
votes
1 answer
Type class for uniting unrelated failure cases in my Scalaz disjunctions
I have a for comprehension over Scalaz disjunctions. The left types on these can be different types of error case classes from other libraries. For example, one failure case can be due to an HTTP timeout while another can represent a Json parsing…
Mad Dog
- 583
- 4
- 18
5
votes
3 answers
Scalaz 7 Iteratee to process large zip file (OutOfMemoryError)
I'm trying to use the scalaz iteratee package to process a large zip file in constant space. I have a long-running process I need to perform on each file in the zip file. Those processes can (and should) be run in parallel.
I created an EnumeratorT…
RJ Regenold
- 1,748
- 13
- 17
5
votes
1 answer
Simple control flow in scalaz effect
Take this simple bit of code:
var line = "";
do {
println("Please enter a non-empty line: ")
line = readLine()
} while (line.isEmpty())
println("You entered a non-empty line: " + line)
It's definitely not particularly elegant, especially with…
Heptic
- 3,076
- 4
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- 51
4
votes
1 answer
Chaining a number of transitions with the state Monad
I am starting to use the state monad to clean up my code. I have got it working for my problem where I process a transaction called CDR and modify the state accordingly.
It is working perfectly fine for individual transactions, using this function…
Luis Sisamon
- 101
- 7
4
votes
1 answer
"private[syntax]" in Scala
What is this "private[syntax]" language feature?
/** Wraps a value `self` and provides methods related to `Show` */
final class ShowOps[F] private[syntax](val self: F)(implicit val F: Show[F]) extends Ops[F] {
////
final def show: Cord =…
Michael Lafayette
- 2,972
- 3
- 20
- 54
4
votes
2 answers
Generic transform/fold/map over tuple/hlist containing some F[_]
I recently asked Map and reduce/fold over HList of scalaz.Validation and got a great answer as to how to transform a fixed sized tuple of Va[T] (which is an alias for scalaz.Validation[String, T]) into a scalaz.ValidationNel[String, T]. I've since…
Erik Kaplun
- 37,128
- 15
- 99
- 111
4
votes
1 answer
Scalaz unboxed tagged type not automatically unboxed
Reading http://eed3si9n.com/learning-scalaz/Tagged+type.html and trying out the sample code:
import scalaz._; import Scalaz._
sealed trait KiloGram
def KiloGram[A](a: A): A @@ KiloGram = Tag[A, KiloGram](a)
val mass = KiloGram(20.0)
2 *…
Erik Kaplun
- 37,128
- 15
- 99
- 111
4
votes
1 answer
How to exit a program properly when using Scalaz Futures and the timed function
This works as expected:
object Planexecutor extends App {
import scalaz.concurrent.Future
import scala.concurrent.duration._
val f = Future.apply(longComputation)
val result = f.run
println(result)
}
This does not:
object…
jedesah
- 2,983
- 2
- 17
- 29
4
votes
1 answer
Iso macro in Scala
If I want to implicitly convert two objects from one to another, is there anyway to do this using something like an Iso macro?
For example, if I have this:
implicit def listToMap[A, B](l: List[(A, B)]): Map[A, B] = l.toMap
implicit def mapToList[A,…
pathikrit
- 32,469
- 37
- 142
- 221
4
votes
1 answer
collapsing \/[A,A] to A
In a web application, I've got an action that can fail in various different ways, or eventually succeed.
In this context success and failure are represented by subclasses of SimpleResult (representing an HTTP response)
I use the monadic operations…
Valentin Kasas
- 203
- 1
- 6
4
votes
1 answer
Scala Implicit generators
If I have an implicit from A to B, how can I auto-get implicits from F[A] to F[B]?
For example, if I have implicit toInt[A](l: List[A]) = l.size and now I want to have an implicit from (List[A], Int) to (Int, Int) which reuses the toInt implicit.…
pathikrit
- 32,469
- 37
- 142
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