I'm guessing that there must be a better functional way of expressing the following: def foo(i: Any) : Int if (foo(a) < foo(b)) a else b So in this example f == foo and p == _ < _. There's bound to be some masterful cleverness in scalaz for this! I can see that using BooleanW I can write: p(f(a), f(b)).option(a).getOrElse(b) But ...
Following watching Nick Partidge's presentation on deriving scalaz, I got to looking at this example, which is just awesome: import scalaz._ import Scalaz._ def even(x: Int) : Validation[NonEmptyList[String], Int] = if (x % 2 ==0) x.success else "not even: %d".format(x).wrapNel.fail println( even(3) <|*|> even(5) ) //prints: Failu...
There is a trait called Kleisli in the scalaz library. Looking at the code: import scalaz._ import Scalaz._ type StringPair = (String, String) val f: Int => List[String] = (i: Int) => List((i |+| 1).toString, (i |+| 2).toString) val g: String => List[StringPair] = (s: String) => List("X" -> s, s -> "Y") val k = kleisli(f) >=> k...
This question isn't meant as flame-bait! As it might be apparent, I've been looking at Scalaz recently. I'm trying to understand why I need some of the functionality that the library provides. Here's something: import scalaz._ import Scalaz._ type NEL[A] = NonEmptyList[A] val NEL = NonEmptyList I put some println statements in my func...
I want to transform a List[Option[T]] into a Option[List[T]]. The signature type of the function is def lo2ol[T](lo: List[Option[T]]): Option[List[T]] The expected behavior is to map a list that contains only Somes into a Some containing a list of the elements inside the elements Some's. On the other hand, if the input list has at lea...
Many of the methods in scalaz have symbolic unicode equivalents, such as forever and ∞ (of course, I have this the wrong way round, the symbolic methods really have ASCII equivalents). The project contains a live templates XML file for IDEA so these can be auto-completed, I believe by using the forever+TAB shortcut (in the above instanc...
The following compiles just fine using scala Beta1 and scalaz snapshot 5.0: val p1: Int => Boolean = (i : Int) => i > 4 val s: List[Int] = List(1, 2, 3) val b1 = s ∃ p1 And yet this does not: val s: Set[Int] = Set(1, 2, 3) val b1 = s ∃ p1 I get the following error: Found: Int => Boolean Required: Boolean => Boolean The sig...
I've been given a java api for connecting to and communicating over a proprietary bus using a callback based style. I'm currently implementing a proof-of-concept application in scala, and I'm trying to work out how I might produce a slightly more idiomatic scala interface. A typical (simplified) application might look something like thi...
Hi! I want to be able to apply an operation f: (T,T) => T to Option[T] values in Scala. I want the result to be None if any of the two values is None. More specifically, I want to know if is there a shorter way to do the following: def opt_apply[T](f: (T,T) => V, x: Option[T], y: Option[T]): Option[T] = { (x,y) match { case (Som...
I try to find out why the call ∅ in scalaz.ListW.<^> works def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => ∅ case h :: t => f(Scalaz.nel(h, t)) } My minimal theory is: trait X[T]{ def y : T } object X{ implicit object IntX extends X[Int]{ def y = 42 } implicit object StringX extends X[Strin...
I have a very large List[A] and a function f: List[A] => List[B]. I would like to split my original list into sub-lists with a maximum size, apply the function to each sublist in turn and then unsplit the result into one big List[B]. This pretty easy: def split[T](l : List[T], max : Int) : List[List[T]] = //TODO def unsplit[T](l : List...
I'm trying to find the 'right' actor implementation for my thesis. I realized there is a bunch of them and it's a bit confusing to pick one. Personally I'm especially interested in remote actors, but I guess a complete overview would be helpful to many others. This is a pretty general question, so feel free to answer just for the impleme...
I try to define the Reader monad with scalaz like this: import scalaz._ import Scalaz._ final class Reader[E,A](private[Reader] val runReader: E => A) object Reader { def apply[E,A](f: E => A) = new Reader[E,A](f) def env[E]: Reader[E,E] = Reader(identity _) implicit def ReaderMonad[E] = new Monad[PartialApply1Of2[Reader,E]#App...
I was playing around with ListW.<^>, the definition of which is as follows: def <^>[B: Zero](f: NonEmptyList[A] => B): B = value match { case Nil => ∅ case h :: t => f(Scalaz.nel(h, t)) } I cannot figure out how come Option is being chosen as the Zero type for this example scala> case class CC(v : Int) defined class CC scala> va...
I tried googling for this but all I got were stories about minor celebrities. Given the lack of documentation, what is a DList? ...
If I have: val f : A => B => C This is shorthand for: val f : Function1[A, Function1[B, C]] How do I get a function g with the signature: val g : (A, B) => C = error("todo") (i.e.) val g : Function2[A, B, C] //or possibly val g : Function1[(A, B), C] in terms of f? ...
I found a blog post today that mention's scalaz's sequence function. Couldn't you do something as simple as: if (l contains None) None else l If so, what would this function signature look like? contains is in SeqLike, right? Also, from the blog post I thought sequence was going to be something similar to map, but one that would br...