Questions about the Scala's PartialFunction type. For questions about the broader concept of partial functions (i.e. functions not defined for all of their inputs), use [partial-functions]. For questions about partially applied functions, use [partial-application].
Questions tagged [partialfunction]
120 questions
6
votes
2 answers
Scala: selecting function returning Option versus PartialFunction
I'm a relative Scala beginner and would like some advice on how to proceed on an implementation that seems like it can be done either with a function returning Option or with PartialFunction. I've read all the related posts I could find (see bottom…
Gregor Scheidt
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6
votes
2 answers
In functional programming terms, what do you call something with an orElse or other fallback method?
Using scala for reference, we see a fallback behavior (orElse) in several places such as PartialFunction, Option, and cats EitherOps.
This feels similar to but not the same as the flattening behavior of a monad. Is there a functional programming…
kag0
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6
votes
2 answers
Scala Partial Function Type Definition
val even: PartialFunction[Int, String] = PartialFunction[Int, String] {
case i if i % 2 == 0 => i + " is even"
}
val isEven: PartialFunction[Int, String] = {
case i if i % 2 == 0 => i + " is even"
}
val odd: PartialFunction[Int, String] =…
pramesh
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6
votes
2 answers
Is there a nicer way of lifting a PartialFunction in Scala?
I occasionally come across the following pattern, where I essentially have a PartialFunction[SomeType,AnotherType], and want to treat it as a Function[SomeType,Option[AnotherType], eg:
def f(s:SomeType):Option[AnotherType] = s match {
case…
Kristian Domagala
- 3,686
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6
votes
3 answers
convert function to partial function scala
I have a sealed trait:
sealed trait ActorMessage
case class AddX(x: Int) extends ActorMessage
case class RemoveX(x: Int) extends ActorMessage
Also I have a function to handle all messages and warn me about non exhaustive match:
def handleMessage:…
kpbochenek
- 469
- 2
- 21
6
votes
3 answers
Using Tuples in map, flatmap,... partial functions
If I do:
val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map { t => t._1 + t._2 }
It's ok.
If I do:
val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map { case (b, n) => b + n }
It's ok too.
But if I do:
val l…
Joan
- 4,079
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6
votes
2 answers
Extending a partially implemented partial function in scala
I'm using the Akka actors library here. The actors library defines a partial function "receive" which an actor that extends "actor" must implement to deal with various messages. I am creating a trait hierarchy for my application where trait…
Alex
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5
votes
2 answers
Scala PartialFunctions from concrete ones
Is there any quick way to use as a concrete function (of type, say, (A) => B) as a PartialFunction[A, B]? The most concise syntax I know of is:
(a: A) => a match { case obj => func(obj) }
Is there an implicit conversion anywhere, something…
Kenneth Allen
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5
votes
3 answers
Understand 'case' keyword in partial functions
I am new to Scala and I am trying to decode its constructs, I learned about pattern matching and the syntax is similar to Java switch statement
val x: Int = Random.nextInt(10)
x match {
case 0 => "zero"
case 1 => "one"
case 2 => "two"
case…
Adelin
- 18,144
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5
votes
2 answers
Scala: Is it possible to get partially applied function from leftfold?
I'm currently learning Scala, and I just wondered at fold-left.
Since fold-left is curried, you should be able to get a partially applied function(PAF) with a first parameter as below.
(0 /: List(1, 2, 3)) _
But actually, I've got an…
Tamajin
- 155
- 5
5
votes
4 answers
Is PartialFunction orElse looser on its type bounds than it should be?
Let's define a PartialFunction[String, String] and a PartialFunction[Any, String]
Now, given the definition of orElse
def orElse[A1 <: A, B1 >: B](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]
I would expect not to be able to compose the…
Gabriele Petronella
- 106,943
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5
votes
2 answers
Define an object extending PartialFunction, implement directly with cases
I'm quite new to Scala but I already love it. I have read tutorials and articles on partial functions. What I would like to achieve is to have an object extending PartialFunction[...,...] and have it defined directly with cases, without needing to…
azyoot
- 1,162
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5
votes
1 answer
Scala value class compilation fails for base type with partial-function-parameter method
Say, I defined a value class as follows
package object p {
class ValueClass[T](val o: Option[T]) extends AnyVal {
def foo: Option[T] =
o collect {
case t => t
}
}
}
The compilation failed with the message:
overriding…
user3281360
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- 3
5
votes
2 answers
PartialFunction and MatchError
There are two ways to define PF: 1) with literal case {} syntax and 2) as explicit class. I need the following function throw a MatchError, but in the second case that doesn't happen.
1) with case
val test: PartialFunction[Int, String] = {
case x…
user1078671
5
votes
1 answer
Scala: Have the type parameter of a collection survive a "collect" when the type parameter is a member type
Normally, when collecting all the elements of a sequence that match a particular type, the resulting collection has both the type of the original collection and the type selected for:
trait Foo
trait Bar
trait Baz {
// Works
def def1(foo:…
drhagen
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