Partial functions are functions which are not defined for all of their inputs. For questions about partially applied functions, use [partial-application] instead.
Questions tagged [partial-functions]
31 questions
66
votes
3 answers
What exactly is meant by "partial function" in functional programming?
According to my understanding, partial functions are functions that we get by passing fewer parameters to a function than expected. For example, if this were directly valid in Python:
>>> def add(x,y):
... return x+y
...
>>> new_function =…
Saurabh kukade
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31
votes
2 answers
In Haskell, why non-exhaustive patterns are not compile-time errors?
This is a follow-up of Why am I getting "Non-exhaustive patterns in function..." when I invoke my Haskell substring function?
I understand that using -Wall, GHC can warn against non-exhaustive patterns. I'm wondering what's the reason behind not…
gawi
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10
votes
2 answers
Why is take a total function
take (-1) [] is [].
What are the reasons to prefer this over a partial function, that is, an error?
Are there use cases where this property is exploited?
false
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9
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5 answers
Scala total function as partial function
Since a total function is a special case of a partial function, I think I should be able to return a function when I need a partial.
Eg,
def partial : PartialFunction[Any,Any] = any => any
Of course this syntax fails to compile. My question is, is…
sksamuel
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6
votes
1 answer
How does Scala Cons pattern matching determine the head and the tail of a List?
How is the head and tail determined in the following statement:
val head::tail = List(1,2,3,4);
//head: 1 tail: List(2,3,4)
Shouldn't there be some piece of code which extracts the first element as head and returns the tail as a new List. I've…
poissondist
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5
votes
1 answer
Is scanl1 really partial?
According to the Haskell wiki, the scanl1 function is partial. I don't understand what inputs result in bottom, though. For list functions, I'm used to the problem inputs either being empty lists (like for head) or infinite ones (like for reverse).…
Joseph Sible-Reinstate Monica
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5
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2 answers
Scala's Partial Functions in Haskell
Scala has a very nice support of partial functions, mainly because in Scala when you define a partial function it also defines an isDefinedAt function for it. And also Scala has orElse and andThen functions to work with partial functions.
Haskell…
Gurmeet Singh
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5
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5 answers
Short circuiting a list mapping with a partial function
So, I have made this function called tryMap which is as follows:
/// tryMap, with failure and success continuations.
let rec tryMapC : 'R -> ('U list -> 'R) -> ('T -> 'U option) -> ('T list) -> 'R =
fun failure success mapping list ->
…
phaz
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4
votes
3 answers
Anonymous PartialFunction syntax
I asked this question earlier: Combine a PartialFunction with a regular function
and then realized, that I haven't actually asked it right.
So, here goes another attempt.
If I do this:
val foo = PartialFunction[Int, String] { case 1 => "foo" }
…
Dima
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2
votes
1 answer
How to getOrElse with another Option in Scala
Let's assume that we have an option foo1 and an option foo2:
val foo1: Option[Foo]
val foo2: Option[Foo]
Is there an operator/function that allows me to return the value of the foo2 when foo1 is None?
val finalFoo: Option[Foo] =…
Yuchen
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2
votes
2 answers
Partial function explanation in the Odersky book
In the Scala Odersky book, he has an example explaining partial functions of page 295. It starts with this function:
val second: List[Int] => Int = {
case x :: y :: _ => y
}
So the above function will succeed if you pass it a three element list…
Jwan622
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2
votes
0 answers
Anonymous partial function in early initializer requires "premature access to class"
Why does this fail to compile:
trait Item
trait StringItem extends Item {
def makeString: String
}
trait SomeOtherItem extends Item
trait DummyTrait
case class Marquee(items: Seq[Item]) extends {
val strings: Seq[String] = items.collect {
…
Ben Kovitz
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2
votes
1 answer
Applying partial functions where defined and a different function where not
This is a motivational example, Given:
List((1,2), (2,1), (3,1))
I'd like to return:
List((1,2),(3,1))
I've tried to do this in several ways. First:
List((1,2), (2,1), (3,1)) map { case (a,b) => if (a > b) (a,b) else (b,a) }
distinct
Then I…
Joselo
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2
votes
1 answer
Explanation of List[_] in pattern matching used in flatten function
I am new to scala and I can not understand the following function
val L = List(List(1, 1), 2, List(3, List(5, 8)))
def flatten(l: List[Any]): List[Any] = l flatMap {
case ms:List[_] => flatten(ms)
case l => List(l)
} …
Donbeo
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vote
1 answer
http4s route matching for GET requests with params on root host
I have simple rout-mapping function which using http4s:
import cats.syntax.all._
import org.http4s._
import org.http4s.circe._
def routeMapper: PartialFunction[Request[F], F[Response[F]]] = {
case r @ POST -> Root => create
case r @ PUT -> Root…
Boris Azanov
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