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]
35 questions
1
vote
1 answer
Factoring out common cases in pattern matching with partial function
I routinely use partial functions to factor out common clauses in exception handling. For example:
val commonHandler: PartialFunction[Throwable, String] = {
case ex: InvalidClassException => "ice"
}
val tried = try {
throw new…
Igor Urisman
- 717
- 1
- 6
- 22
1
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
- 4,408
- 1
- 15
- 28
1
vote
3 answers
Why Scala PartialFunction works without defining isDefinedAt?
It looks First and Second are the same, but why?
First
val iter = List(1, 2, 3, 4, 5).iterator
val first = iter.collect(new PartialFunction[Int, Int]{
def apply(i: Int) = i
def isDefinedAt(i: Int) = i > 0 && i <…
mon
- 18,789
- 22
- 112
- 205
1
vote
3 answers
Scala function composition totalFn(partialFn(totalFn(x)))
I was trying to compose three functions with only the middle one being a PartialFunction. I would expect the resulting type to be PartialFunction as well.
Example:
val mod10: Int => Int = _ % 10
val inverse: PartialFunction[Int, Double] = { case n…
user2697852
1
vote
1 answer
PartialFunction implicit parameters
i have a simple PartialFunction
type ChildMatch = PartialFunction[Option[ActorRef], Unit]
def idMatch(msg: AnyRef, fail: AnyRef)(implicit ctx: ActorContext): ChildMatch = {
case Some(ref) => ref forward msg
case _ => ctx.sender() !…
HoTicE
- 573
- 2
- 13
1
vote
1 answer
How to generate a stack trace upon division by zero with ghc 7.10.3?
If a program is run and crashes with the message "Divide by zero", what is the best way to identify where in the code this error was generated?
kostmo
- 6,222
- 4
- 40
- 51
1
vote
1 answer
Why does this function hang the REPL?
Chapter 9 of Test-Driven Development with Idris presents the following data type and removeElem function.
import Data.Vect
data MyElem : a -> Vect k a -> Type where
MyHere : MyElem x (x :: xs)
MyThere : (later : MyElem x xs) -> MyElem x (y…
Kevin Meredith
- 41,036
- 63
- 209
- 384
1
vote
1 answer
How to use Scala macros to create new partial functions or transform them?
I am having trouble writing a macro that transforms a given partial function and creates a new partial function. For instance, I want to be able to decompose the given partial function into its elements - pattern binder, guard condition, and body;…
winitzki
- 3,179
- 24
- 32
1
vote
1 answer
Idris: function works with Nat parameter and fails type checking with Integer parameter
I am new to Idris. I am experimenting with types and my task is to make an "onion": a function that takes two arguments: a number and whatever and puts whatever into List nested such number of times.
For example, the result for mkOnion 3 "Hello…
O.Phillips
- 351
- 1
- 12
1
vote
2 answers
How to write Haskell partial functions that will never have invalid values?
Let's say want a function, taking a list of numbers, that returns the sum of adjacent pairs of numbers, except at the two edges where it simply returns the edge numbers. For example:
[1,2,3,4,5] --> [1,3,5,7,9,5]
I come up with the following…
user1002430
1
vote
1 answer
Scala partial function composition performance
Is there any difference in the performance of a partial function defined as
val matches = {
case Match(x,y) => ...
case AnotherMatch(x,y,z) => ...
case x:YetAnother => ...
}
and one defined as below?
val match1 = {
case Match(x,y) =>…
Cristian Vrabie
- 3,972
- 5
- 30
- 49
1
vote
5 answers
How to know when to use PartialFunction vs return Option
As an example, we define a function that should convert 1, 3, 42 respectively to "foo", "bar", "qix" and all other integer to "X".
I've come up with 2 implementations :
The method f need to be separate because it can be reuse in other context.
def…
Yann Moisan
- 8,161
- 8
- 47
- 91
0
votes
1 answer
WxPython PyPubSub, using curried function not working
I'm using the PyPubSub module of WxPython, to send messages around, and I want to have a function subscribed to a topic, where the function has some curried parameters. Unfortunately, it doesn't seem to be using the curried function as I would…
John C
- 6,285
- 12
- 45
- 69
0
votes
2 answers
PartialFunction in Scala
I am looking at the PartialFunction source code of Scala. In the file, the trait PartialFunction as well as a companion object PartialFunction are defined. The companion object has methods cond and condOpt.
Link:…
user3103957
- 636
- 4
- 16
0
votes
0 answers
partial functions vs input verification
I really love using total functions. That said, sometimes I'm not sure what the best approach is for guaranteeing that. Lets say that I'm writing a function similar to chunksOf from the split package, where I want to split up a list into sublists…
Nathan Wilson
- 629
- 6
- 11