Either is a type used in functional languages such as Haskell and Scala to represent a value that is one of two parametrized types. In Scala, the Either type is often used as an alternative to scala.Option where Left represents failure (by convention) and Right is akin to Some.
Questions tagged [either]
341 questions
0
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1 answer
Scala - Recursive Patten Matching Using Either
I currently have something that looks like this:
data foreach {
case Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(Left(a))))))))))))))))))) => /* Do something */
case…
Olshansky
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4 answers
Haskell - Maybe Either
-- | Convert a 'Maybe a' to an equivalent 'Either () a'. Should be inverse
-- to 'eitherUnitToMaybe'.
maybeToEitherUnit :: Maybe a -> Either () a
maybeToEitherUnit a = error "Not yet implemented: maybeToEitherUnit"
-- | Convert a 'Either () a' to…
fuuman
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1 answer
Error while compiling print Either value
I'm trying to compile simple code snippet.
main = (putStrLn . show) (Right 3.423)
Compile results in the following error:
No instance for (Show a0) arising from a use of `show'
The type variable `a0' is ambiguous
Possible fix: add a type signature…
Alexander
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2 answers
Project a sequence of 'Left's from a sequence of Eithers?
(Caveat - I'm a scala noob) Given a sequence of Eithers, viz
theResults : Seq[Either[Error, String]]
I am trying to extract all the Errors by using a map on the left(s)
theResults match {
case r if r.exists(_.isLeft) => {
val errors =…
StuartLC
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1 answer
understanding data type in haskell
I am a haskell new bee. I can't just wrap my head around what is going on here
data NestedList a=Elem a | List [NestedList a] deriving Show
append::NestedList a->NestedList a->Either String (NestedList a)
append (Elem x) (Elem y) = Right $ List…
user1792899
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1 answer
haskell Either String (NestedList a)- why doesn't it work
I am trying to append function that works on Nested Lists like regular lists. I want to use Either String (Nested a) so that it returns error or the appended list. But it keeps failing. I am not doing NestedList[NestedList a] anywhere. Why does it…
user1792899
0
votes
2 answers
for comprehensions with if guard throws error
I get one error when I use for comprehensions with if guard in this way.
code:
for {
foo <- Left[String,String]("teststring").right
bar <- Right[String,String]("teststring").right if (foo==bar)
} yield (bar)
error:
error: type mismatch;
found …
angelokh
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Why isn't Vavr Either is recognizing the parameter to map() function?
I am dirtying my hands with the fantastic library of vavr (0.9.2).
Here's a code snippet, that aims to collect an Either:
Either,String>, List> payloadPreparationResult =
new…
Nirmalya
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1 answer
please suggest best way to write an anonymous function here
Please suggest best way to write an inline function at the place where func_1 is being called. Also it should do something what func_1 is trying to do
(I am aware that a function cannot return two things in scala)
I am reading lines from a…
nikhil kekan
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1 answer
"Either Fmap" which Continues until a Right Result has been Reached
If Either fmap is
(a -> b) -> p a a -> p a b
which stops mapping once a Left is returned.
What's name or type signature for a function which doesn't stop until it gets a Right result.
I suspect a bifunctor, but I really need it spelled out - don't…
user3264325
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1 answer
Couldn't match type Synonym with Either
I'm a beginner learning Haskell. But not so sure how Either works in pattern matching.
Here is my code:
type Rank = Either Pip Court
type Pip = Int
type Deck = [Card]
data Card = Joker | Card Suit Rank
data Court = Ace | Jack | Queen | King deriving…
Escutche0n
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