Are we missing a `catch(block, transform, catch)` ...

# arrow-contributors

[phldavies]

Are we missing a catch(block, transform, catch) override? Currently doing the equivalent of catch({ transform(block()) }, catch) would result in any exceptions from transform being handled by the catch function.

[Alejandro Serrano.Mena]

I think that one is simply fold

[phldavies]

I thought so too, but fold is more as it introduces a redundant Raise<Error> and supporting mechanism

[phldavies]

I might push a draft PR with

@RaiseDSL
public inline fun <A, B> catch(block: () -> A, transform: (value: A) -> B, catch: (throwable: Throwable) -> B): B {
  contract {
    callsInPlace(block, AT_MOST_ONCE)
    callsInPlace(transform, AT_MOST_ONCE)
    callsInPlace(catch, AT_MOST_ONCE)
  }
  val value = catch({ block() }, { return catch(it) })
  return transform(value)
}

to discuss

[Alejandro Serrano.Mena]

I just want to be sure we're just not adding overloads just for the sake of it

[phldavies]

Fully with you - this only came up as I had a case that needed it (in my case the "transform" shouldn't throw anything but it still felt wrong to have it within the block, but I still wanted to the catch to return the appropriate type)

[phldavies]

I'd have happily used fold but I had to provide Nothing for Error and realised it would create a redundant DefaultRaise etc

[simon.vergauwen]

I just want to be sure we're just not adding overloads just for the sake of it

I'm open to reviewing the base functions, and seeing if we need to rename or introduce some new signatures for 2.3. I would also consider deprecating any confusing ones because since releasing them we've seen some confusion and gotten repeated questions about recover, catch & fold and when to use what.

[phldavies]

I did push a PR with this overload in https://github.com/arrow-kt/arrow/pull/3751 as in my mind it fills the gap that's covered for the recover and fold but not for catch - if there's to be a review for 2.3 I think it would be good to include it either in 2.2 or at least ensure the use-case is covered by any review of signatures.