Two more noob questions 🙂 : 1. Why is there a need for separate

recover()

and

catch()

functions? Why isn't everything

fold()

? 2. When is the type parameter

B

and parameter

transform

of

fold()

is useful? Wouldn't it be enough to have

// Just an example, this function is not present is Arrow
inline fun <Error, A> fold(
  @BuilderInference block: Raise<Error>.() -> A,
  recover: (error: Error) -> A,
  catch: (throwable: Throwable) -> A = { throw it }
)

and handle the transformation after the

fold()

call? The above is very similar to the actual

recover()

function:

public inline fun <Error, A> recover(
  @BuilderInference block: Raise<Error>.() -> A,
  @BuilderInference recover: (error: Error) -> A,
  @BuilderInference catch: (throwable: Throwable) -> A,
): A = fold(block, catch, recover, ::identity)

These questions popped up because I don't like the naming of the

recover()

and

catch()

functions. I almost always use

recover()

but it is a bit strange that it also has a parameter named

recover

. So although the core function is

fold()

, I never use it because

recover()

with the

transform = ::identity

argument seems to be appropriate always... Thanks.

Hey @Norbi, Okay, question 1 & 2 seem to go hand-in-hand 😅 •

fold

is useful when you need to align types after user code, so when building custom DSLs. I've only really needed it in one place, ior. So

recover

is probably sufficient in 99,99% of the cases. It's also the natural operation for

Raise

. Where you

raise

and

recover

•

recover

with 3 parameters, is basically just an alias for

fold

with

::identity

.

Thanks for the quick answer, now I have some more insight to the design decisions. I'd better get used to the name of

recover()

, it seems that I was the only one not completely satisfied with it 🤔 🙂

Why are you not liking

recover

? From your answer it sounds like you're not fan of the parameter name

recover

resulting in:

fun Raise<String>.example(): Int = 1

recover(
  block = { example() },
  recover = { str -> str.length }
)

Yes, the main reason is that the parameter name is the same as the function name 🙂 Really insignificant "issue", so don't waste your time with it 🙂 Thanks again for the detailed answers!

There is this project that leverages Detekt, but I still need to PR an update for the new DSL. https://github.com/woltapp/arrow-detekt-rules