How do I use `withError` to wrap a function with ...

# arrow

[Ulrich Schuster]

How do I use withError to wrap a function with RaiseAccumulate<MyErrorA> receiver, when the outer error context is Raise<MyErrorB> ?
When I try

context(_: Raise<MyErrorB>)
fun validateOuter(x: X): X = withError({ errors -> MyErrorB(errors) } ) { validateInner(x) }

where

context(_: RaiseAccumulate<MyErrorA>)
fun validateInner(x: X)

the type checker complains about no context argument found for validateInner() How can I tell withError to open a RaiseAccumulate context?

[Youssef Shoaib [MOD]]

The easiest way would be:

iorAccumulate(block).mapLeft(transform).bind()

[Ulrich Schuster]

Ok, thanks.

[Ulrich Schuster]

It doesn't look very elegant for what IMHO is a very common case when writing accumulating validation logic. Is there some glue machinery missing here?

[Youssef Shoaib [MOD]]

It should definitely be added. Any name suggestions? I think just calling it withError might cause resolution issues (especially with context paramters)

[Ulrich Schuster]

withErrorNel?

[Ulrich Schuster]

Is there somewhere a clear explanation for the difference between RaiseAccumulate<Error> and Raise<Nel<Error>> ? I find myself confused sometimes when trying to get the types line up

[Youssef Shoaib [MOD]]

Previously, RaiseAccumulate was just a hidden Raise<Nel<Error>>, which can be accessed through withNel, and it exposes a Raise<Error> to make your life easier.
With the new experimental DSL, RaiseAccumulate now has a whole Accumulate API, which allows you to accumulate errors as you go about your computation. That's what allows for binding Ior, since if you have a Both, the error should go somewhere.
To go from Raise<Nel<Error>> to RaiseAccumulate<Error>, simply use the accumulate { } block.