Can someone help me structure the following code p...

# arrow

[0xf1f1]

Can someone help me structure the following code properly:

fun mkReport(res: Response): EitherNel<Error, SomeType> = either {
when (res.success) {
true -> return SomeType()
false -> {
val ee: List<String> = res.errors
return ee.map { Error(it) }
.toNonEmptyListOrNull()!!
}
}
}

The false condition fails with the following error:

Type mismatch.
Required:
EitherNel<Error, SomeType>
Found:
NonEmptyListError

[Alejandro Serrano.Mena]

what is your goal here?

[Alejandro Serrano.Mena]

the main thing is that to "end with error" you need to use raise

[0xf1f1]

if the response is a success then create the report object, otherwise return a list of errors from the API

[Alejandro Serrano.Mena]

fun mkReport(res: Response): EitherNel<Error, SomeType> = either {
  if (success) {
    SomeType()
  } else {
    val errors = res.errors.map { Error(it) }.toNonEmptyListOrNull()!!
    raise(errors)
  }
}

[Alejandro Serrano.Mena]

some notes:
• because you are inside the lambda in either, you should not use return
• you use raise to specify that you want to end in error

[0xf1f1]

that has worked, thanks. I am a bit confused with the return, should I removed the return from return SomeType() too ?

[Alejandro Serrano.Mena]

there's also another way in which you specify conditions in which you continue

fun mkReport(res: Response): EitherNel<Error, SomeType> = either {
  ensure(res.success) {
    res.errors.map { Error(it) }.toNonEmptyListOrNull()!!
  }
  SomeType()
}

[Alejandro Serrano.Mena]

about the return, this is not particular to Arrow, but the general difference between

fun f() = 3 // no return
fun f() { return 3 } // return needed

[0xf1f1]

yes, that is how I have done it thus far, its just the res.success condition has thrown me off

[0xf1f1]

makes sense, thanks!