Question: is runCatching the equivalent to F#'s result "computational expression"?

[mbucc]

Example computational expression from Scott Wlaschin's book:

https://github.com/swlaschin/DomainModelingMadeFunctional/blob/master/src/OrderTakingEvolved/PlaceOrder.Dto.fs#L71-L81

The alternative (adding more versions of zip with more and more arguments) smells wrong. I noticed in your example service code you use runCatching in a very similar way to the code linked above.

[michaelbull]

I'm not familiar with F# so I don't really understand what's going on in the code linked

runCatching simply runs a bit of code, catching any exceptions and wrapping them in an Err to produce a Result<T, Exception>

[mbucc]

I'm back to my previous question on using unwrap. :)

I'm not an F# user either, but if I think I understand the explanation SW gives in his book, which is:

// A result computational expression:
result {
   // checkAddress returns a Result<Address, Msg>
   // but x1 is of type Address.
   let! x1 = checkAddress unvalidatedAddress
   let! x2 = checkName unvalidatedName
   return ValidatedAddress(x1, x2)
}   // Type of this full expression is Result<ValidatedAddress, Msg>

The closest match I can think of with kotlin-result is unwrap() on each line, all surrounded by runCatching. I know in a previous issue, you suggested not using unwrap() in this way, but I can't think of another way (other than continuing to expand zip).

[michaelbull]

Maybe this comment helps?

[Munzey]

@mbucc just read this and your previous issue. I believe the exact thing you are looking for is called a monad comprehension.
I have opened a pr to add the functionality you are looking for:
#13