implement NonEmptyList.tryZip

[robkuz]

the zip implementation uses List.zip underneath which will fail with a runtime exception

we should have a save zip version

let tryZip (xs: NonEmptyList<'x>) (ys: NonEmptyList<'y>) =
    if xs.Length <> ys.Length then
        None
    else
        NonEmptyList.zip xs ys |> Some

[gusty]

Yes, it fails when list lenghts are different.

I personally don't like this behavior, but that seems to be the standard for List and Arrays in F#, whereas for Seq they use the shortest which is the functionality I would expect otherwise.

So, another option to have a safe version is to define a zipShortest function.

What do you think?

[robkuz]

well, all this comes down to subjective prefs.

What I do these days is this
On types fully under my control I define a

• tryXXX
• unsafeXXX

for types not under my control
i check if they follow the above pattern but do not implement both functions.
if either is missing I might implement it or even alias the existing one.

coming back to your question: no I would not implement a zipShortest at least not primeraly.
I would (and I have) implemented tryZip:: NonEmptyList<'a> -> NonEmptyList<'b> -> Option<NonEmptyList<'a * 'b>>
however to follow the above pattern.

[gusty]

Ok. I don’t see any reason why not to implement your suggestion.

Do you want to submit a PR ?

[robkuz]

will do

[3Rafal]

I've been inspired by this suggestion, and thought that it could be a good idea to add safe zip to F#+. I've implemented it for FSharp.Core types that have unsafe zip implementation and created a PR #370 . I wonder if it could be a first step, then I could expand it to all types with unsafe zip in F#+

[gusty]

the zip implementation uses List.zip underneath which will fail with a runtime exception

Maybe we should change that, make our generic zip safe.

[3Rafal]

@gusty , I guess this can be closed

[gusty]

Not sure, let's ask @robkuz if he's happy with your implementation. I think it's not exactly what he was after.