Add Maybe.unsafe?

[evancz]

With lots of core functions becoming total, it makes sense to consider having a central way to live dangerously.

unsafe : Maybe a -> a

firstNumber =
    unsafe (head numberList)

The unsafe function extracts a value or crashes. But why introduce such a crazy thing?

There are a tiny set of cases where you know it is going to be fine and might want this. For example, imagine you have a Dict and the values are lists. You would never put an empty list in your dictionary, that would be silly, so you know you can always get elements of the list. I have seen this a few times programming in languages like Elm.

The nice part of unsafe is that it makes the risks extremely explicit. Rather than ever creating an unsafe function, you can always return a Maybe and extract it with unsafe. This way, you can search through code for any occurrences of unsafe and quickly identify any risks. It also is a good sign of “maybe you should try to say the same thing a different way?”

This feels similar in spirit to Debug.crash which also makes risks very obvious.

Can you find uses of this in your code? Please share so we can evaluate if it is a good idea!

[haf]

Have you considered adding structural typing on top of lists, to avoid this use case? That way head could be defined totally on the type of non-empty lists.

[haf]

Have you considered adding structural typing on top of lists, to avoid this use case? That way head could be defined totally on the type of non-empty lists.

[lfairy]

I'd suggest requiring a message as well, so that in the (hopefully rare) case that it fails, we'd get some context as to what happened.

[lfairy]

I'd suggest requiring a message as well, so that in the (hopefully rare) case that it fails, we'd get some context as to what happened.

[nixpulvis]

Taking a note from Rust, I've always liked the name expect for this. Unsafe feels weird to me.

[nixpulvis]

Taking a note from Rust, I've always liked the name expect for this. Unsafe feels weird to me.

[jvoigtlaender]

Maybe close this? Like https://github.com/elm-lang/core/issues/216, it doesn't seem to have gotten traction.

[jvoigtlaender]

Maybe close this? Like https://github.com/elm-lang/core/issues/216, it doesn't seem to have gotten traction.

[evancz]

Yeah, I don't think it's necessary given that we made a lot more things return Maybe and it has been pretty fine.

[evancz]

Yeah, I don't think it's necessary given that we made a lot more things return Maybe and it has been pretty fine.