Add fromNonEmpty operation

[garyb]

This kinda sucks maybe? Is there a better way of doing this that you can think of?

[paf31]

I think I'd rather just pass the function in:

foldNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r

[garyb]

I thought about that, but providing the fold doesn't help too much as NonEmpty's constructor is already exported.

[garyb]

Although... maybe. I guess fromNonEmpty cons nel is slightly than having to do the pattern match, etc.

[garyb]

How about this then? One for the lazy, and one for when you want to do it properly? 😉

[paf31]

Why not use Alternative and call it oneOf? It seems like it generalizes certain functions on things like parsers.

[garyb]

Uh, because I foolishly forgot Applicative was a superclass of Alternative. I'm not sure oneOf is quite right though, as you're getting at least one back.

[paf31]

Well it depends how you interpret f I guess. If you pick f as List, do you think f a represents zero or more values a or one value a in a model with multiple worlds? With Parser this view is more obvious - we think of Parser a as one a in a model supporting an ambient text buffer, but we could also think of it as a collection of as indexed by input documents :)

[garyb]

I did see what you were getting at, I just wonder about that naming in the context of NonEmpty?

[paf31]

someOf? I dunno ... :)

[paf31]

Actually, I guess all you need is Alt.

[garyb]

How would that work? You need to put a in f, so need pure:

??? (NonEmpty a fa) = pure a <|> fa

[paf31]

Ah right, I thought Applicative <= Alt, but it's not.

[garyb]

There we go.

[paf31]

👍 Thanks!