Re: Proposal: Add singleton function to Data.List module

Hard -1, , i'm not seeing a useful high impact payoff plus its more verbose and adhoc than pure and more confusing than (:[]) I actually initially thought this thread was about Type Singletons and or Proxy style apis using List as the term level form, it actually took me a few minutes of reading everyone's replies to disambiguate i'm open to changing my mind later if i can convince myself, but -1 for now On Mon, Aug 12, 2019 at 3:53 PM Andrew Lelechenko < andrew.lelechenko@gmail.com> wrote:

- `pure`: Polymorphic, works for any `Functor`.

It is OK to have polymorphic folds and length, so what is wrong with pure?

Adding singleton to Data.List is a breaking change, when Data.Map.singleton was exported unqualified. And there is no singleton in Data.List.NonEmpty as well.

-1 from me.

Best regards, Andrew

On 12 Aug 2019, at 19:36, Brent Yorgey wrote:

At the risk of completely derailing the conversation, I have always called this the "robot monkey operator". I fail to see what is so ninja-like about it.

Anyway, I think I am +1 on adding Data.List.singleton.

-Brent

On Mon, Aug 12, 2019, 12:35 PM Zemyla wrote:

...

I also like the ninja-robot operator, because it's visually interesting and easy to search for.

Also, if you're importing several libraries which already use "singleton", then you have to use "List.singleton" every time, which is far uglier to me.

On Mon, Aug 12, 2019 at 12:03 PM Herbert Valerio Riedel wrote:

...

...

- `(:[])`: Subjectively ugly.

I consider "subjectively ugly" to be a non-technical and thus really weak argument to dismiss the list-idiomatic ninja-robot-operator (:[]) which also happens to be shorter than the proposed alias for it. I for one don't see a significant benefit for adding a redundant synonym to `Data.List` and are thus -1 on this.

...

singleton :: a -> [a] singleton x = [x]

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