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

Weak +1, I'd want it in NonEmpty too if it's going into List. On Tue, 13 Aug 2019 at 13:37, Joseph C. Sible wrote:

-1. AFAICT, "Polymorphic, works for any `Functor`" is an upside of just using `pure`, not a downside. (Please correct me if I'm wrong, and there is some disadvantage that I don't see.) Also, it looks like for everything that has a `singleton`, it's something that isn't an applicative functor, so they have them instead of `pure`, not in addition to it.

Joseph C. Sible

On Mon, Aug 12, 2019 at 12:14 PM Taylor Fausak wrote:

...

I originally made this suggestion on GitLab, but I was told to make it here instead.

https://gitlab.haskell.org/ghc/ghc/issues/17042

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# Add list singleton function

## Motivation

Sometimes it is convenient to have a function to wrap an element in a list. There are many ways to do this already, but none of them are as clear as a separate monomorphic function.

- `pure`: Polymorphic, works for any `Functor`. - `pure @[]`: Noisy, requires `-XTypeApplications`. - `(: [])`: Subjectively ugly. - `(\x -> [x])`: Syntactically noisy.

This Twitter thread includes some additional commentary: https://twitter.com/taylorfausak/status/1159264862247280640

## Proposal

I would like to add a `singleton` function to `Data.List` that mirrors the `singleton` function for other containers: https://www.stackage.org/lts-14.0/hoogle?q=singleton

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

Other Haskell-like languages include this function:

- PureScript: https://pursuit.purescript.org/packages/purescript-lists/5.4.0/docs/Data.Lis... - Elm: https://package.elm-lang.org/packages/elm/core/latest/List#singleton _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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