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

Seq is applicative and also has singleton. Some people like to avoid polymorphism when the use case is clearly monomorphic (c.f. discussion about map vs fmap). I'd like to *point out* that Pointed is sort of the abstraction we really want for this... But I still want a monomorphic function that doesn't delve into Kmett dependencies. On Mon, Aug 12, 2019 at 11:59 PM George Wilson wrote:

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:

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-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:

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I originally made this suggestion on GitLab, but I was told to make it

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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

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- `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

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## Proposal

I would like to add a `singleton` function to `Data.List` that mirrors

here instead. list. There are many ways to do this already, but none of them are as clear as a separate monomorphic function. the `singleton` function for other containers: https://www.stackage.org/lts-14.0/hoogle?q=singleton

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``` 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...

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- 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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