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

I'm +1 on this. I've defined this function in my own code before. Using pure instead leads to harder-to-read code for future me and for collaborators. It also leads to worse type errors in the event that I mess something up. On Tue, Aug 13, 2019 at 5:11 AM David Feuer wrote:

I'm moderately +1 for consistency, and for NonEmpty as well. There is a concept here: create a container containing exactly one value. As Tikhon indicates, this is a different concept from pure. For example, a singleton ZipList has one element, while a pure one has infinitely many elements.

On Mon, Aug 12, 2019, 11:14 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I originally made this suggestion on GitLab, but I was told to make it here instead.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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