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

I have some data to contribute, from our proprietary codebase of some 4MLoC. We are perhaps unusual in having the singleton function on lists already for 10 years, so it is easy to do a comparison of the frequency of use. The robot monkey (:[]) has 378 uses. Monkey with a space (: []) has 36 uses. The list singleton function has 18 uses. We also have many other singleton functions at more than 20 different types (vector, tuple, map, set, interval, relation, dict, expression, etc), totalling 1893 uses, so the concept/vocabulary is pretty well-known. In addition, I counted the number of direct constructions of lists that use :[] unparenthesised, i.e like x:y:[], and there are 489. I find it interesting that given the choice of “singleton” vs direct construction or a partially applied operator, our devs seem to prefer the brevity and naturality of the colon. Regards, Malcolm

On 21 Aug 2019, at 06:31, George Wilson wrote:

Hi Taylor,

I'm on the Core Libraries Committee. Thank you for your proposal. Regarding the +-1 messages in this thread, they are useful to gauge community opinion, but they are not votes because the libraries process is not determined by a vote.

Despite seeming innocuous, the proposed change requires careful consideration: Data.List is specified by the Haskell Report, so adding this function would affect the report. While simple changes to base are typically handled directly by one of base's maintainers, this change is report-affecting, so it is "controversial" (as defined in [1]). Hence the CLC is discussing the proposed change amongst ourselves before a maintainer makes their decision.

[1] https://wiki.haskell.org/Library_submissions

Cheers, George

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On Tue, 20 Aug 2019 at 11:24, Taylor Fausak wrote:

It has been a week since I submitted my proposal. During that time, 28 people voted, with 16 expressing approval and 12 expressing disapproval. To everyone that voted so far: Thank you! You made for interesting discussion.

I still feel that Haskell would be improved by the addition of a `singleton` function to the `Data.List` module. (And also `Data.List.NonEmpty`, even though that wasn't part of my original proposal.) I would be happy to open a merge request adding code, tests, and documentation.

I haven't done so yet because I don't know what the next steps are. Can someone from the CLC tell me how an official approval or rejection can be reached, and how long that might take? Thanks!

On Mon, Aug 19, 2019, at 6:39 AM, Helmut Schmidt wrote:

Andreas, you seem to be mistaken there'd only be one container API? But there's several container APIs besides "Data.Set" which provide some collection of elements!

https://hackage.haskell.org/package/dlist-0.8.0.7/docs/Data-DList.html#v:con...

https://hackage.haskell.org/package/dlist-0.8.0.7/docs/Data-DList.html#v:app...

https://hackage.haskell.org/package/text-1.2.4.0/docs/Data-Text.html#v:cons

https://hackage.haskell.org/package/text-1.2.4.0/docs/Data-Text.html#v:appen...

http://hackage.haskell.org/package/vector-0.12.0.3/docs/Data-Vector.html#v:c...

https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteStrin...

https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteStrin...

Am Mo., 19. Aug. 2019 um 08:16 Uhr schrieb Andreas Abel :

Helmut, do you actually know the container APIs?

Show me cons and append in Data.Set!

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On 2019-08-18 19:40, Helmut Schmidt wrote:

Am So., 18. Aug. 2019 um 17:17 Uhr schrieb Oliver Charles mailto:ollie@ocharles.org.uk>:

On Sun, 18 Aug 2019, 5:47 pm Helmut Schmidt, mailto:helmut.schmidt.4711@gmail.com> wrote:

All these philosophical arguments calling for "consistency" with the container APIs or that function need words for the human mind to comprehend seem short-sighted to me. If we were consistent about the proposal itself we'd also demand to add

cons = (:)

empty = []

toList = id

fromList = id

I honestly have no problem with any of these.

I forgot

append = (++)

We also need to address another elephant in the room... those pesky tuples and their special privileged non-wordy syntax!

pair = (,)

triple = (,,)

quadruple = (,,,)

quituple = (,,,,)

sextuple = (,,,,,)

septuble = (,,,,,,)

octuple = (,,,,,,,)

If Haskell were invented in this century's EU Haskell source code would be littered with €s instead of $s but then again I wonder why £ wasn't picked. But I digress. We can kill two birds with one stone here:

apply = ($)

strictApply = ($!)

compose = (.)

It's fun to imagine how code using those definitions would like! But it's still a -1 for me, sorry!

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