Proposal: Add singleton function to Data.List module

[Andreas Abel]

Right, but the ones you quote are all variants of sequences, not 
collections in general.  They have append and cons.  An interface for 
sequences should name these operations uniformly.  However, I would 
restrict the current discussion to construction of collections in 
general, with the interface

   mempty     -- construct an empty collection
   singleton  -- construct a collection with one element
   mappend    -- join two collections

There is a (next to virginal) attempt to define an API for collections at

 
http://hackage.haskell.org/package/collections-api-1.0.0.0/docs/Data-Collections.html

Incidentally, it has

   singleton :: i -> c
   Creates a collection with a single element.

Cheers,
Andreas

On 2019-08-19 12:38, 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:cons
> 
> https://hackage.haskell.org/package/dlist-0.8.0.7/docs/Data-DList.html#v:append
> 
> 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:append
> 
> http://hackage.haskell.org/package/vector-0.12.0.3/docs/Data-Vector.html#v:cons
> 
> https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteString.html#v:cons
> 
> https://hackage.haskell.org/package/bytestring-0.10.10.0/docs/Data-ByteString.html#v:append
> 
> Am Mo., 19. Aug. 2019 um 08:16 Uhr schrieb Andreas Abel 
> <andreas.abel at ifi.lmu.de <mailto:andreas.abel at ifi.lmu.de>>:
> 
>     Helmut, do you actually know the container APIs?
> 
>     Show me cons and append in Data.Set!
> 
>     On 2019-08-18 19:40, Helmut Schmidt wrote:
>      >
>      >
>      > Am So., 18. Aug. 2019 um 17:17 Uhr schrieb Oliver Charles
>      > <ollie at ocharles.org.uk <mailto:ollie at ocharles.org.uk>
>     <mailto:ollie at ocharles.org.uk <mailto:ollie at ocharles.org.uk>>>:
>      >
>      >     On Sun, 18 Aug 2019, 5:47 pm Helmut Schmidt,
>      >     <helmut.schmidt.4711 at gmail.com
>     <mailto:helmut.schmidt.4711 at gmail.com>
>      >     <mailto:helmut.schmidt.4711 at gmail.com
>     <mailto:helmut.schmidt.4711 at 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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