Echoing Keith's point, "semi" to me means a weaker algebra; i.e. a super-class. Foldable => Semifoldable is thus totally wrong, "Semifoldable" is the sub-class. In particular. The Monoid and Semigroup constraints on their respective methods further show that the fold class hierarchy is *contravariant* with respect to the binary operator class hierarchy. Putting semi-* with semi-* only makes sense for something covariant (e.g. the if methods *returned* `Dict (Semigroup a)` etc).

Semimonad and Semiapplicative are fine with me (I don't really care, not worth fighting one way or the other) but strong -1 on Semifoldable.

On 10/18/19 12:10 PM, Oleg Grenrus wrote:

Please reply to the "Add Data.Foldable1 to base" -thread to keep the discussion in one place.
Otherwise this opinion will most likely be ignored.

- Oleg

P.S. That said, foldMap1/semifoldMap/... can fold over *less* things. It can fold over NonEmpty (list) but not over ordinary [].

On 18.10.2019 18.40, Keith wrote:

Sorry about bikeshedding. However, 'semifoldable' would be super confusing.

If somebody saw 'semifoldMap' in the wild what would they think? Probably not that it can fold _more_ things than 'foldMap'.

'NonemptyFoldable', 'Semigroup.Foldable', 'SemigroupFoldable', and 'Foldable1', with 'sfoldMap', 'sgFoldMap', 'nonemptyFoldMap', or 'Semigroup.foldMap' may be long or meaningless to most, but at least they aren't actively misleading.

–Keith

On October 18, 2019 2:13:51 PM UTC, Oleg Grenrus <oleg.grenrus@iki.fi> wrote:

Relating to Foldable1/NonEmptyFoldable, based in another discussion (in 
my foldable1 to base proposal), it looks like it might be called 
Semifoldable

See https://mail.haskell.org/pipermail/libraries/2019-October/030030.html

Yet, Semiset is different thing (based on wikipedia: 
https://en.wikipedia.org/wiki/Semiset). NonEmptySet is a good name, it 
doesn't need explanation. If someone feels that it's too long, they can 
introduce `type NESet = NonEmptySet` alias in their development.

- Oleg

On 20.9.2019 4.56, Ruben Astudillo wrote:
On 19-09-19 22:17, Alexandre Esteves wrote:
I do like the sound of `instance Foldable1 Set1` more than I do
`instance NonEmptyFoldable NonEmptySet`
<https://hackage.haskell.org/package/semigroupoids-5.3.3/docs/Data-Semigroup-Foldable.html#t:Foldable1>
 I prefer it too, I just wish (future) documentation included a little
 explanation on why the suffix 1 was put.

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