Diagonalization/ dupe for monads and tuples?

[Keith]

Hopping on the bikeshed, I've heard 'Either a a -> a' described as 'untagging' the 'a'. So from a less categorical perspective, I'd call it
+  'untag' (already used in Data.Tagged) 
+ or 'unEither' (because you're directly unwrapping the Either, not using a fallback value like 'fromMaybe').

Either of these should be more immediately clear than 'codiag', 'codup', or 'dedup', which would make more sense as (categorical) class methods.

--Keith

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On September 17, 2020 1:33:40 PM UTC, Carter Schonwald <carter.schonwald at gmail.com> wrote:
>I’m not sure how fromMaybe relates here.  Could someone explain?
>
>For the anti-categorical folks who dislike codiag or related names like
>trace (in linear algebra trace is the sum of the diagonal of a matrix as a
>scalar, an apt analogy I think), another name that I think is descriptive
>is collapse
>
>
>Names bandied about so far:
>
>Dedup
>Codiag
>Fromeither
>
>Things I mentioned above : trace and collapse
>
>Zooming out though, this operation is equiv to “either id id”, so I don’t
>really see how inventing a new name for this specific tiny snippet really
>helps anyone.
>
>
>On Thu, Sep 17, 2020 at 8:54 AM chessai <chessai1996 at gmail.com> wrote:
>
>> My instinct about fromEither's type was the same as Carter's, and I had to
>> remind myself of fromMaybe. I like the name fromEither overall. Seems to
>> fit well with precedent and is straightforward enough.
>>
>> On Thu, Sep 17, 2020, 07:45 Oliver Charles <ollie at ocharles.org.uk> wrote:
>>
>>> You may wish to compare with fromMaybe then, which probably also doesn't
>>> have the type you'd expect :) The type you have there is more like bifoldMap
>>>
>>> On Thu, 17 Sep 2020, at 1:42 PM, Carter Schonwald wrote:
>>>
>>> I’d expect fromEither to be
>>> Either a b -> (a-> c )-> (b-> c) -> c
>>>
>>> Nothing about the name fromEither is suggestive of the Either a a type
>>>
>>> On Thu, Sep 17, 2020 at 3:45 AM Oliver Charles <ollie at ocharles.org.uk>
>>> wrote:
>>>
>>>
>>> Regardless of having a more abstract version, I'm +1 on Jon's suggestion,
>>> and those names. fromEither is something I have reached for many many times
>>> and been surprised it's not within arms reach.
>>>
>>> On Thu, 17 Sep 2020, at 7:16 AM, Jon Purdy wrote:
>>>
>>> I’m strongly for these:
>>>
>>> Data.Tuple.dup :: a → (a, a)
>>>
>>> Data.Either.fromEither :: Either a a → a
>>>
>>>
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>>
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