Diagonalization/ dupe for monads and tuples?

[Carter Schonwald]

Is the join bipure definition taking advantage of the (a->) monad
instance?  Slick!


On Wed, Sep 16, 2020 at 3:39 PM Matthew Farkas-Dyck <strake888 at gmail.com>
wrote:

> We also have
>
>
>
> diag = join bipure
>
>
>
> and (in pseudo-Haskell)
>
>
>
> diag = unJoin . pure
>
>   where
>
>     newtype Join f a = Join { unJoin :: f a a } deriving (Functor)
>
>     deriving instance Biapplicative f => Applicative (Join f)
>
>
>
> The latter seems on its face potentially related to the instance for
>
> lists of fixed length, but i am not sure how deep the connection may
>
> be.
>
>
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