[Haskell-cafe] Is it possible to nest this kind of "continuation" (a -> b -> r)

[Georgi Lyubenov]

Well, if we used type indexed lists (aka just "dynamic tuples") it 
should be possible, right?

I.e.

hunzip :: [HList xs] -> HList (ToList xs)

type family ToList xs where
   ToList '[x] = [x]
   ToList (x ': xs) = [x] ': ToList xs

On 4/19/24 19:59, Tom Ellis wrote:
> On Fri, Apr 19, 2024 at 06:29:23PM +0200, PICCA Frederic-Emmanuel wrote:
>> nest ∷ [(a → r) → r] → ([a] → r) → r
>> nest xs = runCont (Prelude.mapM	cont xs)
>>
>> nest2 ∷ [(a → b → r) → r] → ([a] → [b] → r) → r
>> nest2 xs = ...
>>
>> nest3 :: ...
>>
>> Do you think that there is a generic way to write all these nestX methodes.
> I doubt it.  There's not even a generic way of writing out the
> non-CPSed versions
>
>      nest2 :: [(a, b)] -> ([a], [b])
>      nest3 :: [(a, b, c)] -> ([a], [b], [c])
>
> Instead we just have individually-named unzip functions:
>
> https://www.stackage.org/haddock/lts-22.17/base-4.18.2.0/Prelude.html#v:unzip
> https://www.stackage.org/haddock/lts-22.17/base-4.18.2.0/Prelude.html#v:unzip3
>
> Tom
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