[Haskell-beginners] lost a typeclass maybe?

[Silent Leaf]

hey it does seem to exist, so that would be

foo :: (BiApplicative f) :: (i -> k i -> k i) -> f a b -> f (k a) (k b) ->
f (k a) (k b)
foo f fab fkakb = bipure f f <<$>> fab <<*>> fkakb

pretty neat. i'm not sure the <<$>> operator exist, but the `ap` one does
apparently.
however i'm not sure that many people use BiApplicative ^^ But hey why not.

don't pay attention to my code here, it's terribly typoed, i have no idea
why i put the uppercase on the function Foo...

2017-06-29 20:44 GMT+02:00 Silent Leaf <silent.leaf0 at gmail.com>:

> ah, obviously, the first parameter is meant to be (i -> k i -> k i).
> mind you my opaqueBimap looks very peculiar...
> if i isolate half of f a b:
> Foo :: (i -> k i -> k i) -> f a -> f (k a) -> f (k a)
> Foo f fa fas = lift f fa fas
> so maybe i'd need a BiApplicative?
>
> 2017-06-29 20:38 GMT+02:00 Silent Leaf <silent.leaf0 at gmail.com>:
>
>> well, i sent once more my message too early by mistake.
>> when i say invent IO a b, i don't actually mean an IO type, i meant just,
>> any type you can't manually unbox via pattern matching or otherwise.
>>
>> 2017-06-29 20:36 GMT+02:00 Silent Leaf <silent.leaf0 at gmail.com>:
>>
>>> hi,
>>>
>>> i keep trying to find something that feels terribly obvious but i can't
>>> make any link.
>>>
>>> say i have a function of the following type:
>>>
>>> foo :: (a, b) -> ([a], [b]) -> ([a], [b])
>>> or perhaps more generally:
>>> foo :: SomeClass f => f a b -> f [a] [b] -> f [a] [b]
>>>
>>> is SomeClass supposed to be BiFunctor or something else?
>>> clearly, what i want to do is to combine the elements of the first pair
>>> into the elements of the second, preferrably without pattern matching, that
>>> is, merely in function of (:).
>>>
>>> i think the problem with bifunctor is that it seems to only allow the
>>> application of both arguments in a separate fashion. but here the first
>>> argument is in one block, that is (a,b).
>>> i know, ofc we could do something like:
>>> foo pair pairList = bimap (fst pair :) (snd pair:) pairList
>>> or maybe use curry or whatever. but i'd like my pair to not need to be
>>> unboxed!
>>>
>>> is there not a way to not have to manually call fst and snd? are both of
>>> these functions typeclass methods by any chance? then we could write a
>>> generalized function that could work for any f = (:) or any kind of
>>> pair-like thingy. mind you i'm not sure to which extent it would keep the
>>> opacity of the type constructor (,).
>>>
>>> especially, it's a bit like unboxing the Maybe type constructor: you can
>>> do it manually by pattern matching, but when you have the exact same issue
>>> but with IO, it's not possible anymore to unbox the underlying type
>>> equally, i bet one could invent IO a b, in a way that you could not just
>>> get a and b, but you could somehow implement
>>> opaqueBimap :: (i -> k i) -> f a b -> f (k a) (k b) -> f (k a) (k b)
>>> with here of course f = (,), k = [] or List, and (i -> k i) = (:)
>>>
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/beginners/attachments/20170629/c1e58478/attachment.html>