Proposal: Add a strict version of <$> for monads
Edward Kmett
ekmett at gmail.com
Fri Nov 29 23:11:36 UTC 2013
Figure out how to write one using either of those APIs, and I'll be quite
impressed. =)
I personally use this quite often when working in a monad, in lieu of
`return $!` games.
The argument for implementing a version of it in terms of Monad and not
some new class off to the side of the class hierarchy that Monad doesn't
subclass is that, frankly, if such a thing existed, I'd still have to use
this combinator anyways when working with a transformer stack, etc. and
would derive little benefit.
-Edward
On Fri, Nov 29, 2013 at 12:03 PM, Carter Schonwald <
carter.schonwald at gmail.com> wrote:
> could someone explain to me why this <$!> would be for monads rather being
> more generally also for functors or applicatives?
>
>
> On Fri, Nov 29, 2013 at 10:35 AM, Johan Tibell <johan.tibell at gmail.com>wrote:
>
>> I'm trying to figure out whether this is a property of the functor
>> itself. I guess it is, but at the same time it seems somewhat orthogonal
>> whether to `seq` some value`.
>>
>>
>> On Fri, Nov 29, 2013 at 3:50 PM, Twan van Laarhoven <twanvl at gmail.com>wrote:
>>
>>> On 29/11/13 12:23, Johan Tibell wrote:
>>>
>>>> On Fri, Nov 29, 2013 at 1:19 PM, Twan van Laarhoven <twanvl at gmail.com
>>>> <mailto:twanvl at gmail.com>> wrote:
>>>>
>>>> I don't like that this function is implemented for Monads, I think
>>>> that it
>>>> makes sense for some other functors as well. Though to do this
>>>> 'properly' we
>>>> would probably end up with another typeclass "StrictFunctor" or
>>>> something,
>>>> and that is perhaps too much unnecessary complexity.
>>>>
>>>>
>>>> Do you have an example of such a functor?
>>>>
>>>> -- Johan
>>>>
>>>
>>> The first thing that came to mind was ZipList. Perhaps a more realistic
>>> example would be parsing combinator or FRP libraries that are applicative
>>> but not monadic.
>>>
>>>
>>> Twan
>>>
>>
>>
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>
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