Proposal: Add a strict version of <$> for monads

[Roman Cheplyaka]

No. Evaluation of your 'strictify' function will be delayed for the very
same reason that evaluation of 'f' is delayed in the first place.

It doesn't matter what 'strictify' *does* if it's not even evaluated.

* Nicolas Trangez <nicolas at incubaid.com> [2013-11-30 02:11:02+0100]
> I'm without a doubt overlooking something, but couldn't this be (otoh)
> 
>     fmap' :: Functor f => (a -> b) -> f a -> f b
>     fmap' f = fmap (strictify f)
>       where
>         strictify s = (($!) id) . s
> 
> Nicolas
> On Nov 30, 2013 12:11 AM, "Edward Kmett" <ekmett at gmail.com> wrote:
> 
> > 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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