Charles,
I know you specifically asked for a Control.Lens combinator and I don't have
one for you, but I take the opportunity to show you how easy this is using
fclabels:
tupleUp :: f :-> a
-> f :-> b
-> f :-> (a, b)
tupleUp a b = point $
(,) <$> L.fst >- a -- L.fst, L.snd are lenses from Data.Label.Base
<*> L.snd >- b
In fclabels you can use the Applicative instance (and Alternative for
multi-constructor cases) to derive views like this. If you look at the
structure it'll become clear how easily this scales up to different types of
views.
This particular example uses total monomorphic lenses, but also works for
partial lenses and polymorphic updates.
Maybe there is a similar way in Control.Lens to do this.
Sebastiaan
On Oct 5, 2013, at 1:23 AM, Charlie Paul <[email protected]> wrote:
> Hello,
>
> I'm looking for a combinator along the lines of
> (&&&) :: Lens' a b -> Lens' a b' -> Lens' a (b,b')
> I can see how it could lead to lenses that don't follow the laws, but
> for Lenses which are somehow independent (like _1 and _2), it works
> perfectly well. Is there a way in lens to specify this "independence"?
>
> Thank you,
>
> Charles Paul
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