Hi Alan,
Your pair of functions can be packaged up as a single function, so that
getEpa :: a -> EpaLocation
setEpa :: a -> EpaLocation -> a
becomes
lensEpa :: forall f. Functor f => (EpaLocation -> f EpaLocation) -> (a
-> f a)
And the get/set parts can be recovered by instantiating `f` to either Identity
or Const.
The nice thing about lenses is that they compose, so that if you need nested
access, you could define several lenses, compose them together, and then reach
deep into a data structure. Then lenses might offer some simplification.
Otherwise, an ordinary getter/setter pair is just as good.
- Vlad
> On 3 Oct 2021, at 20:40, Alan & Kim Zimmerman <alan.z...@gmail.com> wrote:
>
> Hi all
>
> I am working on a variant of the exact printer which updates the annotation
> locations from the `EpaSpan` version to the `EpaDelta` version, as the
> printing happens
>
> data EpaLocation = EpaSpan RealSrcSpan
> | EpaDelta DeltaPos
>
> The function doing the work is this
>
> markAnnKw :: (Monad m, Monoid w)
> => EpAnn a -> (a -> EpaLocation) -> (a -> EpaLocation -> a) -> AnnKeywordId
> -> EP w m (EpAnn a)
>
> which gets an annotation, a function to pull a specific location out, and one
> to update it.
>
> I do not know much about lenses, but have a feeling that I could simplify
> things by using one.
>
> Can anyone give me any pointers?
>
> Alan
>
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