[Haskell-cafe] Field types

[David Feuer]

I was just looking for confirmation. I'm playing around with using generics
to make field-based lenses and traversals, and I don't want any unpleasant
surprises.

On Mon, Sep 20, 2021, 1:43 PM Brandon Allbery <allbery.b at gmail.com> wrote:

> Well, there is already an extension that turns off selector-as-function,
> although I don't recall the name off the top of my head. I am not sure
> there's a way to access such fields as this at all if you use it, since
> e.g. HasField probably doesn't let you do types by constructor name.
>
> On Mon, Sep 20, 2021 at 1:21 PM David Feuer <david.feuer at gmail.com> wrote:
>
>> In that hypothetical context, the field name wouldn't be usable as a
>> function—at least without future Dependent Haskell.
>>
>> On Mon, Sep 20, 2021, 1:19 PM Tom Ellis <
>> tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk> wrote:
>>
>>> On Mon, Sep 20, 2021 at 01:13:43PM -0400, David Feuer wrote:
>>> > Does one field name for one datatype always refer to a field with the
>>> same
>>> > type? Or is there some wacky extension that would allow things like
>>> >
>>> > data Foo
>>> >   = Bar { zoom :: Int }
>>> >   | Baz { zoom :: Char }
>>> >
>>> > I'm hoping I don't have to worry about the latter possibility....
>>>
>>> Me too!  Under such circumstances what would the type of
>>> field-as-function be?
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>
>
>
> --
> brandon s allbery kf8nh
> allbery.b at gmail.com
>
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