[Haskell-cafe] Get number of fields for non-record ADTs using Data type class?

Markus Läll markus.l2ll at gmail.com
Mon Oct 29 18:56:02 UTC 2018

Dear list,

Is it possible te get the number of fields for data constructors for a
plain ADT, i.e something with no record fields? E.g for

data T = A Int Double | B String (Maybe String)

it would give 2 for both `A` and `B`.

For a record it's possible using the `constrFields` function from Data.Data.

I was trying to follow this tutorial by Christopher Done
https://chrisdone.com/posts/data-typeable, and I feel that it must be
possible somehow to get these numbers with the gmap*/gfold* functions, but
the use of them is over my head at the moment.


Markus Läll
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