[Haskell-cafe] Get number of fields for non-record ADTs using Data type class?
lysxia at gmail.com
Mon Oct 29 20:34:41 UTC 2018
This maps every field to 1, and folds them together using (+):
Data.Data.gmapQl (+) 0 (const 1) :: T -> Int
(There has to be a similarly easy solution using GHC.Generics instead
but I can't think of one...)
On 10/29/18 2:56 PM, Markus Läll wrote:
> 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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