[Haskell-cafe] Constraint on data type

Vlatko Basic vlatko.basic at gmail.com
Mon Jan 20 11:48:31 UTC 2014

Hi Cafe,

I have these typeclasses defined:

     class UA a where ...
     class RA a where ...

and this data definition

     data (UA u, RA r) => AD u r = AD { ... }

I have another data definition

     data ACT aur c = ACT { x :: aur, ... }

but the type 'aur' should be restricted to (AD u r) only.
(I would like to keep 'aur' as 1 parameter, not as
     data ACT u r c = ACT { x :: AD u r, ... } )

How can such constraint be defined?

Best regards,


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