compiler/ghci/RtClosureInspect.hs¶
Note [Constructor arg types]¶
- Consider a GADT (cf #7386)
data family D a b data instance D [a] a where
MkT :: a -> D [a] (Maybe a) …
In getDataConArgTys * con_app_ty is the known type (from outside) of the constructor application,
say D [Int] Int
The data constructor MkT has a (representation) dataConTyCon = DList, say where
- data DList a where
MkT :: a -> DList a (Maybe a) …
So the dataConTyCon of the data constructor, DList, differs from the “outside” type, D. So we can’t straightforwardly decompose the “outside” type, and we end up in the “_” branch of the case.
Then we match the dataConOrigResTy of the data constructor against the outside type, hoping to get a substitution that tells how to instantiate the representation type constructor. This looks a bit delicate to me, but it seems to work.
Soundness checks
