Re: Defining a wired-in type of a different kind

Hi Jan, mkAlgTyCon is good for making an algebraic datatype -- like Maybe or Bool or Either. It's not what you want for RNil, which is really a data constructor. Instead, rowKindCon should be the algebraic datatype, and RNil should be one of its constructors. Then you get the RNil TyCon via promotion, as Matt suggested. I hope this helps! Richard

On Apr 3, 2019, at 7:06 AM, Jan van Brügge wrote:

Hi,

when trying to get familiar with the GHC code base for my Bachelor's thesis. I followed the GHC Wiki, especially the case study about the bool type. Now I wanted to add a new kind and a new type inhabiting this kind (without having to expose a data constructor, so without datatype promotion).

So in TysWiredIn.hs I added the new TyCons and added them to the list of wired-in types:

-- data Row a b rowKindCon :: TyCon rowKindCon = pcTyCon rowKindConName Nothing [alphaTyVar, betaTyVar] []

rowKind :: Kind rowKind = mkTyConTy rowKindCon

-- data RNil :: Row a b rnilTyCon :: TyCon rnilTyCon = mkAlgTyCon rnilTyConName [] rowKind [] Nothing [] (mkDataTyConRhs []) (VanillaAlgTyCon (mkPrelTyConRepName rnilTyConName)) False

rnilTy :: Type rnilTy = mkTyConTy rnilTyCon

I also added two new empty data decls to ghc-prim, but if I inspect the kind of RNil it is not Row, but Type. So I think I am either understanding res_kind wrong or I have to do something completely different. I am also not sure how to verify that the code in TysWiredIn.hs is working at all, from all what I can tell it could just be the declarations in ghc-prim that result in what I see in ghci.

Thank you and sorry for my beginner question Jan

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