On April 3, 2019 7:06:11 AM EDT, "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

Can you post a full branch? Nothing in particular looks wrong with what you posted here but the PrelNames code is also relevant. Cheers, - Ben

Make sure you add the new wired in this to `TysWiredIn.wiredInTyCons` From: ghc-devs On Behalf Of Jan van Brügge Sent: 03 April 2019 12:06 To: ghc-devs@haskell.org Subject: Defining a wired-in type of a different kind 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

I would suggest that it's easier to define a normal type constructor and data cons and then promote them. This is how the runtime rep polymorphism stuff works for instance so you can look there for inspiration (it's where I look to work out how to implement multiplicity polymorphism). Matt On Wed, Apr 3, 2019 at 12:06 PM 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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