Hello. I’m trying to make a type family with resolving it inside type checking classes, like CmpNat. Its type signature is «type family Cmp (a :: k1) (b :: k2) :: Ordering», so the function is poly kinded. But it seems unclear how to make its TyCon. I’ve tried to follow the CmpNat and CmpSymbol style, and also saw Any TyCon in TysWiredIn. So this is my attempt: typeCmpTyCon :: TyCon typeCmpTyCon = mkFamilyTyCon name (binders ++ (mkTemplateAnonTyConBinders [ input_kind1, input_kind2 ])) orderingKind Nothing (BuiltInSynFamTyCon ops) Nothing NotInjective where name = mkWiredInTyConName UserSyntax gHC_TYPELITS (fsLit "Cmp") typeCmpTyFamNameKey typeCmpTyCon ops = BuiltInSynFamily { sfMatchFam = matchFamCmpType , sfInteractTop = interactTopCmpType , sfInteractInert = \_ _ _ _ -> [] } binders@[kv1, kv2] = mkTemplateKindTyConBinders [ liftedTypeKind, liftedTypeKind ] input_kind1 = mkTyVarTy (binderVar kv1) input_kind2 = mkTyVarTy (binderVar kv2) ghci says this: :kind Cmp Cmp :: forall {k0} {k1}. k0 -> k1 -> Ordering But then I try to apply it to some values and get this exception: :kind! Cmp 4 5 <interactive>:1:15: error: • Expected kind ‘k0’, but ‘4’ has kind ‘Nat’ • In the first argument of ‘Cmp’, namely ‘4’ In the type ‘Cmp 4 5’ <interactive>:1:17: error: • Expected kind ‘k1’, but ‘5’ has kind ‘Nat’ • In the second argument of ‘Cmp’, namely ‘5’ In the type ‘Cmp 4 5’ Does anyone know where I made a mistake? Any help would be appreciated. _______________________________________________ ghc-devs mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs |
Hi Alice,
You'll need mkTemplateTyConBinders, not the two variants of that function you use below. The problem is that both mkTemplateKindTyConBinders and mkTemplateAnonTyConBinders pull Uniques starting from the same value, and so GHC gets very confused when multiple arguments to your TyCon have the same Uniques. mkTemplateTyConBinders, on the other hand, allows you to specify dependency among your arguments without confusing Uniques. You can see a usage of this function in TysPrim.proxyPrimTyCon. I hope this helps! Richard PS: I've made this mistake myself several times, and it's quite baffling to debug!
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Thanks a lot, this helped! But sorry for asking, before this problem I evaluated Cmp on some values with * kinds, and I used (mkTemplateAnonTyConBinders [ liftedTypeKind, liftedTypeKind ]) to make the input kinds for TyCon. Changing function to mkTemplateTyConBinders (right now this part looks like 'binders = mkTemplateTyConBinders [ liftedTypeKind, liftedTypeKind ] (\ks -> ks)') made my type family not evaluating: :kind! Cmp 4 5 Cmp 4 5 :: Ordering = Cmp 4 5 And before that change: :kind! Cmp (Proxy 5) (Proxy 4) Cmp (Proxy 5) (Proxy 4) :: Ordering = 'GT I can see from debug output that before that change functions in BuiltInSynFamily like matchFamCmpType (has the same meaning as matchFamCmpNat) had been applied to values, but now they aren’t. What am I missing?
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I'm afraid I don't know a quick answer to that one. Does anyone else? If no one answers, write back in a few days and I'll look into it.
Richard
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