#14869: Documentation for isLiftedTypeKind is incorrect -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Documentation | Unknown/Multiple bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Amusingly, the `Constraint` counterpart, `isLiftedTypeKind`, actually appears to do [http://git.haskell.org/ghc.git/blob/df2c3b3364834d2fd038192c89348fc50a2e0475... the right thing]: {{{#!hs isConstraintKind :: Kind -> Bool isConstraintKindCon :: TyCon -> Bool isConstraintKindCon tc = tyConUnique tc == constraintKindTyConKey isConstraintKind (TyConApp tc _) = isConstraintKindCon tc isConstraintKind _ = False }}} This actually checks the unique of the tycon, and per `Note [Kind Constraint and kind *]`, the uniques for `Type` and `Constraint` [http://git.haskell.org/ghc.git/blob/df2c3b3364834d2fd038192c89348fc50a2e0475... are different]. Thus: {{{ $ inplace/bin/ghc-stage2 --interactive -package ghc GHCi, version 8.5.20180221: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci λ> :m + Kind TysWiredIn λ> isConstraintKind liftedTypeKind False λ> isConstraintKind constraintKind True }}} Thus, to fix the aforementioned Template Haskell bug, all we'd have to do is make this change: {{{#!diff diff --git a/compiler/typecheck/TcSplice.hs b/compiler/typecheck/TcSplice.hs index 45e18e6..b052e8e 100644 --- a/compiler/typecheck/TcSplice.hs +++ b/compiler/typecheck/TcSplice.hs @@ -1707,8 +1707,8 @@ reifyFamilyInstance is_poly_tvs inst@(FamInst { fi_flavor = flavor ------------------------------ reifyType :: TyCoRep.Type -> TcM TH.Type -- Monadic only because of failure -reifyType ty | isLiftedTypeKind ty = return TH.StarT - | isConstraintKind ty = return TH.ConstraintT +reifyType ty | isConstraintKind ty = return TH.ConstraintT + | isLiftedTypeKind ty = return TH.StarT reifyType ty@(ForAllTy {}) = reify_for_all ty reifyType (LitTy t) = do { r <- reifyTyLit t; return (TH.LitT r) } reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv)) }}} ----- I propose that we: 1. Change the documentation for `isLiftedTypeKind` to reflect the fact that it does not distinguish between `Constraint` and `Type`. 2. Make the above change to `TcSplice` to fix the bug. Does that sound reasonable? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14869#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler