[GHC] #11785: Merge types and kinds in Template Haskell (was: Kinds should be treated like types in TcSplice)

[GHC]

#11785: Merge types and kinds in Template Haskell
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.1
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Actually, there's another way to go about this. Instead of making more
 things pure, we could make more things monadic. This can be accomplished
 with the following combinator:

 {{{#!hs
 bindCore :: DsM (Core (TH.Q a)) -> (Core a -> DsM (Core (TH.Q b)))
          -> DsM (Core (TH.Q b))
 bindCore dsma f
   = do { cqa@(MkC qa) <- dsma
        ; loc <- getSrcSpanDs
        ; a_name <- newNameAt (mkVarOccFS (fsLit "a")) loc
        ; let [a_ty] = tcTyConAppArgs (exprType qa)
        ; let a_id = mkLocalId (localiseName a_name) a_ty
              ca   = MkC (Var a_id)
        ; MkC qb <- f ca
        ; let [b_ty] = tcTyConAppArgs (exprType qb)
        ; repBindQ a_ty b_ty cqa (MkC (Lam a_id qb)) }
 }}}

 With `bindCore`, we can retrofit existing uses of `repLKind` with
 `repLTy`. Here's one example:

 {{{#!diff
 diff --git a/compiler/deSugar/DsMeta.hs b/compiler/deSugar/DsMeta.hs
 index c679981..8acc6eb 100644
 --- a/compiler/deSugar/DsMeta.hs
 +++ b/compiler/deSugar/DsMeta.hs
 @@ -1043,8 +1044,9 @@ repTy (HsEqTy t1 t2) = do
                           repTapps eq [t1', t2']
  repTy (HsKindSig t k)       = do
                                  t1 <- repLTy t
 -                                k1 <- repLKind k
 -                                repTSig t1 k1
 +                                bindCore (repLTy k) $ repTSig t1
 +                                -- k1 <- repLKind k
 +                                -- repTSig t1 k1
  repTy (HsSpliceTy splice _)     = repSplice splice
  repTy (HsExplicitListTy _ _ tys) = do
                                      tys1 <- repLTys tys
 }}}

 It's somewhat unsavory, but it prevents us from having to change a
 truckload of combinators in `Language.Haskell.TH.Lib` to take `KindQ` as
 an argument instead of `Kind`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11785#comment:4>
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