DsMeta.hs 113 KB
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{-# LANGUAGE CPP #-}

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-----------------------------------------------------------------------------
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--
-- (c) The University of Glasgow 2006
--
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-- The purpose of this module is to transform an HsExpr into a CoreExpr which
-- when evaluated, returns a (Meta.Q Meta.Exp) computation analogous to the
-- input HsExpr. We do this in the DsM monad, which supplies access to
-- CoreExpr's of the "smart constructors" of the Meta.Exp datatype.
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--
-- It also defines a bunch of knownKeyNames, in the same way as is done
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-- in prelude/PrelNames.  It's much more convenient to do it here, because
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-- otherwise we have to recompile PrelNames whenever we add a Name, which is
-- a Royal Pain (triggers other recompilation).
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-----------------------------------------------------------------------------

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module DsMeta( dsBracket,
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               templateHaskellNames, qTyConName, nameTyConName,
               liftName, liftStringName, expQTyConName, patQTyConName,
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               decQTyConName, decsQTyConName, typeQTyConName,
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               decTyConName, typeTyConName, mkNameG_dName, mkNameG_vName, mkNameG_tcName,
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               quoteExpName, quotePatName, quoteDecName, quoteTypeName,
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               tExpTyConName, tExpDataConName, unTypeName, unTypeQName,
               unsafeTExpCoerceName
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                ) where
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#include "HsVersions.h"

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import {-# SOURCE #-}   DsExpr ( dsExpr )
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import MatchLit
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import DsMonad

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import qualified Language.Haskell.TH as TH
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import HsSyn
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import Class
import PrelNames
-- To avoid clashes with DsMeta.varName we must make a local alias for
-- OccName.varName we do this by removing varName from the import of
-- OccName above, making a qualified instance of OccName and using
-- OccNameAlias.varName where varName ws previously used in this file.
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import qualified OccName( isDataOcc, isVarOcc, isTcOcc, varName, tcName, dataName )
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import Module
import Id
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import Name hiding( isVarOcc, isTcOcc, varName, tcName )
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import NameEnv
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import TcType
import TyCon
import TysWiredIn
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import TysPrim ( liftedTypeKindTyConName, constraintKindTyConName )
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import CoreSyn
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import MkCore
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import CoreUtils
import SrcLoc
import Unique
import BasicTypes
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import Outputable
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import Bag
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import DynFlags
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import FastString
import ForeignCall
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import Util
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import Data.Maybe
import Control.Monad
import Data.List
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-----------------------------------------------------------------------------
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dsBracket :: HsBracket Name -> [PendingTcSplice] -> DsM CoreExpr
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-- Returns a CoreExpr of type TH.ExpQ
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-- The quoted thing is parameterised over Name, even though it has
-- been type checked.  We don't want all those type decorations!

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dsBracket brack splices
  = dsExtendMetaEnv new_bit (do_brack brack)
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  where
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    new_bit = mkNameEnv [(n, Splice (unLoc e)) | (n, e) <- splices]
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    do_brack (VarBr _ n) = do { MkC e1  <- lookupOcc n ; return e1 }
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    do_brack (ExpBr e)   = do { MkC e1  <- repLE e     ; return e1 }
    do_brack (PatBr p)   = do { MkC p1  <- repTopP p   ; return p1 }
    do_brack (TypBr t)   = do { MkC t1  <- repLTy t    ; return t1 }
    do_brack (DecBrG gp) = do { MkC ds1 <- repTopDs gp ; return ds1 }
    do_brack (DecBrL _)  = panic "dsBracket: unexpected DecBrL"
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    do_brack (TExpBr e)  = do { MkC e1  <- repLE e     ; return e1 }
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{- -------------- Examples --------------------

  [| \x -> x |]
====>
  gensym (unpackString "x"#) `bindQ` \ x1::String ->
  lam (pvar x1) (var x1)


  [| \x -> $(f [| x |]) |]
====>
  gensym (unpackString "x"#) `bindQ` \ x1::String ->
  lam (pvar x1) (f (var x1))
-}


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-------------------------------------------------------
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--                      Declarations
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-------------------------------------------------------

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repTopP :: LPat Name -> DsM (Core TH.PatQ)
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repTopP pat = do { ss <- mkGenSyms (collectPatBinders pat)
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                 ; pat' <- addBinds ss (repLP pat)
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                 ; wrapGenSyms ss pat' }
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repTopDs :: HsGroup Name -> DsM (Core (TH.Q [TH.Dec]))
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repTopDs group@(HsGroup { hs_valds   = valds
                        , hs_splcds  = splcds
                        , hs_tyclds  = tyclds
                        , hs_instds  = instds
                        , hs_derivds = derivds
                        , hs_fixds   = fixds
                        , hs_defds   = defds
                        , hs_fords   = fords
                        , hs_warnds  = warnds
                        , hs_annds   = annds
                        , hs_ruleds  = ruleds
                        , hs_vects   = vects
                        , hs_docs    = docs })
 = do { let { tv_bndrs = hsSigTvBinders valds
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            ; bndrs = tv_bndrs ++ hsGroupBinders group } ;
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        ss <- mkGenSyms bndrs ;
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        -- Bind all the names mainly to avoid repeated use of explicit strings.
        -- Thus we get
        --      do { t :: String <- genSym "T" ;
        --           return (Data t [] ...more t's... }
        -- The other important reason is that the output must mention
        -- only "T", not "Foo:T" where Foo is the current module
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        decls <- addBinds ss (
                  do { val_ds  <- rep_val_binds valds
                     ; _       <- mapM no_splice splcds
                     ; tycl_ds <- mapM repTyClD (tyClGroupConcat tyclds)
                     ; role_ds <- mapM repRoleD (concatMap group_roles tyclds)
                     ; inst_ds <- mapM repInstD instds
                     ; _       <- mapM no_standalone_deriv derivds
                     ; fix_ds  <- mapM repFixD fixds
                     ; _       <- mapM no_default_decl defds
                     ; for_ds  <- mapM repForD fords
                     ; _       <- mapM no_warn warnds
                     ; _       <- mapM no_ann annds
                     ; rule_ds <- mapM repRuleD ruleds
                     ; _       <- mapM no_vect vects
                     ; _       <- mapM no_doc docs

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                        -- more needed
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                     ;  return (de_loc $ sort_by_loc $
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                                val_ds ++ catMaybes tycl_ds ++ role_ds ++ fix_ds
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                                       ++ inst_ds ++ rule_ds ++ for_ds) }) ;
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        decl_ty <- lookupType decQTyConName ;
        let { core_list = coreList' decl_ty decls } ;
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        dec_ty <- lookupType decTyConName ;
        q_decs  <- repSequenceQ dec_ty core_list ;
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        wrapGenSyms ss q_decs
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      }
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  where
    no_splice (L loc _)
      = notHandledL loc "Splices within declaration brackets" empty
    no_standalone_deriv (L loc (DerivDecl { deriv_type = deriv_ty }))
      = notHandledL loc "Standalone-deriving" (ppr deriv_ty)
    no_default_decl (L loc decl)
      = notHandledL loc "Default declarations" (ppr decl)
    no_warn (L loc (Warning thing _))
      = notHandledL loc "WARNING and DEPRECATION pragmas" $
                    text "Pragma for declaration of" <+> ppr thing
    no_ann (L loc decl)
      = notHandledL loc "ANN pragmas" (ppr decl)
    no_vect (L loc decl)
      = notHandledL loc "Vectorisation pragmas" (ppr decl)
    no_doc (L loc _)
      = notHandledL loc "Haddock documentation" empty
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hsSigTvBinders :: HsValBinds Name -> [Name]
-- See Note [Scoped type variables in bindings]
hsSigTvBinders binds
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  = [hsLTyVarName tv | L _ (TypeSig _ (L _ (HsForAllTy Explicit qtvs _ _))) <- sigs
                     , tv <- hsQTvBndrs qtvs]
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  where
    sigs = case binds of
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             ValBindsIn  _ sigs -> sigs
             ValBindsOut _ sigs -> sigs
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{- Notes

Note [Scoped type variables in bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   f :: forall a. a -> a
   f x = x::a
Here the 'forall a' brings 'a' into scope over the binding group.
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To achieve this we
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  a) Gensym a binding for 'a' at the same time as we do one for 'f'
     collecting the relevant binders with hsSigTvBinders

  b) When processing the 'forall', don't gensym

The relevant places are signposted with references to this Note

Note [Binders and occurrences]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When we desugar [d| data T = MkT |]
we want to get
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        Data "T" [] [Con "MkT" []] []
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and *not*
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        Data "Foo:T" [] [Con "Foo:MkT" []] []
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That is, the new data decl should fit into whatever new module it is
asked to fit in.   We do *not* clone, though; no need for this:
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        Data "T79" ....
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But if we see this:
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        data T = MkT
        foo = reifyDecl T
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then we must desugar to
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        foo = Data "Foo:T" [] [Con "Foo:MkT" []] []
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So in repTopDs we bring the binders into scope with mkGenSyms and addBinds.
And we use lookupOcc, rather than lookupBinder
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in repTyClD and repC.

-}

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-- represent associated family instances
--
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repTyClD :: LTyClDecl Name -> DsM (Maybe (SrcSpan, Core TH.DecQ))
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repTyClD (L loc (FamDecl { tcdFam = fam })) = liftM Just $ repFamilyDecl (L loc fam)

repTyClD (L loc (SynDecl { tcdLName = tc, tcdTyVars = tvs, tcdRhs = rhs }))
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  = do { tc1 <- lookupLOcc tc           -- See note [Binders and occurrences]
       ; dec <- addTyClTyVarBinds tvs $ \bndrs ->
                repSynDecl tc1 bndrs rhs
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       ; return (Just (loc, dec)) }
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repTyClD (L loc (DataDecl { tcdLName = tc, tcdTyVars = tvs, tcdDataDefn = defn }))
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  = do { tc1 <- lookupLOcc tc           -- See note [Binders and occurrences]
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       ; tc_tvs <- mk_extra_tvs tc tvs defn
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       ; dec <- addTyClTyVarBinds tc_tvs $ \bndrs ->
                repDataDefn tc1 bndrs Nothing (hsLTyVarNames tc_tvs) defn
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       ; return (Just (loc, dec)) }
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repTyClD (L loc (ClassDecl { tcdCtxt = cxt, tcdLName = cls,
                             tcdTyVars = tvs, tcdFDs = fds,
                             tcdSigs = sigs, tcdMeths = meth_binds,
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                             tcdATs = ats, tcdATDefs = [] }))
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  = do { cls1 <- lookupLOcc cls         -- See note [Binders and occurrences]
       ; dec  <- addTyVarBinds tvs $ \bndrs ->
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           do { cxt1   <- repLContext cxt
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              ; sigs1  <- rep_sigs sigs
              ; binds1 <- rep_binds meth_binds
              ; fds1   <- repLFunDeps fds
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              ; ats1   <- repFamilyDecls ats
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              ; decls1 <- coreList decQTyConName (ats1 ++ sigs1 ++ binds1)
              ; repClass cxt1 cls1 bndrs fds1 decls1
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              }
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       ; return $ Just (loc, dec)
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       }
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-- Un-handled cases
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repTyClD (L loc d) = putSrcSpanDs loc $
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                     do { warnDs (hang ds_msg 4 (ppr d))
                        ; return Nothing }
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-------------------------
repRoleD :: LRoleAnnotDecl Name -> DsM (SrcSpan, Core TH.DecQ)
repRoleD (L loc (RoleAnnotDecl tycon roles))
  = do { tycon1 <- lookupLOcc tycon
       ; roles1 <- mapM repRole roles
       ; roles2 <- coreList roleTyConName roles1
       ; dec <- repRoleAnnotD tycon1 roles2
       ; return (loc, dec) }

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-------------------------
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repDataDefn :: Core TH.Name -> Core [TH.TyVarBndr]
            -> Maybe (Core [TH.TypeQ])
            -> [Name] -> HsDataDefn Name
            -> DsM (Core TH.DecQ)
repDataDefn tc bndrs opt_tys tv_names
          (HsDataDefn { dd_ND = new_or_data, dd_ctxt = cxt
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                      , dd_cons = cons, dd_derivs = mb_derivs })
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  = do { cxt1     <- repLContext cxt
       ; derivs1  <- repDerivs mb_derivs
       ; case new_or_data of
           NewType  -> do { con1 <- repC tv_names (head cons)
                          ; repNewtype cxt1 tc bndrs opt_tys con1 derivs1 }
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           DataType -> do { cons1 <- repList conQTyConName (repC tv_names) cons
                          ; repData cxt1 tc bndrs opt_tys cons1 derivs1 } }
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repSynDecl :: Core TH.Name -> Core [TH.TyVarBndr]
          -> LHsType Name
          -> DsM (Core TH.DecQ)
repSynDecl tc bndrs ty
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  = do { ty1 <- repLTy ty
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       ; repTySyn tc bndrs ty1 }

repFamilyDecl :: LFamilyDecl Name -> DsM (SrcSpan, Core TH.DecQ)
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repFamilyDecl (L loc (FamilyDecl { fdInfo    = info,
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                                   fdLName   = tc,
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                                   fdTyVars  = tvs,
                                   fdKindSig = opt_kind }))
  = do { tc1 <- lookupLOcc tc           -- See note [Binders and occurrences]
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       ; dec <- addTyClTyVarBinds tvs $ \bndrs ->
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           case (opt_kind, info) of
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                  (Nothing, ClosedTypeFamily eqns) ->
                    do { eqns1 <- mapM repTyFamEqn eqns
                       ; eqns2 <- coreList tySynEqnQTyConName eqns1
                       ; repClosedFamilyNoKind tc1 bndrs eqns2 }
                  (Just ki, ClosedTypeFamily eqns) ->
                    do { eqns1 <- mapM repTyFamEqn eqns
                       ; eqns2 <- coreList tySynEqnQTyConName eqns1
                       ; ki1 <- repLKind ki
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                       ; repClosedFamilyKind tc1 bndrs ki1 eqns2 }
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                  (Nothing, _) ->
                    do { info' <- repFamilyInfo info
                       ; repFamilyNoKind info' tc1 bndrs }
                  (Just ki, _) ->
                    do { info' <- repFamilyInfo info
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                       ; ki1 <- repLKind ki
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                       ; repFamilyKind info' tc1 bndrs ki1 }
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       ; return (loc, dec)
       }

repFamilyDecls :: [LFamilyDecl Name] -> DsM [Core TH.DecQ]
repFamilyDecls fds = liftM de_loc (mapM repFamilyDecl fds)
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-------------------------
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mk_extra_tvs :: Located Name -> LHsTyVarBndrs Name
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             -> HsDataDefn Name -> DsM (LHsTyVarBndrs Name)
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-- If there is a kind signature it must be of form
--    k1 -> .. -> kn -> *
-- Return type variables [tv1:k1, tv2:k2, .., tvn:kn]
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mk_extra_tvs tc tvs defn
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  | HsDataDefn { dd_kindSig = Just hs_kind } <- defn
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  = do { extra_tvs <- go hs_kind
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       ; return (tvs { hsq_tvs = hsq_tvs tvs ++ extra_tvs }) }
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  | otherwise
  = return tvs
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  where
    go :: LHsKind Name -> DsM [LHsTyVarBndr Name]
    go (L loc (HsFunTy kind rest))
      = do { uniq <- newUnique
           ; let { occ = mkTyVarOccFS (fsLit "t")
                 ; nm = mkInternalName uniq occ loc
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                 ; hs_tv = L loc (KindedTyVar nm kind) }
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           ; hs_tvs <- go rest
           ; return (hs_tv : hs_tvs) }

    go (L _ (HsTyVar n))
      | n == liftedTypeKindTyConName
      = return []
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    go _ = failWithDs (ptext (sLit "Malformed kind signature for") <+> ppr tc)
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-------------------------
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-- represent fundeps
--
repLFunDeps :: [Located (FunDep Name)] -> DsM (Core [TH.FunDep])
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repLFunDeps fds = repList funDepTyConName repLFunDep fds
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repLFunDep :: Located (FunDep Name) -> DsM (Core TH.FunDep)
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repLFunDep (L _ (xs, ys)) = do xs' <- repList nameTyConName lookupBinder xs
                               ys' <- repList nameTyConName lookupBinder ys
                               repFunDep xs' ys'
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-- represent family declaration flavours
--
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repFamilyInfo :: FamilyInfo Name -> DsM (Core TH.FamFlavour)
repFamilyInfo OpenTypeFamily      = rep2 typeFamName []
repFamilyInfo DataFamily          = rep2 dataFamName []
repFamilyInfo ClosedTypeFamily {} = panic "repFamilyInfo"
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-- Represent instance declarations
--
repInstD :: LInstDecl Name -> DsM (SrcSpan, Core TH.DecQ)
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repInstD (L loc (TyFamInstD { tfid_inst = fi_decl }))
  = do { dec <- repTyFamInstD fi_decl
       ; return (loc, dec) }
repInstD (L loc (DataFamInstD { dfid_inst = fi_decl }))
  = do { dec <- repDataFamInstD fi_decl
       ; return (loc, dec) }
repInstD (L loc (ClsInstD { cid_inst = cls_decl }))
  = do { dec <- repClsInstD cls_decl
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       ; return (loc, dec) }
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repClsInstD :: ClsInstDecl Name -> DsM (Core TH.DecQ)
repClsInstD (ClsInstDecl { cid_poly_ty = ty, cid_binds = binds
                         , cid_sigs = prags, cid_tyfam_insts = ats
                         , cid_datafam_insts = adts })
  = addTyVarBinds tvs $ \_ ->
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            -- We must bring the type variables into scope, so their
            -- occurrences don't fail, even though the binders don't
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            -- appear in the resulting data structure
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            --
            -- But we do NOT bring the binders of 'binds' into scope
            -- because they are properly regarded as occurrences
            -- For example, the method names should be bound to
            -- the selector Ids, not to fresh names (Trac #5410)
            --
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            do { cxt1 <- repContext cxt
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               ; cls_tcon <- repTy (HsTyVar (unLoc cls))
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               ; cls_tys <- repLTys tys
               ; inst_ty1 <- repTapps cls_tcon cls_tys
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               ; binds1 <- rep_binds binds
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               ; prags1 <- rep_sigs prags
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               ; ats1 <- mapM (repTyFamInstD . unLoc) ats
               ; adts1 <- mapM (repDataFamInstD . unLoc) adts
               ; decls <- coreList decQTyConName (ats1 ++ adts1 ++ binds1 ++ prags1)
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               ; repInst cxt1 inst_ty1 decls }
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 where
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   Just (tvs, cxt, cls, tys) = splitLHsInstDeclTy_maybe ty
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repTyFamInstD :: TyFamInstDecl Name -> DsM (Core TH.DecQ)
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repTyFamInstD decl@(TyFamInstDecl { tfid_eqn = eqn })
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  = do { let tc_name = tyFamInstDeclLName decl
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       ; tc <- lookupLOcc tc_name               -- See note [Binders and occurrences]
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       ; eqn1 <- repTyFamEqn eqn
       ; repTySynInst tc eqn1 }
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repTyFamEqn :: LTyFamInstEqn Name -> DsM (Core TH.TySynEqnQ)
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repTyFamEqn (L loc (TyFamEqn { tfe_pats = HsWB { hswb_cts = tys
                                               , hswb_kvs = kv_names
                                               , hswb_tvs = tv_names }
                                 , tfe_rhs = rhs }))
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  = do { let hs_tvs = HsQTvs { hsq_kvs = kv_names
                             , hsq_tvs = userHsTyVarBndrs loc tv_names }   -- Yuk
       ; addTyClTyVarBinds hs_tvs $ \ _ ->
         do { tys1 <- repLTys tys
            ; tys2 <- coreList typeQTyConName tys1
            ; rhs1 <- repLTy rhs
            ; repTySynEqn tys2 rhs1 } }

repDataFamInstD :: DataFamInstDecl Name -> DsM (Core TH.DecQ)
repDataFamInstD (DataFamInstDecl { dfid_tycon = tc_name
                                 , dfid_pats = HsWB { hswb_cts = tys, hswb_kvs = kv_names, hswb_tvs = tv_names }
                                 , dfid_defn = defn })
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  = do { tc <- lookupLOcc tc_name               -- See note [Binders and occurrences]
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       ; let loc = getLoc tc_name
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             hs_tvs = HsQTvs { hsq_kvs = kv_names, hsq_tvs = userHsTyVarBndrs loc tv_names }   -- Yuk
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       ; addTyClTyVarBinds hs_tvs $ \ bndrs ->
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         do { tys1 <- repList typeQTyConName repLTy tys
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            ; repDataDefn tc bndrs (Just tys1) tv_names defn } }
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repForD :: Located (ForeignDecl Name) -> DsM (SrcSpan, Core TH.DecQ)
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repForD (L loc (ForeignImport name typ _ (CImport cc s mch cis)))
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 = do MkC name' <- lookupLOcc name
      MkC typ' <- repLTy typ
      MkC cc' <- repCCallConv cc
      MkC s' <- repSafety s
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      cis' <- conv_cimportspec cis
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      MkC str <- coreStringLit (static ++ chStr ++ cis')
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      dec <- rep2 forImpDName [cc', s', str, name', typ']
      return (loc, dec)
 where
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    conv_cimportspec (CLabel cls) = notHandled "Foreign label" (doubleQuotes (ppr cls))
    conv_cimportspec (CFunction DynamicTarget) = return "dynamic"
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    conv_cimportspec (CFunction (StaticTarget fs _ True)) = return (unpackFS fs)
    conv_cimportspec (CFunction (StaticTarget _  _ False)) = panic "conv_cimportspec: values not supported yet"
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    conv_cimportspec CWrapper = return "wrapper"
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    static = case cis of
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                 CFunction (StaticTarget _ _ _) -> "static "
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                 _ -> ""
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    chStr = case mch of
            Nothing -> ""
            Just (Header h) -> unpackFS h ++ " "
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repForD decl = notHandled "Foreign declaration" (ppr decl)
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repCCallConv :: CCallConv -> DsM (Core TH.Callconv)
repCCallConv CCallConv = rep2 cCallName []
repCCallConv StdCallConv = rep2 stdCallName []
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repCCallConv callConv    = notHandled "repCCallConv" (ppr callConv)
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repSafety :: Safety -> DsM (Core TH.Safety)
repSafety PlayRisky = rep2 unsafeName []
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repSafety PlayInterruptible = rep2 interruptibleName []
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repSafety PlaySafe = rep2 safeName []
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repFixD :: LFixitySig Name -> DsM (SrcSpan, Core TH.DecQ)
repFixD (L loc (FixitySig name (Fixity prec dir)))
  = do { MkC name' <- lookupLOcc name
       ; MkC prec' <- coreIntLit prec
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       ; let rep_fn = case dir of
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                        InfixL -> infixLDName
                        InfixR -> infixRDName
                        InfixN -> infixNDName
       ; dec <- rep2 rep_fn [prec', name']
       ; return (loc, dec) }

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repRuleD :: LRuleDecl Name -> DsM (SrcSpan, Core TH.DecQ)
repRuleD (L loc (HsRule n act bndrs lhs _ rhs _))
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  = do { let bndr_names = concatMap ruleBndrNames bndrs
       ; ss <- mkGenSyms bndr_names
       ; rule1 <- addBinds ss $
                  do { bndrs' <- repList ruleBndrQTyConName repRuleBndr bndrs
                     ; n'   <- coreStringLit $ unpackFS n
                     ; act' <- repPhases act
                     ; lhs' <- repLE lhs
                     ; rhs' <- repLE rhs
                     ; repPragRule n' bndrs' lhs' rhs' act' }
       ; rule2 <- wrapGenSyms ss rule1
       ; return (loc, rule2) }

ruleBndrNames :: RuleBndr Name -> [Name]
ruleBndrNames (RuleBndr n)      = [unLoc n]
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ruleBndrNames (RuleBndrSig n (HsWB { hswb_kvs = kvs, hswb_tvs = tvs }))
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  = unLoc n : kvs ++ tvs
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repRuleBndr :: RuleBndr Name -> DsM (Core TH.RuleBndrQ)
repRuleBndr (RuleBndr n)
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  = do { MkC n' <- lookupLBinder n
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       ; rep2 ruleVarName [n'] }
repRuleBndr (RuleBndrSig n (HsWB { hswb_cts = ty }))
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  = do { MkC n'  <- lookupLBinder n
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       ; MkC ty' <- repLTy ty
       ; rep2 typedRuleVarName [n', ty'] }

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ds_msg :: SDoc
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ds_msg = ptext (sLit "Cannot desugar this Template Haskell declaration:")
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-------------------------------------------------------
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--                      Constructors
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-------------------------------------------------------

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repC :: [Name] -> LConDecl Name -> DsM (Core TH.ConQ)
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repC _ (L _ (ConDecl { con_name = con, con_qvars = con_tvs, con_cxt = L _ []
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                     , con_details = details, con_res = ResTyH98 }))
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  | null (hsQTvBndrs con_tvs)
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  = do { con1 <- lookupLOcc con         -- See Note [Binders and occurrences]
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       ; repConstr con1 details  }
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repC tvs (L _ (ConDecl { con_name = con
                       , con_qvars = con_tvs, con_cxt = L _ ctxt
                       , con_details = details
                       , con_res = res_ty }))
  = do { (eq_ctxt, con_tv_subst) <- mkGadtCtxt tvs res_ty
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       ; let ex_tvs = HsQTvs { hsq_kvs = filterOut (in_subst con_tv_subst) (hsq_kvs con_tvs)
                             , hsq_tvs = filterOut (in_subst con_tv_subst . hsLTyVarName) (hsq_tvs con_tvs) }

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       ; binds <- mapM dupBinder con_tv_subst
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       ; dsExtendMetaEnv (mkNameEnv binds) $     -- Binds some of the con_tvs
         addTyVarBinds ex_tvs $ \ ex_bndrs ->   -- Binds the remaining con_tvs
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    do { con1      <- lookupLOcc con    -- See Note [Binders and occurrences]
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       ; c'        <- repConstr con1 details
       ; ctxt'     <- repContext (eq_ctxt ++ ctxt)
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       ; rep2 forallCName [unC ex_bndrs, unC ctxt', unC c'] } }
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in_subst :: [(Name,Name)] -> Name -> Bool
in_subst []          _ = False
in_subst ((n',_):ns) n = n==n' || in_subst ns n
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mkGadtCtxt :: [Name]            -- Tyvars of the data type
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           -> ResType (LHsType Name)
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           -> DsM (HsContext Name, [(Name,Name)])
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-- Given a data type in GADT syntax, figure out the equality
-- context, so that we can represent it with an explicit
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-- equality context, because that is the only way to express
-- the GADT in TH syntax
--
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-- Example:
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-- data T a b c where { MkT :: forall d e. d -> e -> T d [e] e
--     mkGadtCtxt [a,b,c] [d,e] (T d [e] e)
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--   returns
--     (b~[e], c~e), [d->a]
--
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-- This function is fiddly, but not really hard
mkGadtCtxt _ ResTyH98
  = return ([], [])
mkGadtCtxt data_tvs (ResTyGADT res_ty)
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  , data_tvs `equalLength` tys
  = return (go [] [] (data_tvs `zip` tys))

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  | otherwise
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  = failWithDs (ptext (sLit "Malformed constructor result type:") <+> ppr res_ty)
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  where
    go cxt subst [] = (cxt, subst)
    go cxt subst ((data_tv, ty) : rest)
       | Just con_tv <- is_hs_tyvar ty
       , isTyVarName con_tv
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       , not (in_subst subst con_tv)
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       = go cxt ((con_tv, data_tv) : subst) rest
       | otherwise
       = go (eq_pred : cxt) subst rest
       where
         loc = getLoc ty
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         eq_pred = L loc (HsEqTy (L loc (HsTyVar data_tv)) ty)
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    is_hs_tyvar (L _ (HsTyVar n))  = Just n   -- Type variables *and* tycons
    is_hs_tyvar (L _ (HsParTy ty)) = is_hs_tyvar ty
    is_hs_tyvar _                  = Nothing

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repBangTy :: LBangType Name -> DsM (Core (TH.StrictTypeQ))
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repBangTy ty= do
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  MkC s <- rep2 str []
  MkC t <- repLTy ty'
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  rep2 strictTypeName [s, t]
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  where
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    (str, ty') = case ty of
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                   L _ (HsBangTy (HsUserBang (Just True) True) ty) -> (unpackedName,  ty)
                   L _ (HsBangTy (HsUserBang _     True) ty)       -> (isStrictName,  ty)
                   _                               -> (notStrictName, ty)
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-------------------------------------------------------
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--                      Deriving clause
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-------------------------------------------------------

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repDerivs :: Maybe [LHsType Name] -> DsM (Core [TH.Name])
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repDerivs Nothing = coreList nameTyConName []
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repDerivs (Just ctxt)
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  = repList nameTyConName rep_deriv ctxt
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  where
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    rep_deriv :: LHsType Name -> DsM (Core TH.Name)
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        -- Deriving clauses must have the simple H98 form
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    rep_deriv ty
      | Just (cls, []) <- splitHsClassTy_maybe (unLoc ty)
      = lookupOcc cls
      | otherwise
      = notHandled "Non-H98 deriving clause" (ppr ty)
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-------------------------------------------------------
--   Signatures in a class decl, or a group of bindings
-------------------------------------------------------

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rep_sigs :: [LSig Name] -> DsM [Core TH.DecQ]
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rep_sigs sigs = do locs_cores <- rep_sigs' sigs
                   return $ de_loc $ sort_by_loc locs_cores

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rep_sigs' :: [LSig Name] -> DsM [(SrcSpan, Core TH.DecQ)]
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        -- We silently ignore ones we don't recognise
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rep_sigs' sigs = do { sigs1 <- mapM rep_sig sigs ;
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                     return (concat sigs1) }
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rep_sig :: LSig Name -> DsM [(SrcSpan, Core TH.DecQ)]
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rep_sig (L loc (TypeSig nms ty))      = mapM (rep_ty_sig loc ty) nms
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rep_sig (L _   (PatSynSig {}))        = notHandled "Pattern type signatures" empty
rep_sig (L _   (GenericSig nm _))     = notHandled "Default type signatures" msg
  where msg = text "Illegal default signature for" <+> quotes (ppr nm)
rep_sig d@(L _ (IdSig {}))            = pprPanic "rep_sig IdSig" (ppr d)
rep_sig (L _   (FixSig {}))           = return [] -- fixity sigs at top level
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rep_sig (L loc (InlineSig nm ispec))  = rep_inline nm ispec loc
rep_sig (L loc (SpecSig nm ty ispec)) = rep_specialise nm ty ispec loc
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rep_sig (L loc (SpecInstSig ty))      = rep_specialiseInst ty loc
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rep_sig (L _   (MinimalSig {}))       = notHandled "MINIMAL pragmas" empty
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rep_ty_sig :: SrcSpan -> LHsType Name -> Located Name
           -> DsM (SrcSpan, Core TH.DecQ)
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rep_ty_sig loc (L _ ty) nm
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  = do { nm1 <- lookupLOcc nm
       ; ty1 <- rep_ty ty
       ; sig <- repProto nm1 ty1
       ; return (loc, sig) }
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  where
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    -- We must special-case the top-level explicit for-all of a TypeSig
    -- See Note [Scoped type variables in bindings]
    rep_ty (HsForAllTy Explicit tvs ctxt ty)
      = do { let rep_in_scope_tv tv = do { name <- lookupBinder (hsLTyVarName tv)
                                         ; repTyVarBndrWithKind tv name }
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           ; bndrs1 <- repList tyVarBndrTyConName rep_in_scope_tv (hsQTvBndrs tvs)
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           ; ctxt1  <- repLContext ctxt
           ; ty1    <- repLTy ty
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           ; repTForall bndrs1 ctxt1 ty1 }
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    rep_ty ty = repTy ty
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rep_inline :: Located Name
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           -> InlinePragma      -- Never defaultInlinePragma
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           -> SrcSpan
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           -> DsM [(SrcSpan, Core TH.DecQ)]
rep_inline nm ispec loc
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  = do { nm1    <- lookupLOcc nm
       ; inline <- repInline $ inl_inline ispec
       ; rm     <- repRuleMatch $ inl_rule ispec
       ; phases <- repPhases $ inl_act ispec
       ; pragma <- repPragInl nm1 inline rm phases
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       ; return [(loc, pragma)]
       }

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rep_specialise :: Located Name -> LHsType Name -> InlinePragma -> SrcSpan
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               -> DsM [(SrcSpan, Core TH.DecQ)]
rep_specialise nm ty ispec loc
  = do { nm1 <- lookupLOcc nm
       ; ty1 <- repLTy ty
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       ; phases <- repPhases $ inl_act ispec
       ; let inline = inl_inline ispec
       ; pragma <- if isEmptyInlineSpec inline
                   then -- SPECIALISE
                     repPragSpec nm1 ty1 phases
                   else -- SPECIALISE INLINE
                     do { inline1 <- repInline inline
                        ; repPragSpecInl nm1 ty1 inline1 phases }
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       ; return [(loc, pragma)]
       }
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rep_specialiseInst :: LHsType Name -> SrcSpan -> DsM [(SrcSpan, Core TH.DecQ)]
rep_specialiseInst ty loc
  = do { ty1    <- repLTy ty
       ; pragma <- repPragSpecInst ty1
       ; return [(loc, pragma)] }

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repInline :: InlineSpec -> DsM (Core TH.Inline)
repInline NoInline  = dataCon noInlineDataConName
repInline Inline    = dataCon inlineDataConName
repInline Inlinable = dataCon inlinableDataConName
repInline spec      = notHandled "repInline" (ppr spec)

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repRuleMatch :: RuleMatchInfo -> DsM (Core TH.RuleMatch)
repRuleMatch ConLike = dataCon conLikeDataConName
repRuleMatch FunLike = dataCon funLikeDataConName
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repPhases :: Activation -> DsM (Core TH.Phases)
repPhases (ActiveBefore i) = do { MkC arg <- coreIntLit i
                                ; dataCon' beforePhaseDataConName [arg] }
repPhases (ActiveAfter i)  = do { MkC arg <- coreIntLit i
                                ; dataCon' fromPhaseDataConName [arg] }
repPhases _                = dataCon allPhasesDataConName
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-------------------------------------------------------
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--                      Types
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-------------------------------------------------------
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addTyVarBinds :: LHsTyVarBndrs Name                            -- the binders to be added
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              -> (Core [TH.TyVarBndr] -> DsM (Core (TH.Q a)))  -- action in the ext env
              -> DsM (Core (TH.Q a))
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-- gensym a list of type variables and enter them into the meta environment;
-- the computations passed as the second argument is executed in that extended
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-- meta environment and gets the *new* names on Core-level as an argument
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addTyVarBinds (HsQTvs { hsq_kvs = kvs, hsq_tvs = tvs }) m
  = do { fresh_kv_names <- mkGenSyms kvs
       ; fresh_tv_names <- mkGenSyms (map hsLTyVarName tvs)
       ; let fresh_names = fresh_kv_names ++ fresh_tv_names
       ; term <- addBinds fresh_names $
                 do { kbs <- repList tyVarBndrTyConName mk_tv_bndr (tvs `zip` fresh_tv_names)
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                    ; m kbs }
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       ; wrapGenSyms fresh_names term }
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  where
    mk_tv_bndr (tv, (_,v)) = repTyVarBndrWithKind tv (coreVar v)
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addTyClTyVarBinds :: LHsTyVarBndrs Name
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                  -> (Core [TH.TyVarBndr] -> DsM (Core (TH.Q a)))
                  -> DsM (Core (TH.Q a))
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-- Used for data/newtype declarations, and family instances,
-- so that the nested type variables work right
--    instance C (T a) where
--      type W (T a) = blah
-- The 'a' in the type instance is the one bound by the instance decl
addTyClTyVarBinds tvs m
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  = do { let tv_names = hsLKiTyVarNames tvs
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       ; env <- dsGetMetaEnv
       ; freshNames <- mkGenSyms (filterOut (`elemNameEnv` env) tv_names)
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            -- Make fresh names for the ones that are not already in scope
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            -- This makes things work for family declarations

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       ; term <- addBinds freshNames $
                 do { kbs <- repList tyVarBndrTyConName mk_tv_bndr (hsQTvBndrs tvs)
                    ; m kbs }
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       ; wrapGenSyms freshNames term }
  where
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    mk_tv_bndr tv = do { v <- lookupBinder (hsLTyVarName tv)
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                       ; repTyVarBndrWithKind tv v }
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-- Produce kinded binder constructors from the Haskell tyvar binders
--
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repTyVarBndrWithKind :: LHsTyVarBndr Name
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                     -> Core TH.Name -> DsM (Core TH.TyVarBndr)
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repTyVarBndrWithKind (L _ (UserTyVar _)) nm
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  = repPlainTV nm
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repTyVarBndrWithKind (L _ (KindedTyVar _ ki)) nm
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  = repLKind ki >>= repKindedTV nm
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-- represent a type context
--
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repLContext :: LHsContext Name -> DsM (Core TH.CxtQ)
repLContext (L _ ctxt) = repContext ctxt

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repContext :: HsContext Name -> DsM (Core TH.CxtQ)
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repContext ctxt = do preds <- repList typeQTyConName repLTy ctxt
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                     repCtxt preds
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-- yield the representation of a list of types
--
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repLTys :: [LHsType Name] -> DsM [Core TH.TypeQ]
repLTys tys = mapM repLTy tys
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-- represent a type
--
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repLTy :: LHsType Name -> DsM (Core TH.TypeQ)
repLTy (L _ ty) = repTy ty

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repTy :: HsType Name -> DsM (Core TH.TypeQ)
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repTy (HsForAllTy _ tvs ctxt ty)  =
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  addTyVarBinds tvs $ \bndrs -> do
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    ctxt1  <- repLContext ctxt
    ty1    <- repLTy ty
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    repTForall bndrs ctxt1 ty1
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repTy (HsTyVar n)
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  | isTvOcc occ   = do tv1 <- lookupOcc n
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                       repTvar tv1
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  | isDataOcc occ = do tc1 <- lookupOcc n
                       repPromotedTyCon tc1
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  | otherwise     = do tc1 <- lookupOcc n
                       repNamedTyCon tc1
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  where
    occ = nameOccName n
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repTy (HsAppTy f a)         = do
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                                f1 <- repLTy f
                                a1 <- repLTy a
                                repTapp f1 a1
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repTy (HsFunTy f a)         = do
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                                f1   <- repLTy f
                                a1   <- repLTy a
                                tcon <- repArrowTyCon
                                repTapps tcon [f1, a1]
repTy (HsListTy t)          = do
                                t1   <- repLTy t
                                tcon <- repListTyCon
                                repTapp tcon t1
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repTy (HsPArrTy t)          = do
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                                t1   <- repLTy t
                                tcon <- repTy (HsTyVar (tyConName parrTyCon))
                                repTapp tcon t1
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repTy (HsTupleTy HsUnboxedTuple tys) = do
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                                tys1 <- repLTys tys
                                tcon <- repUnboxedTupleTyCon (length tys)
                                repTapps tcon tys1
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repTy (HsTupleTy _ tys)     = do tys1 <- repLTys tys
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                                 tcon <- repTupleTyCon (length tys)
                                 repTapps tcon tys1
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repTy (HsOpTy ty1 (_, n) ty2) = repLTy ((nlHsTyVar (unLoc n) `nlHsAppTy` ty1)
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                                   `nlHsAppTy` ty2)
repTy (HsParTy t)           = repLTy t
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repTy (HsEqTy t1 t2) = do
                         t1' <- repLTy t1
                         t2' <- repLTy t2
                         eq  <- repTequality
                         repTapps eq [t1', t2']
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repTy (HsKindSig t k)       = do
                                t1 <- repLTy t
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                                k1 <- repLKind k
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                                repTSig t1 k1
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repTy (HsSpliceTy splice _)     = repSplice splice
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repTy (HsExplicitListTy _ tys)  = do
                                    tys1 <- repLTys tys
                                    repTPromotedList tys1
repTy (HsExplicitTupleTy _ tys) = do
                                    tys1 <- repLTys tys
                                    tcon <- repPromotedTupleTyCon (length tys)
                                    repTapps tcon tys1
repTy (HsTyLit lit) = do
                        lit' <- repTyLit lit
                        repTLit lit'
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repTy ty                      = notHandled "Exotic form of type" (ppr ty)
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repTyLit :: HsTyLit -> DsM (Core TH.TyLitQ)
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repTyLit (HsNumTy i) = do iExpr <- mkIntegerExpr i
                          rep2 numTyLitName [iExpr]
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repTyLit (HsStrTy s) = do { s' <- mkStringExprFS s
                         ; rep2 strTyLitName [s']
                         }

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-- represent a kind
--
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repLKind :: LHsKind Name -> DsM (Core TH.Kind)
repLKind ki
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  = do { let (kis, ki') = splitHsFunType ki
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       ; kis_rep <- mapM repLKind kis
       ; ki'_rep <- repNonArrowLKind ki'
       ; kcon <- repKArrow
       ; let f k1 k2 = repKApp kcon k1 >>= flip repKApp k2
       ; foldrM f ki'_rep kis_rep
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       }
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repNonArrowLKind :: LHsKind Name -> DsM (Core TH.Kind)
repNonArrowLKind (L _ ki) = repNonArrowKind ki

repNonArrowKind :: HsKind Name -> DsM (Core TH.Kind)
repNonArrowKind (HsTyVar name)
  | name == liftedTypeKindTyConName = repKStar
  | name == constraintKindTyConName = repKConstraint
  | isTvOcc (nameOccName name)      = lookupOcc name >>= repKVar
  | otherwise                       = lookupOcc name >>= repKCon
repNonArrowKind (HsAppTy f a)       = do  { f' <- repLKind f
                                          ; a' <- repLKind a
                                          ; repKApp f' a'
                                          }
repNonArrowKind (HsListTy k)        = do  { k' <- repLKind k
                                          ; kcon <- repKList
                                          ; repKApp kcon k'
                                          }
repNonArrowKind (HsTupleTy _ ks)    = do  { ks' <- mapM repLKind ks
                                          ; kcon <- repKTuple (length ks)
                                          ; repKApps kcon ks'
                                          }
repNonArrowKind k                   = notHandled "Exotic form of kind" (ppr k)
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repRole :: Located (Maybe Role) -> DsM (Core TH.Role)
repRole (L _ (Just Nominal))          = rep2 nominalRName []
repRole (L _ (Just Representational)) = rep2 representationalRName []
repRole (L _ (Just Phantom))          = rep2 phantomRName []
repRole (L _ Nothing)                 = rep2 inferRName []
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-----------------------------------------------------------------------------
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--              Splices
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-----------------------------------------------------------------------------

repSplice :: HsSplice Name -> DsM (Core a)
-- See Note [How brackets and nested splices are handled] in TcSplice
-- We return a CoreExpr of any old type; the context should know
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repSplice (HsSplice n _)
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 = do { mb_val <- dsLookupMetaEnv n
       ; case mb_val of
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           Just (Splice e) -> do { e' <- dsExpr e
                                 ; return (MkC e') }
           _ -> pprPanic