DsMeta.hs 101 KB
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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
-- in prelude/PrelNames.  It's much more convenient to do it here, becuase
-- 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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{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

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module DsMeta( dsBracket,
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	       templateHaskellNames, qTyConName, nameTyConName,
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	       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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	        ) 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 MonadUtils
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import Util
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import Data.Maybe
import Control.Monad
import Data.List
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-----------------------------------------------------------------------------
dsBracket :: HsBracket Name -> [PendingSplice] -> 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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{- -------------- 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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-------------------------------------------------------
-- 			Declarations
-------------------------------------------------------

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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
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 = do { let { tv_bndrs = hsSigTvBinders (hs_valds group)
            ; 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
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	-- only "T", not "Foo:T" where Foo is the current module
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	decls <- addBinds ss (do {
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                        fix_ds  <- mapM repFixD (hs_fixds group) ;
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			val_ds  <- rep_val_binds (hs_valds group) ;
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			tycl_ds <- mapM repTyClD (concat (hs_tyclds group)) ;
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			inst_ds <- mapM repInstD (hs_instds group) ;
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			rule_ds <- mapM repRuleD (hs_ruleds group) ;
			for_ds  <- mapM repForD  (hs_fords group) ;
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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 ++ fix_ds
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                                       ++ inst_ds ++ rule_ds ++ for_ds) }) ;
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	decl_ty <- lookupType decQTyConName ;
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	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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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
     	     ValBindsIn  _ sigs -> sigs
     	     ValBindsOut _ sigs -> sigs


{- 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
	Data "T" [] [Con "MkT" []] []
and *not*
	Data "Foo:T" [] [Con "Foo:MkT" []] []
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:
	Data "T79" ....

But if we see this:
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	data T = MkT
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	foo = reifyDecl T

then we must desugar to
	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
--
repTyClDs :: [LTyClDecl Name] -> DsM [Core TH.DecQ]
repTyClDs ds = liftM de_loc (mapMaybeM repTyClD ds)


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repTyClD :: LTyClDecl Name -> DsM (Maybe (SrcSpan, Core TH.DecQ))
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repTyClD (L loc (TyFamily { tcdFlavour = flavour,
		            tcdLName   = tc, tcdTyVars = tvs, 
		            tcdKindSig = opt_kind }))
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- addTyClTyVarBinds tvs $ \bndrs ->
           do { flav   <- repFamilyFlavour flavour
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	      ; case opt_kind of 
                  Nothing -> repFamilyNoKind flav tc1 bndrs
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                  Just ki -> do { ki1 <- repLKind ki 
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                                ; repFamilyKind flav tc1 bndrs ki1 }
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              }
       ; return $ Just (loc, dec)
       }
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repTyClD (L loc (TyDecl { tcdLName = tc, tcdTyVars = tvs, tcdTyDefn = defn }))
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences]  
       ; tc_tvs <- mk_extra_tvs tc tvs defn
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       ; dec <- addTyClTyVarBinds tc_tvs $ \bndrs -> 
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	        repTyDefn tc1 bndrs Nothing (hsLTyVarNames tc_tvs) defn
       ; return (Just (loc, dec)) }
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repTyClD (L loc (ClassDecl { tcdCtxt = cxt, tcdLName = cls, 
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		             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 -> 
           do { cxt1   <- repLContext cxt
 	      ; sigs1  <- rep_sigs sigs
 	      ; binds1 <- rep_binds meth_binds
	      ; fds1   <- repLFunDeps fds
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              ; ats1   <- repTyClDs ats
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 	      ; decls1 <- coreList decQTyConName (ats1 ++ sigs1 ++ binds1)
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 	      ; repClass cxt1 cls1 bndrs fds1 decls1 
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              }
       ; return $ Just (loc, dec) 
       }
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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))
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			; return Nothing }
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-------------------------
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repTyDefn :: Core TH.Name -> Core [TH.TyVarBndr]
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          -> Maybe (Core [TH.TypeQ])
          -> [Name] -> HsTyDefn Name
          -> DsM (Core TH.DecQ)
repTyDefn tc bndrs opt_tys tv_names
          (TyData { td_ND = new_or_data, td_ctxt = cxt
		  , td_cons = cons, td_derivs = mb_derivs })
  = 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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repTyDefn tc bndrs opt_tys _ (TySynonym { td_synRhs = ty })
  = do { ty1 <- repLTy ty
       ; repTySyn tc bndrs opt_tys ty1 }

-------------------------
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mk_extra_tvs :: Located Name -> LHsTyVarBndrs Name 
             -> HsTyDefn 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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  | TyData { td_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
--
repFamilyFlavour :: FamilyFlavour -> DsM (Core TH.FamFlavour)
repFamilyFlavour TypeFamily = rep2 typeFamName []
repFamilyFlavour DataFamily = rep2 dataFamName []

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-- Represent instance declarations
--
repInstD :: LInstDecl Name -> DsM (SrcSpan, Core TH.DecQ)
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repInstD (L loc (FamInstD { lid_inst = fi_decl }))
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  = do { dec <- repFamInstD fi_decl
       ; return (loc, dec) }
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repInstD (L loc (ClsInstD { cid_poly_ty = ty, cid_binds = binds
                          , cid_sigs = prags, cid_fam_insts = ats }))
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  = do { dec <- addTyVarBinds tvs $ \_ ->
	    -- We must bring the type variables into scope, so their
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	    -- occurrences don't fail, even though the binders don't
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            -- appear in the resulting data structure
	    --
	    -- But we do NOT bring the binders of 'binds' into scope
	    -- becuase they are properly regarded as occurrences
	    -- For example, the method names should be bound to
	    -- the selector Ids, not to fresh names (Trac #5410)
	    --
            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 (repFamInstD . unLoc) ats
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               ; decls <- coreList decQTyConName (ats1 ++ binds1 ++ prags1)
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               ; repInst cxt1 inst_ty1 decls }
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       ; return (loc, dec) }
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 where
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   Just (tvs, cxt, cls, tys) = splitLHsInstDeclTy_maybe ty
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repFamInstD :: FamInstDecl Name -> DsM (Core TH.DecQ)
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repFamInstD (FamInstDecl { fid_tycon = tc_name
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                         , fid_pats = HsWB { hswb_cts = tys, hswb_kvs = kv_names, hswb_tvs = tv_names }
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                         , fid_defn = defn })
  = WARN( not (null kv_names), ppr kv_names )   -- We have not yet dealt with kind 
                                                -- polymorphism in Template Haskell (sigh)
    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
            ; repTyDefn 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]
ruleBndrNames (RuleBndrSig n (HsWB { hswb_kvs = kvs, hswb_tvs = tvs })) 
  = 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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-------------------------------------------------------
-- 			Constructors
-------------------------------------------------------

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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 
       ; 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)
  | let (head_ty, tys) = splitHsAppTys res_ty []
  , Just _ <- is_hs_tyvar head_ty
  , 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 (HsBang True) ty) -> (unpackedName,  ty)
		   L _ (HsBangTy _ ty)             -> (isStrictName,  ty)
		   _                               -> (notStrictName, ty)
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-------------------------------------------------------
-- 			Deriving clause
-------------------------------------------------------

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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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	-- Singleton => Ok
	-- Empty     => Too hard, signature ignored
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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 _   (GenericSig nm _))     = failWithDs msg
  where msg = vcat  [ ptext (sLit "Illegal default signature for") <+> quotes (ppr nm)
                    , ptext (sLit "Default signatures are not supported by Template Haskell") ]

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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 _                             = return []

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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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-------------------------------------------------------
-- 			Types
-------------------------------------------------------
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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 tvs m
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  = do { freshNames <- mkGenSyms (hsLKiTyVarNames tvs)
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       ; term <- addBinds freshNames $ 
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	    	 do { kbs <- repList tyVarBndrTyConName mk_tv_bndr (hsQTvBndrs tvs `zip` freshNames)
	    	    ; m kbs }
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       ; wrapGenSyms freshNames term }
  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)
       	    -- Make fresh names for the ones that are not already in scope
            -- This makes things work for family declarations

       ; term <- addBinds freshNames $ 
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	    	 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
--
repTyVarBndrWithKind :: LHsTyVarBndr Name 
                     -> Core TH.Name -> DsM (Core TH.TyVarBndr)
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repTyVarBndrWithKind (L _ (UserTyVar {})) nm
  = 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 predQTyConName repLPred ctxt
		     repCtxt preds
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-- represent a type predicate
--
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repLPred :: LHsType Name -> DsM (Core TH.PredQ)
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repLPred (L _ p) = repPred p

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repPred :: HsType Name -> DsM (Core TH.PredQ)
repPred ty
  | Just (cls, tys) <- splitHsClassTy_maybe ty
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  = do
      cls1 <- lookupOcc cls
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      tys1 <- repList typeQTyConName repLTy tys
      repClassP cls1 tys1
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repPred (HsEqTy tyleft tyright)
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  = do
      tyleft1  <- repLTy tyleft
      tyright1 <- repLTy tyright
      repEqualP tyleft1 tyright1
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repPred ty
  = notHandled "Exotic predicate type" (ppr ty)
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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
		       repTvar tv1
  | isDataOcc occ = do tc1 <- lookupOcc n
                       repPromotedTyCon tc1
  | 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
repTy (HsPArrTy t)          = do
			        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
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 dflags <- getDynFlags
                          rep2 numTyLitName [mkIntExpr dflags i]
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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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-----------------------------------------------------------------------------
-- 		Splices
-----------------------------------------------------------------------------

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
	   Just (Splice e) -> do { e' <- dsExpr e
				 ; return (MkC e') }
	   _ -> pprPanic "HsSplice" (ppr n) }
			-- Should not happen; statically checked

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-----------------------------------------------------------------------------
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-- 		Expressions
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-----------------------------------------------------------------------------
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repLEs :: [LHsExpr Name] -> DsM (Core [TH.ExpQ])
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repLEs es = repList expQTyConName repLE es
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-- FIXME: some of these panics should be converted into proper error messages
--	  unless we can make sure that constructs, which are plainly not
--	  supported in TH already lead to error messages at an earlier stage
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repLE :: LHsExpr Name -> DsM (Core TH.ExpQ)
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repLE (L loc e) = putSrcSpanDs loc (repE e)
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repE :: HsExpr Name -> DsM (Core TH.ExpQ)
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repE (HsVar x)            =
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  do { mb_val <- dsLookupMetaEnv x
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     ; case mb_val of
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	Nothing	         -> do { str <- globalVar x
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			       ; repVarOrCon x str }
	Just (Bound y)   -> repVarOrCon x (coreVar y)
	Just (Splice e)  -> do { e' <- dsExpr e
			       ; return (MkC e') } }
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repE e@(HsIPVar _) = notHandled "Implicit parameters" (ppr e)
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	-- Remember, we're desugaring renamer output here, so
	-- HsOverlit can definitely occur
repE (HsOverLit l) = do { a <- repOverloadedLiteral l; repLit a }
repE (HsLit l)     = do { a <- repLiteral l;           repLit a }
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repE (HsLam (MatchGroup [m] _)) = repLambda m
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repE (HsLamCase _ (MatchGroup ms _))
                   = do { ms' <- mapM repMatchTup ms
                        ; repLamCase (nonEmptyCoreList ms') }
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repE (HsApp x y)   = do {a <- repLE x; b <- repLE y; repApp a b}
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repE (OpApp e1 op _ e2) =
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  do { arg1 <- repLE e1;
       arg2 <- repLE e2;
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       the_op <- repLE op ;
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       repInfixApp arg1 the_op arg2 }
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repE (NegApp x _)        = do
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			      a         <- repLE x
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			      negateVar <- lookupOcc negateName >>= repVar
			      negateVar `repApp` a
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repE (HsPar x)            = repLE x
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repE (SectionL x y)       = do { a <- repLE x; b <- repLE y; repSectionL a b }
repE (SectionR x y)       = do { a <- repLE x; b <- repLE y; repSectionR a b }
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repE (HsCase e (MatchGroup ms _))
                          = do { arg <- repLE e
                               ; ms2 <- mapM repMatchTup ms
                               ; repCaseE arg (nonEmptyCoreList ms2) }
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repE (HsIf _ x y z)         = do
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			      a <- repLE x
			      b <- repLE y
			      c <- repLE z
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			      repCond a b c
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repE (HsMultiIf _ alts)
  = do { (binds, alts') <- liftM unzip $ mapM repLGRHS alts
       ; expr' <- repMultiIf (nonEmptyCoreList alts')
       ; wrapGenSyms (concat binds) expr' }
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repE (HsLet bs e)         = do { (ss,ds) <- repBinds bs
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			       ; e2 <- addBinds ss (repLE e)
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			       ; z <- repLetE ds e2
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			       ; wrapGenSyms ss z }
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-- FIXME: I haven't got the types here right yet
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repE e@(HsDo ctxt sts _)
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 | case ctxt of { DoExpr -> True; GhciStmtCtxt -> True; _ -> False }
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 = do { (ss,zs) <- repLSts sts;
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        e'      <- repDoE (nonEmptyCoreList zs);
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        wrapGenSyms ss e' }
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 | ListComp <- ctxt
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 = do { (ss,zs) <- repLSts sts;
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        e'      <- repComp (nonEmptyCoreList zs);
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        wrapGenSyms ss e' }
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  | otherwise
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  = notHandled "mdo, monad comprehension and [: :]" (ppr e)
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repE (ExplicitList _ es) = do { xs <- repLEs es; repListExp xs }
repE e@(ExplicitPArr _ _) = notHandled "Parallel arrays" (ppr e)
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repE e@(ExplicitTuple es boxed)
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  | not (all tupArgPresent es) = notHandled "Tuple sections" (ppr e)
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  | isBoxed boxed              = do { xs <- repLEs [e | Present e <- es]; repTup xs }
  | otherwise                  = do { xs <- repLEs [e | Present e <- es]; repUnboxedTup xs }
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repE (RecordCon c _ flds)
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 = do { x <- lookupLOcc c;
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        fs <- repFields flds;
        repRecCon x fs }
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repE (RecordUpd e flds _ _ _)
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 = do { x <- repLE e;
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        fs <- repFields flds;
        repRecUpd x fs }
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repE (ExprWithTySig e ty) = do { e1 <- repLE e; t1 <- repLTy ty; repSigExp e1 t1 }
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repE (ArithSeq _ aseq) =
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  case aseq of
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    From e              -> do { ds1 <- repLE e; repFrom ds1 }
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    FromThen e1 e2      -> do
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		             ds1 <- repLE e1
			     ds2 <- repLE e2
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			     repFromThen ds1 ds2
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    FromTo   e1 e2      -> do
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			     ds1 <- repLE e1
			     ds2 <- repLE e2
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			     repFromTo ds1 ds2
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    FromThenTo e1 e2 e3 -> do
</