DsMeta.hs 88.7 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, 
	       templateHaskellNames, qTyConName, nameTyConName,
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	       liftName, liftStringName, expQTyConName, patQTyConName, 
               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 ) 
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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 )
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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
import FastString
import ForeignCall
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import MonadUtils
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import Util( equalLength )
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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)
repTopP pat = do { ss <- mkGenSyms (collectPatBinders pat) 
                 ; 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 { 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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			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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			for_ds <- mapM repForD (hs_fords group) ;
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			-- more needed
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			return (de_loc $ sort_by_loc $ 
                                val_ds ++ catMaybes tycl_ds
                                       ++ catMaybes inst_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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{- 	Note [Binders and occurrences]
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:
	data T = MkT 
	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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repTyClD :: LTyClDecl Name -> DsM (Maybe (SrcSpan, Core TH.DecQ))
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repTyClD tydecl@(L _ (TyFamily {}))
  = repTyFamily tydecl addTyVarBinds

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repTyClD (L loc (TyData { tcdND = DataType, tcdCtxt = cxt, 
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		          tcdLName = tc, tcdTyVars = tvs, tcdTyPats = opt_tys,
		          tcdCons = cons, tcdDerivs = mb_derivs }))
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- addTyVarBinds tvs $ \bndrs -> 
           do { cxt1     <- repLContext cxt
              ; opt_tys1 <- maybeMapM repLTys opt_tys   -- only for family insts
              ; opt_tys2 <- maybeMapM (coreList typeQTyConName) opt_tys1
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              ; cons1    <- mapM (repC (hsLTyVarNames tvs)) cons
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      	      ; cons2    <- coreList conQTyConName cons1
      	      ; derivs1  <- repDerivs mb_derivs
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	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
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      	      ; repData cxt1 tc1 bndrs1 opt_tys2 cons2 derivs1 
              }
       ; return $ Just (loc, dec) 
       }
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repTyClD (L loc (TyData { tcdND = NewType, tcdCtxt = cxt, 
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		          tcdLName = tc, tcdTyVars = tvs, tcdTyPats = opt_tys,
		          tcdCons = [con], tcdDerivs = mb_derivs }))
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- addTyVarBinds tvs $ \bndrs -> 
           do { cxt1     <- repLContext cxt
              ; opt_tys1 <- maybeMapM repLTys opt_tys   -- only for family insts
              ; opt_tys2 <- maybeMapM (coreList typeQTyConName) opt_tys1
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              ; con1     <- repC (hsLTyVarNames tvs) con
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      	      ; derivs1  <- repDerivs mb_derivs
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	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
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      	      ; repNewtype cxt1 tc1 bndrs1 opt_tys2 con1 derivs1
              }
       ; return $ Just (loc, dec) 
       }

repTyClD (L loc (TySynonym { tcdLName = tc, tcdTyVars = tvs, tcdTyPats = opt_tys,
                             tcdSynRhs = ty }))
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- addTyVarBinds tvs $ \bndrs -> 
           do { opt_tys1 <- maybeMapM repLTys opt_tys   -- only for family insts
              ; opt_tys2 <- maybeMapM (coreList typeQTyConName) opt_tys1
	      ; ty1      <- repLTy ty
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	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
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	      ; repTySyn tc1 bndrs1 opt_tys2 ty1 
              }
       ; 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
              ; ats1   <- repLAssocFamilys ats
 	      ; decls1 <- coreList decQTyConName (ats1 ++ sigs1 ++ binds1)
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	      ; bndrs1 <- coreList tyVarBndrTyConName bndrs
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 	      ; repClass cxt1 cls1 bndrs1 fds1 decls1 
              }
       ; 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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-- The type variables in the head of families are treated differently when the
-- family declaration is associated.  In that case, they are usage, not binding
-- occurences.
--
repTyFamily :: LTyClDecl Name 
            -> ProcessTyVarBinds TH.Dec
            -> DsM (Maybe (SrcSpan, Core TH.DecQ))
repTyFamily (L loc (TyFamily { tcdFlavour = flavour,
		               tcdLName = tc, tcdTyVars = tvs, 
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		               tcdKind = opt_kind }))
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            tyVarBinds
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- tyVarBinds tvs $ \bndrs ->
           do { flav   <- repFamilyFlavour flavour
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	      ; bndrs1 <- coreList tyVarBndrTyConName bndrs
              ; case opt_kind of 
                  Nothing -> repFamilyNoKind flav tc1 bndrs1
                  Just ki -> do { ki1 <- repKind ki 
                                ; repFamilyKind flav tc1 bndrs1 ki1
                                }
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              }
       ; return $ Just (loc, dec)
       }
repTyFamily _ _ = panic "DsMeta.repTyFamily: internal error"

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-- represent fundeps
--
repLFunDeps :: [Located (FunDep Name)] -> DsM (Core [TH.FunDep])
repLFunDeps fds = do fds' <- mapM repLFunDep fds
                     fdList <- coreList funDepTyConName fds'
                     return fdList

repLFunDep :: Located (FunDep Name) -> DsM (Core TH.FunDep)
repLFunDep (L _ (xs, ys)) = do xs' <- mapM lookupBinder xs
                               ys' <- mapM lookupBinder ys
                               xs_list <- coreList nameTyConName xs'
                               ys_list <- coreList nameTyConName ys'
                               repFunDep xs_list ys_list
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-- represent family declaration flavours
--
repFamilyFlavour :: FamilyFlavour -> DsM (Core TH.FamFlavour)
repFamilyFlavour TypeFamily = rep2 typeFamName []
repFamilyFlavour DataFamily = rep2 dataFamName []

-- represent associated family declarations
--
repLAssocFamilys :: [LTyClDecl Name] -> DsM [Core TH.DecQ]
repLAssocFamilys = mapM repLAssocFamily
  where
    repLAssocFamily tydecl@(L _ (TyFamily {})) 
      = liftM (snd . fromJust) $ repTyFamily tydecl lookupTyVarBinds
    repLAssocFamily tydecl
      = failWithDs msg
      where
        msg = ptext (sLit "Illegal associated declaration in class:") <+> 
              ppr tydecl

-- represent associated family instances
--
repLAssocFamInst :: [LTyClDecl Name] -> DsM [Core TH.DecQ]
repLAssocFamInst = liftM de_loc . mapMaybeM repTyClD

-- represent instance declarations
--
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repInstD :: LInstDecl Name -> DsM (Maybe (SrcSpan, Core TH.DecQ))
repInstD (L loc (FamInstDecl fi_decl))
  = repTyClD (L loc fi_decl)


repInstD (L loc (ClsInstDecl ty binds _ ats))	-- Ignore user pragmas for now
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  = do { dec <- addTyVarBinds tvs $ \_ ->
	    -- We must bring the type variables into scope, so their
	    -- occurrences don't fail, even though the binders don't 
            -- 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 cls)
               ; cls_tys <- repLTys tys
               ; inst_ty1 <- repTapps cls_tcon cls_tys
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               ; binds1 <- rep_binds binds
               ; ats1 <- repLAssocFamInst ats
               ; decls <- coreList decQTyConName (ats1 ++ binds1)
               ; repInst cxt1 inst_ty1 decls }
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       ; return (Just (loc, dec)) }
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 where
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   Just (tvs, cxt, cls, tys) = splitHsInstDeclTy_maybe (unLoc ty)
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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 ch 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
                              ++ unpackFS ch ++ " "
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                              ++ 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 _)) = return (unpackFS fs)
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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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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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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)
repC _ (L _ (ConDecl { con_name = con, con_qvars = [], con_cxt = L _ []
                       , con_details = details, con_res = ResTyH98 }))
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  = do { con1 <- lookupLOcc con 	-- See note [Binders and occurrences] 
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       ; repConstr con1 details  }
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
       ; let ex_tvs = [ tv | tv <- con_tvs, not (hsLTyVarName tv `in_subst` con_tv_subst)]
       ; 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
    do { con1      <- lookupLOcc con 	-- See note [Binders and occurrences] 
       ; c'        <- repConstr con1 details
       ; ctxt'     <- repContext (eq_ctxt ++ ctxt)
       ; ex_bndrs' <- coreList tyVarBndrTyConName ex_bndrs
       ; rep2 forallCName [unC ex_bndrs', unC ctxt', unC c'] } }

in_subst :: Name -> [(Name,Name)] -> Bool
in_subst _ []          = False
in_subst n ((n',_):ns) = n==n' || in_subst n ns

mkGadtCtxt :: [Name]		-- Tyvars of the data type
           -> ResType Name
	   -> DsM (HsContext Name, [(Name,Name)])
-- Given a data type in GADT syntax, figure out the equality 
-- context, so that we can represent it with an explicit 
-- equality context, because that is the only way to express
-- the GADT in TH syntax
--
-- Example:   
-- 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)
--   returns 
--     (b~[e], c~e), [d->a] 
-- 
-- 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))

  | otherwise 
  = failWithDs (ptext (sLit "Malformed constructor result type") <+> ppr res_ty)
  where
    go cxt subst [] = (cxt, subst)
    go cxt subst ((data_tv, ty) : rest)
       | Just con_tv <- is_hs_tyvar ty
       , isTyVarName con_tv
       , not (in_subst con_tv subst)
       = 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 
  MkC s <- rep2 str []
  MkC t <- repLTy ty'
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  rep2 strictTypeName [s, t]
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  where 
    (str, ty') = case ty of
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		   L _ (HsBangTy HsUnpack 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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  = do { strs <- mapM rep_deriv ctxt ; 
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	 coreList nameTyConName strs }
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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))      = rep_proto nms ty loc
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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
rep_sig _                             = return []

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rep_proto :: [Located Name] -> LHsType Name -> SrcSpan
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          -> DsM [(SrcSpan, Core TH.DecQ)]
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rep_proto nms ty loc
  = mapM f nms
  where
    f nm = do { nm1 <- lookupLOcc nm
              ; ty1 <- repLTy ty
              ; sig <- repProto nm1 ty1
              ; return (loc, sig)
              }
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rep_inline :: Located Name 
           -> InlinePragma	-- Never defaultInlinePragma
           -> SrcSpan 
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           -> DsM [(SrcSpan, Core TH.DecQ)]
rep_inline nm ispec loc
  = do { nm1 <- lookupLOcc nm
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       ; ispec1 <- rep_InlinePrag ispec
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       ; pragma <- repPragInl nm1 ispec1
       ; 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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       ; pragma <- if isDefaultInlinePragma ispec
                   then repPragSpec nm1 ty1                  -- SPECIALISE
                   else do { ispec1 <- rep_InlinePrag ispec  -- SPECIALISE INLINE
                           ; repPragSpecInl nm1 ty1 ispec1 } 
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       ; return [(loc, pragma)]
       }
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-- Extract all the information needed to build a TH.InlinePrag
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--
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rep_InlinePrag :: InlinePragma	-- Never defaultInlinePragma
               -> DsM (Core TH.InlineSpecQ)
rep_InlinePrag (InlinePragma { inl_act = activation, inl_rule = match, inl_inline = inline })
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  | Just (flag, phase) <- activation1 
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  = repInlineSpecPhase inline1 match1 flag phase
  | otherwise
  = repInlineSpecNoPhase inline1 match1
  where
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      match1      = coreBool (rep_RuleMatchInfo match)
      activation1 = rep_Activation activation
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      inline1     = case inline of 
                       Inline -> coreBool True
 		       _other -> coreBool False
		       -- We have no representation for Inlinable
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      rep_RuleMatchInfo FunLike = False
      rep_RuleMatchInfo ConLike = True

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      rep_Activation NeverActive          = Nothing	-- We never have NOINLINE/AlwaysActive
      rep_Activation AlwaysActive         = Nothing	-- or            INLINE/NeverActive
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      rep_Activation (ActiveBefore phase) = Just (coreBool False, 
                                                  MkC $ mkIntExprInt phase)
      rep_Activation (ActiveAfter phase)  = Just (coreBool True, 
                                                  MkC $ mkIntExprInt phase)
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-------------------------------------------------------
-- 			Types
-------------------------------------------------------
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-- We process type variable bindings in two ways, either by generating fresh
-- names or looking up existing names.  The difference is crucial for type
-- families, depending on whether they are associated or not.
--
type ProcessTyVarBinds a = 
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         [LHsTyVarBndr Name]	                       -- the binders to be added
      -> ([Core TH.TyVarBndr] -> DsM (Core (TH.Q a)))  -- action in the ext env
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      -> 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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--
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addTyVarBinds :: ProcessTyVarBinds a
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addTyVarBinds tvs m
  = do { freshNames <- mkGenSyms (hsLTyVarNames tvs)
       ; term <- addBinds freshNames $ 
	    	 do { kindedBndrs <- mapM mk_tv_bndr (tvs `zip` freshNames)
	    	    ; m kindedBndrs }
       ; wrapGenSyms freshNames term }
  where
    mk_tv_bndr (tv, (_,v)) = repTyVarBndrWithKind tv (coreVar v)
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-- Look up a list of type variables; the computations passed as the second 
-- argument gets the *new* names on Core-level as an argument
--
lookupTyVarBinds :: ProcessTyVarBinds a
lookupTyVarBinds tvs m =
  do
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    let names       = hsLTyVarNames tvs
        mkWithKinds = map repTyVarBndrWithKind tvs
    bndrs       <- mapM lookupBinder names 
    kindedBndrs <- zipWithM ($) mkWithKinds bndrs
    m kindedBndrs

-- 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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  = repKind 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 
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	            preds    <- mapM repLPred ctxt
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		    predList <- coreList predQTyConName preds
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		    repCtxt predList
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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
      tys1 <- repLTys tys
      tys2 <- coreList typeQTyConName tys1
      repClassP cls1 tys2
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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)
repTy (HsForAllTy _ tvs ctxt ty)  = 
  addTyVarBinds tvs $ \bndrs -> do
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    ctxt1  <- repLContext ctxt
    ty1    <- repLTy ty
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    bndrs1 <- coreList tyVarBndrTyConName bndrs
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    repTForall bndrs1 ctxt1 ty1
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repTy (HsTyVar n)
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  | isTvOcc (nameOccName n) = do 
			        tv1 <- lookupTvOcc n
			        repTvar tv1
  | otherwise		    = do 
			        tc1 <- lookupOcc n
			        repNamedTyCon tc1
repTy (HsAppTy f a)         = do 
			        f1 <- repLTy f
			        a1 <- repLTy a
			        repTapp f1 a1
repTy (HsFunTy f a)         = do 
			        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 
                                 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
                                k1 <- repKind k
                                repTSig t1 k1
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repTy (HsSpliceTy splice _ _) = repSplice splice
repTy ty		      = notHandled "Exotic form of type" (ppr ty)
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-- represent a kind
--
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repKind :: LHsKind Name -> DsM (Core TH.Kind)
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repKind ki
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  = do { let (kis, ki') = splitHsFunType ki
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       ; kis_rep <- mapM repKind kis
       ; ki'_rep <- repNonArrowKind ki'
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       ; foldrM repArrowK ki'_rep kis_rep
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       }
  where
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    repNonArrowKind (L _ (HsTyVar name)) | name == liftedTypeKindTyConName = repStarK
    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
repSplice (HsSplice n _) 
 = 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])
repLEs es = do { es'  <- mapM repLE es ;
		 coreList expQTyConName 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)            =
  do { mb_val <- dsLookupMetaEnv x 
     ; 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 (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; 
       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
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
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; GhciStmt -> 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
    FromTo   e1 e2      -> do 
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			     ds1 <- repLE e1
			     ds2 <- repLE e2
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			     repFromTo ds1 ds2
    FromThenTo e1 e2 e3 -> do 
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			     ds1 <- repLE e1
			     ds2 <- repLE e2
			     ds3 <- repLE e3
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			     repFromThenTo ds1 ds2 ds3
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repE (HsSpliceE splice)  = repSplice splice
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repE e@(PArrSeq {})      = notHandled "Parallel arrays" (ppr e)
repE e@(HsCoreAnn {})    = notHandled "Core annotations" (ppr e)
repE e@(HsSCC {})        = notHandled "Cost centres" (ppr e)
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repE e@(HsTickPragma {}) = notHandled "Tick Pragma" (ppr e)
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repE e@(HsBracketOut {}) = notHandled "TH brackets" (ppr e)
repE e 			 = notHandled "Expression form" (ppr e)
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-----------------------------------------------------------------------------
-- Building representations of auxillary structures like Match, Clause, Stmt, 

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repMatchTup ::  LMatch Name -> DsM (Core TH.MatchQ) 
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repMatchTup (L _ (Match [p] _ (GRHSs guards wheres))) =
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  do { ss1 <- mkGenSyms (collectPatBinders p) 
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     ; addBinds ss1 $ do {
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     ; p1 <- repLP p
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     ; (ss2,ds) <- repBinds wheres
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     ; addBinds ss2 $ do {
     ; gs    <- repGuards guards
     ; match <- repMatch p1 gs ds
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     ; wrapGenSyms (ss1++ss2) match }}}
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repMatchTup _ = panic "repMatchTup: case alt with more than one arg"
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repClauseTup ::  LMatch Name -> DsM (Core TH.ClauseQ)
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repClauseTup (L _ (Match ps _ (GRHSs guards wheres))) =
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  do { ss1 <- mkGenSyms (collectPatsBinders ps) 
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     ; addBinds ss1 $ do {
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       ps1 <- repLPs ps
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     ; (ss2,ds) <- repBinds wheres
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     ; addBinds ss2 $ do {
       gs <- repGuards guards
     ; clause <- repClause ps1 gs ds
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     ; wrapGenSyms (ss1++ss2) clause }}}
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repGuards ::  [LGRHS Name] ->  DsM (Core TH.BodyQ)
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repGuards [L _ (GRHS [] e)]
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  = do {a <- repLE e; repNormal a }
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repGuards other 
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  = do { zs <- mapM process other;
     let {(xs, ys) = unzip zs};
	 gd <- repGuarded (nonEmptyCoreList ys);
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     wrapGenSyms (concat xs) gd }
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  where 
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    process :: LGRHS Name -> DsM ([GenSymBind], (Core (TH.Q (TH.Guard, TH.Exp))))
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    process (L _ (GRHS [L _ (ExprStmt e1 _ _ _)] e2))
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           = do { x <- repLNormalGE e1 e2;
                  return ([], x) }
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    process (L _ (GRHS ss rhs))
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           = do (gs, ss') <- repLSts ss
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		rhs' <- addBinds gs $ repLE rhs
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                g <- repPatGE (nonEmptyCoreList ss') rhs'
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                return (gs, g)
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repFields :: HsRecordBinds Name -> DsM (Core [TH.Q TH.FieldExp])
repFields (HsRecFields { rec_flds = flds })
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  = do	{ fnames <- mapM lookupLOcc (map hsRecFieldId flds)
	; es <- mapM repLE (map hsRecFieldArg flds)
	; fs <- zipWithM repFieldExp fnames es
	; coreList fieldExpQTyConName fs }
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-----------------------------------------------------------------------------
-- Representing Stmt's is tricky, especially if bound variables
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-- shadow each other. Consider:  [| do { x <- f 1; x <- f x; g x } |]
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-- First gensym new names for every variable in any of the patterns.
-- both static (x'1 and x'2), and dynamic ((gensym "x") and (gensym "y"))
-- if variables didn't shaddow, the static gensym wouldn't be necessary
-- and we could reuse the original names (x and x).
--
-- do { x'1 <- gensym "x"
--    ; x'2 <- gensym "x"   
--    ; doE [ BindSt (pvar x'1) [| f 1 |]
--          , BindSt (pvar x'2) [| f x |] 
--          , NoBindSt [| g x |] 
--          ]
--    }

-- The strategy is to translate a whole list of do-bindings by building a
-- bigger environment, and a bigger set of meta bindings 
-- (like:  x'1 <- gensym "x" ) and then combining these with the translations
-- of the expressions within the Do
      
-----------------------------------------------------------------------------
-- The helper function repSts computes the translation of each sub expression
-- and a bunch of prefix bindings denoting the dynamic renaming.

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repLSts :: [LStmt Name] -> DsM ([GenSymBind], [Core TH.StmtQ])
repLSts stmts = repSts (map unLoc stmts)

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repSts :: [Stmt Name] -> DsM ([GenSymBind], [Core TH.StmtQ])
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repSts (BindStmt p e _ _ : ss) =
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      ; addBinds ss1 $ do {
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      ; p1 <- repLP p; 
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      ; (ss2,zs) <- repSts ss
      ; z <- repBindSt p1 e2
      ; return (ss1++ss2, z : zs) }}
repSts (LetStmt bs : ss) =
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      ; z <- repLetSt ds
      ; (ss2,zs) <- addBinds ss1 (repSts ss)
      ; return (ss1++ss2, z : zs) } 
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repSts (ExprStmt e _ _ _ : ss) =       
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   do { e2 <- repLE e
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      ; z <- repNoBindSt e2 
      ; (ss2,zs) <- repSts ss
      ; return (ss2, z : zs) }
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repSts [LastStmt e _] 
  = do { e2 <- repLE e
       ; z <- repNoBindSt e2
       ; return ([], [z]) }
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repSts []    = return ([],[])
repSts other = notHandled "Exotic statement" (ppr other)
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-----------------------------------------------------------
--			Bindings
-----------------------------------------------------------
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repBinds :: HsLocalBinds Name -> DsM ([GenSymBind], Core [TH.DecQ]) 
repBinds EmptyLocalBinds
  = do	{ core_list <- coreList decQTyConName []
	; return ([], core_list) }

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repBinds b@(HsIPBinds _) = notHandled "Implicit parameters" (ppr b)
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repBinds (HsValBinds decs)
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 = do	{ let { bndrs = collectHsValBinders decs }
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		-- No need to worrry about detailed scopes within
		-- the binding group, because we are talking Names
		-- here, so we can safely treat it as a mutually 
		-- recursive group
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	; ss        <- mkGenSyms bndrs
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	; prs       <- addBinds ss (rep_val_binds decs)
	; core_list <- coreList decQTyConName 
				(de_loc (sort_by_loc prs))
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	; return (ss, core_list) }
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rep_val_binds :: HsValBinds Name -> DsM [(SrcSpan, Core TH.DecQ)]
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-- Assumes: all the binders of the binding are alrady in the meta-env
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rep_val_binds (ValBindsOut binds sigs)
 = do { core1 <- rep_binds' (unionManyBags (map snd binds))
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      ;	core2 <- rep_sigs' sigs
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      ;	return (core1 ++ core2) }
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rep_val_binds (ValBindsIn _ _)
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 = panic "rep_val_binds: ValBindsIn"
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rep_binds :: LHsBinds Name -> DsM [Core TH.DecQ]
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rep_binds binds = do { binds_w_locs <- rep_binds' binds
		     ; return (de_loc (sort_by_loc binds_w_locs)) }

rep_binds' :: LHsBinds Name -> DsM [(SrcSpan, Core TH.DecQ)]
rep_binds' binds = mapM rep_bind (bagToList binds)
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rep_bind :: LHsBind Name -> DsM (SrcSpan, Core TH.DecQ)
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-- Assumes: all the binders of the binding are alrady in the meta-env
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-- Note GHC treats declarations of a variable (not a pattern) 
-- e.g.  x = g 5 as a Fun MonoBinds. This is indicated by a single match 
-- with an empty list of patterns
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rep_bind (L loc (FunBind { fun_id = fn, 
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			   fun_matches = MatchGroup [L _ (Match [] _ (GRHSs guards wheres))] _ }))
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 = do { (ss,wherecore) <- repBinds wheres
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	; guardcore <- addBinds ss (repGuards guards)
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	; fn'  <- lookupLBinder fn
	; p    <- repPvar fn'
	; ans  <- repVal p guardcore wherecore
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	; ans' <- wrapGenSyms ss ans
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	; return (loc, ans') }
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rep_bind (L loc (FunBind { fun_id = fn, fun_matches = MatchGroup ms _ }))
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 =   do { ms1 <- mapM repClauseTup ms