DsMeta.hs

-----------------------------------------------------------------------------
--
-- (c) The University of Glasgow 2006
--
-- 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.
--
-- 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).
-----------------------------------------------------------------------------

module DsMeta( dsBracket, 
	       templateHaskellNames, qTyConName, nameTyConName,
	       liftName, liftStringName, expQTyConName, patQTyConName, 
               decQTyConName, decsQTyConName, typeQTyConName,
	       decTyConName, typeTyConName, mkNameG_dName, mkNameG_vName, mkNameG_tcName,
	       quoteExpName, quotePatName, quoteDecName, quoteTypeName
	        ) where

#include "HsVersions.h"

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

import MatchLit
import DsMonad

import qualified Language.Haskell.TH as TH

import HsSyn
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.
import qualified OccName( isDataOcc, isVarOcc, isTcOcc, varName, tcName ) 

import Module
import Id
import Name hiding( isVarOcc, isTcOcc, varName, tcName ) 
import NameEnv
import TcType
import TyCon
import TysWiredIn
import CoreSyn
import MkCore
import CoreUtils
import SrcLoc
import Unique
import BasicTypes
import Outputable
import Bag
import FastString
import ForeignCall
import MonadUtils
import Util( equalLength )

import Data.Maybe
import Control.Monad
import Data.List

-----------------------------------------------------------------------------
dsBracket :: HsBracket Name -> [PendingSplice] -> DsM CoreExpr
-- Returns a CoreExpr of type TH.ExpQ
-- The quoted thing is parameterised over Name, even though it has
-- been type checked.  We don't want all those type decorations!

dsBracket brack splices
  = dsExtendMetaEnv new_bit (do_brack brack)
  where
    new_bit = mkNameEnv [(n, Splice (unLoc e)) | (n,e) <- splices]

    do_brack (VarBr n)   = do { MkC e1  <- lookupOcc n ; return e1 }
    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"

{- -------------- 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))
-}


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

repTopP :: LPat Name -> DsM (Core TH.PatQ)
repTopP pat = do { ss <- mkGenSyms (collectPatBinders pat) 
                 ; pat' <- addBinds ss (repLP pat)
                 ; wrapNongenSyms ss pat' }

repTopDs :: HsGroup Name -> DsM (Core (TH.Q [TH.Dec]))
repTopDs group
 = do { let { bndrs = hsGroupBinders group } ;
	ss <- mkGenSyms bndrs ;

	-- Bind all the names mainly to avoid repeated use of explicit strings.
	-- Thus	we get
	--	do { t :: String <- genSym "T" ;
	--	     return (Data t [] ...more t's... }
	-- The other important reason is that the output must mention
	-- only "T", not "Foo:T" where Foo is the current module

	
	decls <- addBinds ss (do {
			val_ds  <- rep_val_binds (hs_valds group) ;
			tycl_ds <- mapM repTyClD (concat (hs_tyclds group)) ;
			inst_ds <- mapM repInstD' (hs_instds group) ;
			for_ds <- mapM repForD (hs_fords group) ;
			-- more needed
			return (de_loc $ sort_by_loc $ val_ds ++ catMaybes tycl_ds ++ inst_ds ++ for_ds) }) ;

	decl_ty <- lookupType decQTyConName ;
	let { core_list = coreList' decl_ty decls } ;

	dec_ty <- lookupType decTyConName ;
	q_decs  <- repSequenceQ dec_ty core_list ;

	wrapNongenSyms ss q_decs
	-- Do *not* gensym top-level binders
      }


{- 	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" []] []

So in repTopDs we bring the binders into scope with mkGenSyms and addBinds.
And we use lookupOcc, rather than lookupBinder
in repTyClD and repC.

-}

repTyClD :: LTyClDecl Name -> DsM (Maybe (SrcSpan, Core TH.DecQ))

repTyClD tydecl@(L _ (TyFamily {}))
  = repTyFamily tydecl addTyVarBinds

repTyClD (L loc (TyData { tcdND = DataType, tcdCtxt = cxt, 
		          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
              ; cons1    <- mapM (repC (hsLTyVarNames tvs)) cons
      	      ; cons2    <- coreList conQTyConName cons1
      	      ; derivs1  <- repDerivs mb_derivs
	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
      	      ; repData cxt1 tc1 bndrs1 opt_tys2 cons2 derivs1 
              }
       ; return $ Just (loc, dec) 
       }

repTyClD (L loc (TyData { tcdND = NewType, tcdCtxt = cxt, 
		          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
              ; con1     <- repC (hsLTyVarNames tvs) con
      	      ; derivs1  <- repDerivs mb_derivs
	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
      	      ; 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
	      ; bndrs1   <- coreList tyVarBndrTyConName bndrs
	      ; repTySyn tc1 bndrs1 opt_tys2 ty1 
              }
       ; return (Just (loc, dec)) 
       }

repTyClD (L loc (ClassDecl { tcdCtxt = cxt, tcdLName = cls, 
		             tcdTyVars = tvs, tcdFDs = fds,
		             tcdSigs = sigs, tcdMeths = meth_binds, 
                             tcdATs = ats }))
  = 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)
	      ; bndrs1 <- coreList tyVarBndrTyConName bndrs
 	      ; repClass cxt1 cls1 bndrs1 fds1 decls1 
              }
       ; return $ Just (loc, dec) 
       }

-- Un-handled cases
repTyClD (L loc d) = putSrcSpanDs loc $
		     do { warnDs (hang ds_msg 4 (ppr d))
			; return Nothing }

-- 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, 
		               tcdKind = opt_kind }))
            tyVarBinds
  = do { tc1 <- lookupLOcc tc 		-- See note [Binders and occurrences] 
       ; dec <- tyVarBinds tvs $ \bndrs ->
           do { flav   <- repFamilyFlavour flavour
	      ; bndrs1 <- coreList tyVarBndrTyConName bndrs
              ; case opt_kind of 
                  Nothing -> repFamilyNoKind flav tc1 bndrs1
                  Just ki -> do { ki1 <- repKind ki 
                                ; repFamilyKind flav tc1 bndrs1 ki1
                                }
              }
       ; return $ Just (loc, dec)
       }
repTyFamily _ _ = panic "DsMeta.repTyFamily: internal error"

-- 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

-- 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
--
repInstD' :: LInstDecl Name -> DsM (SrcSpan, Core TH.DecQ)
repInstD' (L loc (InstDecl ty binds _ ats))	-- Ignore user pragmas for now
  = do { i <- 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
		do { cxt1 <- repContext cxt
		   ; inst_ty1 <- repPredTy (HsClassP cls tys)
		   ; ss <- mkGenSyms (collectHsBindsBinders binds)
		   ; binds1 <- addBinds ss (rep_binds binds)
                   ; ats1   <- repLAssocFamInst ats
		   ; decls1 <- coreList decQTyConName (ats1 ++ binds1)
		   ; decls2 <- wrapNongenSyms ss decls1
		   -- wrapNongenSyms: do not clone the class op names!
		   -- They must be called 'op' etc, not 'op34'
		   ; repInst cxt1 inst_ty1 (decls2)
                   }
	; return (loc, i)}
 where
   (tvs, cxt, cls, tys) = splitHsInstDeclTy (unLoc ty)

repForD :: Located (ForeignDecl Name) -> DsM (SrcSpan, Core TH.DecQ)
repForD (L loc (ForeignImport name typ (CImport cc s ch cis)))
 = do MkC name' <- lookupLOcc name
      MkC typ' <- repLTy typ
      MkC cc' <- repCCallConv cc
      MkC s' <- repSafety s
      cis' <- conv_cimportspec cis
      MkC str <- coreStringLit $ static
                              ++ unpackFS ch ++ " "
                              ++ cis'
      dec <- rep2 forImpDName [cc', s', str, name', typ']
      return (loc, dec)
 where
    conv_cimportspec (CLabel cls) = notHandled "Foreign label" (doubleQuotes (ppr cls))
    conv_cimportspec (CFunction DynamicTarget) = return "dynamic"
    conv_cimportspec (CFunction (StaticTarget fs _)) = return (unpackFS fs)
    conv_cimportspec CWrapper = return "wrapper"
    static = case cis of
                 CFunction (StaticTarget _ _) -> "static "
                 _ -> ""
repForD decl = notHandled "Foreign declaration" (ppr decl)

repCCallConv :: CCallConv -> DsM (Core TH.Callconv)
repCCallConv CCallConv = rep2 cCallName []
repCCallConv StdCallConv = rep2 stdCallName []
repCCallConv callConv    = notHandled "repCCallConv" (ppr callConv)

repSafety :: Safety -> DsM (Core TH.Safety)
repSafety PlayRisky = rep2 unsafeName []
repSafety PlayInterruptible = rep2 interruptibleName []
repSafety PlaySafe = rep2 safeName []

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

-------------------------------------------------------
-- 			Constructors
-------------------------------------------------------

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 }))
  = do { con1 <- lookupLOcc con 	-- See note [Binders and occurrences] 
       ; 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
         eq_pred = L loc (HsEqualP (L loc (HsTyVar data_tv)) ty)

    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

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

-------------------------------------------------------
-- 			Deriving clause
-------------------------------------------------------

repDerivs :: Maybe [LHsType Name] -> DsM (Core [TH.Name])
repDerivs Nothing = coreList nameTyConName []
repDerivs (Just ctxt)
  = do { strs <- mapM rep_deriv ctxt ; 
	 coreList nameTyConName strs }
  where
    rep_deriv :: LHsType Name -> DsM (Core TH.Name)
	-- Deriving clauses must have the simple H98 form
    rep_deriv (L _ (HsPredTy (HsClassP cls []))) = lookupOcc cls
    rep_deriv other = notHandled "Non-H98 deriving clause" (ppr other)


-------------------------------------------------------
--   Signatures in a class decl, or a group of bindings
-------------------------------------------------------

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

rep_sigs' :: [LSig Name] -> DsM [(SrcSpan, Core TH.DecQ)]
	-- We silently ignore ones we don't recognise
rep_sigs' sigs = do { sigs1 <- mapM rep_sig sigs ;
		     return (concat sigs1) }

rep_sig :: LSig Name -> DsM [(SrcSpan, Core TH.DecQ)]
	-- Singleton => Ok
	-- Empty     => Too hard, signature ignored
rep_sig (L loc (TypeSig nms ty))      = rep_proto nms ty loc
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") ]

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 []

rep_proto :: [Located Name] -> LHsType Name -> SrcSpan
          -> DsM [(SrcSpan, Core TH.DecQ)]
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)
              }

rep_inline :: Located Name 
           -> InlinePragma	-- Never defaultInlinePragma
           -> SrcSpan 
           -> DsM [(SrcSpan, Core TH.DecQ)]
rep_inline nm ispec loc
  = do { nm1 <- lookupLOcc nm
       ; ispec1 <- rep_InlinePrag ispec
       ; pragma <- repPragInl nm1 ispec1
       ; return [(loc, pragma)]
       }

rep_specialise :: Located Name -> LHsType Name -> InlinePragma -> SrcSpan 
               -> DsM [(SrcSpan, Core TH.DecQ)]
rep_specialise nm ty ispec loc
  = do { nm1 <- lookupLOcc nm
       ; ty1 <- repLTy ty
       ; pragma <- if isDefaultInlinePragma ispec
                   then repPragSpec nm1 ty1                  -- SPECIALISE
                   else do { ispec1 <- rep_InlinePrag ispec  -- SPECIALISE INLINE
                           ; repPragSpecInl nm1 ty1 ispec1 } 
       ; return [(loc, pragma)]
       }

-- Extract all the information needed to build a TH.InlinePrag
--
rep_InlinePrag :: InlinePragma	-- Never defaultInlinePragma
               -> DsM (Core TH.InlineSpecQ)
rep_InlinePrag (InlinePragma { inl_act = activation, inl_rule = match, inl_inline = inline })
  | Just (flag, phase) <- activation1 
  = repInlineSpecPhase inline1 match1 flag phase
  | otherwise
  = repInlineSpecNoPhase inline1 match1
  where
      match1      = coreBool (rep_RuleMatchInfo match)
      activation1 = rep_Activation activation
      inline1     = case inline of 
                       Inline -> coreBool True
 		       _other -> coreBool False
		       -- We have no representation for Inlinable

      rep_RuleMatchInfo FunLike = False
      rep_RuleMatchInfo ConLike = True

      rep_Activation NeverActive          = Nothing	-- We never have NOINLINE/AlwaysActive
      rep_Activation AlwaysActive         = Nothing	-- or            INLINE/NeverActive
      rep_Activation (ActiveBefore phase) = Just (coreBool False, 
                                                  MkC $ mkIntExprInt phase)
      rep_Activation (ActiveAfter phase)  = Just (coreBool True, 
                                                  MkC $ mkIntExprInt phase)


-------------------------------------------------------
-- 			Types
-------------------------------------------------------

-- 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 = 
         [LHsTyVarBndr Name]	                       -- the binders to be added
      -> ([Core TH.TyVarBndr] -> DsM (Core (TH.Q a)))  -- action in the ext env
      -> DsM (Core (TH.Q a))

-- 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
-- meta environment and gets the *new* names on Core-level as an argument
--
addTyVarBinds :: ProcessTyVarBinds a
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)

-- 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
    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)
repTyVarBndrWithKind (L _ (UserTyVar {})) nm
  = repPlainTV nm
repTyVarBndrWithKind (L _ (KindedTyVar _ ki)) nm
  = repKind ki >>= repKindedTV nm

-- represent a type context
--
repLContext :: LHsContext Name -> DsM (Core TH.CxtQ)
repLContext (L _ ctxt) = repContext ctxt

repContext :: HsContext Name -> DsM (Core TH.CxtQ)
repContext ctxt = do 
	            preds    <- mapM repLPred ctxt
		    predList <- coreList predQTyConName preds
		    repCtxt predList

-- represent a type predicate
--
repLPred :: LHsPred Name -> DsM (Core TH.PredQ)
repLPred (L _ p) = repPred p

repPred :: HsPred Name -> DsM (Core TH.PredQ)
repPred (HsClassP cls tys) 
  = do
      cls1 <- lookupOcc cls
      tys1 <- repLTys tys
      tys2 <- coreList typeQTyConName tys1
      repClassP cls1 tys2
repPred (HsEqualP tyleft tyright) 
  = do
      tyleft1  <- repLTy tyleft
      tyright1 <- repLTy tyright
      repEqualP tyleft1 tyright1
repPred p@(HsIParam _ _) = notHandled "Implicit parameter constraint" (ppr p)

repPredTy :: HsPred Name -> DsM (Core TH.TypeQ)
repPredTy (HsClassP cls tys) 
  = do
      tcon <- repTy (HsTyVar cls)
      tys1 <- repLTys tys
      repTapps tcon tys1
repPredTy _ = panic "DsMeta.repPredTy: unexpected equality: internal error"

-- yield the representation of a list of types
--
repLTys :: [LHsType Name] -> DsM [Core TH.TypeQ]
repLTys tys = mapM repLTy tys

-- represent a type
--
repLTy :: LHsType Name -> DsM (Core TH.TypeQ)
repLTy (L _ ty) = repTy ty

repTy :: HsType Name -> DsM (Core TH.TypeQ)
repTy (HsForAllTy _ tvs ctxt ty)  = 
  addTyVarBinds tvs $ \bndrs -> do
    ctxt1  <- repLContext ctxt
    ty1    <- repLTy ty
    bndrs1 <- coreList tyVarBndrTyConName bndrs
    repTForall bndrs1 ctxt1 ty1

repTy (HsTyVar n)
  | 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
repTy (HsTupleTy Boxed tys)	    = do
			        tys1 <- repLTys tys 
			        tcon <- repTupleTyCon (length tys)
			        repTapps tcon tys1
repTy (HsTupleTy Unboxed tys)	    = do
			        tys1 <- repLTys tys
			        tcon <- repUnboxedTupleTyCon (length tys)
			        repTapps tcon tys1
repTy (HsOpTy ty1 n ty2)    = repLTy ((nlHsTyVar (unLoc n) `nlHsAppTy` ty1) 
			    	   `nlHsAppTy` ty2)
repTy (HsParTy t)  	    = repLTy t
repTy (HsPredTy pred)       = repPredTy pred
repTy (HsKindSig t k)       = do
                                t1 <- repLTy t
                                k1 <- repKind k
                                repTSig t1 k1
repTy (HsSpliceTy splice _ _) = repSplice splice
repTy ty		      = notHandled "Exotic form of type" (ppr ty)

-- represent a kind
--
repKind :: Kind -> DsM (Core TH.Kind)
repKind ki
  = do { let (kis, ki') = splitKindFunTys ki
       ; kis_rep <- mapM repKind kis
       ; ki'_rep <- repNonArrowKind ki'
       ; foldrM repArrowK ki'_rep kis_rep
       }
  where
    repNonArrowKind k | isLiftedTypeKind k = repStarK
                      | otherwise          = notHandled "Exotic form of kind" 
                                                        (ppr k)

-----------------------------------------------------------------------------
-- 		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

-----------------------------------------------------------------------------
-- 		Expressions
-----------------------------------------------------------------------------

repLEs :: [LHsExpr Name] -> DsM (Core [TH.ExpQ])
repLEs es = do { es'  <- mapM repLE es ;
		 coreList expQTyConName es' }

-- 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
repLE :: LHsExpr Name -> DsM (Core TH.ExpQ)
repLE (L loc e) = putSrcSpanDs loc (repE e)

repE :: HsExpr Name -> DsM (Core TH.ExpQ)
repE (HsVar x)            =
  do { mb_val <- dsLookupMetaEnv x 
     ; case mb_val of
	Nothing	         -> do { str <- globalVar x
			       ; repVarOrCon x str }
	Just (Bound y)   -> repVarOrCon x (coreVar y)
	Just (Splice e)  -> do { e' <- dsExpr e
			       ; return (MkC e') } }
repE e@(HsIPVar _) = notHandled "Implicit parameters" (ppr e)

	-- 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 }
repE (HsLam (MatchGroup [m] _)) = repLambda m
repE (HsApp x y)   = do {a <- repLE x; b <- repLE y; repApp a b}

repE (OpApp e1 op _ e2) =
  do { arg1 <- repLE e1; 
       arg2 <- repLE e2; 
       the_op <- repLE op ;
       repInfixApp arg1 the_op arg2 } 
repE (NegApp x _)        = do
			      a         <- repLE x
			      negateVar <- lookupOcc negateName >>= repVar
			      negateVar `repApp` a
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 } 
repE (HsCase e (MatchGroup ms _)) = do { arg <- repLE e
				       ; ms2 <- mapM repMatchTup ms
				       ; repCaseE arg (nonEmptyCoreList ms2) }
repE (HsIf _ x y z)         = do
			      a <- repLE x
			      b <- repLE y
			      c <- repLE z
			      repCond a b c
repE (HsLet bs e)         = do { (ss,ds) <- repBinds bs
			       ; e2 <- addBinds ss (repLE e)
			       ; z <- repLetE ds e2
			       ; wrapGenSyms ss z }

-- FIXME: I haven't got the types here right yet
repE e@(HsDo ctxt sts _) 
 | case ctxt of { DoExpr -> True; GhciStmt -> True; _ -> False }
 = do { (ss,zs) <- repLSts sts; 
        e'      <- repDoE (nonEmptyCoreList zs);
        wrapGenSyms ss e' }

 | ListComp <- ctxt
 = do { (ss,zs) <- repLSts sts; 
        e'      <- repComp (nonEmptyCoreList zs);
        wrapGenSyms ss e' }

  | otherwise
  = notHandled "mdo, monad comprehension and [: :]" (ppr e)

repE (ExplicitList _ es) = do { xs <- repLEs es; repListExp xs }
repE e@(ExplicitPArr _ _) = notHandled "Parallel arrays" (ppr e)
repE e@(ExplicitTuple es boxed) 
  | not (all tupArgPresent es) = notHandled "Tuple sections" (ppr e)
  | isBoxed boxed              = do { xs <- repLEs [e | Present e <- es]; repTup xs }
  | otherwise                  = do { xs <- repLEs [e | Present e <- es]; repUnboxedTup xs }

repE (RecordCon c _ flds)
 = do { x <- lookupLOcc c;
        fs <- repFields flds;
        repRecCon x fs }
repE (RecordUpd e flds _ _ _)
 = do { x <- repLE e;
        fs <- repFields flds;
        repRecUpd x fs }

repE (ExprWithTySig e ty) = do { e1 <- repLE e; t1 <- repLTy ty; repSigExp e1 t1 }
repE (ArithSeq _ aseq) =
  case aseq of
    From e              -> do { ds1 <- repLE e; repFrom ds1 }
    FromThen e1 e2      -> do 
		             ds1 <- repLE e1
			     ds2 <- repLE e2
			     repFromThen ds1 ds2
    FromTo   e1 e2      -> do 
			     ds1 <- repLE e1
			     ds2 <- repLE e2
			     repFromTo ds1 ds2
    FromThenTo e1 e2 e3 -> do 
			     ds1 <- repLE e1
			     ds2 <- repLE e2
			     ds3 <- repLE e3
			     repFromThenTo ds1 ds2 ds3

repE (HsSpliceE splice)  = repSplice splice
repE e@(PArrSeq {})      = notHandled "Parallel arrays" (ppr e)
repE e@(HsCoreAnn {})    = notHandled "Core annotations" (ppr e)
repE e@(HsSCC {})        = notHandled "Cost centres" (ppr e)
repE e@(HsTickPragma {}) = notHandled "Tick Pragma" (ppr e)
repE e@(HsBracketOut {}) = notHandled "TH brackets" (ppr e)
repE e 			 = notHandled "Expression form" (ppr e)

-----------------------------------------------------------------------------
-- Building representations of auxillary structures like Match, Clause, Stmt, 

repMatchTup ::  LMatch Name -> DsM (Core TH.MatchQ) 
repMatchTup (L _ (Match [p] _ (GRHSs guards wheres))) =
  do { ss1 <- mkGenSyms (collectPatBinders p) 
     ; addBinds ss1 $ do {
     ; p1 <- repLP p
     ; (ss2,ds) <- repBinds wheres
     ; addBinds ss2 $ do {
     ; gs    <- repGuards guards
     ; match <- repMatch p1 gs ds
     ; wrapGenSyms (ss1++ss2) match }}}
repMatchTup _ = panic "repMatchTup: case alt with more than one arg"

repClauseTup ::  LMatch Name -> DsM (Core TH.ClauseQ)
repClauseTup (L _ (Match ps _ (GRHSs guards wheres))) =
  do { ss1 <- mkGenSyms (collectPatsBinders ps) 
     ; addBinds ss1 $ do {
       ps1 <- repLPs ps
     ; (ss2,ds) <- repBinds wheres
     ; addBinds ss2 $ do {
       gs <- repGuards guards
     ; clause <- repClause ps1 gs ds
     ; wrapGenSyms (ss1++ss2) clause }}}

repGuards ::  [LGRHS Name] ->  DsM (Core TH.BodyQ)
repGuards [L _ (GRHS [] e)]
  = do {a <- repLE e; repNormal a }
repGuards other 
  = do { zs <- mapM process other;
     let {(xs, ys) = unzip zs};
	 gd <- repGuarded (nonEmptyCoreList ys);
     wrapGenSyms (concat xs) gd }
  where 
    process :: LGRHS Name -> DsM ([GenSymBind], (Core (TH.Q (TH.Guard, TH.Exp))))
    process (L _ (GRHS [L _ (ExprStmt e1 _ _ _)] e2))
           = do { x <- repLNormalGE e1 e2;
                  return ([], x) }
    process (L _ (GRHS ss rhs))
           = do (gs, ss') <- repLSts ss
		rhs' <- addBinds gs $ repLE rhs
                g <- repPatGE (nonEmptyCoreList ss') rhs'
                return (gs, g)

repFields :: HsRecordBinds Name -> DsM (Core [TH.Q TH.FieldExp])
repFields (HsRecFields { rec_flds = flds })
  = do	{ fnames <- mapM lookupLOcc (map hsRecFieldId flds)
	; es <- mapM repLE (map hsRecFieldArg flds)
	; fs <- zipWithM repFieldExp fnames es
	; coreList fieldExpQTyConName fs }


-----------------------------------------------------------------------------
-- Representing Stmt's is tricky, especially if bound variables
-- shadow each other. Consider:  [| do { x <- f 1; x <- f x; g x } |]
-- 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.

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

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


-----------------------------------------------------------
--			Bindings
-----------------------------------------------------------

repBinds :: HsLocalBinds Name -> DsM ([GenSymBind], Core [TH.DecQ]) 
repBinds EmptyLocalBinds
  = do	{ core_list <- coreList decQTyConName []
	; return ([], core_list) }

repBinds b@(HsIPBinds _) = notHandled "Implicit parameters" (ppr b)

repBinds (HsValBinds decs)
 = do	{ let { bndrs = collectHsValBinders decs }
		-- 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
	; ss        <- mkGenSyms bndrs
	; prs       <- addBinds ss (rep_val_binds decs)
	; core_list <- coreList decQTyConName 
				(de_loc (sort_by_loc prs))
	; return (ss, core_list) }

rep_val_binds :: HsValBinds Name -> DsM [(SrcSpan, Core TH.DecQ)]
-- Assumes: all the binders of the binding are alrady in the meta-env
rep_val_binds (ValBindsOut binds sigs)
 = do { core1 <- rep_binds' (unionManyBags (map snd binds))
      ;	core2 <- rep_sigs' sigs
      ;	return (core1 ++ core2) }
rep_val_binds (ValBindsIn _ _)
 = panic "rep_val_binds: ValBindsIn"

rep_binds :: LHsBinds Name -> DsM [Core TH.DecQ]
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)

rep_bind :: LHsBind Name -> DsM (SrcSpan, Core TH.DecQ)
-- Assumes: all the binders of the binding are alrady in the meta-env

-- 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
rep_bind (L loc (FunBind { fun_id = fn, 
			   fun_matches = MatchGroup [L _ (Match [] _ (GRHSs guards wheres))] _ }))
 = do { (ss,wherecore) <- repBinds wheres
	; guardcore <- addBinds ss (repGuards guards)
	; fn'  <- lookupLBinder fn
	; p    <- repPvar fn'
	; ans  <- repVal p guardcore wherecore
	; ans' <- wrapGenSyms ss ans
	; return (loc, ans') }

rep_bind (L loc (FunBind { fun_id = fn, fun_matches = MatchGroup ms _ }))
 =   do { ms1 <- mapM repClauseTup ms
	; fn' <- lookupLBinder fn
        ; ans <- repFun fn' (nonEmptyCoreList ms1)