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).
-----------------------------------------------------------------------------

{-# OPTIONS -w #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details

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

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

import MatchLit
import DsUtils
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

import Module
import Id
import Name
import NameEnv
import TcType
import TyCon
import TysWiredIn
import CoreSyn
import CoreUtils
import SrcLoc
import PackageConfig
import Unique
import BasicTypes
import Outputable
import Bag
import FastString
import ForeignCall

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  <- repLP p     ; return p1 }
    do_brack (TypBr t)  = do { MkC t1  <- repLTy t    ; return t1 }
    do_brack (DecBr ds) = do { MkC ds1 <- repTopDs ds ; return ds1 }

{- -------------- 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
-------------------------------------------------------

repTopDs :: HsGroup Name -> DsM (Core (TH.Q [TH.Dec]))
repTopDs group
 = do { let { bndrs = map unLoc (groupBinders 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 (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
      }

groupBinders (HsGroup { hs_valds = val_decls, hs_tyclds = tycl_decls,
			hs_fords = foreign_decls })
-- Collect the binders of a Group
  = collectHsValBinders val_decls ++
    [n | d <- tycl_decls, n <- tyClDeclNames (unLoc d)] ++
    [n | L _ (ForeignImport n _ _) <- foreign_decls]


{- 	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 (L loc (TyData { tcdND = DataType, tcdCtxt = cxt, 
		    tcdLName = tc, tcdTyVars = tvs, 
		    tcdCons = cons, tcdDerivs = mb_derivs }))
 = do { tc1 <- lookupLOcc tc ;		-- See note [Binders and occurrences] 
        dec <- addTyVarBinds tvs $ \bndrs -> do {
      	       cxt1    <- repLContext cxt ;
               cons1   <- mapM repC cons ;
      	       cons2   <- coreList conQTyConName cons1 ;
      	       derivs1 <- repDerivs mb_derivs ;
	       bndrs1  <- coreList nameTyConName bndrs ;
      	       repData cxt1 tc1 bndrs1 cons2 derivs1 } ;
        return $ Just (loc, dec) }

repTyClD (L loc (TyData { tcdND = NewType, tcdCtxt = cxt, 
		    tcdLName = tc, tcdTyVars = tvs, 
		    tcdCons = [con], tcdDerivs = mb_derivs }))
 = do { tc1 <- lookupLOcc tc ;		-- See note [Binders and occurrences] 
        dec <- addTyVarBinds tvs $ \bndrs -> do {
      	       cxt1   <- repLContext cxt ;
               con1   <- repC con ;
      	       derivs1 <- repDerivs mb_derivs ;
	       bndrs1  <- coreList nameTyConName bndrs ;
      	       repNewtype cxt1 tc1 bndrs1 con1 derivs1 } ;
        return $ Just (loc, dec) }

repTyClD (L loc (TySynonym { tcdLName = tc, tcdTyVars = tvs, tcdSynRhs = ty }))
 = do { tc1 <- lookupLOcc tc ;		-- See note [Binders and occurrences] 
        dec <- addTyVarBinds tvs $ \bndrs -> do {
	       ty1     <- repLTy ty ;
	       bndrs1  <- coreList nameTyConName bndrs ;
	       repTySyn tc1 bndrs1 ty1 } ;
 	return (Just (loc, dec)) }

repTyClD (L loc (ClassDecl { tcdCtxt = cxt, tcdLName = cls, 
		      tcdTyVars = tvs, 
		      tcdFDs = fds,
		      tcdSigs = sigs, tcdMeths = meth_binds }))
 = 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;
 		  decls1 <- coreList decQTyConName (sigs1 ++ binds1) ;
	          bndrs1 <- coreList nameTyConName 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 }

-- 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

repInstD' (L loc (InstDecl ty binds _ _))		-- Ignore user pragmas for now
 = do	{ i <- addTyVarBinds tvs $ \tv_bndrs ->
		-- 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 <- repPred (HsClassP cls tys)
		   ; ss <- mkGenSyms (collectHsBindBinders binds)
		   ; binds1 <- addBinds ss (rep_binds binds)
		   ; decls1 <- coreList decQTyConName 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 cn 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 ++ " "
                              ++ unpackFS cn ++ " "
                              ++ 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 []

repSafety :: Safety -> DsM (Core TH.Safety)
repSafety PlayRisky = rep2 unsafeName []
repSafety (PlaySafe False) = rep2 safeName []
repSafety (PlaySafe True) = rep2 threadsafeName []

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

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

repC :: LConDecl Name -> DsM (Core TH.ConQ)
repC (L loc (ConDecl con expl [] (L _ []) details ResTyH98 _))
  = do { con1 <- lookupLOcc con ;		-- See note [Binders and occurrences] 
	 repConstr con1 details }
repC (L loc (ConDecl con expl tvs (L cloc ctxt) details ResTyH98 doc))
  = do { addTyVarBinds tvs $ \bndrs -> do {
             c' <- repC (L loc (ConDecl con expl [] (L cloc []) details ResTyH98 doc));
             ctxt' <- repContext ctxt;
             bndrs' <- coreList nameTyConName bndrs;
             rep2 forallCName [unC bndrs', unC ctxt', unC c']
         }
       }
repC (L loc con_decl)		-- GADTs
  = putSrcSpanDs loc $
    notHandled "GADT declaration" (ppr con_decl) 

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 _ ty) -> (isStrictName,  ty)
		   other	       -> (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 nm ty)) = rep_proto nm ty loc
rep_sig other		        = return []

rep_proto :: Located Name -> LHsType Name -> SrcSpan -> DsM [(SrcSpan, Core TH.DecQ)]
rep_proto nm ty loc = do { nm1 <- lookupLOcc nm ; 
		       ty1 <- repLTy ty ; 
		       sig <- repProto nm1 ty1 ;
		       return [(loc, sig)] }


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

-- 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 :: [LHsTyVarBndr Name]	         -- the binders to be added
	      -> ([Core TH.Name] -> DsM (Core (TH.Q a))) -- action in the ext env
	      -> DsM (Core (TH.Q a))
addTyVarBinds tvs m =
  do
    let names = map (hsTyVarName.unLoc) tvs
    freshNames <- mkGenSyms names
    term       <- addBinds freshNames $ do
		    bndrs <- mapM lookupBinder names 
		    m bndrs
    wrapGenSyns freshNames term

-- 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 typeQTyConName preds
		    repCtxt predList

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

repPred :: HsPred Name -> DsM (Core TH.TypeQ)
repPred (HsClassP cls tys) = do
			       tcon <- repTy (HsTyVar cls)
			       tys1 <- repLTys tys
			       repTapps tcon tys1
repPred p@(HsEqualP _ _) = notHandled "Equational constraint" (ppr p)
repPred p@(HsIParam _ _) = notHandled "Implicit parameter constraint" (ppr p)

-- 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 nameTyConName 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 tc tys)	  = do
				      tys1 <- repLTys tys 
				      tcon <- repTupleTyCon (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)             = repPred pred
repTy ty@(HsNumTy _)              = notHandled "Number types (for generics)" (ppr ty)
repTy ty			  = notHandled "Exotic form of type" (ppr ty)


-----------------------------------------------------------------------------
-- 		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 x) = 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 fix e2) =
  do { arg1 <- repLE e1; 
       arg2 <- repLE e2; 
       the_op <- repLE op ;
       repInfixApp arg1 the_op arg2 } 
repE (NegApp x nm)        = 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
			       ; wrapGenSyns ss z }
-- FIXME: I haven't got the types here right yet
repE (HsDo DoExpr sts body ty) 
 = do { (ss,zs) <- repLSts sts; 
	body'	<- addBinds ss $ repLE body;
	ret	<- repNoBindSt body';	
        e       <- repDoE (nonEmptyCoreList (zs ++ [ret]));
        wrapGenSyns ss e }
repE (HsDo ListComp sts body ty) 
 = do { (ss,zs) <- repLSts sts; 
	body'	<- addBinds ss $ repLE body;
	ret	<- repNoBindSt body';	
        e       <- repComp (nonEmptyCoreList (zs ++ [ret]));
        wrapGenSyns ss e }
repE e@(HsDo _ _ _ _) = notHandled "mdo and [: :]" (ppr e)
repE (ExplicitList ty es) = do { xs <- repLEs es; repListExp xs } 
repE e@(ExplicitPArr ty es) = notHandled "Parallel arrays" (ppr e)
repE e@(ExplicitTuple es boxed) 
  | isBoxed boxed         = do { xs <- repLEs es; repTup xs }
  | otherwise		  = notHandled "Unboxed tuples" (ppr e)
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 (HsSplice n _)) 
  = do { mb_val <- dsLookupMetaEnv n
       ; case mb_val of
		 Just (Splice e) -> do { e' <- dsExpr e
				       ; return (MkC e') }
		 other -> pprPanic "HsSplice" (ppr n) }
			-- Should not happen; statically checked

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] ty (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
     ; wrapGenSyns (ss1++ss2) match }}}
repMatchTup other = panic "repMatchTup: case alt with more than one arg"

repClauseTup ::  LMatch Name -> DsM (Core TH.ClauseQ)
repClauseTup (L _ (Match ps ty (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
     ; wrapGenSyns (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);
     wrapGenSyns (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 []    = 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 = map unLoc (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 binds sigs)
 = 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 [] ty (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' <- wrapGenSyns 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)
        ; return (loc, ans) }

rep_bind (L loc (PatBind { pat_lhs = pat, pat_rhs = GRHSs guards wheres }))
 =   do { patcore <- repLP pat 
        ; (ss,wherecore) <- repBinds wheres
	; guardcore <- addBinds ss (repGuards guards)
        ; ans  <- repVal patcore guardcore wherecore
	; ans' <- wrapGenSyns ss ans
        ; return (loc, ans') }

rep_bind (L loc (VarBind { var_id = v, var_rhs = e}))
 =   do { v' <- lookupBinder v 
	; e2 <- repLE e
        ; x <- repNormal e2
        ; patcore <- repPvar v'
	; empty_decls <- coreList decQTyConName [] 
        ; ans <- repVal patcore x empty_decls
        ; return (srcLocSpan (getSrcLoc v), ans) }

rep_bind other = panic "rep_bind: AbsBinds"

-----------------------------------------------------------------------------
-- Since everything in a Bind is mutually recursive we need rename all
-- all the variables simultaneously. For example: 
-- [| AndMonoBinds (f x = x + g 2) (g x = f 1 + 2) |] would translate to
-- do { f'1 <- gensym "f"
--    ; g'2 <- gensym "g"
--    ; [ do { x'3 <- gensym "x"; fun f'1 [pvar x'3] [| x + g2 |]},
--        do { x'4 <- gensym "x"; fun g'2 [pvar x'4] [| f 1 + 2 |]}
--      ]}
-- This requires collecting the bindings (f'1 <- gensym "f"), and the 
-- environment ( f |-> f'1 ) from each binding, and then unioning them 
-- together. As we do this we collect GenSymBinds's which represent the renamed 
-- variables bound by the Bindings. In order not to lose track of these 
-- representations we build a shadow datatype MB with the same structure as 
-- MonoBinds, but which has slots for the representations


-----------------------------------------------------------------------------
-- GHC allows a more general form of lambda abstraction than specified
-- by Haskell 98. In particular it allows guarded lambda's like : 
-- (\  x | even x -> 0 | odd x -> 1) at the moment we can't represent this in
-- Haskell Template's Meta.Exp type so we punt if it isn't a simple thing like
-- (\ p1 .. pn -> exp) by causing an error.  

repLambda :: LMatch Name -> DsM (Core TH.ExpQ)
repLambda (L _ (Match ps _ (GRHSs [L _ (GRHS [] e)] EmptyLocalBinds)))
 = do { let bndrs = collectPatsBinders ps ;
      ; ss  <- mkGenSyms bndrs
      ; lam <- addBinds ss (
		do { xs <- repLPs ps; body <- repLE e; repLam xs body })
      ; wrapGenSyns ss lam }

repLambda (L _ m) = notHandled "Guarded labmdas" (pprMatch (LambdaExpr :: HsMatchContext Name) m)

  
-----------------------------------------------------------------------------
--			Patterns
-- repP deals with patterns.  It assumes that we have already
-- walked over the pattern(s) once to collect the binders, and 
-- have extended the environment.  So every pattern-bound 
-- variable should already appear in the environment.

-- Process a list of patterns
repLPs :: [LPat Name] -> DsM (Core [TH.PatQ])
repLPs ps = do { ps' <- mapM repLP ps ;
		 coreList patQTyConName ps' }

repLP :: LPat Name -> DsM (Core TH.PatQ)
repLP (L _ p) = repP p

repP :: Pat Name -> DsM (Core TH.PatQ)
repP (WildPat _)       = repPwild 
repP (LitPat l)        = do { l2 <- repLiteral l; repPlit l2 }
repP (VarPat x)        = do { x' <- lookupBinder x; repPvar x' }
repP (LazyPat p)       = do { p1 <- repLP p; repPtilde p1 }
repP (AsPat x p)       = do { x' <- lookupLBinder x; p1 <- repLP p; repPaspat x' p1 }
repP (ParPat p)        = repLP p 
repP (ListPat ps _)    = do { qs <- repLPs ps; repPlist qs }
repP (TuplePat ps _ _) = do { qs <- repLPs ps; repPtup qs }
repP (ConPatIn dc details)
 = do { con_str <- lookupLOcc dc
      ; case details of
         PrefixCon ps -> do { qs <- repLPs ps; repPcon con_str qs }
         RecCon rec   -> do { let flds = rec_flds rec
			    ; vs <- sequence $ map lookupLOcc (map hsRecFieldId flds)
                            ; ps <- sequence $ map repLP (map hsRecFieldArg flds)
                            ; fps <- zipWithM (\x y -> rep2 fieldPatName [unC x,unC y]) vs ps
                            ; fps' <- coreList fieldPatQTyConName fps
                            ; repPrec con_str fps' }
         InfixCon p1 p2 -> do { p1' <- repLP p1;
                                p2' <- repLP p2;
                                repPinfix p1' con_str p2' }
   }
repP (NPat l Nothing _)  = do { a <- repOverloadedLiteral l; repPlit a }
repP p@(NPat l (Just _) _) = notHandled "Negative overloaded patterns" (ppr p)
repP p@(SigPatIn {})  = notHandled "Type signatures in patterns" (ppr p)
	-- The problem is to do with scoped type variables.
	-- To implement them, we have to implement the scoping rules
	-- here in DsMeta, and I don't want to do that today!
	--	 do { p' <- repLP p; t' <- repLTy t; repPsig p' t' }
	--	repPsig :: Core TH.PatQ -> Core TH.TypeQ -> DsM (Core TH.PatQ)
	--	repPsig (MkC p) (MkC t) = rep2 sigPName [p, t]

repP other = notHandled "Exotic pattern" (ppr other)

----------------------------------------------------------
-- Declaration ordering helpers

sort_by_loc :: [(SrcSpan, a)] -> [(SrcSpan, a)]
sort_by_loc xs = sortBy comp xs
    where comp x y = compare (fst x) (fst y)

de_loc :: [(a, b)] -> [b]
de_loc = map snd

----------------------------------------------------------
--	The meta-environment

-- A name/identifier association for fresh names of locally bound entities
type GenSymBind = (Name, Id)	-- Gensym the string and bind it to the Id
				-- I.e.		(x, x_id) means
				--	let x_id = gensym "x" in ...

-- Generate a fresh name for a locally bound entity

mkGenSyms :: [Name] -> DsM [GenSymBind]
-- We can use the existing name.  For example:
--	[| \x_77 -> x_77 + x_77 |]
-- desugars to
--	do { x_77 <- genSym "x"; .... }
-- We use the same x_77 in the desugared program, but with the type Bndr
-- instead of Int
--
-- We do make it an Internal name, though (hence localiseName)
--
-- Nevertheless, it's monadic because we have to generate nameTy
mkGenSyms ns = do { var_ty <- lookupType nameTyConName
		  ; return [(nm, mkLocalId (localiseName nm) var_ty) | nm <- ns] }

	     
addBinds :: [GenSymBind] -> DsM a -> DsM a
-- Add a list of fresh names for locally bound entities to the 
-- meta environment (which is part of the state carried around 
-- by the desugarer monad) 
addBinds bs m = dsExtendMetaEnv (mkNameEnv [(n,Bound id) | (n,id) <- bs]) m

-- Look up a locally bound name
--
lookupLBinder :: Located Name -> DsM (Core TH.Name)
lookupLBinder (L _ n) = lookupBinder n

lookupBinder :: Name -> DsM (Core TH.Name)
lookupBinder n 
  = do { mb_val <- dsLookupMetaEnv n;
	 case mb_val of
	    Just (Bound x) -> return (coreVar x)
	    other	   -> failWithDs msg }
  where
    msg = ptext (sLit "DsMeta: failed binder lookup when desugaring a TH bracket:") <+> ppr n

-- Look up a name that is either locally bound or a global name
--
--  * If it is a global name, generate the "original name" representation (ie,
--   the <module>:<name> form) for the associated entity
--
lookupLOcc :: Located Name -> DsM (Core TH.Name)
-- Lookup an occurrence; it can't be a splice.
-- Use the in-scope bindings if they exist
lookupLOcc (L _ n) = lookupOcc n

lookupOcc :: Name -> DsM (Core TH.Name)
lookupOcc n
  = do {  mb_val <- dsLookupMetaEnv n ;
          case mb_val of
		Nothing         -> globalVar n
		Just (Bound x)  -> return (coreVar x)
		Just (Splice _) -> pprPanic "repE:lookupOcc" (ppr n) 
    }

lookupTvOcc :: Name -> DsM (Core TH.Name)
-- Type variables can't be staged and are not lexically scoped in TH
lookupTvOcc n	
  = do {  mb_val <- dsLookupMetaEnv n ;
          case mb_val of
		Just (Bound x)  -> return (coreVar x)
		other	        -> failWithDs msg
    }
  where
    msg = vcat  [ ptext (sLit "Illegal lexically-scoped type variable") <+> quotes (ppr n)
		, ptext (sLit "Lexically scoped type variables are not supported by Template Haskell") ]