% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % TcSplice: Template Haskell splices \begin{code}

    {-# OPTIONS -fno-warn-unused-imports -fno-warn-unused-binds #-}
    -- 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 TcSplice( kcSpliceType, tcSpliceExpr, tcSpliceDecls, tcBracket,
                     lookupThName_maybe,
                     runQuasiQuoteExpr, runQuasiQuotePat,
                     runQuasiQuoteDecl, runQuasiQuoteType,
                     runAnnotation ) where

    #include "HsVersions.h"

    import HscMain
    import TcRnDriver
    	-- These imports are the reason that TcSplice
    	-- is very high up the module hierarchy

    import HsSyn
    import Convert
    import RnExpr
    import RnEnv
    import RdrName
    import RnTypes
    import TcPat
    import TcExpr
    import TcHsSyn
    import TcSimplify
    import TcUnify
    import TcType
    import TcEnv
    import TcMType
    import TcHsType
    import TcIface
    import TypeRep
    import InstEnv
    import Name
    import NameEnv
    import NameSet
    import PrelNames
    import HscTypes
    import OccName
    import Var
    import Module
    import Annotations
    import TcRnMonad
    import Class
    import Inst
    import TyCon
    import DataCon
    import Id
    import IdInfo
    import TysWiredIn
    import DsMeta
    import DsExpr
    import DsMonad hiding (Splice)
    import Serialized
    import ErrUtils
    import SrcLoc
    import Outputable
    import Util		( dropList )
    import Data.List	( mapAccumL )
    import Unique
    import Data.Maybe
    import BasicTypes
    import Panic
    import FastString
    import Exception
    import Control.Monad	( when )

    import qualified Language.Haskell.TH as TH
    -- THSyntax gives access to internal functions and data types
    import qualified Language.Haskell.TH.Syntax as TH

    #ifdef GHCI
    -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
    import GHC.Desugar      ( AnnotationWrapper(..) )
    #endif

    import GHC.Exts		( unsafeCoerce#, Int#, Int(..) )
    import System.IO.Error

\end{code} Note [How top-level splices are handled] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Top-level splices (those not inside a [| .. |] quotation bracket) are handled very straightforwardly: 1. tcTopSpliceExpr: typecheck the body e of the splice $(e) 2. runMetaT: desugar, compile, run it, and convert result back to HsSyn RdrName (of the appropriate flavour, eg HsType RdrName, HsExpr RdrName etc) 3. treat the result as if that's what you saw in the first place e.g for HsType, rename and kind-check for HsExpr, rename and type-check (The last step is different for decls, becuase they can *only* be top-level: we return the result of step 2.) Note [How brackets and nested splices are handled] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Nested splices (those inside a [| .. |] quotation bracket), are treated quite differently. * After typechecking, the bracket [| |] carries a) A mutable list of PendingSplice type PendingSplice = (Name, LHsExpr Id) b) The quoted expression e, *renamed*: (HsExpr Name) The expression e has been typechecked, but the result of that typechecking is discarded. * The brakcet is desugared by DsMeta.dsBracket. It a) Extends the ds_meta environment with the PendingSplices attached to the bracket b) Converts the quoted (HsExpr Name) to a CoreExpr that, when run, will produce a suitable TH expression/type/decl. This is why we leave the *renamed* expression attached to the bracket: the quoted expression should not be decorated with all the goop added by the type checker * Each splice carries a unique Name, called a "splice point", thus ${n}(e). The name is initialised to an (Unqual "splice") when the splice is created; the renamer gives it a unique. * When the type checker type-checks a nested splice ${n}(e), it - typechecks e - adds the typechecked expression (of type (HsExpr Id)) as a pending splice to the enclosing bracket - returns something non-committal Eg for [| f ${n}(g x) |], the typechecker - attaches the typechecked term (g x) to the pending splices for n in the outer bracket - returns a non-committal type \alpha. Remember that the bracket discards the typechecked term altogether * When DsMeta (used to desugar the body of the bracket) comes across a splice, it looks up the splice's Name, n, in the ds_meta envt, to find an (HsExpr Id) that should be substituted for the splice; it just desugars it to get a CoreExpr (DsMeta.repSplice). Example: Source: f = [| Just $(g 3) |] The [| |] part is a HsBracket Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3} The [| |] part is a HsBracketOut, containing *renamed* (not typechecked) expression The "s7" is the "splice point"; the (g Int 3) part is a typechecked expression Desugared: f = do { s7 <- g Int 3 ; return (ConE "Data.Maybe.Just" s7) } Note [Template Haskell state diagram] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here are the ThStages, s, their corresponding level numbers (the result of (thLevel s)), and their state transitions. ----------- $ ------------ $ | Comp | ---------> | Splice | -----| | 1 | | 0 | <----| ----------- ------------ ^ | ^ | $ | | [||] $ | | [||] | v | v -------------- ---------------- | Brack Comp | | Brack Splice | | 2 | | 1 | -------------- ---------------- * Normal top-level declarations start in state Comp (which has level 1). Annotations start in state Splice, since they are treated very like a splice (only without a '$') * Code compiled in state Splice (and only such code) will be *run at compile time*, with the result replacing the splice * The original paper used level -1 instead of 0, etc. * The original paper did not allow a splice within a splice, but there is no reason not to. This is the $ transition in the top right. Note [Template Haskell levels] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Imported things are impLevel (= 0) * In GHCi, variables bound by a previous command are treated as impLevel, because we have bytecode for them. * Variables are bound at the "current level" * The current level starts off at outerLevel (= 1) * The level is decremented by splicing $(..) incremented by brackets [| |] incremented by name-quoting 'f When a variable is used, we compare bind: binding level, and use: current level at usage site Generally bind > use Always error (bound later than used) [| \x -> $(f x) |] bind = use Always OK (bound same stage as used) [| \x -> $(f [| x |]) |] bind < use Inside brackets, it depends Inside splice, OK Inside neither, OK For (bind < use) inside brackets, there are three cases: - Imported things OK f = [| map |] - Top-level things OK g = [| f |] - Non-top-level Only if there is a liftable instance h = \(x:Int) -> [| x |] See Note [What is a top-level Id?] Note [Quoting names] ~~~~~~~~~~~~~~~~~~~~ A quoted name 'n is a bit like a quoted expression [| n |], except that we have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing the use-level to account for the brackets, the cases are: bind > use Error bind = use OK bind < use Imported things OK Top-level things OK Non-top-level Error See Note [What is a top-level Id?] in TcEnv. Examples: f 'map -- OK; also for top-level defns of this module \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by -- cross-stage lifting \y. [| \x. $(f 'y) |] -- Not ok (same reason) [| \x. $(f 'x) |] -- OK Note [What is a top-level Id?] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the level-control criteria above, we need to know what a "top level Id" is. There are three kinds: * Imported from another module (GlobalId, ExternalName) * Bound at the top level of this module (ExternalName) * In GHCi, bound by a previous stmt (GlobalId) It's strange that there is no one criterion tht picks out all three, but that's how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids bound in an earlier Stmt, but what module would you choose? See Note [Interactively-bound Ids in GHCi] in TcRnDriver.) The predicate we use is TcEnv.thTopLevelId. %************************************************************************ %* * \subsection{Main interface + stubs for the non-GHCI case %* * %************************************************************************ \begin{code}

    tcBracket     :: HsBracket Name -> TcRhoType -> TcM (LHsExpr TcId)
    tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
    tcSpliceExpr  :: HsSplice Name -> TcRhoType -> TcM (HsExpr TcId)
    kcSpliceType  :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
    	-- None of these functions add constraints to the LIE

    lookupThName_maybe :: TH.Name -> TcM (Maybe Name)

    runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
    runQuasiQuotePat  :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
    runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
    runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]

    runAnnotation     :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation

    #ifndef GHCI
    tcBracket     x _ = pprPanic "Cant do tcBracket without GHCi"     (ppr x)
    tcSpliceExpr  e   = pprPanic "Cant do tcSpliceExpr without GHCi"  (ppr e)
    tcSpliceDecls x   = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
    kcSpliceType  x fvs = pprPanic "Cant do kcSpliceType without GHCi"  (ppr x)

    lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)

    runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
    runQuasiQuotePat  q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
    runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
    runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
    runAnnotation   _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
    #else

\end{code} %************************************************************************ %* * \subsection{Quoting an expression} %* * %************************************************************************ \begin{code}

    -- See Note [How brackets and nested splices are handled]
    tcBracket brack res_ty
      = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
                       2 (ppr brack)) $
        do { 	-- Check for nested brackets
             cur_stage <- getStage
           ; checkTc (not (isBrackStage cur_stage)) illegalBracket

    	-- Brackets are desugared to code that mentions the TH package
           ; recordThUse

       	-- Typecheck expr to make sure it is valid,
    	-- but throw away the results.  We'll type check
    	-- it again when we actually use it.
           ; pending_splices <- newMutVar []
           ; lie_var <- getConstraintVar
           ; let brack_stage = Brack cur_stage pending_splices lie_var

              -- We want to check that there aren't any constraints that
              -- can't be satisfied (e.g. Show Foo, where Foo has no Show
              -- instance), but we aren't otherwise interested in the
              -- results. Nor do we care about ambiguous dictionaries etc.
              -- We will type check this bracket again at its usage site.
    	  --
    	  -- We build a single implication constraint with a BracketSkol;
    	  -- that in turn tells simplifyCheck to report only definite
    	  -- errors
           ; (_,lie) <- captureConstraints $
                  	    newImplication BracketSkol [] [] $
                  	    setStage brack_stage $
                  	    do { meta_ty <- tc_bracket cur_stage brack
                  	       ; unifyType meta_ty res_ty }

              -- It's best to simplify the constraint now, even though in
    	  -- principle some later unification might be useful for it,
    	  -- because we don't want these essentially-junk TH implication
    	  -- contraints floating around nested inside other constraints
    	  -- See for example Trac #4949
           ; _ <- simplifyTop lie

            -- Return the original expression, not the type-decorated one
           ; pendings <- readMutVar pending_splices
           ; return (noLoc (HsBracketOut brack pendings)) }

    tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
    tc_bracket outer_stage (VarBr name) 	-- Note [Quoting names]
      = do	{ thing <- tcLookup name
    	; case thing of
        	    AGlobal _ -> return ()
        	    ATcId { tct_level = bind_lvl, tct_id = id }
    		| thTopLevelId id	-- C.f TcExpr.checkCrossStageLifting
    		-> keepAliveTc id
    		| otherwise
    		-> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
    				(quotedNameStageErr name) }
    	    _ -> pprPanic "th_bracket" (ppr name)

    	; tcMetaTy nameTyConName 	-- Result type is Var (not Q-monadic)
    	}

    tc_bracket _ (ExpBr expr)
      = do	{ any_ty <- newFlexiTyVarTy liftedTypeKind
    	; _ <- tcMonoExprNC expr any_ty  -- NC for no context; tcBracket does that
    	; tcMetaTy expQTyConName }
    	-- Result type is ExpQ (= Q Exp)

    tc_bracket _ (TypBr typ)
      = do	{ _ <- tcHsSigTypeNC ThBrackCtxt typ
    	; tcMetaTy typeQTyConName }
    	-- Result type is Type (= Q Typ)

    tc_bracket _ (DecBrG decls)
      = do	{ _ <- tcTopSrcDecls emptyModDetails decls
    	       -- Typecheck the declarations, dicarding the result
    	       -- We'll get all that stuff later, when we splice it in

    	       -- Top-level declarations in the bracket get unqualified names
                   -- See Note [Top-level Names in Template Haskell decl quotes] in RnNames

    	; tcMetaTy decsQTyConName } -- Result type is Q [Dec]

    tc_bracket _ (PatBr pat)
      = do	{ any_ty <- newFlexiTyVarTy liftedTypeKind
    	; _ <- tcPat ThPatQuote pat any_ty $
                   return ()
    	; tcMetaTy patQTyConName }
    	-- Result type is PatQ (= Q Pat)

    tc_bracket _ (DecBrL _)
      = panic "tc_bracket: Unexpected DecBrL"

    quotedNameStageErr :: Name -> SDoc
    quotedNameStageErr v
      = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
    	, ptext (sLit "must be used at the same stage at which is is bound")]

\end{code} %************************************************************************ %* * \subsection{Splicing an expression} %* * %************************************************************************ \begin{code}

    tcSpliceExpr (HsSplice name expr) res_ty
      = setSrcSpan (getLoc expr) 	$ do
        { stage <- getStage
        ; case stage of {
    	Splice -> tcTopSplice expr res_ty ;
    	Comp   -> tcTopSplice expr res_ty ;

    	Brack pop_stage ps_var lie_var -> do

            -- See Note [How brackets and nested splices are handled]
    	-- A splice inside brackets
      	-- NB: ignore res_ty, apart from zapping it to a mono-type
    	-- e.g.   [| reverse $(h 4) |]
    	-- Here (h 4) :: Q Exp
    	-- but $(h 4) :: forall a.a 	i.e. anything!

         { meta_exp_ty <- tcMetaTy expQTyConName
         ; expr' <- setStage pop_stage $
                    setConstraintVar lie_var    $
                    tcMonoExpr expr meta_exp_ty

    	-- Write the pending splice into the bucket
         ; ps <- readMutVar ps_var
         ; writeMutVar ps_var ((name,expr') : ps)

         ; return (panic "tcSpliceExpr")	-- The returned expression is ignored
         }}}

    tcTopSplice :: LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
    -- Note [How top-level splices are handled]
    tcTopSplice expr res_ty
      = do { meta_exp_ty <- tcMetaTy expQTyConName

            -- Typecheck the expression
           ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)

            -- Run the expression
           ; expr2 <- runMetaE zonked_q_expr
           ; showSplice "expression" expr (ppr expr2)

            -- Rename it, but bale out if there are errors
            -- otherwise the type checker just gives more spurious errors
           ; addErrCtxt (spliceResultDoc expr) $ do
           { (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)

           ; exp4 <- tcMonoExpr exp3 res_ty
           ; return (unLoc exp4) } }

    spliceResultDoc :: LHsExpr Name -> SDoc
    spliceResultDoc expr
      = sep [ ptext (sLit "In the result of the splice:")
            , nest 2 (char '$' <> pprParendExpr expr)
            , ptext (sLit "To see what the splice expanded to, use -ddump-splices")]

    -------------------
    tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
    -- Note [How top-level splices are handled]
    -- Type check an expression that is the body of a top-level splice
    --   (the caller will compile and run it)
    -- Note that set the level to Splice, regardless of the original level,
    -- before typechecking the expression.  For example:
    --	f x = $( ...$(g 3) ... )
    -- The recursive call to tcMonoExpr will simply expand the
    -- inner escape before dealing with the outer one

    tcTopSpliceExpr tc_action
      = checkNoErrs $  -- checkNoErrs: must not try to run the thing
                       -- if the type checker fails!
        setStage Splice $
        do {    -- Typecheck the expression
             (expr', lie) <- captureConstraints tc_action

    	-- Solve the constraints
    	; const_binds <- simplifyTop lie

              -- Zonk it and tie the knot of dictionary bindings
           ; zonkTopLExpr (mkHsDictLet (EvBinds const_binds) expr') }

\end{code} %************************************************************************ %* * Splicing a type %* * %************************************************************************ Very like splicing an expression, but we don't yet share code. \begin{code}

    kcSpliceType splice@(HsSplice name hs_expr) fvs
      = setSrcSpan (getLoc hs_expr) $ do
        { stage <- getStage
        ; case stage of {
            Splice -> kcTopSpliceType hs_expr ;
        	Comp   -> kcTopSpliceType hs_expr ;

        	Brack pop_level ps_var lie_var -> do
    	   -- See Note [How brackets and nested splices are handled]
    	   -- A splice inside brackets
        { meta_ty <- tcMetaTy typeQTyConName
        ; expr' <- setStage pop_level $
        	       setConstraintVar lie_var $
        	       tcMonoExpr hs_expr meta_ty

        	-- Write the pending splice into the bucket
        ; ps <- readMutVar ps_var
        ; writeMutVar ps_var ((name,expr') : ps)

        -- e.g.   [| f (g :: Int -> $(h 4)) |]
        -- Here (h 4) :: Q Type
        -- but $(h 4) :: a 	i.e. any type, of any kind

        ; kind <- newKindVar
        ; return (HsSpliceTy splice fvs kind, kind)
        }}}

    kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
    -- Note [How top-level splices are handled]
    kcTopSpliceType expr
      = do	{ meta_ty <- tcMetaTy typeQTyConName

    	-- Typecheck the expression
    	; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)

    	-- Run the expression
    	; hs_ty2 <- runMetaT zonked_q_expr
    	; showSplice "type" expr (ppr hs_ty2)

    	-- Rename it, but bale out if there are errors
    	-- otherwise the type checker just gives more spurious errors
            ; addErrCtxt (spliceResultDoc expr) $ do
    	{ let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
    	; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
    	; (ty4, kind) <- kcLHsType hs_ty3
            ; return (unLoc ty4, kind) }}

\end{code} %************************************************************************ %* * \subsection{Splicing an expression} %* * %************************************************************************ \begin{code}

    -- Note [How top-level splices are handled]
    -- Always at top level
    -- Type sig at top of file:
    -- 	tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
    tcSpliceDecls expr
      = do	{ list_q <- tcMetaTy decsQTyConName	-- Q [Dec]
    	; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)

    		-- Run the expression
    	; decls <- runMetaD zonked_q_expr
    	; showSplice "declarations" expr
    		     (ppr (getLoc expr) $$ (vcat (map ppr decls)))

    	; return decls }

\end{code} %************************************************************************ %* * Annotations %* * %************************************************************************ \begin{code}

    runAnnotation target expr = do
        -- Find the classes we want instances for in order to call toAnnotationWrapper
        loc <- getSrcSpanM
        data_class <- tcLookupClass dataClassName
        to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName

        -- Check the instances we require live in another module (we want to execute it..)
        -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
        -- also resolves the LIE constraints to detect e.g. instance ambiguity
        zonked_wrapped_expr' <- tcTopSpliceExpr $
               do { (expr', expr_ty) <- tcInferRhoNC expr
    		-- We manually wrap the typechecked expression in a call to toAnnotationWrapper
                    -- By instantiating the call >here< it gets registered in the
    		-- LIE consulted by tcTopSpliceExpr
                    -- and hence ensures the appropriate dictionary is bound by const_binds
                  ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
                  ; let specialised_to_annotation_wrapper_expr
                          = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
                  ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }

        -- Run the appropriately wrapped expression to get the value of
        -- the annotation and its dictionaries. The return value is of
        -- type AnnotationWrapper by construction, so this conversion is
        -- safe
        flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
            case annotation_wrapper of
                AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
                    -- Got the value and dictionaries: build the serialized value and
    		-- call it a day. We ensure that we seq the entire serialized value
    		-- in order that any errors in the user-written code for the
                    -- annotation are exposed at this point.  This is also why we are
    		-- doing all this stuff inside the context of runMeta: it has the
    		-- facilities to deal with user error in a meta-level expression
                    seqSerialized serialized `seq` Annotation {
                        ann_target = target,
                        ann_value = serialized
                    }

\end{code} %************************************************************************ %* * Quasi-quoting %* * %************************************************************************ Note [Quasi-quote overview] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The GHC "quasi-quote" extension is described by Geoff Mainland's paper "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell Workshop 2007). Briefly, one writes [p| stuff |] and the arbitrary string "stuff" gets parsed by the parser 'p', whose type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be defined in another module, because we are going to run it here. It's a bit like a TH splice: $(p "stuff") However, you can do this in patterns as well as terms. Becuase of this, the splice is run by the *renamer* rather than the type checker. %************************************************************************ %* * \subsubsection{Quasiquotation} %* * %************************************************************************ See Note [Quasi-quote overview] in TcSplice. \begin{code}

    runQuasiQuote :: Outputable hs_syn
                  => HsQuasiQuote RdrName	-- Contains term of type QuasiQuoter, and the String
                  -> Name			-- Of type QuasiQuoter -> String -> Q th_syn
                  -> Name			-- Name of th_syn type
                  -> MetaOps th_syn hs_syn
                  -> RnM hs_syn
    runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
      = do  {     -- Drop the leading "$" from the quoter name, if present
                  -- This is old-style syntax, now deprecated
                  -- NB: when removing this backward-compat, remove
                  --     the matching code in Lexer.x (around line 310)
              let occ_str = occNameString (rdrNameOcc quoter)
            ; quoter <- ASSERT( not (null occ_str) )  -- Lexer ensures this
                        if head occ_str /= '$' then return quoter
                        else do { addWarn (deprecatedDollar quoter)
                                ; return (mkRdrUnqual (mkVarOcc (tail occ_str))) }

            ; quoter' <- lookupOccRn quoter
    		-- We use lookupOcc rather than lookupGlobalOcc because in the
    		-- erroneous case of \x -> [x| ...|] we get a better error message
    		-- (stage restriction rather than out of scope).

            ; when (isUnboundName quoter') failM
    		-- If 'quoter' is not in scope, proceed no further
    		-- The error message was generated by lookupOccRn, but it then
    		-- succeeds with an "unbound name", which makes the subsequent
    		-- attempt to run the quote fail in a confusing way

              -- Check that the quoter is not locally defined, otherwise the TH
              -- machinery will not be able to run the quasiquote.
       	; this_mod <- getModule
            ; let is_local = nameIsLocalOrFrom this_mod quoter'
            ; checkTc (not is_local) (quoteStageError quoter')

    	; traceTc "runQQ" (ppr quoter <+> ppr is_local)

    	  -- Build the expression
          	; let quoterExpr = L q_span $! HsVar $! quoter'
          	; let quoteExpr = L q_span $! HsLit $! HsString quote
          	; let expr = L q_span $
          	             HsApp (L q_span $
          	                    HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
          	; meta_exp_ty <- tcMetaTy meta_ty

          	-- Typecheck the expression
          	; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)

          	-- Run the expression
          	; result <- runMetaQ meta_ops zonked_q_expr
          	; showSplice (mt_desc meta_ops) quoteExpr (ppr result)

          	; return result	}

    runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName  expQTyConName  exprMetaOps
    runQuasiQuotePat  qq = runQuasiQuote qq quotePatName  patQTyConName  patMetaOps
    runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
    runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName  decsQTyConName declMetaOps

    quoteStageError :: Name -> SDoc
    quoteStageError quoter
      = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
             nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]

    deprecatedDollar :: RdrName -> SDoc
    deprecatedDollar quoter
      = hang (ptext (sLit "Deprecated syntax:"))
           2 (ptext (sLit "quasiquotes no longer need a dollar sign:")
              <+> ppr quoter)

\end{code} %************************************************************************ %* * \subsection{Running an expression} %* * %************************************************************************ \begin{code}

    data MetaOps th_syn hs_syn
      = MT { mt_desc :: String	       -- Type of beast (expression, type etc)
           , mt_show :: th_syn -> String   -- How to show the th_syn thing
           , mt_cvt  :: SrcSpan -> th_syn -> Either Message hs_syn
           	 	    	       	       -- How to convert to hs_syn
        }

    exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
    exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }

    patMetaOps :: MetaOps TH.Pat (LPat RdrName)
    patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }

    typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
    typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }

    declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
    declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }

    ----------------
    runMetaAW :: Outputable output
              => (AnnotationWrapper -> output)
              -> LHsExpr Id         -- Of type AnnotationWrapper
              -> TcM output
    runMetaAW k = runMeta False (\_ -> return . Right . k)
        -- We turn off showing the code in meta-level exceptions because doing so exposes
        -- the toAnnotationWrapper function that we slap around the users code

    -----------------
    runMetaQ :: Outputable hs_syn
             => MetaOps th_syn hs_syn
    	 -> LHsExpr Id
    	 -> TcM hs_syn
    runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
      = runMeta True run_and_cvt expr
      where
        run_and_cvt expr_span hval
           = do { th_result <- TH.runQ hval
                ; traceTc "Got TH result:" (text (show_th th_result))
                ; return (cvt expr_span th_result) }

    runMetaE :: LHsExpr Id 		-- Of type (Q Exp)
    	 -> TcM (LHsExpr RdrName)
    runMetaE = runMetaQ exprMetaOps

    runMetaT :: LHsExpr Id 		-- Of type (Q Type)
    	 -> TcM (LHsType RdrName)
    runMetaT = runMetaQ typeMetaOps

    runMetaD :: LHsExpr Id 		-- Of type Q [Dec]
    	 -> TcM [LHsDecl RdrName]
    runMetaD = runMetaQ declMetaOps

    ---------------
    runMeta :: (Outputable hs_syn)
            => Bool                 -- Whether code should be printed in the exception message
            -> (SrcSpan -> x -> TcM (Either Message hs_syn))	-- How to run x
    	-> LHsExpr Id 		-- Of type x; typically x = Q TH.Exp, or something like that
    	-> TcM hs_syn		-- Of type t
    runMeta show_code run_and_convert expr
      = do	{ traceTc "About to run" (ppr expr)

    	-- Desugar
    	; ds_expr <- initDsTc (dsLExpr expr)
    	-- Compile and link it; might fail if linking fails
    	; hsc_env <- getTopEnv
    	; src_span <- getSrcSpanM
    	; either_hval <- tryM $ liftIO $
    			 HscMain.compileExpr hsc_env src_span ds_expr
    	; case either_hval of {
    	    Left exn   -> failWithTc (mk_msg "compile and link" exn) ;
    	    Right hval -> do

    	{ 	-- Coerce it to Q t, and run it

    		-- Running might fail if it throws an exception of any kind (hence tryAllM)
    		-- including, say, a pattern-match exception in the code we are running
    		--
    		-- We also do the TH -> HS syntax conversion inside the same
    		-- exception-cacthing thing so that if there are any lurking
    		-- exceptions in the data structure returned by hval, we'll
    		-- encounter them inside the try
    		--
    		-- See Note [Exceptions in TH]
    	  let expr_span = getLoc expr
    	; either_tval <- tryAllM $
                		 setSrcSpan expr_span $	-- Set the span so that qLocation can
    						-- see where this splice is
    	     do	{ mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
    		; case mb_result of
    		    Left err     -> failWithTc err
    		    Right result -> do { traceTc "Got HsSyn result:" (ppr result)
                                           ; return $! result } }

    	; case either_tval of
    	    Right v -> return v
    	    Left se -> case fromException se of
                        	 Just IOEnvFailure -> failM -- Error already in Tc monad
                        	 _ -> failWithTc (mk_msg "run" se)	-- Exception
            }}}
      where
        mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
    			 nest 2 (text (Panic.showException exn)),
    			 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]

\end{code} Note [Exceptions in TH] ~~~~~~~~~~~~~~~~~~~~~~~ Supppose we have something like this $( f 4 ) where f :: Int -> Q [Dec] f n | n>3 = fail "Too many declarations" | otherwise = ... The 'fail' is a user-generated failure, and should be displayed as a perfectly ordinary compiler error message, not a panic or anything like that. Here's how it's processed: * 'fail' is the monad fail. The monad instance for Q in TH.Syntax effectively transforms (fail s) to qReport True s >> fail where 'qReport' comes from the Quasi class and fail from its monad superclass. * The TcM monad is an instance of Quasi (see TcSplice), and it implements (qReport True s) by using addErr to add an error message to the bag of errors. The 'fail' in TcM raises an IOEnvFailure exception * So, when running a splice, we catch all exceptions; then for - an IOEnvFailure exception, we assume the error is already in the error-bag (above) - other errors, we add an error to the bag and then fail To call runQ in the Tc monad, we need to make TcM an instance of Quasi: \begin{code}

    instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
      qNewName s = do { u <- newUnique
    		  ; let i = getKey u
    		  ; return (TH.mkNameU s i) }

      qReport True msg  = addErr (text msg)
      qReport False msg = addReport (text msg) empty

      qLocation = do { m <- getModule
    		 ; l <- getSrcSpanM
    		 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
    				  , TH.loc_module   = moduleNameString (moduleName m)
    				  , TH.loc_package  = packageIdString (modulePackageId m)
    				  , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
    				  , TH.loc_end = (srcSpanEndLine   l, srcSpanEndCol   l) }) }

      qReify v = reify v
      qClassInstances = lookupClassInstances

    	-- For qRecover, discard error messages if
    	-- the recovery action is chosen.  Otherwise
    	-- we'll only fail higher up.  c.f. tryTcLIE_
      qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
    			     ; case mb_res of
    		  	         Just val -> do { addMessages msgs	-- There might be warnings
    				   	        ; return val }
    		  	         Nothing  -> recover			-- Discard all msgs
    			  }

      qRunIO io = liftIO io

\end{code} %************************************************************************ %* * \subsection{Errors and contexts} %* * %************************************************************************ \begin{code}

    showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
    -- Note that 'before' is *renamed* but not *typechecked*
    -- Reason (a) less typechecking crap
    --        (b) data constructors after type checking have been
    --	      changed to their *wrappers*, and that makes them
    --	      print always fully qualified
    showSplice what before after
      = do { loc <- getSrcSpanM
           ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
    		            nest 2 (sep [nest 2 (ppr before),
    				         text "======>",
    				         nest 2 after])]) }

    illegalBracket :: SDoc
    illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
    #endif 	/* GHCI */

\end{code} %************************************************************************ %* * Instance Testing %* * %************************************************************************ \begin{code}

    lookupClassInstances :: TH.Name -> [TH.Type] -> TcM [TH.Name]
    lookupClassInstances c ts
       = do { loc <- getSrcSpanM
            ; case convertToHsPred loc (TH.ClassP c ts) of
                Left msg -> failWithTc msg
                Right rdr_pred -> do
            { rn_pred <- rnLPred doc rdr_pred	-- Rename
            ; kc_pred <- kcHsLPred rn_pred		-- Kind check
            ; ClassP cls tys <- dsHsLPred kc_pred	-- Type check

    	-- Now look up instances
            ; inst_envs <- tcGetInstEnvs
            ; let (matches, unifies) = lookupInstEnv inst_envs cls tys
                  dfuns = map is_dfun (map fst matches ++ unifies)
            ; return (map reifyName dfuns) } }
      where
        doc = ptext (sLit "TcSplice.classInstances")

\end{code} %************************************************************************ %* * Reification %* * %************************************************************************ \begin{code}

    reify :: TH.Name -> TcM TH.Info
    reify th_name
      = do	{ name <- lookupThName th_name
    	; thing <- tcLookupTh name
    		-- ToDo: this tcLookup could fail, which would give a
    		-- 	 rather unhelpful error message
    	; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
    	; reifyThing thing
        }
      where
        ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
        ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
        ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
        ppr_ns _ = panic "reify/ppr_ns"

    lookupThName :: TH.Name -> TcM Name
    lookupThName th_name = do
        mb_name <- lookupThName_maybe th_name
        case mb_name of
            Nothing   -> failWithTc (notInScope th_name)
            Just name -> return name

    lookupThName_maybe th_name
      =  do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
              -- Pick the first that works
    	  -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
    	; return (listToMaybe names) }
      where
        lookup rdr_name
    	= do { 	-- Repeat much of lookupOccRn, becase we want
    		-- to report errors in a TH-relevant way
    	     ; rdr_env <- getLocalRdrEnv
      	     ; case lookupLocalRdrEnv rdr_env rdr_name of
    		 Just name -> return (Just name)
    	         Nothing   -> lookupGlobalOccRn_maybe rdr_name }

    tcLookupTh :: Name -> TcM TcTyThing
    -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
    -- it gives a reify-related error message on failure, whereas in the normal
    -- tcLookup, failure is a bug.
    tcLookupTh name
      = do	{ (gbl_env, lcl_env) <- getEnvs
    	; case lookupNameEnv (tcl_env lcl_env) name of {
    		Just thing -> return thing;
    		Nothing    -> do
    	{ if nameIsLocalOrFrom (tcg_mod gbl_env) name
    	  then	-- It's defined in this module
    	      case lookupNameEnv (tcg_type_env gbl_env) name of
    		Just thing -> return (AGlobal thing)
    		Nothing	   -> failWithTc (notInEnv name)

    	  else do 		-- It's imported
    	{ (eps,hpt) <- getEpsAndHpt
            ; dflags <- getDOpts
    	; case lookupType dflags hpt (eps_PTE eps) name of
    	    Just thing -> return (AGlobal thing)
    	    Nothing    -> do { thing <- tcImportDecl name
    			     ; return (AGlobal thing) }
    		-- Imported names should always be findable;
    		-- if not, we fail hard in tcImportDecl
        }}}}

    notInScope :: TH.Name -> SDoc
    notInScope th_name = quotes (text (TH.pprint th_name)) <+>
    		     ptext (sLit "is not in scope at a reify")
    	-- Ugh! Rather an indirect way to display the name

    notInEnv :: Name -> SDoc
    notInEnv name = quotes (ppr name) <+>
    		     ptext (sLit "is not in the type environment at a reify")

    ------------------------------
    reifyThing :: TcTyThing -> TcM TH.Info
    -- The only reason this is monadic is for error reporting,
    -- which in turn is mainly for the case when TH can't express
    -- some random GHC extension

    reifyThing (AGlobal (AnId id))
      = do	{ ty <- reifyType (idType id)
    	; fix <- reifyFixity (idName id)
    	; let v = reifyName id
    	; case idDetails id of
    	    ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
    	    _             -> return (TH.VarI     v ty Nothing fix)
        }

    reifyThing (AGlobal (ATyCon tc))  = reifyTyCon tc
    reifyThing (AGlobal (AClass cls)) = reifyClass cls
    reifyThing (AGlobal (ADataCon dc))
      = do	{ let name = dataConName dc
    	; ty <- reifyType (idType (dataConWrapId dc))
    	; fix <- reifyFixity name
    	; return (TH.DataConI (reifyName name) ty
                                  (reifyName (dataConOrigTyCon dc)) fix)
            }

    reifyThing (ATcId {tct_id = id})
      = do	{ ty1 <- zonkTcType (idType id)	-- Make use of all the info we have, even
        					-- though it may be incomplete
    	; ty2 <- reifyType ty1
    	; fix <- reifyFixity (idName id)
    	; return (TH.VarI (reifyName id) ty2 Nothing fix) }

    reifyThing (ATyVar tv ty)
      = do	{ ty1 <- zonkTcType ty
    	; ty2 <- reifyType ty1
    	; return (TH.TyVarI (reifyName tv) ty2) }

    reifyThing (AThing {}) = panic "reifyThing AThing"

    ------------------------------
    reifyTyCon :: TyCon -> TcM TH.Info
    reifyTyCon tc
      | isFunTyCon tc
      = return (TH.PrimTyConI (reifyName tc) 2 		  False)
      | isPrimTyCon tc
      = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
      | isFamilyTyCon tc
      = let flavour = reifyFamFlavour tc
            tvs     = tyConTyVars tc
            kind    = tyConKind tc
            kind'
              | isLiftedTypeKind kind = Nothing
              | otherwise             = Just $ reifyKind kind
        in
        return (TH.TyConI $
                  TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
      | isSynTyCon tc
      = do { let (tvs, rhs) = synTyConDefn tc
           ; rhs' <- reifyType rhs
           ; return (TH.TyConI $
    		   TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
           }

    reifyTyCon tc
      = do 	{ cxt <- reifyCxt (tyConStupidTheta tc)
    	; let tvs = tyConTyVars tc
    	; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
    	; let name = reifyName tc
    	      r_tvs  = reifyTyVars tvs
    	      deriv = []	-- Don't know about deriving
    	      decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
    		   | otherwise	   = TH.DataD    cxt name r_tvs cons 	    deriv
    	; return (TH.TyConI decl) }

    reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
    -- For GADTs etc, see Note [Reifying data constructors]
    reifyDataCon tys dc
      = do { let (tvs, theta, arg_tys, _) = dataConSig dc
                 subst             = mkTopTvSubst (tvs `zip` tys)	-- Dicard ex_tvs
                 (subst', ex_tvs') = mapAccumL substTyVarBndr subst (dropList tys tvs)
                 theta'   = substTheta subst' theta
                 arg_tys' = substTys subst' arg_tys
                 stricts  = map reifyStrict (dataConStrictMarks dc)
    	     fields   = dataConFieldLabels dc
    	     name     = reifyName dc

           ; r_arg_tys <- reifyTypes arg_tys'

           ; let main_con | not (null fields)
                          = TH.RecC name (zip3 (map reifyName fields) stricts r_arg_tys)
                          | dataConIsInfix dc
                          = ASSERT( length arg_tys == 2 )
    	                TH.InfixC (s1,r_a1) name (s2,r_a2)
                          | otherwise
                          = TH.NormalC name (stricts `zip` r_arg_tys)
    	     [r_a1, r_a2] = r_arg_tys
    	     [s1,   s2]   = stricts

           ; ASSERT( length arg_tys == length stricts )
             if null ex_tvs' && null theta then
    	     return main_con
             else do
             { cxt <- reifyCxt theta'
    	 ; return (TH.ForallC (reifyTyVars ex_tvs') cxt main_con) } }

    ------------------------------
    reifyClass :: Class -> TcM TH.Info
    reifyClass cls
      = do	{ cxt <- reifyCxt theta
            ; inst_envs <- tcGetInstEnvs
            ; insts <- mapM reifyClassInstance (InstEnv.classInstances inst_envs cls)
    	; ops <- mapM reify_op op_stuff
            ; let dec = TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops
    	; return (TH.ClassI dec insts ) }
      where
        (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
        fds' = map reifyFunDep fds
        reify_op (op, _) = do { ty <- reifyType (idType op)
    			  ; return (TH.SigD (reifyName op) ty) }

    ------------------------------
    reifyClassInstance :: Instance -> TcM TH.ClassInstance
    reifyClassInstance i
      = do { cxt <- reifyCxt theta
           ; thtypes <- reifyTypes types
           ; return $ (TH.ClassInstance {
                TH.ci_tvs = reifyTyVars tvs,
                TH.ci_cxt = cxt,
                TH.ci_tys = thtypes,
                TH.ci_cls = reifyName cls,
                TH.ci_dfun = reifyName (is_dfun i) }) }
      where
         (tvs, theta, cls, types) = instanceHead i

    ------------------------------
    reifyType :: TypeRep.Type -> TcM TH.Type
    -- Monadic only because of failure
    reifyType ty@(ForAllTy _ _)        = reify_for_all ty
    reifyType ty@(PredTy {} `FunTy` _) = reify_for_all ty	        -- Types like ((?x::Int) => Char -> Char)
    reifyType (TyVarTy tv)	    = return (TH.VarT (reifyName tv))
    reifyType (TyConApp tc tys) = reify_tc_app tc tys   -- Do not expand type synonyms here
    reifyType (AppTy t1 t2)     = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
    reifyType (FunTy t1 t2)     = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
    reifyType ty@(PredTy {})    = pprPanic "reifyType PredTy" (ppr ty)

    reify_for_all :: TypeRep.Type -> TcM TH.Type
    reify_for_all ty
      = do { cxt' <- reifyCxt cxt;
           ; tau' <- reifyType tau
           ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
      where
        (tvs, cxt, tau) = tcSplitSigmaTy ty

    reifyTypes :: [Type] -> TcM [TH.Type]
    reifyTypes = mapM reifyType

    reifyKind :: Kind -> TH.Kind
    reifyKind  ki
      = let (kis, ki') = splitKindFunTys ki
            kis_rep    = map reifyKind kis
            ki'_rep    = reifyNonArrowKind ki'
        in
        foldr TH.ArrowK ki'_rep kis_rep
      where
        reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
                            | otherwise          = pprPanic "Exotic form of kind"
                                                            (ppr k)

    reifyCxt :: [PredType] -> TcM [TH.Pred]
    reifyCxt   = mapM reifyPred

    reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
    reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)

    reifyFamFlavour :: TyCon -> TH.FamFlavour
    reifyFamFlavour tc | isSynFamilyTyCon tc = TH.TypeFam
                       | isFamilyTyCon    tc = TH.DataFam
                       | otherwise
                       = panic "TcSplice.reifyFamFlavour: not a type family"

    reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
    reifyTyVars = map reifyTyVar
      where
        reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV  name
                      | otherwise             = TH.KindedTV name (reifyKind kind)
          where
            kind = tyVarKind tv
            name = reifyName tv

    reify_tc_app :: TyCon -> [TypeRep.Type] -> TcM TH.Type
    reify_tc_app tc tys
      = do { tys' <- reifyTypes tys
           ; return (foldl TH.AppT r_tc tys') }
      where
        n_tys = length tys
        r_tc | isTupleTyCon tc          = TH.TupleT n_tys
             | tc `hasKey` listTyConKey = TH.ListT
             | otherwise                = TH.ConT (reifyName tc)

    reifyPred :: TypeRep.PredType -> TcM TH.Pred
    reifyPred (ClassP cls tys)
      = do { tys' <- reifyTypes tys
           ; return $ TH.ClassP (reifyName cls) tys' }

    reifyPred p@(IParam _ _)   = noTH (sLit "implicit parameters") (ppr p)
    reifyPred (EqPred ty1 ty2)
      = do { ty1' <- reifyType ty1
           ; ty2' <- reifyType ty2
           ; return $ TH.EqualP ty1' ty2'
           }

    ------------------------------
    reifyName :: NamedThing n => n -> TH.Name
    reifyName thing
      | isExternalName name = mk_varg pkg_str mod_str occ_str
      | otherwise	        = TH.mkNameU occ_str (getKey (getUnique name))
    	-- Many of the things we reify have local bindings, and
    	-- NameL's aren't supposed to appear in binding positions, so
    	-- we use NameU.  When/if we start to reify nested things, that
    	-- have free variables, we may need to generate NameL's for them.
      where
        name    = getName thing
        mod     = ASSERT( isExternalName name ) nameModule name
        pkg_str = packageIdString (modulePackageId mod)
        mod_str = moduleNameString (moduleName mod)
        occ_str = occNameString occ
        occ     = nameOccName name
        mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
    	    | OccName.isVarOcc  occ = TH.mkNameG_v
    	    | OccName.isTcOcc   occ = TH.mkNameG_tc
    	    | otherwise		    = pprPanic "reifyName" (ppr name)

    ------------------------------
    reifyFixity :: Name -> TcM TH.Fixity
    reifyFixity name
      = do	{ fix <- lookupFixityRn name
    	; return (conv_fix fix) }
        where
          conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
          conv_dir BasicTypes.InfixR = TH.InfixR
          conv_dir BasicTypes.InfixL = TH.InfixL
          conv_dir BasicTypes.InfixN = TH.InfixN

    reifyStrict :: BasicTypes.HsBang -> TH.Strict
    reifyStrict bang | isBanged bang = TH.IsStrict
                     | otherwise     = TH.NotStrict

    ------------------------------
    noTH :: LitString -> SDoc -> TcM a
    noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
    				ptext (sLit "in Template Haskell:"),
    		 	     nest 2 d])

\end{code} Note [Reifying data constructors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Template Haskell syntax is rich enough to express even GADTs, provided we do so in the equality-predicate form. So a GADT like data T a where MkT1 :: a -> T [a] MkT2 :: T Int will appear in TH syntax like this data T a = forall b. (a ~ [b]) => MkT1 b | (a ~ Int) => MkT2