typecheck/TcSplice.lhs

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

    {-# LANGUAGE ScopedTypeVariables #-}
    {-# OPTIONS_GHC -fno-warn-orphans #-}
    module TcSplice(
         -- These functions are defined in stage1 and stage2
         -- The raise civilised errors in stage1
         tcSpliceExpr, tcTypedBracket, tcUntypedBracket,
         runQuasiQuoteExpr, runQuasiQuotePat,
         runQuasiQuoteDecl, runQuasiQuoteType,
         runAnnotation,

    #ifdef GHCI
         -- These ones are defined only in stage2, and are
         -- called only in stage2 (ie GHCI is on)
         runMetaE, runMetaP, runMetaT, runMetaD, runQuasi,
         tcTopSpliceExpr, lookupThName_maybe,
    #endif
          ) where

    #include "HsVersions.h"

    import HsSyn
    import Annotations
    import Name
    import TcRnMonad
    import RdrName
    import TcType

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

    import HscTypes
    import Convert
    import RnExpr
    import RnEnv
    import RnTypes
    import TcExpr
    import TcHsSyn
    import TcSimplify
    import TcUnify
    import Type
    import Kind
    import NameSet
    import TcEnv
    import TcMType
    import TcHsType
    import TcIface
    import TypeRep
    import FamInst
    import FamInstEnv
    import InstEnv
    import NameEnv
    import PrelNames
    import OccName
    import Hooks
    import Var
    import Module
    import LoadIface
    import Class
    import Inst
    import TyCon
    import CoAxiom
    import PatSyn ( patSynId )
    import ConLike
    import DataCon
    import TcEvidence( TcEvBinds(..) )
    import Id
    import IdInfo
    import DsExpr
    import DsMonad hiding (Splice)
    import Serialized
    import ErrUtils
    import SrcLoc
    import Util
    import Data.List        ( mapAccumL )
    import Unique
    import Data.Maybe
    import BasicTypes hiding( SuccessFlag(..) )
    import Maybes( MaybeErr(..) )
    import DynFlags
    import Panic
    import FastString
    import Outputable
    import Control.Monad    ( when )

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

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

    import qualified Data.Map as Map
    import Data.Dynamic  ( fromDynamic, toDyn )
    import Data.Typeable ( typeOf )
    import Data.Data (Data)
    import GHC.Exts         ( unsafeCoerce# )
    #endif

\end{code} %************************************************************************ %* * \subsection{Main interface + stubs for the non-GHCI case %* * %************************************************************************ \begin{code}

    tcTypedBracket   :: HsBracket Name -> TcRhoType -> TcM (HsExpr TcId)
    tcUntypedBracket :: HsBracket Name -> [PendingRnSplice] -> TcRhoType -> TcM (HsExpr TcId)
    tcSpliceExpr     :: HsSplice Name  -> TcRhoType -> TcM (HsExpr TcId)
            -- None of these functions add constraints to the LIE

    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
    tcTypedBracket   x _   = failTH x "Template Haskell bracket"
    tcUntypedBracket x _ _ = failTH x "Template Haskell bracket"
    tcSpliceExpr  e _      = failTH e "Template Haskell splice"

    runQuasiQuoteExpr q = failTH q "quasiquote"
    runQuasiQuotePat  q = failTH q "pattern quasiquote"
    runQuasiQuoteType q = failTH q "type quasiquote"
    runQuasiQuoteDecl q = failTH q "declaration quasiquote"
    runAnnotation   _ q = failTH q "annotation"

    #else
      -- The whole of the rest of the file is the else-branch (ie stage2 only)

\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, because 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. Remember, there are two forms of bracket typed [|| e ||] and untyped [| e |] The life cycle of a typed bracket: * Starts as HsBracket * When renaming: * Set the ThStage to (Brack s RnPendingTyped) * Rename the body * Result is still a HsBracket * When typechecking: * Set the ThStage to (Brack s (TcPending ps_var lie_var)) * Typecheck the body, and throw away the elaborated result * Nested splices (which must be typed) are typechecked, and the results accumulated in ps_var; their constraints accumulate in lie_var * Result is a HsTcBracketOut rn_brack pending_splices where rn_brack is the incoming renamed bracket The life cycle of a un-typed bracket: * Starts as HsBracket * When renaming: * Set the ThStage to (Brack s (RnPendingUntyped ps_var)) * Rename the body * Nested splices (which must be untyped) are renamed, and the results accumulated in ps_var * Result is still (HsRnBracketOut rn_body pending_splices) * When typechecking a HsRnBracketOut * Typecheck the pending_splices individually * Ignore the body of the bracket; just check that the context expects a bracket of that type (e.g. a [p| pat |] bracket should be in a context needing a (Q Pat) * Result is a HsTcBracketOut rn_brack pending_splices where rn_brack is the incoming renamed bracket In both cases, desugaring happens like this: * HsTcBracketOut 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 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) * However things at level 0 are not *necessarily* imported. eg $( \b -> ... ) here b is bound at level 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 |] To track top-level-ness we use the ThBindEnv in TcLclEnv For example: f = ... g1 = $(map ...) is OK g2 = $(f ...) is not OK; because we havn't compiled f yet %************************************************************************ %* * \subsection{Quoting an expression} %* * %************************************************************************ \begin{code}

    -- See Note [How brackets and nested splices are handled]
    -- tcTypedBracket :: HsBracket Name -> TcRhoType -> TcM (HsExpr TcId)
    tcTypedBracket brack@(TExpBr expr) res_ty
      = addErrCtxt (quotationCtxtDoc brack) $
        do { cur_stage <- getStage
           ; ps_ref <- newMutVar []
           ; lie_var <- getConstraintVar   -- Any constraints arising from nested splices
                                           -- should get thrown into the constraint set
                                           -- from outside the bracket

           -- Typecheck expr to make sure it is valid,
           -- Throw away the typechecked expression but return its type.
           -- We'll typecheck it again when we splice it in somewhere
           ; (_tc_expr, expr_ty) <- setStage (Brack cur_stage (TcPending ps_ref lie_var)) $
                                    tcInferRhoNC expr
                                    -- NC for no context; tcBracket does that

           ; meta_ty <- tcTExpTy expr_ty
           ; co <- unifyType meta_ty res_ty
           ; ps' <- readMutVar ps_ref
           ; texpco <- tcLookupId unsafeTExpCoerceName
           ; return (mkHsWrapCo co (unLoc (mkHsApp (nlHsTyApp texpco [expr_ty])
                                                   (noLoc (HsTcBracketOut brack ps'))))) }
    tcTypedBracket other_brack _
      = pprPanic "tcTypedBracket" (ppr other_brack)

    -- tcUntypedBracket :: HsBracket Name -> [PendingRnSplice] -> TcRhoType -> TcM (HsExpr TcId)
    tcUntypedBracket brack ps res_ty
      = do { traceTc "tc_bracket untyped" (ppr brack $$ ppr ps)
           ; ps' <- mapM tcPendingSplice ps
           ; meta_ty <- tcBrackTy brack
           ; co <- unifyType meta_ty res_ty
           ; traceTc "tc_bracket done untyped" (ppr meta_ty)
           ; return (mkHsWrapCo co (HsTcBracketOut brack ps'))  }

    ---------------
    tcBrackTy :: HsBracket Name -> TcM TcType
    tcBrackTy (VarBr _ _) = tcMetaTy nameTyConName  -- Result type is Var (not Q-monadic)
    tcBrackTy (ExpBr _)   = tcMetaTy expQTyConName  -- Result type is ExpQ (= Q Exp)
    tcBrackTy (TypBr _)   = tcMetaTy typeQTyConName -- Result type is Type (= Q Typ)
    tcBrackTy (DecBrG _)  = tcMetaTy decsQTyConName -- Result type is Q [Dec]
    tcBrackTy (PatBr _)   = tcMetaTy patQTyConName  -- Result type is PatQ (= Q Pat)
    tcBrackTy (DecBrL _)  = panic "tcBrackTy: Unexpected DecBrL"
    tcBrackTy (TExpBr _)  = panic "tcUntypedBracket: Unexpected TExpBr"

    ---------------
    tcPendingSplice :: PendingRnSplice -> TcM PendingTcSplice
    tcPendingSplice (PendingRnExpSplice (HsSplice n expr))
      = do { res_ty <- tcMetaTy expQTyConName
           ; tc_pending_splice n expr res_ty }
    tcPendingSplice (PendingRnPatSplice (HsSplice n expr))
      = do { res_ty <- tcMetaTy patQTyConName
           ; tc_pending_splice n expr res_ty }
    tcPendingSplice (PendingRnTypeSplice (HsSplice n expr))
      = do { res_ty <- tcMetaTy typeQTyConName
           ; tc_pending_splice n expr res_ty }
    tcPendingSplice (PendingRnDeclSplice (HsSplice n expr))
      = do { res_ty <- tcMetaTy decsQTyConName
           ; tc_pending_splice n expr res_ty }

    tcPendingSplice (PendingRnCrossStageSplice n)
      -- Behave like $(lift x); not very pretty
      = do { res_ty <- tcMetaTy expQTyConName
           ; tc_pending_splice n (nlHsApp (nlHsVar liftName) (nlHsVar n)) res_ty }

    ---------------
    tc_pending_splice :: Name -> LHsExpr Name -> TcRhoType -> TcM PendingTcSplice
    tc_pending_splice splice_name expr res_ty
      = do { expr' <- tcMonoExpr expr res_ty
           ; return (splice_name, expr') }

    ---------------
    -- Takes a type tau and returns the type Q (TExp tau)
    tcTExpTy :: TcType -> TcM TcType
    tcTExpTy tau = do
        q <- tcLookupTyCon qTyConName
        texp <- tcLookupTyCon tExpTyConName
        return (mkTyConApp q [mkTyConApp texp [tau]])

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

    tcSpliceExpr splice@(HsSplice name expr) res_ty
      = addErrCtxt (spliceCtxtDoc splice) $
        setSrcSpan (getLoc expr)    $ do
        { stage <- getStage
        ; case stage of
            Splice {}            -> tcTopSplice expr res_ty
            Comp                 -> tcTopSplice expr res_ty
            Brack pop_stage pend -> tcNestedSplice pop_stage pend name expr res_ty }

    tcNestedSplice :: ThStage -> PendingStuff -> Name
                    -> LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
        -- See Note [How brackets and nested splices are handled]
        -- A splice inside brackets
    tcNestedSplice pop_stage (TcPending ps_var lie_var) splice_name expr res_ty
      = do { meta_exp_ty <- tcTExpTy res_ty
           ; expr' <- setStage pop_stage $
                      setConstraintVar lie_var $
                      tcMonoExpr expr meta_exp_ty
           ; untypeq <- tcLookupId unTypeQName
           ; let expr'' = mkHsApp (nlHsTyApp untypeq [res_ty]) expr'
           ; ps <- readMutVar ps_var
           ; writeMutVar ps_var ((splice_name, expr'') : ps)

           -- The returned expression is ignored; it's in the pending splices
           ; return (panic "tcSpliceExpr") }

    tcNestedSplice _ _ splice_name _ _
      = pprPanic "tcNestedSplice: rename stage found" (ppr splice_name)

    tcTopSplice :: LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
    tcTopSplice expr res_ty
      = do { -- Typecheck the expression,
             -- making sure it has type Q (T res_ty)
             meta_exp_ty <- tcTExpTy res_ty
           ; zonked_q_expr <- tcTopSpliceExpr True $
                              tcMonoExpr expr meta_exp_ty

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

             -- Rename and typecheck the spliced-in expression,
             -- making sure it has type res_ty
             -- These steps should never fail; this is a *typed* splice
           ; addErrCtxt (spliceResultDoc expr) $ do
           { (exp3, _fvs) <- rnLExpr expr2
           ; exp4 <- tcMonoExpr exp3 res_ty
           ; return (unLoc exp4) } }

\end{code} %************************************************************************ %* * \subsection{Error messages} %* * %************************************************************************ \begin{code}

    quotationCtxtDoc :: HsBracket Name -> SDoc
    quotationCtxtDoc br_body
      = hang (ptext (sLit "In the Template Haskell quotation"))
             2 (ppr br_body)

    spliceCtxtDoc :: HsSplice Name -> SDoc
    spliceCtxtDoc splice
      = hang (ptext (sLit "In the Template Haskell splice"))
             2 (pprTypedSplice splice)

    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 :: Bool -> 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 isTypedSplice tc_action
      = checkNoErrs $  -- checkNoErrs: must not try to run the thing
                       -- if the type checker fails!
        unsetGOptM Opt_DeferTypeErrors $
                       -- Don't defer type errors.  Not only are we
                       -- going to run this code, but we do an unsafe
                       -- coerce, so we get a seg-fault if, say we
                       -- splice a type into a place where an expression
                       -- is expected (Trac #7276)
        setStage (Splice isTypedSplice) $
        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} Note [Renamer errors] ~~~~~~~~~~~~~~~~~~~~~ It's important to wrap renamer calls in checkNoErrs, because the renamer does not fail for out of scope variables etc. Instead it returns a bogus term/type, so that it can report more than one error. We don't want the type checker to see these bogus unbound variables. %************************************************************************ %* * 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 False $
               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. Because 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)
            ; HsQuasiQuote quoter'' _ quote' <- getHooked runQuasiQuoteHook return >>=
                 ($ HsQuasiQuote quoter' q_span quote)

              -- 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 False (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}

    runQuasi :: TH.Q a -> TcM a
    runQuasi act = TH.runQ act

\end{code} \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 MsgDoc 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

    runMetaP :: LHsExpr Id          -- Of type (Q Pat)
             -> TcM (LPat RdrName)
    runMetaP = runMetaQ patMetaOps

    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 MsgDoc 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)
            ; recordThSpliceUse -- seems to be the best place to do this,
                                -- we catch all kinds of splices and annotations.

            -- Check that we've had no errors of any sort so far.
            -- For example, if we found an error in an earlier defn f, but
            -- recovered giving it type f :: forall a.a, it'd be very dodgy
            -- to carry ont.  Mind you, the staging restrictions mean we won't
            -- actually run f, but it still seems wrong. And, more concretely,
            -- see Trac #5358 for an example that fell over when trying to
            -- reify a function with a "?" kind in it.  (These don't occur
            -- in type-correct programs.
            ; failIfErrsM

            -- Desugar
            ; ds_expr <- initDsTc (dsLExpr expr)
            -- Compile and link it; might fail if linking fails
            ; hsc_env <- getTopEnv
            ; src_span <- getSrcSpanM
            ; traceTc "About to run (desugared)" (ppr ds_expr)
            ; either_hval <- tryM $ liftIO $
                             HscMain.hscCompileCoreExpr hsc_env src_span ds_expr
            ; case either_hval of {
                Left exn   -> fail_with_exn "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
                             _ -> fail_with_exn "run" se -- Exception
            }}}
      where
        -- see Note [Concealed TH exceptions]
        fail_with_exn phase exn = do
            exn_msg <- liftIO $ Panic.safeShowException exn
            let msg = vcat [text "Exception when trying to" <+> text phase <+> text "compile-time code:",
                            nest 2 (text exn_msg),
                            if show_code then text "Code:" <+> ppr expr else empty]
            failWithTc msg

\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 Note [Concealed TH exceptions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When displaying the error message contained in an exception originated from TH code, we need to make sure that the error message itself does not contain an exception. For example, when executing the following splice: $( error ("foo " ++ error "bar") ) the message for the outer exception is a thunk which will throw the inner exception when evaluated. For this reason, we display the message of a TH exception using the 'safeShowException' function, which recursively catches any exception thrown when showing an error message. 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 = addWarn (text msg)

      qLocation = do { m <- getModule
                     ; l <- getSrcSpanM
                     ; r <- case l of
                            UnhelpfulSpan _ -> pprPanic "qLocation: Unhelpful location"
                                                        (ppr l)
                            RealSrcSpan s -> return s
                     ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile r)
                                      , TH.loc_module   = moduleNameString (moduleName m)
                                      , TH.loc_package  = packageIdString (modulePackageId m)
                                      , TH.loc_start = (srcSpanStartLine r, srcSpanStartCol r)
                                      , TH.loc_end = (srcSpanEndLine   r, srcSpanEndCol   r) }) }

      qLookupName       = lookupName
      qReify            = reify
      qReifyInstances   = reifyInstances
      qReifyRoles       = reifyRoles
      qReifyAnnotations = reifyAnnotations
      qReifyModule      = reifyModule

            -- 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

      qAddDependentFile fp = do
        ref <- fmap tcg_dependent_files getGblEnv
        dep_files <- readTcRef ref
        writeTcRef ref (fp:dep_files)

      qAddTopDecls thds = do
          l <- getSrcSpanM
          let either_hval = convertToHsDecls l thds
          ds <- case either_hval of
                  Left exn -> pprPanic "qAddTopDecls: can't convert top-level declarations" exn
                  Right ds -> return ds
          mapM_ (checkTopDecl . unLoc) ds
          th_topdecls_var <- fmap tcg_th_topdecls getGblEnv
          updTcRef th_topdecls_var (\topds -> ds ++ topds)
        where
          checkTopDecl :: HsDecl RdrName -> TcM ()
          checkTopDecl (ValD binds)
            = mapM_ bindName (collectHsBindBinders binds)
          checkTopDecl (SigD _)
            = return ()
          checkTopDecl (ForD (ForeignImport (L _ name) _ _ _))
            = bindName name
          checkTopDecl _
            = addErr $ text "Only function, value, and foreign import declarations may be added with addTopDecl"

          bindName :: RdrName -> TcM ()
          bindName (Exact n)
            = do { th_topnames_var <- fmap tcg_th_topnames getGblEnv
                 ; updTcRef th_topnames_var (\ns -> addOneToNameSet ns n)
                 }

          bindName name =
              addErr $
              hang (ptext (sLit "The binder") <+> quotes (ppr name) <+> ptext (sLit "is not a NameU."))
                 2 (text "Probable cause: you used mkName instead of newName to generate a binding.")

      qAddModFinalizer fin = do
          th_modfinalizers_var <- fmap tcg_th_modfinalizers getGblEnv
          updTcRef th_modfinalizers_var (\fins -> fin:fins)

      qGetQ = do
          th_state_var <- fmap tcg_th_state getGblEnv
          th_state <- readTcRef th_state_var
          let x = Map.lookup (typeOf x) th_state >>= fromDynamic
          return x

      qPutQ x = do
          th_state_var <- fmap tcg_th_state getGblEnv
          updTcRef th_state_var (\m -> Map.insert (typeOf x) (toDyn x) m)

\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])]) }

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

    reifyInstances :: TH.Name -> [TH.Type] -> TcM [TH.Dec]
    reifyInstances th_nm th_tys
       = addErrCtxt (ptext (sLit "In the argument of reifyInstances:")
                     <+> ppr_th th_nm <+> sep (map ppr_th th_tys)) $
         do { loc <- getSrcSpanM
            ; rdr_ty <- cvt loc (mkThAppTs (TH.ConT th_nm) th_tys)
            ; (rn_ty, _fvs) <- checkNoErrs $ rnLHsType doc rdr_ty   -- Rename  to HsType Name
                             -- checkNoErrs: see Note [Renamer errors]
            ; (ty, _kind)  <- tcLHsType rn_ty
            ; ty <- zonkTcTypeToType emptyZonkEnv ty   -- Substitute out the meta type variables
                                                       -- In particular, the type might have kind
                                                       -- variables inside it (Trac #7477)

            ; traceTc "reifyInstances" (ppr ty $$ ppr (typeKind ty))
            ; case splitTyConApp_maybe ty of   -- This expands any type synonyms
                Just (tc, tys)                 -- See Trac #7910
                   | Just cls <- tyConClass_maybe tc
                   -> do { inst_envs <- tcGetInstEnvs
                         ; let (matches, unifies, _) = lookupInstEnv inst_envs cls tys
                         ; traceTc "reifyInstances1" (ppr matches)
                         ; mapM reifyClassInstance (map fst matches ++ unifies) }
                   | isOpenFamilyTyCon tc
                   -> do { inst_envs <- tcGetFamInstEnvs
                         ; let matches = lookupFamInstEnv inst_envs tc tys
                         ; traceTc "reifyInstances2" (ppr matches)
                         ; mapM (reifyFamilyInstance . fim_instance) matches }
                _  -> bale_out (hang (ptext (sLit "reifyInstances:") <+> quotes (ppr ty))
                                   2 (ptext (sLit "is not a class constraint or type family application"))) }
      where
        doc = ClassInstanceCtx
        bale_out msg = failWithTc msg

        cvt :: SrcSpan -> TH.Type -> TcM (LHsType RdrName)
        cvt loc th_ty = case convertToHsType loc th_ty of
                          Left msg -> failWithTc msg
                          Right ty -> return ty

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

    lookupName :: Bool      -- True  <=> type namespace
                            -- False <=> value namespace
               -> String -> TcM (Maybe TH.Name)
    lookupName is_type_name s
      = do { lcl_env <- getLocalRdrEnv
           ; case lookupLocalRdrEnv lcl_env rdr_name of
               Just n  -> return (Just (reifyName n))
               Nothing -> do { mb_nm <- lookupGlobalOccRn_maybe rdr_name
                             ; return (fmap reifyName mb_nm) } }
      where
        th_name = TH.mkName s       -- Parses M.x into a base of 'x' and a module of 'M'

        occ_fs :: FastString
        occ_fs = mkFastString (TH.nameBase th_name)

        occ :: OccName
        occ | is_type_name
            = if isLexCon occ_fs then mkTcOccFS    occ_fs
                                 else mkTyVarOccFS occ_fs
            | otherwise
            = if isLexCon occ_fs then mkDataOccFS occ_fs
                                 else mkVarOccFS  occ_fs

        rdr_name = case TH.nameModule th_name of
                     Nothing  -> mkRdrUnqual occ
                     Just mod -> mkRdrQual (mkModuleName mod) occ

    getThing :: TH.Name -> TcM TcTyThing
    getThing th_name
      = do  { name <- lookupThName th_name
            ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
            ; tcLookupTh name }
            -- ToDo: this tcLookup could fail, which would give a
            --       rather unhelpful error message
      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"

    reify :: TH.Name -> TcM TH.Info
    reify th_name
      = do  { thing <- getThing th_name
            ; reifyThing thing }

    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 -> TcM (Maybe 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    ->

              case lookupNameEnv (tcg_type_env gbl_env) name of {
                    Just thing -> return (AGlobal thing);
                    Nothing    ->

              if nameIsLocalOrFrom (tcg_mod gbl_env) name
              then  -- It's defined in this module
                    failWithTc (notInEnv name)

              else
         do { mb_thing <- tcLookupImported_maybe name
            ; case mb_thing of
                Succeeded thing -> return (AGlobal thing)
                Failed msg      -> failWithTc msg
        }}}}

    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")

    ------------------------------
    reifyRoles :: TH.Name -> TcM [TH.Role]
    reifyRoles th_name
      = do { thing <- getThing th_name
           ; case thing of
               AGlobal (ATyCon tc) -> return (map reify_role (tyConRoles tc))
               _ -> failWithTc (ptext (sLit "No roles associated with") <+> (ppr thing))
           }
      where
        reify_role Nominal          = TH.NominalR
        reify_role Representational = TH.RepresentationalR
        reify_role Phantom          = TH.PhantomR

    ------------------------------
    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 (AConLike (RealDataCon 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 (AGlobal (AConLike (PatSynCon ps)))
      = noTH (sLit "pattern synonyms") (ppr $ patSynId ps)

    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 tv1)
      = do { ty1 <- zonkTcTyVar tv1
           ; ty2 <- reifyType ty1
           ; return (TH.TyVarI (reifyName tv) ty2) }

    reifyThing thing = pprPanic "reifyThing" (pprTcTyThingCategory thing)

    -------------------------------------------
    reifyAxBranch :: CoAxBranch -> TcM TH.TySynEqn
    reifyAxBranch (CoAxBranch { cab_lhs = args, cab_rhs = rhs })
                -- remove kind patterns (#8884)
      = do { args' <- mapM reifyType (filter (not . isKind) args)
           ; rhs'  <- reifyType rhs
           ; return (TH.TySynEqn args' rhs') }

    reifyTyCon :: TyCon -> TcM TH.Info
    reifyTyCon tc
      | Just cls <- tyConClass_maybe tc
      = reifyClass cls

      | isFunTyCon tc
      = return (TH.PrimTyConI (reifyName tc) 2                False)

      | isPrimTyCon tc
      = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))

      | isFamilyTyCon tc
      = do { let tvs      = tyConTyVars tc
                 kind     = tyConKind tc

                 -- we need the *result kind* (see #8884)
                 (kvs, mono_kind) = splitForAllTys kind
                                    -- tyConArity includes *kind* params
                 (_, res_kind)    = splitKindFunTysN (tyConArity tc - length kvs)
                                                     mono_kind
           ; kind' <- fmap Just (reifyKind res_kind)

           ; tvs' <- reifyTyVars tvs
           ; flav' <- reifyFamFlavour tc
           ; case flav' of
             { Left flav ->  -- open type/data family
                 do { fam_envs <- tcGetFamInstEnvs
                    ; instances <- mapM reifyFamilyInstance (familyInstances fam_envs tc)
                    ; return (TH.FamilyI
                                (TH.FamilyD flav (reifyName tc) tvs' kind')
                                instances) }
             ; Right eqns -> -- closed type family
                 return (TH.FamilyI
                          (TH.ClosedTypeFamilyD (reifyName tc) tvs' kind' eqns)
                          []) } }

      | Just (tvs, rhs) <- synTyConDefn_maybe tc  -- Vanilla type synonym
      = do { rhs' <- reifyType rhs
           ; tvs' <- reifyTyVars tvs
           ; return (TH.TyConI
                       (TH.TySynD (reifyName tc) tvs' rhs'))
           }

      | otherwise
      = do  { cxt <- reifyCxt (tyConStupidTheta tc)
            ; let tvs = tyConTyVars tc
            ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
            ; r_tvs <- reifyTyVars tvs
            ; let name = reifyName tc
                  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'
             ; ex_tvs'' <- reifyTyVars ex_tvs'
             ; return (TH.ForallC 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
            ; tvs' <- reifyTyVars tvs
            ; let dec = TH.ClassD cxt (reifyName cls) 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 :: ClsInst -> TcM TH.Dec
    reifyClassInstance i
      = do { cxt <- reifyCxt (drop n_silent theta)
           ; thtypes <- reifyTypes types
           ; let head_ty = mkThAppTs (TH.ConT (reifyName cls)) thtypes
           ; return $ (TH.InstanceD cxt head_ty []) }
      where
         (_tvs, theta, cls, types) = tcSplitDFunTy (idType dfun)
         dfun     = instanceDFunId i
         n_silent = dfunNSilent dfun

    ------------------------------
    reifyFamilyInstance :: FamInst -> TcM TH.Dec
    reifyFamilyInstance (FamInst { fi_flavor = flavor
                                 , fi_fam = fam
                                 , fi_tys = lhs
                                 , fi_rhs = rhs })
      = case flavor of
          SynFamilyInst ->
                   -- remove kind patterns (#8884)
            do { th_lhs <- reifyTypes (filter (not . isKind) lhs)
               ; th_rhs <- reifyType  rhs
               ; return (TH.TySynInstD (reifyName fam) (TH.TySynEqn th_lhs th_rhs)) }

          DataFamilyInst rep_tc ->
            do { let tvs = tyConTyVars rep_tc
                     fam' = reifyName fam
               ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons rep_tc)
               ; th_tys <- reifyTypes lhs
               ; return (if isNewTyCon rep_tc
                         then TH.NewtypeInstD [] fam' th_tys (head cons) []
                         else TH.DataInstD    [] fam' th_tys cons        []) }

    ------------------------------
    reifyType :: TypeRep.Type -> TcM TH.Type
    -- Monadic only because of failure
    reifyType ty@(ForAllTy _ _)        = reify_for_all ty
    reifyType (LitTy t)         = do { r <- reifyTyLit t; return (TH.LitT r) }
    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 ty@(FunTy t1 t2)
      | isPredTy t1 = reify_for_all ty  -- Types like ((?x::Int) => Char -> Char)
      | otherwise   = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }

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

    reifyTyLit :: TypeRep.TyLit -> TcM TH.TyLit
    reifyTyLit (NumTyLit n) = return (TH.NumTyLit n)
    reifyTyLit (StrTyLit s) = return (TH.StrTyLit (unpackFS s))

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

    reifyKind :: Kind -> TcM TH.Kind
    reifyKind  ki
      = do { let (kis, ki') = splitKindFunTys ki
           ; ki'_rep <- reifyNonArrowKind ki'
           ; kis_rep <- mapM reifyKind kis
           ; return (foldr (TH.AppT . TH.AppT TH.ArrowT) ki'_rep kis_rep) }
      where
        reifyNonArrowKind k | isLiftedTypeKind k = return TH.StarT
                            | isConstraintKind k = return TH.ConstraintT
        reifyNonArrowKind (TyVarTy v)            = return (TH.VarT (reifyName v))
        reifyNonArrowKind (ForAllTy _ k)         = reifyKind k
        reifyNonArrowKind (TyConApp kc kis)      = reify_kc_app kc kis
        reifyNonArrowKind (AppTy k1 k2)          = do { k1' <- reifyKind k1
                                                      ; k2' <- reifyKind k2
                                                      ; return (TH.AppT k1' k2')
                                                      }
        reifyNonArrowKind k                      = noTH (sLit "this kind") (ppr k)

    reify_kc_app :: TyCon -> [TypeRep.Kind] -> TcM TH.Kind
    reify_kc_app kc kis
      = fmap (mkThAppTs r_kc) (mapM reifyKind kis)
      where
        r_kc | Just tc <- isPromotedTyCon_maybe kc
             , isTupleTyCon tc          = TH.TupleT (tyConArity kc)
             | kc `hasKey` listTyConKey = TH.ListT
             | otherwise                = TH.ConT (reifyName kc)

    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 -> TcM (Either TH.FamFlavour [TH.TySynEqn])
    reifyFamFlavour tc
      | isOpenSynFamilyTyCon tc = return $ Left TH.TypeFam
      | isDataFamilyTyCon    tc = return $ Left TH.DataFam

        -- this doesn't really handle abstract closed families, but let's not worry
        -- about that now
      | Just ax <- isClosedSynFamilyTyCon_maybe tc
      = do { eqns <- brListMapM reifyAxBranch $ coAxiomBranches ax
           ; return $ Right eqns }

      | otherwise
      = panic "TcSplice.reifyFamFlavour: not a type family"

    reifyTyVars :: [TyVar]
                -> TcM [TH.TyVarBndr]
    reifyTyVars tvs = mapM reify_tv $ filter isTypeVar tvs
      where
        reify_tv tv | isLiftedTypeKind kind = return (TH.PlainTV  name)
                    | otherwise             = do kind' <- reifyKind kind
                                                 return (TH.KindedTV name 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 (removeKinds (tyConKind tc) tys)
           ; return (mkThAppTs r_tc tys') }
      where
        arity = tyConArity tc
        r_tc | isTupleTyCon tc            = if isPromotedDataCon tc
                                            then TH.PromotedTupleT arity
                                            else TH.TupleT arity
             | tc `hasKey` listTyConKey   = TH.ListT
             | tc `hasKey` nilDataConKey  = TH.PromotedNilT
             | tc `hasKey` consDataConKey = TH.PromotedConsT
             | otherwise                  = TH.ConT (reifyName tc)
        removeKinds :: Kind -> [TypeRep.Type] -> [TypeRep.Type]
        removeKinds (FunTy k1 k2) (h:t)
          | isSuperKind k1          = removeKinds k2 t
          | otherwise               = h : removeKinds k2 t
        removeKinds (ForAllTy v k) (h:t)
          | isSuperKind (varType v) = removeKinds k t
          | otherwise               = h : removeKinds k t
        removeKinds _ tys           = tys

    reifyPred :: TypeRep.PredType -> TcM TH.Pred
    reifyPred ty
      -- We could reify the implicit paramter as a class but it seems
      -- nicer to support them properly...
      | isIPPred ty = noTH (sLit "implicit parameters") (ppr ty)
      | otherwise
       = case classifyPredType ty of
      ClassPred cls tys -> do { tys' <- reifyTypes tys
                              ; return $ TH.ClassP (reifyName cls) tys' }
      EqPred ty1 ty2    -> do { ty1' <- reifyType ty1
                              ; ty2' <- reifyType ty2
                              ; return $ TH.EqualP ty1' ty2'
                              }
      TuplePred _ -> noTH (sLit "tuple predicates") (ppr ty)
      IrredPred _ -> noTH (sLit "irreducible predicates") (ppr ty)

    ------------------------------
    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 :: DataCon.HsBang -> TH.Strict
    reifyStrict HsNoBang                      = TH.NotStrict
    reifyStrict (HsUserBang _ False)          = TH.NotStrict
    reifyStrict (HsUserBang (Just True) True) = TH.Unpacked
    reifyStrict (HsUserBang _     True)       = TH.IsStrict
    reifyStrict HsStrict                      = TH.IsStrict
    reifyStrict (HsUnpack {})                 = TH.Unpacked

    ------------------------------
    lookupThAnnLookup :: TH.AnnLookup -> TcM CoreAnnTarget
    lookupThAnnLookup (TH.AnnLookupName th_nm) = fmap NamedTarget (lookupThName th_nm)
    lookupThAnnLookup (TH.AnnLookupModule (TH.Module pn mn))
      = return $ ModuleTarget $
        mkModule (stringToPackageId $ TH.pkgString pn) (mkModuleName $ TH.modString mn)

    reifyAnnotations :: Data a => TH.AnnLookup -> TcM [a]
    reifyAnnotations th_nm
      = do { name <- lookupThAnnLookup th_nm
           ; eps <- getEps
           ; tcg <- getGblEnv
           ; let epsAnns = findAnns deserializeWithData (eps_ann_env eps) name
           ; let envAnns = findAnns deserializeWithData (tcg_ann_env tcg) name
           ; return (envAnns ++ epsAnns) }

    ------------------------------
    modToTHMod :: Module -> TH.Module
    modToTHMod m = TH.Module (TH.PkgName $ packageIdString  $ modulePackageId m)
                             (TH.ModName $ moduleNameString $ moduleName m)

    reifyModule :: TH.Module -> TcM TH.ModuleInfo
    reifyModule (TH.Module (TH.PkgName pkgString) (TH.ModName mString)) = do
      this_mod <- getModule
      let reifMod = mkModule (stringToPackageId pkgString) (mkModuleName mString)
      if (reifMod == this_mod) then reifyThisModule else reifyFromIface reifMod
        where
          reifyThisModule = do
            usages <- fmap (map modToTHMod . moduleEnvKeys . imp_mods) getImports
            return $ TH.ModuleInfo usages

          reifyFromIface reifMod = do
            iface <- loadInterfaceForModule (ptext (sLit "reifying module from TH for") <+> ppr reifMod) reifMod
            let usages = [modToTHMod m | usage <- mi_usages iface,
                                         Just m <- [usageToModule (modulePackageId reifMod) usage] ]
            return $ TH.ModuleInfo usages

          usageToModule :: PackageId -> Usage -> Maybe Module
          usageToModule _ (UsageFile {}) = Nothing
          usageToModule this_pkg (UsageHomeModule { usg_mod_name = mn }) = Just $ mkModule this_pkg mn
          usageToModule _ (UsagePackageModule { usg_mod = m }) = Just m

    ------------------------------
    mkThAppTs :: TH.Type -> [TH.Type] -> TH.Type
    mkThAppTs fun_ty arg_tys = foldl TH.AppT fun_ty arg_tys

    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])

    ppr_th :: TH.Ppr a => a -> SDoc
    ppr_th x = text (TH.pprint x)

\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 \begin{code}

    #endif  /* GHCI */

\end{code}