2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 TcSplice: Template Haskell splices
10 {-# OPTIONS -fno-warn-unused-imports -fno-warn-unused-binds #-}
11 -- The above warning supression flag is a temporary kludge.
12 -- While working on this module you are encouraged to remove it and fix
13 -- any warnings in the module. See
14 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
17 module TcSplice( kcSpliceType, tcSpliceExpr, tcSpliceDecls, tcBracket,
19 runQuasiQuoteExpr, runQuasiQuotePat,
20 runQuasiQuoteDecl, runQuasiQuoteType,
23 #include "HsVersions.h"
27 -- These imports are the reason that TcSplice
28 -- is very high up the module hierarchy
66 import DsMonad hiding (Splice)
77 import Control.Monad ( when )
79 import qualified Language.Haskell.TH as TH
80 -- THSyntax gives access to internal functions and data types
81 import qualified Language.Haskell.TH.Syntax as TH
84 -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
85 import GHC.Desugar ( AnnotationWrapper(..) )
88 import GHC.Exts ( unsafeCoerce#, Int#, Int(..) )
89 import System.IO.Error
92 Note [How top-level splices are handled]
93 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
94 Top-level splices (those not inside a [| .. |] quotation bracket) are handled
95 very straightforwardly:
97 1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
99 2. runMetaT: desugar, compile, run it, and convert result back to
100 HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
103 3. treat the result as if that's what you saw in the first place
104 e.g for HsType, rename and kind-check
105 for HsExpr, rename and type-check
107 (The last step is different for decls, becuase they can *only* be
108 top-level: we return the result of step 2.)
110 Note [How brackets and nested splices are handled]
111 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
112 Nested splices (those inside a [| .. |] quotation bracket), are treated
115 * After typechecking, the bracket [| |] carries
117 a) A mutable list of PendingSplice
118 type PendingSplice = (Name, LHsExpr Id)
120 b) The quoted expression e, *renamed*: (HsExpr Name)
121 The expression e has been typechecked, but the result of
122 that typechecking is discarded.
124 * The brakcet is desugared by DsMeta.dsBracket. It
126 a) Extends the ds_meta environment with the PendingSplices
127 attached to the bracket
129 b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
130 run, will produce a suitable TH expression/type/decl. This
131 is why we leave the *renamed* expression attached to the bracket:
132 the quoted expression should not be decorated with all the goop
133 added by the type checker
135 * Each splice carries a unique Name, called a "splice point", thus
136 ${n}(e). The name is initialised to an (Unqual "splice") when the
137 splice is created; the renamer gives it a unique.
139 * When the type checker type-checks a nested splice ${n}(e), it
141 - adds the typechecked expression (of type (HsExpr Id))
142 as a pending splice to the enclosing bracket
143 - returns something non-committal
144 Eg for [| f ${n}(g x) |], the typechecker
145 - attaches the typechecked term (g x) to the pending splices for n
147 - returns a non-committal type \alpha.
148 Remember that the bracket discards the typechecked term altogether
150 * When DsMeta (used to desugar the body of the bracket) comes across
151 a splice, it looks up the splice's Name, n, in the ds_meta envt,
152 to find an (HsExpr Id) that should be substituted for the splice;
153 it just desugars it to get a CoreExpr (DsMeta.repSplice).
156 Source: f = [| Just $(g 3) |]
157 The [| |] part is a HsBracket
159 Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
160 The [| |] part is a HsBracketOut, containing *renamed*
161 (not typechecked) expression
162 The "s7" is the "splice point"; the (g Int 3) part
163 is a typechecked expression
165 Desugared: f = do { s7 <- g Int 3
166 ; return (ConE "Data.Maybe.Just" s7) }
169 Note [Template Haskell state diagram]
170 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
171 Here are the ThStages, s, their corresponding level numbers
172 (the result of (thLevel s)), and their state transitions.
174 ----------- $ ------------ $
175 | Comp | ---------> | Splice | -----|
177 ----------- ------------
179 $ | | [||] $ | | [||]
181 -------------- ----------------
182 | Brack Comp | | Brack Splice |
184 -------------- ----------------
186 * Normal top-level declarations start in state Comp
188 Annotations start in state Splice, since they are
189 treated very like a splice (only without a '$')
191 * Code compiled in state Splice (and only such code)
192 will be *run at compile time*, with the result replacing
195 * The original paper used level -1 instead of 0, etc.
197 * The original paper did not allow a splice within a
198 splice, but there is no reason not to. This is the
199 $ transition in the top right.
201 Note [Template Haskell levels]
202 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
203 * Imported things are impLevel (= 0)
205 * In GHCi, variables bound by a previous command are treated
206 as impLevel, because we have bytecode for them.
208 * Variables are bound at the "current level"
210 * The current level starts off at outerLevel (= 1)
212 * The level is decremented by splicing $(..)
213 incremented by brackets [| |]
214 incremented by name-quoting 'f
216 When a variable is used, we compare
217 bind: binding level, and
218 use: current level at usage site
221 bind > use Always error (bound later than used)
224 bind = use Always OK (bound same stage as used)
225 [| \x -> $(f [| x |]) |]
227 bind < use Inside brackets, it depends
231 For (bind < use) inside brackets, there are three cases:
232 - Imported things OK f = [| map |]
233 - Top-level things OK g = [| f |]
234 - Non-top-level Only if there is a liftable instance
235 h = \(x:Int) -> [| x |]
237 See Note [What is a top-level Id?]
241 A quoted name 'n is a bit like a quoted expression [| n |], except that we
242 have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
243 the use-level to account for the brackets, the cases are:
252 See Note [What is a top-level Id?] in TcEnv. Examples:
254 f 'map -- OK; also for top-level defns of this module
256 \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
257 -- cross-stage lifting
259 \y. [| \x. $(f 'y) |] -- Not ok (same reason)
261 [| \x. $(f 'x) |] -- OK
264 Note [What is a top-level Id?]
265 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
266 In the level-control criteria above, we need to know what a "top level Id" is.
267 There are three kinds:
268 * Imported from another module (GlobalId, ExternalName)
269 * Bound at the top level of this module (ExternalName)
270 * In GHCi, bound by a previous stmt (GlobalId)
271 It's strange that there is no one criterion tht picks out all three, but that's
272 how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
273 bound in an earlier Stmt, but what module would you choose? See
274 Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
276 The predicate we use is TcEnv.thTopLevelId.
279 %************************************************************************
281 \subsection{Main interface + stubs for the non-GHCI case
283 %************************************************************************
286 tcBracket :: HsBracket Name -> BoxyRhoType -> TcM (LHsExpr TcId)
287 tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
288 tcSpliceExpr :: HsSplice Name -> BoxyRhoType -> TcM (HsExpr TcId)
289 kcSpliceType :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
290 -- None of these functions add constraints to the LIE
292 lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
294 runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
295 runQuasiQuotePat :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
296 runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
297 runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]
299 runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
302 tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
303 tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
304 tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
305 kcSpliceType x fvs = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
307 lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
309 runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
310 runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
311 runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
312 runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
313 runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
317 %************************************************************************
319 \subsection{Quoting an expression}
321 %************************************************************************
325 -- See Note [How brackets and nested splices are handled]
326 tcBracket brack res_ty
327 = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
329 do { -- Check for nested brackets
330 cur_stage <- getStage
331 ; checkTc (not (isBrackStage cur_stage)) illegalBracket
333 -- Brackets are desugared to code that mentions the TH package
336 -- Typecheck expr to make sure it is valid,
337 -- but throw away the results. We'll type check
338 -- it again when we actually use it.
339 ; pending_splices <- newMutVar []
340 ; lie_var <- getLIEVar
342 ; (meta_ty, lie) <- setStage (Brack cur_stage pending_splices lie_var)
343 (getLIE (tc_bracket cur_stage brack))
344 ; tcSimplifyBracket lie
346 -- Make the expected type have the right shape
347 ; _ <- boxyUnify meta_ty res_ty
349 -- Return the original expression, not the type-decorated one
350 ; pendings <- readMutVar pending_splices
351 ; return (noLoc (HsBracketOut brack pendings)) }
353 tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
354 tc_bracket outer_stage (VarBr name) -- Note [Quoting names]
355 = do { thing <- tcLookup name
357 AGlobal _ -> return ()
358 ATcId { tct_level = bind_lvl, tct_id = id }
359 | thTopLevelId id -- C.f TcExpr.checkCrossStageLifting
362 -> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
363 (quotedNameStageErr name) }
364 _ -> pprPanic "th_bracket" (ppr name)
366 ; tcMetaTy nameTyConName -- Result type is Var (not Q-monadic)
369 tc_bracket _ (ExpBr expr)
370 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
371 ; _ <- tcMonoExprNC expr any_ty -- NC for no context; tcBracket does that
372 ; tcMetaTy expQTyConName }
373 -- Result type is ExpQ (= Q Exp)
375 tc_bracket _ (TypBr typ)
376 = do { _ <- tcHsSigTypeNC ThBrackCtxt typ
377 ; tcMetaTy typeQTyConName }
378 -- Result type is Type (= Q Typ)
380 tc_bracket _ (DecBrG decls)
381 = do { _ <- tcTopSrcDecls emptyModDetails decls
382 -- Typecheck the declarations, dicarding the result
383 -- We'll get all that stuff later, when we splice it in
384 ; tcMetaTy decsQTyConName } -- Result type is Q [Dec]
386 tc_bracket _ (PatBr pat)
387 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
388 ; _ <- tcPat ThPatQuote pat any_ty unitTy $ \_ ->
390 ; tcMetaTy patQTyConName }
391 -- Result type is PatQ (= Q Pat)
393 tc_bracket _ (DecBrL _)
394 = panic "tc_bracket: Unexpected DecBrL"
396 quotedNameStageErr :: Name -> SDoc
398 = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
399 , ptext (sLit "must be used at the same stage at which is is bound")]
403 %************************************************************************
405 \subsection{Splicing an expression}
407 %************************************************************************
410 tcSpliceExpr (HsSplice name expr) res_ty
411 = setSrcSpan (getLoc expr) $ do
414 Splice -> tcTopSplice expr res_ty ;
415 Comp -> tcTopSplice expr res_ty ;
417 Brack pop_stage ps_var lie_var -> do
419 -- See Note [How brackets and nested splices are handled]
420 -- A splice inside brackets
421 -- NB: ignore res_ty, apart from zapping it to a mono-type
422 -- e.g. [| reverse $(h 4) |]
423 -- Here (h 4) :: Q Exp
424 -- but $(h 4) :: forall a.a i.e. anything!
427 ; meta_exp_ty <- tcMetaTy expQTyConName
428 ; expr' <- setStage pop_stage $
430 tcMonoExpr expr meta_exp_ty
432 -- Write the pending splice into the bucket
433 ; ps <- readMutVar ps_var
434 ; writeMutVar ps_var ((name,expr') : ps)
436 ; return (panic "tcSpliceExpr") -- The returned expression is ignored
439 tcTopSplice :: LHsExpr Name -> BoxyRhoType -> TcM (HsExpr Id)
440 -- Note [How top-level splices are handled]
441 tcTopSplice expr res_ty
442 = do { meta_exp_ty <- tcMetaTy expQTyConName
444 -- Typecheck the expression
445 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
447 -- Run the expression
448 ; expr2 <- runMetaE zonked_q_expr
449 ; showSplice "expression" expr (ppr expr2)
451 -- Rename it, but bale out if there are errors
452 -- otherwise the type checker just gives more spurious errors
453 ; addErrCtxt (spliceResultDoc expr) $ do
454 { (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
456 ; exp4 <- tcMonoExpr exp3 res_ty
457 ; return (unLoc exp4) } }
459 spliceResultDoc :: LHsExpr Name -> SDoc
461 = sep [ ptext (sLit "In the result of the splice:")
462 , nest 2 (char '$' <> pprParendExpr expr)
463 , ptext (sLit "To see what the splice expanded to, use -ddump-splices")]
466 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
467 -- Note [How top-level splices are handled]
468 -- Type check an expression that is the body of a top-level splice
469 -- (the caller will compile and run it)
470 -- Note that set the level to Splice, regardless of the original level,
471 -- before typechecking the expression. For example:
472 -- f x = $( ...$(g 3) ... )
473 -- The recursive call to tcMonoExpr will simply expand the
474 -- inner escape before dealing with the outer one
476 tcTopSpliceExpr tc_action
477 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
478 -- if the type checker fails!
480 do { -- Typecheck the expression
481 (expr', lie) <- getLIE tc_action
483 -- Solve the constraints
484 ; const_binds <- tcSimplifyTop lie
486 -- Zonk it and tie the knot of dictionary bindings
487 ; zonkTopLExpr (mkHsDictLet const_binds expr') }
491 %************************************************************************
495 %************************************************************************
497 Very like splicing an expression, but we don't yet share code.
500 kcSpliceType splice@(HsSplice name hs_expr) fvs
501 = setSrcSpan (getLoc hs_expr) $ do
504 Splice -> kcTopSpliceType hs_expr ;
505 Comp -> kcTopSpliceType hs_expr ;
507 Brack pop_level ps_var lie_var -> do
508 -- See Note [How brackets and nested splices are handled]
509 -- A splice inside brackets
510 { meta_ty <- tcMetaTy typeQTyConName
511 ; expr' <- setStage pop_level $
513 tcMonoExpr hs_expr meta_ty
515 -- Write the pending splice into the bucket
516 ; ps <- readMutVar ps_var
517 ; writeMutVar ps_var ((name,expr') : ps)
519 -- e.g. [| f (g :: Int -> $(h 4)) |]
520 -- Here (h 4) :: Q Type
521 -- but $(h 4) :: a i.e. any type, of any kind
524 ; return (HsSpliceTy splice fvs kind, kind)
527 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
528 -- Note [How top-level splices are handled]
530 = do { meta_ty <- tcMetaTy typeQTyConName
532 -- Typecheck the expression
533 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
535 -- Run the expression
536 ; hs_ty2 <- runMetaT zonked_q_expr
537 ; showSplice "type" expr (ppr hs_ty2)
539 -- Rename it, but bale out if there are errors
540 -- otherwise the type checker just gives more spurious errors
541 ; addErrCtxt (spliceResultDoc expr) $ do
542 { let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
543 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
544 ; (ty4, kind) <- kcLHsType hs_ty3
545 ; return (unLoc ty4, kind) }}
548 %************************************************************************
550 \subsection{Splicing an expression}
552 %************************************************************************
555 -- Note [How top-level splices are handled]
556 -- Always at top level
557 -- Type sig at top of file:
558 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
560 = do { list_q <- tcMetaTy decsQTyConName -- Q [Dec]
561 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
563 -- Run the expression
564 ; decls <- runMetaD zonked_q_expr
565 ; showSplice "declarations" expr
566 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
572 %************************************************************************
576 %************************************************************************
579 runAnnotation target expr = do
580 -- Find the classes we want instances for in order to call toAnnotationWrapper
582 data_class <- tcLookupClass dataClassName
583 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
585 -- Check the instances we require live in another module (we want to execute it..)
586 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
587 -- also resolves the LIE constraints to detect e.g. instance ambiguity
588 zonked_wrapped_expr' <- tcTopSpliceExpr $
589 do { (expr', expr_ty) <- tcInferRhoNC expr
590 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
591 -- By instantiating the call >here< it gets registered in the
592 -- LIE consulted by tcTopSpliceExpr
593 -- and hence ensures the appropriate dictionary is bound by const_binds
594 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
595 ; let specialised_to_annotation_wrapper_expr
596 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
597 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
599 -- Run the appropriately wrapped expression to get the value of
600 -- the annotation and its dictionaries. The return value is of
601 -- type AnnotationWrapper by construction, so this conversion is
603 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
604 case annotation_wrapper of
605 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
606 -- Got the value and dictionaries: build the serialized value and
607 -- call it a day. We ensure that we seq the entire serialized value
608 -- in order that any errors in the user-written code for the
609 -- annotation are exposed at this point. This is also why we are
610 -- doing all this stuff inside the context of runMeta: it has the
611 -- facilities to deal with user error in a meta-level expression
612 seqSerialized serialized `seq` Annotation {
614 ann_value = serialized
619 %************************************************************************
623 %************************************************************************
625 Note [Quasi-quote overview]
626 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
627 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
628 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
633 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
634 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
635 defined in another module, because we are going to run it here. It's
636 a bit like a TH splice:
639 However, you can do this in patterns as well as terms. Becuase of this,
640 the splice is run by the *renamer* rather than the type checker.
642 %************************************************************************
644 \subsubsection{Quasiquotation}
646 %************************************************************************
648 See Note [Quasi-quote overview] in TcSplice.
651 runQuasiQuote :: Outputable hs_syn
652 => HsQuasiQuote RdrName -- Contains term of type QuasiQuoter, and the String
653 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
654 -> Name -- Name of th_syn type
655 -> MetaOps th_syn hs_syn
657 runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
658 = do { quoter' <- lookupOccRn quoter
659 -- We use lookupOcc rather than lookupGlobalOcc because in the
660 -- erroneous case of \x -> [x| ...|] we get a better error message
661 -- (stage restriction rather than out of scope).
663 ; when (isUnboundName quoter') failM
664 -- If 'quoter' is not in scope, proceed no further
665 -- The error message was generated by lookupOccRn, but it then
666 -- succeeds with an "unbound name", which makes the subsequent
667 -- attempt to run the quote fail in a confusing way
669 -- Check that the quoter is not locally defined, otherwise the TH
670 -- machinery will not be able to run the quasiquote.
671 ; this_mod <- getModule
672 ; let is_local = nameIsLocalOrFrom this_mod quoter'
673 ; checkTc (not is_local) (quoteStageError quoter')
675 ; traceTc (text "runQQ" <+> ppr quoter <+> ppr is_local)
677 -- Build the expression
678 ; let quoterExpr = L q_span $! HsVar $! quoter'
679 ; let quoteExpr = L q_span $! HsLit $! HsString quote
680 ; let expr = L q_span $
682 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
683 ; meta_exp_ty <- tcMetaTy meta_ty
685 -- Typecheck the expression
686 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
688 -- Run the expression
689 ; result <- runMetaQ meta_ops zonked_q_expr
690 ; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
694 runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName expQTyConName exprMetaOps
695 runQuasiQuotePat qq = runQuasiQuote qq quotePatName patQTyConName patMetaOps
696 runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
697 runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName decsQTyConName declMetaOps
699 quoteStageError :: Name -> SDoc
700 quoteStageError quoter
701 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
702 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
706 %************************************************************************
708 \subsection{Running an expression}
710 %************************************************************************
713 data MetaOps th_syn hs_syn
714 = MT { mt_desc :: String -- Type of beast (expression, type etc)
715 , mt_show :: th_syn -> String -- How to show the th_syn thing
716 , mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
717 -- How to convert to hs_syn
720 exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
721 exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
723 patMetaOps :: MetaOps TH.Pat (LPat RdrName)
724 patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
726 typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
727 typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
729 declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
730 declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
733 runMetaAW :: Outputable output
734 => (AnnotationWrapper -> output)
735 -> LHsExpr Id -- Of type AnnotationWrapper
737 runMetaAW k = runMeta False (\_ -> return . Right . k)
738 -- We turn off showing the code in meta-level exceptions because doing so exposes
739 -- the toAnnotationWrapper function that we slap around the users code
742 runMetaQ :: Outputable hs_syn
743 => MetaOps th_syn hs_syn
746 runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
747 = runMeta True run_and_cvt expr
749 run_and_cvt expr_span hval
750 = do { th_result <- TH.runQ hval
751 ; traceTc (text "Got TH result:" <+> text (show_th th_result))
752 ; return (cvt expr_span th_result) }
754 runMetaE :: LHsExpr Id -- Of type (Q Exp)
755 -> TcM (LHsExpr RdrName)
756 runMetaE = runMetaQ exprMetaOps
758 runMetaT :: LHsExpr Id -- Of type (Q Type)
759 -> TcM (LHsType RdrName)
760 runMetaT = runMetaQ typeMetaOps
762 runMetaD :: LHsExpr Id -- Of type Q [Dec]
763 -> TcM [LHsDecl RdrName]
764 runMetaD = runMetaQ declMetaOps
767 runMeta :: (Outputable hs_syn)
768 => Bool -- Whether code should be printed in the exception message
769 -> (SrcSpan -> x -> TcM (Either Message hs_syn)) -- How to run x
770 -> LHsExpr Id -- Of type x; typically x = Q TH.Exp, or something like that
771 -> TcM hs_syn -- Of type t
772 runMeta show_code run_and_convert expr
773 = do { traceTc (text "About to run" <+> ppr expr)
776 ; ds_expr <- initDsTc (dsLExpr expr)
777 -- Compile and link it; might fail if linking fails
778 ; hsc_env <- getTopEnv
779 ; src_span <- getSrcSpanM
780 ; either_hval <- tryM $ liftIO $
781 HscMain.compileExpr hsc_env src_span ds_expr
782 ; case either_hval of {
783 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
786 { -- Coerce it to Q t, and run it
788 -- Running might fail if it throws an exception of any kind (hence tryAllM)
789 -- including, say, a pattern-match exception in the code we are running
791 -- We also do the TH -> HS syntax conversion inside the same
792 -- exception-cacthing thing so that if there are any lurking
793 -- exceptions in the data structure returned by hval, we'll
794 -- encounter them inside the try
796 -- See Note [Exceptions in TH]
797 let expr_span = getLoc expr
798 ; either_tval <- tryAllM $
799 setSrcSpan expr_span $ -- Set the span so that qLocation can
800 -- see where this splice is
801 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
803 Left err -> failWithTc err
804 Right result -> do { traceTc (ptext (sLit "Got HsSyn result:") <+> ppr result)
805 ; return $! result } }
807 ; case either_tval of
809 Left se -> case fromException se of
810 Just IOEnvFailure -> failM -- Error already in Tc monad
811 _ -> failWithTc (mk_msg "run" se) -- Exception
814 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
815 nest 2 (text (Panic.showException exn)),
816 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
819 Note [Exceptions in TH]
820 ~~~~~~~~~~~~~~~~~~~~~~~
821 Supppose we have something like this
825 f n | n>3 = fail "Too many declarations"
828 The 'fail' is a user-generated failure, and should be displayed as a
829 perfectly ordinary compiler error message, not a panic or anything
830 like that. Here's how it's processed:
832 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
833 effectively transforms (fail s) to
834 qReport True s >> fail
835 where 'qReport' comes from the Quasi class and fail from its monad
838 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
839 (qReport True s) by using addErr to add an error message to the bag of errors.
840 The 'fail' in TcM raises an IOEnvFailure exception
842 * So, when running a splice, we catch all exceptions; then for
843 - an IOEnvFailure exception, we assume the error is already
844 in the error-bag (above)
845 - other errors, we add an error to the bag
849 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
852 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
853 qNewName s = do { u <- newUnique
855 ; return (TH.mkNameU s i) }
857 qReport True msg = addErr (text msg)
858 qReport False msg = addReport (text msg) empty
860 qLocation = do { m <- getModule
862 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
863 , TH.loc_module = moduleNameString (moduleName m)
864 , TH.loc_package = packageIdString (modulePackageId m)
865 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
866 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
870 -- For qRecover, discard error messages if
871 -- the recovery action is chosen. Otherwise
872 -- we'll only fail higher up. c.f. tryTcLIE_
873 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
875 Just val -> do { addMessages msgs -- There might be warnings
877 Nothing -> recover -- Discard all msgs
880 qRunIO io = liftIO io
884 %************************************************************************
886 \subsection{Errors and contexts}
888 %************************************************************************
891 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
892 -- Note that 'before' is *renamed* but not *typechecked*
893 -- Reason (a) less typechecking crap
894 -- (b) data constructors after type checking have been
895 -- changed to their *wrappers*, and that makes them
896 -- print always fully qualified
897 showSplice what before after
898 = do { loc <- getSrcSpanM
899 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
900 nest 2 (sep [nest 2 (ppr before),
904 illegalBracket :: SDoc
905 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
910 %************************************************************************
914 %************************************************************************
918 reify :: TH.Name -> TcM TH.Info
920 = do { name <- lookupThName th_name
921 ; thing <- tcLookupTh name
922 -- ToDo: this tcLookup could fail, which would give a
923 -- rather unhelpful error message
924 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
928 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
929 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
930 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
931 ppr_ns _ = panic "reify/ppr_ns"
933 lookupThName :: TH.Name -> TcM Name
934 lookupThName th_name = do
935 mb_name <- lookupThName_maybe th_name
937 Nothing -> failWithTc (notInScope th_name)
938 Just name -> return name
940 lookupThName_maybe th_name
941 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
942 -- Pick the first that works
943 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
944 ; return (listToMaybe names) }
947 = do { -- Repeat much of lookupOccRn, becase we want
948 -- to report errors in a TH-relevant way
949 ; rdr_env <- getLocalRdrEnv
950 ; case lookupLocalRdrEnv rdr_env rdr_name of
951 Just name -> return (Just name)
952 Nothing -> lookupGlobalOccRn_maybe rdr_name }
954 tcLookupTh :: Name -> TcM TcTyThing
955 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
956 -- it gives a reify-related error message on failure, whereas in the normal
957 -- tcLookup, failure is a bug.
959 = do { (gbl_env, lcl_env) <- getEnvs
960 ; case lookupNameEnv (tcl_env lcl_env) name of {
961 Just thing -> return thing;
963 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
964 then -- It's defined in this module
965 case lookupNameEnv (tcg_type_env gbl_env) name of
966 Just thing -> return (AGlobal thing)
967 Nothing -> failWithTc (notInEnv name)
969 else do -- It's imported
970 { (eps,hpt) <- getEpsAndHpt
972 ; case lookupType dflags hpt (eps_PTE eps) name of
973 Just thing -> return (AGlobal thing)
974 Nothing -> do { thing <- tcImportDecl name
975 ; return (AGlobal thing) }
976 -- Imported names should always be findable;
977 -- if not, we fail hard in tcImportDecl
980 notInScope :: TH.Name -> SDoc
981 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
982 ptext (sLit "is not in scope at a reify")
983 -- Ugh! Rather an indirect way to display the name
985 notInEnv :: Name -> SDoc
986 notInEnv name = quotes (ppr name) <+>
987 ptext (sLit "is not in the type environment at a reify")
989 ------------------------------
990 reifyThing :: TcTyThing -> TcM TH.Info
991 -- The only reason this is monadic is for error reporting,
992 -- which in turn is mainly for the case when TH can't express
993 -- some random GHC extension
995 reifyThing (AGlobal (AnId id))
996 = do { ty <- reifyType (idType id)
997 ; fix <- reifyFixity (idName id)
998 ; let v = reifyName id
999 ; case idDetails id of
1000 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
1001 _ -> return (TH.VarI v ty Nothing fix)
1004 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
1005 reifyThing (AGlobal (AClass cls)) = reifyClass cls
1006 reifyThing (AGlobal (ADataCon dc))
1007 = do { let name = dataConName dc
1008 ; ty <- reifyType (idType (dataConWrapId dc))
1009 ; fix <- reifyFixity name
1010 ; return (TH.DataConI (reifyName name) ty
1011 (reifyName (dataConOrigTyCon dc)) fix)
1014 reifyThing (ATcId {tct_id = id, tct_type = ty})
1015 = do { ty1 <- zonkTcType ty -- Make use of all the info we have, even
1016 -- though it may be incomplete
1017 ; ty2 <- reifyType ty1
1018 ; fix <- reifyFixity (idName id)
1019 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
1021 reifyThing (ATyVar tv ty)
1022 = do { ty1 <- zonkTcType ty
1023 ; ty2 <- reifyType ty1
1024 ; return (TH.TyVarI (reifyName tv) ty2) }
1026 reifyThing (AThing {}) = panic "reifyThing AThing"
1028 ------------------------------
1029 reifyTyCon :: TyCon -> TcM TH.Info
1032 = return (TH.PrimTyConI (reifyName tc) 2 False)
1034 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1036 = let flavour = reifyFamFlavour tc
1037 tvs = tyConTyVars tc
1040 | isLiftedTypeKind kind = Nothing
1041 | otherwise = Just $ reifyKind kind
1044 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1046 = do { let (tvs, rhs) = synTyConDefn tc
1047 ; rhs' <- reifyType rhs
1048 ; return (TH.TyConI $
1049 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1053 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1054 ; let tvs = tyConTyVars tc
1055 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1056 ; let name = reifyName tc
1057 r_tvs = reifyTyVars tvs
1058 deriv = [] -- Don't know about deriving
1059 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1060 | otherwise = TH.DataD cxt name r_tvs cons deriv
1061 ; return (TH.TyConI decl) }
1063 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1065 | isVanillaDataCon dc
1066 = do { arg_tys <- reifyTypes (dataConInstOrigArgTys dc tys)
1067 ; let stricts = map reifyStrict (dataConStrictMarks dc)
1068 fields = dataConFieldLabels dc
1072 ; ASSERT( length arg_tys == length stricts )
1073 if not (null fields) then
1074 return (TH.RecC name (zip3 (map reifyName fields) stricts arg_tys))
1076 if dataConIsInfix dc then
1077 ASSERT( length arg_tys == 2 )
1078 return (TH.InfixC (s1,a1) name (s2,a2))
1080 return (TH.NormalC name (stricts `zip` arg_tys)) }
1082 = failWithTc (ptext (sLit "Can't reify a GADT data constructor:")
1083 <+> quotes (ppr dc))
1085 ------------------------------
1086 reifyClass :: Class -> TcM TH.Info
1088 = do { cxt <- reifyCxt theta
1089 ; ops <- mapM reify_op op_stuff
1090 ; return (TH.ClassI $ TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops) }
1092 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1093 fds' = map reifyFunDep fds
1094 reify_op (op, _) = do { ty <- reifyType (idType op)
1095 ; return (TH.SigD (reifyName op) ty) }
1097 ------------------------------
1098 reifyType :: TypeRep.Type -> TcM TH.Type
1099 reifyType ty@(ForAllTy _ _) = reify_for_all ty
1100 reifyType ty@(PredTy {} `FunTy` _) = reify_for_all ty -- Types like ((?x::Int) => Char -> Char)
1101 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1102 reifyType (TyConApp tc tys) = reify_tc_app (reifyName tc) tys -- Do not expand type synonyms here
1103 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1104 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1105 reifyType ty@(PredTy {}) = pprPanic "reifyType PredTy" (ppr ty)
1107 reify_for_all :: TypeRep.Type -> TcM TH.Type
1109 = do { cxt' <- reifyCxt cxt;
1110 ; tau' <- reifyType tau
1111 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1113 (tvs, cxt, tau) = tcSplitSigmaTy ty
1115 reifyTypes :: [Type] -> TcM [TH.Type]
1116 reifyTypes = mapM reifyType
1118 reifyKind :: Kind -> TH.Kind
1120 = let (kis, ki') = splitKindFunTys ki
1121 kis_rep = map reifyKind kis
1122 ki'_rep = reifyNonArrowKind ki'
1124 foldr TH.ArrowK ki'_rep kis_rep
1126 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1127 | otherwise = pprPanic "Exotic form of kind"
1130 reifyCxt :: [PredType] -> TcM [TH.Pred]
1131 reifyCxt = mapM reifyPred
1133 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1134 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1136 reifyFamFlavour :: TyCon -> TH.FamFlavour
1137 reifyFamFlavour tc | isOpenSynTyCon tc = TH.TypeFam
1138 | isOpenTyCon tc = TH.DataFam
1140 = panic "TcSplice.reifyFamFlavour: not a type family"
1142 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1143 reifyTyVars = map reifyTyVar
1145 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1146 | otherwise = TH.KindedTV name (reifyKind kind)
1151 reify_tc_app :: TH.Name -> [TypeRep.Type] -> TcM TH.Type
1152 reify_tc_app tc tys = do { tys' <- reifyTypes tys
1153 ; return (foldl TH.AppT (TH.ConT tc) tys') }
1155 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1156 reifyPred (ClassP cls tys)
1157 = do { tys' <- reifyTypes tys
1158 ; return $ TH.ClassP (reifyName cls) tys'
1160 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1161 reifyPred (EqPred ty1 ty2)
1162 = do { ty1' <- reifyType ty1
1163 ; ty2' <- reifyType ty2
1164 ; return $ TH.EqualP ty1' ty2'
1168 ------------------------------
1169 reifyName :: NamedThing n => n -> TH.Name
1171 | isExternalName name = mk_varg pkg_str mod_str occ_str
1172 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1173 -- Many of the things we reify have local bindings, and
1174 -- NameL's aren't supposed to appear in binding positions, so
1175 -- we use NameU. When/if we start to reify nested things, that
1176 -- have free variables, we may need to generate NameL's for them.
1178 name = getName thing
1179 mod = ASSERT( isExternalName name ) nameModule name
1180 pkg_str = packageIdString (modulePackageId mod)
1181 mod_str = moduleNameString (moduleName mod)
1182 occ_str = occNameString occ
1183 occ = nameOccName name
1184 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1185 | OccName.isVarOcc occ = TH.mkNameG_v
1186 | OccName.isTcOcc occ = TH.mkNameG_tc
1187 | otherwise = pprPanic "reifyName" (ppr name)
1189 ------------------------------
1190 reifyFixity :: Name -> TcM TH.Fixity
1192 = do { fix <- lookupFixityRn name
1193 ; return (conv_fix fix) }
1195 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1196 conv_dir BasicTypes.InfixR = TH.InfixR
1197 conv_dir BasicTypes.InfixL = TH.InfixL
1198 conv_dir BasicTypes.InfixN = TH.InfixN
1200 reifyStrict :: BasicTypes.HsBang -> TH.Strict
1201 reifyStrict bang | isBanged bang = TH.IsStrict
1202 | otherwise = TH.NotStrict
1204 ------------------------------
1205 noTH :: LitString -> SDoc -> TcM a
1206 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1207 ptext (sLit "in Template Haskell:"),