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)
78 import qualified Language.Haskell.TH as TH
79 -- THSyntax gives access to internal functions and data types
80 import qualified Language.Haskell.TH.Syntax as TH
83 -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
84 import GHC.Desugar ( AnnotationWrapper(..) )
87 import GHC.Exts ( unsafeCoerce#, Int#, Int(..) )
88 import System.IO.Error
91 Note [How top-level splices are handled]
92 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
93 Top-level splices (those not inside a [| .. |] quotation bracket) are handled
94 very straightforwardly:
96 1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
98 2. runMetaT: desugar, compile, run it, and convert result back to
99 HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
102 3. treat the result as if that's what you saw in the first place
103 e.g for HsType, rename and kind-check
104 for HsExpr, rename and type-check
106 (The last step is different for decls, becuase they can *only* be
107 top-level: we return the result of step 2.)
109 Note [How brackets and nested splices are handled]
110 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
111 Nested splices (those inside a [| .. |] quotation bracket), are treated
114 * After typechecking, the bracket [| |] carries
116 a) A mutable list of PendingSplice
117 type PendingSplice = (Name, LHsExpr Id)
119 b) The quoted expression e, *renamed*: (HsExpr Name)
120 The expression e has been typechecked, but the result of
121 that typechecking is discarded.
123 * The brakcet is desugared by DsMeta.dsBracket. It
125 a) Extends the ds_meta environment with the PendingSplices
126 attached to the bracket
128 b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
129 run, will produce a suitable TH expression/type/decl. This
130 is why we leave the *renamed* expression attached to the bracket:
131 the quoted expression should not be decorated with all the goop
132 added by the type checker
134 * Each splice carries a unique Name, called a "splice point", thus
135 ${n}(e). The name is initialised to an (Unqual "splice") when the
136 splice is created; the renamer gives it a unique.
138 * When the type checker type-checks a nested splice ${n}(e), it
140 - adds the typechecked expression (of type (HsExpr Id))
141 as a pending splice to the enclosing bracket
142 - returns something non-committal
143 Eg for [| f ${n}(g x) |], the typechecker
144 - attaches the typechecked term (g x) to the pending splices for n
146 - returns a non-committal type \alpha.
147 Remember that the bracket discards the typechecked term altogether
149 * When DsMeta (used to desugar the body of the bracket) comes across
150 a splice, it looks up the splice's Name, n, in the ds_meta envt,
151 to find an (HsExpr Id) that should be substituted for the splice;
152 it just desugars it to get a CoreExpr (DsMeta.repSplice).
155 Source: f = [| Just $(g 3) |]
156 The [| |] part is a HsBracket
158 Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
159 The [| |] part is a HsBracketOut, containing *renamed*
160 (not typechecked) expression
161 The "s7" is the "splice point"; the (g Int 3) part
162 is a typechecked expression
164 Desugared: f = do { s7 <- g Int 3
165 ; return (ConE "Data.Maybe.Just" s7) }
168 Note [Template Haskell state diagram]
169 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
170 Here are the ThStages, s, their corresponding level numbers
171 (the result of (thLevel s)), and their state transitions.
173 ----------- $ ------------ $
174 | Comp | ---------> | Splice | -----|
176 ----------- ------------
178 $ | | [||] $ | | [||]
180 -------------- ----------------
181 | Brack Comp | | Brack Splice |
183 -------------- ----------------
185 * Normal top-level declarations start in state Comp
187 Annotations start in state Splice, since they are
188 treated very like a splice (only without a '$')
190 * Code compiled in state Splice (and only such code)
191 will be *run at compile time*, with the result replacing
194 * The original paper used level -1 instead of 0, etc.
196 * The original paper did not allow a splice within a
197 splice, but there is no reason not to. This is the
198 $ transition in the top right.
200 Note [Template Haskell levels]
201 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
202 * Imported things are impLevel (= 0)
204 * In GHCi, variables bound by a previous command are treated
205 as impLevel, because we have bytecode for them.
207 * Variables are bound at the "current level"
209 * The current level starts off at outerLevel (= 1)
211 * The level is decremented by splicing $(..)
212 incremented by brackets [| |]
213 incremented by name-quoting 'f
215 When a variable is used, we compare
216 bind: binding level, and
217 use: current level at usage site
220 bind > use Always error (bound later than used)
223 bind = use Always OK (bound same stage as used)
224 [| \x -> $(f [| x |]) |]
226 bind < use Inside brackets, it depends
230 For (bind < use) inside brackets, there are three cases:
231 - Imported things OK f = [| map |]
232 - Top-level things OK g = [| f |]
233 - Non-top-level Only if there is a liftable instance
234 h = \(x:Int) -> [| x |]
236 See Note [What is a top-level Id?]
240 A quoted name 'n is a bit like a quoted expression [| n |], except that we
241 have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
242 the use-level to account for the brackets, the cases are:
251 See Note [What is a top-level Id?] in TcEnv. Examples:
253 f 'map -- OK; also for top-level defns of this module
255 \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
256 -- cross-stage lifting
258 \y. [| \x. $(f 'y) |] -- Not ok (same reason)
260 [| \x. $(f 'x) |] -- OK
263 Note [What is a top-level Id?]
264 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
265 In the level-control criteria above, we need to know what a "top level Id" is.
266 There are three kinds:
267 * Imported from another module (GlobalId, ExternalName)
268 * Bound at the top level of this module (ExternalName)
269 * In GHCi, bound by a previous stmt (GlobalId)
270 It's strange that there is no one criterion tht picks out all three, but that's
271 how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
272 bound in an earlier Stmt, but what module would you choose? See
273 Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
275 The predicate we use is TcEnv.thTopLevelId.
278 %************************************************************************
280 \subsection{Main interface + stubs for the non-GHCI case
282 %************************************************************************
285 tcBracket :: HsBracket Name -> BoxyRhoType -> TcM (LHsExpr TcId)
286 tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
287 tcSpliceExpr :: HsSplice Name -> BoxyRhoType -> TcM (HsExpr TcId)
288 kcSpliceType :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
289 -- None of these functions add constraints to the LIE
291 lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
293 runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
294 runQuasiQuotePat :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
295 runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
296 runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]
298 runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
301 tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
302 tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
303 tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
304 kcSpliceType x fvs = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
306 lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
308 runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
309 runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
310 runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
311 runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
312 runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
316 %************************************************************************
318 \subsection{Quoting an expression}
320 %************************************************************************
324 -- See Note [How brackets and nested splices are handled]
325 tcBracket brack res_ty
326 = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
328 do { -- Check for nested brackets
329 cur_stage <- getStage
330 ; checkTc (not (isBrackStage cur_stage)) illegalBracket
332 -- Brackets are desugared to code that mentions the TH package
335 -- Typecheck expr to make sure it is valid,
336 -- but throw away the results. We'll type check
337 -- it again when we actually use it.
338 ; pending_splices <- newMutVar []
339 ; lie_var <- getLIEVar
341 ; (meta_ty, lie) <- setStage (Brack cur_stage pending_splices lie_var)
342 (getLIE (tc_bracket cur_stage brack))
343 ; tcSimplifyBracket lie
345 -- Make the expected type have the right shape
346 ; _ <- boxyUnify meta_ty res_ty
348 -- Return the original expression, not the type-decorated one
349 ; pendings <- readMutVar pending_splices
350 ; return (noLoc (HsBracketOut brack pendings)) }
352 tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
353 tc_bracket outer_stage (VarBr name) -- Note [Quoting names]
354 = do { thing <- tcLookup name
356 AGlobal _ -> return ()
357 ATcId { tct_level = bind_lvl, tct_id = id }
358 | thTopLevelId id -- C.f TcExpr.checkCrossStageLifting
361 -> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
362 (quotedNameStageErr name) }
363 _ -> pprPanic "th_bracket" (ppr name)
365 ; tcMetaTy nameTyConName -- Result type is Var (not Q-monadic)
368 tc_bracket _ (ExpBr expr)
369 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
370 ; _ <- tcMonoExprNC expr any_ty -- NC for no context; tcBracket does that
371 ; tcMetaTy expQTyConName }
372 -- Result type is ExpQ (= Q Exp)
374 tc_bracket _ (TypBr typ)
375 = do { _ <- tcHsSigTypeNC ThBrackCtxt typ
376 ; tcMetaTy typeQTyConName }
377 -- Result type is Type (= Q Typ)
379 tc_bracket _ (DecBrG decls)
380 = do { _ <- tcTopSrcDecls emptyModDetails decls
381 -- Typecheck the declarations, dicarding the result
382 -- We'll get all that stuff later, when we splice it in
383 ; tcMetaTy decsQTyConName } -- Result type is Q [Dec]
385 tc_bracket _ (PatBr pat)
386 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
387 ; _ <- tcPat ThPatQuote pat any_ty unitTy $ \_ ->
389 ; tcMetaTy patQTyConName }
390 -- Result type is PatQ (= Q Pat)
392 tc_bracket _ (DecBrL _)
393 = panic "tc_bracket: Unexpected DecBrL"
395 quotedNameStageErr :: Name -> SDoc
397 = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
398 , ptext (sLit "must be used at the same stage at which is is bound")]
402 %************************************************************************
404 \subsection{Splicing an expression}
406 %************************************************************************
409 tcSpliceExpr (HsSplice name expr) res_ty
410 = setSrcSpan (getLoc expr) $ do
413 Splice -> tcTopSplice expr res_ty ;
414 Comp -> tcTopSplice expr res_ty ;
416 Brack pop_stage ps_var lie_var -> do
418 -- See Note [How brackets and nested splices are handled]
419 -- A splice inside brackets
420 -- NB: ignore res_ty, apart from zapping it to a mono-type
421 -- e.g. [| reverse $(h 4) |]
422 -- Here (h 4) :: Q Exp
423 -- but $(h 4) :: forall a.a i.e. anything!
426 ; meta_exp_ty <- tcMetaTy expQTyConName
427 ; expr' <- setStage pop_stage $
429 tcMonoExpr expr meta_exp_ty
431 -- Write the pending splice into the bucket
432 ; ps <- readMutVar ps_var
433 ; writeMutVar ps_var ((name,expr') : ps)
435 ; return (panic "tcSpliceExpr") -- The returned expression is ignored
438 tcTopSplice :: LHsExpr Name -> BoxyRhoType -> TcM (HsExpr Id)
439 -- Note [How top-level splices are handled]
440 tcTopSplice expr res_ty
441 = do { meta_exp_ty <- tcMetaTy expQTyConName
443 -- Typecheck the expression
444 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
446 -- Run the expression
447 ; expr2 <- runMetaE zonked_q_expr
448 ; showSplice "expression" expr (ppr expr2)
450 -- Rename it, but bale out if there are errors
451 -- otherwise the type checker just gives more spurious errors
452 ; addErrCtxt (spliceResultDoc expr) $ do
453 { (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
455 ; exp4 <- tcMonoExpr exp3 res_ty
456 ; return (unLoc exp4) } }
458 spliceResultDoc :: LHsExpr Name -> SDoc
460 = sep [ ptext (sLit "In the result of the splice:")
461 , nest 2 (char '$' <> pprParendExpr expr)
462 , ptext (sLit "To see what the splice expanded to, use -ddump-splices")]
465 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
466 -- Note [How top-level splices are handled]
467 -- Type check an expression that is the body of a top-level splice
468 -- (the caller will compile and run it)
469 -- Note that set the level to Splice, regardless of the original level,
470 -- before typechecking the expression. For example:
471 -- f x = $( ...$(g 3) ... )
472 -- The recursive call to tcMonoExpr will simply expand the
473 -- inner escape before dealing with the outer one
475 tcTopSpliceExpr tc_action
476 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
477 -- if the type checker fails!
479 do { -- Typecheck the expression
480 (expr', lie) <- getLIE tc_action
482 -- Solve the constraints
483 ; const_binds <- tcSimplifyTop lie
485 -- Zonk it and tie the knot of dictionary bindings
486 ; zonkTopLExpr (mkHsDictLet const_binds expr') }
490 %************************************************************************
494 %************************************************************************
496 Very like splicing an expression, but we don't yet share code.
499 kcSpliceType splice@(HsSplice name hs_expr) fvs
500 = setSrcSpan (getLoc hs_expr) $ do
503 Splice -> kcTopSpliceType hs_expr ;
504 Comp -> kcTopSpliceType hs_expr ;
506 Brack pop_level ps_var lie_var -> do
507 -- See Note [How brackets and nested splices are handled]
508 -- A splice inside brackets
509 { meta_ty <- tcMetaTy typeQTyConName
510 ; expr' <- setStage pop_level $
512 tcMonoExpr hs_expr meta_ty
514 -- Write the pending splice into the bucket
515 ; ps <- readMutVar ps_var
516 ; writeMutVar ps_var ((name,expr') : ps)
518 -- e.g. [| f (g :: Int -> $(h 4)) |]
519 -- Here (h 4) :: Q Type
520 -- but $(h 4) :: a i.e. any type, of any kind
523 ; return (HsSpliceTy splice fvs kind, kind)
526 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
527 -- Note [How top-level splices are handled]
529 = do { meta_ty <- tcMetaTy typeQTyConName
531 -- Typecheck the expression
532 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
534 -- Run the expression
535 ; hs_ty2 <- runMetaT zonked_q_expr
536 ; showSplice "type" expr (ppr hs_ty2)
538 -- Rename it, but bale out if there are errors
539 -- otherwise the type checker just gives more spurious errors
540 ; addErrCtxt (spliceResultDoc expr) $ do
541 { let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
542 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
543 ; (ty4, kind) <- kcLHsType hs_ty3
544 ; return (unLoc ty4, kind) }}
547 %************************************************************************
549 \subsection{Splicing an expression}
551 %************************************************************************
554 -- Note [How top-level splices are handled]
555 -- Always at top level
556 -- Type sig at top of file:
557 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
559 = do { list_q <- tcMetaTy decsQTyConName -- Q [Dec]
560 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
562 -- Run the expression
563 ; decls <- runMetaD zonked_q_expr
564 ; showSplice "declarations" expr
565 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
571 %************************************************************************
575 %************************************************************************
578 runAnnotation target expr = do
579 -- Find the classes we want instances for in order to call toAnnotationWrapper
581 data_class <- tcLookupClass dataClassName
582 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
584 -- Check the instances we require live in another module (we want to execute it..)
585 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
586 -- also resolves the LIE constraints to detect e.g. instance ambiguity
587 zonked_wrapped_expr' <- tcTopSpliceExpr $
588 do { (expr', expr_ty) <- tcInferRhoNC expr
589 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
590 -- By instantiating the call >here< it gets registered in the
591 -- LIE consulted by tcTopSpliceExpr
592 -- and hence ensures the appropriate dictionary is bound by const_binds
593 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
594 ; let specialised_to_annotation_wrapper_expr
595 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
596 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
598 -- Run the appropriately wrapped expression to get the value of
599 -- the annotation and its dictionaries. The return value is of
600 -- type AnnotationWrapper by construction, so this conversion is
602 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
603 case annotation_wrapper of
604 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
605 -- Got the value and dictionaries: build the serialized value and
606 -- call it a day. We ensure that we seq the entire serialized value
607 -- in order that any errors in the user-written code for the
608 -- annotation are exposed at this point. This is also why we are
609 -- doing all this stuff inside the context of runMeta: it has the
610 -- facilities to deal with user error in a meta-level expression
611 seqSerialized serialized `seq` Annotation {
613 ann_value = serialized
618 %************************************************************************
622 %************************************************************************
624 Note [Quasi-quote overview]
625 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
626 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
627 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
632 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
633 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
634 defined in another module, because we are going to run it here. It's
635 a bit like a TH splice:
638 However, you can do this in patterns as well as terms. Becuase of this,
639 the splice is run by the *renamer* rather than the type checker.
641 %************************************************************************
643 \subsubsection{Quasiquotation}
645 %************************************************************************
647 See Note [Quasi-quote overview] in TcSplice.
650 runQuasiQuote :: Outputable hs_syn
651 => HsQuasiQuote RdrName -- Contains term of type QuasiQuoter, and the String
652 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
653 -> Name -- Name of th_syn type
654 -> MetaOps th_syn hs_syn
656 runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
657 = do { quoter' <- lookupOccRn quoter
658 -- If 'quoter' is not in scope, proceed no further
659 -- Otherwise lookupOcc adds an error messsage and returns
660 -- an "unubound name", which makes the subsequent attempt to
661 -- run the quote fail
663 -- We use lookupOcc rather than lookupGlobalOcc because in the
664 -- erroneous case of \x -> [x| ...|] we get a better error message
665 -- (stage restriction rather than out of scope).
667 -- Check that the quoter is not locally defined, otherwise the TH
668 -- machinery will not be able to run the quasiquote.
669 ; this_mod <- getModule
670 ; let is_local = nameIsLocalOrFrom this_mod quoter'
671 ; checkTc (not is_local) (quoteStageError quoter')
673 ; traceTc (text "runQQ" <+> ppr quoter <+> ppr is_local)
675 -- Build the expression
676 ; let quoterExpr = L q_span $! HsVar $! quoter'
677 ; let quoteExpr = L q_span $! HsLit $! HsString quote
678 ; let expr = L q_span $
680 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
681 ; meta_exp_ty <- tcMetaTy meta_ty
683 -- Typecheck the expression
684 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
686 -- Run the expression
687 ; result <- runMetaQ meta_ops zonked_q_expr
688 ; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
692 runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName expQTyConName exprMetaOps
693 runQuasiQuotePat qq = runQuasiQuote qq quotePatName patQTyConName patMetaOps
694 runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
695 runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName decsQTyConName declMetaOps
697 quoteStageError :: Name -> SDoc
698 quoteStageError quoter
699 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
700 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
704 %************************************************************************
706 \subsection{Running an expression}
708 %************************************************************************
711 data MetaOps th_syn hs_syn
712 = MT { mt_desc :: String -- Type of beast (expression, type etc)
713 , mt_show :: th_syn -> String -- How to show the th_syn thing
714 , mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
715 -- How to convert to hs_syn
718 exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
719 exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
721 patMetaOps :: MetaOps TH.Pat (LPat RdrName)
722 patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
724 typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
725 typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
727 declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
728 declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
731 runMetaAW :: Outputable output
732 => (AnnotationWrapper -> output)
733 -> LHsExpr Id -- Of type AnnotationWrapper
735 runMetaAW k = runMeta False (\_ -> return . Right . k)
736 -- We turn off showing the code in meta-level exceptions because doing so exposes
737 -- the toAnnotationWrapper function that we slap around the users code
740 runMetaQ :: Outputable hs_syn
741 => MetaOps th_syn hs_syn
744 runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
745 = runMeta True run_and_cvt expr
747 run_and_cvt expr_span hval
748 = do { th_result <- TH.runQ hval
749 ; traceTc (text "Got TH result:" <+> text (show_th th_result))
750 ; return (cvt expr_span th_result) }
752 runMetaE :: LHsExpr Id -- Of type (Q Exp)
753 -> TcM (LHsExpr RdrName)
754 runMetaE = runMetaQ exprMetaOps
756 runMetaT :: LHsExpr Id -- Of type (Q Type)
757 -> TcM (LHsType RdrName)
758 runMetaT = runMetaQ typeMetaOps
760 runMetaD :: LHsExpr Id -- Of type Q [Dec]
761 -> TcM [LHsDecl RdrName]
762 runMetaD = runMetaQ declMetaOps
765 runMeta :: (Outputable hs_syn)
766 => Bool -- Whether code should be printed in the exception message
767 -> (SrcSpan -> x -> TcM (Either Message hs_syn)) -- How to run x
768 -> LHsExpr Id -- Of type x; typically x = Q TH.Exp, or something like that
769 -> TcM hs_syn -- Of type t
770 runMeta show_code run_and_convert expr
771 = do { traceTc (text "About to run" <+> ppr expr)
774 ; ds_expr <- initDsTc (dsLExpr expr)
775 -- Compile and link it; might fail if linking fails
776 ; hsc_env <- getTopEnv
777 ; src_span <- getSrcSpanM
778 ; either_hval <- tryM $ liftIO $
779 HscMain.compileExpr hsc_env src_span ds_expr
780 ; case either_hval of {
781 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
784 { -- Coerce it to Q t, and run it
786 -- Running might fail if it throws an exception of any kind (hence tryAllM)
787 -- including, say, a pattern-match exception in the code we are running
789 -- We also do the TH -> HS syntax conversion inside the same
790 -- exception-cacthing thing so that if there are any lurking
791 -- exceptions in the data structure returned by hval, we'll
792 -- encounter them inside the try
794 -- See Note [Exceptions in TH]
795 let expr_span = getLoc expr
796 ; either_tval <- tryAllM $
797 setSrcSpan expr_span $ -- Set the span so that qLocation can
798 -- see where this splice is
799 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
801 Left err -> failWithTc err
802 Right result -> do { traceTc (ptext (sLit "Got HsSyn result:") <+> ppr result)
803 ; return $! result } }
805 ; case either_tval of
807 Left se -> case fromException se of
808 Just IOEnvFailure -> failM -- Error already in Tc monad
809 _ -> failWithTc (mk_msg "run" se) -- Exception
812 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
813 nest 2 (text (Panic.showException exn)),
814 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
817 Note [Exceptions in TH]
818 ~~~~~~~~~~~~~~~~~~~~~~~
819 Supppose we have something like this
823 f n | n>3 = fail "Too many declarations"
826 The 'fail' is a user-generated failure, and should be displayed as a
827 perfectly ordinary compiler error message, not a panic or anything
828 like that. Here's how it's processed:
830 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
831 effectively transforms (fail s) to
832 qReport True s >> fail
833 where 'qReport' comes from the Quasi class and fail from its monad
836 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
837 (qReport True s) by using addErr to add an error message to the bag of errors.
838 The 'fail' in TcM raises an IOEnvFailure exception
840 * So, when running a splice, we catch all exceptions; then for
841 - an IOEnvFailure exception, we assume the error is already
842 in the error-bag (above)
843 - other errors, we add an error to the bag
847 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
850 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
851 qNewName s = do { u <- newUnique
853 ; return (TH.mkNameU s i) }
855 qReport True msg = addErr (text msg)
856 qReport False msg = addReport (text msg) empty
858 qLocation = do { m <- getModule
860 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
861 , TH.loc_module = moduleNameString (moduleName m)
862 , TH.loc_package = packageIdString (modulePackageId m)
863 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
864 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
868 -- For qRecover, discard error messages if
869 -- the recovery action is chosen. Otherwise
870 -- we'll only fail higher up. c.f. tryTcLIE_
871 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
873 Just val -> do { addMessages msgs -- There might be warnings
875 Nothing -> recover -- Discard all msgs
878 qRunIO io = liftIO io
882 %************************************************************************
884 \subsection{Errors and contexts}
886 %************************************************************************
889 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
890 -- Note that 'before' is *renamed* but not *typechecked*
891 -- Reason (a) less typechecking crap
892 -- (b) data constructors after type checking have been
893 -- changed to their *wrappers*, and that makes them
894 -- print always fully qualified
895 showSplice what before after
896 = do { loc <- getSrcSpanM
897 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
898 nest 2 (sep [nest 2 (ppr before),
902 illegalBracket :: SDoc
903 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
908 %************************************************************************
912 %************************************************************************
916 reify :: TH.Name -> TcM TH.Info
918 = do { name <- lookupThName th_name
919 ; thing <- tcLookupTh name
920 -- ToDo: this tcLookup could fail, which would give a
921 -- rather unhelpful error message
922 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
926 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
927 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
928 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
929 ppr_ns _ = panic "reify/ppr_ns"
931 lookupThName :: TH.Name -> TcM Name
932 lookupThName th_name = do
933 mb_name <- lookupThName_maybe th_name
935 Nothing -> failWithTc (notInScope th_name)
936 Just name -> return name
938 lookupThName_maybe th_name
939 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
940 -- Pick the first that works
941 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
942 ; return (listToMaybe names) }
945 = do { -- Repeat much of lookupOccRn, becase we want
946 -- to report errors in a TH-relevant way
947 ; rdr_env <- getLocalRdrEnv
948 ; case lookupLocalRdrEnv rdr_env rdr_name of
949 Just name -> return (Just name)
950 Nothing -> lookupGlobalOccRn_maybe rdr_name }
952 tcLookupTh :: Name -> TcM TcTyThing
953 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
954 -- it gives a reify-related error message on failure, whereas in the normal
955 -- tcLookup, failure is a bug.
957 = do { (gbl_env, lcl_env) <- getEnvs
958 ; case lookupNameEnv (tcl_env lcl_env) name of {
959 Just thing -> return thing;
961 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
962 then -- It's defined in this module
963 case lookupNameEnv (tcg_type_env gbl_env) name of
964 Just thing -> return (AGlobal thing)
965 Nothing -> failWithTc (notInEnv name)
967 else do -- It's imported
968 { (eps,hpt) <- getEpsAndHpt
970 ; case lookupType dflags hpt (eps_PTE eps) name of
971 Just thing -> return (AGlobal thing)
972 Nothing -> do { thing <- tcImportDecl name
973 ; return (AGlobal thing) }
974 -- Imported names should always be findable;
975 -- if not, we fail hard in tcImportDecl
978 notInScope :: TH.Name -> SDoc
979 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
980 ptext (sLit "is not in scope at a reify")
981 -- Ugh! Rather an indirect way to display the name
983 notInEnv :: Name -> SDoc
984 notInEnv name = quotes (ppr name) <+>
985 ptext (sLit "is not in the type environment at a reify")
987 ------------------------------
988 reifyThing :: TcTyThing -> TcM TH.Info
989 -- The only reason this is monadic is for error reporting,
990 -- which in turn is mainly for the case when TH can't express
991 -- some random GHC extension
993 reifyThing (AGlobal (AnId id))
994 = do { ty <- reifyType (idType id)
995 ; fix <- reifyFixity (idName id)
996 ; let v = reifyName id
997 ; case idDetails id of
998 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
999 _ -> return (TH.VarI v ty Nothing fix)
1002 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
1003 reifyThing (AGlobal (AClass cls)) = reifyClass cls
1004 reifyThing (AGlobal (ADataCon dc))
1005 = do { let name = dataConName dc
1006 ; ty <- reifyType (idType (dataConWrapId dc))
1007 ; fix <- reifyFixity name
1008 ; return (TH.DataConI (reifyName name) ty
1009 (reifyName (dataConOrigTyCon dc)) fix)
1012 reifyThing (ATcId {tct_id = id, tct_type = ty})
1013 = do { ty1 <- zonkTcType ty -- Make use of all the info we have, even
1014 -- though it may be incomplete
1015 ; ty2 <- reifyType ty1
1016 ; fix <- reifyFixity (idName id)
1017 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
1019 reifyThing (ATyVar tv ty)
1020 = do { ty1 <- zonkTcType ty
1021 ; ty2 <- reifyType ty1
1022 ; return (TH.TyVarI (reifyName tv) ty2) }
1024 reifyThing (AThing {}) = panic "reifyThing AThing"
1026 ------------------------------
1027 reifyTyCon :: TyCon -> TcM TH.Info
1030 = return (TH.PrimTyConI (reifyName tc) 2 False)
1032 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1034 = let flavour = reifyFamFlavour tc
1035 tvs = tyConTyVars tc
1038 | isLiftedTypeKind kind = Nothing
1039 | otherwise = Just $ reifyKind kind
1042 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1044 = do { let (tvs, rhs) = synTyConDefn tc
1045 ; rhs' <- reifyType rhs
1046 ; return (TH.TyConI $
1047 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1051 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1052 ; let tvs = tyConTyVars tc
1053 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1054 ; let name = reifyName tc
1055 r_tvs = reifyTyVars tvs
1056 deriv = [] -- Don't know about deriving
1057 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1058 | otherwise = TH.DataD cxt name r_tvs cons deriv
1059 ; return (TH.TyConI decl) }
1061 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1063 | isVanillaDataCon dc
1064 = do { arg_tys <- reifyTypes (dataConInstOrigArgTys dc tys)
1065 ; let stricts = map reifyStrict (dataConStrictMarks dc)
1066 fields = dataConFieldLabels dc
1070 ; ASSERT( length arg_tys == length stricts )
1071 if not (null fields) then
1072 return (TH.RecC name (zip3 (map reifyName fields) stricts arg_tys))
1074 if dataConIsInfix dc then
1075 ASSERT( length arg_tys == 2 )
1076 return (TH.InfixC (s1,a1) name (s2,a2))
1078 return (TH.NormalC name (stricts `zip` arg_tys)) }
1080 = failWithTc (ptext (sLit "Can't reify a GADT data constructor:")
1081 <+> quotes (ppr dc))
1083 ------------------------------
1084 reifyClass :: Class -> TcM TH.Info
1086 = do { cxt <- reifyCxt theta
1087 ; ops <- mapM reify_op op_stuff
1088 ; return (TH.ClassI $ TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops) }
1090 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1091 fds' = map reifyFunDep fds
1092 reify_op (op, _) = do { ty <- reifyType (idType op)
1093 ; return (TH.SigD (reifyName op) ty) }
1095 ------------------------------
1096 reifyType :: TypeRep.Type -> TcM TH.Type
1097 reifyType ty@(ForAllTy _ _) = reify_for_all ty
1098 reifyType ty@(PredTy {} `FunTy` _) = reify_for_all ty -- Types like ((?x::Int) => Char -> Char)
1099 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1100 reifyType (TyConApp tc tys) = reify_tc_app (reifyName tc) tys -- Do not expand type synonyms here
1101 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1102 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1103 reifyType ty@(PredTy {}) = pprPanic "reifyType PredTy" (ppr ty)
1105 reify_for_all :: TypeRep.Type -> TcM TH.Type
1107 = do { cxt' <- reifyCxt cxt;
1108 ; tau' <- reifyType tau
1109 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1111 (tvs, cxt, tau) = tcSplitSigmaTy ty
1113 reifyTypes :: [Type] -> TcM [TH.Type]
1114 reifyTypes = mapM reifyType
1116 reifyKind :: Kind -> TH.Kind
1118 = let (kis, ki') = splitKindFunTys ki
1119 kis_rep = map reifyKind kis
1120 ki'_rep = reifyNonArrowKind ki'
1122 foldl TH.ArrowK ki'_rep kis_rep
1124 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1125 | otherwise = pprPanic "Exotic form of kind"
1128 reifyCxt :: [PredType] -> TcM [TH.Pred]
1129 reifyCxt = mapM reifyPred
1131 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1132 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1134 reifyFamFlavour :: TyCon -> TH.FamFlavour
1135 reifyFamFlavour tc | isOpenSynTyCon tc = TH.TypeFam
1136 | isOpenTyCon tc = TH.DataFam
1138 = panic "TcSplice.reifyFamFlavour: not a type family"
1140 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1141 reifyTyVars = map reifyTyVar
1143 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1144 | otherwise = TH.KindedTV name (reifyKind kind)
1149 reify_tc_app :: TH.Name -> [TypeRep.Type] -> TcM TH.Type
1150 reify_tc_app tc tys = do { tys' <- reifyTypes tys
1151 ; return (foldl TH.AppT (TH.ConT tc) tys') }
1153 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1154 reifyPred (ClassP cls tys)
1155 = do { tys' <- reifyTypes tys
1156 ; return $ TH.ClassP (reifyName cls) tys'
1158 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1159 reifyPred (EqPred ty1 ty2)
1160 = do { ty1' <- reifyType ty1
1161 ; ty2' <- reifyType ty2
1162 ; return $ TH.EqualP ty1' ty2'
1166 ------------------------------
1167 reifyName :: NamedThing n => n -> TH.Name
1169 | isExternalName name = mk_varg pkg_str mod_str occ_str
1170 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1171 -- Many of the things we reify have local bindings, and
1172 -- NameL's aren't supposed to appear in binding positions, so
1173 -- we use NameU. When/if we start to reify nested things, that
1174 -- have free variables, we may need to generate NameL's for them.
1176 name = getName thing
1177 mod = ASSERT( isExternalName name ) nameModule name
1178 pkg_str = packageIdString (modulePackageId mod)
1179 mod_str = moduleNameString (moduleName mod)
1180 occ_str = occNameString occ
1181 occ = nameOccName name
1182 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1183 | OccName.isVarOcc occ = TH.mkNameG_v
1184 | OccName.isTcOcc occ = TH.mkNameG_tc
1185 | otherwise = pprPanic "reifyName" (ppr name)
1187 ------------------------------
1188 reifyFixity :: Name -> TcM TH.Fixity
1190 = do { fix <- lookupFixityRn name
1191 ; return (conv_fix fix) }
1193 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1194 conv_dir BasicTypes.InfixR = TH.InfixR
1195 conv_dir BasicTypes.InfixL = TH.InfixL
1196 conv_dir BasicTypes.InfixN = TH.InfixN
1198 reifyStrict :: BasicTypes.StrictnessMark -> TH.Strict
1199 reifyStrict MarkedStrict = TH.IsStrict
1200 reifyStrict MarkedUnboxed = TH.IsStrict
1201 reifyStrict NotMarkedStrict = TH.NotStrict
1203 ------------------------------
1204 noTH :: LitString -> SDoc -> TcM a
1205 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1206 ptext (sLit "in Template Haskell:"),