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, runAnnotation ) where
21 #include "HsVersions.h"
25 -- These imports are the reason that TcSplice
26 -- is very high up the module hierarchy
62 import DsMonad hiding (Splice)
74 import qualified Language.Haskell.TH as TH
75 -- THSyntax gives access to internal functions and data types
76 import qualified Language.Haskell.TH.Syntax as TH
79 -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
80 import GHC.Desugar ( AnnotationWrapper(..) )
83 import GHC.Exts ( unsafeCoerce#, Int#, Int(..) )
84 import System.IO.Error
87 Note [How top-level splices are handled]
88 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
89 Top-level splices (those not inside a [| .. |] quotation bracket) are handled
90 very straightforwardly:
92 1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
94 2. runMetaT: desugar, compile, run it, and convert result back to
95 HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
98 3. treat the result as if that's what you saw in the first place
99 e.g for HsType, rename and kind-check
100 for HsExpr, rename and type-check
102 (The last step is different for decls, becuase they can *only* be
103 top-level: we return the result of step 2.)
105 Note [How brackets and nested splices are handled]
106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
107 Nested splices (those inside a [| .. |] quotation bracket), are treated
110 * After typechecking, the bracket [| |] carries
112 a) A mutable list of PendingSplice
113 type PendingSplice = (Name, LHsExpr Id)
115 b) The quoted expression e, *renamed*: (HsExpr Name)
116 The expression e has been typechecked, but the result of
117 that typechecking is discarded.
119 * The brakcet is desugared by DsMeta.dsBracket. It
121 a) Extends the ds_meta environment with the PendingSplices
122 attached to the bracket
124 b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
125 run, will produce a suitable TH expression/type/decl. This
126 is why we leave the *renamed* expression attached to the bracket:
127 the quoted expression should not be decorated with all the goop
128 added by the type checker
130 * Each splice carries a unique Name, called a "splice point", thus
131 ${n}(e). The name is initialised to an (Unqual "splice") when the
132 splice is created; the renamer gives it a unique.
134 * When the type checker type-checks a nested splice ${n}(e), it
136 - adds the typechecked expression (of type (HsExpr Id))
137 as a pending splice to the enclosing bracket
138 - returns something non-committal
139 Eg for [| f ${n}(g x) |], the typechecker
140 - attaches the typechecked term (g x) to the pending splices for n
142 - returns a non-committal type \alpha.
143 Remember that the bracket discards the typechecked term altogether
145 * When DsMeta (used to desugar the body of the bracket) comes across
146 a splice, it looks up the splice's Name, n, in the ds_meta envt,
147 to find an (HsExpr Id) that should be substituted for the splice;
148 it just desugars it to get a CoreExpr (DsMeta.repSplice).
151 Source: f = [| Just $(g 3) |]
152 The [| |] part is a HsBracket
154 Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
155 The [| |] part is a HsBracketOut, containing *renamed*
156 (not typechecked) expression
157 The "s7" is the "splice point"; the (g Int 3) part
158 is a typechecked expression
160 Desugared: f = do { s7 <- g Int 3
161 ; return (ConE "Data.Maybe.Just" s7) }
164 Note [Template Haskell state diagram]
165 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
166 Here are the ThStages, s, their corresponding level numbers
167 (the result of (thLevel s)), and their state transitions.
169 ----------- $ ------------ $
170 | Comp | ---------> | Splice | -----|
172 ----------- ------------
174 $ | | [||] $ | | [||]
176 -------------- ----------------
177 | Brack Comp | | Brack Splice |
179 -------------- ----------------
181 * Normal top-level declarations start in state Comp
183 Annotations start in state Splice, since they are
184 treated very like a splice (only without a '$')
186 * Code compiled in state Splice (and only such code)
187 will be *run at compile time*, with the result replacing
190 * The original paper used level -1 instead of 0, etc.
192 * The original paper did not allow a splice within a
193 splice, but there is no reason not to. This is the
194 $ transition in the top right.
196 Note [Template Haskell levels]
197 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
198 * Imported things are impLevel (= 0)
200 * In GHCi, variables bound by a previous command are treated
201 as impLevel, because we have bytecode for them.
203 * Variables are bound at the "current level"
205 * The current level starts off at outerLevel (= 1)
207 * The level is decremented by splicing $(..)
208 incremented by brackets [| |]
209 incremented by name-quoting 'f
211 When a variable is used, we compare
212 bind: binding level, and
213 use: current level at usage site
216 bind > use Always error (bound later than used)
219 bind = use Always OK (bound same stage as used)
220 [| \x -> $(f [| x |]) |]
222 bind < use Inside brackets, it depends
226 For (bind < use) inside brackets, there are three cases:
227 - Imported things OK f = [| map |]
228 - Top-level things OK g = [| f |]
229 - Non-top-level Only if there is a liftable instance
230 h = \(x:Int) -> [| x |]
232 See Note [What is a top-level Id?]
236 A quoted name 'n is a bit like a quoted expression [| n |], except that we
237 have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
238 the use-level to account for the brackets, the cases are:
247 See Note [What is a top-level Id?] in TcEnv. Examples:
249 f 'map -- OK; also for top-level defns of this module
251 \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
252 -- cross-stage lifting
254 \y. [| \x. $(f 'y) |] -- Not ok (same reason)
256 [| \x. $(f 'x) |] -- OK
259 Note [What is a top-level Id?]
260 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
261 In the level-control criteria above, we need to know what a "top level Id" is.
262 There are three kinds:
263 * Imported from another module (GlobalId, ExternalName)
264 * Bound at the top level of this module (ExternalName)
265 * In GHCi, bound by a previous stmt (GlobalId)
266 It's strange that there is no one criterion tht picks out all three, but that's
267 how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
268 bound in an earlier Stmt, but what module would you choose? See
269 Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
271 The predicate we use is TcEnv.thTopLevelId.
274 %************************************************************************
276 \subsection{Main interface + stubs for the non-GHCI case
278 %************************************************************************
281 tcBracket :: HsBracket Name -> BoxyRhoType -> TcM (LHsExpr TcId)
282 tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
283 tcSpliceExpr :: HsSplice Name -> BoxyRhoType -> TcM (HsExpr TcId)
284 kcSpliceType :: HsSplice Name -> TcM (HsType Name, TcKind)
285 -- None of these functions add constraints to the LIE
287 lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
289 runQuasiQuoteExpr :: HsQuasiQuote Name -> TcM (LHsExpr RdrName)
290 runQuasiQuotePat :: HsQuasiQuote Name -> TcM (LPat RdrName)
291 runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
294 tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
295 tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
296 tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
297 kcSpliceType x = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
299 lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
301 runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
302 runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
303 runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
307 %************************************************************************
309 \subsection{Quoting an expression}
311 %************************************************************************
315 -- See Note [How brackets and nested splices are handled]
316 tcBracket brack res_ty
317 = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
319 do { -- Check for nested brackets
320 cur_stage <- getStage
321 ; checkTc (not (isBrackStage cur_stage)) illegalBracket
323 -- Brackets are desugared to code that mentions the TH package
326 -- Typecheck expr to make sure it is valid,
327 -- but throw away the results. We'll type check
328 -- it again when we actually use it.
329 ; pending_splices <- newMutVar []
330 ; lie_var <- getLIEVar
332 ; (meta_ty, lie) <- setStage (Brack cur_stage pending_splices lie_var)
333 (getLIE (tc_bracket cur_stage brack))
334 ; tcSimplifyBracket lie
336 -- Make the expected type have the right shape
337 ; _ <- boxyUnify meta_ty res_ty
339 -- Return the original expression, not the type-decorated one
340 ; pendings <- readMutVar pending_splices
341 ; return (noLoc (HsBracketOut brack pendings)) }
343 tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
344 tc_bracket outer_stage (VarBr name) -- Note [Quoting names]
345 = do { thing <- tcLookup name
347 AGlobal _ -> return ()
348 ATcId { tct_level = bind_lvl, tct_id = id }
349 | thTopLevelId id -- C.f TcExpr.checkCrossStageLifting
352 -> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
353 (quotedNameStageErr name) }
354 _ -> pprPanic "th_bracket" (ppr name)
356 ; tcMetaTy nameTyConName -- Result type is Var (not Q-monadic)
359 tc_bracket _ (ExpBr expr)
360 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
361 ; _ <- tcMonoExprNC expr any_ty -- NC for no context; tcBracket does that
362 ; tcMetaTy expQTyConName }
363 -- Result type is Expr (= Q Exp)
365 tc_bracket _ (TypBr typ)
366 = do { _ <- tcHsSigTypeNC ThBrackCtxt typ
367 ; tcMetaTy typeQTyConName }
368 -- Result type is Type (= Q Typ)
370 tc_bracket _ (DecBr decls)
371 = do { _ <- tcTopSrcDecls emptyModDetails decls
372 -- Typecheck the declarations, dicarding the result
373 -- We'll get all that stuff later, when we splice it in
375 ; decl_ty <- tcMetaTy decTyConName
376 ; q_ty <- tcMetaTy qTyConName
377 ; return (mkAppTy q_ty (mkListTy decl_ty))
378 -- Result type is Q [Dec]
381 tc_bracket _ (PatBr _)
382 = failWithTc (ptext (sLit "Tempate Haskell pattern brackets are not supported yet"))
384 quotedNameStageErr :: Name -> SDoc
386 = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
387 , ptext (sLit "must be used at the same stage at which is is bound")]
391 %************************************************************************
393 \subsection{Splicing an expression}
395 %************************************************************************
398 tcSpliceExpr (HsSplice name expr) res_ty
399 = setSrcSpan (getLoc expr) $ do
402 Splice -> tcTopSplice expr res_ty ;
403 Comp -> tcTopSplice expr res_ty ;
405 Brack pop_stage ps_var lie_var -> do
407 -- See Note [How brackets and nested splices are handled]
408 -- A splice inside brackets
409 -- NB: ignore res_ty, apart from zapping it to a mono-type
410 -- e.g. [| reverse $(h 4) |]
411 -- Here (h 4) :: Q Exp
412 -- but $(h 4) :: forall a.a i.e. anything!
415 ; meta_exp_ty <- tcMetaTy expQTyConName
416 ; expr' <- setStage pop_stage $
418 tcMonoExpr expr meta_exp_ty
420 -- Write the pending splice into the bucket
421 ; ps <- readMutVar ps_var
422 ; writeMutVar ps_var ((name,expr') : ps)
424 ; return (panic "tcSpliceExpr") -- The returned expression is ignored
427 tcTopSplice :: LHsExpr Name -> BoxyRhoType -> TcM (HsExpr Id)
428 -- Note [How top-level splices are handled]
429 tcTopSplice expr res_ty
430 = do { meta_exp_ty <- tcMetaTy expQTyConName
432 -- Typecheck the expression
433 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
435 -- Run the expression
436 ; traceTc (text "About to run" <+> ppr zonked_q_expr)
437 ; expr2 <- runMetaE convertToHsExpr zonked_q_expr
439 ; traceTc (text "Got result" <+> ppr expr2)
441 ; showSplice "expression" expr (ppr expr2)
443 -- Rename it, but bale out if there are errors
444 -- otherwise the type checker just gives more spurious errors
445 ; (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
447 ; exp4 <- tcMonoExpr exp3 res_ty
448 ; return (unLoc exp4) }
451 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
452 -- Note [How top-level splices are handled]
453 -- Type check an expression that is the body of a top-level splice
454 -- (the caller will compile and run it)
455 -- Note that set the level to Splice, regardless of the original level,
456 -- before typechecking the expression. For example:
457 -- f x = $( ...$(g 3) ... )
458 -- The recursive call to tcMonoExpr will simply expand the
459 -- inner escape before dealing with the outer one
461 tcTopSpliceExpr tc_action
462 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
463 -- if the type checker fails!
465 do { -- Typecheck the expression
466 (expr', lie) <- getLIE tc_action
468 -- Solve the constraints
469 ; const_binds <- tcSimplifyTop lie
471 -- Zonk it and tie the knot of dictionary bindings
472 ; zonkTopLExpr (mkHsDictLet const_binds expr') }
476 %************************************************************************
480 %************************************************************************
482 Very like splicing an expression, but we don't yet share code.
485 kcSpliceType (HsSplice name hs_expr)
486 = setSrcSpan (getLoc hs_expr) $ do
489 Splice -> kcTopSpliceType hs_expr ;
490 Comp -> kcTopSpliceType hs_expr ;
492 Brack pop_level ps_var lie_var -> do
493 -- See Note [How brackets and nested splices are handled]
494 -- A splice inside brackets
495 { meta_ty <- tcMetaTy typeQTyConName
496 ; expr' <- setStage pop_level $
498 tcMonoExpr hs_expr meta_ty
500 -- Write the pending splice into the bucket
501 ; ps <- readMutVar ps_var
502 ; writeMutVar ps_var ((name,expr') : ps)
504 -- e.g. [| f (g :: Int -> $(h 4)) |]
505 -- Here (h 4) :: Q Type
506 -- but $(h 4) :: a i.e. any type, of any kind
508 -- We return a HsSpliceTyOut, which serves to convey the kind to
509 -- the ensuing TcHsType.dsHsType, which makes up a non-committal
510 -- type variable of a suitable kind
512 ; return (HsSpliceTyOut kind, kind)
515 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
516 -- Note [How top-level splices are handled]
518 = do { meta_ty <- tcMetaTy typeQTyConName
520 -- Typecheck the expression
521 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
523 -- Run the expression
524 ; traceTc (text "About to run" <+> ppr zonked_q_expr)
525 ; hs_ty2 <- runMetaT convertToHsType zonked_q_expr
527 ; traceTc (text "Got result" <+> ppr hs_ty2)
529 ; showSplice "type" expr (ppr hs_ty2)
531 -- Rename it, but bale out if there are errors
532 -- otherwise the type checker just gives more spurious errors
533 ; let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
534 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
536 ; (ty4, kind) <- kcLHsType hs_ty3
537 ; return (unLoc ty4, kind) }
540 %************************************************************************
542 \subsection{Splicing an expression}
544 %************************************************************************
547 -- Note [How top-level splices are handled]
548 -- Always at top level
549 -- Type sig at top of file:
550 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
552 = do { meta_dec_ty <- tcMetaTy decTyConName
553 ; meta_q_ty <- tcMetaTy qTyConName
554 ; let list_q = mkAppTy meta_q_ty (mkListTy meta_dec_ty)
555 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
557 -- Run the expression
558 ; traceTc (text "About to run" <+> ppr zonked_q_expr)
559 ; decls <- runMetaD convertToHsDecls zonked_q_expr
561 ; traceTc (text "Got result" <+> vcat (map ppr decls))
562 ; showSplice "declarations"
564 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
569 %************************************************************************
573 %************************************************************************
576 runAnnotation target expr = do
577 -- Find the classes we want instances for in order to call toAnnotationWrapper
579 data_class <- tcLookupClass dataClassName
580 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
582 -- Check the instances we require live in another module (we want to execute it..)
583 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
584 -- also resolves the LIE constraints to detect e.g. instance ambiguity
585 zonked_wrapped_expr' <- tcTopSpliceExpr $
586 do { (expr', expr_ty) <- tcInferRhoNC expr
587 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
588 -- By instantiating the call >here< it gets registered in the
589 -- LIE consulted by tcTopSpliceExpr
590 -- and hence ensures the appropriate dictionary is bound by const_binds
591 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
592 ; let specialised_to_annotation_wrapper_expr
593 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
594 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
596 -- Run the appropriately wrapped expression to get the value of
597 -- the annotation and its dictionaries. The return value is of
598 -- type AnnotationWrapper by construction, so this conversion is
600 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
601 case annotation_wrapper of
602 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
603 -- Got the value and dictionaries: build the serialized value and
604 -- call it a day. We ensure that we seq the entire serialized value
605 -- in order that any errors in the user-written code for the
606 -- annotation are exposed at this point. This is also why we are
607 -- doing all this stuff inside the context of runMeta: it has the
608 -- facilities to deal with user error in a meta-level expression
609 seqSerialized serialized `seq` Annotation {
611 ann_value = serialized
616 %************************************************************************
620 %************************************************************************
622 Note [Quasi-quote overview]
623 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
624 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
625 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
630 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
631 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
632 defined in another module, because we are going to run it here. It's
633 a bit like a TH splice:
636 However, you can do this in patterns as well as terms. Becuase of this,
637 the splice is run by the *renamer* rather than the type checker.
640 runQuasiQuote :: Outputable hs_syn
641 => HsQuasiQuote Name -- Contains term of type QuasiQuoter, and the String
642 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
643 -> String -- Documentation string only
644 -> Name -- Name of th_syn type
645 -> (SrcSpan -> th_syn -> Either Message hs_syn)
647 runQuasiQuote (HsQuasiQuote _name quoter q_span quote) quote_selector desc meta_ty convert
648 = do { -- Check that the quoter is not locally defined, otherwise the TH
649 -- machinery will not be able to run the quasiquote.
650 ; this_mod <- getModule
651 ; let is_local = case nameModule_maybe quoter of
652 Just mod | mod == this_mod -> True
655 ; traceTc (text "runQQ" <+> ppr quoter <+> ppr is_local)
656 ; checkTc (not is_local) (quoteStageError quoter)
658 -- Build the expression
659 ; let quoterExpr = L q_span $! HsVar $! quoter
660 ; let quoteExpr = L q_span $! HsLit $! HsString quote
661 ; let expr = L q_span $
663 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
664 ; meta_exp_ty <- tcMetaTy meta_ty
666 -- Typecheck the expression
667 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
669 -- Run the expression
670 ; traceTc (text "About to run" <+> ppr zonked_q_expr)
671 ; result <- runMetaQ convert zonked_q_expr
672 ; traceTc (text "Got result" <+> ppr result)
673 ; showSplice desc quoteExpr (ppr result)
677 runQuasiQuoteExpr quasiquote
678 = runQuasiQuote quasiquote quoteExpName "expression" expQTyConName convertToHsExpr
680 runQuasiQuotePat quasiquote
681 = runQuasiQuote quasiquote quotePatName "pattern" patQTyConName convertToPat
683 quoteStageError :: Name -> SDoc
684 quoteStageError quoter
685 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
686 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
690 %************************************************************************
692 \subsection{Running an expression}
694 %************************************************************************
697 runMetaAW :: (AnnotationWrapper -> output)
698 -> LHsExpr Id -- Of type AnnotationWrapper
700 runMetaAW k = runMeta False (\_ -> return . Right . k)
701 -- We turn off showing the code in meta-level exceptions because doing so exposes
702 -- the toAnnotationWrapper function that we slap around the users code
704 runQThen :: (SrcSpan -> input -> Either Message output)
707 -> TcM (Either Message output)
708 runQThen f expr_span what = TH.runQ what >>= (return . f expr_span)
710 runMetaQ :: (SrcSpan -> input -> Either Message output)
713 runMetaQ = runMeta True . runQThen
715 runMetaE :: (SrcSpan -> TH.Exp -> Either Message (LHsExpr RdrName))
716 -> LHsExpr Id -- Of type (Q Exp)
717 -> TcM (LHsExpr RdrName)
720 runMetaP :: (SrcSpan -> TH.Pat -> Either Message (Pat RdrName))
721 -> LHsExpr Id -- Of type (Q Pat)
725 runMetaT :: (SrcSpan -> TH.Type -> Either Message (LHsType RdrName))
726 -> LHsExpr Id -- Of type (Q Type)
727 -> TcM (LHsType RdrName)
730 runMetaD :: (SrcSpan -> [TH.Dec] -> Either Message [LHsDecl RdrName])
731 -> LHsExpr Id -- Of type Q [Dec]
732 -> TcM [LHsDecl RdrName]
735 runMeta :: Bool -- Whether code should be printed in the exception message
736 -> (SrcSpan -> input -> TcM (Either Message output))
737 -> LHsExpr Id -- Of type X
738 -> TcM output -- Of type t
739 runMeta show_code run_and_convert expr
741 ds_expr <- initDsTc (dsLExpr expr)
742 -- Compile and link it; might fail if linking fails
743 ; hsc_env <- getTopEnv
744 ; src_span <- getSrcSpanM
745 ; either_hval <- tryM $ liftIO $
746 HscMain.compileExpr hsc_env src_span ds_expr
747 ; case either_hval of {
748 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
751 { -- Coerce it to Q t, and run it
753 -- Running might fail if it throws an exception of any kind (hence tryAllM)
754 -- including, say, a pattern-match exception in the code we are running
756 -- We also do the TH -> HS syntax conversion inside the same
757 -- exception-cacthing thing so that if there are any lurking
758 -- exceptions in the data structure returned by hval, we'll
759 -- encounter them inside the try
761 -- See Note [Exceptions in TH]
762 let expr_span = getLoc expr
763 ; either_tval <- tryAllM $
764 setSrcSpan expr_span $ -- Set the span so that qLocation can
765 -- see where this splice is
766 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
768 Left err -> failWithTc err
769 Right result -> return $! result }
771 ; case either_tval of
774 case fromException se of
776 failM -- Error already in Tc monad
777 _ -> failWithTc (mk_msg "run" se) -- Exception
780 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
781 nest 2 (text (Panic.showException exn)),
782 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
785 Note [Exceptions in TH]
786 ~~~~~~~~~~~~~~~~~~~~~~~
787 Supppose we have something like this
791 f n | n>3 = fail "Too many declarations"
794 The 'fail' is a user-generated failure, and should be displayed as a
795 perfectly ordinary compiler error message, not a panic or anything
796 like that. Here's how it's processed:
798 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
799 effectively transforms (fail s) to
800 qReport True s >> fail
801 where 'qReport' comes from the Quasi class and fail from its monad
804 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
805 (qReport True s) by using addErr to add an error message to the bag of errors.
806 The 'fail' in TcM raises an IOEnvFailure exception
808 * So, when running a splice, we catch all exceptions; then for
809 - an IOEnvFailure exception, we assume the error is already
810 in the error-bag (above)
811 - other errors, we add an error to the bag
815 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
818 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
819 qNewName s = do { u <- newUnique
821 ; return (TH.mkNameU s i) }
823 qReport True msg = addErr (text msg)
824 qReport False msg = addReport (text msg) empty
826 qLocation = do { m <- getModule
828 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
829 , TH.loc_module = moduleNameString (moduleName m)
830 , TH.loc_package = packageIdString (modulePackageId m)
831 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
832 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
836 -- For qRecover, discard error messages if
837 -- the recovery action is chosen. Otherwise
838 -- we'll only fail higher up. c.f. tryTcLIE_
839 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
841 Just val -> do { addMessages msgs -- There might be warnings
843 Nothing -> recover -- Discard all msgs
846 qRunIO io = liftIO io
850 %************************************************************************
852 \subsection{Errors and contexts}
854 %************************************************************************
857 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
858 -- Note that 'before' is *renamed* but not *typechecked*
859 -- Reason (a) less typechecking crap
860 -- (b) data constructors after type checking have been
861 -- changed to their *wrappers*, and that makes them
862 -- print always fully qualified
863 showSplice what before after
864 = do { loc <- getSrcSpanM
865 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
866 nest 2 (sep [nest 2 (ppr before),
870 illegalBracket :: SDoc
871 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
876 %************************************************************************
880 %************************************************************************
884 reify :: TH.Name -> TcM TH.Info
886 = do { name <- lookupThName th_name
887 ; thing <- tcLookupTh name
888 -- ToDo: this tcLookup could fail, which would give a
889 -- rather unhelpful error message
890 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
894 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
895 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
896 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
897 ppr_ns _ = panic "reify/ppr_ns"
899 lookupThName :: TH.Name -> TcM Name
900 lookupThName th_name = do
901 mb_name <- lookupThName_maybe th_name
903 Nothing -> failWithTc (notInScope th_name)
904 Just name -> return name
906 lookupThName_maybe th_name
907 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
908 -- Pick the first that works
909 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
910 ; return (listToMaybe names) }
913 = do { -- Repeat much of lookupOccRn, becase we want
914 -- to report errors in a TH-relevant way
915 ; rdr_env <- getLocalRdrEnv
916 ; case lookupLocalRdrEnv rdr_env rdr_name of
917 Just name -> return (Just name)
918 Nothing -> lookupGlobalOccRn_maybe rdr_name }
920 tcLookupTh :: Name -> TcM TcTyThing
921 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
922 -- it gives a reify-related error message on failure, whereas in the normal
923 -- tcLookup, failure is a bug.
925 = do { (gbl_env, lcl_env) <- getEnvs
926 ; case lookupNameEnv (tcl_env lcl_env) name of {
927 Just thing -> return thing;
929 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
930 then -- It's defined in this module
931 case lookupNameEnv (tcg_type_env gbl_env) name of
932 Just thing -> return (AGlobal thing)
933 Nothing -> failWithTc (notInEnv name)
935 else do -- It's imported
936 { (eps,hpt) <- getEpsAndHpt
938 ; case lookupType dflags hpt (eps_PTE eps) name of
939 Just thing -> return (AGlobal thing)
940 Nothing -> do { thing <- tcImportDecl name
941 ; return (AGlobal thing) }
942 -- Imported names should always be findable;
943 -- if not, we fail hard in tcImportDecl
946 notInScope :: TH.Name -> SDoc
947 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
948 ptext (sLit "is not in scope at a reify")
949 -- Ugh! Rather an indirect way to display the name
951 notInEnv :: Name -> SDoc
952 notInEnv name = quotes (ppr name) <+>
953 ptext (sLit "is not in the type environment at a reify")
955 ------------------------------
956 reifyThing :: TcTyThing -> TcM TH.Info
957 -- The only reason this is monadic is for error reporting,
958 -- which in turn is mainly for the case when TH can't express
959 -- some random GHC extension
961 reifyThing (AGlobal (AnId id))
962 = do { ty <- reifyType (idType id)
963 ; fix <- reifyFixity (idName id)
964 ; let v = reifyName id
965 ; case idDetails id of
966 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
967 _ -> return (TH.VarI v ty Nothing fix)
970 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
971 reifyThing (AGlobal (AClass cls)) = reifyClass cls
972 reifyThing (AGlobal (ADataCon dc))
973 = do { let name = dataConName dc
974 ; ty <- reifyType (idType (dataConWrapId dc))
975 ; fix <- reifyFixity name
976 ; return (TH.DataConI (reifyName name) ty
977 (reifyName (dataConOrigTyCon dc)) fix)
980 reifyThing (ATcId {tct_id = id, tct_type = ty})
981 = do { ty1 <- zonkTcType ty -- Make use of all the info we have, even
982 -- though it may be incomplete
983 ; ty2 <- reifyType ty1
984 ; fix <- reifyFixity (idName id)
985 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
987 reifyThing (ATyVar tv ty)
988 = do { ty1 <- zonkTcType ty
989 ; ty2 <- reifyType ty1
990 ; return (TH.TyVarI (reifyName tv) ty2) }
992 reifyThing (AThing {}) = panic "reifyThing AThing"
994 ------------------------------
995 reifyTyCon :: TyCon -> TcM TH.Info
998 = return (TH.PrimTyConI (reifyName tc) 2 False)
1000 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1002 = let flavour = reifyFamFlavour tc
1003 tvs = tyConTyVars tc
1006 | isLiftedTypeKind kind = Nothing
1007 | otherwise = Just $ reifyKind kind
1010 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1012 = do { let (tvs, rhs) = synTyConDefn tc
1013 ; rhs' <- reifyType rhs
1014 ; return (TH.TyConI $
1015 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1019 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1020 ; let tvs = tyConTyVars tc
1021 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1022 ; let name = reifyName tc
1023 r_tvs = reifyTyVars tvs
1024 deriv = [] -- Don't know about deriving
1025 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1026 | otherwise = TH.DataD cxt name r_tvs cons deriv
1027 ; return (TH.TyConI decl) }
1029 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1031 | isVanillaDataCon dc
1032 = do { arg_tys <- reifyTypes (dataConInstOrigArgTys dc tys)
1033 ; let stricts = map reifyStrict (dataConStrictMarks dc)
1034 fields = dataConFieldLabels dc
1038 ; ASSERT( length arg_tys == length stricts )
1039 if not (null fields) then
1040 return (TH.RecC name (zip3 (map reifyName fields) stricts arg_tys))
1042 if dataConIsInfix dc then
1043 ASSERT( length arg_tys == 2 )
1044 return (TH.InfixC (s1,a1) name (s2,a2))
1046 return (TH.NormalC name (stricts `zip` arg_tys)) }
1048 = failWithTc (ptext (sLit "Can't reify a GADT data constructor:")
1049 <+> quotes (ppr dc))
1051 ------------------------------
1052 reifyClass :: Class -> TcM TH.Info
1054 = do { cxt <- reifyCxt theta
1055 ; ops <- mapM reify_op op_stuff
1056 ; return (TH.ClassI $ TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops) }
1058 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1059 fds' = map reifyFunDep fds
1060 reify_op (op, _) = do { ty <- reifyType (idType op)
1061 ; return (TH.SigD (reifyName op) ty) }
1063 ------------------------------
1064 reifyType :: TypeRep.Type -> TcM TH.Type
1065 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1066 reifyType (TyConApp tc tys) = reify_tc_app (reifyName tc) tys
1067 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1068 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1069 reifyType ty@(ForAllTy _ _) = do { cxt' <- reifyCxt cxt;
1070 ; tau' <- reifyType tau
1071 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1073 (tvs, cxt, tau) = tcSplitSigmaTy ty
1074 reifyType (PredTy {}) = panic "reifyType PredTy"
1076 reifyTypes :: [Type] -> TcM [TH.Type]
1077 reifyTypes = mapM reifyType
1079 reifyKind :: Kind -> TH.Kind
1081 = let (kis, ki') = splitKindFunTys ki
1082 kis_rep = map reifyKind kis
1083 ki'_rep = reifyNonArrowKind ki'
1085 foldl TH.ArrowK ki'_rep kis_rep
1087 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1088 | otherwise = pprPanic "Exotic form of kind"
1091 reifyCxt :: [PredType] -> TcM [TH.Pred]
1092 reifyCxt = mapM reifyPred
1094 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1095 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1097 reifyFamFlavour :: TyCon -> TH.FamFlavour
1098 reifyFamFlavour tc | isOpenSynTyCon tc = TH.TypeFam
1099 | isOpenTyCon tc = TH.DataFam
1101 = panic "TcSplice.reifyFamFlavour: not a type family"
1103 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1104 reifyTyVars = map reifyTyVar
1106 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1107 | otherwise = TH.KindedTV name (reifyKind kind)
1112 reify_tc_app :: TH.Name -> [TypeRep.Type] -> TcM TH.Type
1113 reify_tc_app tc tys = do { tys' <- reifyTypes tys
1114 ; return (foldl TH.AppT (TH.ConT tc) tys') }
1116 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1117 reifyPred (ClassP cls tys)
1118 = do { tys' <- reifyTypes tys
1119 ; return $ TH.ClassP (reifyName cls) tys'
1121 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1122 reifyPred (EqPred ty1 ty2)
1123 = do { ty1' <- reifyType ty1
1124 ; ty2' <- reifyType ty2
1125 ; return $ TH.EqualP ty1' ty2'
1129 ------------------------------
1130 reifyName :: NamedThing n => n -> TH.Name
1132 | isExternalName name = mk_varg pkg_str mod_str occ_str
1133 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1134 -- Many of the things we reify have local bindings, and
1135 -- NameL's aren't supposed to appear in binding positions, so
1136 -- we use NameU. When/if we start to reify nested things, that
1137 -- have free variables, we may need to generate NameL's for them.
1139 name = getName thing
1140 mod = ASSERT( isExternalName name ) nameModule name
1141 pkg_str = packageIdString (modulePackageId mod)
1142 mod_str = moduleNameString (moduleName mod)
1143 occ_str = occNameString occ
1144 occ = nameOccName name
1145 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1146 | OccName.isVarOcc occ = TH.mkNameG_v
1147 | OccName.isTcOcc occ = TH.mkNameG_tc
1148 | otherwise = pprPanic "reifyName" (ppr name)
1150 ------------------------------
1151 reifyFixity :: Name -> TcM TH.Fixity
1153 = do { fix <- lookupFixityRn name
1154 ; return (conv_fix fix) }
1156 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1157 conv_dir BasicTypes.InfixR = TH.InfixR
1158 conv_dir BasicTypes.InfixL = TH.InfixL
1159 conv_dir BasicTypes.InfixN = TH.InfixN
1161 reifyStrict :: BasicTypes.StrictnessMark -> TH.Strict
1162 reifyStrict MarkedStrict = TH.IsStrict
1163 reifyStrict MarkedUnboxed = TH.IsStrict
1164 reifyStrict NotMarkedStrict = TH.NotStrict
1166 ------------------------------
1167 noTH :: LitString -> SDoc -> TcM a
1168 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1169 ptext (sLit "in Template Haskell:"),