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 ; expr2 <- runMetaE zonked_q_expr
437 ; showSplice "expression" expr (ppr expr2)
439 -- Rename it, but bale out if there are errors
440 -- otherwise the type checker just gives more spurious errors
441 ; (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
443 ; exp4 <- tcMonoExpr exp3 res_ty
444 ; return (unLoc exp4) }
447 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
448 -- Note [How top-level splices are handled]
449 -- Type check an expression that is the body of a top-level splice
450 -- (the caller will compile and run it)
451 -- Note that set the level to Splice, regardless of the original level,
452 -- before typechecking the expression. For example:
453 -- f x = $( ...$(g 3) ... )
454 -- The recursive call to tcMonoExpr will simply expand the
455 -- inner escape before dealing with the outer one
457 tcTopSpliceExpr tc_action
458 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
459 -- if the type checker fails!
461 do { -- Typecheck the expression
462 (expr', lie) <- getLIE tc_action
464 -- Solve the constraints
465 ; const_binds <- tcSimplifyTop lie
467 -- Zonk it and tie the knot of dictionary bindings
468 ; zonkTopLExpr (mkHsDictLet const_binds expr') }
472 %************************************************************************
476 %************************************************************************
478 Very like splicing an expression, but we don't yet share code.
481 kcSpliceType (HsSplice name hs_expr)
482 = setSrcSpan (getLoc hs_expr) $ do
485 Splice -> kcTopSpliceType hs_expr ;
486 Comp -> kcTopSpliceType hs_expr ;
488 Brack pop_level ps_var lie_var -> do
489 -- See Note [How brackets and nested splices are handled]
490 -- A splice inside brackets
491 { meta_ty <- tcMetaTy typeQTyConName
492 ; expr' <- setStage pop_level $
494 tcMonoExpr hs_expr meta_ty
496 -- Write the pending splice into the bucket
497 ; ps <- readMutVar ps_var
498 ; writeMutVar ps_var ((name,expr') : ps)
500 -- e.g. [| f (g :: Int -> $(h 4)) |]
501 -- Here (h 4) :: Q Type
502 -- but $(h 4) :: a i.e. any type, of any kind
504 -- We return a HsSpliceTyOut, which serves to convey the kind to
505 -- the ensuing TcHsType.dsHsType, which makes up a non-committal
506 -- type variable of a suitable kind
508 ; return (HsSpliceTyOut kind, kind)
511 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
512 -- Note [How top-level splices are handled]
514 = do { meta_ty <- tcMetaTy typeQTyConName
516 -- Typecheck the expression
517 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
519 -- Run the expression
520 ; hs_ty2 <- runMetaT zonked_q_expr
521 ; showSplice "type" expr (ppr hs_ty2)
523 -- Rename it, but bale out if there are errors
524 -- otherwise the type checker just gives more spurious errors
525 ; let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
526 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
528 ; (ty4, kind) <- kcLHsType hs_ty3
529 ; return (unLoc ty4, kind) }
532 %************************************************************************
534 \subsection{Splicing an expression}
536 %************************************************************************
539 -- Note [How top-level splices are handled]
540 -- Always at top level
541 -- Type sig at top of file:
542 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
544 = do { meta_dec_ty <- tcMetaTy decTyConName
545 ; meta_q_ty <- tcMetaTy qTyConName
546 ; let list_q = mkAppTy meta_q_ty (mkListTy meta_dec_ty)
547 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
549 -- Run the expression
550 ; decls <- runMetaD zonked_q_expr
551 ; showSplice "declarations" expr
552 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
558 %************************************************************************
562 %************************************************************************
565 runAnnotation target expr = do
566 -- Find the classes we want instances for in order to call toAnnotationWrapper
568 data_class <- tcLookupClass dataClassName
569 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
571 -- Check the instances we require live in another module (we want to execute it..)
572 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
573 -- also resolves the LIE constraints to detect e.g. instance ambiguity
574 zonked_wrapped_expr' <- tcTopSpliceExpr $
575 do { (expr', expr_ty) <- tcInferRhoNC expr
576 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
577 -- By instantiating the call >here< it gets registered in the
578 -- LIE consulted by tcTopSpliceExpr
579 -- and hence ensures the appropriate dictionary is bound by const_binds
580 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
581 ; let specialised_to_annotation_wrapper_expr
582 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
583 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
585 -- Run the appropriately wrapped expression to get the value of
586 -- the annotation and its dictionaries. The return value is of
587 -- type AnnotationWrapper by construction, so this conversion is
589 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
590 case annotation_wrapper of
591 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
592 -- Got the value and dictionaries: build the serialized value and
593 -- call it a day. We ensure that we seq the entire serialized value
594 -- in order that any errors in the user-written code for the
595 -- annotation are exposed at this point. This is also why we are
596 -- doing all this stuff inside the context of runMeta: it has the
597 -- facilities to deal with user error in a meta-level expression
598 seqSerialized serialized `seq` Annotation {
600 ann_value = serialized
605 %************************************************************************
609 %************************************************************************
611 Note [Quasi-quote overview]
612 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
613 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
614 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
619 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
620 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
621 defined in another module, because we are going to run it here. It's
622 a bit like a TH splice:
625 However, you can do this in patterns as well as terms. Becuase of this,
626 the splice is run by the *renamer* rather than the type checker.
629 runQuasiQuote :: Outputable hs_syn
630 => HsQuasiQuote Name -- Contains term of type QuasiQuoter, and the String
631 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
632 -> Name -- Name of th_syn type
633 -> MetaOps th_syn hs_syn
635 runQuasiQuote (HsQuasiQuote _name quoter q_span quote) quote_selector meta_ty meta_ops
636 = do { -- Check that the quoter is not locally defined, otherwise the TH
637 -- machinery will not be able to run the quasiquote.
638 ; this_mod <- getModule
639 ; let is_local = case nameModule_maybe quoter of
640 Just mod | mod == this_mod -> True
643 ; traceTc (text "runQQ" <+> ppr quoter <+> ppr is_local)
644 ; checkTc (not is_local) (quoteStageError quoter)
646 -- Build the expression
647 ; let quoterExpr = L q_span $! HsVar $! quoter
648 ; let quoteExpr = L q_span $! HsLit $! HsString quote
649 ; let expr = L q_span $
651 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
652 ; meta_exp_ty <- tcMetaTy meta_ty
654 -- Typecheck the expression
655 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
657 -- Run the expression
658 ; result <- runMetaQ meta_ops zonked_q_expr
659 ; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
663 runQuasiQuoteExpr quasiquote = runQuasiQuote quasiquote quoteExpName expQTyConName exprMetaOps
664 runQuasiQuotePat quasiquote = runQuasiQuote quasiquote quotePatName patQTyConName patMetaOps
666 quoteStageError :: Name -> SDoc
667 quoteStageError quoter
668 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
669 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
673 %************************************************************************
675 \subsection{Running an expression}
677 %************************************************************************
680 data MetaOps th_syn hs_syn
681 = MT { mt_desc :: String -- Type of beast (expression, type etc)
682 , mt_show :: th_syn -> String -- How to show the th_syn thing
683 , mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
684 -- How to convert to hs_syn
687 exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
688 exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
690 patMetaOps :: MetaOps TH.Pat (LPat RdrName)
691 patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
693 typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
694 typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
696 declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
697 declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
700 runMetaAW :: Outputable output
701 => (AnnotationWrapper -> output)
702 -> LHsExpr Id -- Of type AnnotationWrapper
704 runMetaAW k = runMeta False (\_ -> return . Right . k)
705 -- We turn off showing the code in meta-level exceptions because doing so exposes
706 -- the toAnnotationWrapper function that we slap around the users code
709 runMetaQ :: Outputable hs_syn
710 => MetaOps th_syn hs_syn
713 runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
714 = runMeta True run_and_cvt expr
716 run_and_cvt expr_span hval
717 = do { th_result <- TH.runQ hval
718 ; traceTc (text "Got TH result:" <+> text (show_th th_result))
719 ; return (cvt expr_span th_result) }
721 runMetaE :: LHsExpr Id -- Of type (Q Exp)
722 -> TcM (LHsExpr RdrName)
723 runMetaE = runMetaQ exprMetaOps
725 runMetaT :: LHsExpr Id -- Of type (Q Type)
726 -> TcM (LHsType RdrName)
727 runMetaT = runMetaQ typeMetaOps
729 runMetaD :: LHsExpr Id -- Of type Q [Dec]
730 -> TcM [LHsDecl RdrName]
731 runMetaD = runMetaQ declMetaOps
734 runMeta :: (Outputable hs_syn)
735 => Bool -- Whether code should be printed in the exception message
736 -> (SrcSpan -> x -> TcM (Either Message hs_syn)) -- How to run x
737 -> LHsExpr Id -- Of type x; typically x = Q TH.Exp, or something like that
738 -> TcM hs_syn -- Of type t
739 runMeta show_code run_and_convert expr
740 = do { traceTc (text "About to run" <+> ppr expr)
743 ; ds_expr <- initDsTc (dsLExpr expr)
744 -- Compile and link it; might fail if linking fails
745 ; hsc_env <- getTopEnv
746 ; src_span <- getSrcSpanM
747 ; either_hval <- tryM $ liftIO $
748 HscMain.compileExpr hsc_env src_span ds_expr
749 ; case either_hval of {
750 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
753 { -- Coerce it to Q t, and run it
755 -- Running might fail if it throws an exception of any kind (hence tryAllM)
756 -- including, say, a pattern-match exception in the code we are running
758 -- We also do the TH -> HS syntax conversion inside the same
759 -- exception-cacthing thing so that if there are any lurking
760 -- exceptions in the data structure returned by hval, we'll
761 -- encounter them inside the try
763 -- See Note [Exceptions in TH]
764 let expr_span = getLoc expr
765 ; either_tval <- tryAllM $
766 setSrcSpan expr_span $ -- Set the span so that qLocation can
767 -- see where this splice is
768 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
770 Left err -> failWithTc err
771 Right result -> do { traceTc (ptext (sLit "Got HsSyn result:") <+> ppr result)
772 ; return $! result } }
774 ; case either_tval of
776 Left se -> case fromException se of
777 Just IOEnvFailure -> failM -- Error already in Tc monad
778 _ -> failWithTc (mk_msg "run" se) -- Exception
781 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
782 nest 2 (text (Panic.showException exn)),
783 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
786 Note [Exceptions in TH]
787 ~~~~~~~~~~~~~~~~~~~~~~~
788 Supppose we have something like this
792 f n | n>3 = fail "Too many declarations"
795 The 'fail' is a user-generated failure, and should be displayed as a
796 perfectly ordinary compiler error message, not a panic or anything
797 like that. Here's how it's processed:
799 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
800 effectively transforms (fail s) to
801 qReport True s >> fail
802 where 'qReport' comes from the Quasi class and fail from its monad
805 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
806 (qReport True s) by using addErr to add an error message to the bag of errors.
807 The 'fail' in TcM raises an IOEnvFailure exception
809 * So, when running a splice, we catch all exceptions; then for
810 - an IOEnvFailure exception, we assume the error is already
811 in the error-bag (above)
812 - other errors, we add an error to the bag
816 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
819 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
820 qNewName s = do { u <- newUnique
822 ; return (TH.mkNameU s i) }
824 qReport True msg = addErr (text msg)
825 qReport False msg = addReport (text msg) empty
827 qLocation = do { m <- getModule
829 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
830 , TH.loc_module = moduleNameString (moduleName m)
831 , TH.loc_package = packageIdString (modulePackageId m)
832 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
833 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
837 -- For qRecover, discard error messages if
838 -- the recovery action is chosen. Otherwise
839 -- we'll only fail higher up. c.f. tryTcLIE_
840 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
842 Just val -> do { addMessages msgs -- There might be warnings
844 Nothing -> recover -- Discard all msgs
847 qRunIO io = liftIO io
851 %************************************************************************
853 \subsection{Errors and contexts}
855 %************************************************************************
858 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
859 -- Note that 'before' is *renamed* but not *typechecked*
860 -- Reason (a) less typechecking crap
861 -- (b) data constructors after type checking have been
862 -- changed to their *wrappers*, and that makes them
863 -- print always fully qualified
864 showSplice what before after
865 = do { loc <- getSrcSpanM
866 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
867 nest 2 (sep [nest 2 (ppr before),
871 illegalBracket :: SDoc
872 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
877 %************************************************************************
881 %************************************************************************
885 reify :: TH.Name -> TcM TH.Info
887 = do { name <- lookupThName th_name
888 ; thing <- tcLookupTh name
889 -- ToDo: this tcLookup could fail, which would give a
890 -- rather unhelpful error message
891 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
895 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
896 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
897 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
898 ppr_ns _ = panic "reify/ppr_ns"
900 lookupThName :: TH.Name -> TcM Name
901 lookupThName th_name = do
902 mb_name <- lookupThName_maybe th_name
904 Nothing -> failWithTc (notInScope th_name)
905 Just name -> return name
907 lookupThName_maybe th_name
908 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
909 -- Pick the first that works
910 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
911 ; return (listToMaybe names) }
914 = do { -- Repeat much of lookupOccRn, becase we want
915 -- to report errors in a TH-relevant way
916 ; rdr_env <- getLocalRdrEnv
917 ; case lookupLocalRdrEnv rdr_env rdr_name of
918 Just name -> return (Just name)
919 Nothing -> lookupGlobalOccRn_maybe rdr_name }
921 tcLookupTh :: Name -> TcM TcTyThing
922 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
923 -- it gives a reify-related error message on failure, whereas in the normal
924 -- tcLookup, failure is a bug.
926 = do { (gbl_env, lcl_env) <- getEnvs
927 ; case lookupNameEnv (tcl_env lcl_env) name of {
928 Just thing -> return thing;
930 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
931 then -- It's defined in this module
932 case lookupNameEnv (tcg_type_env gbl_env) name of
933 Just thing -> return (AGlobal thing)
934 Nothing -> failWithTc (notInEnv name)
936 else do -- It's imported
937 { (eps,hpt) <- getEpsAndHpt
939 ; case lookupType dflags hpt (eps_PTE eps) name of
940 Just thing -> return (AGlobal thing)
941 Nothing -> do { thing <- tcImportDecl name
942 ; return (AGlobal thing) }
943 -- Imported names should always be findable;
944 -- if not, we fail hard in tcImportDecl
947 notInScope :: TH.Name -> SDoc
948 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
949 ptext (sLit "is not in scope at a reify")
950 -- Ugh! Rather an indirect way to display the name
952 notInEnv :: Name -> SDoc
953 notInEnv name = quotes (ppr name) <+>
954 ptext (sLit "is not in the type environment at a reify")
956 ------------------------------
957 reifyThing :: TcTyThing -> TcM TH.Info
958 -- The only reason this is monadic is for error reporting,
959 -- which in turn is mainly for the case when TH can't express
960 -- some random GHC extension
962 reifyThing (AGlobal (AnId id))
963 = do { ty <- reifyType (idType id)
964 ; fix <- reifyFixity (idName id)
965 ; let v = reifyName id
966 ; case idDetails id of
967 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
968 _ -> return (TH.VarI v ty Nothing fix)
971 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
972 reifyThing (AGlobal (AClass cls)) = reifyClass cls
973 reifyThing (AGlobal (ADataCon dc))
974 = do { let name = dataConName dc
975 ; ty <- reifyType (idType (dataConWrapId dc))
976 ; fix <- reifyFixity name
977 ; return (TH.DataConI (reifyName name) ty
978 (reifyName (dataConOrigTyCon dc)) fix)
981 reifyThing (ATcId {tct_id = id, tct_type = ty})
982 = do { ty1 <- zonkTcType ty -- Make use of all the info we have, even
983 -- though it may be incomplete
984 ; ty2 <- reifyType ty1
985 ; fix <- reifyFixity (idName id)
986 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
988 reifyThing (ATyVar tv ty)
989 = do { ty1 <- zonkTcType ty
990 ; ty2 <- reifyType ty1
991 ; return (TH.TyVarI (reifyName tv) ty2) }
993 reifyThing (AThing {}) = panic "reifyThing AThing"
995 ------------------------------
996 reifyTyCon :: TyCon -> TcM TH.Info
999 = return (TH.PrimTyConI (reifyName tc) 2 False)
1001 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1003 = let flavour = reifyFamFlavour tc
1004 tvs = tyConTyVars tc
1007 | isLiftedTypeKind kind = Nothing
1008 | otherwise = Just $ reifyKind kind
1011 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1013 = do { let (tvs, rhs) = synTyConDefn tc
1014 ; rhs' <- reifyType rhs
1015 ; return (TH.TyConI $
1016 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1020 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1021 ; let tvs = tyConTyVars tc
1022 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1023 ; let name = reifyName tc
1024 r_tvs = reifyTyVars tvs
1025 deriv = [] -- Don't know about deriving
1026 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1027 | otherwise = TH.DataD cxt name r_tvs cons deriv
1028 ; return (TH.TyConI decl) }
1030 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1032 | isVanillaDataCon dc
1033 = do { arg_tys <- reifyTypes (dataConInstOrigArgTys dc tys)
1034 ; let stricts = map reifyStrict (dataConStrictMarks dc)
1035 fields = dataConFieldLabels dc
1039 ; ASSERT( length arg_tys == length stricts )
1040 if not (null fields) then
1041 return (TH.RecC name (zip3 (map reifyName fields) stricts arg_tys))
1043 if dataConIsInfix dc then
1044 ASSERT( length arg_tys == 2 )
1045 return (TH.InfixC (s1,a1) name (s2,a2))
1047 return (TH.NormalC name (stricts `zip` arg_tys)) }
1049 = failWithTc (ptext (sLit "Can't reify a GADT data constructor:")
1050 <+> quotes (ppr dc))
1052 ------------------------------
1053 reifyClass :: Class -> TcM TH.Info
1055 = do { cxt <- reifyCxt theta
1056 ; ops <- mapM reify_op op_stuff
1057 ; return (TH.ClassI $ TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops) }
1059 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1060 fds' = map reifyFunDep fds
1061 reify_op (op, _) = do { ty <- reifyType (idType op)
1062 ; return (TH.SigD (reifyName op) ty) }
1064 ------------------------------
1065 reifyType :: TypeRep.Type -> TcM TH.Type
1066 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1067 reifyType (TyConApp tc tys) = reify_tc_app (reifyName tc) tys
1068 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1069 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1070 reifyType ty@(ForAllTy _ _) = do { cxt' <- reifyCxt cxt;
1071 ; tau' <- reifyType tau
1072 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1074 (tvs, cxt, tau) = tcSplitSigmaTy ty
1075 reifyType (PredTy {}) = panic "reifyType PredTy"
1077 reifyTypes :: [Type] -> TcM [TH.Type]
1078 reifyTypes = mapM reifyType
1080 reifyKind :: Kind -> TH.Kind
1082 = let (kis, ki') = splitKindFunTys ki
1083 kis_rep = map reifyKind kis
1084 ki'_rep = reifyNonArrowKind ki'
1086 foldl TH.ArrowK ki'_rep kis_rep
1088 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1089 | otherwise = pprPanic "Exotic form of kind"
1092 reifyCxt :: [PredType] -> TcM [TH.Pred]
1093 reifyCxt = mapM reifyPred
1095 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1096 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1098 reifyFamFlavour :: TyCon -> TH.FamFlavour
1099 reifyFamFlavour tc | isOpenSynTyCon tc = TH.TypeFam
1100 | isOpenTyCon tc = TH.DataFam
1102 = panic "TcSplice.reifyFamFlavour: not a type family"
1104 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1105 reifyTyVars = map reifyTyVar
1107 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1108 | otherwise = TH.KindedTV name (reifyKind kind)
1113 reify_tc_app :: TH.Name -> [TypeRep.Type] -> TcM TH.Type
1114 reify_tc_app tc tys = do { tys' <- reifyTypes tys
1115 ; return (foldl TH.AppT (TH.ConT tc) tys') }
1117 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1118 reifyPred (ClassP cls tys)
1119 = do { tys' <- reifyTypes tys
1120 ; return $ TH.ClassP (reifyName cls) tys'
1122 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1123 reifyPred (EqPred ty1 ty2)
1124 = do { ty1' <- reifyType ty1
1125 ; ty2' <- reifyType ty2
1126 ; return $ TH.EqualP ty1' ty2'
1130 ------------------------------
1131 reifyName :: NamedThing n => n -> TH.Name
1133 | isExternalName name = mk_varg pkg_str mod_str occ_str
1134 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1135 -- Many of the things we reify have local bindings, and
1136 -- NameL's aren't supposed to appear in binding positions, so
1137 -- we use NameU. When/if we start to reify nested things, that
1138 -- have free variables, we may need to generate NameL's for them.
1140 name = getName thing
1141 mod = ASSERT( isExternalName name ) nameModule name
1142 pkg_str = packageIdString (modulePackageId mod)
1143 mod_str = moduleNameString (moduleName mod)
1144 occ_str = occNameString occ
1145 occ = nameOccName name
1146 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1147 | OccName.isVarOcc occ = TH.mkNameG_v
1148 | OccName.isTcOcc occ = TH.mkNameG_tc
1149 | otherwise = pprPanic "reifyName" (ppr name)
1151 ------------------------------
1152 reifyFixity :: Name -> TcM TH.Fixity
1154 = do { fix <- lookupFixityRn name
1155 ; return (conv_fix fix) }
1157 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1158 conv_dir BasicTypes.InfixR = TH.InfixR
1159 conv_dir BasicTypes.InfixL = TH.InfixL
1160 conv_dir BasicTypes.InfixN = TH.InfixN
1162 reifyStrict :: BasicTypes.StrictnessMark -> TH.Strict
1163 reifyStrict MarkedStrict = TH.IsStrict
1164 reifyStrict MarkedUnboxed = TH.IsStrict
1165 reifyStrict NotMarkedStrict = TH.NotStrict
1167 ------------------------------
1168 noTH :: LitString -> SDoc -> TcM a
1169 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1170 ptext (sLit "in Template Haskell:"),