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)
71 import Util ( dropList )
72 import Data.List ( mapAccumL )
79 import Control.Monad ( when )
81 import qualified Language.Haskell.TH as TH
82 -- THSyntax gives access to internal functions and data types
83 import qualified Language.Haskell.TH.Syntax as TH
86 -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
87 import GHC.Desugar ( AnnotationWrapper(..) )
90 import GHC.Exts ( unsafeCoerce#, Int#, Int(..) )
91 import System.IO.Error
94 Note [How top-level splices are handled]
95 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
96 Top-level splices (those not inside a [| .. |] quotation bracket) are handled
97 very straightforwardly:
99 1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
101 2. runMetaT: desugar, compile, run it, and convert result back to
102 HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
105 3. treat the result as if that's what you saw in the first place
106 e.g for HsType, rename and kind-check
107 for HsExpr, rename and type-check
109 (The last step is different for decls, becuase they can *only* be
110 top-level: we return the result of step 2.)
112 Note [How brackets and nested splices are handled]
113 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
114 Nested splices (those inside a [| .. |] quotation bracket), are treated
117 * After typechecking, the bracket [| |] carries
119 a) A mutable list of PendingSplice
120 type PendingSplice = (Name, LHsExpr Id)
122 b) The quoted expression e, *renamed*: (HsExpr Name)
123 The expression e has been typechecked, but the result of
124 that typechecking is discarded.
126 * The brakcet is desugared by DsMeta.dsBracket. It
128 a) Extends the ds_meta environment with the PendingSplices
129 attached to the bracket
131 b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
132 run, will produce a suitable TH expression/type/decl. This
133 is why we leave the *renamed* expression attached to the bracket:
134 the quoted expression should not be decorated with all the goop
135 added by the type checker
137 * Each splice carries a unique Name, called a "splice point", thus
138 ${n}(e). The name is initialised to an (Unqual "splice") when the
139 splice is created; the renamer gives it a unique.
141 * When the type checker type-checks a nested splice ${n}(e), it
143 - adds the typechecked expression (of type (HsExpr Id))
144 as a pending splice to the enclosing bracket
145 - returns something non-committal
146 Eg for [| f ${n}(g x) |], the typechecker
147 - attaches the typechecked term (g x) to the pending splices for n
149 - returns a non-committal type \alpha.
150 Remember that the bracket discards the typechecked term altogether
152 * When DsMeta (used to desugar the body of the bracket) comes across
153 a splice, it looks up the splice's Name, n, in the ds_meta envt,
154 to find an (HsExpr Id) that should be substituted for the splice;
155 it just desugars it to get a CoreExpr (DsMeta.repSplice).
158 Source: f = [| Just $(g 3) |]
159 The [| |] part is a HsBracket
161 Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
162 The [| |] part is a HsBracketOut, containing *renamed*
163 (not typechecked) expression
164 The "s7" is the "splice point"; the (g Int 3) part
165 is a typechecked expression
167 Desugared: f = do { s7 <- g Int 3
168 ; return (ConE "Data.Maybe.Just" s7) }
171 Note [Template Haskell state diagram]
172 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
173 Here are the ThStages, s, their corresponding level numbers
174 (the result of (thLevel s)), and their state transitions.
176 ----------- $ ------------ $
177 | Comp | ---------> | Splice | -----|
179 ----------- ------------
181 $ | | [||] $ | | [||]
183 -------------- ----------------
184 | Brack Comp | | Brack Splice |
186 -------------- ----------------
188 * Normal top-level declarations start in state Comp
190 Annotations start in state Splice, since they are
191 treated very like a splice (only without a '$')
193 * Code compiled in state Splice (and only such code)
194 will be *run at compile time*, with the result replacing
197 * The original paper used level -1 instead of 0, etc.
199 * The original paper did not allow a splice within a
200 splice, but there is no reason not to. This is the
201 $ transition in the top right.
203 Note [Template Haskell levels]
204 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
205 * Imported things are impLevel (= 0)
207 * In GHCi, variables bound by a previous command are treated
208 as impLevel, because we have bytecode for them.
210 * Variables are bound at the "current level"
212 * The current level starts off at outerLevel (= 1)
214 * The level is decremented by splicing $(..)
215 incremented by brackets [| |]
216 incremented by name-quoting 'f
218 When a variable is used, we compare
219 bind: binding level, and
220 use: current level at usage site
223 bind > use Always error (bound later than used)
226 bind = use Always OK (bound same stage as used)
227 [| \x -> $(f [| x |]) |]
229 bind < use Inside brackets, it depends
233 For (bind < use) inside brackets, there are three cases:
234 - Imported things OK f = [| map |]
235 - Top-level things OK g = [| f |]
236 - Non-top-level Only if there is a liftable instance
237 h = \(x:Int) -> [| x |]
239 See Note [What is a top-level Id?]
243 A quoted name 'n is a bit like a quoted expression [| n |], except that we
244 have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
245 the use-level to account for the brackets, the cases are:
254 See Note [What is a top-level Id?] in TcEnv. Examples:
256 f 'map -- OK; also for top-level defns of this module
258 \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
259 -- cross-stage lifting
261 \y. [| \x. $(f 'y) |] -- Not ok (same reason)
263 [| \x. $(f 'x) |] -- OK
266 Note [What is a top-level Id?]
267 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
268 In the level-control criteria above, we need to know what a "top level Id" is.
269 There are three kinds:
270 * Imported from another module (GlobalId, ExternalName)
271 * Bound at the top level of this module (ExternalName)
272 * In GHCi, bound by a previous stmt (GlobalId)
273 It's strange that there is no one criterion tht picks out all three, but that's
274 how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
275 bound in an earlier Stmt, but what module would you choose? See
276 Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
278 The predicate we use is TcEnv.thTopLevelId.
281 %************************************************************************
283 \subsection{Main interface + stubs for the non-GHCI case
285 %************************************************************************
288 tcBracket :: HsBracket Name -> TcRhoType -> TcM (LHsExpr TcId)
289 tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
290 tcSpliceExpr :: HsSplice Name -> TcRhoType -> TcM (HsExpr TcId)
291 kcSpliceType :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
292 -- None of these functions add constraints to the LIE
294 lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
296 runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
297 runQuasiQuotePat :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
298 runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
299 runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]
301 runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
304 tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
305 tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
306 tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
307 kcSpliceType x fvs = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
309 lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
311 runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
312 runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
313 runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
314 runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
315 runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
319 %************************************************************************
321 \subsection{Quoting an expression}
323 %************************************************************************
327 -- See Note [How brackets and nested splices are handled]
328 tcBracket brack res_ty
329 = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
331 do { -- Check for nested brackets
332 cur_stage <- getStage
333 ; checkTc (not (isBrackStage cur_stage)) illegalBracket
335 -- Brackets are desugared to code that mentions the TH package
338 -- Typecheck expr to make sure it is valid,
339 -- but throw away the results. We'll type check
340 -- it again when we actually use it.
341 ; pending_splices <- newMutVar []
342 ; lie_var <- getConstraintVar
343 ; let brack_stage = Brack cur_stage pending_splices lie_var
345 ; (meta_ty, lie) <- setStage brack_stage $
347 tc_bracket cur_stage brack
349 ; simplifyBracket lie
351 -- Make the expected type have the right shape
352 ; _ <- unifyType meta_ty res_ty
354 -- Return the original expression, not the type-decorated one
355 ; pendings <- readMutVar pending_splices
356 ; return (noLoc (HsBracketOut brack pendings)) }
358 tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
359 tc_bracket outer_stage (VarBr name) -- Note [Quoting names]
360 = do { thing <- tcLookup name
362 AGlobal _ -> return ()
363 ATcId { tct_level = bind_lvl, tct_id = id }
364 | thTopLevelId id -- C.f TcExpr.checkCrossStageLifting
367 -> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
368 (quotedNameStageErr name) }
369 _ -> pprPanic "th_bracket" (ppr name)
371 ; tcMetaTy nameTyConName -- Result type is Var (not Q-monadic)
374 tc_bracket _ (ExpBr expr)
375 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
376 ; _ <- tcMonoExprNC expr any_ty -- NC for no context; tcBracket does that
377 ; tcMetaTy expQTyConName }
378 -- Result type is ExpQ (= Q Exp)
380 tc_bracket _ (TypBr typ)
381 = do { _ <- tcHsSigTypeNC ThBrackCtxt typ
382 ; tcMetaTy typeQTyConName }
383 -- Result type is Type (= Q Typ)
385 tc_bracket _ (DecBrG decls)
386 = do { _ <- tcTopSrcDecls emptyModDetails decls
387 -- Typecheck the declarations, dicarding the result
388 -- We'll get all that stuff later, when we splice it in
390 -- Top-level declarations in the bracket get unqualified names
391 -- See Note [Top-level Names in Template Haskell decl quotes] in RnNames
393 ; tcMetaTy decsQTyConName } -- Result type is Q [Dec]
395 tc_bracket _ (PatBr pat)
396 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
397 ; _ <- tcPat ThPatQuote pat any_ty unitTy $
399 ; tcMetaTy patQTyConName }
400 -- Result type is PatQ (= Q Pat)
402 tc_bracket _ (DecBrL _)
403 = panic "tc_bracket: Unexpected DecBrL"
405 quotedNameStageErr :: Name -> SDoc
407 = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
408 , ptext (sLit "must be used at the same stage at which is is bound")]
412 %************************************************************************
414 \subsection{Splicing an expression}
416 %************************************************************************
419 tcSpliceExpr (HsSplice name expr) res_ty
420 = setSrcSpan (getLoc expr) $ do
423 Splice -> tcTopSplice expr res_ty ;
424 Comp -> tcTopSplice expr res_ty ;
426 Brack pop_stage ps_var lie_var -> do
428 -- See Note [How brackets and nested splices are handled]
429 -- A splice inside brackets
430 -- NB: ignore res_ty, apart from zapping it to a mono-type
431 -- e.g. [| reverse $(h 4) |]
432 -- Here (h 4) :: Q Exp
433 -- but $(h 4) :: forall a.a i.e. anything!
435 { meta_exp_ty <- tcMetaTy expQTyConName
436 ; expr' <- setStage pop_stage $
437 setConstraintVar lie_var $
438 tcMonoExpr expr meta_exp_ty
440 -- Write the pending splice into the bucket
441 ; ps <- readMutVar ps_var
442 ; writeMutVar ps_var ((name,expr') : ps)
444 ; return (panic "tcSpliceExpr") -- The returned expression is ignored
447 tcTopSplice :: LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
448 -- Note [How top-level splices are handled]
449 tcTopSplice expr res_ty
450 = do { meta_exp_ty <- tcMetaTy expQTyConName
452 -- Typecheck the expression
453 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
455 -- Run the expression
456 ; expr2 <- runMetaE zonked_q_expr
457 ; showSplice "expression" expr (ppr expr2)
459 -- Rename it, but bale out if there are errors
460 -- otherwise the type checker just gives more spurious errors
461 ; addErrCtxt (spliceResultDoc expr) $ do
462 { (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
464 ; exp4 <- tcMonoExpr exp3 res_ty
465 ; return (unLoc exp4) } }
467 spliceResultDoc :: LHsExpr Name -> SDoc
469 = sep [ ptext (sLit "In the result of the splice:")
470 , nest 2 (char '$' <> pprParendExpr expr)
471 , ptext (sLit "To see what the splice expanded to, use -ddump-splices")]
474 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
475 -- Note [How top-level splices are handled]
476 -- Type check an expression that is the body of a top-level splice
477 -- (the caller will compile and run it)
478 -- Note that set the level to Splice, regardless of the original level,
479 -- before typechecking the expression. For example:
480 -- f x = $( ...$(g 3) ... )
481 -- The recursive call to tcMonoExpr will simply expand the
482 -- inner escape before dealing with the outer one
484 tcTopSpliceExpr tc_action
485 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
486 -- if the type checker fails!
488 do { -- Typecheck the expression
489 (expr', lie) <- getConstraints tc_action
491 -- Solve the constraints
492 ; const_binds <- simplifyTop lie
494 -- Zonk it and tie the knot of dictionary bindings
495 ; zonkTopLExpr (mkHsDictLet (EvBinds const_binds) expr') }
499 %************************************************************************
503 %************************************************************************
505 Very like splicing an expression, but we don't yet share code.
508 kcSpliceType splice@(HsSplice name hs_expr) fvs
509 = setSrcSpan (getLoc hs_expr) $ do
512 Splice -> kcTopSpliceType hs_expr ;
513 Comp -> kcTopSpliceType hs_expr ;
515 Brack pop_level ps_var lie_var -> do
516 -- See Note [How brackets and nested splices are handled]
517 -- A splice inside brackets
518 { meta_ty <- tcMetaTy typeQTyConName
519 ; expr' <- setStage pop_level $
520 setConstraintVar lie_var $
521 tcMonoExpr hs_expr meta_ty
523 -- Write the pending splice into the bucket
524 ; ps <- readMutVar ps_var
525 ; writeMutVar ps_var ((name,expr') : ps)
527 -- e.g. [| f (g :: Int -> $(h 4)) |]
528 -- Here (h 4) :: Q Type
529 -- but $(h 4) :: a i.e. any type, of any kind
532 ; return (HsSpliceTy splice fvs kind, kind)
535 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
536 -- Note [How top-level splices are handled]
538 = do { meta_ty <- tcMetaTy typeQTyConName
540 -- Typecheck the expression
541 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
543 -- Run the expression
544 ; hs_ty2 <- runMetaT zonked_q_expr
545 ; showSplice "type" expr (ppr hs_ty2)
547 -- Rename it, but bale out if there are errors
548 -- otherwise the type checker just gives more spurious errors
549 ; addErrCtxt (spliceResultDoc expr) $ do
550 { let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
551 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
552 ; (ty4, kind) <- kcLHsType hs_ty3
553 ; return (unLoc ty4, kind) }}
556 %************************************************************************
558 \subsection{Splicing an expression}
560 %************************************************************************
563 -- Note [How top-level splices are handled]
564 -- Always at top level
565 -- Type sig at top of file:
566 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
568 = do { list_q <- tcMetaTy decsQTyConName -- Q [Dec]
569 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
571 -- Run the expression
572 ; decls <- runMetaD zonked_q_expr
573 ; showSplice "declarations" expr
574 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
580 %************************************************************************
584 %************************************************************************
587 runAnnotation target expr = do
588 -- Find the classes we want instances for in order to call toAnnotationWrapper
590 data_class <- tcLookupClass dataClassName
591 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
593 -- Check the instances we require live in another module (we want to execute it..)
594 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
595 -- also resolves the LIE constraints to detect e.g. instance ambiguity
596 zonked_wrapped_expr' <- tcTopSpliceExpr $
597 do { (expr', expr_ty) <- tcInferRhoNC expr
598 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
599 -- By instantiating the call >here< it gets registered in the
600 -- LIE consulted by tcTopSpliceExpr
601 -- and hence ensures the appropriate dictionary is bound by const_binds
602 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
603 ; let specialised_to_annotation_wrapper_expr
604 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
605 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
607 -- Run the appropriately wrapped expression to get the value of
608 -- the annotation and its dictionaries. The return value is of
609 -- type AnnotationWrapper by construction, so this conversion is
611 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
612 case annotation_wrapper of
613 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
614 -- Got the value and dictionaries: build the serialized value and
615 -- call it a day. We ensure that we seq the entire serialized value
616 -- in order that any errors in the user-written code for the
617 -- annotation are exposed at this point. This is also why we are
618 -- doing all this stuff inside the context of runMeta: it has the
619 -- facilities to deal with user error in a meta-level expression
620 seqSerialized serialized `seq` Annotation {
622 ann_value = serialized
627 %************************************************************************
631 %************************************************************************
633 Note [Quasi-quote overview]
634 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
635 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
636 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
641 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
642 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
643 defined in another module, because we are going to run it here. It's
644 a bit like a TH splice:
647 However, you can do this in patterns as well as terms. Becuase of this,
648 the splice is run by the *renamer* rather than the type checker.
650 %************************************************************************
652 \subsubsection{Quasiquotation}
654 %************************************************************************
656 See Note [Quasi-quote overview] in TcSplice.
659 runQuasiQuote :: Outputable hs_syn
660 => HsQuasiQuote RdrName -- Contains term of type QuasiQuoter, and the String
661 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
662 -> Name -- Name of th_syn type
663 -> MetaOps th_syn hs_syn
665 runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
666 = do { quoter' <- lookupOccRn quoter
667 -- We use lookupOcc rather than lookupGlobalOcc because in the
668 -- erroneous case of \x -> [x| ...|] we get a better error message
669 -- (stage restriction rather than out of scope).
671 ; when (isUnboundName quoter') failM
672 -- If 'quoter' is not in scope, proceed no further
673 -- The error message was generated by lookupOccRn, but it then
674 -- succeeds with an "unbound name", which makes the subsequent
675 -- attempt to run the quote fail in a confusing way
677 -- Check that the quoter is not locally defined, otherwise the TH
678 -- machinery will not be able to run the quasiquote.
679 ; this_mod <- getModule
680 ; let is_local = nameIsLocalOrFrom this_mod quoter'
681 ; checkTc (not is_local) (quoteStageError quoter')
683 ; traceTc "runQQ" (ppr quoter <+> ppr is_local)
685 -- Build the expression
686 ; let quoterExpr = L q_span $! HsVar $! quoter'
687 ; let quoteExpr = L q_span $! HsLit $! HsString quote
688 ; let expr = L q_span $
690 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
691 ; meta_exp_ty <- tcMetaTy meta_ty
693 -- Typecheck the expression
694 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
696 -- Run the expression
697 ; result <- runMetaQ meta_ops zonked_q_expr
698 ; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
702 runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName expQTyConName exprMetaOps
703 runQuasiQuotePat qq = runQuasiQuote qq quotePatName patQTyConName patMetaOps
704 runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
705 runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName decsQTyConName declMetaOps
707 quoteStageError :: Name -> SDoc
708 quoteStageError quoter
709 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
710 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
714 %************************************************************************
716 \subsection{Running an expression}
718 %************************************************************************
721 data MetaOps th_syn hs_syn
722 = MT { mt_desc :: String -- Type of beast (expression, type etc)
723 , mt_show :: th_syn -> String -- How to show the th_syn thing
724 , mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
725 -- How to convert to hs_syn
728 exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
729 exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
731 patMetaOps :: MetaOps TH.Pat (LPat RdrName)
732 patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
734 typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
735 typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
737 declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
738 declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
741 runMetaAW :: Outputable output
742 => (AnnotationWrapper -> output)
743 -> LHsExpr Id -- Of type AnnotationWrapper
745 runMetaAW k = runMeta False (\_ -> return . Right . k)
746 -- We turn off showing the code in meta-level exceptions because doing so exposes
747 -- the toAnnotationWrapper function that we slap around the users code
750 runMetaQ :: Outputable hs_syn
751 => MetaOps th_syn hs_syn
754 runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
755 = runMeta True run_and_cvt expr
757 run_and_cvt expr_span hval
758 = do { th_result <- TH.runQ hval
759 ; traceTc "Got TH result:" (text (show_th th_result))
760 ; return (cvt expr_span th_result) }
762 runMetaE :: LHsExpr Id -- Of type (Q Exp)
763 -> TcM (LHsExpr RdrName)
764 runMetaE = runMetaQ exprMetaOps
766 runMetaT :: LHsExpr Id -- Of type (Q Type)
767 -> TcM (LHsType RdrName)
768 runMetaT = runMetaQ typeMetaOps
770 runMetaD :: LHsExpr Id -- Of type Q [Dec]
771 -> TcM [LHsDecl RdrName]
772 runMetaD = runMetaQ declMetaOps
775 runMeta :: (Outputable hs_syn)
776 => Bool -- Whether code should be printed in the exception message
777 -> (SrcSpan -> x -> TcM (Either Message hs_syn)) -- How to run x
778 -> LHsExpr Id -- Of type x; typically x = Q TH.Exp, or something like that
779 -> TcM hs_syn -- Of type t
780 runMeta show_code run_and_convert expr
781 = do { traceTc "About to run" (ppr expr)
784 ; ds_expr <- initDsTc (dsLExpr expr)
785 -- Compile and link it; might fail if linking fails
786 ; hsc_env <- getTopEnv
787 ; src_span <- getSrcSpanM
788 ; either_hval <- tryM $ liftIO $
789 HscMain.compileExpr hsc_env src_span ds_expr
790 ; case either_hval of {
791 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
794 { -- Coerce it to Q t, and run it
796 -- Running might fail if it throws an exception of any kind (hence tryAllM)
797 -- including, say, a pattern-match exception in the code we are running
799 -- We also do the TH -> HS syntax conversion inside the same
800 -- exception-cacthing thing so that if there are any lurking
801 -- exceptions in the data structure returned by hval, we'll
802 -- encounter them inside the try
804 -- See Note [Exceptions in TH]
805 let expr_span = getLoc expr
806 ; either_tval <- tryAllM $
807 setSrcSpan expr_span $ -- Set the span so that qLocation can
808 -- see where this splice is
809 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
811 Left err -> failWithTc err
812 Right result -> do { traceTc "Got HsSyn result:" (ppr result)
813 ; return $! result } }
815 ; case either_tval of
817 Left se -> case fromException se of
818 Just IOEnvFailure -> failM -- Error already in Tc monad
819 _ -> failWithTc (mk_msg "run" se) -- Exception
822 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
823 nest 2 (text (Panic.showException exn)),
824 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
827 Note [Exceptions in TH]
828 ~~~~~~~~~~~~~~~~~~~~~~~
829 Supppose we have something like this
833 f n | n>3 = fail "Too many declarations"
836 The 'fail' is a user-generated failure, and should be displayed as a
837 perfectly ordinary compiler error message, not a panic or anything
838 like that. Here's how it's processed:
840 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
841 effectively transforms (fail s) to
842 qReport True s >> fail
843 where 'qReport' comes from the Quasi class and fail from its monad
846 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
847 (qReport True s) by using addErr to add an error message to the bag of errors.
848 The 'fail' in TcM raises an IOEnvFailure exception
850 * So, when running a splice, we catch all exceptions; then for
851 - an IOEnvFailure exception, we assume the error is already
852 in the error-bag (above)
853 - other errors, we add an error to the bag
857 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
860 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
861 qNewName s = do { u <- newUnique
863 ; return (TH.mkNameU s i) }
865 qReport True msg = addErr (text msg)
866 qReport False msg = addReport (text msg) empty
868 qLocation = do { m <- getModule
870 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
871 , TH.loc_module = moduleNameString (moduleName m)
872 , TH.loc_package = packageIdString (modulePackageId m)
873 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
874 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
878 -- For qRecover, discard error messages if
879 -- the recovery action is chosen. Otherwise
880 -- we'll only fail higher up. c.f. tryTcLIE_
881 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
883 Just val -> do { addMessages msgs -- There might be warnings
885 Nothing -> recover -- Discard all msgs
888 qRunIO io = liftIO io
892 %************************************************************************
894 \subsection{Errors and contexts}
896 %************************************************************************
899 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
900 -- Note that 'before' is *renamed* but not *typechecked*
901 -- Reason (a) less typechecking crap
902 -- (b) data constructors after type checking have been
903 -- changed to their *wrappers*, and that makes them
904 -- print always fully qualified
905 showSplice what before after
906 = do { loc <- getSrcSpanM
907 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
908 nest 2 (sep [nest 2 (ppr before),
912 illegalBracket :: SDoc
913 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
918 %************************************************************************
922 %************************************************************************
926 reify :: TH.Name -> TcM TH.Info
928 = do { name <- lookupThName th_name
929 ; thing <- tcLookupTh name
930 -- ToDo: this tcLookup could fail, which would give a
931 -- rather unhelpful error message
932 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
936 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
937 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
938 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
939 ppr_ns _ = panic "reify/ppr_ns"
941 lookupThName :: TH.Name -> TcM Name
942 lookupThName th_name = do
943 mb_name <- lookupThName_maybe th_name
945 Nothing -> failWithTc (notInScope th_name)
946 Just name -> return name
948 lookupThName_maybe th_name
949 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
950 -- Pick the first that works
951 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
952 ; return (listToMaybe names) }
955 = do { -- Repeat much of lookupOccRn, becase we want
956 -- to report errors in a TH-relevant way
957 ; rdr_env <- getLocalRdrEnv
958 ; case lookupLocalRdrEnv rdr_env rdr_name of
959 Just name -> return (Just name)
960 Nothing -> lookupGlobalOccRn_maybe rdr_name }
962 tcLookupTh :: Name -> TcM TcTyThing
963 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
964 -- it gives a reify-related error message on failure, whereas in the normal
965 -- tcLookup, failure is a bug.
967 = do { (gbl_env, lcl_env) <- getEnvs
968 ; case lookupNameEnv (tcl_env lcl_env) name of {
969 Just thing -> return thing;
971 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
972 then -- It's defined in this module
973 case lookupNameEnv (tcg_type_env gbl_env) name of
974 Just thing -> return (AGlobal thing)
975 Nothing -> failWithTc (notInEnv name)
977 else do -- It's imported
978 { (eps,hpt) <- getEpsAndHpt
980 ; case lookupType dflags hpt (eps_PTE eps) name of
981 Just thing -> return (AGlobal thing)
982 Nothing -> do { thing <- tcImportDecl name
983 ; return (AGlobal thing) }
984 -- Imported names should always be findable;
985 -- if not, we fail hard in tcImportDecl
988 notInScope :: TH.Name -> SDoc
989 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
990 ptext (sLit "is not in scope at a reify")
991 -- Ugh! Rather an indirect way to display the name
993 notInEnv :: Name -> SDoc
994 notInEnv name = quotes (ppr name) <+>
995 ptext (sLit "is not in the type environment at a reify")
997 ------------------------------
998 reifyThing :: TcTyThing -> TcM TH.Info
999 -- The only reason this is monadic is for error reporting,
1000 -- which in turn is mainly for the case when TH can't express
1001 -- some random GHC extension
1003 reifyThing (AGlobal (AnId id))
1004 = do { ty <- reifyType (idType id)
1005 ; fix <- reifyFixity (idName id)
1006 ; let v = reifyName id
1007 ; case idDetails id of
1008 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
1009 _ -> return (TH.VarI v ty Nothing fix)
1012 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
1013 reifyThing (AGlobal (AClass cls)) = reifyClass cls
1014 reifyThing (AGlobal (ADataCon dc))
1015 = do { let name = dataConName dc
1016 ; ty <- reifyType (idType (dataConWrapId dc))
1017 ; fix <- reifyFixity name
1018 ; return (TH.DataConI (reifyName name) ty
1019 (reifyName (dataConOrigTyCon dc)) fix)
1022 reifyThing (ATcId {tct_id = id})
1023 = do { ty1 <- zonkTcType (idType id) -- Make use of all the info we have, even
1024 -- though it may be incomplete
1025 ; ty2 <- reifyType ty1
1026 ; fix <- reifyFixity (idName id)
1027 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
1029 reifyThing (ATyVar tv ty)
1030 = do { ty1 <- zonkTcType ty
1031 ; ty2 <- reifyType ty1
1032 ; return (TH.TyVarI (reifyName tv) ty2) }
1034 reifyThing (AThing {}) = panic "reifyThing AThing"
1036 ------------------------------
1037 reifyTyCon :: TyCon -> TcM TH.Info
1040 = return (TH.PrimTyConI (reifyName tc) 2 False)
1042 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1044 = let flavour = reifyFamFlavour tc
1045 tvs = tyConTyVars tc
1048 | isLiftedTypeKind kind = Nothing
1049 | otherwise = Just $ reifyKind kind
1052 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1054 = do { let (tvs, rhs) = synTyConDefn tc
1055 ; rhs' <- reifyType rhs
1056 ; return (TH.TyConI $
1057 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1061 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1062 ; let tvs = tyConTyVars tc
1063 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1064 ; let name = reifyName tc
1065 r_tvs = reifyTyVars tvs
1066 deriv = [] -- Don't know about deriving
1067 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1068 | otherwise = TH.DataD cxt name r_tvs cons deriv
1069 ; return (TH.TyConI decl) }
1071 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1072 -- For GADTs etc, see Note [Reifying data constructors]
1074 = do { let (tvs, theta, arg_tys, _) = dataConSig dc
1075 subst = mkTopTvSubst (tvs `zip` tys) -- Dicard ex_tvs
1076 (subst', ex_tvs') = mapAccumL substTyVarBndr subst (dropList tys tvs)
1077 theta' = substTheta subst' theta
1078 arg_tys' = substTys subst' arg_tys
1079 stricts = map reifyStrict (dataConStrictMarks dc)
1080 fields = dataConFieldLabels dc
1083 ; r_arg_tys <- reifyTypes arg_tys'
1085 ; let main_con | not (null fields)
1086 = TH.RecC name (zip3 (map reifyName fields) stricts r_arg_tys)
1088 = ASSERT( length arg_tys == 2 )
1089 TH.InfixC (s1,r_a1) name (s2,r_a2)
1091 = TH.NormalC name (stricts `zip` r_arg_tys)
1092 [r_a1, r_a2] = r_arg_tys
1095 ; ASSERT( length arg_tys == length stricts )
1096 if null ex_tvs' && null theta then
1099 { cxt <- reifyCxt theta'
1100 ; return (TH.ForallC (reifyTyVars ex_tvs') cxt main_con) } }
1102 ------------------------------
1103 reifyClass :: Class -> TcM TH.Info
1105 = do { cxt <- reifyCxt theta
1106 ; ops <- mapM reify_op op_stuff
1107 ; return (TH.ClassI $ TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops) }
1109 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1110 fds' = map reifyFunDep fds
1111 reify_op (op, _) = do { ty <- reifyType (idType op)
1112 ; return (TH.SigD (reifyName op) ty) }
1114 ------------------------------
1115 reifyType :: TypeRep.Type -> TcM TH.Type
1116 reifyType ty@(ForAllTy _ _) = reify_for_all ty
1117 reifyType ty@(PredTy {} `FunTy` _) = reify_for_all ty -- Types like ((?x::Int) => Char -> Char)
1118 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1119 reifyType (TyConApp tc tys) = reify_tc_app tc tys -- Do not expand type synonyms here
1120 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1121 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1122 reifyType ty@(PredTy {}) = pprPanic "reifyType PredTy" (ppr ty)
1124 reify_for_all :: TypeRep.Type -> TcM TH.Type
1126 = do { cxt' <- reifyCxt cxt;
1127 ; tau' <- reifyType tau
1128 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1130 (tvs, cxt, tau) = tcSplitSigmaTy ty
1132 reifyTypes :: [Type] -> TcM [TH.Type]
1133 reifyTypes = mapM reifyType
1135 reifyKind :: Kind -> TH.Kind
1137 = let (kis, ki') = splitKindFunTys ki
1138 kis_rep = map reifyKind kis
1139 ki'_rep = reifyNonArrowKind ki'
1141 foldr TH.ArrowK ki'_rep kis_rep
1143 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1144 | otherwise = pprPanic "Exotic form of kind"
1147 reifyCxt :: [PredType] -> TcM [TH.Pred]
1148 reifyCxt = mapM reifyPred
1150 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1151 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1153 reifyFamFlavour :: TyCon -> TH.FamFlavour
1154 reifyFamFlavour tc | isSynFamilyTyCon tc = TH.TypeFam
1155 | isFamilyTyCon tc = TH.DataFam
1157 = panic "TcSplice.reifyFamFlavour: not a type family"
1159 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1160 reifyTyVars = map reifyTyVar
1162 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1163 | otherwise = TH.KindedTV name (reifyKind kind)
1168 reify_tc_app :: TyCon -> [TypeRep.Type] -> TcM TH.Type
1170 = do { tys' <- reifyTypes tys
1171 ; return (foldl TH.AppT r_tc tys') }
1174 r_tc | isTupleTyCon tc = TH.TupleT n_tys
1175 | tc `hasKey` listTyConKey = TH.ListT
1176 | otherwise = TH.ConT (reifyName tc)
1178 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1179 reifyPred (ClassP cls tys)
1180 = do { tys' <- reifyTypes tys
1181 ; return $ TH.ClassP (reifyName cls) tys' }
1183 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1184 reifyPred (EqPred ty1 ty2)
1185 = do { ty1' <- reifyType ty1
1186 ; ty2' <- reifyType ty2
1187 ; return $ TH.EqualP ty1' ty2'
1191 ------------------------------
1192 reifyName :: NamedThing n => n -> TH.Name
1194 | isExternalName name = mk_varg pkg_str mod_str occ_str
1195 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1196 -- Many of the things we reify have local bindings, and
1197 -- NameL's aren't supposed to appear in binding positions, so
1198 -- we use NameU. When/if we start to reify nested things, that
1199 -- have free variables, we may need to generate NameL's for them.
1201 name = getName thing
1202 mod = ASSERT( isExternalName name ) nameModule name
1203 pkg_str = packageIdString (modulePackageId mod)
1204 mod_str = moduleNameString (moduleName mod)
1205 occ_str = occNameString occ
1206 occ = nameOccName name
1207 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1208 | OccName.isVarOcc occ = TH.mkNameG_v
1209 | OccName.isTcOcc occ = TH.mkNameG_tc
1210 | otherwise = pprPanic "reifyName" (ppr name)
1212 ------------------------------
1213 reifyFixity :: Name -> TcM TH.Fixity
1215 = do { fix <- lookupFixityRn name
1216 ; return (conv_fix fix) }
1218 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1219 conv_dir BasicTypes.InfixR = TH.InfixR
1220 conv_dir BasicTypes.InfixL = TH.InfixL
1221 conv_dir BasicTypes.InfixN = TH.InfixN
1223 reifyStrict :: BasicTypes.HsBang -> TH.Strict
1224 reifyStrict bang | isBanged bang = TH.IsStrict
1225 | otherwise = TH.NotStrict
1227 ------------------------------
1228 noTH :: LitString -> SDoc -> TcM a
1229 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1230 ptext (sLit "in Template Haskell:"),
1234 Note [Reifying data constructors]
1235 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1236 Template Haskell syntax is rich enough to express even GADTs,
1237 provided we do so in the equality-predicate form. So a GADT
1244 will appear in TH syntax like this
1246 data T a = forall b. (a ~ [b]) => MkT1 b