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
67 import DsMonad hiding (Splice)
72 import Util ( dropList )
73 import Data.List ( mapAccumL )
80 import Control.Monad ( when )
82 import qualified Language.Haskell.TH as TH
83 -- THSyntax gives access to internal functions and data types
84 import qualified Language.Haskell.TH.Syntax as TH
87 -- Because GHC.Desugar might not be in the base library of the bootstrapping compiler
88 import GHC.Desugar ( AnnotationWrapper(..) )
91 import GHC.Exts ( unsafeCoerce#, Int#, Int(..) )
92 import System.IO.Error
95 Note [How top-level splices are handled]
96 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
97 Top-level splices (those not inside a [| .. |] quotation bracket) are handled
98 very straightforwardly:
100 1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
102 2. runMetaT: desugar, compile, run it, and convert result back to
103 HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
106 3. treat the result as if that's what you saw in the first place
107 e.g for HsType, rename and kind-check
108 for HsExpr, rename and type-check
110 (The last step is different for decls, becuase they can *only* be
111 top-level: we return the result of step 2.)
113 Note [How brackets and nested splices are handled]
114 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
115 Nested splices (those inside a [| .. |] quotation bracket), are treated
118 * After typechecking, the bracket [| |] carries
120 a) A mutable list of PendingSplice
121 type PendingSplice = (Name, LHsExpr Id)
123 b) The quoted expression e, *renamed*: (HsExpr Name)
124 The expression e has been typechecked, but the result of
125 that typechecking is discarded.
127 * The brakcet is desugared by DsMeta.dsBracket. It
129 a) Extends the ds_meta environment with the PendingSplices
130 attached to the bracket
132 b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
133 run, will produce a suitable TH expression/type/decl. This
134 is why we leave the *renamed* expression attached to the bracket:
135 the quoted expression should not be decorated with all the goop
136 added by the type checker
138 * Each splice carries a unique Name, called a "splice point", thus
139 ${n}(e). The name is initialised to an (Unqual "splice") when the
140 splice is created; the renamer gives it a unique.
142 * When the type checker type-checks a nested splice ${n}(e), it
144 - adds the typechecked expression (of type (HsExpr Id))
145 as a pending splice to the enclosing bracket
146 - returns something non-committal
147 Eg for [| f ${n}(g x) |], the typechecker
148 - attaches the typechecked term (g x) to the pending splices for n
150 - returns a non-committal type \alpha.
151 Remember that the bracket discards the typechecked term altogether
153 * When DsMeta (used to desugar the body of the bracket) comes across
154 a splice, it looks up the splice's Name, n, in the ds_meta envt,
155 to find an (HsExpr Id) that should be substituted for the splice;
156 it just desugars it to get a CoreExpr (DsMeta.repSplice).
159 Source: f = [| Just $(g 3) |]
160 The [| |] part is a HsBracket
162 Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
163 The [| |] part is a HsBracketOut, containing *renamed*
164 (not typechecked) expression
165 The "s7" is the "splice point"; the (g Int 3) part
166 is a typechecked expression
168 Desugared: f = do { s7 <- g Int 3
169 ; return (ConE "Data.Maybe.Just" s7) }
172 Note [Template Haskell state diagram]
173 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
174 Here are the ThStages, s, their corresponding level numbers
175 (the result of (thLevel s)), and their state transitions.
177 ----------- $ ------------ $
178 | Comp | ---------> | Splice | -----|
180 ----------- ------------
182 $ | | [||] $ | | [||]
184 -------------- ----------------
185 | Brack Comp | | Brack Splice |
187 -------------- ----------------
189 * Normal top-level declarations start in state Comp
191 Annotations start in state Splice, since they are
192 treated very like a splice (only without a '$')
194 * Code compiled in state Splice (and only such code)
195 will be *run at compile time*, with the result replacing
198 * The original paper used level -1 instead of 0, etc.
200 * The original paper did not allow a splice within a
201 splice, but there is no reason not to. This is the
202 $ transition in the top right.
204 Note [Template Haskell levels]
205 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
206 * Imported things are impLevel (= 0)
208 * In GHCi, variables bound by a previous command are treated
209 as impLevel, because we have bytecode for them.
211 * Variables are bound at the "current level"
213 * The current level starts off at outerLevel (= 1)
215 * The level is decremented by splicing $(..)
216 incremented by brackets [| |]
217 incremented by name-quoting 'f
219 When a variable is used, we compare
220 bind: binding level, and
221 use: current level at usage site
224 bind > use Always error (bound later than used)
227 bind = use Always OK (bound same stage as used)
228 [| \x -> $(f [| x |]) |]
230 bind < use Inside brackets, it depends
234 For (bind < use) inside brackets, there are three cases:
235 - Imported things OK f = [| map |]
236 - Top-level things OK g = [| f |]
237 - Non-top-level Only if there is a liftable instance
238 h = \(x:Int) -> [| x |]
240 See Note [What is a top-level Id?]
244 A quoted name 'n is a bit like a quoted expression [| n |], except that we
245 have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
246 the use-level to account for the brackets, the cases are:
255 See Note [What is a top-level Id?] in TcEnv. Examples:
257 f 'map -- OK; also for top-level defns of this module
259 \x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
260 -- cross-stage lifting
262 \y. [| \x. $(f 'y) |] -- Not ok (same reason)
264 [| \x. $(f 'x) |] -- OK
267 Note [What is a top-level Id?]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 In the level-control criteria above, we need to know what a "top level Id" is.
270 There are three kinds:
271 * Imported from another module (GlobalId, ExternalName)
272 * Bound at the top level of this module (ExternalName)
273 * In GHCi, bound by a previous stmt (GlobalId)
274 It's strange that there is no one criterion tht picks out all three, but that's
275 how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
276 bound in an earlier Stmt, but what module would you choose? See
277 Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
279 The predicate we use is TcEnv.thTopLevelId.
282 %************************************************************************
284 \subsection{Main interface + stubs for the non-GHCI case
286 %************************************************************************
289 tcBracket :: HsBracket Name -> TcRhoType -> TcM (LHsExpr TcId)
290 tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
291 tcSpliceExpr :: HsSplice Name -> TcRhoType -> TcM (HsExpr TcId)
292 kcSpliceType :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
293 -- None of these functions add constraints to the LIE
295 lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
297 runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
298 runQuasiQuotePat :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
299 runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
300 runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]
302 runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
305 tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
306 tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
307 tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
308 kcSpliceType x fvs = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
310 lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
312 runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
313 runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
314 runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
315 runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
316 runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
320 %************************************************************************
322 \subsection{Quoting an expression}
324 %************************************************************************
328 -- See Note [How brackets and nested splices are handled]
329 tcBracket brack res_ty
330 = addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
332 do { -- Check for nested brackets
333 cur_stage <- getStage
334 ; checkTc (not (isBrackStage cur_stage)) illegalBracket
336 -- Brackets are desugared to code that mentions the TH package
339 -- Typecheck expr to make sure it is valid,
340 -- but throw away the results. We'll type check
341 -- it again when we actually use it.
342 ; pending_splices <- newMutVar []
343 ; lie_var <- getConstraintVar
344 ; let brack_stage = Brack cur_stage pending_splices lie_var
346 ; (meta_ty, lie) <- setStage brack_stage $
348 tc_bracket cur_stage brack
350 ; simplifyBracket lie
352 -- Make the expected type have the right shape
353 ; _ <- unifyType meta_ty res_ty
355 -- Return the original expression, not the type-decorated one
356 ; pendings <- readMutVar pending_splices
357 ; return (noLoc (HsBracketOut brack pendings)) }
359 tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
360 tc_bracket outer_stage (VarBr name) -- Note [Quoting names]
361 = do { thing <- tcLookup name
363 AGlobal _ -> return ()
364 ATcId { tct_level = bind_lvl, tct_id = id }
365 | thTopLevelId id -- C.f TcExpr.checkCrossStageLifting
368 -> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
369 (quotedNameStageErr name) }
370 _ -> pprPanic "th_bracket" (ppr name)
372 ; tcMetaTy nameTyConName -- Result type is Var (not Q-monadic)
375 tc_bracket _ (ExpBr expr)
376 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
377 ; _ <- tcMonoExprNC expr any_ty -- NC for no context; tcBracket does that
378 ; tcMetaTy expQTyConName }
379 -- Result type is ExpQ (= Q Exp)
381 tc_bracket _ (TypBr typ)
382 = do { _ <- tcHsSigTypeNC ThBrackCtxt typ
383 ; tcMetaTy typeQTyConName }
384 -- Result type is Type (= Q Typ)
386 tc_bracket _ (DecBrG decls)
387 = do { _ <- tcTopSrcDecls emptyModDetails decls
388 -- Typecheck the declarations, dicarding the result
389 -- We'll get all that stuff later, when we splice it in
391 -- Top-level declarations in the bracket get unqualified names
392 -- See Note [Top-level Names in Template Haskell decl quotes] in RnNames
394 ; tcMetaTy decsQTyConName } -- Result type is Q [Dec]
396 tc_bracket _ (PatBr pat)
397 = do { any_ty <- newFlexiTyVarTy liftedTypeKind
398 ; _ <- tcPat ThPatQuote pat any_ty unitTy $
400 ; tcMetaTy patQTyConName }
401 -- Result type is PatQ (= Q Pat)
403 tc_bracket _ (DecBrL _)
404 = panic "tc_bracket: Unexpected DecBrL"
406 quotedNameStageErr :: Name -> SDoc
408 = sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr (VarBr v)
409 , ptext (sLit "must be used at the same stage at which is is bound")]
413 %************************************************************************
415 \subsection{Splicing an expression}
417 %************************************************************************
420 tcSpliceExpr (HsSplice name expr) res_ty
421 = setSrcSpan (getLoc expr) $ do
424 Splice -> tcTopSplice expr res_ty ;
425 Comp -> tcTopSplice expr res_ty ;
427 Brack pop_stage ps_var lie_var -> do
429 -- See Note [How brackets and nested splices are handled]
430 -- A splice inside brackets
431 -- NB: ignore res_ty, apart from zapping it to a mono-type
432 -- e.g. [| reverse $(h 4) |]
433 -- Here (h 4) :: Q Exp
434 -- but $(h 4) :: forall a.a i.e. anything!
436 { meta_exp_ty <- tcMetaTy expQTyConName
437 ; expr' <- setStage pop_stage $
438 setConstraintVar lie_var $
439 tcMonoExpr expr meta_exp_ty
441 -- Write the pending splice into the bucket
442 ; ps <- readMutVar ps_var
443 ; writeMutVar ps_var ((name,expr') : ps)
445 ; return (panic "tcSpliceExpr") -- The returned expression is ignored
448 tcTopSplice :: LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
449 -- Note [How top-level splices are handled]
450 tcTopSplice expr res_ty
451 = do { meta_exp_ty <- tcMetaTy expQTyConName
453 -- Typecheck the expression
454 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
456 -- Run the expression
457 ; expr2 <- runMetaE zonked_q_expr
458 ; showSplice "expression" expr (ppr expr2)
460 -- Rename it, but bale out if there are errors
461 -- otherwise the type checker just gives more spurious errors
462 ; addErrCtxt (spliceResultDoc expr) $ do
463 { (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
465 ; exp4 <- tcMonoExpr exp3 res_ty
466 ; return (unLoc exp4) } }
468 spliceResultDoc :: LHsExpr Name -> SDoc
470 = sep [ ptext (sLit "In the result of the splice:")
471 , nest 2 (char '$' <> pprParendExpr expr)
472 , ptext (sLit "To see what the splice expanded to, use -ddump-splices")]
475 tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
476 -- Note [How top-level splices are handled]
477 -- Type check an expression that is the body of a top-level splice
478 -- (the caller will compile and run it)
479 -- Note that set the level to Splice, regardless of the original level,
480 -- before typechecking the expression. For example:
481 -- f x = $( ...$(g 3) ... )
482 -- The recursive call to tcMonoExpr will simply expand the
483 -- inner escape before dealing with the outer one
485 tcTopSpliceExpr tc_action
486 = checkNoErrs $ -- checkNoErrs: must not try to run the thing
487 -- if the type checker fails!
489 do { -- Typecheck the expression
490 (expr', lie) <- getConstraints tc_action
492 -- Solve the constraints
493 ; const_binds <- simplifyTop lie
495 -- Zonk it and tie the knot of dictionary bindings
496 ; zonkTopLExpr (mkHsDictLet (EvBinds const_binds) expr') }
500 %************************************************************************
504 %************************************************************************
506 Very like splicing an expression, but we don't yet share code.
509 kcSpliceType splice@(HsSplice name hs_expr) fvs
510 = setSrcSpan (getLoc hs_expr) $ do
513 Splice -> kcTopSpliceType hs_expr ;
514 Comp -> kcTopSpliceType hs_expr ;
516 Brack pop_level ps_var lie_var -> do
517 -- See Note [How brackets and nested splices are handled]
518 -- A splice inside brackets
519 { meta_ty <- tcMetaTy typeQTyConName
520 ; expr' <- setStage pop_level $
521 setConstraintVar lie_var $
522 tcMonoExpr hs_expr meta_ty
524 -- Write the pending splice into the bucket
525 ; ps <- readMutVar ps_var
526 ; writeMutVar ps_var ((name,expr') : ps)
528 -- e.g. [| f (g :: Int -> $(h 4)) |]
529 -- Here (h 4) :: Q Type
530 -- but $(h 4) :: a i.e. any type, of any kind
533 ; return (HsSpliceTy splice fvs kind, kind)
536 kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
537 -- Note [How top-level splices are handled]
539 = do { meta_ty <- tcMetaTy typeQTyConName
541 -- Typecheck the expression
542 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
544 -- Run the expression
545 ; hs_ty2 <- runMetaT zonked_q_expr
546 ; showSplice "type" expr (ppr hs_ty2)
548 -- Rename it, but bale out if there are errors
549 -- otherwise the type checker just gives more spurious errors
550 ; addErrCtxt (spliceResultDoc expr) $ do
551 { let doc = ptext (sLit "In the spliced type") <+> ppr hs_ty2
552 ; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
553 ; (ty4, kind) <- kcLHsType hs_ty3
554 ; return (unLoc ty4, kind) }}
557 %************************************************************************
559 \subsection{Splicing an expression}
561 %************************************************************************
564 -- Note [How top-level splices are handled]
565 -- Always at top level
566 -- Type sig at top of file:
567 -- tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
569 = do { list_q <- tcMetaTy decsQTyConName -- Q [Dec]
570 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
572 -- Run the expression
573 ; decls <- runMetaD zonked_q_expr
574 ; showSplice "declarations" expr
575 (ppr (getLoc expr) $$ (vcat (map ppr decls)))
581 %************************************************************************
585 %************************************************************************
588 runAnnotation target expr = do
589 -- Find the classes we want instances for in order to call toAnnotationWrapper
591 data_class <- tcLookupClass dataClassName
592 to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
594 -- Check the instances we require live in another module (we want to execute it..)
595 -- and check identifiers live in other modules using TH stage checks. tcSimplifyStagedExpr
596 -- also resolves the LIE constraints to detect e.g. instance ambiguity
597 zonked_wrapped_expr' <- tcTopSpliceExpr $
598 do { (expr', expr_ty) <- tcInferRhoNC expr
599 -- We manually wrap the typechecked expression in a call to toAnnotationWrapper
600 -- By instantiating the call >here< it gets registered in the
601 -- LIE consulted by tcTopSpliceExpr
602 -- and hence ensures the appropriate dictionary is bound by const_binds
603 ; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
604 ; let specialised_to_annotation_wrapper_expr
605 = L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
606 ; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
608 -- Run the appropriately wrapped expression to get the value of
609 -- the annotation and its dictionaries. The return value is of
610 -- type AnnotationWrapper by construction, so this conversion is
612 flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
613 case annotation_wrapper of
614 AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
615 -- Got the value and dictionaries: build the serialized value and
616 -- call it a day. We ensure that we seq the entire serialized value
617 -- in order that any errors in the user-written code for the
618 -- annotation are exposed at this point. This is also why we are
619 -- doing all this stuff inside the context of runMeta: it has the
620 -- facilities to deal with user error in a meta-level expression
621 seqSerialized serialized `seq` Annotation {
623 ann_value = serialized
628 %************************************************************************
632 %************************************************************************
634 Note [Quasi-quote overview]
635 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
636 The GHC "quasi-quote" extension is described by Geoff Mainland's paper
637 "Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
642 and the arbitrary string "stuff" gets parsed by the parser 'p', whose
643 type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
644 defined in another module, because we are going to run it here. It's
645 a bit like a TH splice:
648 However, you can do this in patterns as well as terms. Becuase of this,
649 the splice is run by the *renamer* rather than the type checker.
651 %************************************************************************
653 \subsubsection{Quasiquotation}
655 %************************************************************************
657 See Note [Quasi-quote overview] in TcSplice.
660 runQuasiQuote :: Outputable hs_syn
661 => HsQuasiQuote RdrName -- Contains term of type QuasiQuoter, and the String
662 -> Name -- Of type QuasiQuoter -> String -> Q th_syn
663 -> Name -- Name of th_syn type
664 -> MetaOps th_syn hs_syn
666 runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
667 = do { quoter' <- lookupOccRn quoter
668 -- We use lookupOcc rather than lookupGlobalOcc because in the
669 -- erroneous case of \x -> [x| ...|] we get a better error message
670 -- (stage restriction rather than out of scope).
672 ; when (isUnboundName quoter') failM
673 -- If 'quoter' is not in scope, proceed no further
674 -- The error message was generated by lookupOccRn, but it then
675 -- succeeds with an "unbound name", which makes the subsequent
676 -- attempt to run the quote fail in a confusing way
678 -- Check that the quoter is not locally defined, otherwise the TH
679 -- machinery will not be able to run the quasiquote.
680 ; this_mod <- getModule
681 ; let is_local = nameIsLocalOrFrom this_mod quoter'
682 ; checkTc (not is_local) (quoteStageError quoter')
684 ; traceTc "runQQ" (ppr quoter <+> ppr is_local)
686 -- Build the expression
687 ; let quoterExpr = L q_span $! HsVar $! quoter'
688 ; let quoteExpr = L q_span $! HsLit $! HsString quote
689 ; let expr = L q_span $
691 HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
692 ; meta_exp_ty <- tcMetaTy meta_ty
694 -- Typecheck the expression
695 ; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
697 -- Run the expression
698 ; result <- runMetaQ meta_ops zonked_q_expr
699 ; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
703 runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName expQTyConName exprMetaOps
704 runQuasiQuotePat qq = runQuasiQuote qq quotePatName patQTyConName patMetaOps
705 runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
706 runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName decsQTyConName declMetaOps
708 quoteStageError :: Name -> SDoc
709 quoteStageError quoter
710 = sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
711 nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
715 %************************************************************************
717 \subsection{Running an expression}
719 %************************************************************************
722 data MetaOps th_syn hs_syn
723 = MT { mt_desc :: String -- Type of beast (expression, type etc)
724 , mt_show :: th_syn -> String -- How to show the th_syn thing
725 , mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
726 -- How to convert to hs_syn
729 exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
730 exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
732 patMetaOps :: MetaOps TH.Pat (LPat RdrName)
733 patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
735 typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
736 typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
738 declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
739 declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
742 runMetaAW :: Outputable output
743 => (AnnotationWrapper -> output)
744 -> LHsExpr Id -- Of type AnnotationWrapper
746 runMetaAW k = runMeta False (\_ -> return . Right . k)
747 -- We turn off showing the code in meta-level exceptions because doing so exposes
748 -- the toAnnotationWrapper function that we slap around the users code
751 runMetaQ :: Outputable hs_syn
752 => MetaOps th_syn hs_syn
755 runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
756 = runMeta True run_and_cvt expr
758 run_and_cvt expr_span hval
759 = do { th_result <- TH.runQ hval
760 ; traceTc "Got TH result:" (text (show_th th_result))
761 ; return (cvt expr_span th_result) }
763 runMetaE :: LHsExpr Id -- Of type (Q Exp)
764 -> TcM (LHsExpr RdrName)
765 runMetaE = runMetaQ exprMetaOps
767 runMetaT :: LHsExpr Id -- Of type (Q Type)
768 -> TcM (LHsType RdrName)
769 runMetaT = runMetaQ typeMetaOps
771 runMetaD :: LHsExpr Id -- Of type Q [Dec]
772 -> TcM [LHsDecl RdrName]
773 runMetaD = runMetaQ declMetaOps
776 runMeta :: (Outputable hs_syn)
777 => Bool -- Whether code should be printed in the exception message
778 -> (SrcSpan -> x -> TcM (Either Message hs_syn)) -- How to run x
779 -> LHsExpr Id -- Of type x; typically x = Q TH.Exp, or something like that
780 -> TcM hs_syn -- Of type t
781 runMeta show_code run_and_convert expr
782 = do { traceTc "About to run" (ppr expr)
785 ; ds_expr <- initDsTc (dsLExpr expr)
786 -- Compile and link it; might fail if linking fails
787 ; hsc_env <- getTopEnv
788 ; src_span <- getSrcSpanM
789 ; either_hval <- tryM $ liftIO $
790 HscMain.compileExpr hsc_env src_span ds_expr
791 ; case either_hval of {
792 Left exn -> failWithTc (mk_msg "compile and link" exn) ;
795 { -- Coerce it to Q t, and run it
797 -- Running might fail if it throws an exception of any kind (hence tryAllM)
798 -- including, say, a pattern-match exception in the code we are running
800 -- We also do the TH -> HS syntax conversion inside the same
801 -- exception-cacthing thing so that if there are any lurking
802 -- exceptions in the data structure returned by hval, we'll
803 -- encounter them inside the try
805 -- See Note [Exceptions in TH]
806 let expr_span = getLoc expr
807 ; either_tval <- tryAllM $
808 setSrcSpan expr_span $ -- Set the span so that qLocation can
809 -- see where this splice is
810 do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
812 Left err -> failWithTc err
813 Right result -> do { traceTc "Got HsSyn result:" (ppr result)
814 ; return $! result } }
816 ; case either_tval of
818 Left se -> case fromException se of
819 Just IOEnvFailure -> failM -- Error already in Tc monad
820 _ -> failWithTc (mk_msg "run" se) -- Exception
823 mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
824 nest 2 (text (Panic.showException exn)),
825 if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
828 Note [Exceptions in TH]
829 ~~~~~~~~~~~~~~~~~~~~~~~
830 Supppose we have something like this
834 f n | n>3 = fail "Too many declarations"
837 The 'fail' is a user-generated failure, and should be displayed as a
838 perfectly ordinary compiler error message, not a panic or anything
839 like that. Here's how it's processed:
841 * 'fail' is the monad fail. The monad instance for Q in TH.Syntax
842 effectively transforms (fail s) to
843 qReport True s >> fail
844 where 'qReport' comes from the Quasi class and fail from its monad
847 * The TcM monad is an instance of Quasi (see TcSplice), and it implements
848 (qReport True s) by using addErr to add an error message to the bag of errors.
849 The 'fail' in TcM raises an IOEnvFailure exception
851 * So, when running a splice, we catch all exceptions; then for
852 - an IOEnvFailure exception, we assume the error is already
853 in the error-bag (above)
854 - other errors, we add an error to the bag
858 To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
861 instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
862 qNewName s = do { u <- newUnique
864 ; return (TH.mkNameU s i) }
866 qReport True msg = addErr (text msg)
867 qReport False msg = addReport (text msg) empty
869 qLocation = do { m <- getModule
871 ; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile l)
872 , TH.loc_module = moduleNameString (moduleName m)
873 , TH.loc_package = packageIdString (modulePackageId m)
874 , TH.loc_start = (srcSpanStartLine l, srcSpanStartCol l)
875 , TH.loc_end = (srcSpanEndLine l, srcSpanEndCol l) }) }
878 qClassInstances = lookupClassInstances
880 -- For qRecover, discard error messages if
881 -- the recovery action is chosen. Otherwise
882 -- we'll only fail higher up. c.f. tryTcLIE_
883 qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
885 Just val -> do { addMessages msgs -- There might be warnings
887 Nothing -> recover -- Discard all msgs
890 qRunIO io = liftIO io
894 %************************************************************************
896 \subsection{Errors and contexts}
898 %************************************************************************
901 showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
902 -- Note that 'before' is *renamed* but not *typechecked*
903 -- Reason (a) less typechecking crap
904 -- (b) data constructors after type checking have been
905 -- changed to their *wrappers*, and that makes them
906 -- print always fully qualified
907 showSplice what before after
908 = do { loc <- getSrcSpanM
909 ; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
910 nest 2 (sep [nest 2 (ppr before),
914 illegalBracket :: SDoc
915 illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
920 %************************************************************************
924 %************************************************************************
927 lookupClassInstances :: TH.Name -> [TH.Type] -> TcM [TH.Name]
928 lookupClassInstances c ts
929 = do { loc <- getSrcSpanM
930 ; case convertToHsPred loc (TH.ClassP c ts) of
931 Left msg -> failWithTc msg
933 { rn_pred <- rnLPred doc rdr_pred -- Rename
934 ; kc_pred <- kcHsLPred rn_pred -- Kind check
935 ; ClassP cls tys <- dsHsLPred kc_pred -- Type check
937 -- Now look up instances
938 ; inst_envs <- tcGetInstEnvs
939 ; let (matches, unifies) = lookupInstEnv inst_envs cls tys
940 dfuns = map is_dfun (map fst matches ++ unifies)
941 ; return (map reifyName dfuns) } }
943 doc = ptext (sLit "TcSplice.classInstances")
947 %************************************************************************
951 %************************************************************************
955 reify :: TH.Name -> TcM TH.Info
957 = do { name <- lookupThName th_name
958 ; thing <- tcLookupTh name
959 -- ToDo: this tcLookup could fail, which would give a
960 -- rather unhelpful error message
961 ; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
965 ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
966 ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
967 ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
968 ppr_ns _ = panic "reify/ppr_ns"
970 lookupThName :: TH.Name -> TcM Name
971 lookupThName th_name = do
972 mb_name <- lookupThName_maybe th_name
974 Nothing -> failWithTc (notInScope th_name)
975 Just name -> return name
977 lookupThName_maybe th_name
978 = do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
979 -- Pick the first that works
980 -- E.g. reify (mkName "A") will pick the class A in preference to the data constructor A
981 ; return (listToMaybe names) }
984 = do { -- Repeat much of lookupOccRn, becase we want
985 -- to report errors in a TH-relevant way
986 ; rdr_env <- getLocalRdrEnv
987 ; case lookupLocalRdrEnv rdr_env rdr_name of
988 Just name -> return (Just name)
989 Nothing -> lookupGlobalOccRn_maybe rdr_name }
991 tcLookupTh :: Name -> TcM TcTyThing
992 -- This is a specialised version of TcEnv.tcLookup; specialised mainly in that
993 -- it gives a reify-related error message on failure, whereas in the normal
994 -- tcLookup, failure is a bug.
996 = do { (gbl_env, lcl_env) <- getEnvs
997 ; case lookupNameEnv (tcl_env lcl_env) name of {
998 Just thing -> return thing;
1000 { if nameIsLocalOrFrom (tcg_mod gbl_env) name
1001 then -- It's defined in this module
1002 case lookupNameEnv (tcg_type_env gbl_env) name of
1003 Just thing -> return (AGlobal thing)
1004 Nothing -> failWithTc (notInEnv name)
1006 else do -- It's imported
1007 { (eps,hpt) <- getEpsAndHpt
1008 ; dflags <- getDOpts
1009 ; case lookupType dflags hpt (eps_PTE eps) name of
1010 Just thing -> return (AGlobal thing)
1011 Nothing -> do { thing <- tcImportDecl name
1012 ; return (AGlobal thing) }
1013 -- Imported names should always be findable;
1014 -- if not, we fail hard in tcImportDecl
1017 notInScope :: TH.Name -> SDoc
1018 notInScope th_name = quotes (text (TH.pprint th_name)) <+>
1019 ptext (sLit "is not in scope at a reify")
1020 -- Ugh! Rather an indirect way to display the name
1022 notInEnv :: Name -> SDoc
1023 notInEnv name = quotes (ppr name) <+>
1024 ptext (sLit "is not in the type environment at a reify")
1026 ------------------------------
1027 reifyThing :: TcTyThing -> TcM TH.Info
1028 -- The only reason this is monadic is for error reporting,
1029 -- which in turn is mainly for the case when TH can't express
1030 -- some random GHC extension
1032 reifyThing (AGlobal (AnId id))
1033 = do { ty <- reifyType (idType id)
1034 ; fix <- reifyFixity (idName id)
1035 ; let v = reifyName id
1036 ; case idDetails id of
1037 ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
1038 _ -> return (TH.VarI v ty Nothing fix)
1041 reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
1042 reifyThing (AGlobal (AClass cls)) = reifyClass cls
1043 reifyThing (AGlobal (ADataCon dc))
1044 = do { let name = dataConName dc
1045 ; ty <- reifyType (idType (dataConWrapId dc))
1046 ; fix <- reifyFixity name
1047 ; return (TH.DataConI (reifyName name) ty
1048 (reifyName (dataConOrigTyCon dc)) fix)
1051 reifyThing (ATcId {tct_id = id})
1052 = do { ty1 <- zonkTcType (idType id) -- Make use of all the info we have, even
1053 -- though it may be incomplete
1054 ; ty2 <- reifyType ty1
1055 ; fix <- reifyFixity (idName id)
1056 ; return (TH.VarI (reifyName id) ty2 Nothing fix) }
1058 reifyThing (ATyVar tv ty)
1059 = do { ty1 <- zonkTcType ty
1060 ; ty2 <- reifyType ty1
1061 ; return (TH.TyVarI (reifyName tv) ty2) }
1063 reifyThing (AThing {}) = panic "reifyThing AThing"
1065 ------------------------------
1066 reifyTyCon :: TyCon -> TcM TH.Info
1069 = return (TH.PrimTyConI (reifyName tc) 2 False)
1071 = return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
1073 = let flavour = reifyFamFlavour tc
1074 tvs = tyConTyVars tc
1077 | isLiftedTypeKind kind = Nothing
1078 | otherwise = Just $ reifyKind kind
1081 TH.FamilyD flavour (reifyName tc) (reifyTyVars tvs) kind')
1083 = do { let (tvs, rhs) = synTyConDefn tc
1084 ; rhs' <- reifyType rhs
1085 ; return (TH.TyConI $
1086 TH.TySynD (reifyName tc) (reifyTyVars tvs) rhs')
1090 = do { cxt <- reifyCxt (tyConStupidTheta tc)
1091 ; let tvs = tyConTyVars tc
1092 ; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
1093 ; let name = reifyName tc
1094 r_tvs = reifyTyVars tvs
1095 deriv = [] -- Don't know about deriving
1096 decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
1097 | otherwise = TH.DataD cxt name r_tvs cons deriv
1098 ; return (TH.TyConI decl) }
1100 reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
1101 -- For GADTs etc, see Note [Reifying data constructors]
1103 = do { let (tvs, theta, arg_tys, _) = dataConSig dc
1104 subst = mkTopTvSubst (tvs `zip` tys) -- Dicard ex_tvs
1105 (subst', ex_tvs') = mapAccumL substTyVarBndr subst (dropList tys tvs)
1106 theta' = substTheta subst' theta
1107 arg_tys' = substTys subst' arg_tys
1108 stricts = map reifyStrict (dataConStrictMarks dc)
1109 fields = dataConFieldLabels dc
1112 ; r_arg_tys <- reifyTypes arg_tys'
1114 ; let main_con | not (null fields)
1115 = TH.RecC name (zip3 (map reifyName fields) stricts r_arg_tys)
1117 = ASSERT( length arg_tys == 2 )
1118 TH.InfixC (s1,r_a1) name (s2,r_a2)
1120 = TH.NormalC name (stricts `zip` r_arg_tys)
1121 [r_a1, r_a2] = r_arg_tys
1124 ; ASSERT( length arg_tys == length stricts )
1125 if null ex_tvs' && null theta then
1128 { cxt <- reifyCxt theta'
1129 ; return (TH.ForallC (reifyTyVars ex_tvs') cxt main_con) } }
1131 ------------------------------
1132 reifyClass :: Class -> TcM TH.Info
1134 = do { cxt <- reifyCxt theta
1135 ; inst_envs <- tcGetInstEnvs
1136 ; insts <- mapM reifyClassInstance (InstEnv.classInstances inst_envs cls)
1137 ; ops <- mapM reify_op op_stuff
1138 ; let dec = TH.ClassD cxt (reifyName cls) (reifyTyVars tvs) fds' ops
1139 ; return (TH.ClassI dec insts ) }
1141 (tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
1142 fds' = map reifyFunDep fds
1143 reify_op (op, _) = do { ty <- reifyType (idType op)
1144 ; return (TH.SigD (reifyName op) ty) }
1146 ------------------------------
1147 reifyClassInstance :: Instance -> TcM TH.ClassInstance
1148 reifyClassInstance i
1149 = do { cxt <- reifyCxt theta
1150 ; thtypes <- reifyTypes types
1151 ; return $ (TH.ClassInstance {
1152 TH.ci_tvs = reifyTyVars tvs,
1154 TH.ci_tys = thtypes,
1155 TH.ci_cls = reifyName cls,
1156 TH.ci_dfun = reifyName (is_dfun i) }) }
1158 (tvs, theta, cls, types) = instanceHead i
1160 ------------------------------
1161 reifyType :: TypeRep.Type -> TcM TH.Type
1162 -- Monadic only because of failure
1163 reifyType ty@(ForAllTy _ _) = reify_for_all ty
1164 reifyType ty@(PredTy {} `FunTy` _) = reify_for_all ty -- Types like ((?x::Int) => Char -> Char)
1165 reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
1166 reifyType (TyConApp tc tys) = reify_tc_app tc tys -- Do not expand type synonyms here
1167 reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
1168 reifyType (FunTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
1169 reifyType ty@(PredTy {}) = pprPanic "reifyType PredTy" (ppr ty)
1171 reify_for_all :: TypeRep.Type -> TcM TH.Type
1173 = do { cxt' <- reifyCxt cxt;
1174 ; tau' <- reifyType tau
1175 ; return (TH.ForallT (reifyTyVars tvs) cxt' tau') }
1177 (tvs, cxt, tau) = tcSplitSigmaTy ty
1179 reifyTypes :: [Type] -> TcM [TH.Type]
1180 reifyTypes = mapM reifyType
1182 reifyKind :: Kind -> TH.Kind
1184 = let (kis, ki') = splitKindFunTys ki
1185 kis_rep = map reifyKind kis
1186 ki'_rep = reifyNonArrowKind ki'
1188 foldr TH.ArrowK ki'_rep kis_rep
1190 reifyNonArrowKind k | isLiftedTypeKind k = TH.StarK
1191 | otherwise = pprPanic "Exotic form of kind"
1194 reifyCxt :: [PredType] -> TcM [TH.Pred]
1195 reifyCxt = mapM reifyPred
1197 reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
1198 reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
1200 reifyFamFlavour :: TyCon -> TH.FamFlavour
1201 reifyFamFlavour tc | isSynFamilyTyCon tc = TH.TypeFam
1202 | isFamilyTyCon tc = TH.DataFam
1204 = panic "TcSplice.reifyFamFlavour: not a type family"
1206 reifyTyVars :: [TyVar] -> [TH.TyVarBndr]
1207 reifyTyVars = map reifyTyVar
1209 reifyTyVar tv | isLiftedTypeKind kind = TH.PlainTV name
1210 | otherwise = TH.KindedTV name (reifyKind kind)
1215 reify_tc_app :: TyCon -> [TypeRep.Type] -> TcM TH.Type
1217 = do { tys' <- reifyTypes tys
1218 ; return (foldl TH.AppT r_tc tys') }
1221 r_tc | isTupleTyCon tc = TH.TupleT n_tys
1222 | tc `hasKey` listTyConKey = TH.ListT
1223 | otherwise = TH.ConT (reifyName tc)
1225 reifyPred :: TypeRep.PredType -> TcM TH.Pred
1226 reifyPred (ClassP cls tys)
1227 = do { tys' <- reifyTypes tys
1228 ; return $ TH.ClassP (reifyName cls) tys' }
1230 reifyPred p@(IParam _ _) = noTH (sLit "implicit parameters") (ppr p)
1231 reifyPred (EqPred ty1 ty2)
1232 = do { ty1' <- reifyType ty1
1233 ; ty2' <- reifyType ty2
1234 ; return $ TH.EqualP ty1' ty2'
1238 ------------------------------
1239 reifyName :: NamedThing n => n -> TH.Name
1241 | isExternalName name = mk_varg pkg_str mod_str occ_str
1242 | otherwise = TH.mkNameU occ_str (getKey (getUnique name))
1243 -- Many of the things we reify have local bindings, and
1244 -- NameL's aren't supposed to appear in binding positions, so
1245 -- we use NameU. When/if we start to reify nested things, that
1246 -- have free variables, we may need to generate NameL's for them.
1248 name = getName thing
1249 mod = ASSERT( isExternalName name ) nameModule name
1250 pkg_str = packageIdString (modulePackageId mod)
1251 mod_str = moduleNameString (moduleName mod)
1252 occ_str = occNameString occ
1253 occ = nameOccName name
1254 mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
1255 | OccName.isVarOcc occ = TH.mkNameG_v
1256 | OccName.isTcOcc occ = TH.mkNameG_tc
1257 | otherwise = pprPanic "reifyName" (ppr name)
1259 ------------------------------
1260 reifyFixity :: Name -> TcM TH.Fixity
1262 = do { fix <- lookupFixityRn name
1263 ; return (conv_fix fix) }
1265 conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
1266 conv_dir BasicTypes.InfixR = TH.InfixR
1267 conv_dir BasicTypes.InfixL = TH.InfixL
1268 conv_dir BasicTypes.InfixN = TH.InfixN
1270 reifyStrict :: BasicTypes.HsBang -> TH.Strict
1271 reifyStrict bang | isBanged bang = TH.IsStrict
1272 | otherwise = TH.NotStrict
1274 ------------------------------
1275 noTH :: LitString -> SDoc -> TcM a
1276 noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
1277 ptext (sLit "in Template Haskell:"),
1281 Note [Reifying data constructors]
1282 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1283 Template Haskell syntax is rich enough to express even GADTs,
1284 provided we do so in the equality-predicate form. So a GADT
1291 will appear in TH syntax like this
1293 data T a = forall b. (a ~ [b]) => MkT1 b