a6918b6cf844eabf7e369afbd64c65de65a439f8
[ghc.git] / compiler / typecheck / TcExpr.hs
1 {-
2 %
3 (c) The University of Glasgow 2006
4 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5
6 \section[TcExpr]{Typecheck an expression}
7 -}
8
9 {-# LANGUAGE CPP, TupleSections, ScopedTypeVariables #-}
10 {-# LANGUAGE FlexibleContexts #-}
11
12 module TcExpr ( tcPolyExpr, tcMonoExpr, tcMonoExprNC,
13 tcInferSigma, tcInferSigmaNC, tcInferRho, tcInferRhoNC,
14 tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType,
15 tcCheckId,
16 addExprErrCtxt,
17 getFixedTyVars ) where
18
19 #include "HsVersions.h"
20
21 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket )
22 import THNames( liftStringName, liftName )
23
24 import HsSyn
25 import TcHsSyn
26 import TcRnMonad
27 import TcUnify
28 import BasicTypes
29 import Inst
30 import TcBinds ( chooseInferredQuantifiers, tcLocalBinds )
31 import TcSigs ( tcUserTypeSig, tcInstSig )
32 import TcSimplify ( simplifyInfer, InferMode(..) )
33 import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst )
34 import FamInstEnv ( FamInstEnvs )
35 import RnEnv ( addUsedGRE, addNameClashErrRn
36 , unknownSubordinateErr )
37 import TcEnv
38 import TcArrows
39 import TcMatches
40 import TcHsType
41 import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr )
42 import TcPat
43 import TcMType
44 import TcType
45 import DsMonad
46 import Id
47 import IdInfo
48 import ConLike
49 import DataCon
50 import PatSyn
51 import Name
52 import NameEnv
53 import NameSet
54 import RdrName
55 import TyCon
56 import Type
57 import TysPrim ( tYPE )
58 import TcEvidence
59 import VarSet
60 import TysWiredIn
61 import TysPrim( intPrimTy )
62 import PrimOp( tagToEnumKey )
63 import PrelNames
64 import MkId ( proxyHashId )
65 import DynFlags
66 import SrcLoc
67 import Util
68 import VarEnv ( emptyTidyEnv )
69 import ListSetOps
70 import Maybes
71 import Outputable
72 import FastString
73 import Control.Monad
74 import Class(classTyCon)
75 import UniqFM ( nonDetEltsUFM )
76 import qualified GHC.LanguageExtensions as LangExt
77
78 import Data.Function
79 import Data.List
80 import Data.Either
81 import qualified Data.Set as Set
82
83 {-
84 ************************************************************************
85 * *
86 \subsection{Main wrappers}
87 * *
88 ************************************************************************
89 -}
90
91 tcPolyExpr, tcPolyExprNC
92 :: LHsExpr Name -- Expression to type check
93 -> TcSigmaType -- Expected type (could be a polytype)
94 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
95
96 -- tcPolyExpr is a convenient place (frequent but not too frequent)
97 -- place to add context information.
98 -- The NC version does not do so, usually because the caller wants
99 -- to do so himself.
100
101 tcPolyExpr expr res_ty = tc_poly_expr expr (mkCheckExpType res_ty)
102 tcPolyExprNC expr res_ty = tc_poly_expr_nc expr (mkCheckExpType res_ty)
103
104 -- these versions take an ExpType
105 tc_poly_expr, tc_poly_expr_nc :: LHsExpr Name -> ExpSigmaType -> TcM (LHsExpr TcId)
106 tc_poly_expr expr res_ty
107 = addExprErrCtxt expr $
108 do { traceTc "tcPolyExpr" (ppr res_ty); tc_poly_expr_nc expr res_ty }
109
110 tc_poly_expr_nc (L loc expr) res_ty
111 = do { traceTc "tcPolyExprNC" (ppr res_ty)
112 ; (wrap, expr')
113 <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty ->
114 setSrcSpan loc $
115 -- NB: setSrcSpan *after* skolemising, so we get better
116 -- skolem locations
117 tcExpr expr res_ty
118 ; return $ L loc (mkHsWrap wrap expr') }
119
120 ---------------
121 tcMonoExpr, tcMonoExprNC
122 :: LHsExpr Name -- Expression to type check
123 -> ExpRhoType -- Expected type
124 -- Definitely no foralls at the top
125 -> TcM (LHsExpr TcId)
126
127 tcMonoExpr expr res_ty
128 = addErrCtxt (exprCtxt expr) $
129 tcMonoExprNC expr res_ty
130
131 tcMonoExprNC (L loc expr) res_ty
132 = setSrcSpan loc $
133 do { expr' <- tcExpr expr res_ty
134 ; return (L loc expr') }
135
136 ---------------
137 tcInferSigma, tcInferSigmaNC :: LHsExpr Name -> TcM ( LHsExpr TcId
138 , TcSigmaType )
139 -- Infer a *sigma*-type.
140 tcInferSigma expr = addErrCtxt (exprCtxt expr) (tcInferSigmaNC expr)
141
142 tcInferSigmaNC (L loc expr)
143 = setSrcSpan loc $
144 do { (expr', sigma) <- tcInfer (tcExpr expr)
145 ; return (L loc expr', sigma) }
146
147 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
148 -- Infer a *rho*-type. The return type is always (shallowly) instantiated.
149 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
150
151 tcInferRhoNC expr
152 = do { (expr', sigma) <- tcInferSigmaNC expr
153 ; (wrap, rho) <- topInstantiate (exprCtOrigin (unLoc expr)) sigma
154 ; return (mkLHsWrap wrap expr', rho) }
155
156
157 {-
158 ************************************************************************
159 * *
160 tcExpr: the main expression typechecker
161 * *
162 ************************************************************************
163
164 NB: The res_ty is always deeply skolemised.
165 -}
166
167 tcExpr :: HsExpr Name -> ExpRhoType -> TcM (HsExpr TcId)
168 tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty
169 tcExpr (HsUnboundVar uv) res_ty = tcUnboundId uv res_ty
170
171 tcExpr e@(HsApp {}) res_ty = tcApp1 e res_ty
172 tcExpr e@(HsAppType {}) res_ty = tcApp1 e res_ty
173
174 tcExpr e@(HsLit lit) res_ty = do { let lit_ty = hsLitType lit
175 ; tcWrapResult e (HsLit lit) lit_ty res_ty }
176
177 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
178 ; return (HsPar expr') }
179
180 tcExpr (HsSCC src lbl expr) res_ty
181 = do { expr' <- tcMonoExpr expr res_ty
182 ; return (HsSCC src lbl expr') }
183
184 tcExpr (HsTickPragma src info srcInfo expr) res_ty
185 = do { expr' <- tcMonoExpr expr res_ty
186 ; return (HsTickPragma src info srcInfo expr') }
187
188 tcExpr (HsCoreAnn src lbl expr) res_ty
189 = do { expr' <- tcMonoExpr expr res_ty
190 ; return (HsCoreAnn src lbl expr') }
191
192 tcExpr (HsOverLit lit) res_ty
193 = do { lit' <- newOverloadedLit lit res_ty
194 ; return (HsOverLit lit') }
195
196 tcExpr (NegApp expr neg_expr) res_ty
197 = do { (expr', neg_expr')
198 <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $
199 \[arg_ty] ->
200 tcMonoExpr expr (mkCheckExpType arg_ty)
201 ; return (NegApp expr' neg_expr') }
202
203 tcExpr e@(HsIPVar x) res_ty
204 = do { {- Implicit parameters must have a *tau-type* not a
205 type scheme. We enforce this by creating a fresh
206 type variable as its type. (Because res_ty may not
207 be a tau-type.) -}
208 ip_ty <- newOpenFlexiTyVarTy
209 ; let ip_name = mkStrLitTy (hsIPNameFS x)
210 ; ipClass <- tcLookupClass ipClassName
211 ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty])
212 ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var)))
213 ip_ty res_ty }
214 where
215 -- Coerces a dictionary for `IP "x" t` into `t`.
216 fromDict ipClass x ty = HsWrap $ mkWpCastR $
217 unwrapIP $ mkClassPred ipClass [x,ty]
218 origin = IPOccOrigin x
219
220 tcExpr e@(HsOverLabel l) res_ty -- See Note [Type-checking overloaded labels]
221 = do { isLabelClass <- tcLookupClass isLabelClassName
222 ; alpha <- newOpenFlexiTyVarTy
223 ; let lbl = mkStrLitTy l
224 pred = mkClassPred isLabelClass [lbl, alpha]
225 ; loc <- getSrcSpanM
226 ; var <- emitWantedEvVar origin pred
227 ; let proxy_arg = L loc (mkHsWrap (mkWpTyApps [typeSymbolKind, lbl])
228 (HsVar (L loc proxyHashId)))
229 tm = L loc (fromDict pred (HsVar (L loc var))) `HsApp` proxy_arg
230 ; tcWrapResult e tm alpha res_ty }
231 where
232 -- Coerces a dictionary for `IsLabel "x" t` into `Proxy# x -> t`.
233 fromDict pred = HsWrap $ mkWpCastR $ unwrapIP pred
234 origin = OverLabelOrigin l
235
236 tcExpr (HsLam match) res_ty
237 = do { (match', wrap) <- tcMatchLambda herald match_ctxt match res_ty
238 ; return (mkHsWrap wrap (HsLam match')) }
239 where
240 match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody }
241 herald = sep [ text "The lambda expression" <+>
242 quotes (pprSetDepth (PartWay 1) $
243 pprMatches match),
244 -- The pprSetDepth makes the abstraction print briefly
245 text "has"]
246
247 tcExpr e@(HsLamCase matches) res_ty
248 = do { (matches', wrap)
249 <- tcMatchLambda msg match_ctxt matches res_ty
250 -- The laziness annotation is because we don't want to fail here
251 -- if there are multiple arguments
252 ; return (mkHsWrap wrap $ HsLamCase matches') }
253 where
254 msg = sep [ text "The function" <+> quotes (ppr e)
255 , text "requires"]
256 match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
257
258 tcExpr e@(ExprWithTySig expr sig_ty) res_ty
259 = do { let loc = getLoc (hsSigWcType sig_ty)
260 ; sig_info <- checkNoErrs $ -- Avoid error cascade
261 tcUserTypeSig loc sig_ty Nothing
262 ; (expr', poly_ty) <- tcExprSig expr sig_info
263 ; let expr'' = ExprWithTySigOut expr' sig_ty
264 ; tcWrapResult e expr'' poly_ty res_ty }
265
266 {-
267 Note [Type-checking overloaded labels]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 Recall that (in GHC.OverloadedLabels) we have
270
271 class IsLabel (x :: Symbol) a where
272 fromLabel :: Proxy# x -> a
273
274 When we see an overloaded label like `#foo`, we generate a fresh
275 variable `alpha` for the type and emit an `IsLabel "foo" alpha`
276 constraint. Because the `IsLabel` class has a single method, it is
277 represented by a newtype, so we can coerce `IsLabel "foo" alpha` to
278 `Proxy# "foo" -> alpha` (just like for implicit parameters). We then
279 apply it to `proxy#` of type `Proxy# "foo"`.
280
281 That is, we translate `#foo` to `fromLabel (proxy# :: Proxy# "foo")`.
282 -}
283
284
285 {-
286 ************************************************************************
287 * *
288 Infix operators and sections
289 * *
290 ************************************************************************
291
292 Note [Left sections]
293 ~~~~~~~~~~~~~~~~~~~~
294 Left sections, like (4 *), are equivalent to
295 \ x -> (*) 4 x,
296 or, if PostfixOperators is enabled, just
297 (*) 4
298 With PostfixOperators we don't actually require the function to take
299 two arguments at all. For example, (x `not`) means (not x); you get
300 postfix operators! Not Haskell 98, but it's less work and kind of
301 useful.
302
303 Note [Typing rule for ($)]
304 ~~~~~~~~~~~~~~~~~~~~~~~~~~
305 People write
306 runST $ blah
307 so much, where
308 runST :: (forall s. ST s a) -> a
309 that I have finally given in and written a special type-checking
310 rule just for saturated appliations of ($).
311 * Infer the type of the first argument
312 * Decompose it; should be of form (arg2_ty -> res_ty),
313 where arg2_ty might be a polytype
314 * Use arg2_ty to typecheck arg2
315
316 Note [Typing rule for seq]
317 ~~~~~~~~~~~~~~~~~~~~~~~~~~
318 We want to allow
319 x `seq` (# p,q #)
320 which suggests this type for seq:
321 seq :: forall (a:*) (b:Open). a -> b -> b,
322 with (b:Open) meaning that be can be instantiated with an unboxed
323 tuple. The trouble is that this might accept a partially-applied
324 'seq', and I'm just not certain that would work. I'm only sure it's
325 only going to work when it's fully applied, so it turns into
326 case x of _ -> (# p,q #)
327
328 So it seems more uniform to treat 'seq' as it it was a language
329 construct.
330
331 See also Note [seqId magic] in MkId
332 -}
333
334 tcExpr expr@(OpApp arg1 op fix arg2) res_ty
335 | (L loc (HsVar (L lv op_name))) <- op
336 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
337 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
338 ; let arg2_exp_ty = res_ty
339 ; arg1' <- tcArg op arg1 arg1_ty 1
340 ; arg2' <- addErrCtxt (funAppCtxt op arg2 2) $
341 tc_poly_expr_nc arg2 arg2_exp_ty
342 ; arg2_ty <- readExpType arg2_exp_ty
343 ; op_id <- tcLookupId op_name
344 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty])
345 (HsVar (L lv op_id)))
346 ; return $ OpApp arg1' op' fix arg2' }
347
348 | (L loc (HsVar (L lv op_name))) <- op
349 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
350 = do { traceTc "Application rule" (ppr op)
351 ; (arg1', arg1_ty) <- tcInferSigma arg1
352
353 ; let doc = text "The first argument of ($) takes"
354 orig1 = exprCtOrigin (unLoc arg1)
355 ; (wrap_arg1, [arg2_sigma], op_res_ty) <-
356 matchActualFunTys doc orig1 (Just arg1) 1 arg1_ty
357
358 -- We have (arg1 $ arg2)
359 -- So: arg1_ty = arg2_ty -> op_res_ty
360 -- where arg2_sigma maybe polymorphic; that's the point
361
362 ; arg2' <- tcArg op arg2 arg2_sigma 2
363
364 -- Make sure that the argument type has kind '*'
365 -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b
366 -- Eg we do not want to allow (D# $ 4.0#) Trac #5570
367 -- (which gives a seg fault)
368 --
369 -- The *result* type can have any kind (Trac #8739),
370 -- so we don't need to check anything for that
371 ; _ <- unifyKind (Just arg2_sigma) (typeKind arg2_sigma) liftedTypeKind
372 -- ignore the evidence. arg2_sigma must have type * or #,
373 -- because we know arg2_sigma -> or_res_ty is well-kinded
374 -- (because otherwise matchActualFunTys would fail)
375 -- There's no possibility here of, say, a kind family reducing to *.
376
377 ; wrap_res <- tcSubTypeHR orig1 (Just expr) op_res_ty res_ty
378 -- op_res -> res
379
380 ; op_id <- tcLookupId op_name
381 ; res_ty <- readExpType res_ty
382 ; let op' = L loc (HsWrap (mkWpTyApps [ getRuntimeRep "tcExpr ($)" res_ty
383 , arg2_sigma
384 , res_ty])
385 (HsVar (L lv op_id)))
386 -- arg1' :: arg1_ty
387 -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty)
388 -- wrap_res :: op_res_ty "->" res_ty
389 -- op' :: (a2_ty -> res_ty) -> a2_ty -> res_ty
390
391 -- wrap1 :: arg1_ty "->" (arg2_sigma -> res_ty)
392 wrap1 = mkWpFun idHsWrapper wrap_res arg2_sigma res_ty
393 <.> wrap_arg1
394
395 ; return (OpApp (mkLHsWrap wrap1 arg1') op' fix arg2') }
396
397 | (L loc (HsRecFld (Ambiguous lbl _))) <- op
398 , Just sig_ty <- obviousSig (unLoc arg1)
399 -- See Note [Disambiguating record fields]
400 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
401 ; sel_name <- disambiguateSelector lbl sig_tc_ty
402 ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name))
403 ; tcExpr (OpApp arg1 op' fix arg2) res_ty
404 }
405
406 | otherwise
407 = do { traceTc "Non Application rule" (ppr op)
408 ; (wrap, op', [Left arg1', Left arg2'])
409 <- tcApp (Just $ mk_op_msg op)
410 op [Left arg1, Left arg2] res_ty
411 ; return (mkHsWrap wrap $ OpApp arg1' op' fix arg2') }
412
413 -- Right sections, equivalent to \ x -> x `op` expr, or
414 -- \ x -> op x expr
415
416 tcExpr expr@(SectionR op arg2) res_ty
417 = do { (op', op_ty) <- tcInferFun op
418 ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty) <-
419 matchActualFunTys (mk_op_msg op) SectionOrigin (Just op) 2 op_ty
420 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
421 (mkFunTy arg1_ty op_res_ty) res_ty
422 ; arg2' <- tcArg op arg2 arg2_ty 2
423 ; return ( mkHsWrap wrap_res $
424 SectionR (mkLHsWrap wrap_fun op') arg2' ) }
425
426 tcExpr expr@(SectionL arg1 op) res_ty
427 = do { (op', op_ty) <- tcInferFun op
428 ; dflags <- getDynFlags -- Note [Left sections]
429 ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1
430 | otherwise = 2
431
432 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty)
433 <- matchActualFunTys (mk_op_msg op) SectionOrigin (Just op)
434 n_reqd_args op_ty
435 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
436 (mkFunTys arg_tys op_res_ty) res_ty
437 ; arg1' <- tcArg op arg1 arg1_ty 1
438 ; return ( mkHsWrap wrap_res $
439 SectionL arg1' (mkLHsWrap wrap_fn op') ) }
440
441 tcExpr expr@(ExplicitTuple tup_args boxity) res_ty
442 | all tupArgPresent tup_args
443 = do { let arity = length tup_args
444 tup_tc = tupleTyCon boxity arity
445 ; res_ty <- expTypeToType res_ty
446 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
447 -- Unboxed tuples have RuntimeRep vars, which we
448 -- don't care about here
449 -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
450 ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys
451 Boxed -> arg_tys
452 ; tup_args1 <- tcTupArgs tup_args arg_tys'
453 ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
454
455 | otherwise
456 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
457 do { let arity = length tup_args
458
459 ; arg_tys <- case boxity of
460 { Boxed -> newFlexiTyVarTys arity liftedTypeKind
461 ; Unboxed -> replicateM arity newOpenFlexiTyVarTy }
462 ; let actual_res_ty
463 = mkFunTys [ty | (ty, (L _ (Missing _))) <- arg_tys `zip` tup_args]
464 (mkTupleTy boxity arg_tys)
465
466 ; wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "ExpTuple")
467 (Just expr)
468 actual_res_ty res_ty
469
470 -- Handle tuple sections where
471 ; tup_args1 <- tcTupArgs tup_args arg_tys
472
473 ; return $ mkHsWrap wrap (ExplicitTuple tup_args1 boxity) }
474
475 tcExpr (ExplicitList _ witness exprs) res_ty
476 = case witness of
477 Nothing -> do { res_ty <- expTypeToType res_ty
478 ; (coi, elt_ty) <- matchExpectedListTy res_ty
479 ; exprs' <- mapM (tc_elt elt_ty) exprs
480 ; return $
481 mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' }
482
483 Just fln -> do { ((exprs', elt_ty), fln')
484 <- tcSyntaxOp ListOrigin fln
485 [synKnownType intTy, SynList] res_ty $
486 \ [elt_ty] ->
487 do { exprs' <-
488 mapM (tc_elt elt_ty) exprs
489 ; return (exprs', elt_ty) }
490
491 ; return $ ExplicitList elt_ty (Just fln') exprs' }
492 where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
493
494 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
495 = do { res_ty <- expTypeToType res_ty
496 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
497 ; exprs' <- mapM (tc_elt elt_ty) exprs
498 ; return $
499 mkHsWrapCo coi $ ExplicitPArr elt_ty exprs' }
500 where
501 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
502
503 {-
504 ************************************************************************
505 * *
506 Let, case, if, do
507 * *
508 ************************************************************************
509 -}
510
511 tcExpr (HsLet (L l binds) expr) res_ty
512 = do { (binds', expr') <- tcLocalBinds binds $
513 tcMonoExpr expr res_ty
514 ; return (HsLet (L l binds') expr') }
515
516 tcExpr (HsCase scrut matches) res_ty
517 = do { -- We used to typecheck the case alternatives first.
518 -- The case patterns tend to give good type info to use
519 -- when typechecking the scrutinee. For example
520 -- case (map f) of
521 -- (x:xs) -> ...
522 -- will report that map is applied to too few arguments
523 --
524 -- But now, in the GADT world, we need to typecheck the scrutinee
525 -- first, to get type info that may be refined in the case alternatives
526 (scrut', scrut_ty) <- tcInferRho scrut
527
528 ; traceTc "HsCase" (ppr scrut_ty)
529 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
530 ; return (HsCase scrut' matches') }
531 where
532 match_ctxt = MC { mc_what = CaseAlt,
533 mc_body = tcBody }
534
535 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
536 = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy)
537 ; res_ty <- tauifyExpType res_ty
538 -- Just like Note [Case branches must never infer a non-tau type]
539 -- in TcMatches (See #10619)
540
541 ; b1' <- tcMonoExpr b1 res_ty
542 ; b2' <- tcMonoExpr b2 res_ty
543 ; return (HsIf Nothing pred' b1' b2') }
544
545 tcExpr (HsIf (Just fun) pred b1 b2) res_ty
546 = do { ((pred', b1', b2'), fun')
547 <- tcSyntaxOp IfOrigin fun [SynAny, SynAny, SynAny] res_ty $
548 \ [pred_ty, b1_ty, b2_ty] ->
549 do { pred' <- tcPolyExpr pred pred_ty
550 ; b1' <- tcPolyExpr b1 b1_ty
551 ; b2' <- tcPolyExpr b2 b2_ty
552 ; return (pred', b1', b2') }
553 ; return (HsIf (Just fun') pred' b1' b2') }
554
555 tcExpr (HsMultiIf _ alts) res_ty
556 = do { res_ty <- if isSingleton alts
557 then return res_ty
558 else tauifyExpType res_ty
559 -- Just like TcMatches
560 -- Note [Case branches must never infer a non-tau type]
561
562 ; alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
563 ; res_ty <- readExpType res_ty
564 ; return (HsMultiIf res_ty alts') }
565 where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
566
567 tcExpr (HsDo do_or_lc stmts _) res_ty
568 = do { expr' <- tcDoStmts do_or_lc stmts res_ty
569 ; return expr' }
570
571 tcExpr (HsProc pat cmd) res_ty
572 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
573 ; return $ mkHsWrapCo coi (HsProc pat' cmd') }
574
575 -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'.
576 tcExpr (HsStatic fvs expr) res_ty
577 = do { res_ty <- expTypeToType res_ty
578 ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty
579 ; (expr', lie) <- captureConstraints $
580 addErrCtxt (hang (text "In the body of a static form:")
581 2 (ppr expr)
582 ) $
583 tcPolyExprNC expr expr_ty
584 -- Check that the free variables of the static form are closed.
585 -- It's OK to use nonDetEltsUFM here as the only side effects of
586 -- checkClosedInStaticForm are error messages.
587 ; mapM_ checkClosedInStaticForm $ nonDetEltsUFM fvs
588
589 -- Require the type of the argument to be Typeable.
590 -- The evidence is not used, but asking the constraint ensures that
591 -- the current implementation is as restrictive as future versions
592 -- of the StaticPointers extension.
593 ; typeableClass <- tcLookupClass typeableClassName
594 ; _ <- emitWantedEvVar StaticOrigin $
595 mkTyConApp (classTyCon typeableClass)
596 [liftedTypeKind, expr_ty]
597 -- Insert the constraints of the static form in a global list for later
598 -- validation.
599 ; stWC <- tcg_static_wc <$> getGblEnv
600 ; updTcRef stWC (andWC lie)
601 -- Wrap the static form with the 'fromStaticPtr' call.
602 ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty
603 ; let wrap = mkWpTyApps [expr_ty]
604 ; loc <- getSrcSpanM
605 ; return $ mkHsWrapCo co $ HsApp (L loc $ mkHsWrap wrap fromStaticPtr)
606 (L loc (HsStatic fvs expr'))
607 }
608
609 {-
610 ************************************************************************
611 * *
612 Record construction and update
613 * *
614 ************************************************************************
615 -}
616
617 tcExpr expr@(RecordCon { rcon_con_name = L loc con_name
618 , rcon_flds = rbinds }) res_ty
619 = do { con_like <- tcLookupConLike con_name
620
621 -- Check for missing fields
622 ; checkMissingFields con_like rbinds
623
624 ; (con_expr, con_sigma) <- tcInferId con_name
625 ; (con_wrap, con_tau) <-
626 topInstantiate (OccurrenceOf con_name) con_sigma
627 -- a shallow instantiation should really be enough for
628 -- a data constructor.
629 ; let arity = conLikeArity con_like
630 Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau
631 ; case conLikeWrapId_maybe con_like of
632 Nothing -> nonBidirectionalErr (conLikeName con_like)
633 Just con_id -> do {
634 res_wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "RecordCon")
635 (Just expr) actual_res_ty res_ty
636 ; rbinds' <- tcRecordBinds con_like arg_tys rbinds
637 ; return $
638 mkHsWrap res_wrap $
639 RecordCon { rcon_con_name = L loc con_id
640 , rcon_con_expr = mkHsWrap con_wrap con_expr
641 , rcon_con_like = con_like
642 , rcon_flds = rbinds' } } }
643
644 {-
645 Note [Type of a record update]
646 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
647 The main complication with RecordUpd is that we need to explicitly
648 handle the *non-updated* fields. Consider:
649
650 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
651 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
652 | MkT3 { fd :: a }
653
654 upd :: T a b c -> (b',c) -> T a b' c
655 upd t x = t { fb = x}
656
657 The result type should be (T a b' c)
658 not (T a b c), because 'b' *is not* mentioned in a non-updated field
659 not (T a b' c'), because 'c' *is* mentioned in a non-updated field
660 NB that it's not good enough to look at just one constructor; we must
661 look at them all; cf Trac #3219
662
663 After all, upd should be equivalent to:
664 upd t x = case t of
665 MkT1 p q -> MkT1 p x
666 MkT2 a b -> MkT2 p b
667 MkT3 d -> error ...
668
669 So we need to give a completely fresh type to the result record,
670 and then constrain it by the fields that are *not* updated ("p" above).
671 We call these the "fixed" type variables, and compute them in getFixedTyVars.
672
673 Note that because MkT3 doesn't contain all the fields being updated,
674 its RHS is simply an error, so it doesn't impose any type constraints.
675 Hence the use of 'relevant_cont'.
676
677 Note [Implicit type sharing]
678 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
679 We also take into account any "implicit" non-update fields. For example
680 data T a b where { MkT { f::a } :: T a a; ... }
681 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
682
683 Then consider
684 upd t x = t { f=x }
685 We infer the type
686 upd :: T a b -> a -> T a b
687 upd (t::T a b) (x::a)
688 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
689 We can't give it the more general type
690 upd :: T a b -> c -> T c b
691
692 Note [Criteria for update]
693 ~~~~~~~~~~~~~~~~~~~~~~~~~~
694 We want to allow update for existentials etc, provided the updated
695 field isn't part of the existential. For example, this should be ok.
696 data T a where { MkT { f1::a, f2::b->b } :: T a }
697 f :: T a -> b -> T b
698 f t b = t { f1=b }
699
700 The criterion we use is this:
701
702 The types of the updated fields
703 mention only the universally-quantified type variables
704 of the data constructor
705
706 NB: this is not (quite) the same as being a "naughty" record selector
707 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
708 in the case of GADTs. Consider
709 data T a where { MkT :: { f :: a } :: T [a] }
710 Then f is not "naughty" because it has a well-typed record selector.
711 But we don't allow updates for 'f'. (One could consider trying to
712 allow this, but it makes my head hurt. Badly. And no one has asked
713 for it.)
714
715 In principle one could go further, and allow
716 g :: T a -> T a
717 g t = t { f2 = \x -> x }
718 because the expression is polymorphic...but that seems a bridge too far.
719
720 Note [Data family example]
721 ~~~~~~~~~~~~~~~~~~~~~~~~~~
722 data instance T (a,b) = MkT { x::a, y::b }
723 --->
724 data :TP a b = MkT { a::a, y::b }
725 coTP a b :: T (a,b) ~ :TP a b
726
727 Suppose r :: T (t1,t2), e :: t3
728 Then r { x=e } :: T (t3,t1)
729 --->
730 case r |> co1 of
731 MkT x y -> MkT e y |> co2
732 where co1 :: T (t1,t2) ~ :TP t1 t2
733 co2 :: :TP t3 t2 ~ T (t3,t2)
734 The wrapping with co2 is done by the constructor wrapper for MkT
735
736 Outgoing invariants
737 ~~~~~~~~~~~~~~~~~~~
738 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
739
740 * cons are the data constructors to be updated
741
742 * in_inst_tys, out_inst_tys have same length, and instantiate the
743 *representation* tycon of the data cons. In Note [Data
744 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
745
746 Note [Mixed Record Field Updates]
747 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748 Consider the following pattern synonym.
749
750 data MyRec = MyRec { foo :: Int, qux :: String }
751
752 pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}
753
754 This allows updates such as the following
755
756 updater :: MyRec -> MyRec
757 updater a = a {f1 = 1 }
758
759 It would also make sense to allow the following update (which we reject).
760
761 updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"
762
763 This leads to confusing behaviour when the selectors in fact refer the same
764 field.
765
766 updater a = a {f1 = 1, foo = 2} ==? ???
767
768 For this reason, we reject a mixture of pattern synonym and normal record
769 selectors in the same update block. Although of course we still allow the
770 following.
771
772 updater a = (a {f1 = 1}) {foo = 2}
773
774 > updater (MyRec 0 "str")
775 MyRec 2 "str"
776
777 -}
778
779 tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty
780 = ASSERT( notNull rbnds )
781 do { -- STEP -2: typecheck the record_expr, the record to be updated
782 (record_expr', record_rho) <- tcInferRho record_expr
783
784 -- STEP -1 See Note [Disambiguating record fields]
785 -- After this we know that rbinds is unambiguous
786 ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty
787 ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds
788 upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds
789 sel_ids = map selectorAmbiguousFieldOcc upd_flds
790 -- STEP 0
791 -- Check that the field names are really field names
792 -- and they are all field names for proper records or
793 -- all field names for pattern synonyms.
794 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
795 | fld <- rbinds,
796 -- Excludes class ops
797 let L loc sel_id = hsRecUpdFieldId (unLoc fld),
798 not (isRecordSelector sel_id),
799 let fld_name = idName sel_id ]
800 ; unless (null bad_guys) (sequence bad_guys >> failM)
801 -- See note [Mixed Record Selectors]
802 ; let (data_sels, pat_syn_sels) =
803 partition isDataConRecordSelector sel_ids
804 ; MASSERT( all isPatSynRecordSelector pat_syn_sels )
805 ; checkTc ( null data_sels || null pat_syn_sels )
806 ( mixedSelectors data_sels pat_syn_sels )
807
808 -- STEP 1
809 -- Figure out the tycon and data cons from the first field name
810 ; let -- It's OK to use the non-tc splitters here (for a selector)
811 sel_id : _ = sel_ids
812
813 mtycon :: Maybe TyCon
814 mtycon = case idDetails sel_id of
815 RecSelId (RecSelData tycon) _ -> Just tycon
816 _ -> Nothing
817
818 con_likes :: [ConLike]
819 con_likes = case idDetails sel_id of
820 RecSelId (RecSelData tc) _
821 -> map RealDataCon (tyConDataCons tc)
822 RecSelId (RecSelPatSyn ps) _
823 -> [PatSynCon ps]
824 _ -> panic "tcRecordUpd"
825 -- NB: for a data type family, the tycon is the instance tycon
826
827 relevant_cons = conLikesWithFields con_likes upd_fld_occs
828 -- A constructor is only relevant to this process if
829 -- it contains *all* the fields that are being updated
830 -- Other ones will cause a runtime error if they occur
831
832 -- Step 2
833 -- Check that at least one constructor has all the named fields
834 -- i.e. has an empty set of bad fields returned by badFields
835 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes)
836
837 -- Take apart a representative constructor
838 ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
839 (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _)
840 = conLikeFullSig con1
841 con1_flds = map flLabel $ conLikeFieldLabels con1
842 con1_tv_tys = mkTyVarTys con1_tvs
843 con1_res_ty = case mtycon of
844 Just tc -> mkFamilyTyConApp tc con1_tv_tys
845 Nothing -> conLikeResTy con1 con1_tv_tys
846
847 -- Check that we're not dealing with a unidirectional pattern
848 -- synonym
849 ; unless (isJust $ conLikeWrapId_maybe con1)
850 (nonBidirectionalErr (conLikeName con1))
851
852 -- STEP 3 Note [Criteria for update]
853 -- Check that each updated field is polymorphic; that is, its type
854 -- mentions only the universally-quantified variables of the data con
855 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
856 bad_upd_flds = filter bad_fld flds1_w_tys
857 con1_tv_set = mkVarSet con1_tvs
858 bad_fld (fld, ty) = fld `elem` upd_fld_occs &&
859 not (tyCoVarsOfType ty `subVarSet` con1_tv_set)
860 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
861
862 -- STEP 4 Note [Type of a record update]
863 -- Figure out types for the scrutinee and result
864 -- Both are of form (T a b c), with fresh type variables, but with
865 -- common variables where the scrutinee and result must have the same type
866 -- These are variables that appear in *any* arg of *any* of the
867 -- relevant constructors *except* in the updated fields
868 --
869 ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons
870 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
871
872 mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType)
873 -- Deals with instantiation of kind variables
874 -- c.f. TcMType.newMetaTyVars
875 mk_inst_ty subst (tv, result_inst_ty)
876 | is_fixed_tv tv -- Same as result type
877 = return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
878 | otherwise -- Fresh type, of correct kind
879 = do { (subst', new_tv) <- newMetaTyVarX subst tv
880 ; return (subst', mkTyVarTy new_tv) }
881
882 ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs
883 ; let result_inst_tys = mkTyVarTys con1_tvs'
884 init_subst = mkEmptyTCvSubst (getTCvInScope result_subst)
885
886 ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst
887 (con1_tvs `zip` result_inst_tys)
888
889 ; let rec_res_ty = TcType.substTy result_subst con1_res_ty
890 scrut_ty = TcType.substTy scrut_subst con1_res_ty
891 con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
892
893 ; wrap_res <- tcSubTypeHR (exprCtOrigin expr)
894 (Just expr) rec_res_ty res_ty
895 ; co_scrut <- unifyType (Just record_expr) record_rho scrut_ty
896 -- NB: normal unification is OK here (as opposed to subsumption),
897 -- because for this to work out, both record_rho and scrut_ty have
898 -- to be normal datatypes -- no contravariant stuff can go on
899
900 -- STEP 5
901 -- Typecheck the bindings
902 ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds
903
904 -- STEP 6: Deal with the stupid theta
905 ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1)
906 ; instStupidTheta RecordUpdOrigin theta'
907
908 -- Step 7: make a cast for the scrutinee, in the
909 -- case that it's from a data family
910 ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty
911 fam_co | Just tycon <- mtycon
912 , Just co_con <- tyConFamilyCoercion_maybe tycon
913 = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys [])
914 | otherwise
915 = idHsWrapper
916
917 -- Step 8: Check that the req constraints are satisfied
918 -- For normal data constructors req_theta is empty but we must do
919 -- this check for pattern synonyms.
920 ; let req_theta' = substThetaUnchecked scrut_subst req_theta
921 ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta'
922
923 -- Phew!
924 ; return $
925 mkHsWrap wrap_res $
926 RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr')
927 , rupd_flds = rbinds'
928 , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys
929 , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } }
930
931 tcExpr (HsRecFld f) res_ty
932 = tcCheckRecSelId f res_ty
933
934 {-
935 ************************************************************************
936 * *
937 Arithmetic sequences e.g. [a,b..]
938 and their parallel-array counterparts e.g. [: a,b.. :]
939
940 * *
941 ************************************************************************
942 -}
943
944 tcExpr (ArithSeq _ witness seq) res_ty
945 = tcArithSeq witness seq res_ty
946
947 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
948 = do { res_ty <- expTypeToType res_ty
949 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
950 ; expr1' <- tcPolyExpr expr1 elt_ty
951 ; expr2' <- tcPolyExpr expr2 elt_ty
952 ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
953 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
954 (idName enumFromToP) elt_ty
955 ; return $
956 mkHsWrapCo coi $ PArrSeq enum_from_to (FromTo expr1' expr2') }
957
958 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
959 = do { res_ty <- expTypeToType res_ty
960 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
961 ; expr1' <- tcPolyExpr expr1 elt_ty
962 ; expr2' <- tcPolyExpr expr2 elt_ty
963 ; expr3' <- tcPolyExpr expr3 elt_ty
964 ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
965 ; eft <- newMethodFromName (PArrSeqOrigin seq)
966 (idName enumFromThenToP) elt_ty -- !!!FIXME: chak
967 ; return $
968 mkHsWrapCo coi $
969 PArrSeq eft (FromThenTo expr1' expr2' expr3') }
970
971 tcExpr (PArrSeq _ _) _
972 = panic "TcExpr.tcExpr: Infinite parallel array!"
973 -- the parser shouldn't have generated it and the renamer shouldn't have
974 -- let it through
975
976 {-
977 ************************************************************************
978 * *
979 Template Haskell
980 * *
981 ************************************************************************
982 -}
983
984 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceExpr'.
985 -- Here we get rid of it and add the finalizers to the global environment.
986 --
987 -- See Note [Delaying modFinalizers in untyped splices] in RnSplice.
988 tcExpr (HsSpliceE (HsSpliced mod_finalizers (HsSplicedExpr expr)))
989 res_ty
990 = do addModFinalizersWithLclEnv mod_finalizers
991 tcExpr expr res_ty
992 tcExpr (HsSpliceE splice) res_ty
993 = tcSpliceExpr splice res_ty
994 tcExpr (HsBracket brack) res_ty
995 = tcTypedBracket brack res_ty
996 tcExpr (HsRnBracketOut brack ps) res_ty
997 = tcUntypedBracket brack ps res_ty
998
999 {-
1000 ************************************************************************
1001 * *
1002 Catch-all
1003 * *
1004 ************************************************************************
1005 -}
1006
1007 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
1008 -- Include ArrForm, ArrApp, which shouldn't appear at all
1009 -- Also HsTcBracketOut, HsQuasiQuoteE
1010
1011 {-
1012 ************************************************************************
1013 * *
1014 Arithmetic sequences [a..b] etc
1015 * *
1016 ************************************************************************
1017 -}
1018
1019 tcArithSeq :: Maybe (SyntaxExpr Name) -> ArithSeqInfo Name -> ExpRhoType
1020 -> TcM (HsExpr TcId)
1021
1022 tcArithSeq witness seq@(From expr) res_ty
1023 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1024 ; expr' <- tcPolyExpr expr elt_ty
1025 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
1026 enumFromName elt_ty
1027 ; return $ mkHsWrap wrap $
1028 ArithSeq enum_from wit' (From expr') }
1029
1030 tcArithSeq witness seq@(FromThen expr1 expr2) res_ty
1031 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1032 ; expr1' <- tcPolyExpr expr1 elt_ty
1033 ; expr2' <- tcPolyExpr expr2 elt_ty
1034 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
1035 enumFromThenName elt_ty
1036 ; return $ mkHsWrap wrap $
1037 ArithSeq enum_from_then wit' (FromThen expr1' expr2') }
1038
1039 tcArithSeq witness seq@(FromTo expr1 expr2) res_ty
1040 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1041 ; expr1' <- tcPolyExpr expr1 elt_ty
1042 ; expr2' <- tcPolyExpr expr2 elt_ty
1043 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
1044 enumFromToName elt_ty
1045 ; return $ mkHsWrap wrap $
1046 ArithSeq enum_from_to wit' (FromTo expr1' expr2') }
1047
1048 tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty
1049 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1050 ; expr1' <- tcPolyExpr expr1 elt_ty
1051 ; expr2' <- tcPolyExpr expr2 elt_ty
1052 ; expr3' <- tcPolyExpr expr3 elt_ty
1053 ; eft <- newMethodFromName (ArithSeqOrigin seq)
1054 enumFromThenToName elt_ty
1055 ; return $ mkHsWrap wrap $
1056 ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') }
1057
1058 -----------------
1059 arithSeqEltType :: Maybe (SyntaxExpr Name) -> ExpRhoType
1060 -> TcM (HsWrapper, TcType, Maybe (SyntaxExpr Id))
1061 arithSeqEltType Nothing res_ty
1062 = do { res_ty <- expTypeToType res_ty
1063 ; (coi, elt_ty) <- matchExpectedListTy res_ty
1064 ; return (mkWpCastN coi, elt_ty, Nothing) }
1065 arithSeqEltType (Just fl) res_ty
1066 = do { (elt_ty, fl')
1067 <- tcSyntaxOp ListOrigin fl [SynList] res_ty $
1068 \ [elt_ty] -> return elt_ty
1069 ; return (idHsWrapper, elt_ty, Just fl') }
1070
1071 {-
1072 ************************************************************************
1073 * *
1074 Applications
1075 * *
1076 ************************************************************************
1077 -}
1078
1079 type LHsExprArgIn = Either (LHsExpr Name) (LHsWcType Name)
1080 type LHsExprArgOut = Either (LHsExpr TcId) (LHsWcType Name)
1081 -- Left e => argument expression
1082 -- Right ty => visible type application
1083
1084 tcApp1 :: HsExpr Name -- either HsApp or HsAppType
1085 -> ExpRhoType -> TcM (HsExpr TcId)
1086 tcApp1 e res_ty
1087 = do { (wrap, fun, args) <- tcApp Nothing (noLoc e) [] res_ty
1088 ; return (mkHsWrap wrap $ unLoc $ foldl mk_hs_app fun args) }
1089 where
1090 mk_hs_app f (Left a) = mkHsApp f a
1091 mk_hs_app f (Right a) = mkHsAppTypeOut f a
1092
1093 tcApp :: Maybe SDoc -- like "The function `f' is applied to"
1094 -- or leave out to get exactly that message
1095 -> LHsExpr Name -> [LHsExprArgIn] -- Function and args
1096 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1097 -- (wrap, fun, args). For an ordinary function application,
1098 -- these should be assembled as (wrap (fun args)).
1099 -- But OpApp is slightly different, so that's why the caller
1100 -- must assemble
1101
1102 tcApp m_herald orig_fun orig_args res_ty
1103 = go orig_fun orig_args
1104 where
1105 go :: LHsExpr Name -> [LHsExprArgIn]
1106 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1107 go (L _ (HsPar e)) args = go e args
1108 go (L _ (HsApp e1 e2)) args = go e1 (Left e2:args)
1109 go (L _ (HsAppType e t)) args = go e (Right t:args)
1110
1111 go (L loc (HsVar (L _ fun))) args
1112 | fun `hasKey` tagToEnumKey
1113 , count isLeft args == 1
1114 = do { (wrap, expr, args) <- tcTagToEnum loc fun args res_ty
1115 ; return (wrap, expr, args) }
1116
1117 | fun `hasKey` seqIdKey
1118 , count isLeft args == 2
1119 = do { (wrap, expr, args) <- tcSeq loc fun args res_ty
1120 ; return (wrap, expr, args) }
1121
1122 go (L loc (HsRecFld (Ambiguous lbl _))) args@(Left (L _ arg) : _)
1123 | Just sig_ty <- obviousSig arg
1124 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
1125 ; sel_name <- disambiguateSelector lbl sig_tc_ty
1126 ; go (L loc (HsRecFld (Unambiguous lbl sel_name))) args }
1127
1128 go fun args
1129 = do { -- Type-check the function
1130 ; (fun1, fun_sigma) <- tcInferFun fun
1131 ; let orig = exprCtOrigin (unLoc fun)
1132
1133 ; (wrap_fun, args1, actual_res_ty)
1134 <- tcArgs fun fun_sigma orig args
1135 (m_herald `orElse` mk_app_msg fun)
1136
1137 -- this is just like tcWrapResult, but the types don't line
1138 -- up to call that function
1139 ; wrap_res <- addFunResCtxt True (unLoc fun) actual_res_ty res_ty $
1140 tcSubTypeDS_NC_O orig GenSigCtxt
1141 (Just $ foldl mk_hs_app fun args)
1142 actual_res_ty res_ty
1143
1144 ; return (wrap_res, mkLHsWrap wrap_fun fun1, args1) }
1145
1146 mk_hs_app f (Left a) = mkHsApp f a
1147 mk_hs_app f (Right a) = mkHsAppType f a
1148
1149 mk_app_msg :: LHsExpr Name -> SDoc
1150 mk_app_msg fun = sep [ text "The function" <+> quotes (ppr fun)
1151 , text "is applied to"]
1152
1153 mk_op_msg :: LHsExpr Name -> SDoc
1154 mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes"
1155
1156 ----------------
1157 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcSigmaType)
1158 -- Infer type of a function
1159 tcInferFun (L loc (HsVar (L _ name)))
1160 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
1161 -- Don't wrap a context around a plain Id
1162 ; return (L loc fun, ty) }
1163
1164 tcInferFun (L loc (HsRecFld f))
1165 = do { (fun, ty) <- setSrcSpan loc (tcInferRecSelId f)
1166 -- Don't wrap a context around a plain Id
1167 ; return (L loc fun, ty) }
1168
1169 tcInferFun fun
1170 = do { (fun, fun_ty) <- tcInferSigma fun
1171
1172 -- Zonk the function type carefully, to expose any polymorphism
1173 -- E.g. (( \(x::forall a. a->a). blah ) e)
1174 -- We can see the rank-2 type of the lambda in time to generalise e
1175 ; fun_ty' <- zonkTcType fun_ty
1176
1177 ; return (fun, fun_ty') }
1178
1179 ----------------
1180 -- | Type-check the arguments to a function, possibly including visible type
1181 -- applications
1182 tcArgs :: LHsExpr Name -- ^ The function itself (for err msgs only)
1183 -> TcSigmaType -- ^ the (uninstantiated) type of the function
1184 -> CtOrigin -- ^ the origin for the function's type
1185 -> [LHsExprArgIn] -- ^ the args
1186 -> SDoc -- ^ the herald for matchActualFunTys
1187 -> TcM (HsWrapper, [LHsExprArgOut], TcSigmaType)
1188 -- ^ (a wrapper for the function, the tc'd args, result type)
1189 tcArgs fun orig_fun_ty fun_orig orig_args herald
1190 = go [] 1 orig_fun_ty orig_args
1191 where
1192 orig_arity = length orig_args
1193
1194 go _ _ fun_ty [] = return (idHsWrapper, [], fun_ty)
1195
1196 go acc_args n fun_ty (Right hs_ty_arg:args)
1197 = do { (wrap1, upsilon_ty) <- topInstantiateInferred fun_orig fun_ty
1198 -- wrap1 :: fun_ty "->" upsilon_ty
1199 ; case tcSplitForAllTy_maybe upsilon_ty of
1200 Just (tvb, inner_ty) ->
1201 do { let tv = binderVar tvb
1202 vis = binderArgFlag tvb
1203 kind = tyVarKind tv
1204 ; MASSERT2( vis == Specified
1205 , (vcat [ ppr fun_ty, ppr upsilon_ty, ppr tvb
1206 , ppr inner_ty, pprTvBndr tv
1207 , ppr vis ]) )
1208 ; ty_arg <- tcHsTypeApp hs_ty_arg kind
1209 ; let insted_ty = substTyWithUnchecked [tv] [ty_arg] inner_ty
1210 ; (inner_wrap, args', res_ty)
1211 <- go acc_args (n+1) insted_ty args
1212 -- inner_wrap :: insted_ty "->" (map typeOf args') -> res_ty
1213 ; let inst_wrap = mkWpTyApps [ty_arg]
1214 ; return ( inner_wrap <.> inst_wrap <.> wrap1
1215 , Right hs_ty_arg : args'
1216 , res_ty ) }
1217 _ -> ty_app_err upsilon_ty hs_ty_arg }
1218
1219 go acc_args n fun_ty (Left arg : args)
1220 = do { (wrap, [arg_ty], res_ty)
1221 <- matchActualFunTysPart herald fun_orig (Just fun) 1 fun_ty
1222 acc_args orig_arity
1223 -- wrap :: fun_ty "->" arg_ty -> res_ty
1224 ; arg' <- tcArg fun arg arg_ty n
1225 ; (inner_wrap, args', inner_res_ty)
1226 <- go (arg_ty : acc_args) (n+1) res_ty args
1227 -- inner_wrap :: res_ty "->" (map typeOf args') -> inner_res_ty
1228 ; return ( mkWpFun idHsWrapper inner_wrap arg_ty res_ty <.> wrap
1229 , Left arg' : args'
1230 , inner_res_ty ) }
1231
1232 ty_app_err ty arg
1233 = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty
1234 ; failWith $
1235 text "Cannot apply expression of type" <+> quotes (ppr ty) $$
1236 text "to a visible type argument" <+> quotes (ppr arg) }
1237
1238 ----------------
1239 tcArg :: LHsExpr Name -- The function (for error messages)
1240 -> LHsExpr Name -- Actual arguments
1241 -> TcRhoType -- expected arg type
1242 -> Int -- # of argument
1243 -> TcM (LHsExpr TcId) -- Resulting argument
1244 tcArg fun arg ty arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $
1245 tcPolyExprNC arg ty
1246
1247 ----------------
1248 tcTupArgs :: [LHsTupArg Name] -> [TcSigmaType] -> TcM [LHsTupArg TcId]
1249 tcTupArgs args tys
1250 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
1251 where
1252 go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty))
1253 go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
1254 ; return (L l (Present expr')) }
1255
1256 ---------------------------
1257 -- See TcType.SyntaxOpType also for commentary
1258 tcSyntaxOp :: CtOrigin
1259 -> SyntaxExpr Name
1260 -> [SyntaxOpType] -- ^ shape of syntax operator arguments
1261 -> ExpType -- ^ overall result type
1262 -> ([TcSigmaType] -> TcM a) -- ^ Type check any arguments
1263 -> TcM (a, SyntaxExpr TcId)
1264 -- ^ Typecheck a syntax operator
1265 -- The operator is always a variable at this stage (i.e. renamer output)
1266 tcSyntaxOp orig expr arg_tys res_ty
1267 = tcSyntaxOpGen orig expr arg_tys (SynType res_ty)
1268
1269 -- | Slightly more general version of 'tcSyntaxOp' that allows the caller
1270 -- to specify the shape of the result of the syntax operator
1271 tcSyntaxOpGen :: CtOrigin
1272 -> SyntaxExpr Name
1273 -> [SyntaxOpType]
1274 -> SyntaxOpType
1275 -> ([TcSigmaType] -> TcM a)
1276 -> TcM (a, SyntaxExpr TcId)
1277 tcSyntaxOpGen orig (SyntaxExpr { syn_expr = HsVar (L _ op) })
1278 arg_tys res_ty thing_inside
1279 = do { (expr, sigma) <- tcInferId op
1280 ; (result, expr_wrap, arg_wraps, res_wrap)
1281 <- tcSynArgA orig sigma arg_tys res_ty $
1282 thing_inside
1283 ; return (result, SyntaxExpr { syn_expr = mkHsWrap expr_wrap expr
1284 , syn_arg_wraps = arg_wraps
1285 , syn_res_wrap = res_wrap }) }
1286
1287 tcSyntaxOpGen _ other _ _ _ = pprPanic "tcSyntaxOp" (ppr other)
1288
1289 {-
1290 Note [tcSynArg]
1291 ~~~~~~~~~~~~~~~
1292 Because of the rich structure of SyntaxOpType, we must do the
1293 contra-/covariant thing when working down arrows, to get the
1294 instantiation vs. skolemisation decisions correct (and, more
1295 obviously, the orientation of the HsWrappers). We thus have
1296 two tcSynArgs.
1297 -}
1298
1299 -- works on "expected" types, skolemising where necessary
1300 -- See Note [tcSynArg]
1301 tcSynArgE :: CtOrigin
1302 -> TcSigmaType
1303 -> SyntaxOpType -- ^ shape it is expected to have
1304 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1305 -> TcM (a, HsWrapper)
1306 -- ^ returns a wrapper :: (type of right shape) "->" (type passed in)
1307 tcSynArgE orig sigma_ty syn_ty thing_inside
1308 = do { (skol_wrap, (result, ty_wrapper))
1309 <- tcSkolemise GenSigCtxt sigma_ty $ \ _ rho_ty ->
1310 go rho_ty syn_ty
1311 ; return (result, skol_wrap <.> ty_wrapper) }
1312 where
1313 go rho_ty SynAny
1314 = do { result <- thing_inside [rho_ty]
1315 ; return (result, idHsWrapper) }
1316
1317 go rho_ty SynRho -- same as SynAny, because we skolemise eagerly
1318 = do { result <- thing_inside [rho_ty]
1319 ; return (result, idHsWrapper) }
1320
1321 go rho_ty SynList
1322 = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty
1323 ; result <- thing_inside [elt_ty]
1324 ; return (result, mkWpCastN list_co) }
1325
1326 go rho_ty (SynFun arg_shape res_shape)
1327 = do { ( ( ( (result, arg_ty, res_ty)
1328 , res_wrapper ) -- :: res_ty_out "->" res_ty
1329 , arg_wrapper1, [], arg_wrapper2 ) -- :: arg_ty "->" arg_ty_out
1330 , match_wrapper ) -- :: (arg_ty -> res_ty) "->" rho_ty
1331 <- matchExpectedFunTys herald 1 (mkCheckExpType rho_ty) $
1332 \ [arg_ty] res_ty ->
1333 do { arg_tc_ty <- expTypeToType arg_ty
1334 ; res_tc_ty <- expTypeToType res_ty
1335
1336 -- another nested arrow is too much for now,
1337 -- but I bet we'll never need this
1338 ; MASSERT2( case arg_shape of
1339 SynFun {} -> False;
1340 _ -> True
1341 , text "Too many nested arrows in SyntaxOpType" $$
1342 pprCtOrigin orig )
1343
1344 ; tcSynArgA orig arg_tc_ty [] arg_shape $
1345 \ arg_results ->
1346 tcSynArgE orig res_tc_ty res_shape $
1347 \ res_results ->
1348 do { result <- thing_inside (arg_results ++ res_results)
1349 ; return (result, arg_tc_ty, res_tc_ty) }}
1350
1351 ; return ( result
1352 , match_wrapper <.>
1353 mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper
1354 arg_ty res_ty ) }
1355 where
1356 herald = text "This rebindable syntax expects a function with"
1357
1358 go rho_ty (SynType the_ty)
1359 = do { wrap <- tcSubTypeET orig the_ty rho_ty
1360 ; result <- thing_inside []
1361 ; return (result, wrap) }
1362
1363 -- works on "actual" types, instantiating where necessary
1364 -- See Note [tcSynArg]
1365 tcSynArgA :: CtOrigin
1366 -> TcSigmaType
1367 -> [SyntaxOpType] -- ^ argument shapes
1368 -> SyntaxOpType -- ^ result shape
1369 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1370 -> TcM (a, HsWrapper, [HsWrapper], HsWrapper)
1371 -- ^ returns a wrapper to be applied to the original function,
1372 -- wrappers to be applied to arguments
1373 -- and a wrapper to be applied to the overall expression
1374 tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside
1375 = do { (match_wrapper, arg_tys, res_ty)
1376 <- matchActualFunTys herald orig noThing (length arg_shapes) sigma_ty
1377 -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty)
1378 ; ((result, res_wrapper), arg_wrappers)
1379 <- tc_syn_args_e arg_tys arg_shapes $ \ arg_results ->
1380 tc_syn_arg res_ty res_shape $ \ res_results ->
1381 thing_inside (arg_results ++ res_results)
1382 ; return (result, match_wrapper, arg_wrappers, res_wrapper) }
1383 where
1384 herald = text "This rebindable syntax expects a function with"
1385
1386 tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType]
1387 -> ([TcSigmaType] -> TcM a)
1388 -> TcM (a, [HsWrapper])
1389 -- the wrappers are for arguments
1390 tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside
1391 = do { ((result, arg_wraps), arg_wrap)
1392 <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results ->
1393 tc_syn_args_e arg_tys arg_shapes $ \ args_results ->
1394 thing_inside (arg1_results ++ args_results)
1395 ; return (result, arg_wrap : arg_wraps) }
1396 tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside []
1397
1398 tc_syn_arg :: TcSigmaType -> SyntaxOpType
1399 -> ([TcSigmaType] -> TcM a)
1400 -> TcM (a, HsWrapper)
1401 -- the wrapper applies to the overall result
1402 tc_syn_arg res_ty SynAny thing_inside
1403 = do { result <- thing_inside [res_ty]
1404 ; return (result, idHsWrapper) }
1405 tc_syn_arg res_ty SynRho thing_inside
1406 = do { (inst_wrap, rho_ty) <- deeplyInstantiate orig res_ty
1407 -- inst_wrap :: res_ty "->" rho_ty
1408 ; result <- thing_inside [rho_ty]
1409 ; return (result, inst_wrap) }
1410 tc_syn_arg res_ty SynList thing_inside
1411 = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty
1412 -- inst_wrap :: res_ty "->" rho_ty
1413 ; (list_co, elt_ty) <- matchExpectedListTy rho_ty
1414 -- list_co :: [elt_ty] ~N rho_ty
1415 ; result <- thing_inside [elt_ty]
1416 ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) }
1417 tc_syn_arg _ (SynFun {}) _
1418 = pprPanic "tcSynArgA hits a SynFun" (ppr orig)
1419 tc_syn_arg res_ty (SynType the_ty) thing_inside
1420 = do { wrap <- tcSubTypeO orig GenSigCtxt res_ty the_ty
1421 ; result <- thing_inside []
1422 ; return (result, wrap) }
1423
1424 {-
1425 Note [Push result type in]
1426 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1427 Unify with expected result before type-checking the args so that the
1428 info from res_ty percolates to args. This is when we might detect a
1429 too-few args situation. (One can think of cases when the opposite
1430 order would give a better error message.)
1431 experimenting with putting this first.
1432
1433 Here's an example where it actually makes a real difference
1434
1435 class C t a b | t a -> b
1436 instance C Char a Bool
1437
1438 data P t a = forall b. (C t a b) => MkP b
1439 data Q t = MkQ (forall a. P t a)
1440
1441 f1, f2 :: Q Char;
1442 f1 = MkQ (MkP True)
1443 f2 = MkQ (MkP True :: forall a. P Char a)
1444
1445 With the change, f1 will type-check, because the 'Char' info from
1446 the signature is propagated into MkQ's argument. With the check
1447 in the other order, the extra signature in f2 is reqd.
1448
1449 ************************************************************************
1450 * *
1451 Expressions with a type signature
1452 expr :: type
1453 * *
1454 ********************************************************************* -}
1455
1456 tcExprSig :: LHsExpr Name -> TcIdSigInfo -> TcM (LHsExpr TcId, TcType)
1457 tcExprSig expr (CompleteSig { sig_bndr = poly_id, sig_loc = loc })
1458 = setSrcSpan loc $ -- Sets the location for the implication constraint
1459 do { (tv_prs, theta, tau) <- tcInstType (tcInstSigTyVars loc) poly_id
1460 ; given <- newEvVars theta
1461 ; let skol_info = SigSkol ExprSigCtxt (mkPhiTy theta tau)
1462 skol_tvs = map snd tv_prs
1463 ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $
1464 tcExtendTyVarEnv2 tv_prs $
1465 tcPolyExprNC expr tau
1466
1467 ; let poly_wrap = mkWpTyLams skol_tvs
1468 <.> mkWpLams given
1469 <.> mkWpLet ev_binds
1470 ; return (mkLHsWrap poly_wrap expr', idType poly_id) }
1471
1472 tcExprSig expr sig@(PartialSig { psig_name = name, sig_loc = loc })
1473 = setSrcSpan loc $ -- Sets the location for the implication constraint
1474 do { (tclvl, wanted, (expr', sig_inst))
1475 <- pushLevelAndCaptureConstraints $
1476 do { sig_inst <- tcInstSig sig
1477 ; expr' <- tcExtendTyVarEnv2 (sig_inst_skols sig_inst) $
1478 tcExtendTyVarEnv2 (sig_inst_wcs sig_inst) $
1479 tcPolyExprNC expr (sig_inst_tau sig_inst)
1480 ; return (expr', sig_inst) }
1481 -- See Note [Partial expression signatures]
1482 ; let tau = sig_inst_tau sig_inst
1483 infer_mode | null (sig_inst_theta sig_inst)
1484 , isNothing (sig_inst_wcx sig_inst)
1485 = ApplyMR
1486 | otherwise
1487 = NoRestrictions
1488 ; (qtvs, givens, ev_binds)
1489 <- simplifyInfer tclvl infer_mode [sig_inst] [(name, tau)] wanted
1490 ; tau <- zonkTcType tau
1491 ; let inferred_theta = map evVarPred givens
1492 tau_tvs = tyCoVarsOfType tau
1493 ; (binders, my_theta) <- chooseInferredQuantifiers inferred_theta
1494 tau_tvs qtvs (Just sig_inst)
1495 ; let inferred_sigma = mkInfSigmaTy qtvs inferred_theta tau
1496 my_sigma = mkForAllTys binders (mkPhiTy my_theta tau)
1497 ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis.
1498 then return idHsWrapper -- Fast path; also avoids complaint when we infer
1499 -- an ambiguouse type and have AllowAmbiguousType
1500 -- e..g infer x :: forall a. F a -> Int
1501 else tcSubType_NC ExprSigCtxt inferred_sigma
1502 (mkCheckExpType my_sigma)
1503
1504 ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma)
1505 ; let poly_wrap = wrap
1506 <.> mkWpTyLams qtvs
1507 <.> mkWpLams givens
1508 <.> mkWpLet ev_binds
1509 ; return (mkLHsWrap poly_wrap expr', my_sigma) }
1510
1511
1512 {- Note [Partial expression signatures]
1513 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1514 Partial type signatures on expressions are easy to get wrong. But
1515 here is a guiding principile
1516 e :: ty
1517 should behave like
1518 let x :: ty
1519 x = e
1520 in x
1521
1522 So for partial signatures we apply the MR if no context is given. So
1523 e :: IO _ apply the MR
1524 e :: _ => IO _ do not apply the MR
1525 just like in TcBinds.decideGeneralisationPlan
1526
1527 This makes a difference (Trac #11670):
1528 peek :: Ptr a -> IO CLong
1529 peek ptr = peekElemOff undefined 0 :: _
1530 from (peekElemOff undefined 0) we get
1531 type: IO w
1532 constraints: Storable w
1533
1534 We must NOT try to generalise over 'w' because the signature specifies
1535 no constraints so we'll complain about not being able to solve
1536 Storable w. Instead, don't generalise; then _ gets instantiated to
1537 CLong, as it should.
1538 -}
1539
1540 {- *********************************************************************
1541 * *
1542 tcInferId
1543 * *
1544 ********************************************************************* -}
1545
1546 tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr TcId)
1547 tcCheckId name res_ty
1548 = do { (expr, actual_res_ty) <- tcInferId name
1549 ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty])
1550 ; addFunResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty $
1551 tcWrapResultO (OccurrenceOf name) expr actual_res_ty res_ty }
1552
1553 tcCheckRecSelId :: AmbiguousFieldOcc Name -> ExpRhoType -> TcM (HsExpr TcId)
1554 tcCheckRecSelId f@(Unambiguous (L _ lbl) _) res_ty
1555 = do { (expr, actual_res_ty) <- tcInferRecSelId f
1556 ; addFunResCtxt False (HsRecFld f) actual_res_ty res_ty $
1557 tcWrapResultO (OccurrenceOfRecSel lbl) expr actual_res_ty res_ty }
1558 tcCheckRecSelId (Ambiguous lbl _) res_ty
1559 = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of
1560 Nothing -> ambiguousSelector lbl
1561 Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg
1562 ; tcCheckRecSelId (Unambiguous lbl sel_name) res_ty }
1563
1564 ------------------------
1565 tcInferRecSelId :: AmbiguousFieldOcc Name -> TcM (HsExpr TcId, TcRhoType)
1566 tcInferRecSelId (Unambiguous (L _ lbl) sel)
1567 = do { (expr', ty) <- tc_infer_id lbl sel
1568 ; return (expr', ty) }
1569 tcInferRecSelId (Ambiguous lbl _)
1570 = ambiguousSelector lbl
1571
1572 ------------------------
1573 tcInferId :: Name -> TcM (HsExpr TcId, TcSigmaType)
1574 -- Look up an occurrence of an Id
1575 tcInferId id_name
1576 | id_name `hasKey` tagToEnumKey
1577 = failWithTc (text "tagToEnum# must appear applied to one argument")
1578 -- tcApp catches the case (tagToEnum# arg)
1579
1580 | id_name `hasKey` assertIdKey
1581 = do { dflags <- getDynFlags
1582 ; if gopt Opt_IgnoreAsserts dflags
1583 then tc_infer_id (nameRdrName id_name) id_name
1584 else tc_infer_assert id_name }
1585
1586 | otherwise
1587 = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) id_name
1588 ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty)
1589 ; return (expr, ty) }
1590
1591 tc_infer_assert :: Name -> TcM (HsExpr TcId, TcSigmaType)
1592 -- Deal with an occurrence of 'assert'
1593 -- See Note [Adding the implicit parameter to 'assert']
1594 tc_infer_assert assert_name
1595 = do { assert_error_id <- tcLookupId assertErrorName
1596 ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name)
1597 (idType assert_error_id)
1598 ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho)
1599 }
1600
1601 tc_infer_id :: RdrName -> Name -> TcM (HsExpr TcId, TcSigmaType)
1602 tc_infer_id lbl id_name
1603 = do { thing <- tcLookup id_name
1604 ; case thing of
1605 ATcId { tct_id = id }
1606 -> do { check_naughty id -- Note [Local record selectors]
1607 ; checkThLocalId id
1608 ; return_id id }
1609
1610 AGlobal (AnId id)
1611 -> do { check_naughty id
1612 ; return_id id }
1613 -- A global cannot possibly be ill-staged
1614 -- nor does it need the 'lifting' treatment
1615 -- hence no checkTh stuff here
1616
1617 AGlobal (AConLike cl) -> case cl of
1618 RealDataCon con -> return_data_con con
1619 PatSynCon ps -> tcPatSynBuilderOcc ps
1620
1621 _ -> failWithTc $
1622 ppr thing <+> text "used where a value identifier was expected" }
1623 where
1624 return_id id = return (HsVar (noLoc id), idType id)
1625
1626 return_data_con con
1627 -- For data constructors, must perform the stupid-theta check
1628 | null stupid_theta
1629 = return_id con_wrapper_id
1630
1631 | otherwise
1632 -- See Note [Instantiating stupid theta]
1633 = do { let (tvs, theta, rho) = tcSplitSigmaTy (idType con_wrapper_id)
1634 ; (subst, tvs') <- newMetaTyVars tvs
1635 ; let tys' = mkTyVarTys tvs'
1636 theta' = substTheta subst theta
1637 rho' = substTy subst rho
1638 ; wrap <- instCall (OccurrenceOf id_name) tys' theta'
1639 ; addDataConStupidTheta con tys'
1640 ; return (mkHsWrap wrap (HsVar (noLoc con_wrapper_id)), rho') }
1641
1642 where
1643 con_wrapper_id = dataConWrapId con
1644 stupid_theta = dataConStupidTheta con
1645
1646 check_naughty id
1647 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl)
1648 | otherwise = return ()
1649
1650
1651 tcUnboundId :: UnboundVar -> ExpRhoType -> TcM (HsExpr TcId)
1652 -- Typechedk an occurrence of an unbound Id
1653 --
1654 -- Some of these started life as a true hole "_". Others might simply
1655 -- be variables that accidentally have no binding site
1656 --
1657 -- We turn all of them into HsVar, since HsUnboundVar can't contain an
1658 -- Id; and indeed the evidence for the CHoleCan does bind it, so it's
1659 -- not unbound any more!
1660 tcUnboundId unbound res_ty
1661 = do { ty <- newFlexiTyVarTy liftedTypeKind
1662 ; let occ = unboundVarOcc unbound
1663 ; name <- newSysName occ
1664 ; let ev = mkLocalId name ty
1665 ; loc <- getCtLocM HoleOrigin Nothing
1666 ; let can = CHoleCan { cc_ev = CtWanted { ctev_pred = ty
1667 , ctev_dest = EvVarDest ev
1668 , ctev_loc = loc}
1669 , cc_hole = ExprHole unbound }
1670 ; emitInsoluble can
1671 ; tcWrapResultO (UnboundOccurrenceOf occ) (HsVar (noLoc ev)) ty res_ty }
1672
1673
1674 {-
1675 Note [Adding the implicit parameter to 'assert']
1676 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1677 The typechecker transforms (assert e1 e2) to (assertError e1 e2).
1678 This isn't really the Right Thing because there's no way to "undo"
1679 if you want to see the original source code in the typechecker
1680 output. We'll have fix this in due course, when we care more about
1681 being able to reconstruct the exact original program.
1682
1683 Note [tagToEnum#]
1684 ~~~~~~~~~~~~~~~~~
1685 Nasty check to ensure that tagToEnum# is applied to a type that is an
1686 enumeration TyCon. Unification may refine the type later, but this
1687 check won't see that, alas. It's crude, because it relies on our
1688 knowing *now* that the type is ok, which in turn relies on the
1689 eager-unification part of the type checker pushing enough information
1690 here. In theory the Right Thing to do is to have a new form of
1691 constraint but I definitely cannot face that! And it works ok as-is.
1692
1693 Here's are two cases that should fail
1694 f :: forall a. a
1695 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1696
1697 g :: Int
1698 g = tagToEnum# 0 -- Int is not an enumeration
1699
1700 When data type families are involved it's a bit more complicated.
1701 data family F a
1702 data instance F [Int] = A | B | C
1703 Then we want to generate something like
1704 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1705 Usually that coercion is hidden inside the wrappers for
1706 constructors of F [Int] but here we have to do it explicitly.
1707
1708 It's all grotesquely complicated.
1709
1710 Note [Instantiating stupid theta]
1711 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1712 Normally, when we infer the type of an Id, we don't instantiate,
1713 because we wish to allow for visible type application later on.
1714 But if a datacon has a stupid theta, we're a bit stuck. We need
1715 to emit the stupid theta constraints with instantiated types. It's
1716 difficult to defer this to the lazy instantiation, because a stupid
1717 theta has no spot to put it in a type. So we just instantiate eagerly
1718 in this case. Thus, users cannot use visible type application with
1719 a data constructor sporting a stupid theta. I won't feel so bad for
1720 the users that complain.
1721
1722 -}
1723
1724 tcSeq :: SrcSpan -> Name -> [LHsExprArgIn]
1725 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1726 -- (seq e1 e2) :: res_ty
1727 -- We need a special typing rule because res_ty can be unboxed
1728 -- See Note [Typing rule for seq]
1729 tcSeq loc fun_name args res_ty
1730 = do { fun <- tcLookupId fun_name
1731 ; (arg1_ty, args1) <- case args of
1732 (Right hs_ty_arg1 : args1)
1733 -> do { ty_arg1 <- tcHsTypeApp hs_ty_arg1 liftedTypeKind
1734 ; return (ty_arg1, args1) }
1735
1736 _ -> do { arg_ty1 <- newFlexiTyVarTy liftedTypeKind
1737 ; return (arg_ty1, args) }
1738
1739 ; (arg1, arg2, arg2_exp_ty) <- case args1 of
1740 [Right hs_ty_arg2, Left term_arg1, Left term_arg2]
1741 -> do { rr_ty <- newFlexiTyVarTy runtimeRepTy
1742 ; ty_arg2 <- tcHsTypeApp hs_ty_arg2 (tYPE rr_ty)
1743 -- see Note [Typing rule for seq]
1744 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg2 res_ty
1745 ; return (term_arg1, term_arg2, mkCheckExpType ty_arg2) }
1746 [Left term_arg1, Left term_arg2]
1747 -> return (term_arg1, term_arg2, res_ty)
1748 _ -> too_many_args "seq" args
1749
1750 ; arg1' <- tcMonoExpr arg1 (mkCheckExpType arg1_ty)
1751 ; arg2' <- tcMonoExpr arg2 arg2_exp_ty
1752 ; res_ty <- readExpType res_ty -- by now, it's surely filled in
1753 ; let fun' = L loc (HsWrap ty_args (HsVar (L loc fun)))
1754 ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty
1755 ; return (idHsWrapper, fun', [Left arg1', Left arg2']) }
1756
1757 tcTagToEnum :: SrcSpan -> Name -> [LHsExprArgIn] -> ExpRhoType
1758 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1759 -- tagToEnum# :: forall a. Int# -> a
1760 -- See Note [tagToEnum#] Urgh!
1761 tcTagToEnum loc fun_name args res_ty
1762 = do { fun <- tcLookupId fun_name
1763
1764 ; arg <- case args of
1765 [Right hs_ty_arg, Left term_arg]
1766 -> do { ty_arg <- tcHsTypeApp hs_ty_arg liftedTypeKind
1767 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg res_ty
1768 -- other than influencing res_ty, we just
1769 -- don't care about a type arg passed in.
1770 -- So drop the evidence.
1771 ; return term_arg }
1772 [Left term_arg] -> do { _ <- expTypeToType res_ty
1773 ; return term_arg }
1774 _ -> too_many_args "tagToEnum#" args
1775
1776 ; res_ty <- readExpType res_ty
1777 ; ty' <- zonkTcType res_ty
1778
1779 -- Check that the type is algebraic
1780 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1781 Just (tc, tc_args) = mb_tc_app
1782 ; checkTc (isJust mb_tc_app)
1783 (mk_error ty' doc1)
1784
1785 -- Look through any type family
1786 ; fam_envs <- tcGetFamInstEnvs
1787 ; let (rep_tc, rep_args, coi)
1788 = tcLookupDataFamInst fam_envs tc tc_args
1789 -- coi :: tc tc_args ~R rep_tc rep_args
1790
1791 ; checkTc (isEnumerationTyCon rep_tc)
1792 (mk_error ty' doc2)
1793
1794 ; arg' <- tcMonoExpr arg (mkCheckExpType intPrimTy)
1795 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar (L loc fun)))
1796 rep_ty = mkTyConApp rep_tc rep_args
1797
1798 ; return (mkWpCastR (mkTcSymCo coi), fun', [Left arg']) }
1799 -- coi is a Representational coercion
1800 where
1801 doc1 = vcat [ text "Specify the type by giving a type signature"
1802 , text "e.g. (tagToEnum# x) :: Bool" ]
1803 doc2 = text "Result type must be an enumeration type"
1804
1805 mk_error :: TcType -> SDoc -> SDoc
1806 mk_error ty what
1807 = hang (text "Bad call to tagToEnum#"
1808 <+> text "at type" <+> ppr ty)
1809 2 what
1810
1811 too_many_args :: String -> [LHsExprArgIn] -> TcM a
1812 too_many_args fun args
1813 = failWith $
1814 hang (text "Too many type arguments to" <+> text fun <> colon)
1815 2 (sep (map pp args))
1816 where
1817 pp (Left e) = pprParendLExpr e
1818 pp (Right (HsWC { hswc_body = L _ t })) = pprParendHsType t
1819
1820
1821 {-
1822 ************************************************************************
1823 * *
1824 Template Haskell checks
1825 * *
1826 ************************************************************************
1827 -}
1828
1829 checkThLocalId :: Id -> TcM ()
1830 checkThLocalId id
1831 = do { mb_local_use <- getStageAndBindLevel (idName id)
1832 ; case mb_local_use of
1833 Just (top_lvl, bind_lvl, use_stage)
1834 | thLevel use_stage > bind_lvl
1835 , isNotTopLevel top_lvl
1836 -> checkCrossStageLifting id use_stage
1837 _ -> return () -- Not a locally-bound thing, or
1838 -- no cross-stage link
1839 }
1840
1841 --------------------------------------
1842 checkCrossStageLifting :: Id -> ThStage -> TcM ()
1843 -- If we are inside typed brackets, and (use_lvl > bind_lvl)
1844 -- we must check whether there's a cross-stage lift to do
1845 -- Examples \x -> [|| x ||]
1846 -- [|| map ||]
1847 -- There is no error-checking to do, because the renamer did that
1848 --
1849 -- This is similar to checkCrossStageLifting in RnSplice, but
1850 -- this code is applied to *typed* brackets.
1851
1852 checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var))
1853 = -- Nested identifiers, such as 'x' in
1854 -- E.g. \x -> [|| h x ||]
1855 -- We must behave as if the reference to x was
1856 -- h $(lift x)
1857 -- We use 'x' itself as the splice proxy, used by
1858 -- the desugarer to stitch it all back together.
1859 -- If 'x' occurs many times we may get many identical
1860 -- bindings of the same splice proxy, but that doesn't
1861 -- matter, although it's a mite untidy.
1862 do { let id_ty = idType id
1863 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1864 -- If x is polymorphic, its occurrence sites might
1865 -- have different instantiations, so we can't use plain
1866 -- 'x' as the splice proxy name. I don't know how to
1867 -- solve this, and it's probably unimportant, so I'm
1868 -- just going to flag an error for now
1869
1870 ; lift <- if isStringTy id_ty then
1871 do { sid <- tcLookupId THNames.liftStringName
1872 -- See Note [Lifting strings]
1873 ; return (HsVar (noLoc sid)) }
1874 else
1875 setConstraintVar lie_var $
1876 -- Put the 'lift' constraint into the right LIE
1877 newMethodFromName (OccurrenceOf (idName id))
1878 THNames.liftName id_ty
1879
1880 -- Update the pending splices
1881 ; ps <- readMutVar ps_var
1882 ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id))
1883 ; writeMutVar ps_var (pending_splice : ps)
1884
1885 ; return () }
1886
1887 checkCrossStageLifting _ _ = return ()
1888
1889 polySpliceErr :: Id -> SDoc
1890 polySpliceErr id
1891 = text "Can't splice the polymorphic local variable" <+> quotes (ppr id)
1892
1893 {-
1894 Note [Lifting strings]
1895 ~~~~~~~~~~~~~~~~~~~~~~
1896 If we see $(... [| s |] ...) where s::String, we don't want to
1897 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1898 So this conditional short-circuits the lifting mechanism to generate
1899 (liftString "xy") in that case. I didn't want to use overlapping instances
1900 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1901 errors in a polymorphic situation.
1902
1903 If this check fails (which isn't impossible) we get another chance; see
1904 Note [Converting strings] in Convert.hs
1905
1906 Local record selectors
1907 ~~~~~~~~~~~~~~~~~~~~~~
1908 Record selectors for TyCons in this module are ordinary local bindings,
1909 which show up as ATcIds rather than AGlobals. So we need to check for
1910 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1911
1912
1913 ************************************************************************
1914 * *
1915 \subsection{Record bindings}
1916 * *
1917 ************************************************************************
1918 -}
1919
1920 getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet
1921 -- These tyvars must not change across the updates
1922 getFixedTyVars upd_fld_occs univ_tvs cons
1923 = mkVarSet [tv1 | con <- cons
1924 , let (u_tvs, _, eqspec, prov_theta
1925 , req_theta, arg_tys, _)
1926 = conLikeFullSig con
1927 theta = eqSpecPreds eqspec
1928 ++ prov_theta
1929 ++ req_theta
1930 flds = conLikeFieldLabels con
1931 fixed_tvs = exactTyCoVarsOfTypes fixed_tys
1932 -- fixed_tys: See Note [Type of a record update]
1933 `unionVarSet` tyCoVarsOfTypes theta
1934 -- Universally-quantified tyvars that
1935 -- appear in any of the *implicit*
1936 -- arguments to the constructor are fixed
1937 -- See Note [Implict type sharing]
1938
1939 fixed_tys = [ty | (fl, ty) <- zip flds arg_tys
1940 , not (flLabel fl `elem` upd_fld_occs)]
1941 , (tv1,tv) <- univ_tvs `zip` u_tvs
1942 , tv `elemVarSet` fixed_tvs ]
1943
1944 {-
1945 Note [Disambiguating record fields]
1946 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1947 When the -XDuplicateRecordFields extension is used, and the renamer
1948 encounters a record selector or update that it cannot immediately
1949 disambiguate (because it involves fields that belong to multiple
1950 datatypes), it will defer resolution of the ambiguity to the
1951 typechecker. In this case, the `Ambiguous` constructor of
1952 `AmbiguousFieldOcc` is used.
1953
1954 Consider the following definitions:
1955
1956 data S = MkS { foo :: Int }
1957 data T = MkT { foo :: Int, bar :: Int }
1958 data U = MkU { bar :: Int, baz :: Int }
1959
1960 When the renamer sees `foo` as a selector or an update, it will not
1961 know which parent datatype is in use.
1962
1963 For selectors, there are two possible ways to disambiguate:
1964
1965 1. Check if the pushed-in type is a function whose domain is a
1966 datatype, for example:
1967
1968 f s = (foo :: S -> Int) s
1969
1970 g :: T -> Int
1971 g = foo
1972
1973 This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`.
1974
1975 2. Check if the selector is applied to an argument that has a type
1976 signature, for example:
1977
1978 h = foo (s :: S)
1979
1980 This is checked by `tcApp`.
1981
1982
1983 Updates are slightly more complex. The `disambiguateRecordBinds`
1984 function tries to determine the parent datatype in three ways:
1985
1986 1. Check for types that have all the fields being updated. For example:
1987
1988 f x = x { foo = 3, bar = 2 }
1989
1990 Here `f` must be updating `T` because neither `S` nor `U` have
1991 both fields. This may also discover that no possible type exists.
1992 For example the following will be rejected:
1993
1994 f' x = x { foo = 3, baz = 3 }
1995
1996 2. Use the type being pushed in, if it is already a TyConApp. The
1997 following are valid updates to `T`:
1998
1999 g :: T -> T
2000 g x = x { foo = 3 }
2001
2002 g' x = x { foo = 3 } :: T
2003
2004 3. Use the type signature of the record expression, if it exists and
2005 is a TyConApp. Thus this is valid update to `T`:
2006
2007 h x = (x :: T) { foo = 3 }
2008
2009
2010 Note that we do not look up the types of variables being updated, and
2011 no constraint-solving is performed, so for example the following will
2012 be rejected as ambiguous:
2013
2014 let bad (s :: S) = foo s
2015
2016 let r :: T
2017 r = blah
2018 in r { foo = 3 }
2019
2020 \r. (r { foo = 3 }, r :: T )
2021
2022 We could add further tests, of a more heuristic nature. For example,
2023 rather than looking for an explicit signature, we could try to infer
2024 the type of the argument to a selector or the record expression being
2025 updated, in case we are lucky enough to get a TyConApp straight
2026 away. However, it might be hard for programmers to predict whether a
2027 particular update is sufficiently obvious for the signature to be
2028 omitted. Moreover, this might change the behaviour of typechecker in
2029 non-obvious ways.
2030
2031 See also Note [HsRecField and HsRecUpdField] in HsPat.
2032 -}
2033
2034 -- Given a RdrName that refers to multiple record fields, and the type
2035 -- of its argument, try to determine the name of the selector that is
2036 -- meant.
2037 disambiguateSelector :: Located RdrName -> Type -> TcM Name
2038 disambiguateSelector lr@(L _ rdr) parent_type
2039 = do { fam_inst_envs <- tcGetFamInstEnvs
2040 ; case tyConOf fam_inst_envs parent_type of
2041 Nothing -> ambiguousSelector lr
2042 Just p ->
2043 do { xs <- lookupParents rdr
2044 ; let parent = RecSelData p
2045 ; case lookup parent xs of
2046 Just gre -> do { addUsedGRE True gre
2047 ; return (gre_name gre) }
2048 Nothing -> failWithTc (fieldNotInType parent rdr) } }
2049
2050 -- This field name really is ambiguous, so add a suitable "ambiguous
2051 -- occurrence" error, then give up.
2052 ambiguousSelector :: Located RdrName -> TcM a
2053 ambiguousSelector (L _ rdr)
2054 = do { env <- getGlobalRdrEnv
2055 ; let gres = lookupGRE_RdrName rdr env
2056 ; setErrCtxt [] $ addNameClashErrRn rdr gres
2057 ; failM }
2058
2059 -- Disambiguate the fields in a record update.
2060 -- See Note [Disambiguating record fields]
2061 disambiguateRecordBinds :: LHsExpr Name -> TcRhoType
2062 -> [LHsRecUpdField Name] -> ExpRhoType
2063 -> TcM [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2064 disambiguateRecordBinds record_expr record_rho rbnds res_ty
2065 -- Are all the fields unambiguous?
2066 = case mapM isUnambiguous rbnds of
2067 -- If so, just skip to looking up the Ids
2068 -- Always the case if DuplicateRecordFields is off
2069 Just rbnds' -> mapM lookupSelector rbnds'
2070 Nothing -> -- If not, try to identify a single parent
2071 do { fam_inst_envs <- tcGetFamInstEnvs
2072 -- Look up the possible parents for each field
2073 ; rbnds_with_parents <- getUpdFieldsParents
2074 ; let possible_parents = map (map fst . snd) rbnds_with_parents
2075 -- Identify a single parent
2076 ; p <- identifyParent fam_inst_envs possible_parents
2077 -- Pick the right selector with that parent for each field
2078 ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents }
2079 where
2080 -- Extract the selector name of a field update if it is unambiguous
2081 isUnambiguous :: LHsRecUpdField Name -> Maybe (LHsRecUpdField Name, Name)
2082 isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of
2083 Unambiguous _ sel_name -> Just (x, sel_name)
2084 Ambiguous{} -> Nothing
2085
2086 -- Look up the possible parents and selector GREs for each field
2087 getUpdFieldsParents :: TcM [(LHsRecUpdField Name
2088 , [(RecSelParent, GlobalRdrElt)])]
2089 getUpdFieldsParents
2090 = fmap (zip rbnds) $ mapM
2091 (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc)
2092 rbnds
2093
2094 -- Given a the lists of possible parents for each field,
2095 -- identify a single parent
2096 identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent
2097 identifyParent fam_inst_envs possible_parents
2098 = case foldr1 intersect possible_parents of
2099 -- No parents for all fields: record update is ill-typed
2100 [] -> failWithTc (noPossibleParents rbnds)
2101
2102 -- Exactly one datatype with all the fields: use that
2103 [p] -> return p
2104
2105 -- Multiple possible parents: try harder to disambiguate
2106 -- Can we get a parent TyCon from the pushed-in type?
2107 _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p)
2108
2109 -- Does the expression being updated have a type signature?
2110 -- If so, try to extract a parent TyCon from it
2111 | Just {} <- obviousSig (unLoc record_expr)
2112 , Just tc <- tyConOf fam_inst_envs record_rho
2113 -> return (RecSelData tc)
2114
2115 -- Nothing else we can try...
2116 _ -> failWithTc badOverloadedUpdate
2117
2118 -- Make a field unambiguous by choosing the given parent.
2119 -- Emits an error if the field cannot have that parent,
2120 -- e.g. if the user writes
2121 -- r { x = e } :: T
2122 -- where T does not have field x.
2123 pickParent :: RecSelParent
2124 -> (LHsRecUpdField Name, [(RecSelParent, GlobalRdrElt)])
2125 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2126 pickParent p (upd, xs)
2127 = case lookup p xs of
2128 -- Phew! The parent is valid for this field.
2129 -- Previously ambiguous fields must be marked as
2130 -- used now that we know which one is meant, but
2131 -- unambiguous ones shouldn't be recorded again
2132 -- (giving duplicate deprecation warnings).
2133 Just gre -> do { unless (null (tail xs)) $ do
2134 let L loc _ = hsRecFieldLbl (unLoc upd)
2135 setSrcSpan loc $ addUsedGRE True gre
2136 ; lookupSelector (upd, gre_name gre) }
2137 -- The field doesn't belong to this parent, so report
2138 -- an error but keep going through all the fields
2139 Nothing -> do { addErrTc (fieldNotInType p
2140 (unLoc (hsRecUpdFieldRdr (unLoc upd))))
2141 ; lookupSelector (upd, gre_name (snd (head xs))) }
2142
2143 -- Given a (field update, selector name) pair, look up the
2144 -- selector to give a field update with an unambiguous Id
2145 lookupSelector :: (LHsRecUpdField Name, Name)
2146 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2147 lookupSelector (L l upd, n)
2148 = do { i <- tcLookupId n
2149 ; let L loc af = hsRecFieldLbl upd
2150 lbl = rdrNameAmbiguousFieldOcc af
2151 ; return $ L l upd { hsRecFieldLbl
2152 = L loc (Unambiguous (L loc lbl) i) } }
2153
2154
2155 -- Extract the outermost TyCon of a type, if there is one; for
2156 -- data families this is the representation tycon (because that's
2157 -- where the fields live).
2158 tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon
2159 tyConOf fam_inst_envs ty0
2160 = case tcSplitTyConApp_maybe ty of
2161 Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys))
2162 Nothing -> Nothing
2163 where
2164 (_, _, ty) = tcSplitSigmaTy ty0
2165
2166 -- Variant of tyConOf that works for ExpTypes
2167 tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon
2168 tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0
2169
2170 -- For an ambiguous record field, find all the candidate record
2171 -- selectors (as GlobalRdrElts) and their parents.
2172 lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)]
2173 lookupParents rdr
2174 = do { env <- getGlobalRdrEnv
2175 ; let gres = lookupGRE_RdrName rdr env
2176 ; mapM lookupParent gres }
2177 where
2178 lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt)
2179 lookupParent gre = do { id <- tcLookupId (gre_name gre)
2180 ; if isRecordSelector id
2181 then return (recordSelectorTyCon id, gre)
2182 else failWithTc (notSelector (gre_name gre)) }
2183
2184 -- A type signature on the argument of an ambiguous record selector or
2185 -- the record expression in an update must be "obvious", i.e. the
2186 -- outermost constructor ignoring parentheses.
2187 obviousSig :: HsExpr Name -> Maybe (LHsSigWcType Name)
2188 obviousSig (ExprWithTySig _ ty) = Just ty
2189 obviousSig (HsPar p) = obviousSig (unLoc p)
2190 obviousSig _ = Nothing
2191
2192
2193 {-
2194 Game plan for record bindings
2195 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2196 1. Find the TyCon for the bindings, from the first field label.
2197
2198 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
2199
2200 For each binding field = value
2201
2202 3. Instantiate the field type (from the field label) using the type
2203 envt from step 2.
2204
2205 4 Type check the value using tcArg, passing the field type as
2206 the expected argument type.
2207
2208 This extends OK when the field types are universally quantified.
2209 -}
2210
2211 tcRecordBinds
2212 :: ConLike
2213 -> [TcType] -- Expected type for each field
2214 -> HsRecordBinds Name
2215 -> TcM (HsRecordBinds TcId)
2216
2217 tcRecordBinds con_like arg_tys (HsRecFields rbinds dd)
2218 = do { mb_binds <- mapM do_bind rbinds
2219 ; return (HsRecFields (catMaybes mb_binds) dd) }
2220 where
2221 fields = map flLabel $ conLikeFieldLabels con_like
2222 flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys
2223
2224 do_bind :: LHsRecField Name (LHsExpr Name)
2225 -> TcM (Maybe (LHsRecField TcId (LHsExpr TcId)))
2226 do_bind (L l fld@(HsRecField { hsRecFieldLbl = f
2227 , hsRecFieldArg = rhs }))
2228
2229 = do { mb <- tcRecordField con_like flds_w_tys f rhs
2230 ; case mb of
2231 Nothing -> return Nothing
2232 Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f'
2233 , hsRecFieldArg = rhs' }))) }
2234
2235 tcRecordUpd
2236 :: ConLike
2237 -> [TcType] -- Expected type for each field
2238 -> [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2239 -> TcM [LHsRecUpdField TcId]
2240
2241 tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds
2242 where
2243 flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys
2244
2245 do_bind :: LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name) -> TcM (Maybe (LHsRecUpdField TcId))
2246 do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af
2247 , hsRecFieldArg = rhs }))
2248 = do { let lbl = rdrNameAmbiguousFieldOcc af
2249 sel_id = selectorAmbiguousFieldOcc af
2250 f = L loc (FieldOcc (L loc lbl) (idName sel_id))
2251 ; mb <- tcRecordField con_like flds_w_tys f rhs
2252 ; case mb of
2253 Nothing -> return Nothing
2254 Just (f', rhs') ->
2255 return (Just
2256 (L l (fld { hsRecFieldLbl
2257 = L loc (Unambiguous (L loc lbl)
2258 (selectorFieldOcc (unLoc f')))
2259 , hsRecFieldArg = rhs' }))) }
2260
2261 tcRecordField :: ConLike -> Assoc FieldLabelString Type -> LFieldOcc Name -> LHsExpr Name
2262 -> TcM (Maybe (LFieldOcc Id, LHsExpr Id))
2263 tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs
2264 | Just field_ty <- assocMaybe flds_w_tys field_lbl
2265 = addErrCtxt (fieldCtxt field_lbl) $
2266 do { rhs' <- tcPolyExprNC rhs field_ty
2267 ; let field_id = mkUserLocal (nameOccName sel_name)
2268 (nameUnique sel_name)
2269 field_ty loc
2270 -- Yuk: the field_id has the *unique* of the selector Id
2271 -- (so we can find it easily)
2272 -- but is a LocalId with the appropriate type of the RHS
2273 -- (so the desugarer knows the type of local binder to make)
2274 ; return (Just (L loc (FieldOcc lbl field_id), rhs')) }
2275 | otherwise
2276 = do { addErrTc (badFieldCon con_like field_lbl)
2277 ; return Nothing }
2278 where
2279 field_lbl = occNameFS $ rdrNameOcc (unLoc lbl)
2280
2281
2282 checkMissingFields :: ConLike -> HsRecordBinds Name -> TcM ()
2283 checkMissingFields con_like rbinds
2284 | null field_labels -- Not declared as a record;
2285 -- But C{} is still valid if no strict fields
2286 = if any isBanged field_strs then
2287 -- Illegal if any arg is strict
2288 addErrTc (missingStrictFields con_like [])
2289 else
2290 return ()
2291
2292 | otherwise = do -- A record
2293 unless (null missing_s_fields)
2294 (addErrTc (missingStrictFields con_like missing_s_fields))
2295
2296 warn <- woptM Opt_WarnMissingFields
2297 unless (not (warn && notNull missing_ns_fields))
2298 (warnTc (Reason Opt_WarnMissingFields) True
2299 (missingFields con_like missing_ns_fields))
2300
2301 where
2302 missing_s_fields
2303 = [ flLabel fl | (fl, str) <- field_info,
2304 isBanged str,
2305 not (fl `elemField` field_names_used)
2306 ]
2307 missing_ns_fields
2308 = [ flLabel fl | (fl, str) <- field_info,
2309 not (isBanged str),
2310 not (fl `elemField` field_names_used)
2311 ]
2312
2313 field_names_used = hsRecFields rbinds
2314 field_labels = conLikeFieldLabels con_like
2315
2316 field_info = zipEqual "missingFields"
2317 field_labels
2318 field_strs
2319
2320 field_strs = conLikeImplBangs con_like
2321
2322 fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds
2323
2324 {-
2325 ************************************************************************
2326 * *
2327 \subsection{Errors and contexts}
2328 * *
2329 ************************************************************************
2330
2331 Boring and alphabetical:
2332 -}
2333
2334 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
2335 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
2336
2337 exprCtxt :: LHsExpr Name -> SDoc
2338 exprCtxt expr
2339 = hang (text "In the expression:") 2 (ppr expr)
2340
2341 fieldCtxt :: FieldLabelString -> SDoc
2342 fieldCtxt field_name
2343 = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
2344
2345 addFunResCtxt :: Bool -- There is at least one argument
2346 -> HsExpr Name -> TcType -> ExpRhoType
2347 -> TcM a -> TcM a
2348 -- When we have a mis-match in the return type of a function
2349 -- try to give a helpful message about too many/few arguments
2350 --
2351 -- Used for naked variables too; but with has_args = False
2352 addFunResCtxt has_args fun fun_res_ty env_ty
2353 = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg)
2354 -- NB: use a landmark error context, so that an empty context
2355 -- doesn't suppress some more useful context
2356 where
2357 mk_msg
2358 = do { mb_env_ty <- readExpType_maybe env_ty
2359 -- by the time the message is rendered, the ExpType
2360 -- will be filled in (except if we're debugging)
2361 ; fun_res' <- zonkTcType fun_res_ty
2362 ; env' <- case mb_env_ty of
2363 Just env_ty -> zonkTcType env_ty
2364 Nothing ->
2365 do { dumping <- doptM Opt_D_dump_tc_trace
2366 ; MASSERT( dumping )
2367 ; newFlexiTyVarTy liftedTypeKind }
2368 ; let (_, _, fun_tau) = tcSplitSigmaTy fun_res'
2369 (_, _, env_tau) = tcSplitSigmaTy env'
2370 (args_fun, res_fun) = tcSplitFunTys fun_tau
2371 (args_env, res_env) = tcSplitFunTys env_tau
2372 n_fun = length args_fun
2373 n_env = length args_env
2374 info | n_fun == n_env = Outputable.empty
2375 | n_fun > n_env
2376 , not_fun res_env
2377 = text "Probable cause:" <+> quotes (ppr fun)
2378 <+> text "is applied to too few arguments"
2379
2380 | has_args
2381 , not_fun res_fun
2382 = text "Possible cause:" <+> quotes (ppr fun)
2383 <+> text "is applied to too many arguments"
2384
2385 | otherwise
2386 = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args!
2387 ; return info }
2388 where
2389 not_fun ty -- ty is definitely not an arrow type,
2390 -- and cannot conceivably become one
2391 = case tcSplitTyConApp_maybe ty of
2392 Just (tc, _) -> isAlgTyCon tc
2393 Nothing -> False
2394
2395 badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc
2396 badFieldTypes prs
2397 = hang (text "Record update for insufficiently polymorphic field"
2398 <> plural prs <> colon)
2399 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
2400
2401 badFieldsUpd
2402 :: [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -- Field names that don't belong to a single datacon
2403 -> [ConLike] -- Data cons of the type which the first field name belongs to
2404 -> SDoc
2405 badFieldsUpd rbinds data_cons
2406 = hang (text "No constructor has all these fields:")
2407 2 (pprQuotedList conflictingFields)
2408 -- See Note [Finding the conflicting fields]
2409 where
2410 -- A (preferably small) set of fields such that no constructor contains
2411 -- all of them. See Note [Finding the conflicting fields]
2412 conflictingFields = case nonMembers of
2413 -- nonMember belongs to a different type.
2414 (nonMember, _) : _ -> [aMember, nonMember]
2415 [] -> let
2416 -- All of rbinds belong to one type. In this case, repeatedly add
2417 -- a field to the set until no constructor contains the set.
2418
2419 -- Each field, together with a list indicating which constructors
2420 -- have all the fields so far.
2421 growingSets :: [(FieldLabelString, [Bool])]
2422 growingSets = scanl1 combine membership
2423 combine (_, setMem) (field, fldMem)
2424 = (field, zipWith (&&) setMem fldMem)
2425 in
2426 -- Fields that don't change the membership status of the set
2427 -- are redundant and can be dropped.
2428 map (fst . head) $ groupBy ((==) `on` snd) growingSets
2429
2430 aMember = ASSERT( not (null members) ) fst (head members)
2431 (members, nonMembers) = partition (or . snd) membership
2432
2433 -- For each field, which constructors contain the field?
2434 membership :: [(FieldLabelString, [Bool])]
2435 membership = sortMembership $
2436 map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $
2437 map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds
2438
2439 fieldLabelSets :: [Set.Set FieldLabelString]
2440 fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons
2441
2442 -- Sort in order of increasing number of True, so that a smaller
2443 -- conflicting set can be found.
2444 sortMembership =
2445 map snd .
2446 sortBy (compare `on` fst) .
2447 map (\ item@(_, membershipRow) -> (countTrue membershipRow, item))
2448
2449 countTrue = length . filter id
2450
2451 {-
2452 Note [Finding the conflicting fields]
2453 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2454 Suppose we have
2455 data A = A {a0, a1 :: Int}
2456 | B {b0, b1 :: Int}
2457 and we see a record update
2458 x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 }
2459 Then we'd like to find the smallest subset of fields that no
2460 constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc.
2461 We don't really want to report that no constructor has all of
2462 {a0,a1,b0,b1}, because when there are hundreds of fields it's
2463 hard to see what was really wrong.
2464
2465 We may need more than two fields, though; eg
2466 data T = A { x,y :: Int, v::Int }
2467 | B { y,z :: Int, v::Int }
2468 | C { z,x :: Int, v::Int }
2469 with update
2470 r { x=e1, y=e2, z=e3 }, we
2471
2472 Finding the smallest subset is hard, so the code here makes
2473 a decent stab, no more. See Trac #7989.
2474 -}
2475
2476 naughtyRecordSel :: RdrName -> SDoc
2477 naughtyRecordSel sel_id
2478 = text "Cannot use record selector" <+> quotes (ppr sel_id) <+>
2479 text "as a function due to escaped type variables" $$
2480 text "Probable fix: use pattern-matching syntax instead"
2481
2482 notSelector :: Name -> SDoc
2483 notSelector field
2484 = hsep [quotes (ppr field), text "is not a record selector"]
2485
2486 mixedSelectors :: [Id] -> [Id] -> SDoc
2487 mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_)
2488 = ptext
2489 (sLit "Cannot use a mixture of pattern synonym and record selectors") $$
2490 text "Record selectors defined by"
2491 <+> quotes (ppr (tyConName rep_dc))
2492 <> text ":"
2493 <+> pprWithCommas ppr data_sels $$
2494 text "Pattern synonym selectors defined by"
2495 <+> quotes (ppr (patSynName rep_ps))
2496 <> text ":"
2497 <+> pprWithCommas ppr pat_syn_sels
2498 where
2499 RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id
2500 RecSelData rep_dc = recordSelectorTyCon dc_rep_id
2501 mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists"
2502
2503
2504 missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc
2505 missingStrictFields con fields
2506 = header <> rest
2507 where
2508 rest | null fields = Outputable.empty -- Happens for non-record constructors
2509 -- with strict fields
2510 | otherwise = colon <+> pprWithCommas ppr fields
2511
2512 header = text "Constructor" <+> quotes (ppr con) <+>
2513 text "does not have the required strict field(s)"
2514
2515 missingFields :: ConLike -> [FieldLabelString] -> SDoc
2516 missingFields con fields
2517 = text "Fields of" <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
2518 <+> pprWithCommas ppr fields
2519
2520 -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl mkHsApp fun args))
2521
2522 noPossibleParents :: [LHsRecUpdField Name] -> SDoc
2523 noPossibleParents rbinds
2524 = hang (text "No type has all these fields:")
2525 2 (pprQuotedList fields)
2526 where
2527 fields = map (hsRecFieldLbl . unLoc) rbinds
2528
2529 badOverloadedUpdate :: SDoc
2530 badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature"
2531
2532 fieldNotInType :: RecSelParent -> RdrName -> SDoc
2533 fieldNotInType p rdr
2534 = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr
2535
2536 {-
2537 ************************************************************************
2538 * *
2539 \subsection{Static Pointers}
2540 * *
2541 ************************************************************************
2542 -}
2543
2544 -- | A data type to describe why a variable is not closed.
2545 data NotClosedReason = NotLetBoundReason
2546 | NotTypeClosed VarSet
2547 | NotClosed Name NotClosedReason
2548
2549 -- | Checks if the given name is closed and emits an error if not.
2550 --
2551 -- See Note [Not-closed error messages].
2552 checkClosedInStaticForm :: Name -> TcM ()
2553 checkClosedInStaticForm name = do
2554 type_env <- getLclTypeEnv
2555 case checkClosed type_env name of
2556 Nothing -> return ()
2557 Just reason -> addErrTc $ explain name reason
2558 where
2559 -- See Note [Checking closedness].
2560 checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason
2561 checkClosed type_env n = checkLoop type_env (unitNameSet n) n
2562
2563 checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason
2564 checkLoop type_env visited n = do
2565 -- The @visited@ set is an accumulating parameter that contains the set of
2566 -- visited nodes, so we avoid repeating cycles in the traversal.
2567 case lookupNameEnv type_env n of
2568 Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of
2569 ClosedLet -> Nothing
2570 NotLetBound -> Just NotLetBoundReason
2571 NonClosedLet fvs type_closed -> listToMaybe $
2572 -- Look for a non-closed variable in fvs
2573 [ NotClosed n' reason
2574 | n' <- nameSetElemsStable fvs
2575 , not (elemNameSet n' visited)
2576 , Just reason <- [checkLoop type_env (extendNameSet visited n') n']
2577 ] ++
2578 if type_closed then
2579 []
2580 else
2581 -- We consider non-let-bound variables easier to figure out than
2582 -- non-closed types, so we report non-closed types to the user
2583 -- only if we cannot spot the former.
2584 [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ]
2585 -- The binding is closed.
2586 _ -> Nothing
2587
2588 -- Converts a reason into a human-readable sentence.
2589 --
2590 -- @explain name reason@ starts with
2591 --
2592 -- "<name> is used in a static form but it is not closed because it"
2593 --
2594 -- and then follows a list of causes. For each id in the path, the text
2595 --
2596 -- "uses <id> which"
2597 --
2598 -- is appended, yielding something like
2599 --
2600 -- "uses <id> which uses <id1> which uses <id2> which"
2601 --
2602 -- until the end of the path is reached, which is reported as either
2603 --
2604 -- "is not let-bound"
2605 --
2606 -- when the final node is not let-bound, or
2607 --
2608 -- "has a non-closed type because it contains the type variables:
2609 -- v1, v2, v3"
2610 --
2611 -- when the final node has a non-closed type.
2612 --
2613 explain :: Name -> NotClosedReason -> SDoc
2614 explain name reason =
2615 quotes (ppr name) <+> text "is used in a static form but it is not closed"
2616 <+> text "because it"
2617 $$
2618 sep (causes reason)
2619
2620 causes :: NotClosedReason -> [SDoc]
2621 causes NotLetBoundReason = [text "is not let-bound."]
2622 causes (NotTypeClosed vs) =
2623 [ text "has a non-closed type because it contains the"
2624 , text "type variables:" <+>
2625 pprVarSet vs (hsep . punctuate comma . map (quotes . ppr))
2626 ]
2627 causes (NotClosed n reason) =
2628 let msg = text "uses" <+> quotes (ppr n) <+> text "which"
2629 in case reason of
2630 NotClosed _ _ -> msg : causes reason
2631 _ -> let (xs0, xs1) = splitAt 1 $ causes reason
2632 in fmap (msg <+>) xs0 ++ xs1
2633
2634 -- Note [Not-closed error messages]
2635 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2636 --
2637 -- When variables in a static form are not closed, we go through the trouble
2638 -- of explaining why they aren't.
2639 --
2640 -- Thus, the following program
2641 --
2642 -- > {-# LANGUAGE StaticPointers #-}
2643 -- > module M where
2644 -- >
2645 -- > f x = static g
2646 -- > where
2647 -- > g = h
2648 -- > h = x
2649 --
2650 -- produces the error
2651 --
2652 -- 'g' is used in a static form but it is not closed because it
2653 -- uses 'h' which uses 'x' which is not let-bound.
2654 --
2655 -- And a program like
2656 --
2657 -- > {-# LANGUAGE StaticPointers #-}
2658 -- > module M where
2659 -- >
2660 -- > import Data.Typeable
2661 -- > import GHC.StaticPtr
2662 -- >
2663 -- > f :: Typeable a => a -> StaticPtr TypeRep
2664 -- > f x = const (static (g undefined)) (h x)
2665 -- > where
2666 -- > g = h
2667 -- > h = typeOf
2668 --
2669 -- produces the error
2670 --
2671 -- 'g' is used in a static form but it is not closed because it
2672 -- uses 'h' which has a non-closed type because it contains the
2673 -- type variables: 'a'
2674 --
2675
2676 -- Note [Checking closedness]
2677 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~
2678 --
2679 -- @checkClosed@ checks if a binding is closed and returns a reason if it is
2680 -- not.
2681 --
2682 -- The bindings define a graph where the nodes are ids, and there is an edge
2683 -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free
2684 -- variables.
2685 --
2686 -- When @n@ is not closed, it has to exist in the graph some node reachable
2687 -- from @n@ that it is not a let-bound variable or that it has a non-closed
2688 -- type. Thus, the "reason" is a path from @n@ to this offending node.
2689 --
2690 -- When @n@ is not closed, we traverse the graph reachable from @n@ to build
2691 -- the reason.
2692 --