efaa4c642e25e5fd991c0cd4dc03e929af27c45f
[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 {-# LANGUAGE TypeFamilies #-}
12
13 module TcExpr ( tcPolyExpr, tcMonoExpr, tcMonoExprNC,
14 tcInferSigma, tcInferSigmaNC, tcInferRho, tcInferRhoNC,
15 tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType,
16 tcCheckId,
17 addExprErrCtxt,
18 getFixedTyVars ) where
19
20 #include "HsVersions.h"
21
22 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket )
23 import THNames( liftStringName, liftName )
24
25 import HsSyn
26 import TcHsSyn
27 import TcRnMonad
28 import TcUnify
29 import BasicTypes
30 import Inst
31 import TcBinds ( chooseInferredQuantifiers, tcLocalBinds )
32 import TcSigs ( tcUserTypeSig, tcInstSig )
33 import TcSimplify ( simplifyInfer, InferMode(..) )
34 import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst )
35 import FamInstEnv ( FamInstEnvs )
36 import RnEnv ( addUsedGRE )
37 import RnUtils ( addNameClashErrRn, unknownSubordinateErr )
38 import TcEnv
39 import TcArrows
40 import TcMatches
41 import TcHsType
42 import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr )
43 import TcPat
44 import TcMType
45 import TcType
46 import DsMonad
47 import Id
48 import IdInfo
49 import ConLike
50 import DataCon
51 import PatSyn
52 import Name
53 import NameEnv
54 import NameSet
55 import RdrName
56 import TyCon
57 import TyCoRep
58 import Type
59 import TcEvidence
60 import VarSet
61 import TysWiredIn
62 import TysPrim( intPrimTy )
63 import PrimOp( tagToEnumKey )
64 import PrelNames
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 UniqSet ( nonDetEltsUniqSet )
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 GhcRn -- Expression to type check
93 -> TcSigmaType -- Expected type (could be a polytype)
94 -> TcM (LHsExpr GhcTcId) -- 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 GhcRn -> ExpSigmaType
106 -> TcM (LHsExpr GhcTcId)
107 tc_poly_expr expr res_ty
108 = addExprErrCtxt expr $
109 do { traceTc "tcPolyExpr" (ppr res_ty); tc_poly_expr_nc expr res_ty }
110
111 tc_poly_expr_nc (L loc expr) res_ty
112 = do { traceTc "tcPolyExprNC" (ppr res_ty)
113 ; (wrap, expr')
114 <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty ->
115 setSrcSpan loc $
116 -- NB: setSrcSpan *after* skolemising, so we get better
117 -- skolem locations
118 tcExpr expr res_ty
119 ; return $ L loc (mkHsWrap wrap expr') }
120
121 ---------------
122 tcMonoExpr, tcMonoExprNC
123 :: LHsExpr GhcRn -- Expression to type check
124 -> ExpRhoType -- Expected type
125 -- Definitely no foralls at the top
126 -> TcM (LHsExpr GhcTcId)
127
128 tcMonoExpr expr res_ty
129 = addErrCtxt (exprCtxt expr) $
130 tcMonoExprNC expr res_ty
131
132 tcMonoExprNC (L loc expr) res_ty
133 = setSrcSpan loc $
134 do { expr' <- tcExpr expr res_ty
135 ; return (L loc expr') }
136
137 ---------------
138 tcInferSigma, tcInferSigmaNC :: LHsExpr GhcRn -> TcM ( LHsExpr GhcTcId
139 , TcSigmaType )
140 -- Infer a *sigma*-type.
141 tcInferSigma expr = addErrCtxt (exprCtxt expr) (tcInferSigmaNC expr)
142
143 tcInferSigmaNC (L loc expr)
144 = setSrcSpan loc $
145 do { (expr', sigma) <- tcInferNoInst (tcExpr expr)
146 ; return (L loc expr', sigma) }
147
148 tcInferRho, tcInferRhoNC :: LHsExpr GhcRn -> TcM (LHsExpr GhcTcId, TcRhoType)
149 -- Infer a *rho*-type. The return type is always (shallowly) instantiated.
150 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
151
152 tcInferRhoNC expr
153 = do { (expr', sigma) <- tcInferSigmaNC expr
154 ; (wrap, rho) <- topInstantiate (lexprCtOrigin expr) sigma
155 ; return (mkLHsWrap wrap expr', rho) }
156
157
158 {-
159 ************************************************************************
160 * *
161 tcExpr: the main expression typechecker
162 * *
163 ************************************************************************
164
165 NB: The res_ty is always deeply skolemised.
166 -}
167
168 tcExpr :: HsExpr GhcRn -> ExpRhoType -> TcM (HsExpr GhcTcId)
169 tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty
170 tcExpr e@(HsUnboundVar uv) res_ty = tcUnboundId e uv res_ty
171
172 tcExpr e@(HsApp {}) res_ty = tcApp1 e res_ty
173 tcExpr e@(HsAppType {}) res_ty = tcApp1 e res_ty
174
175 tcExpr e@(HsLit lit) res_ty
176 = do { let lit_ty = hsLitType lit
177 ; tcWrapResult e (HsLit (convertLit lit)) lit_ty res_ty }
178
179 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
180 ; return (HsPar expr') }
181
182 tcExpr (HsSCC src lbl expr) res_ty
183 = do { expr' <- tcMonoExpr expr res_ty
184 ; return (HsSCC src lbl expr') }
185
186 tcExpr (HsTickPragma src info srcInfo expr) res_ty
187 = do { expr' <- tcMonoExpr expr res_ty
188 ; return (HsTickPragma src info srcInfo expr') }
189
190 tcExpr (HsCoreAnn src lbl expr) res_ty
191 = do { expr' <- tcMonoExpr expr res_ty
192 ; return (HsCoreAnn src lbl expr') }
193
194 tcExpr (HsOverLit lit) res_ty
195 = do { lit' <- newOverloadedLit lit res_ty
196 ; return (HsOverLit lit') }
197
198 tcExpr (NegApp expr neg_expr) res_ty
199 = do { (expr', neg_expr')
200 <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $
201 \[arg_ty] ->
202 tcMonoExpr expr (mkCheckExpType arg_ty)
203 ; return (NegApp expr' neg_expr') }
204
205 tcExpr e@(HsIPVar x) res_ty
206 = do { {- Implicit parameters must have a *tau-type* not a
207 type scheme. We enforce this by creating a fresh
208 type variable as its type. (Because res_ty may not
209 be a tau-type.) -}
210 ip_ty <- newOpenFlexiTyVarTy
211 ; let ip_name = mkStrLitTy (hsIPNameFS x)
212 ; ipClass <- tcLookupClass ipClassName
213 ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty])
214 ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var)))
215 ip_ty res_ty }
216 where
217 -- Coerces a dictionary for `IP "x" t` into `t`.
218 fromDict ipClass x ty = mkHsWrap $ mkWpCastR $
219 unwrapIP $ mkClassPred ipClass [x,ty]
220 origin = IPOccOrigin x
221
222 tcExpr e@(HsOverLabel mb_fromLabel l) res_ty
223 = do { -- See Note [Type-checking overloaded labels]
224 loc <- getSrcSpanM
225 ; case mb_fromLabel of
226 Just fromLabel -> tcExpr (applyFromLabel loc fromLabel) res_ty
227 Nothing -> do { isLabelClass <- tcLookupClass isLabelClassName
228 ; alpha <- newFlexiTyVarTy liftedTypeKind
229 ; let pred = mkClassPred isLabelClass [lbl, alpha]
230 ; loc <- getSrcSpanM
231 ; var <- emitWantedEvVar origin pred
232 ; tcWrapResult e (fromDict pred (HsVar (L loc var)))
233 alpha res_ty } }
234 where
235 -- Coerces a dictionary for `IsLabel "x" t` into `t`,
236 -- or `HasField "x" r a into `r -> a`.
237 fromDict pred = mkHsWrap $ mkWpCastR $ unwrapIP pred
238 origin = OverLabelOrigin l
239 lbl = mkStrLitTy l
240
241 applyFromLabel loc fromLabel =
242 L loc (HsVar (L loc fromLabel)) `HsAppType`
243 mkEmptyWildCardBndrs (L loc (HsTyLit (HsStrTy NoSourceText l)))
244
245 tcExpr (HsLam match) res_ty
246 = do { (match', wrap) <- tcMatchLambda herald match_ctxt match res_ty
247 ; return (mkHsWrap wrap (HsLam match')) }
248 where
249 match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody }
250 herald = sep [ text "The lambda expression" <+>
251 quotes (pprSetDepth (PartWay 1) $
252 pprMatches match),
253 -- The pprSetDepth makes the abstraction print briefly
254 text "has"]
255
256 tcExpr e@(HsLamCase matches) res_ty
257 = do { (matches', wrap)
258 <- tcMatchLambda msg match_ctxt matches res_ty
259 -- The laziness annotation is because we don't want to fail here
260 -- if there are multiple arguments
261 ; return (mkHsWrap wrap $ HsLamCase matches') }
262 where
263 msg = sep [ text "The function" <+> quotes (ppr e)
264 , text "requires"]
265 match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
266
267 tcExpr e@(ExprWithTySig expr sig_ty) res_ty
268 = do { let loc = getLoc (hsSigWcType sig_ty)
269 ; sig_info <- checkNoErrs $ -- Avoid error cascade
270 tcUserTypeSig loc sig_ty Nothing
271 ; (expr', poly_ty) <- tcExprSig expr sig_info
272 ; let expr'' = ExprWithTySigOut expr' sig_ty
273 ; tcWrapResult e expr'' poly_ty res_ty }
274
275 {-
276 Note [Type-checking overloaded labels]
277 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
278 Recall that we have
279
280 module GHC.OverloadedLabels where
281 class IsLabel (x :: Symbol) a where
282 fromLabel :: a
283
284 We translate `#foo` to `fromLabel @"foo"`, where we use
285
286 * the in-scope `fromLabel` if `RebindableSyntax` is enabled; or if not
287 * `GHC.OverloadedLabels.fromLabel`.
288
289 In the `RebindableSyntax` case, the renamer will have filled in the
290 first field of `HsOverLabel` with the `fromLabel` function to use, and
291 we simply apply it to the appropriate visible type argument.
292
293 In the `OverloadedLabels` case, when we see an overloaded label like
294 `#foo`, we generate a fresh variable `alpha` for the type and emit an
295 `IsLabel "foo" alpha` constraint. Because the `IsLabel` class has a
296 single method, it is represented by a newtype, so we can coerce
297 `IsLabel "foo" alpha` to `alpha` (just like for implicit parameters).
298
299 -}
300
301
302 {-
303 ************************************************************************
304 * *
305 Infix operators and sections
306 * *
307 ************************************************************************
308
309 Note [Left sections]
310 ~~~~~~~~~~~~~~~~~~~~
311 Left sections, like (4 *), are equivalent to
312 \ x -> (*) 4 x,
313 or, if PostfixOperators is enabled, just
314 (*) 4
315 With PostfixOperators we don't actually require the function to take
316 two arguments at all. For example, (x `not`) means (not x); you get
317 postfix operators! Not Haskell 98, but it's less work and kind of
318 useful.
319
320 Note [Typing rule for ($)]
321 ~~~~~~~~~~~~~~~~~~~~~~~~~~
322 People write
323 runST $ blah
324 so much, where
325 runST :: (forall s. ST s a) -> a
326 that I have finally given in and written a special type-checking
327 rule just for saturated applications of ($).
328 * Infer the type of the first argument
329 * Decompose it; should be of form (arg2_ty -> res_ty),
330 where arg2_ty might be a polytype
331 * Use arg2_ty to typecheck arg2
332
333 Note [Typing rule for seq]
334 ~~~~~~~~~~~~~~~~~~~~~~~~~~
335 We want to allow
336 x `seq` (# p,q #)
337 which suggests this type for seq:
338 seq :: forall (a:*) (b:Open). a -> b -> b,
339 with (b:Open) meaning that be can be instantiated with an unboxed
340 tuple. The trouble is that this might accept a partially-applied
341 'seq', and I'm just not certain that would work. I'm only sure it's
342 only going to work when it's fully applied, so it turns into
343 case x of _ -> (# p,q #)
344
345 So it seems more uniform to treat 'seq' as if it was a language
346 construct.
347
348 See also Note [seqId magic] in MkId
349 -}
350
351 tcExpr expr@(OpApp arg1 op fix arg2) res_ty
352 | (L loc (HsVar (L lv op_name))) <- op
353 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
354 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
355 ; let arg2_exp_ty = res_ty
356 ; arg1' <- tcArg op arg1 arg1_ty 1
357 ; arg2' <- addErrCtxt (funAppCtxt op arg2 2) $
358 tc_poly_expr_nc arg2 arg2_exp_ty
359 ; arg2_ty <- readExpType arg2_exp_ty
360 ; op_id <- tcLookupId op_name
361 ; let op' = L loc (mkHsWrap (mkWpTyApps [arg1_ty, arg2_ty])
362 (HsVar (L lv op_id)))
363 ; return $ OpApp arg1' op' fix arg2' }
364
365 | (L loc (HsVar (L lv op_name))) <- op
366 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
367 = do { traceTc "Application rule" (ppr op)
368 ; (arg1', arg1_ty) <- tcInferSigma arg1
369
370 ; let doc = text "The first argument of ($) takes"
371 orig1 = lexprCtOrigin arg1
372 ; (wrap_arg1, [arg2_sigma], op_res_ty) <-
373 matchActualFunTys doc orig1 (Just (unLoc arg1)) 1 arg1_ty
374
375 -- We have (arg1 $ arg2)
376 -- So: arg1_ty = arg2_ty -> op_res_ty
377 -- where arg2_sigma maybe polymorphic; that's the point
378
379 ; arg2' <- tcArg op arg2 arg2_sigma 2
380
381 -- Make sure that the argument type has kind '*'
382 -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b
383 -- Eg we do not want to allow (D# $ 4.0#) Trac #5570
384 -- (which gives a seg fault)
385 --
386 -- The *result* type can have any kind (Trac #8739),
387 -- so we don't need to check anything for that
388 ; _ <- unifyKind (Just (HsCoreTy arg2_sigma)) (typeKind arg2_sigma) liftedTypeKind
389 -- ignore the evidence. arg2_sigma must have type * or #,
390 -- because we know arg2_sigma -> or_res_ty is well-kinded
391 -- (because otherwise matchActualFunTys would fail)
392 -- There's no possibility here of, say, a kind family reducing to *.
393
394 ; wrap_res <- tcSubTypeHR orig1 (Just expr) op_res_ty res_ty
395 -- op_res -> res
396
397 ; op_id <- tcLookupId op_name
398 ; res_ty <- readExpType res_ty
399 ; let op' = L loc (mkHsWrap (mkWpTyApps [ getRuntimeRep res_ty
400 , arg2_sigma
401 , res_ty])
402 (HsVar (L lv op_id)))
403 -- arg1' :: arg1_ty
404 -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty)
405 -- wrap_res :: op_res_ty "->" res_ty
406 -- op' :: (a2_ty -> res_ty) -> a2_ty -> res_ty
407
408 -- wrap1 :: arg1_ty "->" (arg2_sigma -> res_ty)
409 wrap1 = mkWpFun idHsWrapper wrap_res arg2_sigma res_ty doc
410 <.> wrap_arg1
411 doc = text "When looking at the argument to ($)"
412
413 ; return (OpApp (mkLHsWrap wrap1 arg1') op' fix arg2') }
414
415 | (L loc (HsRecFld (Ambiguous lbl _))) <- op
416 , Just sig_ty <- obviousSig (unLoc arg1)
417 -- See Note [Disambiguating record fields]
418 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
419 ; sel_name <- disambiguateSelector lbl sig_tc_ty
420 ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name))
421 ; tcExpr (OpApp arg1 op' fix arg2) res_ty
422 }
423
424 | otherwise
425 = do { traceTc "Non Application rule" (ppr op)
426 ; (wrap, op', [Left arg1', Left arg2'])
427 <- tcApp (Just $ mk_op_msg op)
428 op [Left arg1, Left arg2] res_ty
429 ; return (mkHsWrap wrap $ OpApp arg1' op' fix arg2') }
430
431 -- Right sections, equivalent to \ x -> x `op` expr, or
432 -- \ x -> op x expr
433
434 tcExpr expr@(SectionR op arg2) res_ty
435 = do { (op', op_ty) <- tcInferFun op
436 ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty)
437 <- matchActualFunTys (mk_op_msg op) fn_orig (Just (unLoc op)) 2 op_ty
438 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
439 (mkFunTy arg1_ty op_res_ty) res_ty
440 ; arg2' <- tcArg op arg2 arg2_ty 2
441 ; return ( mkHsWrap wrap_res $
442 SectionR (mkLHsWrap wrap_fun op') arg2' ) }
443 where
444 fn_orig = lexprCtOrigin op
445 -- It's important to use the origin of 'op', so that call-stacks
446 -- come out right; they are driven by the OccurrenceOf CtOrigin
447 -- See Trac #13285
448
449 tcExpr expr@(SectionL arg1 op) res_ty
450 = do { (op', op_ty) <- tcInferFun op
451 ; dflags <- getDynFlags -- Note [Left sections]
452 ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1
453 | otherwise = 2
454
455 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty)
456 <- matchActualFunTys (mk_op_msg op) fn_orig (Just (unLoc op))
457 n_reqd_args op_ty
458 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
459 (mkFunTys arg_tys op_res_ty) res_ty
460 ; arg1' <- tcArg op arg1 arg1_ty 1
461 ; return ( mkHsWrap wrap_res $
462 SectionL arg1' (mkLHsWrap wrap_fn op') ) }
463 where
464 fn_orig = lexprCtOrigin op
465 -- It's important to use the origin of 'op', so that call-stacks
466 -- come out right; they are driven by the OccurrenceOf CtOrigin
467 -- See Trac #13285
468
469 tcExpr expr@(ExplicitTuple tup_args boxity) res_ty
470 | all tupArgPresent tup_args
471 = do { let arity = length tup_args
472 tup_tc = tupleTyCon boxity arity
473 ; res_ty <- expTypeToType res_ty
474 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
475 -- Unboxed tuples have RuntimeRep vars, which we
476 -- don't care about here
477 -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
478 ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys
479 Boxed -> arg_tys
480 ; tup_args1 <- tcTupArgs tup_args arg_tys'
481 ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
482
483 | otherwise
484 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
485 do { let arity = length tup_args
486
487 ; arg_tys <- case boxity of
488 { Boxed -> newFlexiTyVarTys arity liftedTypeKind
489 ; Unboxed -> replicateM arity newOpenFlexiTyVarTy }
490 ; let actual_res_ty
491 = mkFunTys [ty | (ty, (L _ (Missing _))) <- arg_tys `zip` tup_args]
492 (mkTupleTy boxity arg_tys)
493
494 ; wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "ExpTuple")
495 (Just expr)
496 actual_res_ty res_ty
497
498 -- Handle tuple sections where
499 ; tup_args1 <- tcTupArgs tup_args arg_tys
500
501 ; return $ mkHsWrap wrap (ExplicitTuple tup_args1 boxity) }
502
503 tcExpr (ExplicitSum alt arity expr _) res_ty
504 = do { let sum_tc = sumTyCon arity
505 ; res_ty <- expTypeToType res_ty
506 ; (coi, arg_tys) <- matchExpectedTyConApp sum_tc res_ty
507 ; -- Drop levity vars, we don't care about them here
508 let arg_tys' = drop arity arg_tys
509 ; expr' <- tcPolyExpr expr (arg_tys' `getNth` (alt - 1))
510 ; return $ mkHsWrapCo coi (ExplicitSum alt arity expr' arg_tys') }
511
512 tcExpr (ExplicitList _ witness exprs) res_ty
513 = case witness of
514 Nothing -> do { res_ty <- expTypeToType res_ty
515 ; (coi, elt_ty) <- matchExpectedListTy res_ty
516 ; exprs' <- mapM (tc_elt elt_ty) exprs
517 ; return $
518 mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' }
519
520 Just fln -> do { ((exprs', elt_ty), fln')
521 <- tcSyntaxOp ListOrigin fln
522 [synKnownType intTy, SynList] res_ty $
523 \ [elt_ty] ->
524 do { exprs' <-
525 mapM (tc_elt elt_ty) exprs
526 ; return (exprs', elt_ty) }
527
528 ; return $ ExplicitList elt_ty (Just fln') exprs' }
529 where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
530
531 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
532 = do { res_ty <- expTypeToType res_ty
533 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
534 ; exprs' <- mapM (tc_elt elt_ty) exprs
535 ; return $
536 mkHsWrapCo coi $ ExplicitPArr elt_ty exprs' }
537 where
538 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
539
540 {-
541 ************************************************************************
542 * *
543 Let, case, if, do
544 * *
545 ************************************************************************
546 -}
547
548 tcExpr (HsLet (L l binds) expr) res_ty
549 = do { (binds', expr') <- tcLocalBinds binds $
550 tcMonoExpr expr res_ty
551 ; return (HsLet (L l binds') expr') }
552
553 tcExpr (HsCase scrut matches) res_ty
554 = do { -- We used to typecheck the case alternatives first.
555 -- The case patterns tend to give good type info to use
556 -- when typechecking the scrutinee. For example
557 -- case (map f) of
558 -- (x:xs) -> ...
559 -- will report that map is applied to too few arguments
560 --
561 -- But now, in the GADT world, we need to typecheck the scrutinee
562 -- first, to get type info that may be refined in the case alternatives
563 (scrut', scrut_ty) <- tcInferRho scrut
564
565 ; traceTc "HsCase" (ppr scrut_ty)
566 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
567 ; return (HsCase scrut' matches') }
568 where
569 match_ctxt = MC { mc_what = CaseAlt,
570 mc_body = tcBody }
571
572 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
573 = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy)
574 ; res_ty <- tauifyExpType res_ty
575 -- Just like Note [Case branches must never infer a non-tau type]
576 -- in TcMatches (See #10619)
577
578 ; b1' <- tcMonoExpr b1 res_ty
579 ; b2' <- tcMonoExpr b2 res_ty
580 ; return (HsIf Nothing pred' b1' b2') }
581
582 tcExpr (HsIf (Just fun) pred b1 b2) res_ty
583 = do { ((pred', b1', b2'), fun')
584 <- tcSyntaxOp IfOrigin fun [SynAny, SynAny, SynAny] res_ty $
585 \ [pred_ty, b1_ty, b2_ty] ->
586 do { pred' <- tcPolyExpr pred pred_ty
587 ; b1' <- tcPolyExpr b1 b1_ty
588 ; b2' <- tcPolyExpr b2 b2_ty
589 ; return (pred', b1', b2') }
590 ; return (HsIf (Just fun') pred' b1' b2') }
591
592 tcExpr (HsMultiIf _ alts) res_ty
593 = do { res_ty <- if isSingleton alts
594 then return res_ty
595 else tauifyExpType res_ty
596 -- Just like TcMatches
597 -- Note [Case branches must never infer a non-tau type]
598
599 ; alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
600 ; res_ty <- readExpType res_ty
601 ; return (HsMultiIf res_ty alts') }
602 where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
603
604 tcExpr (HsDo do_or_lc stmts _) res_ty
605 = do { expr' <- tcDoStmts do_or_lc stmts res_ty
606 ; return expr' }
607
608 tcExpr (HsProc pat cmd) res_ty
609 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
610 ; return $ mkHsWrapCo coi (HsProc pat' cmd') }
611
612 -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'.
613 -- See Note [Grand plan for static forms] in StaticPtrTable for an overview.
614 -- To type check
615 -- (static e) :: p a
616 -- we want to check (e :: a),
617 -- and wrap (static e) in a call to
618 -- fromStaticPtr :: IsStatic p => StaticPtr a -> p a
619
620 tcExpr (HsStatic fvs expr) res_ty
621 = do { res_ty <- expTypeToType res_ty
622 ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty
623 ; (expr', lie) <- captureConstraints $
624 addErrCtxt (hang (text "In the body of a static form:")
625 2 (ppr expr)
626 ) $
627 tcPolyExprNC expr expr_ty
628
629 -- Check that the free variables of the static form are closed.
630 -- It's OK to use nonDetEltsUniqSet here as the only side effects of
631 -- checkClosedInStaticForm are error messages.
632 ; mapM_ checkClosedInStaticForm $ nonDetEltsUniqSet fvs
633
634 -- Require the type of the argument to be Typeable.
635 -- The evidence is not used, but asking the constraint ensures that
636 -- the current implementation is as restrictive as future versions
637 -- of the StaticPointers extension.
638 ; typeableClass <- tcLookupClass typeableClassName
639 ; _ <- emitWantedEvVar StaticOrigin $
640 mkTyConApp (classTyCon typeableClass)
641 [liftedTypeKind, expr_ty]
642
643 -- Insert the constraints of the static form in a global list for later
644 -- validation.
645 ; emitStaticConstraints lie
646
647 -- Wrap the static form with the 'fromStaticPtr' call.
648 ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty
649 ; let wrap = mkWpTyApps [expr_ty]
650 ; loc <- getSrcSpanM
651 ; return $ mkHsWrapCo co $ HsApp (L loc $ mkHsWrap wrap fromStaticPtr)
652 (L loc (HsStatic fvs expr'))
653 }
654
655 {-
656 ************************************************************************
657 * *
658 Record construction and update
659 * *
660 ************************************************************************
661 -}
662
663 tcExpr expr@(RecordCon { rcon_con_name = L loc con_name
664 , rcon_flds = rbinds }) res_ty
665 = do { con_like <- tcLookupConLike con_name
666
667 -- Check for missing fields
668 ; checkMissingFields con_like rbinds
669
670 ; (con_expr, con_sigma) <- tcInferId con_name
671 ; (con_wrap, con_tau) <-
672 topInstantiate (OccurrenceOf con_name) con_sigma
673 -- a shallow instantiation should really be enough for
674 -- a data constructor.
675 ; let arity = conLikeArity con_like
676 Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau
677 ; case conLikeWrapId_maybe con_like of
678 Nothing -> nonBidirectionalErr (conLikeName con_like)
679 Just con_id -> do {
680 res_wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "RecordCon")
681 (Just expr) actual_res_ty res_ty
682 ; rbinds' <- tcRecordBinds con_like arg_tys rbinds
683 ; return $
684 mkHsWrap res_wrap $
685 RecordCon { rcon_con_name = L loc con_id
686 , rcon_con_expr = mkHsWrap con_wrap con_expr
687 , rcon_con_like = con_like
688 , rcon_flds = rbinds' } } }
689
690 {-
691 Note [Type of a record update]
692 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
693 The main complication with RecordUpd is that we need to explicitly
694 handle the *non-updated* fields. Consider:
695
696 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
697 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
698 | MkT3 { fd :: a }
699
700 upd :: T a b c -> (b',c) -> T a b' c
701 upd t x = t { fb = x}
702
703 The result type should be (T a b' c)
704 not (T a b c), because 'b' *is not* mentioned in a non-updated field
705 not (T a b' c'), because 'c' *is* mentioned in a non-updated field
706 NB that it's not good enough to look at just one constructor; we must
707 look at them all; cf Trac #3219
708
709 After all, upd should be equivalent to:
710 upd t x = case t of
711 MkT1 p q -> MkT1 p x
712 MkT2 a b -> MkT2 p b
713 MkT3 d -> error ...
714
715 So we need to give a completely fresh type to the result record,
716 and then constrain it by the fields that are *not* updated ("p" above).
717 We call these the "fixed" type variables, and compute them in getFixedTyVars.
718
719 Note that because MkT3 doesn't contain all the fields being updated,
720 its RHS is simply an error, so it doesn't impose any type constraints.
721 Hence the use of 'relevant_cont'.
722
723 Note [Implicit type sharing]
724 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
725 We also take into account any "implicit" non-update fields. For example
726 data T a b where { MkT { f::a } :: T a a; ... }
727 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
728
729 Then consider
730 upd t x = t { f=x }
731 We infer the type
732 upd :: T a b -> a -> T a b
733 upd (t::T a b) (x::a)
734 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
735 We can't give it the more general type
736 upd :: T a b -> c -> T c b
737
738 Note [Criteria for update]
739 ~~~~~~~~~~~~~~~~~~~~~~~~~~
740 We want to allow update for existentials etc, provided the updated
741 field isn't part of the existential. For example, this should be ok.
742 data T a where { MkT { f1::a, f2::b->b } :: T a }
743 f :: T a -> b -> T b
744 f t b = t { f1=b }
745
746 The criterion we use is this:
747
748 The types of the updated fields
749 mention only the universally-quantified type variables
750 of the data constructor
751
752 NB: this is not (quite) the same as being a "naughty" record selector
753 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
754 in the case of GADTs. Consider
755 data T a where { MkT :: { f :: a } :: T [a] }
756 Then f is not "naughty" because it has a well-typed record selector.
757 But we don't allow updates for 'f'. (One could consider trying to
758 allow this, but it makes my head hurt. Badly. And no one has asked
759 for it.)
760
761 In principle one could go further, and allow
762 g :: T a -> T a
763 g t = t { f2 = \x -> x }
764 because the expression is polymorphic...but that seems a bridge too far.
765
766 Note [Data family example]
767 ~~~~~~~~~~~~~~~~~~~~~~~~~~
768 data instance T (a,b) = MkT { x::a, y::b }
769 --->
770 data :TP a b = MkT { a::a, y::b }
771 coTP a b :: T (a,b) ~ :TP a b
772
773 Suppose r :: T (t1,t2), e :: t3
774 Then r { x=e } :: T (t3,t1)
775 --->
776 case r |> co1 of
777 MkT x y -> MkT e y |> co2
778 where co1 :: T (t1,t2) ~ :TP t1 t2
779 co2 :: :TP t3 t2 ~ T (t3,t2)
780 The wrapping with co2 is done by the constructor wrapper for MkT
781
782 Outgoing invariants
783 ~~~~~~~~~~~~~~~~~~~
784 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
785
786 * cons are the data constructors to be updated
787
788 * in_inst_tys, out_inst_tys have same length, and instantiate the
789 *representation* tycon of the data cons. In Note [Data
790 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
791
792 Note [Mixed Record Field Updates]
793 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
794 Consider the following pattern synonym.
795
796 data MyRec = MyRec { foo :: Int, qux :: String }
797
798 pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}
799
800 This allows updates such as the following
801
802 updater :: MyRec -> MyRec
803 updater a = a {f1 = 1 }
804
805 It would also make sense to allow the following update (which we reject).
806
807 updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"
808
809 This leads to confusing behaviour when the selectors in fact refer the same
810 field.
811
812 updater a = a {f1 = 1, foo = 2} ==? ???
813
814 For this reason, we reject a mixture of pattern synonym and normal record
815 selectors in the same update block. Although of course we still allow the
816 following.
817
818 updater a = (a {f1 = 1}) {foo = 2}
819
820 > updater (MyRec 0 "str")
821 MyRec 2 "str"
822
823 -}
824
825 tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty
826 = ASSERT( notNull rbnds )
827 do { -- STEP -2: typecheck the record_expr, the record to be updated
828 (record_expr', record_rho) <- tcInferRho record_expr
829
830 -- STEP -1 See Note [Disambiguating record fields]
831 -- After this we know that rbinds is unambiguous
832 ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty
833 ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds
834 upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds
835 sel_ids = map selectorAmbiguousFieldOcc upd_flds
836 -- STEP 0
837 -- Check that the field names are really field names
838 -- and they are all field names for proper records or
839 -- all field names for pattern synonyms.
840 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
841 | fld <- rbinds,
842 -- Excludes class ops
843 let L loc sel_id = hsRecUpdFieldId (unLoc fld),
844 not (isRecordSelector sel_id),
845 let fld_name = idName sel_id ]
846 ; unless (null bad_guys) (sequence bad_guys >> failM)
847 -- See note [Mixed Record Selectors]
848 ; let (data_sels, pat_syn_sels) =
849 partition isDataConRecordSelector sel_ids
850 ; MASSERT( all isPatSynRecordSelector pat_syn_sels )
851 ; checkTc ( null data_sels || null pat_syn_sels )
852 ( mixedSelectors data_sels pat_syn_sels )
853
854 -- STEP 1
855 -- Figure out the tycon and data cons from the first field name
856 ; let -- It's OK to use the non-tc splitters here (for a selector)
857 sel_id : _ = sel_ids
858
859 mtycon :: Maybe TyCon
860 mtycon = case idDetails sel_id of
861 RecSelId (RecSelData tycon) _ -> Just tycon
862 _ -> Nothing
863
864 con_likes :: [ConLike]
865 con_likes = case idDetails sel_id of
866 RecSelId (RecSelData tc) _
867 -> map RealDataCon (tyConDataCons tc)
868 RecSelId (RecSelPatSyn ps) _
869 -> [PatSynCon ps]
870 _ -> panic "tcRecordUpd"
871 -- NB: for a data type family, the tycon is the instance tycon
872
873 relevant_cons = conLikesWithFields con_likes upd_fld_occs
874 -- A constructor is only relevant to this process if
875 -- it contains *all* the fields that are being updated
876 -- Other ones will cause a runtime error if they occur
877
878 -- Step 2
879 -- Check that at least one constructor has all the named fields
880 -- i.e. has an empty set of bad fields returned by badFields
881 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes)
882
883 -- Take apart a representative constructor
884 ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
885 (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _)
886 = conLikeFullSig con1
887 con1_flds = map flLabel $ conLikeFieldLabels con1
888 con1_tv_tys = mkTyVarTys con1_tvs
889 con1_res_ty = case mtycon of
890 Just tc -> mkFamilyTyConApp tc con1_tv_tys
891 Nothing -> conLikeResTy con1 con1_tv_tys
892
893 -- Check that we're not dealing with a unidirectional pattern
894 -- synonym
895 ; unless (isJust $ conLikeWrapId_maybe con1)
896 (nonBidirectionalErr (conLikeName con1))
897
898 -- STEP 3 Note [Criteria for update]
899 -- Check that each updated field is polymorphic; that is, its type
900 -- mentions only the universally-quantified variables of the data con
901 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
902 bad_upd_flds = filter bad_fld flds1_w_tys
903 con1_tv_set = mkVarSet con1_tvs
904 bad_fld (fld, ty) = fld `elem` upd_fld_occs &&
905 not (tyCoVarsOfType ty `subVarSet` con1_tv_set)
906 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
907
908 -- STEP 4 Note [Type of a record update]
909 -- Figure out types for the scrutinee and result
910 -- Both are of form (T a b c), with fresh type variables, but with
911 -- common variables where the scrutinee and result must have the same type
912 -- These are variables that appear in *any* arg of *any* of the
913 -- relevant constructors *except* in the updated fields
914 --
915 ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons
916 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
917
918 mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType)
919 -- Deals with instantiation of kind variables
920 -- c.f. TcMType.newMetaTyVars
921 mk_inst_ty subst (tv, result_inst_ty)
922 | is_fixed_tv tv -- Same as result type
923 = return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
924 | otherwise -- Fresh type, of correct kind
925 = do { (subst', new_tv) <- newMetaTyVarX subst tv
926 ; return (subst', mkTyVarTy new_tv) }
927
928 ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs
929 ; let result_inst_tys = mkTyVarTys con1_tvs'
930 init_subst = mkEmptyTCvSubst (getTCvInScope result_subst)
931
932 ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst
933 (con1_tvs `zip` result_inst_tys)
934
935 ; let rec_res_ty = TcType.substTy result_subst con1_res_ty
936 scrut_ty = TcType.substTy scrut_subst con1_res_ty
937 con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
938
939 ; wrap_res <- tcSubTypeHR (exprCtOrigin expr)
940 (Just expr) rec_res_ty res_ty
941 ; co_scrut <- unifyType (Just (unLoc record_expr)) record_rho scrut_ty
942 -- NB: normal unification is OK here (as opposed to subsumption),
943 -- because for this to work out, both record_rho and scrut_ty have
944 -- to be normal datatypes -- no contravariant stuff can go on
945
946 -- STEP 5
947 -- Typecheck the bindings
948 ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds
949
950 -- STEP 6: Deal with the stupid theta
951 ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1)
952 ; instStupidTheta RecordUpdOrigin theta'
953
954 -- Step 7: make a cast for the scrutinee, in the
955 -- case that it's from a data family
956 ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty
957 fam_co | Just tycon <- mtycon
958 , Just co_con <- tyConFamilyCoercion_maybe tycon
959 = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys [])
960 | otherwise
961 = idHsWrapper
962
963 -- Step 8: Check that the req constraints are satisfied
964 -- For normal data constructors req_theta is empty but we must do
965 -- this check for pattern synonyms.
966 ; let req_theta' = substThetaUnchecked scrut_subst req_theta
967 ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta'
968
969 -- Phew!
970 ; return $
971 mkHsWrap wrap_res $
972 RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr')
973 , rupd_flds = rbinds'
974 , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys
975 , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } }
976
977 tcExpr e@(HsRecFld f) res_ty
978 = tcCheckRecSelId e f res_ty
979
980 {-
981 ************************************************************************
982 * *
983 Arithmetic sequences e.g. [a,b..]
984 and their parallel-array counterparts e.g. [: a,b.. :]
985
986 * *
987 ************************************************************************
988 -}
989
990 tcExpr (ArithSeq _ witness seq) res_ty
991 = tcArithSeq witness seq res_ty
992
993 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
994 = do { res_ty <- expTypeToType res_ty
995 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
996 ; expr1' <- tcPolyExpr expr1 elt_ty
997 ; expr2' <- tcPolyExpr expr2 elt_ty
998 ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
999 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
1000 (idName enumFromToP) elt_ty
1001 ; return $
1002 mkHsWrapCo coi $ PArrSeq enum_from_to (FromTo expr1' expr2') }
1003
1004 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
1005 = do { res_ty <- expTypeToType res_ty
1006 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
1007 ; expr1' <- tcPolyExpr expr1 elt_ty
1008 ; expr2' <- tcPolyExpr expr2 elt_ty
1009 ; expr3' <- tcPolyExpr expr3 elt_ty
1010 ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
1011 ; eft <- newMethodFromName (PArrSeqOrigin seq)
1012 (idName enumFromThenToP) elt_ty -- !!!FIXME: chak
1013 ; return $
1014 mkHsWrapCo coi $
1015 PArrSeq eft (FromThenTo expr1' expr2' expr3') }
1016
1017 tcExpr (PArrSeq _ _) _
1018 = panic "TcExpr.tcExpr: Infinite parallel array!"
1019 -- the parser shouldn't have generated it and the renamer shouldn't have
1020 -- let it through
1021
1022 {-
1023 ************************************************************************
1024 * *
1025 Template Haskell
1026 * *
1027 ************************************************************************
1028 -}
1029
1030 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceExpr'.
1031 -- Here we get rid of it and add the finalizers to the global environment.
1032 --
1033 -- See Note [Delaying modFinalizers in untyped splices] in RnSplice.
1034 tcExpr (HsSpliceE (HsSpliced mod_finalizers (HsSplicedExpr expr)))
1035 res_ty
1036 = do addModFinalizersWithLclEnv mod_finalizers
1037 tcExpr expr res_ty
1038 tcExpr (HsSpliceE splice) res_ty
1039 = tcSpliceExpr splice res_ty
1040 tcExpr e@(HsBracket brack) res_ty
1041 = tcTypedBracket e brack res_ty
1042 tcExpr e@(HsRnBracketOut brack ps) res_ty
1043 = tcUntypedBracket e brack ps res_ty
1044
1045 {-
1046 ************************************************************************
1047 * *
1048 Catch-all
1049 * *
1050 ************************************************************************
1051 -}
1052
1053 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
1054 -- Include ArrForm, ArrApp, which shouldn't appear at all
1055 -- Also HsTcBracketOut, HsQuasiQuoteE
1056
1057 {-
1058 ************************************************************************
1059 * *
1060 Arithmetic sequences [a..b] etc
1061 * *
1062 ************************************************************************
1063 -}
1064
1065 tcArithSeq :: Maybe (SyntaxExpr GhcRn) -> ArithSeqInfo GhcRn -> ExpRhoType
1066 -> TcM (HsExpr GhcTcId)
1067
1068 tcArithSeq witness seq@(From expr) res_ty
1069 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1070 ; expr' <- tcPolyExpr expr elt_ty
1071 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
1072 enumFromName elt_ty
1073 ; return $ mkHsWrap wrap $
1074 ArithSeq enum_from wit' (From expr') }
1075
1076 tcArithSeq witness seq@(FromThen expr1 expr2) res_ty
1077 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1078 ; expr1' <- tcPolyExpr expr1 elt_ty
1079 ; expr2' <- tcPolyExpr expr2 elt_ty
1080 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
1081 enumFromThenName elt_ty
1082 ; return $ mkHsWrap wrap $
1083 ArithSeq enum_from_then wit' (FromThen expr1' expr2') }
1084
1085 tcArithSeq witness seq@(FromTo expr1 expr2) res_ty
1086 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1087 ; expr1' <- tcPolyExpr expr1 elt_ty
1088 ; expr2' <- tcPolyExpr expr2 elt_ty
1089 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
1090 enumFromToName elt_ty
1091 ; return $ mkHsWrap wrap $
1092 ArithSeq enum_from_to wit' (FromTo expr1' expr2') }
1093
1094 tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty
1095 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1096 ; expr1' <- tcPolyExpr expr1 elt_ty
1097 ; expr2' <- tcPolyExpr expr2 elt_ty
1098 ; expr3' <- tcPolyExpr expr3 elt_ty
1099 ; eft <- newMethodFromName (ArithSeqOrigin seq)
1100 enumFromThenToName elt_ty
1101 ; return $ mkHsWrap wrap $
1102 ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') }
1103
1104 -----------------
1105 arithSeqEltType :: Maybe (SyntaxExpr GhcRn) -> ExpRhoType
1106 -> TcM (HsWrapper, TcType, Maybe (SyntaxExpr GhcTc))
1107 arithSeqEltType Nothing res_ty
1108 = do { res_ty <- expTypeToType res_ty
1109 ; (coi, elt_ty) <- matchExpectedListTy res_ty
1110 ; return (mkWpCastN coi, elt_ty, Nothing) }
1111 arithSeqEltType (Just fl) res_ty
1112 = do { (elt_ty, fl')
1113 <- tcSyntaxOp ListOrigin fl [SynList] res_ty $
1114 \ [elt_ty] -> return elt_ty
1115 ; return (idHsWrapper, elt_ty, Just fl') }
1116
1117 {-
1118 ************************************************************************
1119 * *
1120 Applications
1121 * *
1122 ************************************************************************
1123 -}
1124
1125 type LHsExprArgIn = Either (LHsExpr GhcRn) (LHsWcType GhcRn)
1126 type LHsExprArgOut = Either (LHsExpr GhcTcId) (LHsWcType GhcRn)
1127 -- Left e => argument expression
1128 -- Right ty => visible type application
1129
1130 tcApp1 :: HsExpr GhcRn -- either HsApp or HsAppType
1131 -> ExpRhoType -> TcM (HsExpr GhcTcId)
1132 tcApp1 e res_ty
1133 = do { (wrap, fun, args) <- tcApp Nothing (noLoc e) [] res_ty
1134 ; return (mkHsWrap wrap $ unLoc $ foldl mk_hs_app fun args) }
1135 where
1136 mk_hs_app f (Left a) = mkHsApp f a
1137 mk_hs_app f (Right a) = mkHsAppTypeOut f a
1138
1139 tcApp :: Maybe SDoc -- like "The function `f' is applied to"
1140 -- or leave out to get exactly that message
1141 -> LHsExpr GhcRn -> [LHsExprArgIn] -- Function and args
1142 -> ExpRhoType -> TcM (HsWrapper, LHsExpr GhcTcId, [LHsExprArgOut])
1143 -- (wrap, fun, args). For an ordinary function application,
1144 -- these should be assembled as (wrap (fun args)).
1145 -- But OpApp is slightly different, so that's why the caller
1146 -- must assemble
1147
1148 tcApp m_herald orig_fun orig_args res_ty
1149 = go orig_fun orig_args
1150 where
1151 go :: LHsExpr GhcRn -> [LHsExprArgIn]
1152 -> TcM (HsWrapper, LHsExpr GhcTcId, [LHsExprArgOut])
1153 go (L _ (HsPar e)) args = go e args
1154 go (L _ (HsApp e1 e2)) args = go e1 (Left e2:args)
1155 go (L _ (HsAppType e t)) args = go e (Right t:args)
1156
1157 go (L loc (HsVar (L _ fun))) args
1158 | fun `hasKey` tagToEnumKey
1159 , count isLeft args == 1
1160 = do { (wrap, expr, args) <- tcTagToEnum loc fun args res_ty
1161 ; return (wrap, expr, args) }
1162
1163 | fun `hasKey` seqIdKey
1164 , count isLeft args == 2
1165 = do { (wrap, expr, args) <- tcSeq loc fun args res_ty
1166 ; return (wrap, expr, args) }
1167
1168 go (L loc (HsRecFld (Ambiguous lbl _))) args@(Left (L _ arg) : _)
1169 | Just sig_ty <- obviousSig arg
1170 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
1171 ; sel_name <- disambiguateSelector lbl sig_tc_ty
1172 ; go (L loc (HsRecFld (Unambiguous lbl sel_name))) args }
1173
1174 -- See Note [Visible type application for the empty list constructor]
1175 go (L loc (ExplicitList _ Nothing [])) [Right ty_arg]
1176 = do { ty_arg' <- tcHsTypeApp ty_arg liftedTypeKind
1177 ; let list_ty = TyConApp listTyCon [ty_arg']
1178 ; _ <- tcSubTypeDS (OccurrenceOf nilDataConName) GenSigCtxt
1179 list_ty res_ty
1180 ; let expr :: LHsExpr GhcTcId
1181 expr = L loc $ ExplicitList ty_arg' Nothing []
1182 ; return (idHsWrapper, expr, []) }
1183
1184 go fun args
1185 = do { -- Type-check the function
1186 ; (fun1, fun_sigma) <- tcInferFun fun
1187 ; let orig = lexprCtOrigin fun
1188
1189 ; (wrap_fun, args1, actual_res_ty)
1190 <- tcArgs fun fun_sigma orig args
1191 (m_herald `orElse` mk_app_msg fun args)
1192
1193 -- this is just like tcWrapResult, but the types don't line
1194 -- up to call that function
1195 ; wrap_res <- addFunResCtxt True (unLoc fun) actual_res_ty res_ty $
1196 tcSubTypeDS_NC_O orig GenSigCtxt
1197 (Just $ unLoc $ foldl mk_hs_app fun args)
1198 actual_res_ty res_ty
1199
1200 ; return (wrap_res, mkLHsWrap wrap_fun fun1, args1) }
1201
1202 mk_hs_app f (Left a) = mkHsApp f a
1203 mk_hs_app f (Right a) = mkHsAppType f a
1204
1205 mk_app_msg :: LHsExpr GhcRn -> [LHsExprArgIn] -> SDoc
1206 mk_app_msg fun args = sep [ text "The" <+> text what <+> quotes (ppr expr)
1207 , text "is applied to"]
1208 where
1209 what | null type_app_args = "function"
1210 | otherwise = "expression"
1211 -- Include visible type arguments (but not other arguments) in the herald.
1212 -- See Note [Herald for matchExpectedFunTys] in TcUnify.
1213 expr = mkHsAppTypes fun type_app_args
1214 type_app_args = rights args
1215
1216 mk_op_msg :: LHsExpr GhcRn -> SDoc
1217 mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes"
1218
1219 {-
1220 Note [Visible type application for the empty list constructor]
1221 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1222 Getting the expression [] @Int to typecheck is slightly tricky since [] isn't
1223 an ordinary data constructor. By default, when tcExpr typechecks a list
1224 expression, it wraps the expression in a coercion, which gives it a type to the
1225 effect of p[a]. It isn't until later zonking that the type becomes
1226 forall a. [a], but that's too late for visible type application.
1227
1228 The workaround is to check for empty list expressions that have a visible type
1229 argument in tcApp, and if so, directly typecheck [] @ty data constructor name.
1230 This avoids the intermediate coercion and produces an expression of type [ty],
1231 as one would intuitively expect.
1232
1233 Unfortunately, this workaround isn't terribly robust, since more involved
1234 expressions such as (let in []) @Int won't work. Until a more elegant fix comes
1235 along, however, this at least allows direct type application on [] to work,
1236 which is better than before.
1237 -}
1238
1239 ----------------
1240 tcInferFun :: LHsExpr GhcRn -> TcM (LHsExpr GhcTcId, TcSigmaType)
1241 -- Infer type of a function
1242 tcInferFun (L loc (HsVar (L _ name)))
1243 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
1244 -- Don't wrap a context around a plain Id
1245 ; return (L loc fun, ty) }
1246
1247 tcInferFun (L loc (HsRecFld f))
1248 = do { (fun, ty) <- setSrcSpan loc (tcInferRecSelId f)
1249 -- Don't wrap a context around a plain Id
1250 ; return (L loc fun, ty) }
1251
1252 tcInferFun fun
1253 = tcInferSigma fun
1254 -- NB: tcInferSigma; see TcUnify
1255 -- Note [Deep instantiation of InferResult]
1256
1257
1258 ----------------
1259 -- | Type-check the arguments to a function, possibly including visible type
1260 -- applications
1261 tcArgs :: LHsExpr GhcRn -- ^ The function itself (for err msgs only)
1262 -> TcSigmaType -- ^ the (uninstantiated) type of the function
1263 -> CtOrigin -- ^ the origin for the function's type
1264 -> [LHsExprArgIn] -- ^ the args
1265 -> SDoc -- ^ the herald for matchActualFunTys
1266 -> TcM (HsWrapper, [LHsExprArgOut], TcSigmaType)
1267 -- ^ (a wrapper for the function, the tc'd args, result type)
1268 tcArgs fun orig_fun_ty fun_orig orig_args herald
1269 = go [] 1 orig_fun_ty orig_args
1270 where
1271 -- Don't count visible type arguments when determining how many arguments
1272 -- an expression is given in an arity mismatch error, since visible type
1273 -- arguments reported as a part of the expression herald itself.
1274 -- See Note [Herald for matchExpectedFunTys] in TcUnify.
1275 orig_expr_args_arity = length $ lefts orig_args
1276
1277 go _ _ fun_ty [] = return (idHsWrapper, [], fun_ty)
1278
1279 go acc_args n fun_ty (Right hs_ty_arg:args)
1280 = do { (wrap1, upsilon_ty) <- topInstantiateInferred fun_orig fun_ty
1281 -- wrap1 :: fun_ty "->" upsilon_ty
1282 ; case tcSplitForAllTy_maybe upsilon_ty of
1283 Just (tvb, inner_ty) ->
1284 do { let tv = binderVar tvb
1285 vis = binderArgFlag tvb
1286 kind = tyVarKind tv
1287 ; MASSERT2( vis == Specified
1288 , (vcat [ ppr fun_ty, ppr upsilon_ty, ppr tvb
1289 , ppr inner_ty, pprTyVar tv
1290 , ppr vis ]) )
1291 ; ty_arg <- tcHsTypeApp hs_ty_arg kind
1292 ; let insted_ty = substTyWithUnchecked [tv] [ty_arg] inner_ty
1293 ; (inner_wrap, args', res_ty)
1294 <- go acc_args (n+1) insted_ty args
1295 -- inner_wrap :: insted_ty "->" (map typeOf args') -> res_ty
1296 ; let inst_wrap = mkWpTyApps [ty_arg]
1297 ; return ( inner_wrap <.> inst_wrap <.> wrap1
1298 , Right hs_ty_arg : args'
1299 , res_ty ) }
1300 _ -> ty_app_err upsilon_ty hs_ty_arg }
1301
1302 go acc_args n fun_ty (Left arg : args)
1303 = do { (wrap, [arg_ty], res_ty)
1304 <- matchActualFunTysPart herald fun_orig (Just (unLoc fun)) 1 fun_ty
1305 acc_args orig_expr_args_arity
1306 -- wrap :: fun_ty "->" arg_ty -> res_ty
1307 ; arg' <- tcArg fun arg arg_ty n
1308 ; (inner_wrap, args', inner_res_ty)
1309 <- go (arg_ty : acc_args) (n+1) res_ty args
1310 -- inner_wrap :: res_ty "->" (map typeOf args') -> inner_res_ty
1311 ; return ( mkWpFun idHsWrapper inner_wrap arg_ty res_ty doc <.> wrap
1312 , Left arg' : args'
1313 , inner_res_ty ) }
1314 where
1315 doc = text "When checking the" <+> speakNth n <+>
1316 text "argument to" <+> quotes (ppr fun)
1317
1318 ty_app_err ty arg
1319 = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty
1320 ; failWith $
1321 text "Cannot apply expression of type" <+> quotes (ppr ty) $$
1322 text "to a visible type argument" <+> quotes (ppr arg) }
1323
1324 ----------------
1325 tcArg :: LHsExpr GhcRn -- The function (for error messages)
1326 -> LHsExpr GhcRn -- Actual arguments
1327 -> TcRhoType -- expected arg type
1328 -> Int -- # of argument
1329 -> TcM (LHsExpr GhcTcId) -- Resulting argument
1330 tcArg fun arg ty arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $
1331 tcPolyExprNC arg ty
1332
1333 ----------------
1334 tcTupArgs :: [LHsTupArg GhcRn] -> [TcSigmaType] -> TcM [LHsTupArg GhcTcId]
1335 tcTupArgs args tys
1336 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
1337 where
1338 go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty))
1339 go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
1340 ; return (L l (Present expr')) }
1341
1342 ---------------------------
1343 -- See TcType.SyntaxOpType also for commentary
1344 tcSyntaxOp :: CtOrigin
1345 -> SyntaxExpr GhcRn
1346 -> [SyntaxOpType] -- ^ shape of syntax operator arguments
1347 -> ExpRhoType -- ^ overall result type
1348 -> ([TcSigmaType] -> TcM a) -- ^ Type check any arguments
1349 -> TcM (a, SyntaxExpr GhcTcId)
1350 -- ^ Typecheck a syntax operator
1351 -- The operator is always a variable at this stage (i.e. renamer output)
1352 tcSyntaxOp orig expr arg_tys res_ty
1353 = tcSyntaxOpGen orig expr arg_tys (SynType res_ty)
1354
1355 -- | Slightly more general version of 'tcSyntaxOp' that allows the caller
1356 -- to specify the shape of the result of the syntax operator
1357 tcSyntaxOpGen :: CtOrigin
1358 -> SyntaxExpr GhcRn
1359 -> [SyntaxOpType]
1360 -> SyntaxOpType
1361 -> ([TcSigmaType] -> TcM a)
1362 -> TcM (a, SyntaxExpr GhcTcId)
1363 tcSyntaxOpGen orig (SyntaxExpr { syn_expr = HsVar (L _ op) })
1364 arg_tys res_ty thing_inside
1365 = do { (expr, sigma) <- tcInferId op
1366 ; (result, expr_wrap, arg_wraps, res_wrap)
1367 <- tcSynArgA orig sigma arg_tys res_ty $
1368 thing_inside
1369 ; return (result, SyntaxExpr { syn_expr = mkHsWrap expr_wrap expr
1370 , syn_arg_wraps = arg_wraps
1371 , syn_res_wrap = res_wrap }) }
1372
1373 tcSyntaxOpGen _ other _ _ _ = pprPanic "tcSyntaxOp" (ppr other)
1374
1375 {-
1376 Note [tcSynArg]
1377 ~~~~~~~~~~~~~~~
1378 Because of the rich structure of SyntaxOpType, we must do the
1379 contra-/covariant thing when working down arrows, to get the
1380 instantiation vs. skolemisation decisions correct (and, more
1381 obviously, the orientation of the HsWrappers). We thus have
1382 two tcSynArgs.
1383 -}
1384
1385 -- works on "expected" types, skolemising where necessary
1386 -- See Note [tcSynArg]
1387 tcSynArgE :: CtOrigin
1388 -> TcSigmaType
1389 -> SyntaxOpType -- ^ shape it is expected to have
1390 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1391 -> TcM (a, HsWrapper)
1392 -- ^ returns a wrapper :: (type of right shape) "->" (type passed in)
1393 tcSynArgE orig sigma_ty syn_ty thing_inside
1394 = do { (skol_wrap, (result, ty_wrapper))
1395 <- tcSkolemise GenSigCtxt sigma_ty $ \ _ rho_ty ->
1396 go rho_ty syn_ty
1397 ; return (result, skol_wrap <.> ty_wrapper) }
1398 where
1399 go rho_ty SynAny
1400 = do { result <- thing_inside [rho_ty]
1401 ; return (result, idHsWrapper) }
1402
1403 go rho_ty SynRho -- same as SynAny, because we skolemise eagerly
1404 = do { result <- thing_inside [rho_ty]
1405 ; return (result, idHsWrapper) }
1406
1407 go rho_ty SynList
1408 = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty
1409 ; result <- thing_inside [elt_ty]
1410 ; return (result, mkWpCastN list_co) }
1411
1412 go rho_ty (SynFun arg_shape res_shape)
1413 = do { ( ( ( (result, arg_ty, res_ty)
1414 , res_wrapper ) -- :: res_ty_out "->" res_ty
1415 , arg_wrapper1, [], arg_wrapper2 ) -- :: arg_ty "->" arg_ty_out
1416 , match_wrapper ) -- :: (arg_ty -> res_ty) "->" rho_ty
1417 <- matchExpectedFunTys herald 1 (mkCheckExpType rho_ty) $
1418 \ [arg_ty] res_ty ->
1419 do { arg_tc_ty <- expTypeToType arg_ty
1420 ; res_tc_ty <- expTypeToType res_ty
1421
1422 -- another nested arrow is too much for now,
1423 -- but I bet we'll never need this
1424 ; MASSERT2( case arg_shape of
1425 SynFun {} -> False;
1426 _ -> True
1427 , text "Too many nested arrows in SyntaxOpType" $$
1428 pprCtOrigin orig )
1429
1430 ; tcSynArgA orig arg_tc_ty [] arg_shape $
1431 \ arg_results ->
1432 tcSynArgE orig res_tc_ty res_shape $
1433 \ res_results ->
1434 do { result <- thing_inside (arg_results ++ res_results)
1435 ; return (result, arg_tc_ty, res_tc_ty) }}
1436
1437 ; return ( result
1438 , match_wrapper <.>
1439 mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper
1440 arg_ty res_ty doc ) }
1441 where
1442 herald = text "This rebindable syntax expects a function with"
1443 doc = text "When checking a rebindable syntax operator arising from" <+> ppr orig
1444
1445 go rho_ty (SynType the_ty)
1446 = do { wrap <- tcSubTypeET orig GenSigCtxt the_ty rho_ty
1447 ; result <- thing_inside []
1448 ; return (result, wrap) }
1449
1450 -- works on "actual" types, instantiating where necessary
1451 -- See Note [tcSynArg]
1452 tcSynArgA :: CtOrigin
1453 -> TcSigmaType
1454 -> [SyntaxOpType] -- ^ argument shapes
1455 -> SyntaxOpType -- ^ result shape
1456 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1457 -> TcM (a, HsWrapper, [HsWrapper], HsWrapper)
1458 -- ^ returns a wrapper to be applied to the original function,
1459 -- wrappers to be applied to arguments
1460 -- and a wrapper to be applied to the overall expression
1461 tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside
1462 = do { (match_wrapper, arg_tys, res_ty)
1463 <- matchActualFunTys herald orig Nothing (length arg_shapes) sigma_ty
1464 -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty)
1465 ; ((result, res_wrapper), arg_wrappers)
1466 <- tc_syn_args_e arg_tys arg_shapes $ \ arg_results ->
1467 tc_syn_arg res_ty res_shape $ \ res_results ->
1468 thing_inside (arg_results ++ res_results)
1469 ; return (result, match_wrapper, arg_wrappers, res_wrapper) }
1470 where
1471 herald = text "This rebindable syntax expects a function with"
1472
1473 tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType]
1474 -> ([TcSigmaType] -> TcM a)
1475 -> TcM (a, [HsWrapper])
1476 -- the wrappers are for arguments
1477 tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside
1478 = do { ((result, arg_wraps), arg_wrap)
1479 <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results ->
1480 tc_syn_args_e arg_tys arg_shapes $ \ args_results ->
1481 thing_inside (arg1_results ++ args_results)
1482 ; return (result, arg_wrap : arg_wraps) }
1483 tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside []
1484
1485 tc_syn_arg :: TcSigmaType -> SyntaxOpType
1486 -> ([TcSigmaType] -> TcM a)
1487 -> TcM (a, HsWrapper)
1488 -- the wrapper applies to the overall result
1489 tc_syn_arg res_ty SynAny thing_inside
1490 = do { result <- thing_inside [res_ty]
1491 ; return (result, idHsWrapper) }
1492 tc_syn_arg res_ty SynRho thing_inside
1493 = do { (inst_wrap, rho_ty) <- deeplyInstantiate orig res_ty
1494 -- inst_wrap :: res_ty "->" rho_ty
1495 ; result <- thing_inside [rho_ty]
1496 ; return (result, inst_wrap) }
1497 tc_syn_arg res_ty SynList thing_inside
1498 = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty
1499 -- inst_wrap :: res_ty "->" rho_ty
1500 ; (list_co, elt_ty) <- matchExpectedListTy rho_ty
1501 -- list_co :: [elt_ty] ~N rho_ty
1502 ; result <- thing_inside [elt_ty]
1503 ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) }
1504 tc_syn_arg _ (SynFun {}) _
1505 = pprPanic "tcSynArgA hits a SynFun" (ppr orig)
1506 tc_syn_arg res_ty (SynType the_ty) thing_inside
1507 = do { wrap <- tcSubTypeO orig GenSigCtxt res_ty the_ty
1508 ; result <- thing_inside []
1509 ; return (result, wrap) }
1510
1511 {-
1512 Note [Push result type in]
1513 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1514 Unify with expected result before type-checking the args so that the
1515 info from res_ty percolates to args. This is when we might detect a
1516 too-few args situation. (One can think of cases when the opposite
1517 order would give a better error message.)
1518 experimenting with putting this first.
1519
1520 Here's an example where it actually makes a real difference
1521
1522 class C t a b | t a -> b
1523 instance C Char a Bool
1524
1525 data P t a = forall b. (C t a b) => MkP b
1526 data Q t = MkQ (forall a. P t a)
1527
1528 f1, f2 :: Q Char;
1529 f1 = MkQ (MkP True)
1530 f2 = MkQ (MkP True :: forall a. P Char a)
1531
1532 With the change, f1 will type-check, because the 'Char' info from
1533 the signature is propagated into MkQ's argument. With the check
1534 in the other order, the extra signature in f2 is reqd.
1535
1536 ************************************************************************
1537 * *
1538 Expressions with a type signature
1539 expr :: type
1540 * *
1541 ********************************************************************* -}
1542
1543 tcExprSig :: LHsExpr GhcRn -> TcIdSigInfo -> TcM (LHsExpr GhcTcId, TcType)
1544 tcExprSig expr (CompleteSig { sig_bndr = poly_id, sig_loc = loc })
1545 = setSrcSpan loc $ -- Sets the location for the implication constraint
1546 do { (tv_prs, theta, tau) <- tcInstType tcInstSkolTyVars poly_id
1547 ; given <- newEvVars theta
1548 ; let skol_info = SigSkol ExprSigCtxt (idType poly_id) tv_prs
1549 skol_tvs = map snd tv_prs
1550 ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $
1551 tcExtendTyVarEnv2 tv_prs $
1552 tcPolyExprNC expr tau
1553
1554 ; let poly_wrap = mkWpTyLams skol_tvs
1555 <.> mkWpLams given
1556 <.> mkWpLet ev_binds
1557 ; return (mkLHsWrap poly_wrap expr', idType poly_id) }
1558
1559 tcExprSig expr sig@(PartialSig { psig_name = name, sig_loc = loc })
1560 = setSrcSpan loc $ -- Sets the location for the implication constraint
1561 do { (tclvl, wanted, (expr', sig_inst))
1562 <- pushLevelAndCaptureConstraints $
1563 do { sig_inst <- tcInstSig sig
1564 ; expr' <- tcExtendTyVarEnv2 (sig_inst_skols sig_inst) $
1565 tcExtendTyVarEnv2 (sig_inst_wcs sig_inst) $
1566 tcPolyExprNC expr (sig_inst_tau sig_inst)
1567 ; return (expr', sig_inst) }
1568 -- See Note [Partial expression signatures]
1569 ; let tau = sig_inst_tau sig_inst
1570 infer_mode | null (sig_inst_theta sig_inst)
1571 , isNothing (sig_inst_wcx sig_inst)
1572 = ApplyMR
1573 | otherwise
1574 = NoRestrictions
1575 ; (qtvs, givens, ev_binds, _)
1576 <- simplifyInfer tclvl infer_mode [sig_inst] [(name, tau)] wanted
1577 ; tau <- zonkTcType tau
1578 ; let inferred_theta = map evVarPred givens
1579 tau_tvs = tyCoVarsOfType tau
1580 ; (binders, my_theta) <- chooseInferredQuantifiers inferred_theta
1581 tau_tvs qtvs (Just sig_inst)
1582 ; let inferred_sigma = mkInfSigmaTy qtvs inferred_theta tau
1583 my_sigma = mkForAllTys binders (mkPhiTy my_theta tau)
1584 ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis.
1585 then return idHsWrapper -- Fast path; also avoids complaint when we infer
1586 -- an ambiguous type and have AllowAmbiguousType
1587 -- e..g infer x :: forall a. F a -> Int
1588 else tcSubType_NC ExprSigCtxt inferred_sigma my_sigma
1589
1590 ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma)
1591 ; let poly_wrap = wrap
1592 <.> mkWpTyLams qtvs
1593 <.> mkWpLams givens
1594 <.> mkWpLet ev_binds
1595 ; return (mkLHsWrap poly_wrap expr', my_sigma) }
1596
1597
1598 {- Note [Partial expression signatures]
1599 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1600 Partial type signatures on expressions are easy to get wrong. But
1601 here is a guiding principile
1602 e :: ty
1603 should behave like
1604 let x :: ty
1605 x = e
1606 in x
1607
1608 So for partial signatures we apply the MR if no context is given. So
1609 e :: IO _ apply the MR
1610 e :: _ => IO _ do not apply the MR
1611 just like in TcBinds.decideGeneralisationPlan
1612
1613 This makes a difference (Trac #11670):
1614 peek :: Ptr a -> IO CLong
1615 peek ptr = peekElemOff undefined 0 :: _
1616 from (peekElemOff undefined 0) we get
1617 type: IO w
1618 constraints: Storable w
1619
1620 We must NOT try to generalise over 'w' because the signature specifies
1621 no constraints so we'll complain about not being able to solve
1622 Storable w. Instead, don't generalise; then _ gets instantiated to
1623 CLong, as it should.
1624 -}
1625
1626 {- *********************************************************************
1627 * *
1628 tcInferId
1629 * *
1630 ********************************************************************* -}
1631
1632 tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr GhcTcId)
1633 tcCheckId name res_ty
1634 = do { (expr, actual_res_ty) <- tcInferId name
1635 ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty])
1636 ; addFunResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty $
1637 tcWrapResultO (OccurrenceOf name) (HsVar (noLoc name)) expr actual_res_ty res_ty }
1638
1639 tcCheckRecSelId :: HsExpr GhcRn -> AmbiguousFieldOcc GhcRn -> ExpRhoType -> TcM (HsExpr GhcTcId)
1640 tcCheckRecSelId rn_expr f@(Unambiguous (L _ lbl) _) res_ty
1641 = do { (expr, actual_res_ty) <- tcInferRecSelId f
1642 ; addFunResCtxt False (HsRecFld f) actual_res_ty res_ty $
1643 tcWrapResultO (OccurrenceOfRecSel lbl) rn_expr expr actual_res_ty res_ty }
1644 tcCheckRecSelId rn_expr (Ambiguous lbl _) res_ty
1645 = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of
1646 Nothing -> ambiguousSelector lbl
1647 Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg
1648 ; tcCheckRecSelId rn_expr (Unambiguous lbl sel_name) res_ty }
1649
1650 ------------------------
1651 tcInferRecSelId :: AmbiguousFieldOcc GhcRn -> TcM (HsExpr GhcTcId, TcRhoType)
1652 tcInferRecSelId (Unambiguous (L _ lbl) sel)
1653 = do { (expr', ty) <- tc_infer_id lbl sel
1654 ; return (expr', ty) }
1655 tcInferRecSelId (Ambiguous lbl _)
1656 = ambiguousSelector lbl
1657
1658 ------------------------
1659 tcInferId :: Name -> TcM (HsExpr GhcTcId, TcSigmaType)
1660 -- Look up an occurrence of an Id
1661 -- Do not instantiate its type
1662 tcInferId id_name
1663 | id_name `hasKey` tagToEnumKey
1664 = failWithTc (text "tagToEnum# must appear applied to one argument")
1665 -- tcApp catches the case (tagToEnum# arg)
1666
1667 | id_name `hasKey` assertIdKey
1668 = do { dflags <- getDynFlags
1669 ; if gopt Opt_IgnoreAsserts dflags
1670 then tc_infer_id (nameRdrName id_name) id_name
1671 else tc_infer_assert id_name }
1672
1673 | otherwise
1674 = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) id_name
1675 ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty)
1676 ; return (expr, ty) }
1677
1678 tc_infer_assert :: Name -> TcM (HsExpr GhcTcId, TcSigmaType)
1679 -- Deal with an occurrence of 'assert'
1680 -- See Note [Adding the implicit parameter to 'assert']
1681 tc_infer_assert assert_name
1682 = do { assert_error_id <- tcLookupId assertErrorName
1683 ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name)
1684 (idType assert_error_id)
1685 ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho)
1686 }
1687
1688 tc_infer_id :: RdrName -> Name -> TcM (HsExpr GhcTcId, TcSigmaType)
1689 tc_infer_id lbl id_name
1690 = do { thing <- tcLookup id_name
1691 ; case thing of
1692 ATcId { tct_id = id }
1693 -> do { check_naughty id -- Note [Local record selectors]
1694 ; checkThLocalId id
1695 ; return_id id }
1696
1697 AGlobal (AnId id)
1698 -> do { check_naughty id
1699 ; return_id id }
1700 -- A global cannot possibly be ill-staged
1701 -- nor does it need the 'lifting' treatment
1702 -- hence no checkTh stuff here
1703
1704 AGlobal (AConLike cl) -> case cl of
1705 RealDataCon con -> return_data_con con
1706 PatSynCon ps -> tcPatSynBuilderOcc ps
1707
1708 _ -> failWithTc $
1709 ppr thing <+> text "used where a value identifier was expected" }
1710 where
1711 return_id id = return (HsVar (noLoc id), idType id)
1712
1713 return_data_con con
1714 -- For data constructors, must perform the stupid-theta check
1715 | null stupid_theta
1716 = return (HsConLikeOut (RealDataCon con), con_ty)
1717
1718 | otherwise
1719 -- See Note [Instantiating stupid theta]
1720 = do { let (tvs, theta, rho) = tcSplitSigmaTy con_ty
1721 ; (subst, tvs') <- newMetaTyVars tvs
1722 ; let tys' = mkTyVarTys tvs'
1723 theta' = substTheta subst theta
1724 rho' = substTy subst rho
1725 ; wrap <- instCall (OccurrenceOf id_name) tys' theta'
1726 ; addDataConStupidTheta con tys'
1727 ; return (mkHsWrap wrap (HsConLikeOut (RealDataCon con)), rho') }
1728
1729 where
1730 con_ty = dataConUserType con
1731 stupid_theta = dataConStupidTheta con
1732
1733 check_naughty id
1734 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl)
1735 | otherwise = return ()
1736
1737
1738 tcUnboundId :: HsExpr GhcRn -> UnboundVar -> ExpRhoType -> TcM (HsExpr GhcTcId)
1739 -- Typecheck an occurrence of an unbound Id
1740 --
1741 -- Some of these started life as a true expression hole "_".
1742 -- Others might simply be variables that accidentally have no binding site
1743 --
1744 -- We turn all of them into HsVar, since HsUnboundVar can't contain an
1745 -- Id; and indeed the evidence for the CHoleCan does bind it, so it's
1746 -- not unbound any more!
1747 tcUnboundId rn_expr unbound res_ty
1748 = do { ty <- newOpenFlexiTyVarTy -- Allow Int# etc (Trac #12531)
1749 ; let occ = unboundVarOcc unbound
1750 ; name <- newSysName occ
1751 ; let ev = mkLocalId name ty
1752 ; loc <- getCtLocM HoleOrigin Nothing
1753 ; let can = CHoleCan { cc_ev = CtWanted { ctev_pred = ty
1754 , ctev_dest = EvVarDest ev
1755 , ctev_nosh = WDeriv
1756 , ctev_loc = loc}
1757 , cc_hole = ExprHole unbound }
1758 ; emitInsoluble can
1759 ; tcWrapResultO (UnboundOccurrenceOf occ) rn_expr (HsVar (noLoc ev)) ty res_ty }
1760
1761
1762 {-
1763 Note [Adding the implicit parameter to 'assert']
1764 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1765 The typechecker transforms (assert e1 e2) to (assertError e1 e2).
1766 This isn't really the Right Thing because there's no way to "undo"
1767 if you want to see the original source code in the typechecker
1768 output. We'll have fix this in due course, when we care more about
1769 being able to reconstruct the exact original program.
1770
1771 Note [tagToEnum#]
1772 ~~~~~~~~~~~~~~~~~
1773 Nasty check to ensure that tagToEnum# is applied to a type that is an
1774 enumeration TyCon. Unification may refine the type later, but this
1775 check won't see that, alas. It's crude, because it relies on our
1776 knowing *now* that the type is ok, which in turn relies on the
1777 eager-unification part of the type checker pushing enough information
1778 here. In theory the Right Thing to do is to have a new form of
1779 constraint but I definitely cannot face that! And it works ok as-is.
1780
1781 Here's are two cases that should fail
1782 f :: forall a. a
1783 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1784
1785 g :: Int
1786 g = tagToEnum# 0 -- Int is not an enumeration
1787
1788 When data type families are involved it's a bit more complicated.
1789 data family F a
1790 data instance F [Int] = A | B | C
1791 Then we want to generate something like
1792 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1793 Usually that coercion is hidden inside the wrappers for
1794 constructors of F [Int] but here we have to do it explicitly.
1795
1796 It's all grotesquely complicated.
1797
1798 Note [Instantiating stupid theta]
1799 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1800 Normally, when we infer the type of an Id, we don't instantiate,
1801 because we wish to allow for visible type application later on.
1802 But if a datacon has a stupid theta, we're a bit stuck. We need
1803 to emit the stupid theta constraints with instantiated types. It's
1804 difficult to defer this to the lazy instantiation, because a stupid
1805 theta has no spot to put it in a type. So we just instantiate eagerly
1806 in this case. Thus, users cannot use visible type application with
1807 a data constructor sporting a stupid theta. I won't feel so bad for
1808 the users that complain.
1809
1810 -}
1811
1812 tcSeq :: SrcSpan -> Name -> [LHsExprArgIn]
1813 -> ExpRhoType -> TcM (HsWrapper, LHsExpr GhcTcId, [LHsExprArgOut])
1814 -- (seq e1 e2) :: res_ty
1815 -- We need a special typing rule because res_ty can be unboxed
1816 -- See Note [Typing rule for seq]
1817 tcSeq loc fun_name args res_ty
1818 = do { fun <- tcLookupId fun_name
1819 ; (arg1_ty, args1) <- case args of
1820 (Right hs_ty_arg1 : args1)
1821 -> do { ty_arg1 <- tcHsTypeApp hs_ty_arg1 liftedTypeKind
1822 ; return (ty_arg1, args1) }
1823
1824 _ -> do { arg_ty1 <- newFlexiTyVarTy liftedTypeKind
1825 ; return (arg_ty1, args) }
1826
1827 ; (arg1, arg2, arg2_exp_ty) <- case args1 of
1828 [Right hs_ty_arg2, Left term_arg1, Left term_arg2]
1829 -> do { arg2_kind <- newOpenTypeKind
1830 ; ty_arg2 <- tcHsTypeApp hs_ty_arg2 arg2_kind
1831 -- see Note [Typing rule for seq]
1832 ; _ <- tcSubTypeDS (OccurrenceOf fun_name) GenSigCtxt ty_arg2 res_ty
1833 ; return (term_arg1, term_arg2, mkCheckExpType ty_arg2) }
1834 [Left term_arg1, Left term_arg2]
1835 -> return (term_arg1, term_arg2, res_ty)
1836 _ -> too_many_args "seq" args
1837
1838 ; arg1' <- tcMonoExpr arg1 (mkCheckExpType arg1_ty)
1839 ; arg2' <- tcMonoExpr arg2 arg2_exp_ty
1840 ; res_ty <- readExpType res_ty -- by now, it's surely filled in
1841 ; let fun' = L loc (mkHsWrap ty_args (HsVar (L loc fun)))
1842 ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty
1843 ; return (idHsWrapper, fun', [Left arg1', Left arg2']) }
1844
1845 tcTagToEnum :: SrcSpan -> Name -> [LHsExprArgIn] -> ExpRhoType
1846 -> TcM (HsWrapper, LHsExpr GhcTcId, [LHsExprArgOut])
1847 -- tagToEnum# :: forall a. Int# -> a
1848 -- See Note [tagToEnum#] Urgh!
1849 tcTagToEnum loc fun_name args res_ty
1850 = do { fun <- tcLookupId fun_name
1851
1852 ; arg <- case args of
1853 [Right hs_ty_arg, Left term_arg]
1854 -> do { ty_arg <- tcHsTypeApp hs_ty_arg liftedTypeKind
1855 ; _ <- tcSubTypeDS (OccurrenceOf fun_name) GenSigCtxt ty_arg res_ty
1856 -- other than influencing res_ty, we just
1857 -- don't care about a type arg passed in.
1858 -- So drop the evidence.
1859 ; return term_arg }
1860 [Left term_arg] -> do { _ <- expTypeToType res_ty
1861 ; return term_arg }
1862 _ -> too_many_args "tagToEnum#" args
1863
1864 ; res_ty <- readExpType res_ty
1865 ; ty' <- zonkTcType res_ty
1866
1867 -- Check that the type is algebraic
1868 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1869 Just (tc, tc_args) = mb_tc_app
1870 ; checkTc (isJust mb_tc_app)
1871 (mk_error ty' doc1)
1872
1873 -- Look through any type family
1874 ; fam_envs <- tcGetFamInstEnvs
1875 ; let (rep_tc, rep_args, coi)
1876 = tcLookupDataFamInst fam_envs tc tc_args
1877 -- coi :: tc tc_args ~R rep_tc rep_args
1878
1879 ; checkTc (isEnumerationTyCon rep_tc)
1880 (mk_error ty' doc2)
1881
1882 ; arg' <- tcMonoExpr arg (mkCheckExpType intPrimTy)
1883 ; let fun' = L loc (mkHsWrap (WpTyApp rep_ty) (HsVar (L loc fun)))
1884 rep_ty = mkTyConApp rep_tc rep_args
1885
1886 ; return (mkWpCastR (mkTcSymCo coi), fun', [Left arg']) }
1887 -- coi is a Representational coercion
1888 where
1889 doc1 = vcat [ text "Specify the type by giving a type signature"
1890 , text "e.g. (tagToEnum# x) :: Bool" ]
1891 doc2 = text "Result type must be an enumeration type"
1892
1893 mk_error :: TcType -> SDoc -> SDoc
1894 mk_error ty what
1895 = hang (text "Bad call to tagToEnum#"
1896 <+> text "at type" <+> ppr ty)
1897 2 what
1898
1899 too_many_args :: String -> [LHsExprArgIn] -> TcM a
1900 too_many_args fun args
1901 = failWith $
1902 hang (text "Too many type arguments to" <+> text fun <> colon)
1903 2 (sep (map pp args))
1904 where
1905 pp (Left e) = ppr e
1906 pp (Right (HsWC { hswc_body = L _ t })) = pprHsType t
1907
1908
1909 {-
1910 ************************************************************************
1911 * *
1912 Template Haskell checks
1913 * *
1914 ************************************************************************
1915 -}
1916
1917 checkThLocalId :: Id -> TcM ()
1918 checkThLocalId id
1919 = do { mb_local_use <- getStageAndBindLevel (idName id)
1920 ; case mb_local_use of
1921 Just (top_lvl, bind_lvl, use_stage)
1922 | thLevel use_stage > bind_lvl
1923 , isNotTopLevel top_lvl
1924 -> checkCrossStageLifting id use_stage
1925 _ -> return () -- Not a locally-bound thing, or
1926 -- no cross-stage link
1927 }
1928
1929 --------------------------------------
1930 checkCrossStageLifting :: Id -> ThStage -> TcM ()
1931 -- If we are inside typed brackets, and (use_lvl > bind_lvl)
1932 -- we must check whether there's a cross-stage lift to do
1933 -- Examples \x -> [|| x ||]
1934 -- [|| map ||]
1935 -- There is no error-checking to do, because the renamer did that
1936 --
1937 -- This is similar to checkCrossStageLifting in RnSplice, but
1938 -- this code is applied to *typed* brackets.
1939
1940 checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var))
1941 = -- Nested identifiers, such as 'x' in
1942 -- E.g. \x -> [|| h x ||]
1943 -- We must behave as if the reference to x was
1944 -- h $(lift x)
1945 -- We use 'x' itself as the splice proxy, used by
1946 -- the desugarer to stitch it all back together.
1947 -- If 'x' occurs many times we may get many identical
1948 -- bindings of the same splice proxy, but that doesn't
1949 -- matter, although it's a mite untidy.
1950 do { let id_ty = idType id
1951 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1952 -- If x is polymorphic, its occurrence sites might
1953 -- have different instantiations, so we can't use plain
1954 -- 'x' as the splice proxy name. I don't know how to
1955 -- solve this, and it's probably unimportant, so I'm
1956 -- just going to flag an error for now
1957
1958 ; lift <- if isStringTy id_ty then
1959 do { sid <- tcLookupId THNames.liftStringName
1960 -- See Note [Lifting strings]
1961 ; return (HsVar (noLoc sid)) }
1962 else
1963 setConstraintVar lie_var $
1964 -- Put the 'lift' constraint into the right LIE
1965 newMethodFromName (OccurrenceOf (idName id))
1966 THNames.liftName id_ty
1967
1968 -- Update the pending splices
1969 ; ps <- readMutVar ps_var
1970 ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id))
1971 ; writeMutVar ps_var (pending_splice : ps)
1972
1973 ; return () }
1974
1975 checkCrossStageLifting _ _ = return ()
1976
1977 polySpliceErr :: Id -> SDoc
1978 polySpliceErr id
1979 = text "Can't splice the polymorphic local variable" <+> quotes (ppr id)
1980
1981 {-
1982 Note [Lifting strings]
1983 ~~~~~~~~~~~~~~~~~~~~~~
1984 If we see $(... [| s |] ...) where s::String, we don't want to
1985 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1986 So this conditional short-circuits the lifting mechanism to generate
1987 (liftString "xy") in that case. I didn't want to use overlapping instances
1988 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1989 errors in a polymorphic situation.
1990
1991 If this check fails (which isn't impossible) we get another chance; see
1992 Note [Converting strings] in Convert.hs
1993
1994 Local record selectors
1995 ~~~~~~~~~~~~~~~~~~~~~~
1996 Record selectors for TyCons in this module are ordinary local bindings,
1997 which show up as ATcIds rather than AGlobals. So we need to check for
1998 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1999
2000
2001 ************************************************************************
2002 * *
2003 \subsection{Record bindings}
2004 * *
2005 ************************************************************************
2006 -}
2007
2008 getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet
2009 -- These tyvars must not change across the updates
2010 getFixedTyVars upd_fld_occs univ_tvs cons
2011 = mkVarSet [tv1 | con <- cons
2012 , let (u_tvs, _, eqspec, prov_theta
2013 , req_theta, arg_tys, _)
2014 = conLikeFullSig con
2015 theta = eqSpecPreds eqspec
2016 ++ prov_theta
2017 ++ req_theta
2018 flds = conLikeFieldLabels con
2019 fixed_tvs = exactTyCoVarsOfTypes fixed_tys
2020 -- fixed_tys: See Note [Type of a record update]
2021 `unionVarSet` tyCoVarsOfTypes theta
2022 -- Universally-quantified tyvars that
2023 -- appear in any of the *implicit*
2024 -- arguments to the constructor are fixed
2025 -- See Note [Implicit type sharing]
2026
2027 fixed_tys = [ty | (fl, ty) <- zip flds arg_tys
2028 , not (flLabel fl `elem` upd_fld_occs)]
2029 , (tv1,tv) <- univ_tvs `zip` u_tvs
2030 , tv `elemVarSet` fixed_tvs ]
2031
2032 {-
2033 Note [Disambiguating record fields]
2034 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2035 When the -XDuplicateRecordFields extension is used, and the renamer
2036 encounters a record selector or update that it cannot immediately
2037 disambiguate (because it involves fields that belong to multiple
2038 datatypes), it will defer resolution of the ambiguity to the
2039 typechecker. In this case, the `Ambiguous` constructor of
2040 `AmbiguousFieldOcc` is used.
2041
2042 Consider the following definitions:
2043
2044 data S = MkS { foo :: Int }
2045 data T = MkT { foo :: Int, bar :: Int }
2046 data U = MkU { bar :: Int, baz :: Int }
2047
2048 When the renamer sees `foo` as a selector or an update, it will not
2049 know which parent datatype is in use.
2050
2051 For selectors, there are two possible ways to disambiguate:
2052
2053 1. Check if the pushed-in type is a function whose domain is a
2054 datatype, for example:
2055
2056 f s = (foo :: S -> Int) s
2057
2058 g :: T -> Int
2059 g = foo
2060
2061 This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`.
2062
2063 2. Check if the selector is applied to an argument that has a type
2064 signature, for example:
2065
2066 h = foo (s :: S)
2067
2068 This is checked by `tcApp`.
2069
2070
2071 Updates are slightly more complex. The `disambiguateRecordBinds`
2072 function tries to determine the parent datatype in three ways:
2073
2074 1. Check for types that have all the fields being updated. For example:
2075
2076 f x = x { foo = 3, bar = 2 }
2077
2078 Here `f` must be updating `T` because neither `S` nor `U` have
2079 both fields. This may also discover that no possible type exists.
2080 For example the following will be rejected:
2081
2082 f' x = x { foo = 3, baz = 3 }
2083
2084 2. Use the type being pushed in, if it is already a TyConApp. The
2085 following are valid updates to `T`:
2086
2087 g :: T -> T
2088 g x = x { foo = 3 }
2089
2090 g' x = x { foo = 3 } :: T
2091
2092 3. Use the type signature of the record expression, if it exists and
2093 is a TyConApp. Thus this is valid update to `T`:
2094
2095 h x = (x :: T) { foo = 3 }
2096
2097
2098 Note that we do not look up the types of variables being updated, and
2099 no constraint-solving is performed, so for example the following will
2100 be rejected as ambiguous:
2101
2102 let bad (s :: S) = foo s
2103
2104 let r :: T
2105 r = blah
2106 in r { foo = 3 }
2107
2108 \r. (r { foo = 3 }, r :: T )
2109
2110 We could add further tests, of a more heuristic nature. For example,
2111 rather than looking for an explicit signature, we could try to infer
2112 the type of the argument to a selector or the record expression being
2113 updated, in case we are lucky enough to get a TyConApp straight
2114 away. However, it might be hard for programmers to predict whether a
2115 particular update is sufficiently obvious for the signature to be
2116 omitted. Moreover, this might change the behaviour of typechecker in
2117 non-obvious ways.
2118
2119 See also Note [HsRecField and HsRecUpdField] in HsPat.
2120 -}
2121
2122 -- Given a RdrName that refers to multiple record fields, and the type
2123 -- of its argument, try to determine the name of the selector that is
2124 -- meant.
2125 disambiguateSelector :: Located RdrName -> Type -> TcM Name
2126 disambiguateSelector lr@(L _ rdr) parent_type
2127 = do { fam_inst_envs <- tcGetFamInstEnvs
2128 ; case tyConOf fam_inst_envs parent_type of
2129 Nothing -> ambiguousSelector lr
2130 Just p ->
2131 do { xs <- lookupParents rdr
2132 ; let parent = RecSelData p
2133 ; case lookup parent xs of
2134 Just gre -> do { addUsedGRE True gre
2135 ; return (gre_name gre) }
2136 Nothing -> failWithTc (fieldNotInType parent rdr) } }
2137
2138 -- This field name really is ambiguous, so add a suitable "ambiguous
2139 -- occurrence" error, then give up.
2140 ambiguousSelector :: Located RdrName -> TcM a
2141 ambiguousSelector (L _ rdr)
2142 = do { env <- getGlobalRdrEnv
2143 ; let gres = lookupGRE_RdrName rdr env
2144 ; setErrCtxt [] $ addNameClashErrRn rdr gres
2145 ; failM }
2146
2147 -- Disambiguate the fields in a record update.
2148 -- See Note [Disambiguating record fields]
2149 disambiguateRecordBinds :: LHsExpr GhcRn -> TcRhoType
2150 -> [LHsRecUpdField GhcRn] -> ExpRhoType
2151 -> TcM [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)]
2152 disambiguateRecordBinds record_expr record_rho rbnds res_ty
2153 -- Are all the fields unambiguous?
2154 = case mapM isUnambiguous rbnds of
2155 -- If so, just skip to looking up the Ids
2156 -- Always the case if DuplicateRecordFields is off
2157 Just rbnds' -> mapM lookupSelector rbnds'
2158 Nothing -> -- If not, try to identify a single parent
2159 do { fam_inst_envs <- tcGetFamInstEnvs
2160 -- Look up the possible parents for each field
2161 ; rbnds_with_parents <- getUpdFieldsParents
2162 ; let possible_parents = map (map fst . snd) rbnds_with_parents
2163 -- Identify a single parent
2164 ; p <- identifyParent fam_inst_envs possible_parents
2165 -- Pick the right selector with that parent for each field
2166 ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents }
2167 where
2168 -- Extract the selector name of a field update if it is unambiguous
2169 isUnambiguous :: LHsRecUpdField GhcRn -> Maybe (LHsRecUpdField GhcRn,Name)
2170 isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of
2171 Unambiguous _ sel_name -> Just (x, sel_name)
2172 Ambiguous{} -> Nothing
2173
2174 -- Look up the possible parents and selector GREs for each field
2175 getUpdFieldsParents :: TcM [(LHsRecUpdField GhcRn
2176 , [(RecSelParent, GlobalRdrElt)])]
2177 getUpdFieldsParents
2178 = fmap (zip rbnds) $ mapM
2179 (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc)
2180 rbnds
2181
2182 -- Given a the lists of possible parents for each field,
2183 -- identify a single parent
2184 identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent
2185 identifyParent fam_inst_envs possible_parents
2186 = case foldr1 intersect possible_parents of
2187 -- No parents for all fields: record update is ill-typed
2188 [] -> failWithTc (noPossibleParents rbnds)
2189
2190 -- Exactly one datatype with all the fields: use that
2191 [p] -> return p
2192
2193 -- Multiple possible parents: try harder to disambiguate
2194 -- Can we get a parent TyCon from the pushed-in type?
2195 _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p)
2196
2197 -- Does the expression being updated have a type signature?
2198 -- If so, try to extract a parent TyCon from it
2199 | Just {} <- obviousSig (unLoc record_expr)
2200 , Just tc <- tyConOf fam_inst_envs record_rho
2201 -> return (RecSelData tc)
2202
2203 -- Nothing else we can try...
2204 _ -> failWithTc badOverloadedUpdate
2205
2206 -- Make a field unambiguous by choosing the given parent.
2207 -- Emits an error if the field cannot have that parent,
2208 -- e.g. if the user writes
2209 -- r { x = e } :: T
2210 -- where T does not have field x.
2211 pickParent :: RecSelParent
2212 -> (LHsRecUpdField GhcRn, [(RecSelParent, GlobalRdrElt)])
2213 -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn))
2214 pickParent p (upd, xs)
2215 = case lookup p xs of
2216 -- Phew! The parent is valid for this field.
2217 -- Previously ambiguous fields must be marked as
2218 -- used now that we know which one is meant, but
2219 -- unambiguous ones shouldn't be recorded again
2220 -- (giving duplicate deprecation warnings).
2221 Just gre -> do { unless (null (tail xs)) $ do
2222 let L loc _ = hsRecFieldLbl (unLoc upd)
2223 setSrcSpan loc $ addUsedGRE True gre
2224 ; lookupSelector (upd, gre_name gre) }
2225 -- The field doesn't belong to this parent, so report
2226 -- an error but keep going through all the fields
2227 Nothing -> do { addErrTc (fieldNotInType p
2228 (unLoc (hsRecUpdFieldRdr (unLoc upd))))
2229 ; lookupSelector (upd, gre_name (snd (head xs))) }
2230
2231 -- Given a (field update, selector name) pair, look up the
2232 -- selector to give a field update with an unambiguous Id
2233 lookupSelector :: (LHsRecUpdField GhcRn, Name)
2234 -> TcM (LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn))
2235 lookupSelector (L l upd, n)
2236 = do { i <- tcLookupId n
2237 ; let L loc af = hsRecFieldLbl upd
2238 lbl = rdrNameAmbiguousFieldOcc af
2239 ; return $ L l upd { hsRecFieldLbl
2240 = L loc (Unambiguous (L loc lbl) i) } }
2241
2242
2243 -- Extract the outermost TyCon of a type, if there is one; for
2244 -- data families this is the representation tycon (because that's
2245 -- where the fields live).
2246 tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon
2247 tyConOf fam_inst_envs ty0
2248 = case tcSplitTyConApp_maybe ty of
2249 Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys))
2250 Nothing -> Nothing
2251 where
2252 (_, _, ty) = tcSplitSigmaTy ty0
2253
2254 -- Variant of tyConOf that works for ExpTypes
2255 tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon
2256 tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0
2257
2258 -- For an ambiguous record field, find all the candidate record
2259 -- selectors (as GlobalRdrElts) and their parents.
2260 lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)]
2261 lookupParents rdr
2262 = do { env <- getGlobalRdrEnv
2263 ; let gres = lookupGRE_RdrName rdr env
2264 ; mapM lookupParent gres }
2265 where
2266 lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt)
2267 lookupParent gre = do { id <- tcLookupId (gre_name gre)
2268 ; if isRecordSelector id
2269 then return (recordSelectorTyCon id, gre)
2270 else failWithTc (notSelector (gre_name gre)) }
2271
2272 -- A type signature on the argument of an ambiguous record selector or
2273 -- the record expression in an update must be "obvious", i.e. the
2274 -- outermost constructor ignoring parentheses.
2275 obviousSig :: HsExpr GhcRn -> Maybe (LHsSigWcType GhcRn)
2276 obviousSig (ExprWithTySig _ ty) = Just ty
2277 obviousSig (HsPar p) = obviousSig (unLoc p)
2278 obviousSig _ = Nothing
2279
2280
2281 {-
2282 Game plan for record bindings
2283 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2284 1. Find the TyCon for the bindings, from the first field label.
2285
2286 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
2287
2288 For each binding field = value
2289
2290 3. Instantiate the field type (from the field label) using the type
2291 envt from step 2.
2292
2293 4 Type check the value using tcArg, passing the field type as
2294 the expected argument type.
2295
2296 This extends OK when the field types are universally quantified.
2297 -}
2298
2299 tcRecordBinds
2300 :: ConLike
2301 -> [TcType] -- Expected type for each field
2302 -> HsRecordBinds GhcRn
2303 -> TcM (HsRecordBinds GhcTcId)
2304
2305 tcRecordBinds con_like arg_tys (HsRecFields rbinds dd)
2306 = do { mb_binds <- mapM do_bind rbinds
2307 ; return (HsRecFields (catMaybes mb_binds) dd) }
2308 where
2309 fields = map flLabel $ conLikeFieldLabels con_like
2310 flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys
2311
2312 do_bind :: LHsRecField GhcRn (LHsExpr GhcRn)
2313 -> TcM (Maybe (LHsRecField GhcTcId (LHsExpr GhcTcId)))
2314 do_bind (L l fld@(HsRecField { hsRecFieldLbl = f
2315 , hsRecFieldArg = rhs }))
2316
2317 = do { mb <- tcRecordField con_like flds_w_tys f rhs
2318 ; case mb of
2319 Nothing -> return Nothing
2320 Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f'
2321 , hsRecFieldArg = rhs' }))) }
2322
2323 tcRecordUpd
2324 :: ConLike
2325 -> [TcType] -- Expected type for each field
2326 -> [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)]
2327 -> TcM [LHsRecUpdField GhcTcId]
2328
2329 tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds
2330 where
2331 flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys
2332
2333 do_bind :: LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)
2334 -> TcM (Maybe (LHsRecUpdField GhcTcId))
2335 do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af
2336 , hsRecFieldArg = rhs }))
2337 = do { let lbl = rdrNameAmbiguousFieldOcc af
2338 sel_id = selectorAmbiguousFieldOcc af
2339 f = L loc (FieldOcc (L loc lbl) (idName sel_id))
2340 ; mb <- tcRecordField con_like flds_w_tys f rhs
2341 ; case mb of
2342 Nothing -> return Nothing
2343 Just (f', rhs') ->
2344 return (Just
2345 (L l (fld { hsRecFieldLbl
2346 = L loc (Unambiguous (L loc lbl)
2347 (selectorFieldOcc (unLoc f')))
2348 , hsRecFieldArg = rhs' }))) }
2349
2350 tcRecordField :: ConLike -> Assoc FieldLabelString Type
2351 -> LFieldOcc GhcRn -> LHsExpr GhcRn
2352 -> TcM (Maybe (LFieldOcc GhcTc, LHsExpr GhcTc))
2353 tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs
2354 | Just field_ty <- assocMaybe flds_w_tys field_lbl
2355 = addErrCtxt (fieldCtxt field_lbl) $
2356 do { rhs' <- tcPolyExprNC rhs field_ty
2357 ; let field_id = mkUserLocal (nameOccName sel_name)
2358 (nameUnique sel_name)
2359 field_ty loc
2360 -- Yuk: the field_id has the *unique* of the selector Id
2361 -- (so we can find it easily)
2362 -- but is a LocalId with the appropriate type of the RHS
2363 -- (so the desugarer knows the type of local binder to make)
2364 ; return (Just (L loc (FieldOcc lbl field_id), rhs')) }
2365 | otherwise
2366 = do { addErrTc (badFieldCon con_like field_lbl)
2367 ; return Nothing }
2368 where
2369 field_lbl = occNameFS $ rdrNameOcc (unLoc lbl)
2370
2371
2372 checkMissingFields :: ConLike -> HsRecordBinds GhcRn -> TcM ()
2373 checkMissingFields con_like rbinds
2374 | null field_labels -- Not declared as a record;
2375 -- But C{} is still valid if no strict fields
2376 = if any isBanged field_strs then
2377 -- Illegal if any arg is strict
2378 addErrTc (missingStrictFields con_like [])
2379 else
2380 return ()
2381
2382 | otherwise = do -- A record
2383 unless (null missing_s_fields)
2384 (addErrTc (missingStrictFields con_like missing_s_fields))
2385
2386 warn <- woptM Opt_WarnMissingFields
2387 unless (not (warn && notNull missing_ns_fields))
2388 (warnTc (Reason Opt_WarnMissingFields) True
2389 (missingFields con_like missing_ns_fields))
2390
2391 where
2392 missing_s_fields
2393 = [ flLabel fl | (fl, str) <- field_info,
2394 isBanged str,
2395 not (fl `elemField` field_names_used)
2396 ]
2397 missing_ns_fields
2398 = [ flLabel fl | (fl, str) <- field_info,
2399 not (isBanged str),
2400 not (fl `elemField` field_names_used)
2401 ]
2402
2403 field_names_used = hsRecFields rbinds
2404 field_labels = conLikeFieldLabels con_like
2405
2406 field_info = zipEqual "missingFields"
2407 field_labels
2408 field_strs
2409
2410 field_strs = conLikeImplBangs con_like
2411
2412 fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds
2413
2414 {-
2415 ************************************************************************
2416 * *
2417 \subsection{Errors and contexts}
2418 * *
2419 ************************************************************************
2420
2421 Boring and alphabetical:
2422 -}
2423
2424 addExprErrCtxt :: LHsExpr GhcRn -> TcM a -> TcM a
2425 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
2426
2427 exprCtxt :: LHsExpr GhcRn -> SDoc
2428 exprCtxt expr
2429 = hang (text "In the expression:") 2 (ppr expr)
2430
2431 fieldCtxt :: FieldLabelString -> SDoc
2432 fieldCtxt field_name
2433 = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
2434
2435 addFunResCtxt :: Bool -- There is at least one argument
2436 -> HsExpr GhcRn -> TcType -> ExpRhoType
2437 -> TcM a -> TcM a
2438 -- When we have a mis-match in the return type of a function
2439 -- try to give a helpful message about too many/few arguments
2440 --
2441 -- Used for naked variables too; but with has_args = False
2442 addFunResCtxt has_args fun fun_res_ty env_ty
2443 = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg)
2444 -- NB: use a landmark error context, so that an empty context
2445 -- doesn't suppress some more useful context
2446 where
2447 mk_msg
2448 = do { mb_env_ty <- readExpType_maybe env_ty
2449 -- by the time the message is rendered, the ExpType
2450 -- will be filled in (except if we're debugging)
2451 ; fun_res' <- zonkTcType fun_res_ty
2452 ; env' <- case mb_env_ty of
2453 Just env_ty -> zonkTcType env_ty
2454 Nothing ->
2455 do { dumping <- doptM Opt_D_dump_tc_trace
2456 ; MASSERT( dumping )
2457 ; newFlexiTyVarTy liftedTypeKind }
2458 ; let -- See Note [Splitting nested sigma types in mismatched
2459 -- function types]
2460 (_, _, fun_tau) = tcSplitNestedSigmaTys fun_res'
2461 -- No need to call tcSplitNestedSigmaTys here, since env_ty is
2462 -- an ExpRhoTy, i.e., it's already deeply instantiated.
2463 (_, _, env_tau) = tcSplitSigmaTy env'
2464 (args_fun, res_fun) = tcSplitFunTys fun_tau
2465 (args_env, res_env) = tcSplitFunTys env_tau
2466 n_fun = length args_fun
2467 n_env = length args_env
2468 info | n_fun == n_env = Outputable.empty
2469 | n_fun > n_env
2470 , not_fun res_env
2471 = text "Probable cause:" <+> quotes (ppr fun)
2472 <+> text "is applied to too few arguments"
2473
2474 | has_args
2475 , not_fun res_fun
2476 = text "Possible cause:" <+> quotes (ppr fun)
2477 <+> text "is applied to too many arguments"
2478
2479 | otherwise
2480 = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args!
2481 ; return info }
2482 where
2483 not_fun ty -- ty is definitely not an arrow type,
2484 -- and cannot conceivably become one
2485 = case tcSplitTyConApp_maybe ty of
2486 Just (tc, _) -> isAlgTyCon tc
2487 Nothing -> False
2488
2489 {-
2490 Note [Splitting nested sigma types in mismatched function types]
2491 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2492 When one applies a function to too few arguments, GHC tries to determine this
2493 fact if possible so that it may give a helpful error message. It accomplishes
2494 this by checking if the type of the applied function has more argument types
2495 than supplied arguments.
2496
2497 Previously, GHC computed the number of argument types through tcSplitSigmaTy.
2498 This is incorrect in the face of nested foralls, however! This caused Trac
2499 #13311, for instance:
2500
2501 f :: forall a. (Monoid a) => forall b. (Monoid b) => Maybe a -> Maybe b
2502
2503 If one uses `f` like so:
2504
2505 do { f; putChar 'a' }
2506
2507 Then tcSplitSigmaTy will decompose the type of `f` into:
2508
2509 Tyvars: [a]
2510 Context: (Monoid a)
2511 Argument types: []
2512 Return type: forall b. Monoid b => Maybe a -> Maybe b
2513
2514 That is, it will conclude that there are *no* argument types, and since `f`
2515 was given no arguments, it won't print a helpful error message. On the other
2516 hand, tcSplitNestedSigmaTys correctly decomposes `f`'s type down to:
2517
2518 Tyvars: [a, b]
2519 Context: (Monoid a, Monoid b)
2520 Argument types: [Maybe a]
2521 Return type: Maybe b
2522
2523 So now GHC recognizes that `f` has one more argument type than it was actually
2524 provided.
2525 -}
2526
2527 badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc
2528 badFieldTypes prs
2529 = hang (text "Record update for insufficiently polymorphic field"
2530 <> plural prs <> colon)
2531 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
2532
2533 badFieldsUpd
2534 :: [LHsRecField' (AmbiguousFieldOcc GhcTc) (LHsExpr GhcRn)]
2535 -- Field names that don't belong to a single datacon
2536 -> [ConLike] -- Data cons of the type which the first field name belongs to
2537 -> SDoc
2538 badFieldsUpd rbinds data_cons
2539 = hang (text "No constructor has all these fields:")
2540 2 (pprQuotedList conflictingFields)
2541 -- See Note [Finding the conflicting fields]
2542 where
2543 -- A (preferably small) set of fields such that no constructor contains
2544 -- all of them. See Note [Finding the conflicting fields]
2545 conflictingFields = case nonMembers of
2546 -- nonMember belongs to a different type.
2547 (nonMember, _) : _ -> [aMember, nonMember]
2548 [] -> let
2549 -- All of rbinds belong to one type. In this case, repeatedly add
2550 -- a field to the set until no constructor contains the set.
2551
2552 -- Each field, together with a list indicating which constructors
2553 -- have all the fields so far.
2554 growingSets :: [(FieldLabelString, [Bool])]
2555 growingSets = scanl1 combine membership
2556 combine (_, setMem) (field, fldMem)
2557 = (field, zipWith (&&) setMem fldMem)
2558 in
2559 -- Fields that don't change the membership status of the set
2560 -- are redundant and can be dropped.
2561 map (fst . head) $ groupBy ((==) `on` snd) growingSets
2562
2563 aMember = ASSERT( not (null members) ) fst (head members)
2564 (members, nonMembers) = partition (or . snd) membership
2565
2566 -- For each field, which constructors contain the field?
2567 membership :: [(FieldLabelString, [Bool])]
2568 membership = sortMembership $
2569 map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $
2570 map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds
2571
2572 fieldLabelSets :: [Set.Set FieldLabelString]
2573 fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons
2574
2575 -- Sort in order of increasing number of True, so that a smaller
2576 -- conflicting set can be found.
2577 sortMembership =
2578 map snd .
2579 sortBy (compare `on` fst) .
2580 map (\ item@(_, membershipRow) -> (countTrue membershipRow, item))
2581
2582 countTrue = count id
2583
2584 {-
2585 Note [Finding the conflicting fields]
2586 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2587 Suppose we have
2588 data A = A {a0, a1 :: Int}
2589 | B {b0, b1 :: Int}
2590 and we see a record update
2591 x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 }
2592 Then we'd like to find the smallest subset of fields that no
2593 constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc.
2594 We don't really want to report that no constructor has all of
2595 {a0,a1,b0,b1}, because when there are hundreds of fields it's
2596 hard to see what was really wrong.
2597
2598 We may need more than two fields, though; eg
2599 data T = A { x,y :: Int, v::Int }
2600 | B { y,z :: Int, v::Int }
2601 | C { z,x :: Int, v::Int }
2602 with update
2603 r { x=e1, y=e2, z=e3 }, we
2604
2605 Finding the smallest subset is hard, so the code here makes
2606 a decent stab, no more. See Trac #7989.
2607 -}
2608
2609 naughtyRecordSel :: RdrName -> SDoc
2610 naughtyRecordSel sel_id
2611 = text "Cannot use record selector" <+> quotes (ppr sel_id) <+>
2612 text "as a function due to escaped type variables" $$
2613 text "Probable fix: use pattern-matching syntax instead"
2614
2615 notSelector :: Name -> SDoc
2616 notSelector field
2617 = hsep [quotes (ppr field), text "is not a record selector"]
2618
2619 mixedSelectors :: [Id] -> [Id] -> SDoc
2620 mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_)
2621 = ptext
2622 (sLit "Cannot use a mixture of pattern synonym and record selectors") $$
2623 text "Record selectors defined by"
2624 <+> quotes (ppr (tyConName rep_dc))
2625 <> text ":"
2626 <+> pprWithCommas ppr data_sels $$
2627 text "Pattern synonym selectors defined by"
2628 <+> quotes (ppr (patSynName rep_ps))
2629 <> text ":"
2630 <+> pprWithCommas ppr pat_syn_sels
2631 where
2632 RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id
2633 RecSelData rep_dc = recordSelectorTyCon dc_rep_id
2634 mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists"
2635
2636
2637 missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc
2638 missingStrictFields con fields
2639 = header <> rest
2640 where
2641 rest | null fields = Outputable.empty -- Happens for non-record constructors
2642 -- with strict fields
2643 | otherwise = colon <+> pprWithCommas ppr fields
2644
2645 header = text "Constructor" <+> quotes (ppr con) <+>
2646 text "does not have the required strict field(s)"
2647
2648 missingFields :: ConLike -> [FieldLabelString] -> SDoc
2649 missingFields con fields
2650 = text "Fields of" <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
2651 <+> pprWithCommas ppr fields
2652
2653 -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl mkHsApp fun args))
2654
2655 noPossibleParents :: [LHsRecUpdField GhcRn] -> SDoc
2656 noPossibleParents rbinds
2657 = hang (text "No type has all these fields:")
2658 2 (pprQuotedList fields)
2659 where
2660 fields = map (hsRecFieldLbl . unLoc) rbinds
2661
2662 badOverloadedUpdate :: SDoc
2663 badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature"
2664
2665 fieldNotInType :: RecSelParent -> RdrName -> SDoc
2666 fieldNotInType p rdr
2667 = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr
2668
2669 {-
2670 ************************************************************************
2671 * *
2672 \subsection{Static Pointers}
2673 * *
2674 ************************************************************************
2675 -}
2676
2677 -- | A data type to describe why a variable is not closed.
2678 data NotClosedReason = NotLetBoundReason
2679 | NotTypeClosed VarSet
2680 | NotClosed Name NotClosedReason
2681
2682 -- | Checks if the given name is closed and emits an error if not.
2683 --
2684 -- See Note [Not-closed error messages].
2685 checkClosedInStaticForm :: Name -> TcM ()
2686 checkClosedInStaticForm name = do
2687 type_env <- getLclTypeEnv
2688 case checkClosed type_env name of
2689 Nothing -> return ()
2690 Just reason -> addErrTc $ explain name reason
2691 where
2692 -- See Note [Checking closedness].
2693 checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason
2694 checkClosed type_env n = checkLoop type_env (unitNameSet n) n
2695
2696 checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason
2697 checkLoop type_env visited n = do
2698 -- The @visited@ set is an accumulating parameter that contains the set of
2699 -- visited nodes, so we avoid repeating cycles in the traversal.
2700 case lookupNameEnv type_env n of
2701 Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of
2702 ClosedLet -> Nothing
2703 NotLetBound -> Just NotLetBoundReason
2704 NonClosedLet fvs type_closed -> listToMaybe $
2705 -- Look for a non-closed variable in fvs
2706 [ NotClosed n' reason
2707 | n' <- nameSetElemsStable fvs
2708 , not (elemNameSet n' visited)
2709 , Just reason <- [checkLoop type_env (extendNameSet visited n') n']
2710 ] ++
2711 if type_closed then
2712 []
2713 else
2714 -- We consider non-let-bound variables easier to figure out than
2715 -- non-closed types, so we report non-closed types to the user
2716 -- only if we cannot spot the former.
2717 [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ]
2718 -- The binding is closed.
2719 _ -> Nothing
2720
2721 -- Converts a reason into a human-readable sentence.
2722 --
2723 -- @explain name reason@ starts with
2724 --
2725 -- "<name> is used in a static form but it is not closed because it"
2726 --
2727 -- and then follows a list of causes. For each id in the path, the text
2728 --
2729 -- "uses <id> which"
2730 --
2731 -- is appended, yielding something like
2732 --
2733 -- "uses <id> which uses <id1> which uses <id2> which"
2734 --
2735 -- until the end of the path is reached, which is reported as either
2736 --
2737 -- "is not let-bound"
2738 --
2739 -- when the final node is not let-bound, or
2740 --
2741 -- "has a non-closed type because it contains the type variables:
2742 -- v1, v2, v3"
2743 --
2744 -- when the final node has a non-closed type.
2745 --
2746 explain :: Name -> NotClosedReason -> SDoc
2747 explain name reason =
2748 quotes (ppr name) <+> text "is used in a static form but it is not closed"
2749 <+> text "because it"
2750 $$
2751 sep (causes reason)
2752
2753 causes :: NotClosedReason -> [SDoc]
2754 causes NotLetBoundReason = [text "is not let-bound."]
2755 causes (NotTypeClosed vs) =
2756 [ text "has a non-closed type because it contains the"
2757 , text "type variables:" <+>
2758 pprVarSet vs (hsep . punctuate comma . map (quotes . ppr))
2759 ]
2760 causes (NotClosed n reason) =
2761 let msg = text "uses" <+> quotes (ppr n) <+> text "which"
2762 in case reason of
2763 NotClosed _ _ -> msg : causes reason
2764 _ -> let (xs0, xs1) = splitAt 1 $ causes reason
2765 in fmap (msg <+>) xs0 ++ xs1
2766
2767 -- Note [Not-closed error messages]
2768 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2769 --
2770 -- When variables in a static form are not closed, we go through the trouble
2771 -- of explaining why they aren't.
2772 --
2773 -- Thus, the following program
2774 --
2775 -- > {-# LANGUAGE StaticPointers #-}
2776 -- > module M where
2777 -- >
2778 -- > f x = static g
2779 -- > where
2780 -- > g = h
2781 -- > h = x
2782 --
2783 -- produces the error
2784 --
2785 -- 'g' is used in a static form but it is not closed because it
2786 -- uses 'h' which uses 'x' which is not let-bound.
2787 --
2788 -- And a program like
2789 --
2790 -- > {-# LANGUAGE StaticPointers #-}
2791 -- > module M where
2792 -- >
2793 -- > import Data.Typeable
2794 -- > import GHC.StaticPtr
2795 -- >
2796 -- > f :: Typeable a => a -> StaticPtr TypeRep
2797 -- > f x = const (static (g undefined)) (h x)
2798 -- > where
2799 -- > g = h
2800 -- > h = typeOf
2801 --
2802 -- produces the error
2803 --
2804 -- 'g' is used in a static form but it is not closed because it
2805 -- uses 'h' which has a non-closed type because it contains the
2806 -- type variables: 'a'
2807 --
2808
2809 -- Note [Checking closedness]
2810 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~
2811 --
2812 -- @checkClosed@ checks if a binding is closed and returns a reason if it is
2813 -- not.
2814 --
2815 -- The bindings define a graph where the nodes are ids, and there is an edge
2816 -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free
2817 -- variables.
2818 --
2819 -- When @n@ is not closed, it has to exist in the graph some node reachable
2820 -- from @n@ that it is not a let-bound variable or that it has a non-closed
2821 -- type. Thus, the "reason" is a path from @n@ to this offending node.
2822 --
2823 -- When @n@ is not closed, we traverse the graph reachable from @n@ to build
2824 -- the reason.
2825 --