Emit wild-card constraints in the right place
[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
11 module TcExpr ( tcPolyExpr, tcMonoExpr, tcMonoExprNC,
12 tcInferSigma, tcInferSigmaNC, tcInferRho, tcInferRhoNC,
13 tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType,
14 tcCheckId,
15 addExprErrCtxt,
16 getFixedTyVars ) where
17
18 #include "HsVersions.h"
19
20 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket )
21 import THNames( liftStringName, liftName )
22
23 import HsSyn
24 import TcHsSyn
25 import TcRnMonad
26 import TcUnify
27 import BasicTypes
28 import Inst
29 import TcBinds ( chooseInferredQuantifiers, tcLocalBinds
30 , tcUserTypeSig, tcExtendTyVarEnvFromSig )
31 import TcSimplify ( simplifyInfer )
32 import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst )
33 import FamInstEnv ( FamInstEnvs )
34 import RnEnv ( addUsedGRE, addNameClashErrRn
35 , unknownSubordinateErr )
36 import TcEnv
37 import TcArrows
38 import TcMatches
39 import TcHsType
40 import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr )
41 import TcPat
42 import TcMType
43 import TcType
44 import DsMonad
45 import Id
46 import IdInfo
47 import ConLike
48 import DataCon
49 import PatSyn
50 import Name
51 import RdrName
52 import TyCon
53 import Type
54 import TysPrim ( tYPE )
55 import TcEvidence
56 import VarSet
57 import TysWiredIn
58 import TysPrim( intPrimTy )
59 import PrimOp( tagToEnumKey )
60 import PrelNames
61 import MkId ( proxyHashId )
62 import DynFlags
63 import SrcLoc
64 import Util
65 import VarEnv ( emptyTidyEnv )
66 import ListSetOps
67 import Maybes
68 import Outputable
69 import FastString
70 import Control.Monad
71 import Class(classTyCon)
72 import qualified GHC.LanguageExtensions as LangExt
73
74 import Data.Function
75 import Data.List
76 import Data.Either
77 import qualified Data.Set as Set
78
79 {-
80 ************************************************************************
81 * *
82 \subsection{Main wrappers}
83 * *
84 ************************************************************************
85 -}
86
87 tcPolyExpr, tcPolyExprNC
88 :: LHsExpr Name -- Expression to type check
89 -> TcSigmaType -- Expected type (could be a polytype)
90 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
91
92 -- tcPolyExpr is a convenient place (frequent but not too frequent)
93 -- place to add context information.
94 -- The NC version does not do so, usually because the caller wants
95 -- to do so himself.
96
97 tcPolyExpr expr res_ty = tc_poly_expr expr (mkCheckExpType res_ty)
98 tcPolyExprNC expr res_ty = tc_poly_expr_nc expr (mkCheckExpType res_ty)
99
100 -- these versions take an ExpType
101 tc_poly_expr, tc_poly_expr_nc :: LHsExpr Name -> ExpSigmaType -> TcM (LHsExpr TcId)
102 tc_poly_expr expr res_ty
103 = addExprErrCtxt expr $
104 do { traceTc "tcPolyExpr" (ppr res_ty); tc_poly_expr_nc expr res_ty }
105
106 tc_poly_expr_nc (L loc expr) res_ty
107 = do { traceTc "tcPolyExprNC" (ppr res_ty)
108 ; (wrap, expr')
109 <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty ->
110 setSrcSpan loc $
111 -- NB: setSrcSpan *after* skolemising, so we get better
112 -- skolem locations
113 tcExpr expr res_ty
114 ; return $ L loc (mkHsWrap wrap expr') }
115
116 ---------------
117 tcMonoExpr, tcMonoExprNC
118 :: LHsExpr Name -- Expression to type check
119 -> ExpRhoType -- Expected type
120 -- Definitely no foralls at the top
121 -> TcM (LHsExpr TcId)
122
123 tcMonoExpr expr res_ty
124 = addErrCtxt (exprCtxt expr) $
125 tcMonoExprNC expr res_ty
126
127 tcMonoExprNC (L loc expr) res_ty
128 = setSrcSpan loc $
129 do { expr' <- tcExpr expr res_ty
130 ; return (L loc expr') }
131
132 ---------------
133 tcInferSigma, tcInferSigmaNC :: LHsExpr Name -> TcM ( LHsExpr TcId
134 , TcSigmaType )
135 -- Infer a *sigma*-type.
136 tcInferSigma expr = addErrCtxt (exprCtxt expr) (tcInferSigmaNC expr)
137
138 tcInferSigmaNC (L loc expr)
139 = setSrcSpan loc $
140 do { (expr', sigma) <- tcInfer (tcExpr expr)
141 ; return (L loc expr', sigma) }
142
143 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
144 -- Infer a *rho*-type. The return type is always (shallowly) instantiated.
145 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
146
147 tcInferRhoNC expr
148 = do { (expr', sigma) <- tcInferSigmaNC expr
149 ; (wrap, rho) <- topInstantiate (exprCtOrigin (unLoc expr)) sigma
150 ; return (mkLHsWrap wrap expr', rho) }
151
152
153 {-
154 ************************************************************************
155 * *
156 tcExpr: the main expression typechecker
157 * *
158 ************************************************************************
159
160 NB: The res_ty is always deeply skolemised.
161 -}
162
163 tcExpr :: HsExpr Name -> ExpRhoType -> TcM (HsExpr TcId)
164 tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty
165 tcExpr (HsUnboundVar uv) res_ty = tcUnboundId uv res_ty
166
167 tcExpr e@(HsApp {}) res_ty = tcApp1 e res_ty
168 tcExpr e@(HsAppType {}) res_ty = tcApp1 e res_ty
169
170 tcExpr e@(HsLit lit) res_ty = do { let lit_ty = hsLitType lit
171 ; tcWrapResult e (HsLit lit) lit_ty res_ty }
172
173 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
174 ; return (HsPar expr') }
175
176 tcExpr (HsSCC src lbl expr) res_ty
177 = do { expr' <- tcMonoExpr expr res_ty
178 ; return (HsSCC src lbl expr') }
179
180 tcExpr (HsTickPragma src info srcInfo expr) res_ty
181 = do { expr' <- tcMonoExpr expr res_ty
182 ; return (HsTickPragma src info srcInfo expr') }
183
184 tcExpr (HsCoreAnn src lbl expr) res_ty
185 = do { expr' <- tcMonoExpr expr res_ty
186 ; return (HsCoreAnn src lbl expr') }
187
188 tcExpr (HsOverLit lit) res_ty
189 = do { lit' <- newOverloadedLit lit res_ty
190 ; return (HsOverLit lit') }
191
192 tcExpr (NegApp expr neg_expr) res_ty
193 = do { (expr', neg_expr')
194 <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $
195 \[arg_ty] ->
196 tcMonoExpr expr (mkCheckExpType arg_ty)
197 ; return (NegApp expr' neg_expr') }
198
199 tcExpr e@(HsIPVar x) res_ty
200 = do { {- Implicit parameters must have a *tau-type* not a
201 type scheme. We enforce this by creating a fresh
202 type variable as its type. (Because res_ty may not
203 be a tau-type.) -}
204 ip_ty <- newOpenFlexiTyVarTy
205 ; let ip_name = mkStrLitTy (hsIPNameFS x)
206 ; ipClass <- tcLookupClass ipClassName
207 ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty])
208 ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var)))
209 ip_ty res_ty }
210 where
211 -- Coerces a dictionary for `IP "x" t` into `t`.
212 fromDict ipClass x ty = HsWrap $ mkWpCastR $
213 unwrapIP $ mkClassPred ipClass [x,ty]
214 origin = IPOccOrigin x
215
216 tcExpr e@(HsOverLabel l) res_ty -- See Note [Type-checking overloaded labels]
217 = do { isLabelClass <- tcLookupClass isLabelClassName
218 ; alpha <- newOpenFlexiTyVarTy
219 ; let lbl = mkStrLitTy l
220 pred = mkClassPred isLabelClass [lbl, alpha]
221 ; loc <- getSrcSpanM
222 ; var <- emitWantedEvVar origin pred
223 ; let proxy_arg = L loc (mkHsWrap (mkWpTyApps [typeSymbolKind, lbl])
224 (HsVar (L loc proxyHashId)))
225 tm = L loc (fromDict pred (HsVar (L loc var))) `HsApp` proxy_arg
226 ; tcWrapResult e tm alpha res_ty }
227 where
228 -- Coerces a dictionary for `IsLabel "x" t` into `Proxy# x -> t`.
229 fromDict pred = HsWrap $ mkWpCastR $ unwrapIP pred
230 origin = OverLabelOrigin l
231
232 tcExpr (HsLam match) res_ty
233 = do { (match', wrap) <- tcMatchLambda herald match_ctxt match res_ty
234 ; return (mkHsWrap wrap (HsLam match')) }
235 where
236 match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody }
237 herald = sep [ text "The lambda expression" <+>
238 quotes (pprSetDepth (PartWay 1) $
239 pprMatches (LambdaExpr :: HsMatchContext Name) match),
240 -- The pprSetDepth makes the abstraction print briefly
241 text "has"]
242
243 tcExpr e@(HsLamCase matches) res_ty
244 = do { (matches', wrap)
245 <- tcMatchLambda msg match_ctxt matches res_ty
246 -- The laziness annotation is because we don't want to fail here
247 -- if there are multiple arguments
248 ; return (mkHsWrap wrap $ HsLamCase matches') }
249 where
250 msg = sep [ text "The function" <+> quotes (ppr e)
251 , text "requires"]
252 match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
253
254 tcExpr e@(ExprWithTySig expr sig_ty) res_ty
255 = do { sig_info <- checkNoErrs $ -- Avoid error cascade
256 tcUserTypeSig sig_ty Nothing
257 ; (expr', poly_ty) <- tcExprSig expr sig_info
258 ; let expr'' = ExprWithTySigOut expr' sig_ty
259 ; tcWrapResult e expr'' poly_ty res_ty }
260
261 {-
262 Note [Type-checking overloaded labels]
263 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
264 Recall that (in GHC.OverloadedLabels) we have
265
266 class IsLabel (x :: Symbol) a where
267 fromLabel :: Proxy# x -> a
268
269 When we see an overloaded label like `#foo`, we generate a fresh
270 variable `alpha` for the type and emit an `IsLabel "foo" alpha`
271 constraint. Because the `IsLabel` class has a single method, it is
272 represented by a newtype, so we can coerce `IsLabel "foo" alpha` to
273 `Proxy# "foo" -> alpha` (just like for implicit parameters). We then
274 apply it to `proxy#` of type `Proxy# "foo"`.
275
276 That is, we translate `#foo` to `fromLabel (proxy# :: Proxy# "foo")`.
277 -}
278
279
280 {-
281 ************************************************************************
282 * *
283 Infix operators and sections
284 * *
285 ************************************************************************
286
287 Note [Left sections]
288 ~~~~~~~~~~~~~~~~~~~~
289 Left sections, like (4 *), are equivalent to
290 \ x -> (*) 4 x,
291 or, if PostfixOperators is enabled, just
292 (*) 4
293 With PostfixOperators we don't actually require the function to take
294 two arguments at all. For example, (x `not`) means (not x); you get
295 postfix operators! Not Haskell 98, but it's less work and kind of
296 useful.
297
298 Note [Typing rule for ($)]
299 ~~~~~~~~~~~~~~~~~~~~~~~~~~
300 People write
301 runST $ blah
302 so much, where
303 runST :: (forall s. ST s a) -> a
304 that I have finally given in and written a special type-checking
305 rule just for saturated appliations of ($).
306 * Infer the type of the first argument
307 * Decompose it; should be of form (arg2_ty -> res_ty),
308 where arg2_ty might be a polytype
309 * Use arg2_ty to typecheck arg2
310
311 Note [Typing rule for seq]
312 ~~~~~~~~~~~~~~~~~~~~~~~~~~
313 We want to allow
314 x `seq` (# p,q #)
315 which suggests this type for seq:
316 seq :: forall (a:*) (b:Open). a -> b -> b,
317 with (b:Open) meaning that be can be instantiated with an unboxed
318 tuple. The trouble is that this might accept a partially-applied
319 'seq', and I'm just not certain that would work. I'm only sure it's
320 only going to work when it's fully applied, so it turns into
321 case x of _ -> (# p,q #)
322
323 So it seems more uniform to treat 'seq' as it it was a language
324 construct.
325
326 See also Note [seqId magic] in MkId
327 -}
328
329 tcExpr expr@(OpApp arg1 op fix arg2) res_ty
330 | (L loc (HsVar (L lv op_name))) <- op
331 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
332 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
333 ; let arg2_exp_ty = res_ty
334 ; arg1' <- tcArg op arg1 arg1_ty 1
335 ; arg2' <- addErrCtxt (funAppCtxt op arg2 2) $
336 tc_poly_expr_nc arg2 arg2_exp_ty
337 ; arg2_ty <- readExpType arg2_exp_ty
338 ; op_id <- tcLookupId op_name
339 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty])
340 (HsVar (L lv op_id)))
341 ; return $ OpApp arg1' op' fix arg2' }
342
343 | (L loc (HsVar (L lv op_name))) <- op
344 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
345 = do { traceTc "Application rule" (ppr op)
346 ; (arg1', arg1_ty) <- tcInferSigma arg1
347
348 ; let doc = text "The first argument of ($) takes"
349 orig1 = exprCtOrigin (unLoc arg1)
350 ; (wrap_arg1, [arg2_sigma], op_res_ty) <-
351 matchActualFunTys doc orig1 (Just arg1) 1 arg1_ty
352
353 -- We have (arg1 $ arg2)
354 -- So: arg1_ty = arg2_ty -> op_res_ty
355 -- where arg2_sigma maybe polymorphic; that's the point
356
357 ; arg2' <- tcArg op arg2 arg2_sigma 2
358
359 -- Make sure that the argument type has kind '*'
360 -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b
361 -- Eg we do not want to allow (D# $ 4.0#) Trac #5570
362 -- (which gives a seg fault)
363 --
364 -- The *result* type can have any kind (Trac #8739),
365 -- so we don't need to check anything for that
366 ; _ <- unifyKind (Just arg2_sigma) (typeKind arg2_sigma) liftedTypeKind
367 -- ignore the evidence. arg2_sigma must have type * or #,
368 -- because we know arg2_sigma -> or_res_ty is well-kinded
369 -- (because otherwise matchActualFunTys would fail)
370 -- There's no possibility here of, say, a kind family reducing to *.
371
372 ; wrap_res <- tcSubTypeHR orig1 (Just expr) op_res_ty res_ty
373 -- op_res -> res
374
375 ; op_id <- tcLookupId op_name
376 ; res_ty <- readExpType res_ty
377 ; let op' = L loc (HsWrap (mkWpTyApps [ getRuntimeRep "tcExpr ($)" res_ty
378 , arg2_sigma
379 , res_ty])
380 (HsVar (L lv op_id)))
381 -- arg1' :: arg1_ty
382 -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty)
383 -- wrap_res :: op_res_ty "->" res_ty
384 -- op' :: (a2_ty -> res_ty) -> a2_ty -> res_ty
385
386 -- wrap1 :: arg1_ty "->" (arg2_sigma -> res_ty)
387 wrap1 = mkWpFun idHsWrapper wrap_res arg2_sigma res_ty
388 <.> wrap_arg1
389
390 ; return (OpApp (mkLHsWrap wrap1 arg1') op' fix arg2') }
391
392 | (L loc (HsRecFld (Ambiguous lbl _))) <- op
393 , Just sig_ty <- obviousSig (unLoc arg1)
394 -- See Note [Disambiguating record fields]
395 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
396 ; sel_name <- disambiguateSelector lbl sig_tc_ty
397 ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name))
398 ; tcExpr (OpApp arg1 op' fix arg2) res_ty
399 }
400
401 | otherwise
402 = do { traceTc "Non Application rule" (ppr op)
403 ; (wrap, op', [Left arg1', Left arg2'])
404 <- tcApp (Just $ mk_op_msg op)
405 op [Left arg1, Left arg2] res_ty
406 ; return (mkHsWrap wrap $ OpApp arg1' op' fix arg2') }
407
408 -- Right sections, equivalent to \ x -> x `op` expr, or
409 -- \ x -> op x expr
410
411 tcExpr expr@(SectionR op arg2) res_ty
412 = do { (op', op_ty) <- tcInferFun op
413 ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty) <-
414 matchActualFunTys (mk_op_msg op) SectionOrigin (Just op) 2 op_ty
415 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
416 (mkFunTy arg1_ty op_res_ty) res_ty
417 ; arg2' <- tcArg op arg2 arg2_ty 2
418 ; return ( mkHsWrap wrap_res $
419 SectionR (mkLHsWrap wrap_fun op') arg2' ) }
420
421 tcExpr expr@(SectionL arg1 op) res_ty
422 = do { (op', op_ty) <- tcInferFun op
423 ; dflags <- getDynFlags -- Note [Left sections]
424 ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1
425 | otherwise = 2
426
427 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty)
428 <- matchActualFunTys (mk_op_msg op) SectionOrigin (Just op)
429 n_reqd_args op_ty
430 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
431 (mkFunTys arg_tys op_res_ty) res_ty
432 ; arg1' <- tcArg op arg1 arg1_ty 1
433 ; return ( mkHsWrap wrap_res $
434 SectionL arg1' (mkLHsWrap wrap_fn op') ) }
435
436 tcExpr expr@(ExplicitTuple tup_args boxity) res_ty
437 | all tupArgPresent tup_args
438 = do { let arity = length tup_args
439 tup_tc = tupleTyCon boxity arity
440 ; res_ty <- expTypeToType res_ty
441 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
442 -- Unboxed tuples have RuntimeRep vars, which we
443 -- don't care about here
444 -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
445 ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys
446 Boxed -> arg_tys
447 ; tup_args1 <- tcTupArgs tup_args arg_tys'
448 ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
449
450 | otherwise
451 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
452 do { let arity = length tup_args
453
454 ; arg_tys <- case boxity of
455 { Boxed -> newFlexiTyVarTys arity liftedTypeKind
456 ; Unboxed -> replicateM arity newOpenFlexiTyVarTy }
457 ; let actual_res_ty
458 = mkFunTys [ty | (ty, (L _ (Missing _))) <- arg_tys `zip` tup_args]
459 (mkTupleTy boxity arg_tys)
460
461 ; wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "ExpTuple")
462 (Just expr)
463 actual_res_ty res_ty
464
465 -- Handle tuple sections where
466 ; tup_args1 <- tcTupArgs tup_args arg_tys
467
468 ; return $ mkHsWrap wrap (ExplicitTuple tup_args1 boxity) }
469
470 tcExpr (ExplicitList _ witness exprs) res_ty
471 = case witness of
472 Nothing -> do { res_ty <- expTypeToType res_ty
473 ; (coi, elt_ty) <- matchExpectedListTy res_ty
474 ; exprs' <- mapM (tc_elt elt_ty) exprs
475 ; return $
476 mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' }
477
478 Just fln -> do { ((exprs', elt_ty), fln')
479 <- tcSyntaxOp ListOrigin fln
480 [synKnownType intTy, SynList] res_ty $
481 \ [elt_ty] ->
482 do { exprs' <-
483 mapM (tc_elt elt_ty) exprs
484 ; return (exprs', elt_ty) }
485
486 ; return $ ExplicitList elt_ty (Just fln') exprs' }
487 where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
488
489 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
490 = do { res_ty <- expTypeToType res_ty
491 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
492 ; exprs' <- mapM (tc_elt elt_ty) exprs
493 ; return $
494 mkHsWrapCo coi $ ExplicitPArr elt_ty exprs' }
495 where
496 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
497
498 {-
499 ************************************************************************
500 * *
501 Let, case, if, do
502 * *
503 ************************************************************************
504 -}
505
506 tcExpr (HsLet (L l binds) expr) res_ty
507 = do { (binds', expr') <- tcLocalBinds binds $
508 tcMonoExpr expr res_ty
509 ; return (HsLet (L l binds') expr') }
510
511 tcExpr (HsCase scrut matches) res_ty
512 = do { -- We used to typecheck the case alternatives first.
513 -- The case patterns tend to give good type info to use
514 -- when typechecking the scrutinee. For example
515 -- case (map f) of
516 -- (x:xs) -> ...
517 -- will report that map is applied to too few arguments
518 --
519 -- But now, in the GADT world, we need to typecheck the scrutinee
520 -- first, to get type info that may be refined in the case alternatives
521 (scrut', scrut_ty) <- tcInferRho scrut
522
523 ; traceTc "HsCase" (ppr scrut_ty)
524 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
525 ; return (HsCase scrut' matches') }
526 where
527 match_ctxt = MC { mc_what = CaseAlt,
528 mc_body = tcBody }
529
530 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
531 = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy)
532 -- this forces the branches to be fully instantiated
533 -- (See #10619)
534 ; res_ty <- mkCheckExpType <$> expTypeToType res_ty
535 ; b1' <- tcMonoExpr b1 res_ty
536 ; b2' <- tcMonoExpr b2 res_ty
537 ; return (HsIf Nothing pred' b1' b2') }
538
539 tcExpr (HsIf (Just fun) pred b1 b2) res_ty
540 = do { ((pred', b1', b2'), fun')
541 <- tcSyntaxOp IfOrigin fun [SynAny, SynAny, SynAny] res_ty $
542 \ [pred_ty, b1_ty, b2_ty] ->
543 do { pred' <- tcPolyExpr pred pred_ty
544 ; b1' <- tcPolyExpr b1 b1_ty
545 ; b2' <- tcPolyExpr b2 b2_ty
546 ; return (pred', b1', b2') }
547 ; return (HsIf (Just fun') pred' b1' b2') }
548
549 tcExpr (HsMultiIf _ alts) res_ty
550 = do { res_ty <- if isSingleton alts
551 then return res_ty
552 else mkCheckExpType <$> expTypeToType res_ty
553 -- Just like Note [Case branches must never infer a non-tau type]
554 -- in TcMatches
555 ; alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
556 ; res_ty <- readExpType res_ty
557 ; return (HsMultiIf res_ty alts') }
558 where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
559
560 tcExpr (HsDo do_or_lc stmts _) res_ty
561 = do { expr' <- tcDoStmts do_or_lc stmts res_ty
562 ; return expr' }
563
564 tcExpr (HsProc pat cmd) res_ty
565 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
566 ; return $ mkHsWrapCo coi (HsProc pat' cmd') }
567
568 -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'.
569 tcExpr (HsStatic fvs expr) res_ty
570 = do { res_ty <- expTypeToType res_ty
571 ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty
572 ; (expr', lie) <- captureConstraints $
573 addErrCtxt (hang (text "In the body of a static form:")
574 2 (ppr expr)
575 ) $
576 tcPolyExprNC expr expr_ty
577 -- Check that the free variables of the static form are closed.
578 ; mapM_ checkClosedInStaticForm fvs
579
580 -- Require the type of the argument to be Typeable.
581 -- The evidence is not used, but asking the constraint ensures that
582 -- the current implementation is as restrictive as future versions
583 -- of the StaticPointers extension.
584 ; typeableClass <- tcLookupClass typeableClassName
585 ; _ <- emitWantedEvVar StaticOrigin $
586 mkTyConApp (classTyCon typeableClass)
587 [liftedTypeKind, expr_ty]
588 -- Insert the constraints of the static form in a global list for later
589 -- validation.
590 ; stWC <- tcg_static_wc <$> getGblEnv
591 ; updTcRef stWC (andWC lie)
592 -- Wrap the static form with the 'fromStaticPtr' call.
593 ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty
594 ; let wrap = mkWpTyApps [expr_ty]
595 ; loc <- getSrcSpanM
596 ; return $ mkHsWrapCo co $ HsApp (L loc $ mkHsWrap wrap fromStaticPtr)
597 (L loc (HsStatic fvs expr'))
598 }
599
600 {-
601 ************************************************************************
602 * *
603 Record construction and update
604 * *
605 ************************************************************************
606 -}
607
608 tcExpr expr@(RecordCon { rcon_con_name = L loc con_name
609 , rcon_flds = rbinds }) res_ty
610 = do { con_like <- tcLookupConLike con_name
611
612 -- Check for missing fields
613 ; checkMissingFields con_like rbinds
614
615 ; (con_expr, con_sigma) <- tcInferId con_name
616 ; (con_wrap, con_tau) <-
617 topInstantiate (OccurrenceOf con_name) con_sigma
618 -- a shallow instantiation should really be enough for
619 -- a data constructor.
620 ; let arity = conLikeArity con_like
621 (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
622 ; case conLikeWrapId_maybe con_like of
623 Nothing -> nonBidirectionalErr (conLikeName con_like)
624 Just con_id -> do {
625 res_wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "RecordCon")
626 (Just expr) actual_res_ty res_ty
627 ; rbinds' <- tcRecordBinds con_like arg_tys rbinds
628 ; return $
629 mkHsWrap res_wrap $
630 RecordCon { rcon_con_name = L loc con_id
631 , rcon_con_expr = mkHsWrap con_wrap con_expr
632 , rcon_con_like = con_like
633 , rcon_flds = rbinds' } } }
634
635 {-
636 Note [Type of a record update]
637 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
638 The main complication with RecordUpd is that we need to explicitly
639 handle the *non-updated* fields. Consider:
640
641 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
642 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
643 | MkT3 { fd :: a }
644
645 upd :: T a b c -> (b',c) -> T a b' c
646 upd t x = t { fb = x}
647
648 The result type should be (T a b' c)
649 not (T a b c), because 'b' *is not* mentioned in a non-updated field
650 not (T a b' c'), because 'c' *is* mentioned in a non-updated field
651 NB that it's not good enough to look at just one constructor; we must
652 look at them all; cf Trac #3219
653
654 After all, upd should be equivalent to:
655 upd t x = case t of
656 MkT1 p q -> MkT1 p x
657 MkT2 a b -> MkT2 p b
658 MkT3 d -> error ...
659
660 So we need to give a completely fresh type to the result record,
661 and then constrain it by the fields that are *not* updated ("p" above).
662 We call these the "fixed" type variables, and compute them in getFixedTyVars.
663
664 Note that because MkT3 doesn't contain all the fields being updated,
665 its RHS is simply an error, so it doesn't impose any type constraints.
666 Hence the use of 'relevant_cont'.
667
668 Note [Implicit type sharing]
669 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
670 We also take into account any "implicit" non-update fields. For example
671 data T a b where { MkT { f::a } :: T a a; ... }
672 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
673
674 Then consider
675 upd t x = t { f=x }
676 We infer the type
677 upd :: T a b -> a -> T a b
678 upd (t::T a b) (x::a)
679 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
680 We can't give it the more general type
681 upd :: T a b -> c -> T c b
682
683 Note [Criteria for update]
684 ~~~~~~~~~~~~~~~~~~~~~~~~~~
685 We want to allow update for existentials etc, provided the updated
686 field isn't part of the existential. For example, this should be ok.
687 data T a where { MkT { f1::a, f2::b->b } :: T a }
688 f :: T a -> b -> T b
689 f t b = t { f1=b }
690
691 The criterion we use is this:
692
693 The types of the updated fields
694 mention only the universally-quantified type variables
695 of the data constructor
696
697 NB: this is not (quite) the same as being a "naughty" record selector
698 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
699 in the case of GADTs. Consider
700 data T a where { MkT :: { f :: a } :: T [a] }
701 Then f is not "naughty" because it has a well-typed record selector.
702 But we don't allow updates for 'f'. (One could consider trying to
703 allow this, but it makes my head hurt. Badly. And no one has asked
704 for it.)
705
706 In principle one could go further, and allow
707 g :: T a -> T a
708 g t = t { f2 = \x -> x }
709 because the expression is polymorphic...but that seems a bridge too far.
710
711 Note [Data family example]
712 ~~~~~~~~~~~~~~~~~~~~~~~~~~
713 data instance T (a,b) = MkT { x::a, y::b }
714 --->
715 data :TP a b = MkT { a::a, y::b }
716 coTP a b :: T (a,b) ~ :TP a b
717
718 Suppose r :: T (t1,t2), e :: t3
719 Then r { x=e } :: T (t3,t1)
720 --->
721 case r |> co1 of
722 MkT x y -> MkT e y |> co2
723 where co1 :: T (t1,t2) ~ :TP t1 t2
724 co2 :: :TP t3 t2 ~ T (t3,t2)
725 The wrapping with co2 is done by the constructor wrapper for MkT
726
727 Outgoing invariants
728 ~~~~~~~~~~~~~~~~~~~
729 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
730
731 * cons are the data constructors to be updated
732
733 * in_inst_tys, out_inst_tys have same length, and instantiate the
734 *representation* tycon of the data cons. In Note [Data
735 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
736
737 Note [Mixed Record Field Updates]
738 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
739 Consider the following pattern synonym.
740
741 data MyRec = MyRec { foo :: Int, qux :: String }
742
743 pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}
744
745 This allows updates such as the following
746
747 updater :: MyRec -> MyRec
748 updater a = a {f1 = 1 }
749
750 It would also make sense to allow the following update (which we reject).
751
752 updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"
753
754 This leads to confusing behaviour when the selectors in fact refer the same
755 field.
756
757 updater a = a {f1 = 1, foo = 2} ==? ???
758
759 For this reason, we reject a mixture of pattern synonym and normal record
760 selectors in the same update block. Although of course we still allow the
761 following.
762
763 updater a = (a {f1 = 1}) {foo = 2}
764
765 > updater (MyRec 0 "str")
766 MyRec 2 "str"
767
768 -}
769
770 tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty
771 = ASSERT( notNull rbnds )
772 do { -- STEP -2: typecheck the record_expr, the record to be updated
773 (record_expr', record_rho) <- tcInferRho record_expr
774
775 -- STEP -1 See Note [Disambiguating record fields]
776 -- After this we know that rbinds is unambiguous
777 ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty
778 ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds
779 upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds
780 sel_ids = map selectorAmbiguousFieldOcc upd_flds
781 -- STEP 0
782 -- Check that the field names are really field names
783 -- and they are all field names for proper records or
784 -- all field names for pattern synonyms.
785 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
786 | fld <- rbinds,
787 -- Excludes class ops
788 let L loc sel_id = hsRecUpdFieldId (unLoc fld),
789 not (isRecordSelector sel_id),
790 let fld_name = idName sel_id ]
791 ; unless (null bad_guys) (sequence bad_guys >> failM)
792 -- See note [Mixed Record Selectors]
793 ; let (data_sels, pat_syn_sels) =
794 partition isDataConRecordSelector sel_ids
795 ; MASSERT( all isPatSynRecordSelector pat_syn_sels )
796 ; checkTc ( null data_sels || null pat_syn_sels )
797 ( mixedSelectors data_sels pat_syn_sels )
798
799 -- STEP 1
800 -- Figure out the tycon and data cons from the first field name
801 ; let -- It's OK to use the non-tc splitters here (for a selector)
802 sel_id : _ = sel_ids
803
804 mtycon :: Maybe TyCon
805 mtycon = case idDetails sel_id of
806 RecSelId (RecSelData tycon) _ -> Just tycon
807 _ -> Nothing
808
809 con_likes :: [ConLike]
810 con_likes = case idDetails sel_id of
811 RecSelId (RecSelData tc) _
812 -> map RealDataCon (tyConDataCons tc)
813 RecSelId (RecSelPatSyn ps) _
814 -> [PatSynCon ps]
815 _ -> panic "tcRecordUpd"
816 -- NB: for a data type family, the tycon is the instance tycon
817
818 relevant_cons = conLikesWithFields con_likes upd_fld_occs
819 -- A constructor is only relevant to this process if
820 -- it contains *all* the fields that are being updated
821 -- Other ones will cause a runtime error if they occur
822
823 -- Step 2
824 -- Check that at least one constructor has all the named fields
825 -- i.e. has an empty set of bad fields returned by badFields
826 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes)
827
828 -- Take apart a representative constructor
829 ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
830 (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _)
831 = conLikeFullSig con1
832 con1_flds = map flLabel $ conLikeFieldLabels con1
833 con1_tv_tys = mkTyVarTys con1_tvs
834 con1_res_ty = case mtycon of
835 Just tc -> mkFamilyTyConApp tc con1_tv_tys
836 Nothing -> conLikeResTy con1 con1_tv_tys
837
838 -- Check that we're not dealing with a unidirectional pattern
839 -- synonym
840 ; unless (isJust $ conLikeWrapId_maybe con1)
841 (nonBidirectionalErr (conLikeName con1))
842
843 -- STEP 3 Note [Criteria for update]
844 -- Check that each updated field is polymorphic; that is, its type
845 -- mentions only the universally-quantified variables of the data con
846 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
847 bad_upd_flds = filter bad_fld flds1_w_tys
848 con1_tv_set = mkVarSet con1_tvs
849 bad_fld (fld, ty) = fld `elem` upd_fld_occs &&
850 not (tyCoVarsOfType ty `subVarSet` con1_tv_set)
851 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
852
853 -- STEP 4 Note [Type of a record update]
854 -- Figure out types for the scrutinee and result
855 -- Both are of form (T a b c), with fresh type variables, but with
856 -- common variables where the scrutinee and result must have the same type
857 -- These are variables that appear in *any* arg of *any* of the
858 -- relevant constructors *except* in the updated fields
859 --
860 ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons
861 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
862
863 mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType)
864 -- Deals with instantiation of kind variables
865 -- c.f. TcMType.newMetaTyVars
866 mk_inst_ty subst (tv, result_inst_ty)
867 | is_fixed_tv tv -- Same as result type
868 = return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
869 | otherwise -- Fresh type, of correct kind
870 = do { (subst', new_tv) <- newMetaTyVarX subst tv
871 ; return (subst', mkTyVarTy new_tv) }
872
873 ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs
874 ; let result_inst_tys = mkTyVarTys con1_tvs'
875
876 ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty emptyTCvSubst
877 (con1_tvs `zip` result_inst_tys)
878
879 ; let rec_res_ty = TcType.substTy result_subst con1_res_ty
880 scrut_ty = TcType.substTyUnchecked scrut_subst con1_res_ty
881 con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
882
883 ; wrap_res <- tcSubTypeHR (exprCtOrigin expr)
884 (Just expr) rec_res_ty res_ty
885 ; co_scrut <- unifyType (Just record_expr) record_rho scrut_ty
886 -- NB: normal unification is OK here (as opposed to subsumption),
887 -- because for this to work out, both record_rho and scrut_ty have
888 -- to be normal datatypes -- no contravariant stuff can go on
889
890 -- STEP 5
891 -- Typecheck the bindings
892 ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds
893
894 -- STEP 6: Deal with the stupid theta
895 ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1)
896 ; instStupidTheta RecordUpdOrigin theta'
897
898 -- Step 7: make a cast for the scrutinee, in the
899 -- case that it's from a data family
900 ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty
901 fam_co | Just tycon <- mtycon
902 , Just co_con <- tyConFamilyCoercion_maybe tycon
903 = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys [])
904 | otherwise
905 = idHsWrapper
906
907 -- Step 8: Check that the req constraints are satisfied
908 -- For normal data constructors req_theta is empty but we must do
909 -- this check for pattern synonyms.
910 ; let req_theta' = substThetaUnchecked scrut_subst req_theta
911 ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta'
912
913 -- Phew!
914 ; return $
915 mkHsWrap wrap_res $
916 RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr')
917 , rupd_flds = rbinds'
918 , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys
919 , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } }
920
921 tcExpr (HsRecFld f) res_ty
922 = tcCheckRecSelId f res_ty
923
924 {-
925 ************************************************************************
926 * *
927 Arithmetic sequences e.g. [a,b..]
928 and their parallel-array counterparts e.g. [: a,b.. :]
929
930 * *
931 ************************************************************************
932 -}
933
934 tcExpr (ArithSeq _ witness seq) res_ty
935 = tcArithSeq witness seq res_ty
936
937 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
938 = do { res_ty <- expTypeToType res_ty
939 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
940 ; expr1' <- tcPolyExpr expr1 elt_ty
941 ; expr2' <- tcPolyExpr expr2 elt_ty
942 ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
943 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
944 (idName enumFromToP) elt_ty
945 ; return $
946 mkHsWrapCo coi $ PArrSeq enum_from_to (FromTo expr1' expr2') }
947
948 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
949 = do { res_ty <- expTypeToType res_ty
950 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
951 ; expr1' <- tcPolyExpr expr1 elt_ty
952 ; expr2' <- tcPolyExpr expr2 elt_ty
953 ; expr3' <- tcPolyExpr expr3 elt_ty
954 ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
955 ; eft <- newMethodFromName (PArrSeqOrigin seq)
956 (idName enumFromThenToP) elt_ty -- !!!FIXME: chak
957 ; return $
958 mkHsWrapCo coi $
959 PArrSeq eft (FromThenTo expr1' expr2' expr3') }
960
961 tcExpr (PArrSeq _ _) _
962 = panic "TcExpr.tcExpr: Infinite parallel array!"
963 -- the parser shouldn't have generated it and the renamer shouldn't have
964 -- let it through
965
966 {-
967 ************************************************************************
968 * *
969 Template Haskell
970 * *
971 ************************************************************************
972 -}
973
974 tcExpr (HsSpliceE splice) res_ty
975 = tcSpliceExpr splice res_ty
976 tcExpr (HsBracket brack) res_ty
977 = tcTypedBracket brack res_ty
978 tcExpr (HsRnBracketOut brack ps) res_ty
979 = tcUntypedBracket brack ps res_ty
980
981 {-
982 ************************************************************************
983 * *
984 Catch-all
985 * *
986 ************************************************************************
987 -}
988
989 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
990 -- Include ArrForm, ArrApp, which shouldn't appear at all
991 -- Also HsTcBracketOut, HsQuasiQuoteE
992
993 {-
994 ************************************************************************
995 * *
996 Arithmetic sequences [a..b] etc
997 * *
998 ************************************************************************
999 -}
1000
1001 tcArithSeq :: Maybe (SyntaxExpr Name) -> ArithSeqInfo Name -> ExpRhoType
1002 -> TcM (HsExpr TcId)
1003
1004 tcArithSeq witness seq@(From expr) res_ty
1005 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1006 ; expr' <- tcPolyExpr expr elt_ty
1007 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
1008 enumFromName elt_ty
1009 ; return $ mkHsWrap wrap $
1010 ArithSeq enum_from wit' (From expr') }
1011
1012 tcArithSeq witness seq@(FromThen expr1 expr2) res_ty
1013 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1014 ; expr1' <- tcPolyExpr expr1 elt_ty
1015 ; expr2' <- tcPolyExpr expr2 elt_ty
1016 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
1017 enumFromThenName elt_ty
1018 ; return $ mkHsWrap wrap $
1019 ArithSeq enum_from_then wit' (FromThen expr1' expr2') }
1020
1021 tcArithSeq witness seq@(FromTo expr1 expr2) res_ty
1022 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1023 ; expr1' <- tcPolyExpr expr1 elt_ty
1024 ; expr2' <- tcPolyExpr expr2 elt_ty
1025 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
1026 enumFromToName elt_ty
1027 ; return $ mkHsWrap wrap $
1028 ArithSeq enum_from_to wit' (FromTo expr1' expr2') }
1029
1030 tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty
1031 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1032 ; expr1' <- tcPolyExpr expr1 elt_ty
1033 ; expr2' <- tcPolyExpr expr2 elt_ty
1034 ; expr3' <- tcPolyExpr expr3 elt_ty
1035 ; eft <- newMethodFromName (ArithSeqOrigin seq)
1036 enumFromThenToName elt_ty
1037 ; return $ mkHsWrap wrap $
1038 ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') }
1039
1040 -----------------
1041 arithSeqEltType :: Maybe (SyntaxExpr Name) -> ExpRhoType
1042 -> TcM (HsWrapper, TcType, Maybe (SyntaxExpr Id))
1043 arithSeqEltType Nothing res_ty
1044 = do { res_ty <- expTypeToType res_ty
1045 ; (coi, elt_ty) <- matchExpectedListTy res_ty
1046 ; return (mkWpCastN coi, elt_ty, Nothing) }
1047 arithSeqEltType (Just fl) res_ty
1048 = do { (elt_ty, fl')
1049 <- tcSyntaxOp ListOrigin fl [SynList] res_ty $
1050 \ [elt_ty] -> return elt_ty
1051 ; return (idHsWrapper, elt_ty, Just fl') }
1052
1053 {-
1054 ************************************************************************
1055 * *
1056 Applications
1057 * *
1058 ************************************************************************
1059 -}
1060
1061 type LHsExprArgIn = Either (LHsExpr Name) (LHsWcType Name)
1062 type LHsExprArgOut = Either (LHsExpr TcId) (LHsWcType Name)
1063
1064 tcApp1 :: HsExpr Name -- either HsApp or HsAppType
1065 -> ExpRhoType -> TcM (HsExpr TcId)
1066 tcApp1 e res_ty
1067 = do { (wrap, fun, args) <- tcApp Nothing (noLoc e) [] res_ty
1068 ; return (mkHsWrap wrap $ unLoc $ foldl mk_hs_app fun args) }
1069 where
1070 mk_hs_app f (Left a) = mkHsApp f a
1071 mk_hs_app f (Right a) = mkHsAppTypeOut f a
1072
1073 tcApp :: Maybe SDoc -- like "The function `f' is applied to"
1074 -- or leave out to get exactly that message
1075 -> LHsExpr Name -> [LHsExprArgIn] -- Function and args
1076 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1077 -- (wrap, fun, args). For an ordinary function application,
1078 -- these should be assembled as (wrap (fun args)).
1079 -- But OpApp is slightly different, so that's why the caller
1080 -- must assemble
1081
1082 tcApp m_herald orig_fun orig_args res_ty
1083 = go orig_fun orig_args
1084 where
1085 go :: LHsExpr Name -> [LHsExprArgIn]
1086 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1087 go (L _ (HsPar e)) args = go e args
1088 go (L _ (HsApp e1 e2)) args = go e1 (Left e2:args)
1089 go (L _ (HsAppType e t)) args = go e (Right t:args)
1090
1091 go (L loc (HsVar (L _ fun))) args
1092 | fun `hasKey` tagToEnumKey
1093 , count isLeft args == 1
1094 = do { (wrap, expr, args) <- tcTagToEnum loc fun args res_ty
1095 ; return (wrap, expr, args) }
1096
1097 | fun `hasKey` seqIdKey
1098 , count isLeft args == 2
1099 = do { (wrap, expr, args) <- tcSeq loc fun args res_ty
1100 ; return (wrap, expr, args) }
1101
1102 go (L loc (HsRecFld (Ambiguous lbl _))) args@(Left (L _ arg) : _)
1103 | Just sig_ty <- obviousSig arg
1104 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
1105 ; sel_name <- disambiguateSelector lbl sig_tc_ty
1106 ; go (L loc (HsRecFld (Unambiguous lbl sel_name))) args }
1107
1108 go fun args
1109 = do { -- Type-check the function
1110 ; (fun1, fun_sigma) <- tcInferFun fun
1111 ; let orig = exprCtOrigin (unLoc fun)
1112
1113 ; (wrap_fun, args1, actual_res_ty)
1114 <- tcArgs fun fun_sigma orig args
1115 (m_herald `orElse` mk_app_msg fun)
1116
1117 -- this is just like tcWrapResult, but the types don't line
1118 -- up to call that function
1119 ; wrap_res <- addFunResCtxt True (unLoc fun) actual_res_ty res_ty $
1120 tcSubTypeDS_NC_O orig GenSigCtxt
1121 (Just $ foldl mk_hs_app fun args)
1122 actual_res_ty res_ty
1123
1124 ; return (wrap_res, mkLHsWrap wrap_fun fun1, args1) }
1125
1126 mk_hs_app f (Left a) = mkHsApp f a
1127 mk_hs_app f (Right a) = mkHsAppType f a
1128
1129 mk_app_msg :: LHsExpr Name -> SDoc
1130 mk_app_msg fun = sep [ text "The function" <+> quotes (ppr fun)
1131 , text "is applied to"]
1132
1133 mk_op_msg :: LHsExpr Name -> SDoc
1134 mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes"
1135
1136 ----------------
1137 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcSigmaType)
1138 -- Infer type of a function
1139 tcInferFun (L loc (HsVar (L _ name)))
1140 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
1141 -- Don't wrap a context around a plain Id
1142 ; return (L loc fun, ty) }
1143
1144 tcInferFun (L loc (HsRecFld f))
1145 = do { (fun, ty) <- setSrcSpan loc (tcInferRecSelId f)
1146 -- Don't wrap a context around a plain Id
1147 ; return (L loc fun, ty) }
1148
1149 tcInferFun fun
1150 = do { (fun, fun_ty) <- tcInferSigma fun
1151
1152 -- Zonk the function type carefully, to expose any polymorphism
1153 -- E.g. (( \(x::forall a. a->a). blah ) e)
1154 -- We can see the rank-2 type of the lambda in time to generalise e
1155 ; fun_ty' <- zonkTcType fun_ty
1156
1157 ; return (fun, fun_ty') }
1158
1159 ----------------
1160 -- | Type-check the arguments to a function, possibly including visible type
1161 -- applications
1162 tcArgs :: LHsExpr Name -- ^ The function itself (for err msgs only)
1163 -> TcSigmaType -- ^ the (uninstantiated) type of the function
1164 -> CtOrigin -- ^ the origin for the function's type
1165 -> [LHsExprArgIn] -- ^ the args
1166 -> SDoc -- ^ the herald for matchActualFunTys
1167 -> TcM (HsWrapper, [LHsExprArgOut], TcSigmaType)
1168 -- ^ (a wrapper for the function, the tc'd args, result type)
1169 tcArgs fun orig_fun_ty fun_orig orig_args herald
1170 = go [] 1 orig_fun_ty orig_args
1171 where
1172 orig_arity = length orig_args
1173
1174 go _ _ fun_ty [] = return (idHsWrapper, [], fun_ty)
1175
1176 go acc_args n fun_ty (Right hs_ty_arg:args)
1177 = do { (wrap1, upsilon_ty) <- topInstantiateInferred fun_orig fun_ty
1178 -- wrap1 :: fun_ty "->" upsilon_ty
1179 ; case tcSplitForAllTy_maybe upsilon_ty of
1180 Just (binder, inner_ty)
1181 | Just tv <- binderVar_maybe binder ->
1182 ASSERT2( binderVisibility binder == Specified
1183 , (vcat [ ppr fun_ty, ppr upsilon_ty, ppr binder
1184 , ppr inner_ty, pprTvBndr tv
1185 , ppr (binderVisibility binder) ]) )
1186 do { let kind = tyVarKind tv
1187 ; ty_arg <- tcHsTypeApp hs_ty_arg kind
1188 ; let insted_ty = substTyWithUnchecked [tv] [ty_arg] inner_ty
1189 ; (inner_wrap, args', res_ty)
1190 <- go acc_args (n+1) insted_ty args
1191 -- inner_wrap :: insted_ty "->" (map typeOf args') -> res_ty
1192 ; let inst_wrap = mkWpTyApps [ty_arg]
1193 ; return ( inner_wrap <.> inst_wrap <.> wrap1
1194 , Right hs_ty_arg : args'
1195 , res_ty ) }
1196 _ -> ty_app_err upsilon_ty hs_ty_arg }
1197
1198 go acc_args n fun_ty (Left arg : args)
1199 = do { (wrap, [arg_ty], res_ty)
1200 <- matchActualFunTysPart herald fun_orig (Just fun) 1 fun_ty
1201 acc_args orig_arity
1202 -- wrap :: fun_ty "->" arg_ty -> res_ty
1203 ; arg' <- tcArg fun arg arg_ty n
1204 ; (inner_wrap, args', inner_res_ty)
1205 <- go (arg_ty : acc_args) (n+1) res_ty args
1206 -- inner_wrap :: res_ty "->" (map typeOf args') -> inner_res_ty
1207 ; return ( mkWpFun idHsWrapper inner_wrap arg_ty res_ty <.> wrap
1208 , Left arg' : args'
1209 , inner_res_ty ) }
1210
1211 ty_app_err ty arg
1212 = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty
1213 ; failWith $
1214 text "Cannot apply expression of type" <+> quotes (ppr ty) $$
1215 text "to a visible type argument" <+> quotes (ppr arg) }
1216
1217 ----------------
1218 tcArg :: LHsExpr Name -- The function (for error messages)
1219 -> LHsExpr Name -- Actual arguments
1220 -> TcRhoType -- expected arg type
1221 -> Int -- # of argument
1222 -> TcM (LHsExpr TcId) -- Resulting argument
1223 tcArg fun arg ty arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $
1224 tcPolyExprNC arg ty
1225
1226 ----------------
1227 tcTupArgs :: [LHsTupArg Name] -> [TcSigmaType] -> TcM [LHsTupArg TcId]
1228 tcTupArgs args tys
1229 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
1230 where
1231 go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty))
1232 go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
1233 ; return (L l (Present expr')) }
1234
1235 ---------------------------
1236 -- See TcType.SyntaxOpType also for commentary
1237 tcSyntaxOp :: CtOrigin
1238 -> SyntaxExpr Name
1239 -> [SyntaxOpType] -- ^ shape of syntax operator arguments
1240 -> ExpType -- ^ overall result type
1241 -> ([TcSigmaType] -> TcM a) -- ^ Type check any arguments
1242 -> TcM (a, SyntaxExpr TcId)
1243 -- ^ Typecheck a syntax operator
1244 -- The operator is always a variable at this stage (i.e. renamer output)
1245 tcSyntaxOp orig expr arg_tys res_ty
1246 = tcSyntaxOpGen orig expr arg_tys (SynType res_ty)
1247
1248 -- | Slightly more general version of 'tcSyntaxOp' that allows the caller
1249 -- to specify the shape of the result of the syntax operator
1250 tcSyntaxOpGen :: CtOrigin
1251 -> SyntaxExpr Name
1252 -> [SyntaxOpType]
1253 -> SyntaxOpType
1254 -> ([TcSigmaType] -> TcM a)
1255 -> TcM (a, SyntaxExpr TcId)
1256 tcSyntaxOpGen orig (SyntaxExpr { syn_expr = HsVar (L _ op) })
1257 arg_tys res_ty thing_inside
1258 = do { (expr, sigma) <- tcInferId op
1259 ; (result, expr_wrap, arg_wraps, res_wrap)
1260 <- tcSynArgA orig sigma arg_tys res_ty $
1261 thing_inside
1262 ; return (result, SyntaxExpr { syn_expr = mkHsWrap expr_wrap expr
1263 , syn_arg_wraps = arg_wraps
1264 , syn_res_wrap = res_wrap }) }
1265
1266 tcSyntaxOpGen _ other _ _ _ = pprPanic "tcSyntaxOp" (ppr other)
1267
1268 {-
1269 Note [tcSynArg]
1270 ~~~~~~~~~~~~~~~
1271 Because of the rich structure of SyntaxOpType, we must do the
1272 contra-/covariant thing when working down arrows, to get the
1273 instantiation vs. skolemisation decisions correct (and, more
1274 obviously, the orientation of the HsWrappers). We thus have
1275 two tcSynArgs.
1276 -}
1277
1278 -- works on "expected" types, skolemising where necessary
1279 -- See Note [tcSynArg]
1280 tcSynArgE :: CtOrigin
1281 -> TcSigmaType
1282 -> SyntaxOpType -- ^ shape it is expected to have
1283 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1284 -> TcM (a, HsWrapper)
1285 -- ^ returns a wrapper :: (type of right shape) "->" (type passed in)
1286 tcSynArgE orig sigma_ty syn_ty thing_inside
1287 = do { (skol_wrap, (result, ty_wrapper))
1288 <- tcSkolemise GenSigCtxt sigma_ty $ \ _ rho_ty ->
1289 go rho_ty syn_ty
1290 ; return (result, skol_wrap <.> ty_wrapper) }
1291 where
1292 go rho_ty SynAny
1293 = do { result <- thing_inside [rho_ty]
1294 ; return (result, idHsWrapper) }
1295
1296 go rho_ty SynRho -- same as SynAny, because we skolemise eagerly
1297 = do { result <- thing_inside [rho_ty]
1298 ; return (result, idHsWrapper) }
1299
1300 go rho_ty SynList
1301 = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty
1302 ; result <- thing_inside [elt_ty]
1303 ; return (result, mkWpCastN list_co) }
1304
1305 go rho_ty (SynFun arg_shape res_shape)
1306 = do { ( ( ( (result, arg_ty, res_ty)
1307 , res_wrapper ) -- :: res_ty_out "->" res_ty
1308 , arg_wrapper1, [], arg_wrapper2 ) -- :: arg_ty "->" arg_ty_out
1309 , match_wrapper ) -- :: (arg_ty -> res_ty) "->" rho_ty
1310 <- matchExpectedFunTys herald 1 (mkCheckExpType rho_ty) $
1311 \ [arg_ty] res_ty ->
1312 do { arg_tc_ty <- expTypeToType arg_ty
1313 ; res_tc_ty <- expTypeToType res_ty
1314
1315 -- another nested arrow is too much for now,
1316 -- but I bet we'll never need this
1317 ; MASSERT2( case arg_shape of
1318 SynFun {} -> False;
1319 _ -> True
1320 , text "Too many nested arrows in SyntaxOpType" $$
1321 pprCtOrigin orig )
1322
1323 ; tcSynArgA orig arg_tc_ty [] arg_shape $
1324 \ arg_results ->
1325 tcSynArgE orig res_tc_ty res_shape $
1326 \ res_results ->
1327 do { result <- thing_inside (arg_results ++ res_results)
1328 ; return (result, arg_tc_ty, res_tc_ty) }}
1329
1330 ; return ( result
1331 , match_wrapper <.>
1332 mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper
1333 arg_ty res_ty ) }
1334 where
1335 herald = text "This rebindable syntax expects a function with"
1336
1337 go rho_ty (SynType the_ty)
1338 = do { wrap <- tcSubTypeET orig the_ty rho_ty
1339 ; result <- thing_inside []
1340 ; return (result, wrap) }
1341
1342 -- works on "actual" types, instantiating where necessary
1343 -- See Note [tcSynArg]
1344 tcSynArgA :: CtOrigin
1345 -> TcSigmaType
1346 -> [SyntaxOpType] -- ^ argument shapes
1347 -> SyntaxOpType -- ^ result shape
1348 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1349 -> TcM (a, HsWrapper, [HsWrapper], HsWrapper)
1350 -- ^ returns a wrapper to be applied to the original function,
1351 -- wrappers to be applied to arguments
1352 -- and a wrapper to be applied to the overall expression
1353 tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside
1354 = do { (match_wrapper, arg_tys, res_ty)
1355 <- matchActualFunTys herald orig noThing (length arg_shapes) sigma_ty
1356 -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty)
1357 ; ((result, res_wrapper), arg_wrappers)
1358 <- tc_syn_args_e arg_tys arg_shapes $ \ arg_results ->
1359 tc_syn_arg res_ty res_shape $ \ res_results ->
1360 thing_inside (arg_results ++ res_results)
1361 ; return (result, match_wrapper, arg_wrappers, res_wrapper) }
1362 where
1363 herald = text "This rebindable syntax expects a function with"
1364
1365 tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType]
1366 -> ([TcSigmaType] -> TcM a)
1367 -> TcM (a, [HsWrapper])
1368 -- the wrappers are for arguments
1369 tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside
1370 = do { ((result, arg_wraps), arg_wrap)
1371 <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results ->
1372 tc_syn_args_e arg_tys arg_shapes $ \ args_results ->
1373 thing_inside (arg1_results ++ args_results)
1374 ; return (result, arg_wrap : arg_wraps) }
1375 tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside []
1376
1377 tc_syn_arg :: TcSigmaType -> SyntaxOpType
1378 -> ([TcSigmaType] -> TcM a)
1379 -> TcM (a, HsWrapper)
1380 -- the wrapper applies to the overall result
1381 tc_syn_arg res_ty SynAny thing_inside
1382 = do { result <- thing_inside [res_ty]
1383 ; return (result, idHsWrapper) }
1384 tc_syn_arg res_ty SynRho thing_inside
1385 = do { (inst_wrap, rho_ty) <- deeplyInstantiate orig res_ty
1386 -- inst_wrap :: res_ty "->" rho_ty
1387 ; result <- thing_inside [rho_ty]
1388 ; return (result, inst_wrap) }
1389 tc_syn_arg res_ty SynList thing_inside
1390 = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty
1391 -- inst_wrap :: res_ty "->" rho_ty
1392 ; (list_co, elt_ty) <- matchExpectedListTy rho_ty
1393 -- list_co :: [elt_ty] ~N rho_ty
1394 ; result <- thing_inside [elt_ty]
1395 ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) }
1396 tc_syn_arg _ (SynFun {}) _
1397 = pprPanic "tcSynArgA hits a SynFun" (ppr orig)
1398 tc_syn_arg res_ty (SynType the_ty) thing_inside
1399 = do { wrap <- tcSubTypeO orig GenSigCtxt res_ty the_ty
1400 ; result <- thing_inside []
1401 ; return (result, wrap) }
1402
1403 {-
1404 Note [Push result type in]
1405 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1406 Unify with expected result before type-checking the args so that the
1407 info from res_ty percolates to args. This is when we might detect a
1408 too-few args situation. (One can think of cases when the opposite
1409 order would give a better error message.)
1410 experimenting with putting this first.
1411
1412 Here's an example where it actually makes a real difference
1413
1414 class C t a b | t a -> b
1415 instance C Char a Bool
1416
1417 data P t a = forall b. (C t a b) => MkP b
1418 data Q t = MkQ (forall a. P t a)
1419
1420 f1, f2 :: Q Char;
1421 f1 = MkQ (MkP True)
1422 f2 = MkQ (MkP True :: forall a. P Char a)
1423
1424 With the change, f1 will type-check, because the 'Char' info from
1425 the signature is propagated into MkQ's argument. With the check
1426 in the other order, the extra signature in f2 is reqd.
1427
1428 ************************************************************************
1429 * *
1430 Expressions with a type signature
1431 expr :: type
1432 * *
1433 ********************************************************************* -}
1434
1435 tcExprSig :: LHsExpr Name -> TcIdSigInfo -> TcM (LHsExpr TcId, TcType)
1436 tcExprSig expr sig@(TISI { sig_bndr = s_bndr
1437 , sig_skols = skol_prs
1438 , sig_theta = theta
1439 , sig_tau = tau })
1440 | null skol_prs -- Fast path when there is no quantification at all
1441 , null theta
1442 , CompleteSig {} <- s_bndr
1443 = do { expr' <- tcPolyExprNC expr tau
1444 ; return (expr', tau) }
1445
1446 | CompleteSig poly_id <- s_bndr
1447 = do { given <- newEvVars theta
1448 ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $
1449 tcExtendTyVarEnvFromSig sig $
1450 tcPolyExprNC expr tau
1451
1452 ; let poly_wrap = mkWpTyLams skol_tvs
1453 <.> mkWpLams given
1454 <.> mkWpLet ev_binds
1455 ; return (mkLHsWrap poly_wrap expr', idType poly_id) }
1456
1457 | PartialSig { sig_name = name, sig_wcs = wc_prs, sig_hs_ty = hs_ty } <- s_bndr
1458 = do { (tclvl, wanted, expr')
1459 <- pushLevelAndCaptureConstraints $
1460 tcExtendTyVarEnvFromSig sig $
1461 do { addErrCtxt (pprSigCtxt ExprSigCtxt (ppr hs_ty)) $
1462 emitWildCardHoleConstraints wc_prs
1463 ; tcPolyExprNC expr tau }
1464 ; (qtvs, givens, ev_binds)
1465 <- simplifyInfer tclvl False [sig] [(name, tau)] wanted
1466 ; tau <- zonkTcType tau
1467 ; let inferred_theta = map evVarPred givens
1468 tau_tvs = tyCoVarsOfType tau
1469 ; (binders, my_theta) <- chooseInferredQuantifiers inferred_theta
1470 tau_tvs qtvs (Just sig)
1471 ; let inferred_sigma = mkInvSigmaTy qtvs inferred_theta tau
1472 my_sigma = mkForAllTys binders (mkPhiTy my_theta tau)
1473 ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis.
1474 then return idHsWrapper -- Fast path; also avoids complaint when we infer
1475 -- an ambiguouse type and have AllowAmbiguousType
1476 -- e..g infer x :: forall a. F a -> Int
1477 else tcSubType_NC ExprSigCtxt inferred_sigma
1478 (mkCheckExpType my_sigma)
1479
1480 ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma)
1481 ; let poly_wrap = wrap
1482 <.> mkWpTyLams qtvs
1483 <.> mkWpLams givens
1484 <.> mkWpLet ev_binds
1485 ; return (mkLHsWrap poly_wrap expr', my_sigma) }
1486
1487 | otherwise = panic "tcExprSig" -- Can't happen
1488 where
1489 skol_info = SigSkol ExprSigCtxt (mkPhiTy theta tau)
1490 skol_tvs = map snd skol_prs
1491
1492 {- *********************************************************************
1493 * *
1494 tcInferId
1495 * *
1496 ********************************************************************* -}
1497
1498 tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr TcId)
1499 tcCheckId name res_ty
1500 = do { (expr, actual_res_ty) <- tcInferId name
1501 ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty])
1502 ; addFunResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty $
1503 tcWrapResultO (OccurrenceOf name) expr actual_res_ty res_ty }
1504
1505 tcCheckRecSelId :: AmbiguousFieldOcc Name -> ExpRhoType -> TcM (HsExpr TcId)
1506 tcCheckRecSelId f@(Unambiguous (L _ lbl) _) res_ty
1507 = do { (expr, actual_res_ty) <- tcInferRecSelId f
1508 ; addFunResCtxt False (HsRecFld f) actual_res_ty res_ty $
1509 tcWrapResultO (OccurrenceOfRecSel lbl) expr actual_res_ty res_ty }
1510 tcCheckRecSelId (Ambiguous lbl _) res_ty
1511 = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of
1512 Nothing -> ambiguousSelector lbl
1513 Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg
1514 ; tcCheckRecSelId (Unambiguous lbl sel_name) res_ty }
1515
1516 ------------------------
1517 tcInferRecSelId :: AmbiguousFieldOcc Name -> TcM (HsExpr TcId, TcRhoType)
1518 tcInferRecSelId (Unambiguous (L _ lbl) sel)
1519 = do { (expr', ty) <- tc_infer_id lbl sel
1520 ; return (expr', ty) }
1521 tcInferRecSelId (Ambiguous lbl _)
1522 = ambiguousSelector lbl
1523
1524 ------------------------
1525 tcInferId :: Name -> TcM (HsExpr TcId, TcSigmaType)
1526 -- Look up an occurrence of an Id
1527 tcInferId id_name
1528 | id_name `hasKey` tagToEnumKey
1529 = failWithTc (text "tagToEnum# must appear applied to one argument")
1530 -- tcApp catches the case (tagToEnum# arg)
1531
1532 | id_name `hasKey` assertIdKey
1533 = do { dflags <- getDynFlags
1534 ; if gopt Opt_IgnoreAsserts dflags
1535 then tc_infer_id (nameRdrName id_name) id_name
1536 else tc_infer_assert id_name }
1537
1538 | otherwise
1539 = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) id_name
1540 ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty)
1541 ; return (expr, ty) }
1542
1543 tc_infer_assert :: Name -> TcM (HsExpr TcId, TcSigmaType)
1544 -- Deal with an occurrence of 'assert'
1545 -- See Note [Adding the implicit parameter to 'assert']
1546 tc_infer_assert assert_name
1547 = do { assert_error_id <- tcLookupId assertErrorName
1548 ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name)
1549 (idType assert_error_id)
1550 ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho)
1551 }
1552
1553 tc_infer_id :: RdrName -> Name -> TcM (HsExpr TcId, TcSigmaType)
1554 tc_infer_id lbl id_name
1555 = do { thing <- tcLookup id_name
1556 ; case thing of
1557 ATcId { tct_id = id }
1558 -> do { check_naughty id -- Note [Local record selectors]
1559 ; checkThLocalId id
1560 ; return_id id }
1561
1562 AGlobal (AnId id)
1563 -> do { check_naughty id
1564 ; return_id id }
1565 -- A global cannot possibly be ill-staged
1566 -- nor does it need the 'lifting' treatment
1567 -- hence no checkTh stuff here
1568
1569 AGlobal (AConLike cl) -> case cl of
1570 RealDataCon con -> return_data_con con
1571 PatSynCon ps -> tcPatSynBuilderOcc ps
1572
1573 _ -> failWithTc $
1574 ppr thing <+> text "used where a value identifier was expected" }
1575 where
1576 return_id id = return (HsVar (noLoc id), idType id)
1577
1578 return_data_con con
1579 -- For data constructors, must perform the stupid-theta check
1580 | null stupid_theta
1581 = return_id con_wrapper_id
1582
1583 | otherwise
1584 -- See Note [Instantiating stupid theta]
1585 = do { let (tvs, theta, rho) = tcSplitSigmaTy (idType con_wrapper_id)
1586 ; (subst, tvs') <- newMetaTyVars tvs
1587 ; let tys' = mkTyVarTys tvs'
1588 theta' = substTheta subst theta
1589 rho' = substTy subst rho
1590 ; wrap <- instCall (OccurrenceOf id_name) tys' theta'
1591 ; addDataConStupidTheta con tys'
1592 ; return (mkHsWrap wrap (HsVar (noLoc con_wrapper_id)), rho') }
1593
1594 where
1595 con_wrapper_id = dataConWrapId con
1596 stupid_theta = dataConStupidTheta con
1597
1598 check_naughty id
1599 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl)
1600 | otherwise = return ()
1601
1602
1603 tcUnboundId :: UnboundVar -> ExpRhoType -> TcM (HsExpr TcId)
1604 -- Typechedk an occurrence of an unbound Id
1605 --
1606 -- Some of these started life as a true hole "_". Others might simply
1607 -- be variables that accidentally have no binding site
1608 --
1609 -- We turn all of them into HsVar, since HsUnboundVar can't contain an
1610 -- Id; and indeed the evidence for the CHoleCan does bind it, so it's
1611 -- not unbound any more!
1612 tcUnboundId unbound res_ty
1613 = do { ty <- newFlexiTyVarTy liftedTypeKind
1614 ; let occ = unboundVarOcc unbound
1615 ; name <- newSysName occ
1616 ; let ev = mkLocalId name ty
1617 ; loc <- getCtLocM HoleOrigin Nothing
1618 ; let can = CHoleCan { cc_ev = CtWanted { ctev_pred = ty
1619 , ctev_dest = EvVarDest ev
1620 , ctev_loc = loc}
1621 , cc_hole = ExprHole unbound }
1622 ; emitInsoluble can
1623 ; tcWrapResultO (UnboundOccurrenceOf occ) (HsVar (noLoc ev)) ty res_ty }
1624
1625
1626 {-
1627 Note [Adding the implicit parameter to 'assert']
1628 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1629 The typechecker transforms (assert e1 e2) to (assertError e1 e2).
1630 This isn't really the Right Thing because there's no way to "undo"
1631 if you want to see the original source code in the typechecker
1632 output. We'll have fix this in due course, when we care more about
1633 being able to reconstruct the exact original program.
1634
1635 Note [tagToEnum#]
1636 ~~~~~~~~~~~~~~~~~
1637 Nasty check to ensure that tagToEnum# is applied to a type that is an
1638 enumeration TyCon. Unification may refine the type later, but this
1639 check won't see that, alas. It's crude, because it relies on our
1640 knowing *now* that the type is ok, which in turn relies on the
1641 eager-unification part of the type checker pushing enough information
1642 here. In theory the Right Thing to do is to have a new form of
1643 constraint but I definitely cannot face that! And it works ok as-is.
1644
1645 Here's are two cases that should fail
1646 f :: forall a. a
1647 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1648
1649 g :: Int
1650 g = tagToEnum# 0 -- Int is not an enumeration
1651
1652 When data type families are involved it's a bit more complicated.
1653 data family F a
1654 data instance F [Int] = A | B | C
1655 Then we want to generate something like
1656 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1657 Usually that coercion is hidden inside the wrappers for
1658 constructors of F [Int] but here we have to do it explicitly.
1659
1660 It's all grotesquely complicated.
1661
1662 Note [Instantiating stupid theta]
1663 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1664 Normally, when we infer the type of an Id, we don't instantiate,
1665 because we wish to allow for visible type application later on.
1666 But if a datacon has a stupid theta, we're a bit stuck. We need
1667 to emit the stupid theta constraints with instantiated types. It's
1668 difficult to defer this to the lazy instantiation, because a stupid
1669 theta has no spot to put it in a type. So we just instantiate eagerly
1670 in this case. Thus, users cannot use visible type application with
1671 a data constructor sporting a stupid theta. I won't feel so bad for
1672 the users that complain.
1673
1674 -}
1675
1676 tcSeq :: SrcSpan -> Name -> [LHsExprArgIn]
1677 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1678 -- (seq e1 e2) :: res_ty
1679 -- We need a special typing rule because res_ty can be unboxed
1680 -- See Note [Typing rule for seq]
1681 tcSeq loc fun_name args res_ty
1682 = do { fun <- tcLookupId fun_name
1683 ; (arg1_ty, args1) <- case args of
1684 (Right hs_ty_arg1 : args1)
1685 -> do { ty_arg1 <- tcHsTypeApp hs_ty_arg1 liftedTypeKind
1686 ; return (ty_arg1, args1) }
1687
1688 _ -> do { arg_ty1 <- newFlexiTyVarTy liftedTypeKind
1689 ; return (arg_ty1, args) }
1690
1691 ; (arg1, arg2, arg2_exp_ty) <- case args1 of
1692 [Right hs_ty_arg2, Left term_arg1, Left term_arg2]
1693 -> do { rr_ty <- newFlexiTyVarTy runtimeRepTy
1694 ; ty_arg2 <- tcHsTypeApp hs_ty_arg2 (tYPE rr_ty)
1695 -- see Note [Typing rule for seq]
1696 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg2 res_ty
1697 ; return (term_arg1, term_arg2, mkCheckExpType ty_arg2) }
1698 [Left term_arg1, Left term_arg2]
1699 -> return (term_arg1, term_arg2, res_ty)
1700 _ -> too_many_args "seq" args
1701
1702 ; arg1' <- tcMonoExpr arg1 (mkCheckExpType arg1_ty)
1703 ; arg2' <- tcMonoExpr arg2 arg2_exp_ty
1704 ; res_ty <- readExpType res_ty -- by now, it's surely filled in
1705 ; let fun' = L loc (HsWrap ty_args (HsVar (L loc fun)))
1706 ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty
1707 ; return (idHsWrapper, fun', [Left arg1', Left arg2']) }
1708
1709 tcTagToEnum :: SrcSpan -> Name -> [LHsExprArgIn] -> ExpRhoType
1710 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1711 -- tagToEnum# :: forall a. Int# -> a
1712 -- See Note [tagToEnum#] Urgh!
1713 tcTagToEnum loc fun_name args res_ty
1714 = do { fun <- tcLookupId fun_name
1715
1716 ; arg <- case args of
1717 [Right hs_ty_arg, Left term_arg]
1718 -> do { ty_arg <- tcHsTypeApp hs_ty_arg liftedTypeKind
1719 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg res_ty
1720 -- other than influencing res_ty, we just
1721 -- don't care about a type arg passed in.
1722 -- So drop the evidence.
1723 ; return term_arg }
1724 [Left term_arg] -> do { _ <- expTypeToType res_ty
1725 ; return term_arg }
1726 _ -> too_many_args "tagToEnum#" args
1727
1728 ; res_ty <- readExpType res_ty
1729 ; ty' <- zonkTcType res_ty
1730
1731 -- Check that the type is algebraic
1732 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1733 Just (tc, tc_args) = mb_tc_app
1734 ; checkTc (isJust mb_tc_app)
1735 (mk_error ty' doc1)
1736
1737 -- Look through any type family
1738 ; fam_envs <- tcGetFamInstEnvs
1739 ; let (rep_tc, rep_args, coi)
1740 = tcLookupDataFamInst fam_envs tc tc_args
1741 -- coi :: tc tc_args ~R rep_tc rep_args
1742
1743 ; checkTc (isEnumerationTyCon rep_tc)
1744 (mk_error ty' doc2)
1745
1746 ; arg' <- tcMonoExpr arg (mkCheckExpType intPrimTy)
1747 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar (L loc fun)))
1748 rep_ty = mkTyConApp rep_tc rep_args
1749
1750 ; return (mkWpCastR (mkTcSymCo coi), fun', [Left arg']) }
1751 -- coi is a Representational coercion
1752 where
1753 doc1 = vcat [ text "Specify the type by giving a type signature"
1754 , text "e.g. (tagToEnum# x) :: Bool" ]
1755 doc2 = text "Result type must be an enumeration type"
1756
1757 mk_error :: TcType -> SDoc -> SDoc
1758 mk_error ty what
1759 = hang (text "Bad call to tagToEnum#"
1760 <+> text "at type" <+> ppr ty)
1761 2 what
1762
1763 too_many_args :: String -> [LHsExprArgIn] -> TcM a
1764 too_many_args fun args
1765 = failWith $
1766 hang (text "Too many type arguments to" <+> text fun <> colon)
1767 2 (sep (map pp args))
1768 where
1769 pp (Left e) = pprParendLExpr e
1770 pp (Right (HsWC { hswc_body = L _ t })) = pprParendHsType t
1771
1772
1773 {-
1774 ************************************************************************
1775 * *
1776 Template Haskell checks
1777 * *
1778 ************************************************************************
1779 -}
1780
1781 checkThLocalId :: Id -> TcM ()
1782 checkThLocalId id
1783 = do { mb_local_use <- getStageAndBindLevel (idName id)
1784 ; case mb_local_use of
1785 Just (top_lvl, bind_lvl, use_stage)
1786 | thLevel use_stage > bind_lvl
1787 , isNotTopLevel top_lvl
1788 -> checkCrossStageLifting id use_stage
1789 _ -> return () -- Not a locally-bound thing, or
1790 -- no cross-stage link
1791 }
1792
1793 --------------------------------------
1794 checkCrossStageLifting :: Id -> ThStage -> TcM ()
1795 -- If we are inside typed brackets, and (use_lvl > bind_lvl)
1796 -- we must check whether there's a cross-stage lift to do
1797 -- Examples \x -> [|| x ||]
1798 -- [|| map ||]
1799 -- There is no error-checking to do, because the renamer did that
1800 --
1801 -- This is similar to checkCrossStageLifting in RnSplice, but
1802 -- this code is applied to *typed* brackets.
1803
1804 checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var))
1805 = -- Nested identifiers, such as 'x' in
1806 -- E.g. \x -> [|| h x ||]
1807 -- We must behave as if the reference to x was
1808 -- h $(lift x)
1809 -- We use 'x' itself as the splice proxy, used by
1810 -- the desugarer to stitch it all back together.
1811 -- If 'x' occurs many times we may get many identical
1812 -- bindings of the same splice proxy, but that doesn't
1813 -- matter, although it's a mite untidy.
1814 do { let id_ty = idType id
1815 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1816 -- If x is polymorphic, its occurrence sites might
1817 -- have different instantiations, so we can't use plain
1818 -- 'x' as the splice proxy name. I don't know how to
1819 -- solve this, and it's probably unimportant, so I'm
1820 -- just going to flag an error for now
1821
1822 ; lift <- if isStringTy id_ty then
1823 do { sid <- tcLookupId THNames.liftStringName
1824 -- See Note [Lifting strings]
1825 ; return (HsVar (noLoc sid)) }
1826 else
1827 setConstraintVar lie_var $
1828 -- Put the 'lift' constraint into the right LIE
1829 newMethodFromName (OccurrenceOf (idName id))
1830 THNames.liftName id_ty
1831
1832 -- Update the pending splices
1833 ; ps <- readMutVar ps_var
1834 ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id))
1835 ; writeMutVar ps_var (pending_splice : ps)
1836
1837 ; return () }
1838
1839 checkCrossStageLifting _ _ = return ()
1840
1841 polySpliceErr :: Id -> SDoc
1842 polySpliceErr id
1843 = text "Can't splice the polymorphic local variable" <+> quotes (ppr id)
1844
1845 {-
1846 Note [Lifting strings]
1847 ~~~~~~~~~~~~~~~~~~~~~~
1848 If we see $(... [| s |] ...) where s::String, we don't want to
1849 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1850 So this conditional short-circuits the lifting mechanism to generate
1851 (liftString "xy") in that case. I didn't want to use overlapping instances
1852 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1853 errors in a polymorphic situation.
1854
1855 If this check fails (which isn't impossible) we get another chance; see
1856 Note [Converting strings] in Convert.hs
1857
1858 Local record selectors
1859 ~~~~~~~~~~~~~~~~~~~~~~
1860 Record selectors for TyCons in this module are ordinary local bindings,
1861 which show up as ATcIds rather than AGlobals. So we need to check for
1862 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1863
1864
1865 ************************************************************************
1866 * *
1867 \subsection{Record bindings}
1868 * *
1869 ************************************************************************
1870 -}
1871
1872 getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet
1873 -- These tyvars must not change across the updates
1874 getFixedTyVars upd_fld_occs univ_tvs cons
1875 = mkVarSet [tv1 | con <- cons
1876 , let (u_tvs, _, eqspec, prov_theta
1877 , req_theta, arg_tys, _)
1878 = conLikeFullSig con
1879 theta = eqSpecPreds eqspec
1880 ++ prov_theta
1881 ++ req_theta
1882 flds = conLikeFieldLabels con
1883 fixed_tvs = exactTyCoVarsOfTypes fixed_tys
1884 -- fixed_tys: See Note [Type of a record update]
1885 `unionVarSet` tyCoVarsOfTypes theta
1886 -- Universally-quantified tyvars that
1887 -- appear in any of the *implicit*
1888 -- arguments to the constructor are fixed
1889 -- See Note [Implict type sharing]
1890
1891 fixed_tys = [ty | (fl, ty) <- zip flds arg_tys
1892 , not (flLabel fl `elem` upd_fld_occs)]
1893 , (tv1,tv) <- univ_tvs `zip` u_tvs
1894 , tv `elemVarSet` fixed_tvs ]
1895
1896 {-
1897 Note [Disambiguating record fields]
1898 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1899 When the -XDuplicateRecordFields extension is used, and the renamer
1900 encounters a record selector or update that it cannot immediately
1901 disambiguate (because it involves fields that belong to multiple
1902 datatypes), it will defer resolution of the ambiguity to the
1903 typechecker. In this case, the `Ambiguous` constructor of
1904 `AmbiguousFieldOcc` is used.
1905
1906 Consider the following definitions:
1907
1908 data S = MkS { foo :: Int }
1909 data T = MkT { foo :: Int, bar :: Int }
1910 data U = MkU { bar :: Int, baz :: Int }
1911
1912 When the renamer sees `foo` as a selector or an update, it will not
1913 know which parent datatype is in use.
1914
1915 For selectors, there are two possible ways to disambiguate:
1916
1917 1. Check if the pushed-in type is a function whose domain is a
1918 datatype, for example:
1919
1920 f s = (foo :: S -> Int) s
1921
1922 g :: T -> Int
1923 g = foo
1924
1925 This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`.
1926
1927 2. Check if the selector is applied to an argument that has a type
1928 signature, for example:
1929
1930 h = foo (s :: S)
1931
1932 This is checked by `tcApp`.
1933
1934
1935 Updates are slightly more complex. The `disambiguateRecordBinds`
1936 function tries to determine the parent datatype in three ways:
1937
1938 1. Check for types that have all the fields being updated. For example:
1939
1940 f x = x { foo = 3, bar = 2 }
1941
1942 Here `f` must be updating `T` because neither `S` nor `U` have
1943 both fields. This may also discover that no possible type exists.
1944 For example the following will be rejected:
1945
1946 f' x = x { foo = 3, baz = 3 }
1947
1948 2. Use the type being pushed in, if it is already a TyConApp. The
1949 following are valid updates to `T`:
1950
1951 g :: T -> T
1952 g x = x { foo = 3 }
1953
1954 g' x = x { foo = 3 } :: T
1955
1956 3. Use the type signature of the record expression, if it exists and
1957 is a TyConApp. Thus this is valid update to `T`:
1958
1959 h x = (x :: T) { foo = 3 }
1960
1961
1962 Note that we do not look up the types of variables being updated, and
1963 no constraint-solving is performed, so for example the following will
1964 be rejected as ambiguous:
1965
1966 let bad (s :: S) = foo s
1967
1968 let r :: T
1969 r = blah
1970 in r { foo = 3 }
1971
1972 \r. (r { foo = 3 }, r :: T )
1973
1974 We could add further tests, of a more heuristic nature. For example,
1975 rather than looking for an explicit signature, we could try to infer
1976 the type of the argument to a selector or the record expression being
1977 updated, in case we are lucky enough to get a TyConApp straight
1978 away. However, it might be hard for programmers to predict whether a
1979 particular update is sufficiently obvious for the signature to be
1980 omitted. Moreover, this might change the behaviour of typechecker in
1981 non-obvious ways.
1982
1983 See also Note [HsRecField and HsRecUpdField] in HsPat.
1984 -}
1985
1986 -- Given a RdrName that refers to multiple record fields, and the type
1987 -- of its argument, try to determine the name of the selector that is
1988 -- meant.
1989 disambiguateSelector :: Located RdrName -> Type -> TcM Name
1990 disambiguateSelector lr@(L _ rdr) parent_type
1991 = do { fam_inst_envs <- tcGetFamInstEnvs
1992 ; case tyConOf fam_inst_envs parent_type of
1993 Nothing -> ambiguousSelector lr
1994 Just p ->
1995 do { xs <- lookupParents rdr
1996 ; let parent = RecSelData p
1997 ; case lookup parent xs of
1998 Just gre -> do { addUsedGRE True gre
1999 ; return (gre_name gre) }
2000 Nothing -> failWithTc (fieldNotInType parent rdr) } }
2001
2002 -- This field name really is ambiguous, so add a suitable "ambiguous
2003 -- occurrence" error, then give up.
2004 ambiguousSelector :: Located RdrName -> TcM a
2005 ambiguousSelector (L _ rdr)
2006 = do { env <- getGlobalRdrEnv
2007 ; let gres = lookupGRE_RdrName rdr env
2008 ; setErrCtxt [] $ addNameClashErrRn rdr gres
2009 ; failM }
2010
2011 -- Disambiguate the fields in a record update.
2012 -- See Note [Disambiguating record fields]
2013 disambiguateRecordBinds :: LHsExpr Name -> TcRhoType
2014 -> [LHsRecUpdField Name] -> ExpRhoType
2015 -> TcM [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2016 disambiguateRecordBinds record_expr record_rho rbnds res_ty
2017 -- Are all the fields unambiguous?
2018 = case mapM isUnambiguous rbnds of
2019 -- If so, just skip to looking up the Ids
2020 -- Always the case if DuplicateRecordFields is off
2021 Just rbnds' -> mapM lookupSelector rbnds'
2022 Nothing -> -- If not, try to identify a single parent
2023 do { fam_inst_envs <- tcGetFamInstEnvs
2024 -- Look up the possible parents for each field
2025 ; rbnds_with_parents <- getUpdFieldsParents
2026 ; let possible_parents = map (map fst . snd) rbnds_with_parents
2027 -- Identify a single parent
2028 ; p <- identifyParent fam_inst_envs possible_parents
2029 -- Pick the right selector with that parent for each field
2030 ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents }
2031 where
2032 -- Extract the selector name of a field update if it is unambiguous
2033 isUnambiguous :: LHsRecUpdField Name -> Maybe (LHsRecUpdField Name, Name)
2034 isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of
2035 Unambiguous _ sel_name -> Just (x, sel_name)
2036 Ambiguous{} -> Nothing
2037
2038 -- Look up the possible parents and selector GREs for each field
2039 getUpdFieldsParents :: TcM [(LHsRecUpdField Name
2040 , [(RecSelParent, GlobalRdrElt)])]
2041 getUpdFieldsParents
2042 = fmap (zip rbnds) $ mapM
2043 (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc)
2044 rbnds
2045
2046 -- Given a the lists of possible parents for each field,
2047 -- identify a single parent
2048 identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent
2049 identifyParent fam_inst_envs possible_parents
2050 = case foldr1 intersect possible_parents of
2051 -- No parents for all fields: record update is ill-typed
2052 [] -> failWithTc (noPossibleParents rbnds)
2053
2054 -- Exactly one datatype with all the fields: use that
2055 [p] -> return p
2056
2057 -- Multiple possible parents: try harder to disambiguate
2058 -- Can we get a parent TyCon from the pushed-in type?
2059 _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p)
2060
2061 -- Does the expression being updated have a type signature?
2062 -- If so, try to extract a parent TyCon from it
2063 | Just {} <- obviousSig (unLoc record_expr)
2064 , Just tc <- tyConOf fam_inst_envs record_rho
2065 -> return (RecSelData tc)
2066
2067 -- Nothing else we can try...
2068 _ -> failWithTc badOverloadedUpdate
2069
2070 -- Make a field unambiguous by choosing the given parent.
2071 -- Emits an error if the field cannot have that parent,
2072 -- e.g. if the user writes
2073 -- r { x = e } :: T
2074 -- where T does not have field x.
2075 pickParent :: RecSelParent
2076 -> (LHsRecUpdField Name, [(RecSelParent, GlobalRdrElt)])
2077 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2078 pickParent p (upd, xs)
2079 = case lookup p xs of
2080 -- Phew! The parent is valid for this field.
2081 -- Previously ambiguous fields must be marked as
2082 -- used now that we know which one is meant, but
2083 -- unambiguous ones shouldn't be recorded again
2084 -- (giving duplicate deprecation warnings).
2085 Just gre -> do { unless (null (tail xs)) $ do
2086 let L loc _ = hsRecFieldLbl (unLoc upd)
2087 setSrcSpan loc $ addUsedGRE True gre
2088 ; lookupSelector (upd, gre_name gre) }
2089 -- The field doesn't belong to this parent, so report
2090 -- an error but keep going through all the fields
2091 Nothing -> do { addErrTc (fieldNotInType p
2092 (unLoc (hsRecUpdFieldRdr (unLoc upd))))
2093 ; lookupSelector (upd, gre_name (snd (head xs))) }
2094
2095 -- Given a (field update, selector name) pair, look up the
2096 -- selector to give a field update with an unambiguous Id
2097 lookupSelector :: (LHsRecUpdField Name, Name)
2098 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2099 lookupSelector (L l upd, n)
2100 = do { i <- tcLookupId n
2101 ; let L loc af = hsRecFieldLbl upd
2102 lbl = rdrNameAmbiguousFieldOcc af
2103 ; return $ L l upd { hsRecFieldLbl
2104 = L loc (Unambiguous (L loc lbl) i) } }
2105
2106
2107 -- Extract the outermost TyCon of a type, if there is one; for
2108 -- data families this is the representation tycon (because that's
2109 -- where the fields live).
2110 tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon
2111 tyConOf fam_inst_envs ty0
2112 = case tcSplitTyConApp_maybe ty of
2113 Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys))
2114 Nothing -> Nothing
2115 where
2116 (_, _, ty) = tcSplitSigmaTy ty0
2117
2118 -- Variant of tyConOf that works for ExpTypes
2119 tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon
2120 tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0
2121
2122 -- For an ambiguous record field, find all the candidate record
2123 -- selectors (as GlobalRdrElts) and their parents.
2124 lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)]
2125 lookupParents rdr
2126 = do { env <- getGlobalRdrEnv
2127 ; let gres = lookupGRE_RdrName rdr env
2128 ; mapM lookupParent gres }
2129 where
2130 lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt)
2131 lookupParent gre = do { id <- tcLookupId (gre_name gre)
2132 ; if isRecordSelector id
2133 then return (recordSelectorTyCon id, gre)
2134 else failWithTc (notSelector (gre_name gre)) }
2135
2136 -- A type signature on the argument of an ambiguous record selector or
2137 -- the record expression in an update must be "obvious", i.e. the
2138 -- outermost constructor ignoring parentheses.
2139 obviousSig :: HsExpr Name -> Maybe (LHsSigWcType Name)
2140 obviousSig (ExprWithTySig _ ty) = Just ty
2141 obviousSig (HsPar p) = obviousSig (unLoc p)
2142 obviousSig _ = Nothing
2143
2144
2145 {-
2146 Game plan for record bindings
2147 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2148 1. Find the TyCon for the bindings, from the first field label.
2149
2150 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
2151
2152 For each binding field = value
2153
2154 3. Instantiate the field type (from the field label) using the type
2155 envt from step 2.
2156
2157 4 Type check the value using tcArg, passing the field type as
2158 the expected argument type.
2159
2160 This extends OK when the field types are universally quantified.
2161 -}
2162
2163 tcRecordBinds
2164 :: ConLike
2165 -> [TcType] -- Expected type for each field
2166 -> HsRecordBinds Name
2167 -> TcM (HsRecordBinds TcId)
2168
2169 tcRecordBinds con_like arg_tys (HsRecFields rbinds dd)
2170 = do { mb_binds <- mapM do_bind rbinds
2171 ; return (HsRecFields (catMaybes mb_binds) dd) }
2172 where
2173 fields = map flLabel $ conLikeFieldLabels con_like
2174 flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys
2175
2176 do_bind :: LHsRecField Name (LHsExpr Name)
2177 -> TcM (Maybe (LHsRecField TcId (LHsExpr TcId)))
2178 do_bind (L l fld@(HsRecField { hsRecFieldLbl = f
2179 , hsRecFieldArg = rhs }))
2180
2181 = do { mb <- tcRecordField con_like flds_w_tys f rhs
2182 ; case mb of
2183 Nothing -> return Nothing
2184 Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f'
2185 , hsRecFieldArg = rhs' }))) }
2186
2187 tcRecordUpd
2188 :: ConLike
2189 -> [TcType] -- Expected type for each field
2190 -> [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2191 -> TcM [LHsRecUpdField TcId]
2192
2193 tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds
2194 where
2195 flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys
2196
2197 do_bind :: LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name) -> TcM (Maybe (LHsRecUpdField TcId))
2198 do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af
2199 , hsRecFieldArg = rhs }))
2200 = do { let lbl = rdrNameAmbiguousFieldOcc af
2201 sel_id = selectorAmbiguousFieldOcc af
2202 f = L loc (FieldOcc (L loc lbl) (idName sel_id))
2203 ; mb <- tcRecordField con_like flds_w_tys f rhs
2204 ; case mb of
2205 Nothing -> return Nothing
2206 Just (f', rhs') ->
2207 return (Just
2208 (L l (fld { hsRecFieldLbl
2209 = L loc (Unambiguous (L loc lbl)
2210 (selectorFieldOcc (unLoc f')))
2211 , hsRecFieldArg = rhs' }))) }
2212
2213 tcRecordField :: ConLike -> Assoc FieldLabelString Type -> LFieldOcc Name -> LHsExpr Name
2214 -> TcM (Maybe (LFieldOcc Id, LHsExpr Id))
2215 tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs
2216 | Just field_ty <- assocMaybe flds_w_tys field_lbl
2217 = addErrCtxt (fieldCtxt field_lbl) $
2218 do { rhs' <- tcPolyExprNC rhs field_ty
2219 ; let field_id = mkUserLocal (nameOccName sel_name)
2220 (nameUnique sel_name)
2221 field_ty loc
2222 -- Yuk: the field_id has the *unique* of the selector Id
2223 -- (so we can find it easily)
2224 -- but is a LocalId with the appropriate type of the RHS
2225 -- (so the desugarer knows the type of local binder to make)
2226 ; return (Just (L loc (FieldOcc lbl field_id), rhs')) }
2227 | otherwise
2228 = do { addErrTc (badFieldCon con_like field_lbl)
2229 ; return Nothing }
2230 where
2231 field_lbl = occNameFS $ rdrNameOcc (unLoc lbl)
2232
2233
2234 checkMissingFields :: ConLike -> HsRecordBinds Name -> TcM ()
2235 checkMissingFields con_like rbinds
2236 | null field_labels -- Not declared as a record;
2237 -- But C{} is still valid if no strict fields
2238 = if any isBanged field_strs then
2239 -- Illegal if any arg is strict
2240 addErrTc (missingStrictFields con_like [])
2241 else
2242 return ()
2243
2244 | otherwise = do -- A record
2245 unless (null missing_s_fields)
2246 (addErrTc (missingStrictFields con_like missing_s_fields))
2247
2248 warn <- woptM Opt_WarnMissingFields
2249 unless (not (warn && notNull missing_ns_fields))
2250 (warnTc (Reason Opt_WarnMissingFields) True
2251 (missingFields con_like missing_ns_fields))
2252
2253 where
2254 missing_s_fields
2255 = [ flLabel fl | (fl, str) <- field_info,
2256 isBanged str,
2257 not (fl `elemField` field_names_used)
2258 ]
2259 missing_ns_fields
2260 = [ flLabel fl | (fl, str) <- field_info,
2261 not (isBanged str),
2262 not (fl `elemField` field_names_used)
2263 ]
2264
2265 field_names_used = hsRecFields rbinds
2266 field_labels = conLikeFieldLabels con_like
2267
2268 field_info = zipEqual "missingFields"
2269 field_labels
2270 field_strs
2271
2272 field_strs = conLikeImplBangs con_like
2273
2274 fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds
2275
2276 {-
2277 ************************************************************************
2278 * *
2279 \subsection{Errors and contexts}
2280 * *
2281 ************************************************************************
2282
2283 Boring and alphabetical:
2284 -}
2285
2286 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
2287 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
2288
2289 exprCtxt :: LHsExpr Name -> SDoc
2290 exprCtxt expr
2291 = hang (text "In the expression:") 2 (ppr expr)
2292
2293 fieldCtxt :: FieldLabelString -> SDoc
2294 fieldCtxt field_name
2295 = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
2296
2297 addFunResCtxt :: Bool -- There is at least one argument
2298 -> HsExpr Name -> TcType -> ExpRhoType
2299 -> TcM a -> TcM a
2300 -- When we have a mis-match in the return type of a function
2301 -- try to give a helpful message about too many/few arguments
2302 --
2303 -- Used for naked variables too; but with has_args = False
2304 addFunResCtxt has_args fun fun_res_ty env_ty
2305 = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg)
2306 -- NB: use a landmark error context, so that an empty context
2307 -- doesn't suppress some more useful context
2308 where
2309 mk_msg
2310 = do { mb_env_ty <- readExpType_maybe env_ty
2311 -- by the time the message is rendered, the ExpType
2312 -- will be filled in (except if we're debugging)
2313 ; fun_res' <- zonkTcType fun_res_ty
2314 ; env' <- case mb_env_ty of
2315 Just env_ty -> zonkTcType env_ty
2316 Nothing ->
2317 do { dumping <- doptM Opt_D_dump_tc_trace
2318 ; MASSERT( dumping )
2319 ; newFlexiTyVarTy liftedTypeKind }
2320 ; let (_, _, fun_tau) = tcSplitSigmaTy fun_res'
2321 (_, _, env_tau) = tcSplitSigmaTy env'
2322 (args_fun, res_fun) = tcSplitFunTys fun_tau
2323 (args_env, res_env) = tcSplitFunTys env_tau
2324 n_fun = length args_fun
2325 n_env = length args_env
2326 info | n_fun == n_env = Outputable.empty
2327 | n_fun > n_env
2328 , not_fun res_env
2329 = text "Probable cause:" <+> quotes (ppr fun)
2330 <+> text "is applied to too few arguments"
2331
2332 | has_args
2333 , not_fun res_fun
2334 = text "Possible cause:" <+> quotes (ppr fun)
2335 <+> text "is applied to too many arguments"
2336
2337 | otherwise
2338 = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args!
2339 ; return info }
2340 where
2341 not_fun ty -- ty is definitely not an arrow type,
2342 -- and cannot conceivably become one
2343 = case tcSplitTyConApp_maybe ty of
2344 Just (tc, _) -> isAlgTyCon tc
2345 Nothing -> False
2346
2347 badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc
2348 badFieldTypes prs
2349 = hang (text "Record update for insufficiently polymorphic field"
2350 <> plural prs <> colon)
2351 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
2352
2353 badFieldsUpd
2354 :: [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -- Field names that don't belong to a single datacon
2355 -> [ConLike] -- Data cons of the type which the first field name belongs to
2356 -> SDoc
2357 badFieldsUpd rbinds data_cons
2358 = hang (text "No constructor has all these fields:")
2359 2 (pprQuotedList conflictingFields)
2360 -- See Note [Finding the conflicting fields]
2361 where
2362 -- A (preferably small) set of fields such that no constructor contains
2363 -- all of them. See Note [Finding the conflicting fields]
2364 conflictingFields = case nonMembers of
2365 -- nonMember belongs to a different type.
2366 (nonMember, _) : _ -> [aMember, nonMember]
2367 [] -> let
2368 -- All of rbinds belong to one type. In this case, repeatedly add
2369 -- a field to the set until no constructor contains the set.
2370
2371 -- Each field, together with a list indicating which constructors
2372 -- have all the fields so far.
2373 growingSets :: [(FieldLabelString, [Bool])]
2374 growingSets = scanl1 combine membership
2375 combine (_, setMem) (field, fldMem)
2376 = (field, zipWith (&&) setMem fldMem)
2377 in
2378 -- Fields that don't change the membership status of the set
2379 -- are redundant and can be dropped.
2380 map (fst . head) $ groupBy ((==) `on` snd) growingSets
2381
2382 aMember = ASSERT( not (null members) ) fst (head members)
2383 (members, nonMembers) = partition (or . snd) membership
2384
2385 -- For each field, which constructors contain the field?
2386 membership :: [(FieldLabelString, [Bool])]
2387 membership = sortMembership $
2388 map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $
2389 map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds
2390
2391 fieldLabelSets :: [Set.Set FieldLabelString]
2392 fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons
2393
2394 -- Sort in order of increasing number of True, so that a smaller
2395 -- conflicting set can be found.
2396 sortMembership =
2397 map snd .
2398 sortBy (compare `on` fst) .
2399 map (\ item@(_, membershipRow) -> (countTrue membershipRow, item))
2400
2401 countTrue = length . filter id
2402
2403 {-
2404 Note [Finding the conflicting fields]
2405 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2406 Suppose we have
2407 data A = A {a0, a1 :: Int}
2408 | B {b0, b1 :: Int}
2409 and we see a record update
2410 x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 }
2411 Then we'd like to find the smallest subset of fields that no
2412 constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc.
2413 We don't really want to report that no constructor has all of
2414 {a0,a1,b0,b1}, because when there are hundreds of fields it's
2415 hard to see what was really wrong.
2416
2417 We may need more than two fields, though; eg
2418 data T = A { x,y :: Int, v::Int }
2419 | B { y,z :: Int, v::Int }
2420 | C { z,x :: Int, v::Int }
2421 with update
2422 r { x=e1, y=e2, z=e3 }, we
2423
2424 Finding the smallest subset is hard, so the code here makes
2425 a decent stab, no more. See Trac #7989.
2426 -}
2427
2428 naughtyRecordSel :: RdrName -> SDoc
2429 naughtyRecordSel sel_id
2430 = text "Cannot use record selector" <+> quotes (ppr sel_id) <+>
2431 text "as a function due to escaped type variables" $$
2432 text "Probable fix: use pattern-matching syntax instead"
2433
2434 notSelector :: Name -> SDoc
2435 notSelector field
2436 = hsep [quotes (ppr field), text "is not a record selector"]
2437
2438 mixedSelectors :: [Id] -> [Id] -> SDoc
2439 mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_)
2440 = ptext
2441 (sLit "Cannot use a mixture of pattern synonym and record selectors") $$
2442 text "Record selectors defined by"
2443 <+> quotes (ppr (tyConName rep_dc))
2444 <> text ":"
2445 <+> pprWithCommas ppr data_sels $$
2446 text "Pattern synonym selectors defined by"
2447 <+> quotes (ppr (patSynName rep_ps))
2448 <> text ":"
2449 <+> pprWithCommas ppr pat_syn_sels
2450 where
2451 RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id
2452 RecSelData rep_dc = recordSelectorTyCon dc_rep_id
2453 mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists"
2454
2455
2456 missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc
2457 missingStrictFields con fields
2458 = header <> rest
2459 where
2460 rest | null fields = Outputable.empty -- Happens for non-record constructors
2461 -- with strict fields
2462 | otherwise = colon <+> pprWithCommas ppr fields
2463
2464 header = text "Constructor" <+> quotes (ppr con) <+>
2465 text "does not have the required strict field(s)"
2466
2467 missingFields :: ConLike -> [FieldLabelString] -> SDoc
2468 missingFields con fields
2469 = text "Fields of" <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
2470 <+> pprWithCommas ppr fields
2471
2472 -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl mkHsApp fun args))
2473
2474 noPossibleParents :: [LHsRecUpdField Name] -> SDoc
2475 noPossibleParents rbinds
2476 = hang (text "No type has all these fields:")
2477 2 (pprQuotedList fields)
2478 where
2479 fields = map (hsRecFieldLbl . unLoc) rbinds
2480
2481 badOverloadedUpdate :: SDoc
2482 badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature"
2483
2484 fieldNotInType :: RecSelParent -> RdrName -> SDoc
2485 fieldNotInType p rdr
2486 = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr
2487
2488 {-
2489 ************************************************************************
2490 * *
2491 \subsection{Static Pointers}
2492 * *
2493 ************************************************************************
2494 -}
2495
2496 checkClosedInStaticForm :: Name -> TcM ()
2497 checkClosedInStaticForm name = do
2498 thing <- tcLookup name
2499 case thing of
2500 ATcId { tct_closed = NotTopLevel } ->
2501 addErrTc $ quotes (ppr name) <+>
2502 text "is used in a static form but it is not closed."
2503 _ -> return ()