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