Improve typechecking of let-bindings
[ghc.git] / compiler / typecheck / TcExpr.hs
1 {-
2 %
3 (c) The University of Glasgow 2006
4 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5
6 \section[TcExpr]{Typecheck an expression}
7 -}
8
9 {-# LANGUAGE CPP, TupleSections, ScopedTypeVariables #-}
10 {-# LANGUAGE FlexibleContexts #-}
11
12 module TcExpr ( tcPolyExpr, tcMonoExpr, tcMonoExprNC,
13 tcInferSigma, tcInferSigmaNC, tcInferRho, tcInferRhoNC,
14 tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType,
15 tcCheckId,
16 addExprErrCtxt,
17 getFixedTyVars ) where
18
19 #include "HsVersions.h"
20
21 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket )
22 import THNames( liftStringName, liftName )
23
24 import HsSyn
25 import TcHsSyn
26 import TcRnMonad
27 import TcUnify
28 import BasicTypes
29 import Inst
30 import TcBinds ( chooseInferredQuantifiers, tcLocalBinds )
31 import TcSigs ( tcUserTypeSig, tcInstSig )
32 import TcSimplify ( simplifyInfer )
33 import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst )
34 import FamInstEnv ( FamInstEnvs )
35 import RnEnv ( addUsedGRE, addNameClashErrRn
36 , unknownSubordinateErr )
37 import TcEnv
38 import TcArrows
39 import TcMatches
40 import TcHsType
41 import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr )
42 import TcPat
43 import TcMType
44 import TcType
45 import DsMonad
46 import Id
47 import IdInfo
48 import ConLike
49 import DataCon
50 import PatSyn
51 import Name
52 import NameEnv
53 import NameSet
54 import RdrName
55 import TyCon
56 import Type
57 import TysPrim ( tYPE )
58 import TcEvidence
59 import VarSet
60 import TysWiredIn
61 import TysPrim( intPrimTy )
62 import PrimOp( tagToEnumKey )
63 import PrelNames
64 import MkId ( proxyHashId )
65 import DynFlags
66 import SrcLoc
67 import Util
68 import VarEnv ( emptyTidyEnv )
69 import ListSetOps
70 import Maybes
71 import Outputable
72 import FastString
73 import Control.Monad
74 import Class(classTyCon)
75 import UniqFM ( nonDetEltsUFM )
76 import qualified GHC.LanguageExtensions as LangExt
77
78 import Data.Function
79 import Data.List
80 import Data.Either
81 import qualified Data.Set as Set
82
83 {-
84 ************************************************************************
85 * *
86 \subsection{Main wrappers}
87 * *
88 ************************************************************************
89 -}
90
91 tcPolyExpr, tcPolyExprNC
92 :: LHsExpr Name -- Expression to type check
93 -> TcSigmaType -- Expected type (could be a polytype)
94 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
95
96 -- tcPolyExpr is a convenient place (frequent but not too frequent)
97 -- place to add context information.
98 -- The NC version does not do so, usually because the caller wants
99 -- to do so himself.
100
101 tcPolyExpr expr res_ty = tc_poly_expr expr (mkCheckExpType res_ty)
102 tcPolyExprNC expr res_ty = tc_poly_expr_nc expr (mkCheckExpType res_ty)
103
104 -- these versions take an ExpType
105 tc_poly_expr, tc_poly_expr_nc :: LHsExpr Name -> ExpSigmaType -> TcM (LHsExpr TcId)
106 tc_poly_expr expr res_ty
107 = addExprErrCtxt expr $
108 do { traceTc "tcPolyExpr" (ppr res_ty); tc_poly_expr_nc expr res_ty }
109
110 tc_poly_expr_nc (L loc expr) res_ty
111 = do { traceTc "tcPolyExprNC" (ppr res_ty)
112 ; (wrap, expr')
113 <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty ->
114 setSrcSpan loc $
115 -- NB: setSrcSpan *after* skolemising, so we get better
116 -- skolem locations
117 tcExpr expr res_ty
118 ; return $ L loc (mkHsWrap wrap expr') }
119
120 ---------------
121 tcMonoExpr, tcMonoExprNC
122 :: LHsExpr Name -- Expression to type check
123 -> ExpRhoType -- Expected type
124 -- Definitely no foralls at the top
125 -> TcM (LHsExpr TcId)
126
127 tcMonoExpr expr res_ty
128 = addErrCtxt (exprCtxt expr) $
129 tcMonoExprNC expr res_ty
130
131 tcMonoExprNC (L loc expr) res_ty
132 = setSrcSpan loc $
133 do { expr' <- tcExpr expr res_ty
134 ; return (L loc expr') }
135
136 ---------------
137 tcInferSigma, tcInferSigmaNC :: LHsExpr Name -> TcM ( LHsExpr TcId
138 , TcSigmaType )
139 -- Infer a *sigma*-type.
140 tcInferSigma expr = addErrCtxt (exprCtxt expr) (tcInferSigmaNC expr)
141
142 tcInferSigmaNC (L loc expr)
143 = setSrcSpan loc $
144 do { (expr', sigma) <- tcInfer (tcExpr expr)
145 ; return (L loc expr', sigma) }
146
147 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
148 -- Infer a *rho*-type. The return type is always (shallowly) instantiated.
149 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
150
151 tcInferRhoNC expr
152 = do { (expr', sigma) <- tcInferSigmaNC expr
153 ; (wrap, rho) <- topInstantiate (exprCtOrigin (unLoc expr)) sigma
154 ; return (mkLHsWrap wrap expr', rho) }
155
156
157 {-
158 ************************************************************************
159 * *
160 tcExpr: the main expression typechecker
161 * *
162 ************************************************************************
163
164 NB: The res_ty is always deeply skolemised.
165 -}
166
167 tcExpr :: HsExpr Name -> ExpRhoType -> TcM (HsExpr TcId)
168 tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty
169 tcExpr (HsUnboundVar uv) res_ty = tcUnboundId uv res_ty
170
171 tcExpr e@(HsApp {}) res_ty = tcApp1 e res_ty
172 tcExpr e@(HsAppType {}) res_ty = tcApp1 e res_ty
173
174 tcExpr e@(HsLit lit) res_ty = do { let lit_ty = hsLitType lit
175 ; tcWrapResult e (HsLit lit) lit_ty res_ty }
176
177 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
178 ; return (HsPar expr') }
179
180 tcExpr (HsSCC src lbl expr) res_ty
181 = do { expr' <- tcMonoExpr expr res_ty
182 ; return (HsSCC src lbl expr') }
183
184 tcExpr (HsTickPragma src info srcInfo expr) res_ty
185 = do { expr' <- tcMonoExpr expr res_ty
186 ; return (HsTickPragma src info srcInfo expr') }
187
188 tcExpr (HsCoreAnn src lbl expr) res_ty
189 = do { expr' <- tcMonoExpr expr res_ty
190 ; return (HsCoreAnn src lbl expr') }
191
192 tcExpr (HsOverLit lit) res_ty
193 = do { lit' <- newOverloadedLit lit res_ty
194 ; return (HsOverLit lit') }
195
196 tcExpr (NegApp expr neg_expr) res_ty
197 = do { (expr', neg_expr')
198 <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $
199 \[arg_ty] ->
200 tcMonoExpr expr (mkCheckExpType arg_ty)
201 ; return (NegApp expr' neg_expr') }
202
203 tcExpr e@(HsIPVar x) res_ty
204 = do { {- Implicit parameters must have a *tau-type* not a
205 type scheme. We enforce this by creating a fresh
206 type variable as its type. (Because res_ty may not
207 be a tau-type.) -}
208 ip_ty <- newOpenFlexiTyVarTy
209 ; let ip_name = mkStrLitTy (hsIPNameFS x)
210 ; ipClass <- tcLookupClass ipClassName
211 ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty])
212 ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var)))
213 ip_ty res_ty }
214 where
215 -- Coerces a dictionary for `IP "x" t` into `t`.
216 fromDict ipClass x ty = HsWrap $ mkWpCastR $
217 unwrapIP $ mkClassPred ipClass [x,ty]
218 origin = IPOccOrigin x
219
220 tcExpr e@(HsOverLabel l) res_ty -- See Note [Type-checking overloaded labels]
221 = do { isLabelClass <- tcLookupClass isLabelClassName
222 ; alpha <- newOpenFlexiTyVarTy
223 ; let lbl = mkStrLitTy l
224 pred = mkClassPred isLabelClass [lbl, alpha]
225 ; loc <- getSrcSpanM
226 ; var <- emitWantedEvVar origin pred
227 ; let proxy_arg = L loc (mkHsWrap (mkWpTyApps [typeSymbolKind, lbl])
228 (HsVar (L loc proxyHashId)))
229 tm = L loc (fromDict pred (HsVar (L loc var))) `HsApp` proxy_arg
230 ; tcWrapResult e tm alpha res_ty }
231 where
232 -- Coerces a dictionary for `IsLabel "x" t` into `Proxy# x -> t`.
233 fromDict pred = HsWrap $ mkWpCastR $ unwrapIP pred
234 origin = OverLabelOrigin l
235
236 tcExpr (HsLam match) res_ty
237 = do { (match', wrap) <- tcMatchLambda herald match_ctxt match res_ty
238 ; return (mkHsWrap wrap (HsLam match')) }
239 where
240 match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody }
241 herald = sep [ text "The lambda expression" <+>
242 quotes (pprSetDepth (PartWay 1) $
243 pprMatches match),
244 -- The pprSetDepth makes the abstraction print briefly
245 text "has"]
246
247 tcExpr e@(HsLamCase matches) res_ty
248 = do { (matches', wrap)
249 <- tcMatchLambda msg match_ctxt matches res_ty
250 -- The laziness annotation is because we don't want to fail here
251 -- if there are multiple arguments
252 ; return (mkHsWrap wrap $ HsLamCase matches') }
253 where
254 msg = sep [ text "The function" <+> quotes (ppr e)
255 , text "requires"]
256 match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
257
258 tcExpr e@(ExprWithTySig expr sig_ty) res_ty
259 = do { let loc = getLoc (hsSigWcType sig_ty)
260 ; sig_info <- checkNoErrs $ -- Avoid error cascade
261 tcUserTypeSig loc sig_ty Nothing
262 ; (expr', poly_ty) <- tcExprSig expr sig_info
263 ; let expr'' = ExprWithTySigOut expr' sig_ty
264 ; tcWrapResult e expr'' poly_ty res_ty }
265
266 {-
267 Note [Type-checking overloaded labels]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 Recall that (in GHC.OverloadedLabels) we have
270
271 class IsLabel (x :: Symbol) a where
272 fromLabel :: Proxy# x -> a
273
274 When we see an overloaded label like `#foo`, we generate a fresh
275 variable `alpha` for the type and emit an `IsLabel "foo" alpha`
276 constraint. Because the `IsLabel` class has a single method, it is
277 represented by a newtype, so we can coerce `IsLabel "foo" alpha` to
278 `Proxy# "foo" -> alpha` (just like for implicit parameters). We then
279 apply it to `proxy#` of type `Proxy# "foo"`.
280
281 That is, we translate `#foo` to `fromLabel (proxy# :: Proxy# "foo")`.
282 -}
283
284
285 {-
286 ************************************************************************
287 * *
288 Infix operators and sections
289 * *
290 ************************************************************************
291
292 Note [Left sections]
293 ~~~~~~~~~~~~~~~~~~~~
294 Left sections, like (4 *), are equivalent to
295 \ x -> (*) 4 x,
296 or, if PostfixOperators is enabled, just
297 (*) 4
298 With PostfixOperators we don't actually require the function to take
299 two arguments at all. For example, (x `not`) means (not x); you get
300 postfix operators! Not Haskell 98, but it's less work and kind of
301 useful.
302
303 Note [Typing rule for ($)]
304 ~~~~~~~~~~~~~~~~~~~~~~~~~~
305 People write
306 runST $ blah
307 so much, where
308 runST :: (forall s. ST s a) -> a
309 that I have finally given in and written a special type-checking
310 rule just for saturated appliations of ($).
311 * Infer the type of the first argument
312 * Decompose it; should be of form (arg2_ty -> res_ty),
313 where arg2_ty might be a polytype
314 * Use arg2_ty to typecheck arg2
315
316 Note [Typing rule for seq]
317 ~~~~~~~~~~~~~~~~~~~~~~~~~~
318 We want to allow
319 x `seq` (# p,q #)
320 which suggests this type for seq:
321 seq :: forall (a:*) (b:Open). a -> b -> b,
322 with (b:Open) meaning that be can be instantiated with an unboxed
323 tuple. The trouble is that this might accept a partially-applied
324 'seq', and I'm just not certain that would work. I'm only sure it's
325 only going to work when it's fully applied, so it turns into
326 case x of _ -> (# p,q #)
327
328 So it seems more uniform to treat 'seq' as it it was a language
329 construct.
330
331 See also Note [seqId magic] in MkId
332 -}
333
334 tcExpr expr@(OpApp arg1 op fix arg2) res_ty
335 | (L loc (HsVar (L lv op_name))) <- op
336 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
337 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
338 ; let arg2_exp_ty = res_ty
339 ; arg1' <- tcArg op arg1 arg1_ty 1
340 ; arg2' <- addErrCtxt (funAppCtxt op arg2 2) $
341 tc_poly_expr_nc arg2 arg2_exp_ty
342 ; arg2_ty <- readExpType arg2_exp_ty
343 ; op_id <- tcLookupId op_name
344 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty])
345 (HsVar (L lv op_id)))
346 ; return $ OpApp arg1' op' fix arg2' }
347
348 | (L loc (HsVar (L lv op_name))) <- op
349 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
350 = do { traceTc "Application rule" (ppr op)
351 ; (arg1', arg1_ty) <- tcInferSigma arg1
352
353 ; let doc = text "The first argument of ($) takes"
354 orig1 = exprCtOrigin (unLoc arg1)
355 ; (wrap_arg1, [arg2_sigma], op_res_ty) <-
356 matchActualFunTys doc orig1 (Just arg1) 1 arg1_ty
357
358 -- We have (arg1 $ arg2)
359 -- So: arg1_ty = arg2_ty -> op_res_ty
360 -- where arg2_sigma maybe polymorphic; that's the point
361
362 ; arg2' <- tcArg op arg2 arg2_sigma 2
363
364 -- Make sure that the argument type has kind '*'
365 -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b
366 -- Eg we do not want to allow (D# $ 4.0#) Trac #5570
367 -- (which gives a seg fault)
368 --
369 -- The *result* type can have any kind (Trac #8739),
370 -- so we don't need to check anything for that
371 ; _ <- unifyKind (Just arg2_sigma) (typeKind arg2_sigma) liftedTypeKind
372 -- ignore the evidence. arg2_sigma must have type * or #,
373 -- because we know arg2_sigma -> or_res_ty is well-kinded
374 -- (because otherwise matchActualFunTys would fail)
375 -- There's no possibility here of, say, a kind family reducing to *.
376
377 ; wrap_res <- tcSubTypeHR orig1 (Just expr) op_res_ty res_ty
378 -- op_res -> res
379
380 ; op_id <- tcLookupId op_name
381 ; res_ty <- readExpType res_ty
382 ; let op' = L loc (HsWrap (mkWpTyApps [ getRuntimeRep "tcExpr ($)" res_ty
383 , arg2_sigma
384 , res_ty])
385 (HsVar (L lv op_id)))
386 -- arg1' :: arg1_ty
387 -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty)
388 -- wrap_res :: op_res_ty "->" res_ty
389 -- op' :: (a2_ty -> res_ty) -> a2_ty -> res_ty
390
391 -- wrap1 :: arg1_ty "->" (arg2_sigma -> res_ty)
392 wrap1 = mkWpFun idHsWrapper wrap_res arg2_sigma res_ty
393 <.> wrap_arg1
394
395 ; return (OpApp (mkLHsWrap wrap1 arg1') op' fix arg2') }
396
397 | (L loc (HsRecFld (Ambiguous lbl _))) <- op
398 , Just sig_ty <- obviousSig (unLoc arg1)
399 -- See Note [Disambiguating record fields]
400 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
401 ; sel_name <- disambiguateSelector lbl sig_tc_ty
402 ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name))
403 ; tcExpr (OpApp arg1 op' fix arg2) res_ty
404 }
405
406 | otherwise
407 = do { traceTc "Non Application rule" (ppr op)
408 ; (wrap, op', [Left arg1', Left arg2'])
409 <- tcApp (Just $ mk_op_msg op)
410 op [Left arg1, Left arg2] res_ty
411 ; return (mkHsWrap wrap $ OpApp arg1' op' fix arg2') }
412
413 -- Right sections, equivalent to \ x -> x `op` expr, or
414 -- \ x -> op x expr
415
416 tcExpr expr@(SectionR op arg2) res_ty
417 = do { (op', op_ty) <- tcInferFun op
418 ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty) <-
419 matchActualFunTys (mk_op_msg op) SectionOrigin (Just op) 2 op_ty
420 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
421 (mkFunTy arg1_ty op_res_ty) res_ty
422 ; arg2' <- tcArg op arg2 arg2_ty 2
423 ; return ( mkHsWrap wrap_res $
424 SectionR (mkLHsWrap wrap_fun op') arg2' ) }
425
426 tcExpr expr@(SectionL arg1 op) res_ty
427 = do { (op', op_ty) <- tcInferFun op
428 ; dflags <- getDynFlags -- Note [Left sections]
429 ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1
430 | otherwise = 2
431
432 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty)
433 <- matchActualFunTys (mk_op_msg op) SectionOrigin (Just op)
434 n_reqd_args op_ty
435 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
436 (mkFunTys arg_tys op_res_ty) res_ty
437 ; arg1' <- tcArg op arg1 arg1_ty 1
438 ; return ( mkHsWrap wrap_res $
439 SectionL arg1' (mkLHsWrap wrap_fn op') ) }
440
441 tcExpr expr@(ExplicitTuple tup_args boxity) res_ty
442 | all tupArgPresent tup_args
443 = do { let arity = length tup_args
444 tup_tc = tupleTyCon boxity arity
445 ; res_ty <- expTypeToType res_ty
446 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
447 -- Unboxed tuples have RuntimeRep vars, which we
448 -- don't care about here
449 -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
450 ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys
451 Boxed -> arg_tys
452 ; tup_args1 <- tcTupArgs tup_args arg_tys'
453 ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
454
455 | otherwise
456 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
457 do { let arity = length tup_args
458
459 ; arg_tys <- case boxity of
460 { Boxed -> newFlexiTyVarTys arity liftedTypeKind
461 ; Unboxed -> replicateM arity newOpenFlexiTyVarTy }
462 ; let actual_res_ty
463 = mkFunTys [ty | (ty, (L _ (Missing _))) <- arg_tys `zip` tup_args]
464 (mkTupleTy boxity arg_tys)
465
466 ; wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "ExpTuple")
467 (Just expr)
468 actual_res_ty res_ty
469
470 -- Handle tuple sections where
471 ; tup_args1 <- tcTupArgs tup_args arg_tys
472
473 ; return $ mkHsWrap wrap (ExplicitTuple tup_args1 boxity) }
474
475 tcExpr (ExplicitList _ witness exprs) res_ty
476 = case witness of
477 Nothing -> do { res_ty <- expTypeToType res_ty
478 ; (coi, elt_ty) <- matchExpectedListTy res_ty
479 ; exprs' <- mapM (tc_elt elt_ty) exprs
480 ; return $
481 mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' }
482
483 Just fln -> do { ((exprs', elt_ty), fln')
484 <- tcSyntaxOp ListOrigin fln
485 [synKnownType intTy, SynList] res_ty $
486 \ [elt_ty] ->
487 do { exprs' <-
488 mapM (tc_elt elt_ty) exprs
489 ; return (exprs', elt_ty) }
490
491 ; return $ ExplicitList elt_ty (Just fln') exprs' }
492 where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
493
494 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
495 = do { res_ty <- expTypeToType res_ty
496 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
497 ; exprs' <- mapM (tc_elt elt_ty) exprs
498 ; return $
499 mkHsWrapCo coi $ ExplicitPArr elt_ty exprs' }
500 where
501 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
502
503 {-
504 ************************************************************************
505 * *
506 Let, case, if, do
507 * *
508 ************************************************************************
509 -}
510
511 tcExpr (HsLet (L l binds) expr) res_ty
512 = do { (binds', expr') <- tcLocalBinds binds $
513 tcMonoExpr expr res_ty
514 ; return (HsLet (L l binds') expr') }
515
516 tcExpr (HsCase scrut matches) res_ty
517 = do { -- We used to typecheck the case alternatives first.
518 -- The case patterns tend to give good type info to use
519 -- when typechecking the scrutinee. For example
520 -- case (map f) of
521 -- (x:xs) -> ...
522 -- will report that map is applied to too few arguments
523 --
524 -- But now, in the GADT world, we need to typecheck the scrutinee
525 -- first, to get type info that may be refined in the case alternatives
526 (scrut', scrut_ty) <- tcInferRho scrut
527
528 ; traceTc "HsCase" (ppr scrut_ty)
529 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
530 ; return (HsCase scrut' matches') }
531 where
532 match_ctxt = MC { mc_what = CaseAlt,
533 mc_body = tcBody }
534
535 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
536 = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy)
537 ; res_ty <- tauifyExpType res_ty
538 -- Just like Note [Case branches must never infer a non-tau type]
539 -- in TcMatches (See #10619)
540
541 ; b1' <- tcMonoExpr b1 res_ty
542 ; b2' <- tcMonoExpr b2 res_ty
543 ; return (HsIf Nothing pred' b1' b2') }
544
545 tcExpr (HsIf (Just fun) pred b1 b2) res_ty
546 = do { ((pred', b1', b2'), fun')
547 <- tcSyntaxOp IfOrigin fun [SynAny, SynAny, SynAny] res_ty $
548 \ [pred_ty, b1_ty, b2_ty] ->
549 do { pred' <- tcPolyExpr pred pred_ty
550 ; b1' <- tcPolyExpr b1 b1_ty
551 ; b2' <- tcPolyExpr b2 b2_ty
552 ; return (pred', b1', b2') }
553 ; return (HsIf (Just fun') pred' b1' b2') }
554
555 tcExpr (HsMultiIf _ alts) res_ty
556 = do { res_ty <- if isSingleton alts
557 then return res_ty
558 else tauifyExpType res_ty
559 -- Just like TcMatches
560 -- Note [Case branches must never infer a non-tau type]
561
562 ; alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
563 ; res_ty <- readExpType res_ty
564 ; return (HsMultiIf res_ty alts') }
565 where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
566
567 tcExpr (HsDo do_or_lc stmts _) res_ty
568 = do { expr' <- tcDoStmts do_or_lc stmts res_ty
569 ; return expr' }
570
571 tcExpr (HsProc pat cmd) res_ty
572 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
573 ; return $ mkHsWrapCo coi (HsProc pat' cmd') }
574
575 -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'.
576 tcExpr (HsStatic fvs expr) res_ty
577 = do { res_ty <- expTypeToType res_ty
578 ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty
579 ; (expr', lie) <- captureConstraints $
580 addErrCtxt (hang (text "In the body of a static form:")
581 2 (ppr expr)
582 ) $
583 tcPolyExprNC expr expr_ty
584 -- Check that the free variables of the static form are closed.
585 -- It's OK to use nonDetEltsUFM here as the only side effects of
586 -- checkClosedInStaticForm are error messages.
587 ; mapM_ checkClosedInStaticForm $ nonDetEltsUFM fvs
588
589 -- Require the type of the argument to be Typeable.
590 -- The evidence is not used, but asking the constraint ensures that
591 -- the current implementation is as restrictive as future versions
592 -- of the StaticPointers extension.
593 ; typeableClass <- tcLookupClass typeableClassName
594 ; _ <- emitWantedEvVar StaticOrigin $
595 mkTyConApp (classTyCon typeableClass)
596 [liftedTypeKind, expr_ty]
597 -- Insert the constraints of the static form in a global list for later
598 -- validation.
599 ; stWC <- tcg_static_wc <$> getGblEnv
600 ; updTcRef stWC (andWC lie)
601 -- Wrap the static form with the 'fromStaticPtr' call.
602 ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty
603 ; let wrap = mkWpTyApps [expr_ty]
604 ; loc <- getSrcSpanM
605 ; return $ mkHsWrapCo co $ HsApp (L loc $ mkHsWrap wrap fromStaticPtr)
606 (L loc (HsStatic fvs expr'))
607 }
608
609 {-
610 ************************************************************************
611 * *
612 Record construction and update
613 * *
614 ************************************************************************
615 -}
616
617 tcExpr expr@(RecordCon { rcon_con_name = L loc con_name
618 , rcon_flds = rbinds }) res_ty
619 = do { con_like <- tcLookupConLike con_name
620
621 -- Check for missing fields
622 ; checkMissingFields con_like rbinds
623
624 ; (con_expr, con_sigma) <- tcInferId con_name
625 ; (con_wrap, con_tau) <-
626 topInstantiate (OccurrenceOf con_name) con_sigma
627 -- a shallow instantiation should really be enough for
628 -- a data constructor.
629 ; let arity = conLikeArity con_like
630 Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau
631 ; case conLikeWrapId_maybe con_like of
632 Nothing -> nonBidirectionalErr (conLikeName con_like)
633 Just con_id -> do {
634 res_wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "RecordCon")
635 (Just expr) actual_res_ty res_ty
636 ; rbinds' <- tcRecordBinds con_like arg_tys rbinds
637 ; return $
638 mkHsWrap res_wrap $
639 RecordCon { rcon_con_name = L loc con_id
640 , rcon_con_expr = mkHsWrap con_wrap con_expr
641 , rcon_con_like = con_like
642 , rcon_flds = rbinds' } } }
643
644 {-
645 Note [Type of a record update]
646 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
647 The main complication with RecordUpd is that we need to explicitly
648 handle the *non-updated* fields. Consider:
649
650 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
651 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
652 | MkT3 { fd :: a }
653
654 upd :: T a b c -> (b',c) -> T a b' c
655 upd t x = t { fb = x}
656
657 The result type should be (T a b' c)
658 not (T a b c), because 'b' *is not* mentioned in a non-updated field
659 not (T a b' c'), because 'c' *is* mentioned in a non-updated field
660 NB that it's not good enough to look at just one constructor; we must
661 look at them all; cf Trac #3219
662
663 After all, upd should be equivalent to:
664 upd t x = case t of
665 MkT1 p q -> MkT1 p x
666 MkT2 a b -> MkT2 p b
667 MkT3 d -> error ...
668
669 So we need to give a completely fresh type to the result record,
670 and then constrain it by the fields that are *not* updated ("p" above).
671 We call these the "fixed" type variables, and compute them in getFixedTyVars.
672
673 Note that because MkT3 doesn't contain all the fields being updated,
674 its RHS is simply an error, so it doesn't impose any type constraints.
675 Hence the use of 'relevant_cont'.
676
677 Note [Implicit type sharing]
678 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
679 We also take into account any "implicit" non-update fields. For example
680 data T a b where { MkT { f::a } :: T a a; ... }
681 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
682
683 Then consider
684 upd t x = t { f=x }
685 We infer the type
686 upd :: T a b -> a -> T a b
687 upd (t::T a b) (x::a)
688 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
689 We can't give it the more general type
690 upd :: T a b -> c -> T c b
691
692 Note [Criteria for update]
693 ~~~~~~~~~~~~~~~~~~~~~~~~~~
694 We want to allow update for existentials etc, provided the updated
695 field isn't part of the existential. For example, this should be ok.
696 data T a where { MkT { f1::a, f2::b->b } :: T a }
697 f :: T a -> b -> T b
698 f t b = t { f1=b }
699
700 The criterion we use is this:
701
702 The types of the updated fields
703 mention only the universally-quantified type variables
704 of the data constructor
705
706 NB: this is not (quite) the same as being a "naughty" record selector
707 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
708 in the case of GADTs. Consider
709 data T a where { MkT :: { f :: a } :: T [a] }
710 Then f is not "naughty" because it has a well-typed record selector.
711 But we don't allow updates for 'f'. (One could consider trying to
712 allow this, but it makes my head hurt. Badly. And no one has asked
713 for it.)
714
715 In principle one could go further, and allow
716 g :: T a -> T a
717 g t = t { f2 = \x -> x }
718 because the expression is polymorphic...but that seems a bridge too far.
719
720 Note [Data family example]
721 ~~~~~~~~~~~~~~~~~~~~~~~~~~
722 data instance T (a,b) = MkT { x::a, y::b }
723 --->
724 data :TP a b = MkT { a::a, y::b }
725 coTP a b :: T (a,b) ~ :TP a b
726
727 Suppose r :: T (t1,t2), e :: t3
728 Then r { x=e } :: T (t3,t1)
729 --->
730 case r |> co1 of
731 MkT x y -> MkT e y |> co2
732 where co1 :: T (t1,t2) ~ :TP t1 t2
733 co2 :: :TP t3 t2 ~ T (t3,t2)
734 The wrapping with co2 is done by the constructor wrapper for MkT
735
736 Outgoing invariants
737 ~~~~~~~~~~~~~~~~~~~
738 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
739
740 * cons are the data constructors to be updated
741
742 * in_inst_tys, out_inst_tys have same length, and instantiate the
743 *representation* tycon of the data cons. In Note [Data
744 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
745
746 Note [Mixed Record Field Updates]
747 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748 Consider the following pattern synonym.
749
750 data MyRec = MyRec { foo :: Int, qux :: String }
751
752 pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}
753
754 This allows updates such as the following
755
756 updater :: MyRec -> MyRec
757 updater a = a {f1 = 1 }
758
759 It would also make sense to allow the following update (which we reject).
760
761 updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"
762
763 This leads to confusing behaviour when the selectors in fact refer the same
764 field.
765
766 updater a = a {f1 = 1, foo = 2} ==? ???
767
768 For this reason, we reject a mixture of pattern synonym and normal record
769 selectors in the same update block. Although of course we still allow the
770 following.
771
772 updater a = (a {f1 = 1}) {foo = 2}
773
774 > updater (MyRec 0 "str")
775 MyRec 2 "str"
776
777 -}
778
779 tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty
780 = ASSERT( notNull rbnds )
781 do { -- STEP -2: typecheck the record_expr, the record to be updated
782 (record_expr', record_rho) <- tcInferRho record_expr
783
784 -- STEP -1 See Note [Disambiguating record fields]
785 -- After this we know that rbinds is unambiguous
786 ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty
787 ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds
788 upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds
789 sel_ids = map selectorAmbiguousFieldOcc upd_flds
790 -- STEP 0
791 -- Check that the field names are really field names
792 -- and they are all field names for proper records or
793 -- all field names for pattern synonyms.
794 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
795 | fld <- rbinds,
796 -- Excludes class ops
797 let L loc sel_id = hsRecUpdFieldId (unLoc fld),
798 not (isRecordSelector sel_id),
799 let fld_name = idName sel_id ]
800 ; unless (null bad_guys) (sequence bad_guys >> failM)
801 -- See note [Mixed Record Selectors]
802 ; let (data_sels, pat_syn_sels) =
803 partition isDataConRecordSelector sel_ids
804 ; MASSERT( all isPatSynRecordSelector pat_syn_sels )
805 ; checkTc ( null data_sels || null pat_syn_sels )
806 ( mixedSelectors data_sels pat_syn_sels )
807
808 -- STEP 1
809 -- Figure out the tycon and data cons from the first field name
810 ; let -- It's OK to use the non-tc splitters here (for a selector)
811 sel_id : _ = sel_ids
812
813 mtycon :: Maybe TyCon
814 mtycon = case idDetails sel_id of
815 RecSelId (RecSelData tycon) _ -> Just tycon
816 _ -> Nothing
817
818 con_likes :: [ConLike]
819 con_likes = case idDetails sel_id of
820 RecSelId (RecSelData tc) _
821 -> map RealDataCon (tyConDataCons tc)
822 RecSelId (RecSelPatSyn ps) _
823 -> [PatSynCon ps]
824 _ -> panic "tcRecordUpd"
825 -- NB: for a data type family, the tycon is the instance tycon
826
827 relevant_cons = conLikesWithFields con_likes upd_fld_occs
828 -- A constructor is only relevant to this process if
829 -- it contains *all* the fields that are being updated
830 -- Other ones will cause a runtime error if they occur
831
832 -- Step 2
833 -- Check that at least one constructor has all the named fields
834 -- i.e. has an empty set of bad fields returned by badFields
835 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes)
836
837 -- Take apart a representative constructor
838 ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
839 (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _)
840 = conLikeFullSig con1
841 con1_flds = map flLabel $ conLikeFieldLabels con1
842 con1_tv_tys = mkTyVarTys con1_tvs
843 con1_res_ty = case mtycon of
844 Just tc -> mkFamilyTyConApp tc con1_tv_tys
845 Nothing -> conLikeResTy con1 con1_tv_tys
846
847 -- Check that we're not dealing with a unidirectional pattern
848 -- synonym
849 ; unless (isJust $ conLikeWrapId_maybe con1)
850 (nonBidirectionalErr (conLikeName con1))
851
852 -- STEP 3 Note [Criteria for update]
853 -- Check that each updated field is polymorphic; that is, its type
854 -- mentions only the universally-quantified variables of the data con
855 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
856 bad_upd_flds = filter bad_fld flds1_w_tys
857 con1_tv_set = mkVarSet con1_tvs
858 bad_fld (fld, ty) = fld `elem` upd_fld_occs &&
859 not (tyCoVarsOfType ty `subVarSet` con1_tv_set)
860 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
861
862 -- STEP 4 Note [Type of a record update]
863 -- Figure out types for the scrutinee and result
864 -- Both are of form (T a b c), with fresh type variables, but with
865 -- common variables where the scrutinee and result must have the same type
866 -- These are variables that appear in *any* arg of *any* of the
867 -- relevant constructors *except* in the updated fields
868 --
869 ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons
870 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
871
872 mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType)
873 -- Deals with instantiation of kind variables
874 -- c.f. TcMType.newMetaTyVars
875 mk_inst_ty subst (tv, result_inst_ty)
876 | is_fixed_tv tv -- Same as result type
877 = return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
878 | otherwise -- Fresh type, of correct kind
879 = do { (subst', new_tv) <- newMetaTyVarX subst tv
880 ; return (subst', mkTyVarTy new_tv) }
881
882 ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs
883 ; let result_inst_tys = mkTyVarTys con1_tvs'
884 init_subst = mkEmptyTCvSubst (getTCvInScope result_subst)
885
886 ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst
887 (con1_tvs `zip` result_inst_tys)
888
889 ; let rec_res_ty = TcType.substTy result_subst con1_res_ty
890 scrut_ty = TcType.substTy scrut_subst con1_res_ty
891 con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
892
893 ; wrap_res <- tcSubTypeHR (exprCtOrigin expr)
894 (Just expr) rec_res_ty res_ty
895 ; co_scrut <- unifyType (Just record_expr) record_rho scrut_ty
896 -- NB: normal unification is OK here (as opposed to subsumption),
897 -- because for this to work out, both record_rho and scrut_ty have
898 -- to be normal datatypes -- no contravariant stuff can go on
899
900 -- STEP 5
901 -- Typecheck the bindings
902 ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds
903
904 -- STEP 6: Deal with the stupid theta
905 ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1)
906 ; instStupidTheta RecordUpdOrigin theta'
907
908 -- Step 7: make a cast for the scrutinee, in the
909 -- case that it's from a data family
910 ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty
911 fam_co | Just tycon <- mtycon
912 , Just co_con <- tyConFamilyCoercion_maybe tycon
913 = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys [])
914 | otherwise
915 = idHsWrapper
916
917 -- Step 8: Check that the req constraints are satisfied
918 -- For normal data constructors req_theta is empty but we must do
919 -- this check for pattern synonyms.
920 ; let req_theta' = substThetaUnchecked scrut_subst req_theta
921 ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta'
922
923 -- Phew!
924 ; return $
925 mkHsWrap wrap_res $
926 RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr')
927 , rupd_flds = rbinds'
928 , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys
929 , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } }
930
931 tcExpr (HsRecFld f) res_ty
932 = tcCheckRecSelId f res_ty
933
934 {-
935 ************************************************************************
936 * *
937 Arithmetic sequences e.g. [a,b..]
938 and their parallel-array counterparts e.g. [: a,b.. :]
939
940 * *
941 ************************************************************************
942 -}
943
944 tcExpr (ArithSeq _ witness seq) res_ty
945 = tcArithSeq witness seq res_ty
946
947 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
948 = do { res_ty <- expTypeToType res_ty
949 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
950 ; expr1' <- tcPolyExpr expr1 elt_ty
951 ; expr2' <- tcPolyExpr expr2 elt_ty
952 ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
953 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
954 (idName enumFromToP) elt_ty
955 ; return $
956 mkHsWrapCo coi $ PArrSeq enum_from_to (FromTo expr1' expr2') }
957
958 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
959 = do { res_ty <- expTypeToType res_ty
960 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
961 ; expr1' <- tcPolyExpr expr1 elt_ty
962 ; expr2' <- tcPolyExpr expr2 elt_ty
963 ; expr3' <- tcPolyExpr expr3 elt_ty
964 ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
965 ; eft <- newMethodFromName (PArrSeqOrigin seq)
966 (idName enumFromThenToP) elt_ty -- !!!FIXME: chak
967 ; return $
968 mkHsWrapCo coi $
969 PArrSeq eft (FromThenTo expr1' expr2' expr3') }
970
971 tcExpr (PArrSeq _ _) _
972 = panic "TcExpr.tcExpr: Infinite parallel array!"
973 -- the parser shouldn't have generated it and the renamer shouldn't have
974 -- let it through
975
976 {-
977 ************************************************************************
978 * *
979 Template Haskell
980 * *
981 ************************************************************************
982 -}
983
984 tcExpr (HsSpliceE splice) res_ty
985 = tcSpliceExpr splice res_ty
986 tcExpr (HsBracket brack) res_ty
987 = tcTypedBracket brack res_ty
988 tcExpr (HsRnBracketOut brack ps) res_ty
989 = tcUntypedBracket brack ps res_ty
990
991 {-
992 ************************************************************************
993 * *
994 Catch-all
995 * *
996 ************************************************************************
997 -}
998
999 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
1000 -- Include ArrForm, ArrApp, which shouldn't appear at all
1001 -- Also HsTcBracketOut, HsQuasiQuoteE
1002
1003 {-
1004 ************************************************************************
1005 * *
1006 Arithmetic sequences [a..b] etc
1007 * *
1008 ************************************************************************
1009 -}
1010
1011 tcArithSeq :: Maybe (SyntaxExpr Name) -> ArithSeqInfo Name -> ExpRhoType
1012 -> TcM (HsExpr TcId)
1013
1014 tcArithSeq witness seq@(From expr) res_ty
1015 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1016 ; expr' <- tcPolyExpr expr elt_ty
1017 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
1018 enumFromName elt_ty
1019 ; return $ mkHsWrap wrap $
1020 ArithSeq enum_from wit' (From expr') }
1021
1022 tcArithSeq witness seq@(FromThen expr1 expr2) res_ty
1023 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1024 ; expr1' <- tcPolyExpr expr1 elt_ty
1025 ; expr2' <- tcPolyExpr expr2 elt_ty
1026 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
1027 enumFromThenName elt_ty
1028 ; return $ mkHsWrap wrap $
1029 ArithSeq enum_from_then wit' (FromThen expr1' expr2') }
1030
1031 tcArithSeq witness seq@(FromTo expr1 expr2) res_ty
1032 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1033 ; expr1' <- tcPolyExpr expr1 elt_ty
1034 ; expr2' <- tcPolyExpr expr2 elt_ty
1035 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
1036 enumFromToName elt_ty
1037 ; return $ mkHsWrap wrap $
1038 ArithSeq enum_from_to wit' (FromTo expr1' expr2') }
1039
1040 tcArithSeq witness seq@(FromThenTo expr1 expr2 expr3) res_ty
1041 = do { (wrap, elt_ty, wit') <- arithSeqEltType witness res_ty
1042 ; expr1' <- tcPolyExpr expr1 elt_ty
1043 ; expr2' <- tcPolyExpr expr2 elt_ty
1044 ; expr3' <- tcPolyExpr expr3 elt_ty
1045 ; eft <- newMethodFromName (ArithSeqOrigin seq)
1046 enumFromThenToName elt_ty
1047 ; return $ mkHsWrap wrap $
1048 ArithSeq eft wit' (FromThenTo expr1' expr2' expr3') }
1049
1050 -----------------
1051 arithSeqEltType :: Maybe (SyntaxExpr Name) -> ExpRhoType
1052 -> TcM (HsWrapper, TcType, Maybe (SyntaxExpr Id))
1053 arithSeqEltType Nothing res_ty
1054 = do { res_ty <- expTypeToType res_ty
1055 ; (coi, elt_ty) <- matchExpectedListTy res_ty
1056 ; return (mkWpCastN coi, elt_ty, Nothing) }
1057 arithSeqEltType (Just fl) res_ty
1058 = do { (elt_ty, fl')
1059 <- tcSyntaxOp ListOrigin fl [SynList] res_ty $
1060 \ [elt_ty] -> return elt_ty
1061 ; return (idHsWrapper, elt_ty, Just fl') }
1062
1063 {-
1064 ************************************************************************
1065 * *
1066 Applications
1067 * *
1068 ************************************************************************
1069 -}
1070
1071 type LHsExprArgIn = Either (LHsExpr Name) (LHsWcType Name)
1072 type LHsExprArgOut = Either (LHsExpr TcId) (LHsWcType Name)
1073 -- Left e => argument expression
1074 -- Right ty => visible type application
1075
1076 tcApp1 :: HsExpr Name -- either HsApp or HsAppType
1077 -> ExpRhoType -> TcM (HsExpr TcId)
1078 tcApp1 e res_ty
1079 = do { (wrap, fun, args) <- tcApp Nothing (noLoc e) [] res_ty
1080 ; return (mkHsWrap wrap $ unLoc $ foldl mk_hs_app fun args) }
1081 where
1082 mk_hs_app f (Left a) = mkHsApp f a
1083 mk_hs_app f (Right a) = mkHsAppTypeOut f a
1084
1085 tcApp :: Maybe SDoc -- like "The function `f' is applied to"
1086 -- or leave out to get exactly that message
1087 -> LHsExpr Name -> [LHsExprArgIn] -- Function and args
1088 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1089 -- (wrap, fun, args). For an ordinary function application,
1090 -- these should be assembled as (wrap (fun args)).
1091 -- But OpApp is slightly different, so that's why the caller
1092 -- must assemble
1093
1094 tcApp m_herald orig_fun orig_args res_ty
1095 = go orig_fun orig_args
1096 where
1097 go :: LHsExpr Name -> [LHsExprArgIn]
1098 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1099 go (L _ (HsPar e)) args = go e args
1100 go (L _ (HsApp e1 e2)) args = go e1 (Left e2:args)
1101 go (L _ (HsAppType e t)) args = go e (Right t:args)
1102
1103 go (L loc (HsVar (L _ fun))) args
1104 | fun `hasKey` tagToEnumKey
1105 , count isLeft args == 1
1106 = do { (wrap, expr, args) <- tcTagToEnum loc fun args res_ty
1107 ; return (wrap, expr, args) }
1108
1109 | fun `hasKey` seqIdKey
1110 , count isLeft args == 2
1111 = do { (wrap, expr, args) <- tcSeq loc fun args res_ty
1112 ; return (wrap, expr, args) }
1113
1114 go (L loc (HsRecFld (Ambiguous lbl _))) args@(Left (L _ arg) : _)
1115 | Just sig_ty <- obviousSig arg
1116 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
1117 ; sel_name <- disambiguateSelector lbl sig_tc_ty
1118 ; go (L loc (HsRecFld (Unambiguous lbl sel_name))) args }
1119
1120 go fun args
1121 = do { -- Type-check the function
1122 ; (fun1, fun_sigma) <- tcInferFun fun
1123 ; let orig = exprCtOrigin (unLoc fun)
1124
1125 ; (wrap_fun, args1, actual_res_ty)
1126 <- tcArgs fun fun_sigma orig args
1127 (m_herald `orElse` mk_app_msg fun)
1128
1129 -- this is just like tcWrapResult, but the types don't line
1130 -- up to call that function
1131 ; wrap_res <- addFunResCtxt True (unLoc fun) actual_res_ty res_ty $
1132 tcSubTypeDS_NC_O orig GenSigCtxt
1133 (Just $ foldl mk_hs_app fun args)
1134 actual_res_ty res_ty
1135
1136 ; return (wrap_res, mkLHsWrap wrap_fun fun1, args1) }
1137
1138 mk_hs_app f (Left a) = mkHsApp f a
1139 mk_hs_app f (Right a) = mkHsAppType f a
1140
1141 mk_app_msg :: LHsExpr Name -> SDoc
1142 mk_app_msg fun = sep [ text "The function" <+> quotes (ppr fun)
1143 , text "is applied to"]
1144
1145 mk_op_msg :: LHsExpr Name -> SDoc
1146 mk_op_msg op = text "The operator" <+> quotes (ppr op) <+> text "takes"
1147
1148 ----------------
1149 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcSigmaType)
1150 -- Infer type of a function
1151 tcInferFun (L loc (HsVar (L _ name)))
1152 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
1153 -- Don't wrap a context around a plain Id
1154 ; return (L loc fun, ty) }
1155
1156 tcInferFun (L loc (HsRecFld f))
1157 = do { (fun, ty) <- setSrcSpan loc (tcInferRecSelId f)
1158 -- Don't wrap a context around a plain Id
1159 ; return (L loc fun, ty) }
1160
1161 tcInferFun fun
1162 = do { (fun, fun_ty) <- tcInferSigma fun
1163
1164 -- Zonk the function type carefully, to expose any polymorphism
1165 -- E.g. (( \(x::forall a. a->a). blah ) e)
1166 -- We can see the rank-2 type of the lambda in time to generalise e
1167 ; fun_ty' <- zonkTcType fun_ty
1168
1169 ; return (fun, fun_ty') }
1170
1171 ----------------
1172 -- | Type-check the arguments to a function, possibly including visible type
1173 -- applications
1174 tcArgs :: LHsExpr Name -- ^ The function itself (for err msgs only)
1175 -> TcSigmaType -- ^ the (uninstantiated) type of the function
1176 -> CtOrigin -- ^ the origin for the function's type
1177 -> [LHsExprArgIn] -- ^ the args
1178 -> SDoc -- ^ the herald for matchActualFunTys
1179 -> TcM (HsWrapper, [LHsExprArgOut], TcSigmaType)
1180 -- ^ (a wrapper for the function, the tc'd args, result type)
1181 tcArgs fun orig_fun_ty fun_orig orig_args herald
1182 = go [] 1 orig_fun_ty orig_args
1183 where
1184 orig_arity = length orig_args
1185
1186 go _ _ fun_ty [] = return (idHsWrapper, [], fun_ty)
1187
1188 go acc_args n fun_ty (Right hs_ty_arg:args)
1189 = do { (wrap1, upsilon_ty) <- topInstantiateInferred fun_orig fun_ty
1190 -- wrap1 :: fun_ty "->" upsilon_ty
1191 ; case tcSplitForAllTy_maybe upsilon_ty of
1192 Just (binder, inner_ty)
1193 | Just tv <- binderVar_maybe binder ->
1194 ASSERT2( binderVisibility binder == Specified
1195 , (vcat [ ppr fun_ty, ppr upsilon_ty, ppr binder
1196 , ppr inner_ty, pprTvBndr tv
1197 , ppr (binderVisibility binder) ]) )
1198 do { let kind = tyVarKind tv
1199 ; ty_arg <- tcHsTypeApp hs_ty_arg kind
1200 ; let insted_ty = substTyWithUnchecked [tv] [ty_arg] inner_ty
1201 ; (inner_wrap, args', res_ty)
1202 <- go acc_args (n+1) insted_ty args
1203 -- inner_wrap :: insted_ty "->" (map typeOf args') -> res_ty
1204 ; let inst_wrap = mkWpTyApps [ty_arg]
1205 ; return ( inner_wrap <.> inst_wrap <.> wrap1
1206 , Right hs_ty_arg : args'
1207 , res_ty ) }
1208 _ -> ty_app_err upsilon_ty hs_ty_arg }
1209
1210 go acc_args n fun_ty (Left arg : args)
1211 = do { (wrap, [arg_ty], res_ty)
1212 <- matchActualFunTysPart herald fun_orig (Just fun) 1 fun_ty
1213 acc_args orig_arity
1214 -- wrap :: fun_ty "->" arg_ty -> res_ty
1215 ; arg' <- tcArg fun arg arg_ty n
1216 ; (inner_wrap, args', inner_res_ty)
1217 <- go (arg_ty : acc_args) (n+1) res_ty args
1218 -- inner_wrap :: res_ty "->" (map typeOf args') -> inner_res_ty
1219 ; return ( mkWpFun idHsWrapper inner_wrap arg_ty res_ty <.> wrap
1220 , Left arg' : args'
1221 , inner_res_ty ) }
1222
1223 ty_app_err ty arg
1224 = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty
1225 ; failWith $
1226 text "Cannot apply expression of type" <+> quotes (ppr ty) $$
1227 text "to a visible type argument" <+> quotes (ppr arg) }
1228
1229 ----------------
1230 tcArg :: LHsExpr Name -- The function (for error messages)
1231 -> LHsExpr Name -- Actual arguments
1232 -> TcRhoType -- expected arg type
1233 -> Int -- # of argument
1234 -> TcM (LHsExpr TcId) -- Resulting argument
1235 tcArg fun arg ty arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $
1236 tcPolyExprNC arg ty
1237
1238 ----------------
1239 tcTupArgs :: [LHsTupArg Name] -> [TcSigmaType] -> TcM [LHsTupArg TcId]
1240 tcTupArgs args tys
1241 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
1242 where
1243 go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty))
1244 go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
1245 ; return (L l (Present expr')) }
1246
1247 ---------------------------
1248 -- See TcType.SyntaxOpType also for commentary
1249 tcSyntaxOp :: CtOrigin
1250 -> SyntaxExpr Name
1251 -> [SyntaxOpType] -- ^ shape of syntax operator arguments
1252 -> ExpType -- ^ overall result type
1253 -> ([TcSigmaType] -> TcM a) -- ^ Type check any arguments
1254 -> TcM (a, SyntaxExpr TcId)
1255 -- ^ Typecheck a syntax operator
1256 -- The operator is always a variable at this stage (i.e. renamer output)
1257 tcSyntaxOp orig expr arg_tys res_ty
1258 = tcSyntaxOpGen orig expr arg_tys (SynType res_ty)
1259
1260 -- | Slightly more general version of 'tcSyntaxOp' that allows the caller
1261 -- to specify the shape of the result of the syntax operator
1262 tcSyntaxOpGen :: CtOrigin
1263 -> SyntaxExpr Name
1264 -> [SyntaxOpType]
1265 -> SyntaxOpType
1266 -> ([TcSigmaType] -> TcM a)
1267 -> TcM (a, SyntaxExpr TcId)
1268 tcSyntaxOpGen orig (SyntaxExpr { syn_expr = HsVar (L _ op) })
1269 arg_tys res_ty thing_inside
1270 = do { (expr, sigma) <- tcInferId op
1271 ; (result, expr_wrap, arg_wraps, res_wrap)
1272 <- tcSynArgA orig sigma arg_tys res_ty $
1273 thing_inside
1274 ; return (result, SyntaxExpr { syn_expr = mkHsWrap expr_wrap expr
1275 , syn_arg_wraps = arg_wraps
1276 , syn_res_wrap = res_wrap }) }
1277
1278 tcSyntaxOpGen _ other _ _ _ = pprPanic "tcSyntaxOp" (ppr other)
1279
1280 {-
1281 Note [tcSynArg]
1282 ~~~~~~~~~~~~~~~
1283 Because of the rich structure of SyntaxOpType, we must do the
1284 contra-/covariant thing when working down arrows, to get the
1285 instantiation vs. skolemisation decisions correct (and, more
1286 obviously, the orientation of the HsWrappers). We thus have
1287 two tcSynArgs.
1288 -}
1289
1290 -- works on "expected" types, skolemising where necessary
1291 -- See Note [tcSynArg]
1292 tcSynArgE :: CtOrigin
1293 -> TcSigmaType
1294 -> SyntaxOpType -- ^ shape it is expected to have
1295 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1296 -> TcM (a, HsWrapper)
1297 -- ^ returns a wrapper :: (type of right shape) "->" (type passed in)
1298 tcSynArgE orig sigma_ty syn_ty thing_inside
1299 = do { (skol_wrap, (result, ty_wrapper))
1300 <- tcSkolemise GenSigCtxt sigma_ty $ \ _ rho_ty ->
1301 go rho_ty syn_ty
1302 ; return (result, skol_wrap <.> ty_wrapper) }
1303 where
1304 go rho_ty SynAny
1305 = do { result <- thing_inside [rho_ty]
1306 ; return (result, idHsWrapper) }
1307
1308 go rho_ty SynRho -- same as SynAny, because we skolemise eagerly
1309 = do { result <- thing_inside [rho_ty]
1310 ; return (result, idHsWrapper) }
1311
1312 go rho_ty SynList
1313 = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty
1314 ; result <- thing_inside [elt_ty]
1315 ; return (result, mkWpCastN list_co) }
1316
1317 go rho_ty (SynFun arg_shape res_shape)
1318 = do { ( ( ( (result, arg_ty, res_ty)
1319 , res_wrapper ) -- :: res_ty_out "->" res_ty
1320 , arg_wrapper1, [], arg_wrapper2 ) -- :: arg_ty "->" arg_ty_out
1321 , match_wrapper ) -- :: (arg_ty -> res_ty) "->" rho_ty
1322 <- matchExpectedFunTys herald 1 (mkCheckExpType rho_ty) $
1323 \ [arg_ty] res_ty ->
1324 do { arg_tc_ty <- expTypeToType arg_ty
1325 ; res_tc_ty <- expTypeToType res_ty
1326
1327 -- another nested arrow is too much for now,
1328 -- but I bet we'll never need this
1329 ; MASSERT2( case arg_shape of
1330 SynFun {} -> False;
1331 _ -> True
1332 , text "Too many nested arrows in SyntaxOpType" $$
1333 pprCtOrigin orig )
1334
1335 ; tcSynArgA orig arg_tc_ty [] arg_shape $
1336 \ arg_results ->
1337 tcSynArgE orig res_tc_ty res_shape $
1338 \ res_results ->
1339 do { result <- thing_inside (arg_results ++ res_results)
1340 ; return (result, arg_tc_ty, res_tc_ty) }}
1341
1342 ; return ( result
1343 , match_wrapper <.>
1344 mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper
1345 arg_ty res_ty ) }
1346 where
1347 herald = text "This rebindable syntax expects a function with"
1348
1349 go rho_ty (SynType the_ty)
1350 = do { wrap <- tcSubTypeET orig the_ty rho_ty
1351 ; result <- thing_inside []
1352 ; return (result, wrap) }
1353
1354 -- works on "actual" types, instantiating where necessary
1355 -- See Note [tcSynArg]
1356 tcSynArgA :: CtOrigin
1357 -> TcSigmaType
1358 -> [SyntaxOpType] -- ^ argument shapes
1359 -> SyntaxOpType -- ^ result shape
1360 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1361 -> TcM (a, HsWrapper, [HsWrapper], HsWrapper)
1362 -- ^ returns a wrapper to be applied to the original function,
1363 -- wrappers to be applied to arguments
1364 -- and a wrapper to be applied to the overall expression
1365 tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside
1366 = do { (match_wrapper, arg_tys, res_ty)
1367 <- matchActualFunTys herald orig noThing (length arg_shapes) sigma_ty
1368 -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty)
1369 ; ((result, res_wrapper), arg_wrappers)
1370 <- tc_syn_args_e arg_tys arg_shapes $ \ arg_results ->
1371 tc_syn_arg res_ty res_shape $ \ res_results ->
1372 thing_inside (arg_results ++ res_results)
1373 ; return (result, match_wrapper, arg_wrappers, res_wrapper) }
1374 where
1375 herald = text "This rebindable syntax expects a function with"
1376
1377 tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType]
1378 -> ([TcSigmaType] -> TcM a)
1379 -> TcM (a, [HsWrapper])
1380 -- the wrappers are for arguments
1381 tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside
1382 = do { ((result, arg_wraps), arg_wrap)
1383 <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results ->
1384 tc_syn_args_e arg_tys arg_shapes $ \ args_results ->
1385 thing_inside (arg1_results ++ args_results)
1386 ; return (result, arg_wrap : arg_wraps) }
1387 tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside []
1388
1389 tc_syn_arg :: TcSigmaType -> SyntaxOpType
1390 -> ([TcSigmaType] -> TcM a)
1391 -> TcM (a, HsWrapper)
1392 -- the wrapper applies to the overall result
1393 tc_syn_arg res_ty SynAny thing_inside
1394 = do { result <- thing_inside [res_ty]
1395 ; return (result, idHsWrapper) }
1396 tc_syn_arg res_ty SynRho thing_inside
1397 = do { (inst_wrap, rho_ty) <- deeplyInstantiate orig res_ty
1398 -- inst_wrap :: res_ty "->" rho_ty
1399 ; result <- thing_inside [rho_ty]
1400 ; return (result, inst_wrap) }
1401 tc_syn_arg res_ty SynList thing_inside
1402 = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty
1403 -- inst_wrap :: res_ty "->" rho_ty
1404 ; (list_co, elt_ty) <- matchExpectedListTy rho_ty
1405 -- list_co :: [elt_ty] ~N rho_ty
1406 ; result <- thing_inside [elt_ty]
1407 ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) }
1408 tc_syn_arg _ (SynFun {}) _
1409 = pprPanic "tcSynArgA hits a SynFun" (ppr orig)
1410 tc_syn_arg res_ty (SynType the_ty) thing_inside
1411 = do { wrap <- tcSubTypeO orig GenSigCtxt res_ty the_ty
1412 ; result <- thing_inside []
1413 ; return (result, wrap) }
1414
1415 {-
1416 Note [Push result type in]
1417 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1418 Unify with expected result before type-checking the args so that the
1419 info from res_ty percolates to args. This is when we might detect a
1420 too-few args situation. (One can think of cases when the opposite
1421 order would give a better error message.)
1422 experimenting with putting this first.
1423
1424 Here's an example where it actually makes a real difference
1425
1426 class C t a b | t a -> b
1427 instance C Char a Bool
1428
1429 data P t a = forall b. (C t a b) => MkP b
1430 data Q t = MkQ (forall a. P t a)
1431
1432 f1, f2 :: Q Char;
1433 f1 = MkQ (MkP True)
1434 f2 = MkQ (MkP True :: forall a. P Char a)
1435
1436 With the change, f1 will type-check, because the 'Char' info from
1437 the signature is propagated into MkQ's argument. With the check
1438 in the other order, the extra signature in f2 is reqd.
1439
1440 ************************************************************************
1441 * *
1442 Expressions with a type signature
1443 expr :: type
1444 * *
1445 ********************************************************************* -}
1446
1447 tcExprSig :: LHsExpr Name -> TcIdSigInfo -> TcM (LHsExpr TcId, TcType)
1448 tcExprSig expr (CompleteSig { sig_bndr = poly_id, sig_loc = loc })
1449 = setSrcSpan loc $ -- Sets the location for the implication constraint
1450 do { (tv_prs, theta, tau) <- tcInstType (tcInstSigTyVars loc) poly_id
1451 ; given <- newEvVars theta
1452 ; let skol_info = SigSkol ExprSigCtxt (mkPhiTy theta tau)
1453 skol_tvs = map snd tv_prs
1454 ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $
1455 tcExtendTyVarEnv2 tv_prs $
1456 tcPolyExprNC expr tau
1457
1458 ; let poly_wrap = mkWpTyLams skol_tvs
1459 <.> mkWpLams given
1460 <.> mkWpLet ev_binds
1461 ; return (mkLHsWrap poly_wrap expr', idType poly_id) }
1462
1463 tcExprSig expr sig@(PartialSig { psig_name = name, sig_loc = loc })
1464 = setSrcSpan loc $ -- Sets the location for the implication constraint
1465 do { (tclvl, wanted, (expr', sig_inst))
1466 <- pushLevelAndCaptureConstraints $
1467 do { sig_inst <- tcInstSig sig
1468 ; expr' <- tcExtendTyVarEnv2 (sig_inst_skols sig_inst) $
1469 tcExtendTyVarEnv2 (sig_inst_wcs sig_inst) $
1470 tcPolyExprNC expr (sig_inst_tau sig_inst)
1471 ; return (expr', sig_inst) }
1472 -- See Note [Partial expression signatures]
1473 ; let tau = sig_inst_tau sig_inst
1474 mr = null (sig_inst_theta sig_inst) &&
1475 isNothing (sig_inst_wcx sig_inst)
1476 ; (qtvs, givens, ev_binds)
1477 <- simplifyInfer tclvl mr [sig_inst] [(name, tau)] wanted
1478 ; tau <- zonkTcType tau
1479 ; let inferred_theta = map evVarPred givens
1480 tau_tvs = tyCoVarsOfType tau
1481 ; (binders, my_theta) <- chooseInferredQuantifiers inferred_theta
1482 tau_tvs qtvs (Just sig_inst)
1483 ; let inferred_sigma = mkInvSigmaTy qtvs inferred_theta tau
1484 my_sigma = mkForAllTys binders (mkPhiTy my_theta tau)
1485 ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis.
1486 then return idHsWrapper -- Fast path; also avoids complaint when we infer
1487 -- an ambiguouse type and have AllowAmbiguousType
1488 -- e..g infer x :: forall a. F a -> Int
1489 else tcSubType_NC ExprSigCtxt inferred_sigma
1490 (mkCheckExpType my_sigma)
1491
1492 ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma)
1493 ; let poly_wrap = wrap
1494 <.> mkWpTyLams qtvs
1495 <.> mkWpLams givens
1496 <.> mkWpLet ev_binds
1497 ; return (mkLHsWrap poly_wrap expr', my_sigma) }
1498
1499
1500 {- Note [Partial expression signatures]
1501 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1502 Partial type signatures on expressions are easy to get wrong. But
1503 here is a guiding principile
1504 e :: ty
1505 should behave like
1506 let x :: ty
1507 x = e
1508 in x
1509
1510 So for partial signatures we apply the MR if no context is given. So
1511 e :: IO _ apply the MR
1512 e :: _ => IO _ do not apply the MR
1513 just like in TcBinds.decideGeneralisationPlan
1514
1515 This makes a difference (Trac #11670):
1516 peek :: Ptr a -> IO CLong
1517 peek ptr = peekElemOff undefined 0 :: _
1518 from (peekElemOff undefined 0) we get
1519 type: IO w
1520 constraints: Storable w
1521
1522 We must NOT try to generalise over 'w' because the signature specifies
1523 no constraints so we'll complain about not being able to solve
1524 Storable w. Instead, don't generalise; then _ gets instantiated to
1525 CLong, as it should.
1526 -}
1527
1528 {- *********************************************************************
1529 * *
1530 tcInferId
1531 * *
1532 ********************************************************************* -}
1533
1534 tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr TcId)
1535 tcCheckId name res_ty
1536 = do { (expr, actual_res_ty) <- tcInferId name
1537 ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty])
1538 ; addFunResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty $
1539 tcWrapResultO (OccurrenceOf name) expr actual_res_ty res_ty }
1540
1541 tcCheckRecSelId :: AmbiguousFieldOcc Name -> ExpRhoType -> TcM (HsExpr TcId)
1542 tcCheckRecSelId f@(Unambiguous (L _ lbl) _) res_ty
1543 = do { (expr, actual_res_ty) <- tcInferRecSelId f
1544 ; addFunResCtxt False (HsRecFld f) actual_res_ty res_ty $
1545 tcWrapResultO (OccurrenceOfRecSel lbl) expr actual_res_ty res_ty }
1546 tcCheckRecSelId (Ambiguous lbl _) res_ty
1547 = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of
1548 Nothing -> ambiguousSelector lbl
1549 Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg
1550 ; tcCheckRecSelId (Unambiguous lbl sel_name) res_ty }
1551
1552 ------------------------
1553 tcInferRecSelId :: AmbiguousFieldOcc Name -> TcM (HsExpr TcId, TcRhoType)
1554 tcInferRecSelId (Unambiguous (L _ lbl) sel)
1555 = do { (expr', ty) <- tc_infer_id lbl sel
1556 ; return (expr', ty) }
1557 tcInferRecSelId (Ambiguous lbl _)
1558 = ambiguousSelector lbl
1559
1560 ------------------------
1561 tcInferId :: Name -> TcM (HsExpr TcId, TcSigmaType)
1562 -- Look up an occurrence of an Id
1563 tcInferId id_name
1564 | id_name `hasKey` tagToEnumKey
1565 = failWithTc (text "tagToEnum# must appear applied to one argument")
1566 -- tcApp catches the case (tagToEnum# arg)
1567
1568 | id_name `hasKey` assertIdKey
1569 = do { dflags <- getDynFlags
1570 ; if gopt Opt_IgnoreAsserts dflags
1571 then tc_infer_id (nameRdrName id_name) id_name
1572 else tc_infer_assert id_name }
1573
1574 | otherwise
1575 = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) id_name
1576 ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty)
1577 ; return (expr, ty) }
1578
1579 tc_infer_assert :: Name -> TcM (HsExpr TcId, TcSigmaType)
1580 -- Deal with an occurrence of 'assert'
1581 -- See Note [Adding the implicit parameter to 'assert']
1582 tc_infer_assert assert_name
1583 = do { assert_error_id <- tcLookupId assertErrorName
1584 ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name)
1585 (idType assert_error_id)
1586 ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho)
1587 }
1588
1589 tc_infer_id :: RdrName -> Name -> TcM (HsExpr TcId, TcSigmaType)
1590 tc_infer_id lbl id_name
1591 = do { thing <- tcLookup id_name
1592 ; case thing of
1593 ATcId { tct_id = id }
1594 -> do { check_naughty id -- Note [Local record selectors]
1595 ; checkThLocalId id
1596 ; return_id id }
1597
1598 AGlobal (AnId id)
1599 -> do { check_naughty id
1600 ; return_id id }
1601 -- A global cannot possibly be ill-staged
1602 -- nor does it need the 'lifting' treatment
1603 -- hence no checkTh stuff here
1604
1605 AGlobal (AConLike cl) -> case cl of
1606 RealDataCon con -> return_data_con con
1607 PatSynCon ps -> tcPatSynBuilderOcc ps
1608
1609 _ -> failWithTc $
1610 ppr thing <+> text "used where a value identifier was expected" }
1611 where
1612 return_id id = return (HsVar (noLoc id), idType id)
1613
1614 return_data_con con
1615 -- For data constructors, must perform the stupid-theta check
1616 | null stupid_theta
1617 = return_id con_wrapper_id
1618
1619 | otherwise
1620 -- See Note [Instantiating stupid theta]
1621 = do { let (tvs, theta, rho) = tcSplitSigmaTy (idType con_wrapper_id)
1622 ; (subst, tvs') <- newMetaTyVars tvs
1623 ; let tys' = mkTyVarTys tvs'
1624 theta' = substTheta subst theta
1625 rho' = substTy subst rho
1626 ; wrap <- instCall (OccurrenceOf id_name) tys' theta'
1627 ; addDataConStupidTheta con tys'
1628 ; return (mkHsWrap wrap (HsVar (noLoc con_wrapper_id)), rho') }
1629
1630 where
1631 con_wrapper_id = dataConWrapId con
1632 stupid_theta = dataConStupidTheta con
1633
1634 check_naughty id
1635 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl)
1636 | otherwise = return ()
1637
1638
1639 tcUnboundId :: UnboundVar -> ExpRhoType -> TcM (HsExpr TcId)
1640 -- Typechedk an occurrence of an unbound Id
1641 --
1642 -- Some of these started life as a true hole "_". Others might simply
1643 -- be variables that accidentally have no binding site
1644 --
1645 -- We turn all of them into HsVar, since HsUnboundVar can't contain an
1646 -- Id; and indeed the evidence for the CHoleCan does bind it, so it's
1647 -- not unbound any more!
1648 tcUnboundId unbound res_ty
1649 = do { ty <- newFlexiTyVarTy liftedTypeKind
1650 ; let occ = unboundVarOcc unbound
1651 ; name <- newSysName occ
1652 ; let ev = mkLocalId name ty
1653 ; loc <- getCtLocM HoleOrigin Nothing
1654 ; let can = CHoleCan { cc_ev = CtWanted { ctev_pred = ty
1655 , ctev_dest = EvVarDest ev
1656 , ctev_loc = loc}
1657 , cc_hole = ExprHole unbound }
1658 ; emitInsoluble can
1659 ; tcWrapResultO (UnboundOccurrenceOf occ) (HsVar (noLoc ev)) ty res_ty }
1660
1661
1662 {-
1663 Note [Adding the implicit parameter to 'assert']
1664 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1665 The typechecker transforms (assert e1 e2) to (assertError e1 e2).
1666 This isn't really the Right Thing because there's no way to "undo"
1667 if you want to see the original source code in the typechecker
1668 output. We'll have fix this in due course, when we care more about
1669 being able to reconstruct the exact original program.
1670
1671 Note [tagToEnum#]
1672 ~~~~~~~~~~~~~~~~~
1673 Nasty check to ensure that tagToEnum# is applied to a type that is an
1674 enumeration TyCon. Unification may refine the type later, but this
1675 check won't see that, alas. It's crude, because it relies on our
1676 knowing *now* that the type is ok, which in turn relies on the
1677 eager-unification part of the type checker pushing enough information
1678 here. In theory the Right Thing to do is to have a new form of
1679 constraint but I definitely cannot face that! And it works ok as-is.
1680
1681 Here's are two cases that should fail
1682 f :: forall a. a
1683 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1684
1685 g :: Int
1686 g = tagToEnum# 0 -- Int is not an enumeration
1687
1688 When data type families are involved it's a bit more complicated.
1689 data family F a
1690 data instance F [Int] = A | B | C
1691 Then we want to generate something like
1692 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1693 Usually that coercion is hidden inside the wrappers for
1694 constructors of F [Int] but here we have to do it explicitly.
1695
1696 It's all grotesquely complicated.
1697
1698 Note [Instantiating stupid theta]
1699 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1700 Normally, when we infer the type of an Id, we don't instantiate,
1701 because we wish to allow for visible type application later on.
1702 But if a datacon has a stupid theta, we're a bit stuck. We need
1703 to emit the stupid theta constraints with instantiated types. It's
1704 difficult to defer this to the lazy instantiation, because a stupid
1705 theta has no spot to put it in a type. So we just instantiate eagerly
1706 in this case. Thus, users cannot use visible type application with
1707 a data constructor sporting a stupid theta. I won't feel so bad for
1708 the users that complain.
1709
1710 -}
1711
1712 tcSeq :: SrcSpan -> Name -> [LHsExprArgIn]
1713 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1714 -- (seq e1 e2) :: res_ty
1715 -- We need a special typing rule because res_ty can be unboxed
1716 -- See Note [Typing rule for seq]
1717 tcSeq loc fun_name args res_ty
1718 = do { fun <- tcLookupId fun_name
1719 ; (arg1_ty, args1) <- case args of
1720 (Right hs_ty_arg1 : args1)
1721 -> do { ty_arg1 <- tcHsTypeApp hs_ty_arg1 liftedTypeKind
1722 ; return (ty_arg1, args1) }
1723
1724 _ -> do { arg_ty1 <- newFlexiTyVarTy liftedTypeKind
1725 ; return (arg_ty1, args) }
1726
1727 ; (arg1, arg2, arg2_exp_ty) <- case args1 of
1728 [Right hs_ty_arg2, Left term_arg1, Left term_arg2]
1729 -> do { rr_ty <- newFlexiTyVarTy runtimeRepTy
1730 ; ty_arg2 <- tcHsTypeApp hs_ty_arg2 (tYPE rr_ty)
1731 -- see Note [Typing rule for seq]
1732 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg2 res_ty
1733 ; return (term_arg1, term_arg2, mkCheckExpType ty_arg2) }
1734 [Left term_arg1, Left term_arg2]
1735 -> return (term_arg1, term_arg2, res_ty)
1736 _ -> too_many_args "seq" args
1737
1738 ; arg1' <- tcMonoExpr arg1 (mkCheckExpType arg1_ty)
1739 ; arg2' <- tcMonoExpr arg2 arg2_exp_ty
1740 ; res_ty <- readExpType res_ty -- by now, it's surely filled in
1741 ; let fun' = L loc (HsWrap ty_args (HsVar (L loc fun)))
1742 ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty
1743 ; return (idHsWrapper, fun', [Left arg1', Left arg2']) }
1744
1745 tcTagToEnum :: SrcSpan -> Name -> [LHsExprArgIn] -> ExpRhoType
1746 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1747 -- tagToEnum# :: forall a. Int# -> a
1748 -- See Note [tagToEnum#] Urgh!
1749 tcTagToEnum loc fun_name args res_ty
1750 = do { fun <- tcLookupId fun_name
1751
1752 ; arg <- case args of
1753 [Right hs_ty_arg, Left term_arg]
1754 -> do { ty_arg <- tcHsTypeApp hs_ty_arg liftedTypeKind
1755 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg res_ty
1756 -- other than influencing res_ty, we just
1757 -- don't care about a type arg passed in.
1758 -- So drop the evidence.
1759 ; return term_arg }
1760 [Left term_arg] -> do { _ <- expTypeToType res_ty
1761 ; return term_arg }
1762 _ -> too_many_args "tagToEnum#" args
1763
1764 ; res_ty <- readExpType res_ty
1765 ; ty' <- zonkTcType res_ty
1766
1767 -- Check that the type is algebraic
1768 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1769 Just (tc, tc_args) = mb_tc_app
1770 ; checkTc (isJust mb_tc_app)
1771 (mk_error ty' doc1)
1772
1773 -- Look through any type family
1774 ; fam_envs <- tcGetFamInstEnvs
1775 ; let (rep_tc, rep_args, coi)
1776 = tcLookupDataFamInst fam_envs tc tc_args
1777 -- coi :: tc tc_args ~R rep_tc rep_args
1778
1779 ; checkTc (isEnumerationTyCon rep_tc)
1780 (mk_error ty' doc2)
1781
1782 ; arg' <- tcMonoExpr arg (mkCheckExpType intPrimTy)
1783 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar (L loc fun)))
1784 rep_ty = mkTyConApp rep_tc rep_args
1785
1786 ; return (mkWpCastR (mkTcSymCo coi), fun', [Left arg']) }
1787 -- coi is a Representational coercion
1788 where
1789 doc1 = vcat [ text "Specify the type by giving a type signature"
1790 , text "e.g. (tagToEnum# x) :: Bool" ]
1791 doc2 = text "Result type must be an enumeration type"
1792
1793 mk_error :: TcType -> SDoc -> SDoc
1794 mk_error ty what
1795 = hang (text "Bad call to tagToEnum#"
1796 <+> text "at type" <+> ppr ty)
1797 2 what
1798
1799 too_many_args :: String -> [LHsExprArgIn] -> TcM a
1800 too_many_args fun args
1801 = failWith $
1802 hang (text "Too many type arguments to" <+> text fun <> colon)
1803 2 (sep (map pp args))
1804 where
1805 pp (Left e) = pprParendLExpr e
1806 pp (Right (HsWC { hswc_body = L _ t })) = pprParendHsType t
1807
1808
1809 {-
1810 ************************************************************************
1811 * *
1812 Template Haskell checks
1813 * *
1814 ************************************************************************
1815 -}
1816
1817 checkThLocalId :: Id -> TcM ()
1818 checkThLocalId id
1819 = do { mb_local_use <- getStageAndBindLevel (idName id)
1820 ; case mb_local_use of
1821 Just (top_lvl, bind_lvl, use_stage)
1822 | thLevel use_stage > bind_lvl
1823 , isNotTopLevel top_lvl
1824 -> checkCrossStageLifting id use_stage
1825 _ -> return () -- Not a locally-bound thing, or
1826 -- no cross-stage link
1827 }
1828
1829 --------------------------------------
1830 checkCrossStageLifting :: Id -> ThStage -> TcM ()
1831 -- If we are inside typed brackets, and (use_lvl > bind_lvl)
1832 -- we must check whether there's a cross-stage lift to do
1833 -- Examples \x -> [|| x ||]
1834 -- [|| map ||]
1835 -- There is no error-checking to do, because the renamer did that
1836 --
1837 -- This is similar to checkCrossStageLifting in RnSplice, but
1838 -- this code is applied to *typed* brackets.
1839
1840 checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var))
1841 = -- Nested identifiers, such as 'x' in
1842 -- E.g. \x -> [|| h x ||]
1843 -- We must behave as if the reference to x was
1844 -- h $(lift x)
1845 -- We use 'x' itself as the splice proxy, used by
1846 -- the desugarer to stitch it all back together.
1847 -- If 'x' occurs many times we may get many identical
1848 -- bindings of the same splice proxy, but that doesn't
1849 -- matter, although it's a mite untidy.
1850 do { let id_ty = idType id
1851 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1852 -- If x is polymorphic, its occurrence sites might
1853 -- have different instantiations, so we can't use plain
1854 -- 'x' as the splice proxy name. I don't know how to
1855 -- solve this, and it's probably unimportant, so I'm
1856 -- just going to flag an error for now
1857
1858 ; lift <- if isStringTy id_ty then
1859 do { sid <- tcLookupId THNames.liftStringName
1860 -- See Note [Lifting strings]
1861 ; return (HsVar (noLoc sid)) }
1862 else
1863 setConstraintVar lie_var $
1864 -- Put the 'lift' constraint into the right LIE
1865 newMethodFromName (OccurrenceOf (idName id))
1866 THNames.liftName id_ty
1867
1868 -- Update the pending splices
1869 ; ps <- readMutVar ps_var
1870 ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id))
1871 ; writeMutVar ps_var (pending_splice : ps)
1872
1873 ; return () }
1874
1875 checkCrossStageLifting _ _ = return ()
1876
1877 polySpliceErr :: Id -> SDoc
1878 polySpliceErr id
1879 = text "Can't splice the polymorphic local variable" <+> quotes (ppr id)
1880
1881 {-
1882 Note [Lifting strings]
1883 ~~~~~~~~~~~~~~~~~~~~~~
1884 If we see $(... [| s |] ...) where s::String, we don't want to
1885 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1886 So this conditional short-circuits the lifting mechanism to generate
1887 (liftString "xy") in that case. I didn't want to use overlapping instances
1888 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1889 errors in a polymorphic situation.
1890
1891 If this check fails (which isn't impossible) we get another chance; see
1892 Note [Converting strings] in Convert.hs
1893
1894 Local record selectors
1895 ~~~~~~~~~~~~~~~~~~~~~~
1896 Record selectors for TyCons in this module are ordinary local bindings,
1897 which show up as ATcIds rather than AGlobals. So we need to check for
1898 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1899
1900
1901 ************************************************************************
1902 * *
1903 \subsection{Record bindings}
1904 * *
1905 ************************************************************************
1906 -}
1907
1908 getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet
1909 -- These tyvars must not change across the updates
1910 getFixedTyVars upd_fld_occs univ_tvs cons
1911 = mkVarSet [tv1 | con <- cons
1912 , let (u_tvs, _, eqspec, prov_theta
1913 , req_theta, arg_tys, _)
1914 = conLikeFullSig con
1915 theta = eqSpecPreds eqspec
1916 ++ prov_theta
1917 ++ req_theta
1918 flds = conLikeFieldLabels con
1919 fixed_tvs = exactTyCoVarsOfTypes fixed_tys
1920 -- fixed_tys: See Note [Type of a record update]
1921 `unionVarSet` tyCoVarsOfTypes theta
1922 -- Universally-quantified tyvars that
1923 -- appear in any of the *implicit*
1924 -- arguments to the constructor are fixed
1925 -- See Note [Implict type sharing]
1926
1927 fixed_tys = [ty | (fl, ty) <- zip flds arg_tys
1928 , not (flLabel fl `elem` upd_fld_occs)]
1929 , (tv1,tv) <- univ_tvs `zip` u_tvs
1930 , tv `elemVarSet` fixed_tvs ]
1931
1932 {-
1933 Note [Disambiguating record fields]
1934 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1935 When the -XDuplicateRecordFields extension is used, and the renamer
1936 encounters a record selector or update that it cannot immediately
1937 disambiguate (because it involves fields that belong to multiple
1938 datatypes), it will defer resolution of the ambiguity to the
1939 typechecker. In this case, the `Ambiguous` constructor of
1940 `AmbiguousFieldOcc` is used.
1941
1942 Consider the following definitions:
1943
1944 data S = MkS { foo :: Int }
1945 data T = MkT { foo :: Int, bar :: Int }
1946 data U = MkU { bar :: Int, baz :: Int }
1947
1948 When the renamer sees `foo` as a selector or an update, it will not
1949 know which parent datatype is in use.
1950
1951 For selectors, there are two possible ways to disambiguate:
1952
1953 1. Check if the pushed-in type is a function whose domain is a
1954 datatype, for example:
1955
1956 f s = (foo :: S -> Int) s
1957
1958 g :: T -> Int
1959 g = foo
1960
1961 This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`.
1962
1963 2. Check if the selector is applied to an argument that has a type
1964 signature, for example:
1965
1966 h = foo (s :: S)
1967
1968 This is checked by `tcApp`.
1969
1970
1971 Updates are slightly more complex. The `disambiguateRecordBinds`
1972 function tries to determine the parent datatype in three ways:
1973
1974 1. Check for types that have all the fields being updated. For example:
1975
1976 f x = x { foo = 3, bar = 2 }
1977
1978 Here `f` must be updating `T` because neither `S` nor `U` have
1979 both fields. This may also discover that no possible type exists.
1980 For example the following will be rejected:
1981
1982 f' x = x { foo = 3, baz = 3 }
1983
1984 2. Use the type being pushed in, if it is already a TyConApp. The
1985 following are valid updates to `T`:
1986
1987 g :: T -> T
1988 g x = x { foo = 3 }
1989
1990 g' x = x { foo = 3 } :: T
1991
1992 3. Use the type signature of the record expression, if it exists and
1993 is a TyConApp. Thus this is valid update to `T`:
1994
1995 h x = (x :: T) { foo = 3 }
1996
1997
1998 Note that we do not look up the types of variables being updated, and
1999 no constraint-solving is performed, so for example the following will
2000 be rejected as ambiguous:
2001
2002 let bad (s :: S) = foo s
2003
2004 let r :: T
2005 r = blah
2006 in r { foo = 3 }
2007
2008 \r. (r { foo = 3 }, r :: T )
2009
2010 We could add further tests, of a more heuristic nature. For example,
2011 rather than looking for an explicit signature, we could try to infer
2012 the type of the argument to a selector or the record expression being
2013 updated, in case we are lucky enough to get a TyConApp straight
2014 away. However, it might be hard for programmers to predict whether a
2015 particular update is sufficiently obvious for the signature to be
2016 omitted. Moreover, this might change the behaviour of typechecker in
2017 non-obvious ways.
2018
2019 See also Note [HsRecField and HsRecUpdField] in HsPat.
2020 -}
2021
2022 -- Given a RdrName that refers to multiple record fields, and the type
2023 -- of its argument, try to determine the name of the selector that is
2024 -- meant.
2025 disambiguateSelector :: Located RdrName -> Type -> TcM Name
2026 disambiguateSelector lr@(L _ rdr) parent_type
2027 = do { fam_inst_envs <- tcGetFamInstEnvs
2028 ; case tyConOf fam_inst_envs parent_type of
2029 Nothing -> ambiguousSelector lr
2030 Just p ->
2031 do { xs <- lookupParents rdr
2032 ; let parent = RecSelData p
2033 ; case lookup parent xs of
2034 Just gre -> do { addUsedGRE True gre
2035 ; return (gre_name gre) }
2036 Nothing -> failWithTc (fieldNotInType parent rdr) } }
2037
2038 -- This field name really is ambiguous, so add a suitable "ambiguous
2039 -- occurrence" error, then give up.
2040 ambiguousSelector :: Located RdrName -> TcM a
2041 ambiguousSelector (L _ rdr)
2042 = do { env <- getGlobalRdrEnv
2043 ; let gres = lookupGRE_RdrName rdr env
2044 ; setErrCtxt [] $ addNameClashErrRn rdr gres
2045 ; failM }
2046
2047 -- Disambiguate the fields in a record update.
2048 -- See Note [Disambiguating record fields]
2049 disambiguateRecordBinds :: LHsExpr Name -> TcRhoType
2050 -> [LHsRecUpdField Name] -> ExpRhoType
2051 -> TcM [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2052 disambiguateRecordBinds record_expr record_rho rbnds res_ty
2053 -- Are all the fields unambiguous?
2054 = case mapM isUnambiguous rbnds of
2055 -- If so, just skip to looking up the Ids
2056 -- Always the case if DuplicateRecordFields is off
2057 Just rbnds' -> mapM lookupSelector rbnds'
2058 Nothing -> -- If not, try to identify a single parent
2059 do { fam_inst_envs <- tcGetFamInstEnvs
2060 -- Look up the possible parents for each field
2061 ; rbnds_with_parents <- getUpdFieldsParents
2062 ; let possible_parents = map (map fst . snd) rbnds_with_parents
2063 -- Identify a single parent
2064 ; p <- identifyParent fam_inst_envs possible_parents
2065 -- Pick the right selector with that parent for each field
2066 ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents }
2067 where
2068 -- Extract the selector name of a field update if it is unambiguous
2069 isUnambiguous :: LHsRecUpdField Name -> Maybe (LHsRecUpdField Name, Name)
2070 isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of
2071 Unambiguous _ sel_name -> Just (x, sel_name)
2072 Ambiguous{} -> Nothing
2073
2074 -- Look up the possible parents and selector GREs for each field
2075 getUpdFieldsParents :: TcM [(LHsRecUpdField Name
2076 , [(RecSelParent, GlobalRdrElt)])]
2077 getUpdFieldsParents
2078 = fmap (zip rbnds) $ mapM
2079 (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc)
2080 rbnds
2081
2082 -- Given a the lists of possible parents for each field,
2083 -- identify a single parent
2084 identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent
2085 identifyParent fam_inst_envs possible_parents
2086 = case foldr1 intersect possible_parents of
2087 -- No parents for all fields: record update is ill-typed
2088 [] -> failWithTc (noPossibleParents rbnds)
2089
2090 -- Exactly one datatype with all the fields: use that
2091 [p] -> return p
2092
2093 -- Multiple possible parents: try harder to disambiguate
2094 -- Can we get a parent TyCon from the pushed-in type?
2095 _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p)
2096
2097 -- Does the expression being updated have a type signature?
2098 -- If so, try to extract a parent TyCon from it
2099 | Just {} <- obviousSig (unLoc record_expr)
2100 , Just tc <- tyConOf fam_inst_envs record_rho
2101 -> return (RecSelData tc)
2102
2103 -- Nothing else we can try...
2104 _ -> failWithTc badOverloadedUpdate
2105
2106 -- Make a field unambiguous by choosing the given parent.
2107 -- Emits an error if the field cannot have that parent,
2108 -- e.g. if the user writes
2109 -- r { x = e } :: T
2110 -- where T does not have field x.
2111 pickParent :: RecSelParent
2112 -> (LHsRecUpdField Name, [(RecSelParent, GlobalRdrElt)])
2113 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2114 pickParent p (upd, xs)
2115 = case lookup p xs of
2116 -- Phew! The parent is valid for this field.
2117 -- Previously ambiguous fields must be marked as
2118 -- used now that we know which one is meant, but
2119 -- unambiguous ones shouldn't be recorded again
2120 -- (giving duplicate deprecation warnings).
2121 Just gre -> do { unless (null (tail xs)) $ do
2122 let L loc _ = hsRecFieldLbl (unLoc upd)
2123 setSrcSpan loc $ addUsedGRE True gre
2124 ; lookupSelector (upd, gre_name gre) }
2125 -- The field doesn't belong to this parent, so report
2126 -- an error but keep going through all the fields
2127 Nothing -> do { addErrTc (fieldNotInType p
2128 (unLoc (hsRecUpdFieldRdr (unLoc upd))))
2129 ; lookupSelector (upd, gre_name (snd (head xs))) }
2130
2131 -- Given a (field update, selector name) pair, look up the
2132 -- selector to give a field update with an unambiguous Id
2133 lookupSelector :: (LHsRecUpdField Name, Name)
2134 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2135 lookupSelector (L l upd, n)
2136 = do { i <- tcLookupId n
2137 ; let L loc af = hsRecFieldLbl upd
2138 lbl = rdrNameAmbiguousFieldOcc af
2139 ; return $ L l upd { hsRecFieldLbl
2140 = L loc (Unambiguous (L loc lbl) i) } }
2141
2142
2143 -- Extract the outermost TyCon of a type, if there is one; for
2144 -- data families this is the representation tycon (because that's
2145 -- where the fields live).
2146 tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon
2147 tyConOf fam_inst_envs ty0
2148 = case tcSplitTyConApp_maybe ty of
2149 Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys))
2150 Nothing -> Nothing
2151 where
2152 (_, _, ty) = tcSplitSigmaTy ty0
2153
2154 -- Variant of tyConOf that works for ExpTypes
2155 tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon
2156 tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0
2157
2158 -- For an ambiguous record field, find all the candidate record
2159 -- selectors (as GlobalRdrElts) and their parents.
2160 lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)]
2161 lookupParents rdr
2162 = do { env <- getGlobalRdrEnv
2163 ; let gres = lookupGRE_RdrName rdr env
2164 ; mapM lookupParent gres }
2165 where
2166 lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt)
2167 lookupParent gre = do { id <- tcLookupId (gre_name gre)
2168 ; if isRecordSelector id
2169 then return (recordSelectorTyCon id, gre)
2170 else failWithTc (notSelector (gre_name gre)) }
2171
2172 -- A type signature on the argument of an ambiguous record selector or
2173 -- the record expression in an update must be "obvious", i.e. the
2174 -- outermost constructor ignoring parentheses.
2175 obviousSig :: HsExpr Name -> Maybe (LHsSigWcType Name)
2176 obviousSig (ExprWithTySig _ ty) = Just ty
2177 obviousSig (HsPar p) = obviousSig (unLoc p)
2178 obviousSig _ = Nothing
2179
2180
2181 {-
2182 Game plan for record bindings
2183 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2184 1. Find the TyCon for the bindings, from the first field label.
2185
2186 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
2187
2188 For each binding field = value
2189
2190 3. Instantiate the field type (from the field label) using the type
2191 envt from step 2.
2192
2193 4 Type check the value using tcArg, passing the field type as
2194 the expected argument type.
2195
2196 This extends OK when the field types are universally quantified.
2197 -}
2198
2199 tcRecordBinds
2200 :: ConLike
2201 -> [TcType] -- Expected type for each field
2202 -> HsRecordBinds Name
2203 -> TcM (HsRecordBinds TcId)
2204
2205 tcRecordBinds con_like arg_tys (HsRecFields rbinds dd)
2206 = do { mb_binds <- mapM do_bind rbinds
2207 ; return (HsRecFields (catMaybes mb_binds) dd) }
2208 where
2209 fields = map flLabel $ conLikeFieldLabels con_like
2210 flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys
2211
2212 do_bind :: LHsRecField Name (LHsExpr Name)
2213 -> TcM (Maybe (LHsRecField TcId (LHsExpr TcId)))
2214 do_bind (L l fld@(HsRecField { hsRecFieldLbl = f
2215 , hsRecFieldArg = rhs }))
2216
2217 = do { mb <- tcRecordField con_like flds_w_tys f rhs
2218 ; case mb of
2219 Nothing -> return Nothing
2220 Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f'
2221 , hsRecFieldArg = rhs' }))) }
2222
2223 tcRecordUpd
2224 :: ConLike
2225 -> [TcType] -- Expected type for each field
2226 -> [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2227 -> TcM [LHsRecUpdField TcId]
2228
2229 tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds
2230 where
2231 flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys
2232
2233 do_bind :: LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name) -> TcM (Maybe (LHsRecUpdField TcId))
2234 do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af
2235 , hsRecFieldArg = rhs }))
2236 = do { let lbl = rdrNameAmbiguousFieldOcc af
2237 sel_id = selectorAmbiguousFieldOcc af
2238 f = L loc (FieldOcc (L loc lbl) (idName sel_id))
2239 ; mb <- tcRecordField con_like flds_w_tys f rhs
2240 ; case mb of
2241 Nothing -> return Nothing
2242 Just (f', rhs') ->
2243 return (Just
2244 (L l (fld { hsRecFieldLbl
2245 = L loc (Unambiguous (L loc lbl)
2246 (selectorFieldOcc (unLoc f')))
2247 , hsRecFieldArg = rhs' }))) }
2248
2249 tcRecordField :: ConLike -> Assoc FieldLabelString Type -> LFieldOcc Name -> LHsExpr Name
2250 -> TcM (Maybe (LFieldOcc Id, LHsExpr Id))
2251 tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs
2252 | Just field_ty <- assocMaybe flds_w_tys field_lbl
2253 = addErrCtxt (fieldCtxt field_lbl) $
2254 do { rhs' <- tcPolyExprNC rhs field_ty
2255 ; let field_id = mkUserLocal (nameOccName sel_name)
2256 (nameUnique sel_name)
2257 field_ty loc
2258 -- Yuk: the field_id has the *unique* of the selector Id
2259 -- (so we can find it easily)
2260 -- but is a LocalId with the appropriate type of the RHS
2261 -- (so the desugarer knows the type of local binder to make)
2262 ; return (Just (L loc (FieldOcc lbl field_id), rhs')) }
2263 | otherwise
2264 = do { addErrTc (badFieldCon con_like field_lbl)
2265 ; return Nothing }
2266 where
2267 field_lbl = occNameFS $ rdrNameOcc (unLoc lbl)
2268
2269
2270 checkMissingFields :: ConLike -> HsRecordBinds Name -> TcM ()
2271 checkMissingFields con_like rbinds
2272 | null field_labels -- Not declared as a record;
2273 -- But C{} is still valid if no strict fields
2274 = if any isBanged field_strs then
2275 -- Illegal if any arg is strict
2276 addErrTc (missingStrictFields con_like [])
2277 else
2278 return ()
2279
2280 | otherwise = do -- A record
2281 unless (null missing_s_fields)
2282 (addErrTc (missingStrictFields con_like missing_s_fields))
2283
2284 warn <- woptM Opt_WarnMissingFields
2285 unless (not (warn && notNull missing_ns_fields))
2286 (warnTc (Reason Opt_WarnMissingFields) True
2287 (missingFields con_like missing_ns_fields))
2288
2289 where
2290 missing_s_fields
2291 = [ flLabel fl | (fl, str) <- field_info,
2292 isBanged str,
2293 not (fl `elemField` field_names_used)
2294 ]
2295 missing_ns_fields
2296 = [ flLabel fl | (fl, str) <- field_info,
2297 not (isBanged str),
2298 not (fl `elemField` field_names_used)
2299 ]
2300
2301 field_names_used = hsRecFields rbinds
2302 field_labels = conLikeFieldLabels con_like
2303
2304 field_info = zipEqual "missingFields"
2305 field_labels
2306 field_strs
2307
2308 field_strs = conLikeImplBangs con_like
2309
2310 fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds
2311
2312 {-
2313 ************************************************************************
2314 * *
2315 \subsection{Errors and contexts}
2316 * *
2317 ************************************************************************
2318
2319 Boring and alphabetical:
2320 -}
2321
2322 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
2323 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
2324
2325 exprCtxt :: LHsExpr Name -> SDoc
2326 exprCtxt expr
2327 = hang (text "In the expression:") 2 (ppr expr)
2328
2329 fieldCtxt :: FieldLabelString -> SDoc
2330 fieldCtxt field_name
2331 = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
2332
2333 addFunResCtxt :: Bool -- There is at least one argument
2334 -> HsExpr Name -> TcType -> ExpRhoType
2335 -> TcM a -> TcM a
2336 -- When we have a mis-match in the return type of a function
2337 -- try to give a helpful message about too many/few arguments
2338 --
2339 -- Used for naked variables too; but with has_args = False
2340 addFunResCtxt has_args fun fun_res_ty env_ty
2341 = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg)
2342 -- NB: use a landmark error context, so that an empty context
2343 -- doesn't suppress some more useful context
2344 where
2345 mk_msg
2346 = do { mb_env_ty <- readExpType_maybe env_ty
2347 -- by the time the message is rendered, the ExpType
2348 -- will be filled in (except if we're debugging)
2349 ; fun_res' <- zonkTcType fun_res_ty
2350 ; env' <- case mb_env_ty of
2351 Just env_ty -> zonkTcType env_ty
2352 Nothing ->
2353 do { dumping <- doptM Opt_D_dump_tc_trace
2354 ; MASSERT( dumping )
2355 ; newFlexiTyVarTy liftedTypeKind }
2356 ; let (_, _, fun_tau) = tcSplitSigmaTy fun_res'
2357 (_, _, env_tau) = tcSplitSigmaTy env'
2358 (args_fun, res_fun) = tcSplitFunTys fun_tau
2359 (args_env, res_env) = tcSplitFunTys env_tau
2360 n_fun = length args_fun
2361 n_env = length args_env
2362 info | n_fun == n_env = Outputable.empty
2363 | n_fun > n_env
2364 , not_fun res_env
2365 = text "Probable cause:" <+> quotes (ppr fun)
2366 <+> text "is applied to too few arguments"
2367
2368 | has_args
2369 , not_fun res_fun
2370 = text "Possible cause:" <+> quotes (ppr fun)
2371 <+> text "is applied to too many arguments"
2372
2373 | otherwise
2374 = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args!
2375 ; return info }
2376 where
2377 not_fun ty -- ty is definitely not an arrow type,
2378 -- and cannot conceivably become one
2379 = case tcSplitTyConApp_maybe ty of
2380 Just (tc, _) -> isAlgTyCon tc
2381 Nothing -> False
2382
2383 badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc
2384 badFieldTypes prs
2385 = hang (text "Record update for insufficiently polymorphic field"
2386 <> plural prs <> colon)
2387 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
2388
2389 badFieldsUpd
2390 :: [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -- Field names that don't belong to a single datacon
2391 -> [ConLike] -- Data cons of the type which the first field name belongs to
2392 -> SDoc
2393 badFieldsUpd rbinds data_cons
2394 = hang (text "No constructor has all these fields:")
2395 2 (pprQuotedList conflictingFields)
2396 -- See Note [Finding the conflicting fields]
2397 where
2398 -- A (preferably small) set of fields such that no constructor contains
2399 -- all of them. See Note [Finding the conflicting fields]
2400 conflictingFields = case nonMembers of
2401 -- nonMember belongs to a different type.
2402 (nonMember, _) : _ -> [aMember, nonMember]
2403 [] -> let
2404 -- All of rbinds belong to one type. In this case, repeatedly add
2405 -- a field to the set until no constructor contains the set.
2406
2407 -- Each field, together with a list indicating which constructors
2408 -- have all the fields so far.
2409 growingSets :: [(FieldLabelString, [Bool])]
2410 growingSets = scanl1 combine membership
2411 combine (_, setMem) (field, fldMem)
2412 = (field, zipWith (&&) setMem fldMem)
2413 in
2414 -- Fields that don't change the membership status of the set
2415 -- are redundant and can be dropped.
2416 map (fst . head) $ groupBy ((==) `on` snd) growingSets
2417
2418 aMember = ASSERT( not (null members) ) fst (head members)
2419 (members, nonMembers) = partition (or . snd) membership
2420
2421 -- For each field, which constructors contain the field?
2422 membership :: [(FieldLabelString, [Bool])]
2423 membership = sortMembership $
2424 map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $
2425 map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds
2426
2427 fieldLabelSets :: [Set.Set FieldLabelString]
2428 fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons
2429
2430 -- Sort in order of increasing number of True, so that a smaller
2431 -- conflicting set can be found.
2432 sortMembership =
2433 map snd .
2434 sortBy (compare `on` fst) .
2435 map (\ item@(_, membershipRow) -> (countTrue membershipRow, item))
2436
2437 countTrue = length . filter id
2438
2439 {-
2440 Note [Finding the conflicting fields]
2441 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2442 Suppose we have
2443 data A = A {a0, a1 :: Int}
2444 | B {b0, b1 :: Int}
2445 and we see a record update
2446 x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 }
2447 Then we'd like to find the smallest subset of fields that no
2448 constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc.
2449 We don't really want to report that no constructor has all of
2450 {a0,a1,b0,b1}, because when there are hundreds of fields it's
2451 hard to see what was really wrong.
2452
2453 We may need more than two fields, though; eg
2454 data T = A { x,y :: Int, v::Int }
2455 | B { y,z :: Int, v::Int }
2456 | C { z,x :: Int, v::Int }
2457 with update
2458 r { x=e1, y=e2, z=e3 }, we
2459
2460 Finding the smallest subset is hard, so the code here makes
2461 a decent stab, no more. See Trac #7989.
2462 -}
2463
2464 naughtyRecordSel :: RdrName -> SDoc
2465 naughtyRecordSel sel_id
2466 = text "Cannot use record selector" <+> quotes (ppr sel_id) <+>
2467 text "as a function due to escaped type variables" $$
2468 text "Probable fix: use pattern-matching syntax instead"
2469
2470 notSelector :: Name -> SDoc
2471 notSelector field
2472 = hsep [quotes (ppr field), text "is not a record selector"]
2473
2474 mixedSelectors :: [Id] -> [Id] -> SDoc
2475 mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_)
2476 = ptext
2477 (sLit "Cannot use a mixture of pattern synonym and record selectors") $$
2478 text "Record selectors defined by"
2479 <+> quotes (ppr (tyConName rep_dc))
2480 <> text ":"
2481 <+> pprWithCommas ppr data_sels $$
2482 text "Pattern synonym selectors defined by"
2483 <+> quotes (ppr (patSynName rep_ps))
2484 <> text ":"
2485 <+> pprWithCommas ppr pat_syn_sels
2486 where
2487 RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id
2488 RecSelData rep_dc = recordSelectorTyCon dc_rep_id
2489 mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists"
2490
2491
2492 missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc
2493 missingStrictFields con fields
2494 = header <> rest
2495 where
2496 rest | null fields = Outputable.empty -- Happens for non-record constructors
2497 -- with strict fields
2498 | otherwise = colon <+> pprWithCommas ppr fields
2499
2500 header = text "Constructor" <+> quotes (ppr con) <+>
2501 text "does not have the required strict field(s)"
2502
2503 missingFields :: ConLike -> [FieldLabelString] -> SDoc
2504 missingFields con fields
2505 = text "Fields of" <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
2506 <+> pprWithCommas ppr fields
2507
2508 -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl mkHsApp fun args))
2509
2510 noPossibleParents :: [LHsRecUpdField Name] -> SDoc
2511 noPossibleParents rbinds
2512 = hang (text "No type has all these fields:")
2513 2 (pprQuotedList fields)
2514 where
2515 fields = map (hsRecFieldLbl . unLoc) rbinds
2516
2517 badOverloadedUpdate :: SDoc
2518 badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature"
2519
2520 fieldNotInType :: RecSelParent -> RdrName -> SDoc
2521 fieldNotInType p rdr
2522 = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr
2523
2524 {-
2525 ************************************************************************
2526 * *
2527 \subsection{Static Pointers}
2528 * *
2529 ************************************************************************
2530 -}
2531
2532 -- | A data type to describe why a variable is not closed.
2533 data NotClosedReason = NotLetBoundReason
2534 | NotTypeClosed VarSet
2535 | NotClosed Name NotClosedReason
2536
2537 -- | Checks if the given name is closed and emits an error if not.
2538 --
2539 -- See Note [Not-closed error messages].
2540 checkClosedInStaticForm :: Name -> TcM ()
2541 checkClosedInStaticForm name = do
2542 type_env <- getLclTypeEnv
2543 case checkClosed type_env name of
2544 Nothing -> return ()
2545 Just reason -> addErrTc $ explain name reason
2546 where
2547 -- See Note [Checking closedness].
2548 checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason
2549 checkClosed type_env n = checkLoop type_env (unitNameSet n) n
2550
2551 checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason
2552 checkLoop type_env visited n = do
2553 -- The @visited@ set is an accumulating parameter that contains the set of
2554 -- visited nodes, so we avoid repeating cycles in the traversal.
2555 case lookupNameEnv type_env n of
2556 Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of
2557 ClosedLet -> Nothing
2558 NotLetBound -> Just NotLetBoundReason
2559 NonClosedLet fvs type_closed -> listToMaybe $
2560 -- Look for a non-closed variable in fvs
2561 [ NotClosed n' reason
2562 | n' <- nameSetElemsStable fvs
2563 , not (elemNameSet n' visited)
2564 , Just reason <- [checkLoop type_env (extendNameSet visited n') n']
2565 ] ++
2566 if type_closed then
2567 []
2568 else
2569 -- We consider non-let-bound variables easier to figure out than
2570 -- non-closed types, so we report non-closed types to the user
2571 -- only if we cannot spot the former.
2572 [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ]
2573 -- The binding is closed.
2574 _ -> Nothing
2575
2576 -- Converts a reason into a human-readable sentence.
2577 --
2578 -- @explain name reason@ starts with
2579 --
2580 -- "<name> is used in a static form but it is not closed because it"
2581 --
2582 -- and then follows a list of causes. For each id in the path, the text
2583 --
2584 -- "uses <id> which"
2585 --
2586 -- is appended, yielding something like
2587 --
2588 -- "uses <id> which uses <id1> which uses <id2> which"
2589 --
2590 -- until the end of the path is reached, which is reported as either
2591 --
2592 -- "is not let-bound"
2593 --
2594 -- when the final node is not let-bound, or
2595 --
2596 -- "has a non-closed type because it contains the type variables:
2597 -- v1, v2, v3"
2598 --
2599 -- when the final node has a non-closed type.
2600 --
2601 explain :: Name -> NotClosedReason -> SDoc
2602 explain name reason =
2603 quotes (ppr name) <+> text "is used in a static form but it is not closed"
2604 <+> text "because it"
2605 $$
2606 sep (causes reason)
2607
2608 causes :: NotClosedReason -> [SDoc]
2609 causes NotLetBoundReason = [text "is not let-bound."]
2610 causes (NotTypeClosed vs) =
2611 [ text "has a non-closed type because it contains the"
2612 , text "type variables:" <+>
2613 pprVarSet vs (hsep . punctuate comma . map (quotes . ppr))
2614 ]
2615 causes (NotClosed n reason) =
2616 let msg = text "uses" <+> quotes (ppr n) <+> text "which"
2617 in case reason of
2618 NotClosed _ _ -> msg : causes reason
2619 _ -> let (xs0, xs1) = splitAt 1 $ causes reason
2620 in fmap (msg <+>) xs0 ++ xs1
2621
2622 -- Note [Not-closed error messages]
2623 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2624 --
2625 -- When variables in a static form are not closed, we go through the trouble
2626 -- of explaining why they aren't.
2627 --
2628 -- Thus, the following program
2629 --
2630 -- > {-# LANGUAGE StaticPointers #-}
2631 -- > module M where
2632 -- >
2633 -- > f x = static g
2634 -- > where
2635 -- > g = h
2636 -- > h = x
2637 --
2638 -- produces the error
2639 --
2640 -- 'g' is used in a static form but it is not closed because it
2641 -- uses 'h' which uses 'x' which is not let-bound.
2642 --
2643 -- And a program like
2644 --
2645 -- > {-# LANGUAGE StaticPointers #-}
2646 -- > module M where
2647 -- >
2648 -- > import Data.Typeable
2649 -- > import GHC.StaticPtr
2650 -- >
2651 -- > f :: Typeable a => a -> StaticPtr TypeRep
2652 -- > f x = const (static (g undefined)) (h x)
2653 -- > where
2654 -- > g = h
2655 -- > h = typeOf
2656 --
2657 -- produces the error
2658 --
2659 -- 'g' is used in a static form but it is not closed because it
2660 -- uses 'h' which has a non-closed type because it contains the
2661 -- type variables: 'a'
2662 --
2663
2664 -- Note [Checking closedness]
2665 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~
2666 --
2667 -- @checkClosed@ checks if a binding is closed and returns a reason if it is
2668 -- not.
2669 --
2670 -- The bindings define a graph where the nodes are ids, and there is an edge
2671 -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free
2672 -- variables.
2673 --
2674 -- When @n@ is not closed, it has to exist in the graph some node reachable
2675 -- from @n@ that it is not a let-bound variable or that it has a non-closed
2676 -- type. Thus, the "reason" is a path from @n@ to this offending node.
2677 --
2678 -- When @n@ is not closed, we traverse the graph reachable from @n@ to build
2679 -- the reason.
2680 --