Fix #10963 and #11975 by adding new cmds to GHCi.
[ghc.git] / compiler / typecheck / TcExpr.hs
1 {-
2 %
3 (c) The University of Glasgow 2006
4 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5
6 \section[TcExpr]{Typecheck an expression}
7 -}
8
9 {-# LANGUAGE CPP, TupleSections, ScopedTypeVariables #-}
10 {-# LANGUAGE FlexibleContexts #-}
11
12 module TcExpr ( tcPolyExpr, tcMonoExpr, tcMonoExprNC,
13 tcInferSigma, tcInferSigmaNC, tcInferRho, tcInferRhoNC,
14 tcSyntaxOp, tcSyntaxOpGen, SyntaxOpType(..), synKnownType,
15 tcCheckId,
16 addExprErrCtxt,
17 getFixedTyVars ) where
18
19 #include "HsVersions.h"
20
21 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcTypedBracket, tcUntypedBracket )
22 import THNames( liftStringName, liftName )
23
24 import HsSyn
25 import TcHsSyn
26 import TcRnMonad
27 import TcUnify
28 import BasicTypes
29 import Inst
30 import TcBinds ( chooseInferredQuantifiers, tcLocalBinds )
31 import TcSigs ( tcUserTypeSig, tcInstSig )
32 import TcSimplify ( simplifyInfer, InferMode(..) )
33 import FamInst ( tcGetFamInstEnvs, tcLookupDataFamInst )
34 import FamInstEnv ( FamInstEnvs )
35 import RnEnv ( addUsedGRE, addNameClashErrRn
36 , unknownSubordinateErr )
37 import TcEnv
38 import TcArrows
39 import TcMatches
40 import TcHsType
41 import TcPatSyn( tcPatSynBuilderOcc, nonBidirectionalErr )
42 import TcPat
43 import TcMType
44 import TcType
45 import DsMonad
46 import Id
47 import IdInfo
48 import ConLike
49 import DataCon
50 import PatSyn
51 import Name
52 import NameEnv
53 import NameSet
54 import RdrName
55 import TyCon
56 import Type
57 import TysPrim ( tYPE )
58 import TcEvidence
59 import VarSet
60 import TysWiredIn
61 import TysPrim( intPrimTy )
62 import PrimOp( tagToEnumKey )
63 import PrelNames
64 import MkId ( proxyHashId )
65 import DynFlags
66 import SrcLoc
67 import Util
68 import VarEnv ( emptyTidyEnv )
69 import ListSetOps
70 import Maybes
71 import Outputable
72 import FastString
73 import Control.Monad
74 import Class(classTyCon)
75 import UniqFM ( nonDetEltsUFM )
76 import qualified GHC.LanguageExtensions as LangExt
77
78 import Data.Function
79 import Data.List
80 import Data.Either
81 import qualified Data.Set as Set
82
83 {-
84 ************************************************************************
85 * *
86 \subsection{Main wrappers}
87 * *
88 ************************************************************************
89 -}
90
91 tcPolyExpr, tcPolyExprNC
92 :: LHsExpr Name -- Expression to type check
93 -> TcSigmaType -- Expected type (could be a polytype)
94 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
95
96 -- tcPolyExpr is a convenient place (frequent but not too frequent)
97 -- place to add context information.
98 -- The NC version does not do so, usually because the caller wants
99 -- to do so himself.
100
101 tcPolyExpr expr res_ty = tc_poly_expr expr (mkCheckExpType res_ty)
102 tcPolyExprNC expr res_ty = tc_poly_expr_nc expr (mkCheckExpType res_ty)
103
104 -- these versions take an ExpType
105 tc_poly_expr, tc_poly_expr_nc :: LHsExpr Name -> ExpSigmaType -> TcM (LHsExpr TcId)
106 tc_poly_expr expr res_ty
107 = addExprErrCtxt expr $
108 do { traceTc "tcPolyExpr" (ppr res_ty); tc_poly_expr_nc expr res_ty }
109
110 tc_poly_expr_nc (L loc expr) res_ty
111 = do { traceTc "tcPolyExprNC" (ppr res_ty)
112 ; (wrap, expr')
113 <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty ->
114 setSrcSpan loc $
115 -- NB: setSrcSpan *after* skolemising, so we get better
116 -- skolem locations
117 tcExpr expr res_ty
118 ; return $ L loc (mkHsWrap wrap expr') }
119
120 ---------------
121 tcMonoExpr, tcMonoExprNC
122 :: LHsExpr Name -- Expression to type check
123 -> ExpRhoType -- Expected type
124 -- Definitely no foralls at the top
125 -> TcM (LHsExpr TcId)
126
127 tcMonoExpr expr res_ty
128 = addErrCtxt (exprCtxt expr) $
129 tcMonoExprNC expr res_ty
130
131 tcMonoExprNC (L loc expr) res_ty
132 = setSrcSpan loc $
133 do { expr' <- tcExpr expr res_ty
134 ; return (L loc expr') }
135
136 ---------------
137 tcInferSigma, tcInferSigmaNC :: LHsExpr Name -> TcM ( LHsExpr TcId
138 , TcSigmaType )
139 -- Infer a *sigma*-type.
140 tcInferSigma expr = addErrCtxt (exprCtxt expr) (tcInferSigmaNC expr)
141
142 tcInferSigmaNC (L loc expr)
143 = setSrcSpan loc $
144 do { (expr', sigma) <- tcInfer (tcExpr expr)
145 ; return (L loc expr', sigma) }
146
147 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
148 -- Infer a *rho*-type. The return type is always (shallowly) instantiated.
149 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
150
151 tcInferRhoNC expr
152 = do { (expr', sigma) <- tcInferSigmaNC expr
153 ; (wrap, rho) <- topInstantiate (exprCtOrigin (unLoc expr)) sigma
154 ; return (mkLHsWrap wrap expr', rho) }
155
156
157 {-
158 ************************************************************************
159 * *
160 tcExpr: the main expression typechecker
161 * *
162 ************************************************************************
163
164 NB: The res_ty is always deeply skolemised.
165 -}
166
167 tcExpr :: HsExpr Name -> ExpRhoType -> TcM (HsExpr TcId)
168 tcExpr (HsVar (L _ name)) res_ty = tcCheckId name res_ty
169 tcExpr (HsUnboundVar uv) res_ty = tcUnboundId uv res_ty
170
171 tcExpr e@(HsApp {}) res_ty = tcApp1 e res_ty
172 tcExpr e@(HsAppType {}) res_ty = tcApp1 e res_ty
173
174 tcExpr e@(HsLit lit) res_ty = do { let lit_ty = hsLitType lit
175 ; tcWrapResult e (HsLit lit) lit_ty res_ty }
176
177 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
178 ; return (HsPar expr') }
179
180 tcExpr (HsSCC src lbl expr) res_ty
181 = do { expr' <- tcMonoExpr expr res_ty
182 ; return (HsSCC src lbl expr') }
183
184 tcExpr (HsTickPragma src info srcInfo expr) res_ty
185 = do { expr' <- tcMonoExpr expr res_ty
186 ; return (HsTickPragma src info srcInfo expr') }
187
188 tcExpr (HsCoreAnn src lbl expr) res_ty
189 = do { expr' <- tcMonoExpr expr res_ty
190 ; return (HsCoreAnn src lbl expr') }
191
192 tcExpr (HsOverLit lit) res_ty
193 = do { lit' <- newOverloadedLit lit res_ty
194 ; return (HsOverLit lit') }
195
196 tcExpr (NegApp expr neg_expr) res_ty
197 = do { (expr', neg_expr')
198 <- tcSyntaxOp NegateOrigin neg_expr [SynAny] res_ty $
199 \[arg_ty] ->
200 tcMonoExpr expr (mkCheckExpType arg_ty)
201 ; return (NegApp expr' neg_expr') }
202
203 tcExpr e@(HsIPVar x) res_ty
204 = do { {- Implicit parameters must have a *tau-type* not a
205 type scheme. We enforce this by creating a fresh
206 type variable as its type. (Because res_ty may not
207 be a tau-type.) -}
208 ip_ty <- newOpenFlexiTyVarTy
209 ; let ip_name = mkStrLitTy (hsIPNameFS x)
210 ; ipClass <- tcLookupClass ipClassName
211 ; ip_var <- emitWantedEvVar origin (mkClassPred ipClass [ip_name, ip_ty])
212 ; tcWrapResult e (fromDict ipClass ip_name ip_ty (HsVar (noLoc ip_var)))
213 ip_ty res_ty }
214 where
215 -- Coerces a dictionary for `IP "x" t` into `t`.
216 fromDict ipClass x ty = HsWrap $ mkWpCastR $
217 unwrapIP $ mkClassPred ipClass [x,ty]
218 origin = IPOccOrigin x
219
220 tcExpr e@(HsOverLabel l) res_ty -- See Note [Type-checking overloaded labels]
221 = do { isLabelClass <- tcLookupClass isLabelClassName
222 ; alpha <- newOpenFlexiTyVarTy
223 ; let lbl = mkStrLitTy l
224 pred = mkClassPred isLabelClass [lbl, alpha]
225 ; loc <- getSrcSpanM
226 ; var <- emitWantedEvVar origin pred
227 ; let proxy_arg = L loc (mkHsWrap (mkWpTyApps [typeSymbolKind, lbl])
228 (HsVar (L loc proxyHashId)))
229 tm = L loc (fromDict pred (HsVar (L loc var))) `HsApp` proxy_arg
230 ; tcWrapResult e tm alpha res_ty }
231 where
232 -- Coerces a dictionary for `IsLabel "x" t` into `Proxy# x -> t`.
233 fromDict pred = HsWrap $ mkWpCastR $ unwrapIP pred
234 origin = OverLabelOrigin l
235
236 tcExpr (HsLam match) res_ty
237 = do { (match', wrap) <- tcMatchLambda herald match_ctxt match res_ty
238 ; return (mkHsWrap wrap (HsLam match')) }
239 where
240 match_ctxt = MC { mc_what = LambdaExpr, mc_body = tcBody }
241 herald = sep [ text "The lambda expression" <+>
242 quotes (pprSetDepth (PartWay 1) $
243 pprMatches match),
244 -- The pprSetDepth makes the abstraction print briefly
245 text "has"]
246
247 tcExpr e@(HsLamCase matches) res_ty
248 = do { (matches', wrap)
249 <- tcMatchLambda msg match_ctxt matches res_ty
250 -- The laziness annotation is because we don't want to fail here
251 -- if there are multiple arguments
252 ; return (mkHsWrap wrap $ HsLamCase matches') }
253 where
254 msg = sep [ text "The function" <+> quotes (ppr e)
255 , text "requires"]
256 match_ctxt = MC { mc_what = CaseAlt, mc_body = tcBody }
257
258 tcExpr e@(ExprWithTySig expr sig_ty) res_ty
259 = do { let loc = getLoc (hsSigWcType sig_ty)
260 ; sig_info <- checkNoErrs $ -- Avoid error cascade
261 tcUserTypeSig loc sig_ty Nothing
262 ; (expr', poly_ty) <- tcExprSig expr sig_info
263 ; let expr'' = ExprWithTySigOut expr' sig_ty
264 ; tcWrapResult e expr'' poly_ty res_ty }
265
266 {-
267 Note [Type-checking overloaded labels]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 Recall that (in GHC.OverloadedLabels) we have
270
271 class IsLabel (x :: Symbol) a where
272 fromLabel :: Proxy# x -> a
273
274 When we see an overloaded label like `#foo`, we generate a fresh
275 variable `alpha` for the type and emit an `IsLabel "foo" alpha`
276 constraint. Because the `IsLabel` class has a single method, it is
277 represented by a newtype, so we can coerce `IsLabel "foo" alpha` to
278 `Proxy# "foo" -> alpha` (just like for implicit parameters). We then
279 apply it to `proxy#` of type `Proxy# "foo"`.
280
281 That is, we translate `#foo` to `fromLabel (proxy# :: Proxy# "foo")`.
282 -}
283
284
285 {-
286 ************************************************************************
287 * *
288 Infix operators and sections
289 * *
290 ************************************************************************
291
292 Note [Left sections]
293 ~~~~~~~~~~~~~~~~~~~~
294 Left sections, like (4 *), are equivalent to
295 \ x -> (*) 4 x,
296 or, if PostfixOperators is enabled, just
297 (*) 4
298 With PostfixOperators we don't actually require the function to take
299 two arguments at all. For example, (x `not`) means (not x); you get
300 postfix operators! Not Haskell 98, but it's less work and kind of
301 useful.
302
303 Note [Typing rule for ($)]
304 ~~~~~~~~~~~~~~~~~~~~~~~~~~
305 People write
306 runST $ blah
307 so much, where
308 runST :: (forall s. ST s a) -> a
309 that I have finally given in and written a special type-checking
310 rule just for saturated appliations of ($).
311 * Infer the type of the first argument
312 * Decompose it; should be of form (arg2_ty -> res_ty),
313 where arg2_ty might be a polytype
314 * Use arg2_ty to typecheck arg2
315
316 Note [Typing rule for seq]
317 ~~~~~~~~~~~~~~~~~~~~~~~~~~
318 We want to allow
319 x `seq` (# p,q #)
320 which suggests this type for seq:
321 seq :: forall (a:*) (b:Open). a -> b -> b,
322 with (b:Open) meaning that be can be instantiated with an unboxed
323 tuple. The trouble is that this might accept a partially-applied
324 'seq', and I'm just not certain that would work. I'm only sure it's
325 only going to work when it's fully applied, so it turns into
326 case x of _ -> (# p,q #)
327
328 So it seems more uniform to treat 'seq' as it it was a language
329 construct.
330
331 See also Note [seqId magic] in MkId
332 -}
333
334 tcExpr expr@(OpApp arg1 op fix arg2) res_ty
335 | (L loc (HsVar (L lv op_name))) <- op
336 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
337 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
338 ; let arg2_exp_ty = res_ty
339 ; arg1' <- tcArg op arg1 arg1_ty 1
340 ; arg2' <- addErrCtxt (funAppCtxt op arg2 2) $
341 tc_poly_expr_nc arg2 arg2_exp_ty
342 ; arg2_ty <- readExpType arg2_exp_ty
343 ; op_id <- tcLookupId op_name
344 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty])
345 (HsVar (L lv op_id)))
346 ; return $ OpApp arg1' op' fix arg2' }
347
348 | (L loc (HsVar (L lv op_name))) <- op
349 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
350 = do { traceTc "Application rule" (ppr op)
351 ; (arg1', arg1_ty) <- tcInferSigma arg1
352
353 ; let doc = text "The first argument of ($) takes"
354 orig1 = exprCtOrigin (unLoc arg1)
355 ; (wrap_arg1, [arg2_sigma], op_res_ty) <-
356 matchActualFunTys doc orig1 (Just arg1) 1 arg1_ty
357
358 -- We have (arg1 $ arg2)
359 -- So: arg1_ty = arg2_ty -> op_res_ty
360 -- where arg2_sigma maybe polymorphic; that's the point
361
362 ; arg2' <- tcArg op arg2 arg2_sigma 2
363
364 -- Make sure that the argument type has kind '*'
365 -- ($) :: forall (r:RuntimeRep) (a:*) (b:TYPE r). (a->b) -> a -> b
366 -- Eg we do not want to allow (D# $ 4.0#) Trac #5570
367 -- (which gives a seg fault)
368 --
369 -- The *result* type can have any kind (Trac #8739),
370 -- so we don't need to check anything for that
371 ; _ <- unifyKind (Just arg2_sigma) (typeKind arg2_sigma) liftedTypeKind
372 -- ignore the evidence. arg2_sigma must have type * or #,
373 -- because we know arg2_sigma -> or_res_ty is well-kinded
374 -- (because otherwise matchActualFunTys would fail)
375 -- There's no possibility here of, say, a kind family reducing to *.
376
377 ; wrap_res <- tcSubTypeHR orig1 (Just expr) op_res_ty res_ty
378 -- op_res -> res
379
380 ; op_id <- tcLookupId op_name
381 ; res_ty <- readExpType res_ty
382 ; let op' = L loc (HsWrap (mkWpTyApps [ getRuntimeRep "tcExpr ($)" res_ty
383 , arg2_sigma
384 , res_ty])
385 (HsVar (L lv op_id)))
386 -- arg1' :: arg1_ty
387 -- wrap_arg1 :: arg1_ty "->" (arg2_sigma -> op_res_ty)
388 -- wrap_res :: op_res_ty "->" res_ty
389 -- op' :: (a2_ty -> res_ty) -> a2_ty -> res_ty
390
391 -- wrap1 :: arg1_ty "->" (arg2_sigma -> res_ty)
392 wrap1 = mkWpFun idHsWrapper wrap_res arg2_sigma res_ty
393 <.> wrap_arg1
394
395 ; return (OpApp (mkLHsWrap wrap1 arg1') op' fix arg2') }
396
397 | (L loc (HsRecFld (Ambiguous lbl _))) <- op
398 , Just sig_ty <- obviousSig (unLoc arg1)
399 -- See Note [Disambiguating record fields]
400 = do { sig_tc_ty <- tcHsSigWcType ExprSigCtxt sig_ty
401 ; sel_name <- disambiguateSelector lbl sig_tc_ty
402 ; let op' = L loc (HsRecFld (Unambiguous lbl sel_name))
403 ; tcExpr (OpApp arg1 op' fix arg2) res_ty
404 }
405
406 | otherwise
407 = do { traceTc "Non Application rule" (ppr op)
408 ; (wrap, op', [Left arg1', Left arg2'])
409 <- tcApp (Just $ mk_op_msg op)
410 op [Left arg1, Left arg2] res_ty
411 ; return (mkHsWrap wrap $ OpApp arg1' op' fix arg2') }
412
413 -- Right sections, equivalent to \ x -> x `op` expr, or
414 -- \ x -> op x expr
415
416 tcExpr expr@(SectionR op arg2) res_ty
417 = do { (op', op_ty) <- tcInferFun op
418 ; (wrap_fun, [arg1_ty, arg2_ty], op_res_ty) <-
419 matchActualFunTys (mk_op_msg op) SectionOrigin (Just op) 2 op_ty
420 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
421 (mkFunTy arg1_ty op_res_ty) res_ty
422 ; arg2' <- tcArg op arg2 arg2_ty 2
423 ; return ( mkHsWrap wrap_res $
424 SectionR (mkLHsWrap wrap_fun op') arg2' ) }
425
426 tcExpr expr@(SectionL arg1 op) res_ty
427 = do { (op', op_ty) <- tcInferFun op
428 ; dflags <- getDynFlags -- Note [Left sections]
429 ; let n_reqd_args | xopt LangExt.PostfixOperators dflags = 1
430 | otherwise = 2
431
432 ; (wrap_fn, (arg1_ty:arg_tys), op_res_ty)
433 <- matchActualFunTys (mk_op_msg op) SectionOrigin (Just op)
434 n_reqd_args op_ty
435 ; wrap_res <- tcSubTypeHR SectionOrigin (Just expr)
436 (mkFunTys arg_tys op_res_ty) res_ty
437 ; arg1' <- tcArg op arg1 arg1_ty 1
438 ; return ( mkHsWrap wrap_res $
439 SectionL arg1' (mkLHsWrap wrap_fn op') ) }
440
441 tcExpr expr@(ExplicitTuple tup_args boxity) res_ty
442 | all tupArgPresent tup_args
443 = do { let arity = length tup_args
444 tup_tc = tupleTyCon boxity arity
445 ; res_ty <- expTypeToType res_ty
446 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
447 -- Unboxed tuples have RuntimeRep vars, which we
448 -- don't care about here
449 -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
450 ; let arg_tys' = case boxity of Unboxed -> drop arity arg_tys
451 Boxed -> arg_tys
452 ; tup_args1 <- tcTupArgs tup_args arg_tys'
453 ; return $ mkHsWrapCo coi (ExplicitTuple tup_args1 boxity) }
454
455 | otherwise
456 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
457 do { let arity = length tup_args
458
459 ; arg_tys <- case boxity of
460 { Boxed -> newFlexiTyVarTys arity liftedTypeKind
461 ; Unboxed -> replicateM arity newOpenFlexiTyVarTy }
462 ; let actual_res_ty
463 = mkFunTys [ty | (ty, (L _ (Missing _))) <- arg_tys `zip` tup_args]
464 (mkTupleTy boxity arg_tys)
465
466 ; wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "ExpTuple")
467 (Just expr)
468 actual_res_ty res_ty
469
470 -- Handle tuple sections where
471 ; tup_args1 <- tcTupArgs tup_args arg_tys
472
473 ; return $ mkHsWrap wrap (ExplicitTuple tup_args1 boxity) }
474
475 tcExpr (ExplicitList _ witness exprs) res_ty
476 = case witness of
477 Nothing -> do { res_ty <- expTypeToType res_ty
478 ; (coi, elt_ty) <- matchExpectedListTy res_ty
479 ; exprs' <- mapM (tc_elt elt_ty) exprs
480 ; return $
481 mkHsWrapCo coi $ ExplicitList elt_ty Nothing exprs' }
482
483 Just fln -> do { ((exprs', elt_ty), fln')
484 <- tcSyntaxOp ListOrigin fln
485 [synKnownType intTy, SynList] res_ty $
486 \ [elt_ty] ->
487 do { exprs' <-
488 mapM (tc_elt elt_ty) exprs
489 ; return (exprs', elt_ty) }
490
491 ; return $ ExplicitList elt_ty (Just fln') exprs' }
492 where tc_elt elt_ty expr = tcPolyExpr expr elt_ty
493
494 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
495 = do { res_ty <- expTypeToType res_ty
496 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
497 ; exprs' <- mapM (tc_elt elt_ty) exprs
498 ; return $
499 mkHsWrapCo coi $ ExplicitPArr elt_ty exprs' }
500 where
501 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
502
503 {-
504 ************************************************************************
505 * *
506 Let, case, if, do
507 * *
508 ************************************************************************
509 -}
510
511 tcExpr (HsLet (L l binds) expr) res_ty
512 = do { (binds', expr') <- tcLocalBinds binds $
513 tcMonoExpr expr res_ty
514 ; return (HsLet (L l binds') expr') }
515
516 tcExpr (HsCase scrut matches) res_ty
517 = do { -- We used to typecheck the case alternatives first.
518 -- The case patterns tend to give good type info to use
519 -- when typechecking the scrutinee. For example
520 -- case (map f) of
521 -- (x:xs) -> ...
522 -- will report that map is applied to too few arguments
523 --
524 -- But now, in the GADT world, we need to typecheck the scrutinee
525 -- first, to get type info that may be refined in the case alternatives
526 (scrut', scrut_ty) <- tcInferRho scrut
527
528 ; traceTc "HsCase" (ppr scrut_ty)
529 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches res_ty
530 ; return (HsCase scrut' matches') }
531 where
532 match_ctxt = MC { mc_what = CaseAlt,
533 mc_body = tcBody }
534
535 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
536 = do { pred' <- tcMonoExpr pred (mkCheckExpType boolTy)
537 ; res_ty <- tauifyExpType res_ty
538 -- Just like Note [Case branches must never infer a non-tau type]
539 -- in TcMatches (See #10619)
540
541 ; b1' <- tcMonoExpr b1 res_ty
542 ; b2' <- tcMonoExpr b2 res_ty
543 ; return (HsIf Nothing pred' b1' b2') }
544
545 tcExpr (HsIf (Just fun) pred b1 b2) res_ty
546 = do { ((pred', b1', b2'), fun')
547 <- tcSyntaxOp IfOrigin fun [SynAny, SynAny, SynAny] res_ty $
548 \ [pred_ty, b1_ty, b2_ty] ->
549 do { pred' <- tcPolyExpr pred pred_ty
550 ; b1' <- tcPolyExpr b1 b1_ty
551 ; b2' <- tcPolyExpr b2 b2_ty
552 ; return (pred', b1', b2') }
553 ; return (HsIf (Just fun') pred' b1' b2') }
554
555 tcExpr (HsMultiIf _ alts) res_ty
556 = do { res_ty <- if isSingleton alts
557 then return res_ty
558 else tauifyExpType res_ty
559 -- Just like TcMatches
560 -- Note [Case branches must never infer a non-tau type]
561
562 ; alts' <- mapM (wrapLocM $ tcGRHS match_ctxt res_ty) alts
563 ; res_ty <- readExpType res_ty
564 ; return (HsMultiIf res_ty alts') }
565 where match_ctxt = MC { mc_what = IfAlt, mc_body = tcBody }
566
567 tcExpr (HsDo do_or_lc stmts _) res_ty
568 = do { expr' <- tcDoStmts do_or_lc stmts res_ty
569 ; return expr' }
570
571 tcExpr (HsProc pat cmd) res_ty
572 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
573 ; return $ mkHsWrapCo coi (HsProc pat' cmd') }
574
575 -- Typechecks the static form and wraps it with a call to 'fromStaticPtr'.
576 tcExpr (HsStatic fvs expr) res_ty
577 = do { res_ty <- expTypeToType res_ty
578 ; (co, (p_ty, expr_ty)) <- matchExpectedAppTy res_ty
579 ; (expr', lie) <- captureConstraints $
580 addErrCtxt (hang (text "In the body of a static form:")
581 2 (ppr expr)
582 ) $
583 tcPolyExprNC expr expr_ty
584 -- Check that the free variables of the static form are closed.
585 -- It's OK to use nonDetEltsUFM here as the only side effects of
586 -- checkClosedInStaticForm are error messages.
587 ; mapM_ checkClosedInStaticForm $ nonDetEltsUFM fvs
588
589 -- Require the type of the argument to be Typeable.
590 -- The evidence is not used, but asking the constraint ensures that
591 -- the current implementation is as restrictive as future versions
592 -- of the StaticPointers extension.
593 ; typeableClass <- tcLookupClass typeableClassName
594 ; _ <- emitWantedEvVar StaticOrigin $
595 mkTyConApp (classTyCon typeableClass)
596 [liftedTypeKind, expr_ty]
597 -- Insert the constraints of the static form in a global list for later
598 -- validation.
599 ; stWC <- tcg_static_wc <$> getGblEnv
600 ; updTcRef stWC (andWC lie)
601 -- Wrap the static form with the 'fromStaticPtr' call.
602 ; fromStaticPtr <- newMethodFromName StaticOrigin fromStaticPtrName p_ty
603 ; let wrap = mkWpTyApps [expr_ty]
604 ; loc <- getSrcSpanM
605 ; return $ mkHsWrapCo co $ HsApp (L loc $ mkHsWrap wrap fromStaticPtr)
606 (L loc (HsStatic fvs expr'))
607 }
608
609 {-
610 ************************************************************************
611 * *
612 Record construction and update
613 * *
614 ************************************************************************
615 -}
616
617 tcExpr expr@(RecordCon { rcon_con_name = L loc con_name
618 , rcon_flds = rbinds }) res_ty
619 = do { con_like <- tcLookupConLike con_name
620
621 -- Check for missing fields
622 ; checkMissingFields con_like rbinds
623
624 ; (con_expr, con_sigma) <- tcInferId con_name
625 ; (con_wrap, con_tau) <-
626 topInstantiate (OccurrenceOf con_name) con_sigma
627 -- a shallow instantiation should really be enough for
628 -- a data constructor.
629 ; let arity = conLikeArity con_like
630 Right (arg_tys, actual_res_ty) = tcSplitFunTysN arity con_tau
631 ; case conLikeWrapId_maybe con_like of
632 Nothing -> nonBidirectionalErr (conLikeName con_like)
633 Just con_id -> do {
634 res_wrap <- tcSubTypeHR (Shouldn'tHappenOrigin "RecordCon")
635 (Just expr) actual_res_ty res_ty
636 ; rbinds' <- tcRecordBinds con_like arg_tys rbinds
637 ; return $
638 mkHsWrap res_wrap $
639 RecordCon { rcon_con_name = L loc con_id
640 , rcon_con_expr = mkHsWrap con_wrap con_expr
641 , rcon_con_like = con_like
642 , rcon_flds = rbinds' } } }
643
644 {-
645 Note [Type of a record update]
646 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
647 The main complication with RecordUpd is that we need to explicitly
648 handle the *non-updated* fields. Consider:
649
650 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
651 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
652 | MkT3 { fd :: a }
653
654 upd :: T a b c -> (b',c) -> T a b' c
655 upd t x = t { fb = x}
656
657 The result type should be (T a b' c)
658 not (T a b c), because 'b' *is not* mentioned in a non-updated field
659 not (T a b' c'), because 'c' *is* mentioned in a non-updated field
660 NB that it's not good enough to look at just one constructor; we must
661 look at them all; cf Trac #3219
662
663 After all, upd should be equivalent to:
664 upd t x = case t of
665 MkT1 p q -> MkT1 p x
666 MkT2 a b -> MkT2 p b
667 MkT3 d -> error ...
668
669 So we need to give a completely fresh type to the result record,
670 and then constrain it by the fields that are *not* updated ("p" above).
671 We call these the "fixed" type variables, and compute them in getFixedTyVars.
672
673 Note that because MkT3 doesn't contain all the fields being updated,
674 its RHS is simply an error, so it doesn't impose any type constraints.
675 Hence the use of 'relevant_cont'.
676
677 Note [Implicit type sharing]
678 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
679 We also take into account any "implicit" non-update fields. For example
680 data T a b where { MkT { f::a } :: T a a; ... }
681 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
682
683 Then consider
684 upd t x = t { f=x }
685 We infer the type
686 upd :: T a b -> a -> T a b
687 upd (t::T a b) (x::a)
688 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
689 We can't give it the more general type
690 upd :: T a b -> c -> T c b
691
692 Note [Criteria for update]
693 ~~~~~~~~~~~~~~~~~~~~~~~~~~
694 We want to allow update for existentials etc, provided the updated
695 field isn't part of the existential. For example, this should be ok.
696 data T a where { MkT { f1::a, f2::b->b } :: T a }
697 f :: T a -> b -> T b
698 f t b = t { f1=b }
699
700 The criterion we use is this:
701
702 The types of the updated fields
703 mention only the universally-quantified type variables
704 of the data constructor
705
706 NB: this is not (quite) the same as being a "naughty" record selector
707 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
708 in the case of GADTs. Consider
709 data T a where { MkT :: { f :: a } :: T [a] }
710 Then f is not "naughty" because it has a well-typed record selector.
711 But we don't allow updates for 'f'. (One could consider trying to
712 allow this, but it makes my head hurt. Badly. And no one has asked
713 for it.)
714
715 In principle one could go further, and allow
716 g :: T a -> T a
717 g t = t { f2 = \x -> x }
718 because the expression is polymorphic...but that seems a bridge too far.
719
720 Note [Data family example]
721 ~~~~~~~~~~~~~~~~~~~~~~~~~~
722 data instance T (a,b) = MkT { x::a, y::b }
723 --->
724 data :TP a b = MkT { a::a, y::b }
725 coTP a b :: T (a,b) ~ :TP a b
726
727 Suppose r :: T (t1,t2), e :: t3
728 Then r { x=e } :: T (t3,t1)
729 --->
730 case r |> co1 of
731 MkT x y -> MkT e y |> co2
732 where co1 :: T (t1,t2) ~ :TP t1 t2
733 co2 :: :TP t3 t2 ~ T (t3,t2)
734 The wrapping with co2 is done by the constructor wrapper for MkT
735
736 Outgoing invariants
737 ~~~~~~~~~~~~~~~~~~~
738 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
739
740 * cons are the data constructors to be updated
741
742 * in_inst_tys, out_inst_tys have same length, and instantiate the
743 *representation* tycon of the data cons. In Note [Data
744 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
745
746 Note [Mixed Record Field Updates]
747 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748 Consider the following pattern synonym.
749
750 data MyRec = MyRec { foo :: Int, qux :: String }
751
752 pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}
753
754 This allows updates such as the following
755
756 updater :: MyRec -> MyRec
757 updater a = a {f1 = 1 }
758
759 It would also make sense to allow the following update (which we reject).
760
761 updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"
762
763 This leads to confusing behaviour when the selectors in fact refer the same
764 field.
765
766 updater a = a {f1 = 1, foo = 2} ==? ???
767
768 For this reason, we reject a mixture of pattern synonym and normal record
769 selectors in the same update block. Although of course we still allow the
770 following.
771
772 updater a = (a {f1 = 1}) {foo = 2}
773
774 > updater (MyRec 0 "str")
775 MyRec 2 "str"
776
777 -}
778
779 tcExpr expr@(RecordUpd { rupd_expr = record_expr, rupd_flds = rbnds }) res_ty
780 = ASSERT( notNull rbnds )
781 do { -- STEP -2: typecheck the record_expr, the record to be updated
782 (record_expr', record_rho) <- tcInferRho record_expr
783
784 -- STEP -1 See Note [Disambiguating record fields]
785 -- After this we know that rbinds is unambiguous
786 ; rbinds <- disambiguateRecordBinds record_expr record_rho rbnds res_ty
787 ; let upd_flds = map (unLoc . hsRecFieldLbl . unLoc) rbinds
788 upd_fld_occs = map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc) upd_flds
789 sel_ids = map selectorAmbiguousFieldOcc upd_flds
790 -- STEP 0
791 -- Check that the field names are really field names
792 -- and they are all field names for proper records or
793 -- all field names for pattern synonyms.
794 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
795 | fld <- rbinds,
796 -- Excludes class ops
797 let L loc sel_id = hsRecUpdFieldId (unLoc fld),
798 not (isRecordSelector sel_id),
799 let fld_name = idName sel_id ]
800 ; unless (null bad_guys) (sequence bad_guys >> failM)
801 -- See note [Mixed Record Selectors]
802 ; let (data_sels, pat_syn_sels) =
803 partition isDataConRecordSelector sel_ids
804 ; MASSERT( all isPatSynRecordSelector pat_syn_sels )
805 ; checkTc ( null data_sels || null pat_syn_sels )
806 ( mixedSelectors data_sels pat_syn_sels )
807
808 -- STEP 1
809 -- Figure out the tycon and data cons from the first field name
810 ; let -- It's OK to use the non-tc splitters here (for a selector)
811 sel_id : _ = sel_ids
812
813 mtycon :: Maybe TyCon
814 mtycon = case idDetails sel_id of
815 RecSelId (RecSelData tycon) _ -> Just tycon
816 _ -> Nothing
817
818 con_likes :: [ConLike]
819 con_likes = case idDetails sel_id of
820 RecSelId (RecSelData tc) _
821 -> map RealDataCon (tyConDataCons tc)
822 RecSelId (RecSelPatSyn ps) _
823 -> [PatSynCon ps]
824 _ -> panic "tcRecordUpd"
825 -- NB: for a data type family, the tycon is the instance tycon
826
827 relevant_cons = conLikesWithFields con_likes upd_fld_occs
828 -- A constructor is only relevant to this process if
829 -- it contains *all* the fields that are being updated
830 -- Other ones will cause a runtime error if they occur
831
832 -- Step 2
833 -- Check that at least one constructor has all the named fields
834 -- i.e. has an empty set of bad fields returned by badFields
835 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds con_likes)
836
837 -- Take apart a representative constructor
838 ; let con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
839 (con1_tvs, _, _, _prov_theta, req_theta, con1_arg_tys, _)
840 = conLikeFullSig con1
841 con1_flds = map flLabel $ conLikeFieldLabels con1
842 con1_tv_tys = mkTyVarTys con1_tvs
843 con1_res_ty = case mtycon of
844 Just tc -> mkFamilyTyConApp tc con1_tv_tys
845 Nothing -> conLikeResTy con1 con1_tv_tys
846
847 -- Check that we're not dealing with a unidirectional pattern
848 -- synonym
849 ; unless (isJust $ conLikeWrapId_maybe con1)
850 (nonBidirectionalErr (conLikeName con1))
851
852 -- STEP 3 Note [Criteria for update]
853 -- Check that each updated field is polymorphic; that is, its type
854 -- mentions only the universally-quantified variables of the data con
855 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
856 bad_upd_flds = filter bad_fld flds1_w_tys
857 con1_tv_set = mkVarSet con1_tvs
858 bad_fld (fld, ty) = fld `elem` upd_fld_occs &&
859 not (tyCoVarsOfType ty `subVarSet` con1_tv_set)
860 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
861
862 -- STEP 4 Note [Type of a record update]
863 -- Figure out types for the scrutinee and result
864 -- Both are of form (T a b c), with fresh type variables, but with
865 -- common variables where the scrutinee and result must have the same type
866 -- These are variables that appear in *any* arg of *any* of the
867 -- relevant constructors *except* in the updated fields
868 --
869 ; let fixed_tvs = getFixedTyVars upd_fld_occs con1_tvs relevant_cons
870 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
871
872 mk_inst_ty :: TCvSubst -> (TyVar, TcType) -> TcM (TCvSubst, TcType)
873 -- Deals with instantiation of kind variables
874 -- c.f. TcMType.newMetaTyVars
875 mk_inst_ty subst (tv, result_inst_ty)
876 | is_fixed_tv tv -- Same as result type
877 = return (extendTvSubst subst tv result_inst_ty, result_inst_ty)
878 | otherwise -- Fresh type, of correct kind
879 = do { (subst', new_tv) <- newMetaTyVarX subst tv
880 ; return (subst', mkTyVarTy new_tv) }
881
882 ; (result_subst, con1_tvs') <- newMetaTyVars con1_tvs
883 ; let result_inst_tys = mkTyVarTys con1_tvs'
884 init_subst = mkEmptyTCvSubst (getTCvInScope result_subst)
885
886 ; (scrut_subst, scrut_inst_tys) <- mapAccumLM mk_inst_ty init_subst
887 (con1_tvs `zip` result_inst_tys)
888
889 ; let rec_res_ty = TcType.substTy result_subst con1_res_ty
890 scrut_ty = TcType.substTy scrut_subst con1_res_ty
891 con1_arg_tys' = map (TcType.substTy result_subst) con1_arg_tys
892
893 ; wrap_res <- tcSubTypeHR (exprCtOrigin expr)
894 (Just expr) rec_res_ty res_ty
895 ; co_scrut <- unifyType (Just record_expr) record_rho scrut_ty
896 -- NB: normal unification is OK here (as opposed to subsumption),
897 -- because for this to work out, both record_rho and scrut_ty have
898 -- to be normal datatypes -- no contravariant stuff can go on
899
900 -- STEP 5
901 -- Typecheck the bindings
902 ; rbinds' <- tcRecordUpd con1 con1_arg_tys' rbinds
903
904 -- STEP 6: Deal with the stupid theta
905 ; let theta' = substThetaUnchecked scrut_subst (conLikeStupidTheta con1)
906 ; instStupidTheta RecordUpdOrigin theta'
907
908 -- Step 7: make a cast for the scrutinee, in the
909 -- case that it's from a data family
910 ; let fam_co :: HsWrapper -- RepT t1 .. tn ~R scrut_ty
911 fam_co | Just tycon <- mtycon
912 , Just co_con <- tyConFamilyCoercion_maybe tycon
913 = mkWpCastR (mkTcUnbranchedAxInstCo co_con scrut_inst_tys [])
914 | otherwise
915 = idHsWrapper
916
917 -- Step 8: Check that the req constraints are satisfied
918 -- For normal data constructors req_theta is empty but we must do
919 -- this check for pattern synonyms.
920 ; let req_theta' = substThetaUnchecked scrut_subst req_theta
921 ; req_wrap <- instCallConstraints RecordUpdOrigin req_theta'
922
923 -- Phew!
924 ; return $
925 mkHsWrap wrap_res $
926 RecordUpd { rupd_expr = mkLHsWrap fam_co (mkLHsWrapCo co_scrut record_expr')
927 , rupd_flds = rbinds'
928 , rupd_cons = relevant_cons, rupd_in_tys = scrut_inst_tys
929 , rupd_out_tys = result_inst_tys, rupd_wrap = req_wrap } }
930
931 tcExpr (HsRecFld f) res_ty
932 = tcCheckRecSelId f res_ty
933
934 {-
935 ************************************************************************
936 * *
937 Arithmetic sequences e.g. [a,b..]
938 and their parallel-array counterparts e.g. [: a,b.. :]
939
940 * *
941 ************************************************************************
942 -}
943
944 tcExpr (ArithSeq _ witness seq) res_ty
945 = tcArithSeq witness seq res_ty
946
947 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
948 = do { res_ty <- expTypeToType res_ty
949 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
950 ; expr1' <- tcPolyExpr expr1 elt_ty
951 ; expr2' <- tcPolyExpr expr2 elt_ty
952 ; enumFromToP <- initDsTc $ dsDPHBuiltin enumFromToPVar
953 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
954 (idName enumFromToP) elt_ty
955 ; return $
956 mkHsWrapCo coi $ PArrSeq enum_from_to (FromTo expr1' expr2') }
957
958 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
959 = do { res_ty <- expTypeToType res_ty
960 ; (coi, elt_ty) <- matchExpectedPArrTy res_ty
961 ; expr1' <- tcPolyExpr expr1 elt_ty
962 ; expr2' <- tcPolyExpr expr2 elt_ty
963 ; expr3' <- tcPolyExpr expr3 elt_ty
964 ; enumFromThenToP <- initDsTc $ dsDPHBuiltin enumFromThenToPVar
965 ; eft <- newMethodFromName (PArrSeqOrigin seq)
966 (idName enumFromThenToP) elt_ty -- !!!FIXME: chak
967 ; return $
968 mkHsWrapCo coi $
969 PArrSeq eft (FromThenTo expr1' expr2' expr3') }
970
971 tcExpr (PArrSeq _ _) _
972 = panic "TcExpr.tcExpr: Infinite parallel array!"
973 -- the parser shouldn't have generated it and the renamer shouldn't have
974 -- let it through
975
976 {-
977 ************************************************************************
978 * *
979 Template Haskell
980 * *
981 ************************************************************************
982 -}
983
984 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 (tvb, inner_ty) ->
1193 do { let tv = binderVar tvb
1194 vis = binderVisibility tvb
1195 kind = tyVarKind tv
1196 ; MASSERT2( vis == Specified
1197 , (vcat [ ppr fun_ty, ppr upsilon_ty, ppr tvb
1198 , ppr inner_ty, pprTvBndr tv
1199 , ppr vis ]) )
1200 ; ty_arg <- tcHsTypeApp hs_ty_arg kind
1201 ; let insted_ty = substTyWithUnchecked [tv] [ty_arg] inner_ty
1202 ; (inner_wrap, args', res_ty)
1203 <- go acc_args (n+1) insted_ty args
1204 -- inner_wrap :: insted_ty "->" (map typeOf args') -> res_ty
1205 ; let inst_wrap = mkWpTyApps [ty_arg]
1206 ; return ( inner_wrap <.> inst_wrap <.> wrap1
1207 , Right hs_ty_arg : args'
1208 , res_ty ) }
1209 _ -> ty_app_err upsilon_ty hs_ty_arg }
1210
1211 go acc_args n fun_ty (Left arg : args)
1212 = do { (wrap, [arg_ty], res_ty)
1213 <- matchActualFunTysPart herald fun_orig (Just fun) 1 fun_ty
1214 acc_args orig_arity
1215 -- wrap :: fun_ty "->" arg_ty -> res_ty
1216 ; arg' <- tcArg fun arg arg_ty n
1217 ; (inner_wrap, args', inner_res_ty)
1218 <- go (arg_ty : acc_args) (n+1) res_ty args
1219 -- inner_wrap :: res_ty "->" (map typeOf args') -> inner_res_ty
1220 ; return ( mkWpFun idHsWrapper inner_wrap arg_ty res_ty <.> wrap
1221 , Left arg' : args'
1222 , inner_res_ty ) }
1223
1224 ty_app_err ty arg
1225 = do { (_, ty) <- zonkTidyTcType emptyTidyEnv ty
1226 ; failWith $
1227 text "Cannot apply expression of type" <+> quotes (ppr ty) $$
1228 text "to a visible type argument" <+> quotes (ppr arg) }
1229
1230 ----------------
1231 tcArg :: LHsExpr Name -- The function (for error messages)
1232 -> LHsExpr Name -- Actual arguments
1233 -> TcRhoType -- expected arg type
1234 -> Int -- # of argument
1235 -> TcM (LHsExpr TcId) -- Resulting argument
1236 tcArg fun arg ty arg_no = addErrCtxt (funAppCtxt fun arg arg_no) $
1237 tcPolyExprNC arg ty
1238
1239 ----------------
1240 tcTupArgs :: [LHsTupArg Name] -> [TcSigmaType] -> TcM [LHsTupArg TcId]
1241 tcTupArgs args tys
1242 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
1243 where
1244 go (L l (Missing {}), arg_ty) = return (L l (Missing arg_ty))
1245 go (L l (Present expr), arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
1246 ; return (L l (Present expr')) }
1247
1248 ---------------------------
1249 -- See TcType.SyntaxOpType also for commentary
1250 tcSyntaxOp :: CtOrigin
1251 -> SyntaxExpr Name
1252 -> [SyntaxOpType] -- ^ shape of syntax operator arguments
1253 -> ExpType -- ^ overall result type
1254 -> ([TcSigmaType] -> TcM a) -- ^ Type check any arguments
1255 -> TcM (a, SyntaxExpr TcId)
1256 -- ^ Typecheck a syntax operator
1257 -- The operator is always a variable at this stage (i.e. renamer output)
1258 tcSyntaxOp orig expr arg_tys res_ty
1259 = tcSyntaxOpGen orig expr arg_tys (SynType res_ty)
1260
1261 -- | Slightly more general version of 'tcSyntaxOp' that allows the caller
1262 -- to specify the shape of the result of the syntax operator
1263 tcSyntaxOpGen :: CtOrigin
1264 -> SyntaxExpr Name
1265 -> [SyntaxOpType]
1266 -> SyntaxOpType
1267 -> ([TcSigmaType] -> TcM a)
1268 -> TcM (a, SyntaxExpr TcId)
1269 tcSyntaxOpGen orig (SyntaxExpr { syn_expr = HsVar (L _ op) })
1270 arg_tys res_ty thing_inside
1271 = do { (expr, sigma) <- tcInferId op
1272 ; (result, expr_wrap, arg_wraps, res_wrap)
1273 <- tcSynArgA orig sigma arg_tys res_ty $
1274 thing_inside
1275 ; return (result, SyntaxExpr { syn_expr = mkHsWrap expr_wrap expr
1276 , syn_arg_wraps = arg_wraps
1277 , syn_res_wrap = res_wrap }) }
1278
1279 tcSyntaxOpGen _ other _ _ _ = pprPanic "tcSyntaxOp" (ppr other)
1280
1281 {-
1282 Note [tcSynArg]
1283 ~~~~~~~~~~~~~~~
1284 Because of the rich structure of SyntaxOpType, we must do the
1285 contra-/covariant thing when working down arrows, to get the
1286 instantiation vs. skolemisation decisions correct (and, more
1287 obviously, the orientation of the HsWrappers). We thus have
1288 two tcSynArgs.
1289 -}
1290
1291 -- works on "expected" types, skolemising where necessary
1292 -- See Note [tcSynArg]
1293 tcSynArgE :: CtOrigin
1294 -> TcSigmaType
1295 -> SyntaxOpType -- ^ shape it is expected to have
1296 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1297 -> TcM (a, HsWrapper)
1298 -- ^ returns a wrapper :: (type of right shape) "->" (type passed in)
1299 tcSynArgE orig sigma_ty syn_ty thing_inside
1300 = do { (skol_wrap, (result, ty_wrapper))
1301 <- tcSkolemise GenSigCtxt sigma_ty $ \ _ rho_ty ->
1302 go rho_ty syn_ty
1303 ; return (result, skol_wrap <.> ty_wrapper) }
1304 where
1305 go rho_ty SynAny
1306 = do { result <- thing_inside [rho_ty]
1307 ; return (result, idHsWrapper) }
1308
1309 go rho_ty SynRho -- same as SynAny, because we skolemise eagerly
1310 = do { result <- thing_inside [rho_ty]
1311 ; return (result, idHsWrapper) }
1312
1313 go rho_ty SynList
1314 = do { (list_co, elt_ty) <- matchExpectedListTy rho_ty
1315 ; result <- thing_inside [elt_ty]
1316 ; return (result, mkWpCastN list_co) }
1317
1318 go rho_ty (SynFun arg_shape res_shape)
1319 = do { ( ( ( (result, arg_ty, res_ty)
1320 , res_wrapper ) -- :: res_ty_out "->" res_ty
1321 , arg_wrapper1, [], arg_wrapper2 ) -- :: arg_ty "->" arg_ty_out
1322 , match_wrapper ) -- :: (arg_ty -> res_ty) "->" rho_ty
1323 <- matchExpectedFunTys herald 1 (mkCheckExpType rho_ty) $
1324 \ [arg_ty] res_ty ->
1325 do { arg_tc_ty <- expTypeToType arg_ty
1326 ; res_tc_ty <- expTypeToType res_ty
1327
1328 -- another nested arrow is too much for now,
1329 -- but I bet we'll never need this
1330 ; MASSERT2( case arg_shape of
1331 SynFun {} -> False;
1332 _ -> True
1333 , text "Too many nested arrows in SyntaxOpType" $$
1334 pprCtOrigin orig )
1335
1336 ; tcSynArgA orig arg_tc_ty [] arg_shape $
1337 \ arg_results ->
1338 tcSynArgE orig res_tc_ty res_shape $
1339 \ res_results ->
1340 do { result <- thing_inside (arg_results ++ res_results)
1341 ; return (result, arg_tc_ty, res_tc_ty) }}
1342
1343 ; return ( result
1344 , match_wrapper <.>
1345 mkWpFun (arg_wrapper2 <.> arg_wrapper1) res_wrapper
1346 arg_ty res_ty ) }
1347 where
1348 herald = text "This rebindable syntax expects a function with"
1349
1350 go rho_ty (SynType the_ty)
1351 = do { wrap <- tcSubTypeET orig the_ty rho_ty
1352 ; result <- thing_inside []
1353 ; return (result, wrap) }
1354
1355 -- works on "actual" types, instantiating where necessary
1356 -- See Note [tcSynArg]
1357 tcSynArgA :: CtOrigin
1358 -> TcSigmaType
1359 -> [SyntaxOpType] -- ^ argument shapes
1360 -> SyntaxOpType -- ^ result shape
1361 -> ([TcSigmaType] -> TcM a) -- ^ check the arguments
1362 -> TcM (a, HsWrapper, [HsWrapper], HsWrapper)
1363 -- ^ returns a wrapper to be applied to the original function,
1364 -- wrappers to be applied to arguments
1365 -- and a wrapper to be applied to the overall expression
1366 tcSynArgA orig sigma_ty arg_shapes res_shape thing_inside
1367 = do { (match_wrapper, arg_tys, res_ty)
1368 <- matchActualFunTys herald orig noThing (length arg_shapes) sigma_ty
1369 -- match_wrapper :: sigma_ty "->" (arg_tys -> res_ty)
1370 ; ((result, res_wrapper), arg_wrappers)
1371 <- tc_syn_args_e arg_tys arg_shapes $ \ arg_results ->
1372 tc_syn_arg res_ty res_shape $ \ res_results ->
1373 thing_inside (arg_results ++ res_results)
1374 ; return (result, match_wrapper, arg_wrappers, res_wrapper) }
1375 where
1376 herald = text "This rebindable syntax expects a function with"
1377
1378 tc_syn_args_e :: [TcSigmaType] -> [SyntaxOpType]
1379 -> ([TcSigmaType] -> TcM a)
1380 -> TcM (a, [HsWrapper])
1381 -- the wrappers are for arguments
1382 tc_syn_args_e (arg_ty : arg_tys) (arg_shape : arg_shapes) thing_inside
1383 = do { ((result, arg_wraps), arg_wrap)
1384 <- tcSynArgE orig arg_ty arg_shape $ \ arg1_results ->
1385 tc_syn_args_e arg_tys arg_shapes $ \ args_results ->
1386 thing_inside (arg1_results ++ args_results)
1387 ; return (result, arg_wrap : arg_wraps) }
1388 tc_syn_args_e _ _ thing_inside = (, []) <$> thing_inside []
1389
1390 tc_syn_arg :: TcSigmaType -> SyntaxOpType
1391 -> ([TcSigmaType] -> TcM a)
1392 -> TcM (a, HsWrapper)
1393 -- the wrapper applies to the overall result
1394 tc_syn_arg res_ty SynAny thing_inside
1395 = do { result <- thing_inside [res_ty]
1396 ; return (result, idHsWrapper) }
1397 tc_syn_arg res_ty SynRho thing_inside
1398 = do { (inst_wrap, rho_ty) <- deeplyInstantiate orig res_ty
1399 -- inst_wrap :: res_ty "->" rho_ty
1400 ; result <- thing_inside [rho_ty]
1401 ; return (result, inst_wrap) }
1402 tc_syn_arg res_ty SynList thing_inside
1403 = do { (inst_wrap, rho_ty) <- topInstantiate orig res_ty
1404 -- inst_wrap :: res_ty "->" rho_ty
1405 ; (list_co, elt_ty) <- matchExpectedListTy rho_ty
1406 -- list_co :: [elt_ty] ~N rho_ty
1407 ; result <- thing_inside [elt_ty]
1408 ; return (result, mkWpCastN (mkTcSymCo list_co) <.> inst_wrap) }
1409 tc_syn_arg _ (SynFun {}) _
1410 = pprPanic "tcSynArgA hits a SynFun" (ppr orig)
1411 tc_syn_arg res_ty (SynType the_ty) thing_inside
1412 = do { wrap <- tcSubTypeO orig GenSigCtxt res_ty the_ty
1413 ; result <- thing_inside []
1414 ; return (result, wrap) }
1415
1416 {-
1417 Note [Push result type in]
1418 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1419 Unify with expected result before type-checking the args so that the
1420 info from res_ty percolates to args. This is when we might detect a
1421 too-few args situation. (One can think of cases when the opposite
1422 order would give a better error message.)
1423 experimenting with putting this first.
1424
1425 Here's an example where it actually makes a real difference
1426
1427 class C t a b | t a -> b
1428 instance C Char a Bool
1429
1430 data P t a = forall b. (C t a b) => MkP b
1431 data Q t = MkQ (forall a. P t a)
1432
1433 f1, f2 :: Q Char;
1434 f1 = MkQ (MkP True)
1435 f2 = MkQ (MkP True :: forall a. P Char a)
1436
1437 With the change, f1 will type-check, because the 'Char' info from
1438 the signature is propagated into MkQ's argument. With the check
1439 in the other order, the extra signature in f2 is reqd.
1440
1441 ************************************************************************
1442 * *
1443 Expressions with a type signature
1444 expr :: type
1445 * *
1446 ********************************************************************* -}
1447
1448 tcExprSig :: LHsExpr Name -> TcIdSigInfo -> TcM (LHsExpr TcId, TcType)
1449 tcExprSig expr (CompleteSig { sig_bndr = poly_id, sig_loc = loc })
1450 = setSrcSpan loc $ -- Sets the location for the implication constraint
1451 do { (tv_prs, theta, tau) <- tcInstType (tcInstSigTyVars loc) poly_id
1452 ; given <- newEvVars theta
1453 ; let skol_info = SigSkol ExprSigCtxt (mkPhiTy theta tau)
1454 skol_tvs = map snd tv_prs
1455 ; (ev_binds, expr') <- checkConstraints skol_info skol_tvs given $
1456 tcExtendTyVarEnv2 tv_prs $
1457 tcPolyExprNC expr tau
1458
1459 ; let poly_wrap = mkWpTyLams skol_tvs
1460 <.> mkWpLams given
1461 <.> mkWpLet ev_binds
1462 ; return (mkLHsWrap poly_wrap expr', idType poly_id) }
1463
1464 tcExprSig expr sig@(PartialSig { psig_name = name, sig_loc = loc })
1465 = setSrcSpan loc $ -- Sets the location for the implication constraint
1466 do { (tclvl, wanted, (expr', sig_inst))
1467 <- pushLevelAndCaptureConstraints $
1468 do { sig_inst <- tcInstSig sig
1469 ; expr' <- tcExtendTyVarEnv2 (sig_inst_skols sig_inst) $
1470 tcExtendTyVarEnv2 (sig_inst_wcs sig_inst) $
1471 tcPolyExprNC expr (sig_inst_tau sig_inst)
1472 ; return (expr', sig_inst) }
1473 -- See Note [Partial expression signatures]
1474 ; let tau = sig_inst_tau sig_inst
1475 infer_mode | null (sig_inst_theta sig_inst)
1476 , isNothing (sig_inst_wcx sig_inst)
1477 = ApplyMR
1478 | otherwise
1479 = NoRestrictions
1480 ; (qtvs, givens, ev_binds)
1481 <- simplifyInfer tclvl infer_mode [sig_inst] [(name, tau)] wanted
1482 ; tau <- zonkTcType tau
1483 ; let inferred_theta = map evVarPred givens
1484 tau_tvs = tyCoVarsOfType tau
1485 ; (binders, my_theta) <- chooseInferredQuantifiers inferred_theta
1486 tau_tvs qtvs (Just sig_inst)
1487 ; let inferred_sigma = mkInvSigmaTy qtvs inferred_theta tau
1488 my_sigma = mkForAllTys binders (mkPhiTy my_theta tau)
1489 ; wrap <- if inferred_sigma `eqType` my_sigma -- NB: eqType ignores vis.
1490 then return idHsWrapper -- Fast path; also avoids complaint when we infer
1491 -- an ambiguouse type and have AllowAmbiguousType
1492 -- e..g infer x :: forall a. F a -> Int
1493 else tcSubType_NC ExprSigCtxt inferred_sigma
1494 (mkCheckExpType my_sigma)
1495
1496 ; traceTc "tcExpSig" (ppr qtvs $$ ppr givens $$ ppr inferred_sigma $$ ppr my_sigma)
1497 ; let poly_wrap = wrap
1498 <.> mkWpTyLams qtvs
1499 <.> mkWpLams givens
1500 <.> mkWpLet ev_binds
1501 ; return (mkLHsWrap poly_wrap expr', my_sigma) }
1502
1503
1504 {- Note [Partial expression signatures]
1505 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1506 Partial type signatures on expressions are easy to get wrong. But
1507 here is a guiding principile
1508 e :: ty
1509 should behave like
1510 let x :: ty
1511 x = e
1512 in x
1513
1514 So for partial signatures we apply the MR if no context is given. So
1515 e :: IO _ apply the MR
1516 e :: _ => IO _ do not apply the MR
1517 just like in TcBinds.decideGeneralisationPlan
1518
1519 This makes a difference (Trac #11670):
1520 peek :: Ptr a -> IO CLong
1521 peek ptr = peekElemOff undefined 0 :: _
1522 from (peekElemOff undefined 0) we get
1523 type: IO w
1524 constraints: Storable w
1525
1526 We must NOT try to generalise over 'w' because the signature specifies
1527 no constraints so we'll complain about not being able to solve
1528 Storable w. Instead, don't generalise; then _ gets instantiated to
1529 CLong, as it should.
1530 -}
1531
1532 {- *********************************************************************
1533 * *
1534 tcInferId
1535 * *
1536 ********************************************************************* -}
1537
1538 tcCheckId :: Name -> ExpRhoType -> TcM (HsExpr TcId)
1539 tcCheckId name res_ty
1540 = do { (expr, actual_res_ty) <- tcInferId name
1541 ; traceTc "tcCheckId" (vcat [ppr name, ppr actual_res_ty, ppr res_ty])
1542 ; addFunResCtxt False (HsVar (noLoc name)) actual_res_ty res_ty $
1543 tcWrapResultO (OccurrenceOf name) expr actual_res_ty res_ty }
1544
1545 tcCheckRecSelId :: AmbiguousFieldOcc Name -> ExpRhoType -> TcM (HsExpr TcId)
1546 tcCheckRecSelId f@(Unambiguous (L _ lbl) _) res_ty
1547 = do { (expr, actual_res_ty) <- tcInferRecSelId f
1548 ; addFunResCtxt False (HsRecFld f) actual_res_ty res_ty $
1549 tcWrapResultO (OccurrenceOfRecSel lbl) expr actual_res_ty res_ty }
1550 tcCheckRecSelId (Ambiguous lbl _) res_ty
1551 = case tcSplitFunTy_maybe =<< checkingExpType_maybe res_ty of
1552 Nothing -> ambiguousSelector lbl
1553 Just (arg, _) -> do { sel_name <- disambiguateSelector lbl arg
1554 ; tcCheckRecSelId (Unambiguous lbl sel_name) res_ty }
1555
1556 ------------------------
1557 tcInferRecSelId :: AmbiguousFieldOcc Name -> TcM (HsExpr TcId, TcRhoType)
1558 tcInferRecSelId (Unambiguous (L _ lbl) sel)
1559 = do { (expr', ty) <- tc_infer_id lbl sel
1560 ; return (expr', ty) }
1561 tcInferRecSelId (Ambiguous lbl _)
1562 = ambiguousSelector lbl
1563
1564 ------------------------
1565 tcInferId :: Name -> TcM (HsExpr TcId, TcSigmaType)
1566 -- Look up an occurrence of an Id
1567 tcInferId id_name
1568 | id_name `hasKey` tagToEnumKey
1569 = failWithTc (text "tagToEnum# must appear applied to one argument")
1570 -- tcApp catches the case (tagToEnum# arg)
1571
1572 | id_name `hasKey` assertIdKey
1573 = do { dflags <- getDynFlags
1574 ; if gopt Opt_IgnoreAsserts dflags
1575 then tc_infer_id (nameRdrName id_name) id_name
1576 else tc_infer_assert id_name }
1577
1578 | otherwise
1579 = do { (expr, ty) <- tc_infer_id (nameRdrName id_name) id_name
1580 ; traceTc "tcInferId" (ppr id_name <+> dcolon <+> ppr ty)
1581 ; return (expr, ty) }
1582
1583 tc_infer_assert :: Name -> TcM (HsExpr TcId, TcSigmaType)
1584 -- Deal with an occurrence of 'assert'
1585 -- See Note [Adding the implicit parameter to 'assert']
1586 tc_infer_assert assert_name
1587 = do { assert_error_id <- tcLookupId assertErrorName
1588 ; (wrap, id_rho) <- topInstantiate (OccurrenceOf assert_name)
1589 (idType assert_error_id)
1590 ; return (mkHsWrap wrap (HsVar (noLoc assert_error_id)), id_rho)
1591 }
1592
1593 tc_infer_id :: RdrName -> Name -> TcM (HsExpr TcId, TcSigmaType)
1594 tc_infer_id lbl id_name
1595 = do { thing <- tcLookup id_name
1596 ; case thing of
1597 ATcId { tct_id = id }
1598 -> do { check_naughty id -- Note [Local record selectors]
1599 ; checkThLocalId id
1600 ; return_id id }
1601
1602 AGlobal (AnId id)
1603 -> do { check_naughty id
1604 ; return_id id }
1605 -- A global cannot possibly be ill-staged
1606 -- nor does it need the 'lifting' treatment
1607 -- hence no checkTh stuff here
1608
1609 AGlobal (AConLike cl) -> case cl of
1610 RealDataCon con -> return_data_con con
1611 PatSynCon ps -> tcPatSynBuilderOcc ps
1612
1613 _ -> failWithTc $
1614 ppr thing <+> text "used where a value identifier was expected" }
1615 where
1616 return_id id = return (HsVar (noLoc id), idType id)
1617
1618 return_data_con con
1619 -- For data constructors, must perform the stupid-theta check
1620 | null stupid_theta
1621 = return_id con_wrapper_id
1622
1623 | otherwise
1624 -- See Note [Instantiating stupid theta]
1625 = do { let (tvs, theta, rho) = tcSplitSigmaTy (idType con_wrapper_id)
1626 ; (subst, tvs') <- newMetaTyVars tvs
1627 ; let tys' = mkTyVarTys tvs'
1628 theta' = substTheta subst theta
1629 rho' = substTy subst rho
1630 ; wrap <- instCall (OccurrenceOf id_name) tys' theta'
1631 ; addDataConStupidTheta con tys'
1632 ; return (mkHsWrap wrap (HsVar (noLoc con_wrapper_id)), rho') }
1633
1634 where
1635 con_wrapper_id = dataConWrapId con
1636 stupid_theta = dataConStupidTheta con
1637
1638 check_naughty id
1639 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel lbl)
1640 | otherwise = return ()
1641
1642
1643 tcUnboundId :: UnboundVar -> ExpRhoType -> TcM (HsExpr TcId)
1644 -- Typechedk an occurrence of an unbound Id
1645 --
1646 -- Some of these started life as a true hole "_". Others might simply
1647 -- be variables that accidentally have no binding site
1648 --
1649 -- We turn all of them into HsVar, since HsUnboundVar can't contain an
1650 -- Id; and indeed the evidence for the CHoleCan does bind it, so it's
1651 -- not unbound any more!
1652 tcUnboundId unbound res_ty
1653 = do { ty <- newFlexiTyVarTy liftedTypeKind
1654 ; let occ = unboundVarOcc unbound
1655 ; name <- newSysName occ
1656 ; let ev = mkLocalId name ty
1657 ; loc <- getCtLocM HoleOrigin Nothing
1658 ; let can = CHoleCan { cc_ev = CtWanted { ctev_pred = ty
1659 , ctev_dest = EvVarDest ev
1660 , ctev_loc = loc}
1661 , cc_hole = ExprHole unbound }
1662 ; emitInsoluble can
1663 ; tcWrapResultO (UnboundOccurrenceOf occ) (HsVar (noLoc ev)) ty res_ty }
1664
1665
1666 {-
1667 Note [Adding the implicit parameter to 'assert']
1668 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1669 The typechecker transforms (assert e1 e2) to (assertError e1 e2).
1670 This isn't really the Right Thing because there's no way to "undo"
1671 if you want to see the original source code in the typechecker
1672 output. We'll have fix this in due course, when we care more about
1673 being able to reconstruct the exact original program.
1674
1675 Note [tagToEnum#]
1676 ~~~~~~~~~~~~~~~~~
1677 Nasty check to ensure that tagToEnum# is applied to a type that is an
1678 enumeration TyCon. Unification may refine the type later, but this
1679 check won't see that, alas. It's crude, because it relies on our
1680 knowing *now* that the type is ok, which in turn relies on the
1681 eager-unification part of the type checker pushing enough information
1682 here. In theory the Right Thing to do is to have a new form of
1683 constraint but I definitely cannot face that! And it works ok as-is.
1684
1685 Here's are two cases that should fail
1686 f :: forall a. a
1687 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1688
1689 g :: Int
1690 g = tagToEnum# 0 -- Int is not an enumeration
1691
1692 When data type families are involved it's a bit more complicated.
1693 data family F a
1694 data instance F [Int] = A | B | C
1695 Then we want to generate something like
1696 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1697 Usually that coercion is hidden inside the wrappers for
1698 constructors of F [Int] but here we have to do it explicitly.
1699
1700 It's all grotesquely complicated.
1701
1702 Note [Instantiating stupid theta]
1703 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1704 Normally, when we infer the type of an Id, we don't instantiate,
1705 because we wish to allow for visible type application later on.
1706 But if a datacon has a stupid theta, we're a bit stuck. We need
1707 to emit the stupid theta constraints with instantiated types. It's
1708 difficult to defer this to the lazy instantiation, because a stupid
1709 theta has no spot to put it in a type. So we just instantiate eagerly
1710 in this case. Thus, users cannot use visible type application with
1711 a data constructor sporting a stupid theta. I won't feel so bad for
1712 the users that complain.
1713
1714 -}
1715
1716 tcSeq :: SrcSpan -> Name -> [LHsExprArgIn]
1717 -> ExpRhoType -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1718 -- (seq e1 e2) :: res_ty
1719 -- We need a special typing rule because res_ty can be unboxed
1720 -- See Note [Typing rule for seq]
1721 tcSeq loc fun_name args res_ty
1722 = do { fun <- tcLookupId fun_name
1723 ; (arg1_ty, args1) <- case args of
1724 (Right hs_ty_arg1 : args1)
1725 -> do { ty_arg1 <- tcHsTypeApp hs_ty_arg1 liftedTypeKind
1726 ; return (ty_arg1, args1) }
1727
1728 _ -> do { arg_ty1 <- newFlexiTyVarTy liftedTypeKind
1729 ; return (arg_ty1, args) }
1730
1731 ; (arg1, arg2, arg2_exp_ty) <- case args1 of
1732 [Right hs_ty_arg2, Left term_arg1, Left term_arg2]
1733 -> do { rr_ty <- newFlexiTyVarTy runtimeRepTy
1734 ; ty_arg2 <- tcHsTypeApp hs_ty_arg2 (tYPE rr_ty)
1735 -- see Note [Typing rule for seq]
1736 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg2 res_ty
1737 ; return (term_arg1, term_arg2, mkCheckExpType ty_arg2) }
1738 [Left term_arg1, Left term_arg2]
1739 -> return (term_arg1, term_arg2, res_ty)
1740 _ -> too_many_args "seq" args
1741
1742 ; arg1' <- tcMonoExpr arg1 (mkCheckExpType arg1_ty)
1743 ; arg2' <- tcMonoExpr arg2 arg2_exp_ty
1744 ; res_ty <- readExpType res_ty -- by now, it's surely filled in
1745 ; let fun' = L loc (HsWrap ty_args (HsVar (L loc fun)))
1746 ty_args = WpTyApp res_ty <.> WpTyApp arg1_ty
1747 ; return (idHsWrapper, fun', [Left arg1', Left arg2']) }
1748
1749 tcTagToEnum :: SrcSpan -> Name -> [LHsExprArgIn] -> ExpRhoType
1750 -> TcM (HsWrapper, LHsExpr TcId, [LHsExprArgOut])
1751 -- tagToEnum# :: forall a. Int# -> a
1752 -- See Note [tagToEnum#] Urgh!
1753 tcTagToEnum loc fun_name args res_ty
1754 = do { fun <- tcLookupId fun_name
1755
1756 ; arg <- case args of
1757 [Right hs_ty_arg, Left term_arg]
1758 -> do { ty_arg <- tcHsTypeApp hs_ty_arg liftedTypeKind
1759 ; _ <- tcSubTypeDS GenSigCtxt noThing ty_arg res_ty
1760 -- other than influencing res_ty, we just
1761 -- don't care about a type arg passed in.
1762 -- So drop the evidence.
1763 ; return term_arg }
1764 [Left term_arg] -> do { _ <- expTypeToType res_ty
1765 ; return term_arg }
1766 _ -> too_many_args "tagToEnum#" args
1767
1768 ; res_ty <- readExpType res_ty
1769 ; ty' <- zonkTcType res_ty
1770
1771 -- Check that the type is algebraic
1772 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1773 Just (tc, tc_args) = mb_tc_app
1774 ; checkTc (isJust mb_tc_app)
1775 (mk_error ty' doc1)
1776
1777 -- Look through any type family
1778 ; fam_envs <- tcGetFamInstEnvs
1779 ; let (rep_tc, rep_args, coi)
1780 = tcLookupDataFamInst fam_envs tc tc_args
1781 -- coi :: tc tc_args ~R rep_tc rep_args
1782
1783 ; checkTc (isEnumerationTyCon rep_tc)
1784 (mk_error ty' doc2)
1785
1786 ; arg' <- tcMonoExpr arg (mkCheckExpType intPrimTy)
1787 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar (L loc fun)))
1788 rep_ty = mkTyConApp rep_tc rep_args
1789
1790 ; return (mkWpCastR (mkTcSymCo coi), fun', [Left arg']) }
1791 -- coi is a Representational coercion
1792 where
1793 doc1 = vcat [ text "Specify the type by giving a type signature"
1794 , text "e.g. (tagToEnum# x) :: Bool" ]
1795 doc2 = text "Result type must be an enumeration type"
1796
1797 mk_error :: TcType -> SDoc -> SDoc
1798 mk_error ty what
1799 = hang (text "Bad call to tagToEnum#"
1800 <+> text "at type" <+> ppr ty)
1801 2 what
1802
1803 too_many_args :: String -> [LHsExprArgIn] -> TcM a
1804 too_many_args fun args
1805 = failWith $
1806 hang (text "Too many type arguments to" <+> text fun <> colon)
1807 2 (sep (map pp args))
1808 where
1809 pp (Left e) = pprParendLExpr e
1810 pp (Right (HsWC { hswc_body = L _ t })) = pprParendHsType t
1811
1812
1813 {-
1814 ************************************************************************
1815 * *
1816 Template Haskell checks
1817 * *
1818 ************************************************************************
1819 -}
1820
1821 checkThLocalId :: Id -> TcM ()
1822 checkThLocalId id
1823 = do { mb_local_use <- getStageAndBindLevel (idName id)
1824 ; case mb_local_use of
1825 Just (top_lvl, bind_lvl, use_stage)
1826 | thLevel use_stage > bind_lvl
1827 , isNotTopLevel top_lvl
1828 -> checkCrossStageLifting id use_stage
1829 _ -> return () -- Not a locally-bound thing, or
1830 -- no cross-stage link
1831 }
1832
1833 --------------------------------------
1834 checkCrossStageLifting :: Id -> ThStage -> TcM ()
1835 -- If we are inside typed brackets, and (use_lvl > bind_lvl)
1836 -- we must check whether there's a cross-stage lift to do
1837 -- Examples \x -> [|| x ||]
1838 -- [|| map ||]
1839 -- There is no error-checking to do, because the renamer did that
1840 --
1841 -- This is similar to checkCrossStageLifting in RnSplice, but
1842 -- this code is applied to *typed* brackets.
1843
1844 checkCrossStageLifting id (Brack _ (TcPending ps_var lie_var))
1845 = -- Nested identifiers, such as 'x' in
1846 -- E.g. \x -> [|| h x ||]
1847 -- We must behave as if the reference to x was
1848 -- h $(lift x)
1849 -- We use 'x' itself as the splice proxy, used by
1850 -- the desugarer to stitch it all back together.
1851 -- If 'x' occurs many times we may get many identical
1852 -- bindings of the same splice proxy, but that doesn't
1853 -- matter, although it's a mite untidy.
1854 do { let id_ty = idType id
1855 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1856 -- If x is polymorphic, its occurrence sites might
1857 -- have different instantiations, so we can't use plain
1858 -- 'x' as the splice proxy name. I don't know how to
1859 -- solve this, and it's probably unimportant, so I'm
1860 -- just going to flag an error for now
1861
1862 ; lift <- if isStringTy id_ty then
1863 do { sid <- tcLookupId THNames.liftStringName
1864 -- See Note [Lifting strings]
1865 ; return (HsVar (noLoc sid)) }
1866 else
1867 setConstraintVar lie_var $
1868 -- Put the 'lift' constraint into the right LIE
1869 newMethodFromName (OccurrenceOf (idName id))
1870 THNames.liftName id_ty
1871
1872 -- Update the pending splices
1873 ; ps <- readMutVar ps_var
1874 ; let pending_splice = PendingTcSplice (idName id) (nlHsApp (noLoc lift) (nlHsVar id))
1875 ; writeMutVar ps_var (pending_splice : ps)
1876
1877 ; return () }
1878
1879 checkCrossStageLifting _ _ = return ()
1880
1881 polySpliceErr :: Id -> SDoc
1882 polySpliceErr id
1883 = text "Can't splice the polymorphic local variable" <+> quotes (ppr id)
1884
1885 {-
1886 Note [Lifting strings]
1887 ~~~~~~~~~~~~~~~~~~~~~~
1888 If we see $(... [| s |] ...) where s::String, we don't want to
1889 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1890 So this conditional short-circuits the lifting mechanism to generate
1891 (liftString "xy") in that case. I didn't want to use overlapping instances
1892 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1893 errors in a polymorphic situation.
1894
1895 If this check fails (which isn't impossible) we get another chance; see
1896 Note [Converting strings] in Convert.hs
1897
1898 Local record selectors
1899 ~~~~~~~~~~~~~~~~~~~~~~
1900 Record selectors for TyCons in this module are ordinary local bindings,
1901 which show up as ATcIds rather than AGlobals. So we need to check for
1902 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1903
1904
1905 ************************************************************************
1906 * *
1907 \subsection{Record bindings}
1908 * *
1909 ************************************************************************
1910 -}
1911
1912 getFixedTyVars :: [FieldLabelString] -> [TyVar] -> [ConLike] -> TyVarSet
1913 -- These tyvars must not change across the updates
1914 getFixedTyVars upd_fld_occs univ_tvs cons
1915 = mkVarSet [tv1 | con <- cons
1916 , let (u_tvs, _, eqspec, prov_theta
1917 , req_theta, arg_tys, _)
1918 = conLikeFullSig con
1919 theta = eqSpecPreds eqspec
1920 ++ prov_theta
1921 ++ req_theta
1922 flds = conLikeFieldLabels con
1923 fixed_tvs = exactTyCoVarsOfTypes fixed_tys
1924 -- fixed_tys: See Note [Type of a record update]
1925 `unionVarSet` tyCoVarsOfTypes theta
1926 -- Universally-quantified tyvars that
1927 -- appear in any of the *implicit*
1928 -- arguments to the constructor are fixed
1929 -- See Note [Implict type sharing]
1930
1931 fixed_tys = [ty | (fl, ty) <- zip flds arg_tys
1932 , not (flLabel fl `elem` upd_fld_occs)]
1933 , (tv1,tv) <- univ_tvs `zip` u_tvs
1934 , tv `elemVarSet` fixed_tvs ]
1935
1936 {-
1937 Note [Disambiguating record fields]
1938 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1939 When the -XDuplicateRecordFields extension is used, and the renamer
1940 encounters a record selector or update that it cannot immediately
1941 disambiguate (because it involves fields that belong to multiple
1942 datatypes), it will defer resolution of the ambiguity to the
1943 typechecker. In this case, the `Ambiguous` constructor of
1944 `AmbiguousFieldOcc` is used.
1945
1946 Consider the following definitions:
1947
1948 data S = MkS { foo :: Int }
1949 data T = MkT { foo :: Int, bar :: Int }
1950 data U = MkU { bar :: Int, baz :: Int }
1951
1952 When the renamer sees `foo` as a selector or an update, it will not
1953 know which parent datatype is in use.
1954
1955 For selectors, there are two possible ways to disambiguate:
1956
1957 1. Check if the pushed-in type is a function whose domain is a
1958 datatype, for example:
1959
1960 f s = (foo :: S -> Int) s
1961
1962 g :: T -> Int
1963 g = foo
1964
1965 This is checked by `tcCheckRecSelId` when checking `HsRecFld foo`.
1966
1967 2. Check if the selector is applied to an argument that has a type
1968 signature, for example:
1969
1970 h = foo (s :: S)
1971
1972 This is checked by `tcApp`.
1973
1974
1975 Updates are slightly more complex. The `disambiguateRecordBinds`
1976 function tries to determine the parent datatype in three ways:
1977
1978 1. Check for types that have all the fields being updated. For example:
1979
1980 f x = x { foo = 3, bar = 2 }
1981
1982 Here `f` must be updating `T` because neither `S` nor `U` have
1983 both fields. This may also discover that no possible type exists.
1984 For example the following will be rejected:
1985
1986 f' x = x { foo = 3, baz = 3 }
1987
1988 2. Use the type being pushed in, if it is already a TyConApp. The
1989 following are valid updates to `T`:
1990
1991 g :: T -> T
1992 g x = x { foo = 3 }
1993
1994 g' x = x { foo = 3 } :: T
1995
1996 3. Use the type signature of the record expression, if it exists and
1997 is a TyConApp. Thus this is valid update to `T`:
1998
1999 h x = (x :: T) { foo = 3 }
2000
2001
2002 Note that we do not look up the types of variables being updated, and
2003 no constraint-solving is performed, so for example the following will
2004 be rejected as ambiguous:
2005
2006 let bad (s :: S) = foo s
2007
2008 let r :: T
2009 r = blah
2010 in r { foo = 3 }
2011
2012 \r. (r { foo = 3 }, r :: T )
2013
2014 We could add further tests, of a more heuristic nature. For example,
2015 rather than looking for an explicit signature, we could try to infer
2016 the type of the argument to a selector or the record expression being
2017 updated, in case we are lucky enough to get a TyConApp straight
2018 away. However, it might be hard for programmers to predict whether a
2019 particular update is sufficiently obvious for the signature to be
2020 omitted. Moreover, this might change the behaviour of typechecker in
2021 non-obvious ways.
2022
2023 See also Note [HsRecField and HsRecUpdField] in HsPat.
2024 -}
2025
2026 -- Given a RdrName that refers to multiple record fields, and the type
2027 -- of its argument, try to determine the name of the selector that is
2028 -- meant.
2029 disambiguateSelector :: Located RdrName -> Type -> TcM Name
2030 disambiguateSelector lr@(L _ rdr) parent_type
2031 = do { fam_inst_envs <- tcGetFamInstEnvs
2032 ; case tyConOf fam_inst_envs parent_type of
2033 Nothing -> ambiguousSelector lr
2034 Just p ->
2035 do { xs <- lookupParents rdr
2036 ; let parent = RecSelData p
2037 ; case lookup parent xs of
2038 Just gre -> do { addUsedGRE True gre
2039 ; return (gre_name gre) }
2040 Nothing -> failWithTc (fieldNotInType parent rdr) } }
2041
2042 -- This field name really is ambiguous, so add a suitable "ambiguous
2043 -- occurrence" error, then give up.
2044 ambiguousSelector :: Located RdrName -> TcM a
2045 ambiguousSelector (L _ rdr)
2046 = do { env <- getGlobalRdrEnv
2047 ; let gres = lookupGRE_RdrName rdr env
2048 ; setErrCtxt [] $ addNameClashErrRn rdr gres
2049 ; failM }
2050
2051 -- Disambiguate the fields in a record update.
2052 -- See Note [Disambiguating record fields]
2053 disambiguateRecordBinds :: LHsExpr Name -> TcRhoType
2054 -> [LHsRecUpdField Name] -> ExpRhoType
2055 -> TcM [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2056 disambiguateRecordBinds record_expr record_rho rbnds res_ty
2057 -- Are all the fields unambiguous?
2058 = case mapM isUnambiguous rbnds of
2059 -- If so, just skip to looking up the Ids
2060 -- Always the case if DuplicateRecordFields is off
2061 Just rbnds' -> mapM lookupSelector rbnds'
2062 Nothing -> -- If not, try to identify a single parent
2063 do { fam_inst_envs <- tcGetFamInstEnvs
2064 -- Look up the possible parents for each field
2065 ; rbnds_with_parents <- getUpdFieldsParents
2066 ; let possible_parents = map (map fst . snd) rbnds_with_parents
2067 -- Identify a single parent
2068 ; p <- identifyParent fam_inst_envs possible_parents
2069 -- Pick the right selector with that parent for each field
2070 ; checkNoErrs $ mapM (pickParent p) rbnds_with_parents }
2071 where
2072 -- Extract the selector name of a field update if it is unambiguous
2073 isUnambiguous :: LHsRecUpdField Name -> Maybe (LHsRecUpdField Name, Name)
2074 isUnambiguous x = case unLoc (hsRecFieldLbl (unLoc x)) of
2075 Unambiguous _ sel_name -> Just (x, sel_name)
2076 Ambiguous{} -> Nothing
2077
2078 -- Look up the possible parents and selector GREs for each field
2079 getUpdFieldsParents :: TcM [(LHsRecUpdField Name
2080 , [(RecSelParent, GlobalRdrElt)])]
2081 getUpdFieldsParents
2082 = fmap (zip rbnds) $ mapM
2083 (lookupParents . unLoc . hsRecUpdFieldRdr . unLoc)
2084 rbnds
2085
2086 -- Given a the lists of possible parents for each field,
2087 -- identify a single parent
2088 identifyParent :: FamInstEnvs -> [[RecSelParent]] -> TcM RecSelParent
2089 identifyParent fam_inst_envs possible_parents
2090 = case foldr1 intersect possible_parents of
2091 -- No parents for all fields: record update is ill-typed
2092 [] -> failWithTc (noPossibleParents rbnds)
2093
2094 -- Exactly one datatype with all the fields: use that
2095 [p] -> return p
2096
2097 -- Multiple possible parents: try harder to disambiguate
2098 -- Can we get a parent TyCon from the pushed-in type?
2099 _:_ | Just p <- tyConOfET fam_inst_envs res_ty -> return (RecSelData p)
2100
2101 -- Does the expression being updated have a type signature?
2102 -- If so, try to extract a parent TyCon from it
2103 | Just {} <- obviousSig (unLoc record_expr)
2104 , Just tc <- tyConOf fam_inst_envs record_rho
2105 -> return (RecSelData tc)
2106
2107 -- Nothing else we can try...
2108 _ -> failWithTc badOverloadedUpdate
2109
2110 -- Make a field unambiguous by choosing the given parent.
2111 -- Emits an error if the field cannot have that parent,
2112 -- e.g. if the user writes
2113 -- r { x = e } :: T
2114 -- where T does not have field x.
2115 pickParent :: RecSelParent
2116 -> (LHsRecUpdField Name, [(RecSelParent, GlobalRdrElt)])
2117 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2118 pickParent p (upd, xs)
2119 = case lookup p xs of
2120 -- Phew! The parent is valid for this field.
2121 -- Previously ambiguous fields must be marked as
2122 -- used now that we know which one is meant, but
2123 -- unambiguous ones shouldn't be recorded again
2124 -- (giving duplicate deprecation warnings).
2125 Just gre -> do { unless (null (tail xs)) $ do
2126 let L loc _ = hsRecFieldLbl (unLoc upd)
2127 setSrcSpan loc $ addUsedGRE True gre
2128 ; lookupSelector (upd, gre_name gre) }
2129 -- The field doesn't belong to this parent, so report
2130 -- an error but keep going through all the fields
2131 Nothing -> do { addErrTc (fieldNotInType p
2132 (unLoc (hsRecUpdFieldRdr (unLoc upd))))
2133 ; lookupSelector (upd, gre_name (snd (head xs))) }
2134
2135 -- Given a (field update, selector name) pair, look up the
2136 -- selector to give a field update with an unambiguous Id
2137 lookupSelector :: (LHsRecUpdField Name, Name)
2138 -> TcM (LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name))
2139 lookupSelector (L l upd, n)
2140 = do { i <- tcLookupId n
2141 ; let L loc af = hsRecFieldLbl upd
2142 lbl = rdrNameAmbiguousFieldOcc af
2143 ; return $ L l upd { hsRecFieldLbl
2144 = L loc (Unambiguous (L loc lbl) i) } }
2145
2146
2147 -- Extract the outermost TyCon of a type, if there is one; for
2148 -- data families this is the representation tycon (because that's
2149 -- where the fields live).
2150 tyConOf :: FamInstEnvs -> TcSigmaType -> Maybe TyCon
2151 tyConOf fam_inst_envs ty0
2152 = case tcSplitTyConApp_maybe ty of
2153 Just (tc, tys) -> Just (fstOf3 (tcLookupDataFamInst fam_inst_envs tc tys))
2154 Nothing -> Nothing
2155 where
2156 (_, _, ty) = tcSplitSigmaTy ty0
2157
2158 -- Variant of tyConOf that works for ExpTypes
2159 tyConOfET :: FamInstEnvs -> ExpRhoType -> Maybe TyCon
2160 tyConOfET fam_inst_envs ty0 = tyConOf fam_inst_envs =<< checkingExpType_maybe ty0
2161
2162 -- For an ambiguous record field, find all the candidate record
2163 -- selectors (as GlobalRdrElts) and their parents.
2164 lookupParents :: RdrName -> RnM [(RecSelParent, GlobalRdrElt)]
2165 lookupParents rdr
2166 = do { env <- getGlobalRdrEnv
2167 ; let gres = lookupGRE_RdrName rdr env
2168 ; mapM lookupParent gres }
2169 where
2170 lookupParent :: GlobalRdrElt -> RnM (RecSelParent, GlobalRdrElt)
2171 lookupParent gre = do { id <- tcLookupId (gre_name gre)
2172 ; if isRecordSelector id
2173 then return (recordSelectorTyCon id, gre)
2174 else failWithTc (notSelector (gre_name gre)) }
2175
2176 -- A type signature on the argument of an ambiguous record selector or
2177 -- the record expression in an update must be "obvious", i.e. the
2178 -- outermost constructor ignoring parentheses.
2179 obviousSig :: HsExpr Name -> Maybe (LHsSigWcType Name)
2180 obviousSig (ExprWithTySig _ ty) = Just ty
2181 obviousSig (HsPar p) = obviousSig (unLoc p)
2182 obviousSig _ = Nothing
2183
2184
2185 {-
2186 Game plan for record bindings
2187 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2188 1. Find the TyCon for the bindings, from the first field label.
2189
2190 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
2191
2192 For each binding field = value
2193
2194 3. Instantiate the field type (from the field label) using the type
2195 envt from step 2.
2196
2197 4 Type check the value using tcArg, passing the field type as
2198 the expected argument type.
2199
2200 This extends OK when the field types are universally quantified.
2201 -}
2202
2203 tcRecordBinds
2204 :: ConLike
2205 -> [TcType] -- Expected type for each field
2206 -> HsRecordBinds Name
2207 -> TcM (HsRecordBinds TcId)
2208
2209 tcRecordBinds con_like arg_tys (HsRecFields rbinds dd)
2210 = do { mb_binds <- mapM do_bind rbinds
2211 ; return (HsRecFields (catMaybes mb_binds) dd) }
2212 where
2213 fields = map flLabel $ conLikeFieldLabels con_like
2214 flds_w_tys = zipEqual "tcRecordBinds" fields arg_tys
2215
2216 do_bind :: LHsRecField Name (LHsExpr Name)
2217 -> TcM (Maybe (LHsRecField TcId (LHsExpr TcId)))
2218 do_bind (L l fld@(HsRecField { hsRecFieldLbl = f
2219 , hsRecFieldArg = rhs }))
2220
2221 = do { mb <- tcRecordField con_like flds_w_tys f rhs
2222 ; case mb of
2223 Nothing -> return Nothing
2224 Just (f', rhs') -> return (Just (L l (fld { hsRecFieldLbl = f'
2225 , hsRecFieldArg = rhs' }))) }
2226
2227 tcRecordUpd
2228 :: ConLike
2229 -> [TcType] -- Expected type for each field
2230 -> [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)]
2231 -> TcM [LHsRecUpdField TcId]
2232
2233 tcRecordUpd con_like arg_tys rbinds = fmap catMaybes $ mapM do_bind rbinds
2234 where
2235 flds_w_tys = zipEqual "tcRecordUpd" (map flLabel $ conLikeFieldLabels con_like) arg_tys
2236
2237 do_bind :: LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name) -> TcM (Maybe (LHsRecUpdField TcId))
2238 do_bind (L l fld@(HsRecField { hsRecFieldLbl = L loc af
2239 , hsRecFieldArg = rhs }))
2240 = do { let lbl = rdrNameAmbiguousFieldOcc af
2241 sel_id = selectorAmbiguousFieldOcc af
2242 f = L loc (FieldOcc (L loc lbl) (idName sel_id))
2243 ; mb <- tcRecordField con_like flds_w_tys f rhs
2244 ; case mb of
2245 Nothing -> return Nothing
2246 Just (f', rhs') ->
2247 return (Just
2248 (L l (fld { hsRecFieldLbl
2249 = L loc (Unambiguous (L loc lbl)
2250 (selectorFieldOcc (unLoc f')))
2251 , hsRecFieldArg = rhs' }))) }
2252
2253 tcRecordField :: ConLike -> Assoc FieldLabelString Type -> LFieldOcc Name -> LHsExpr Name
2254 -> TcM (Maybe (LFieldOcc Id, LHsExpr Id))
2255 tcRecordField con_like flds_w_tys (L loc (FieldOcc lbl sel_name)) rhs
2256 | Just field_ty <- assocMaybe flds_w_tys field_lbl
2257 = addErrCtxt (fieldCtxt field_lbl) $
2258 do { rhs' <- tcPolyExprNC rhs field_ty
2259 ; let field_id = mkUserLocal (nameOccName sel_name)
2260 (nameUnique sel_name)
2261 field_ty loc
2262 -- Yuk: the field_id has the *unique* of the selector Id
2263 -- (so we can find it easily)
2264 -- but is a LocalId with the appropriate type of the RHS
2265 -- (so the desugarer knows the type of local binder to make)
2266 ; return (Just (L loc (FieldOcc lbl field_id), rhs')) }
2267 | otherwise
2268 = do { addErrTc (badFieldCon con_like field_lbl)
2269 ; return Nothing }
2270 where
2271 field_lbl = occNameFS $ rdrNameOcc (unLoc lbl)
2272
2273
2274 checkMissingFields :: ConLike -> HsRecordBinds Name -> TcM ()
2275 checkMissingFields con_like rbinds
2276 | null field_labels -- Not declared as a record;
2277 -- But C{} is still valid if no strict fields
2278 = if any isBanged field_strs then
2279 -- Illegal if any arg is strict
2280 addErrTc (missingStrictFields con_like [])
2281 else
2282 return ()
2283
2284 | otherwise = do -- A record
2285 unless (null missing_s_fields)
2286 (addErrTc (missingStrictFields con_like missing_s_fields))
2287
2288 warn <- woptM Opt_WarnMissingFields
2289 unless (not (warn && notNull missing_ns_fields))
2290 (warnTc (Reason Opt_WarnMissingFields) True
2291 (missingFields con_like missing_ns_fields))
2292
2293 where
2294 missing_s_fields
2295 = [ flLabel fl | (fl, str) <- field_info,
2296 isBanged str,
2297 not (fl `elemField` field_names_used)
2298 ]
2299 missing_ns_fields
2300 = [ flLabel fl | (fl, str) <- field_info,
2301 not (isBanged str),
2302 not (fl `elemField` field_names_used)
2303 ]
2304
2305 field_names_used = hsRecFields rbinds
2306 field_labels = conLikeFieldLabels con_like
2307
2308 field_info = zipEqual "missingFields"
2309 field_labels
2310 field_strs
2311
2312 field_strs = conLikeImplBangs con_like
2313
2314 fl `elemField` flds = any (\ fl' -> flSelector fl == fl') flds
2315
2316 {-
2317 ************************************************************************
2318 * *
2319 \subsection{Errors and contexts}
2320 * *
2321 ************************************************************************
2322
2323 Boring and alphabetical:
2324 -}
2325
2326 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
2327 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
2328
2329 exprCtxt :: LHsExpr Name -> SDoc
2330 exprCtxt expr
2331 = hang (text "In the expression:") 2 (ppr expr)
2332
2333 fieldCtxt :: FieldLabelString -> SDoc
2334 fieldCtxt field_name
2335 = text "In the" <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
2336
2337 addFunResCtxt :: Bool -- There is at least one argument
2338 -> HsExpr Name -> TcType -> ExpRhoType
2339 -> TcM a -> TcM a
2340 -- When we have a mis-match in the return type of a function
2341 -- try to give a helpful message about too many/few arguments
2342 --
2343 -- Used for naked variables too; but with has_args = False
2344 addFunResCtxt has_args fun fun_res_ty env_ty
2345 = addLandmarkErrCtxtM (\env -> (env, ) <$> mk_msg)
2346 -- NB: use a landmark error context, so that an empty context
2347 -- doesn't suppress some more useful context
2348 where
2349 mk_msg
2350 = do { mb_env_ty <- readExpType_maybe env_ty
2351 -- by the time the message is rendered, the ExpType
2352 -- will be filled in (except if we're debugging)
2353 ; fun_res' <- zonkTcType fun_res_ty
2354 ; env' <- case mb_env_ty of
2355 Just env_ty -> zonkTcType env_ty
2356 Nothing ->
2357 do { dumping <- doptM Opt_D_dump_tc_trace
2358 ; MASSERT( dumping )
2359 ; newFlexiTyVarTy liftedTypeKind }
2360 ; let (_, _, fun_tau) = tcSplitSigmaTy fun_res'
2361 (_, _, env_tau) = tcSplitSigmaTy env'
2362 (args_fun, res_fun) = tcSplitFunTys fun_tau
2363 (args_env, res_env) = tcSplitFunTys env_tau
2364 n_fun = length args_fun
2365 n_env = length args_env
2366 info | n_fun == n_env = Outputable.empty
2367 | n_fun > n_env
2368 , not_fun res_env
2369 = text "Probable cause:" <+> quotes (ppr fun)
2370 <+> text "is applied to too few arguments"
2371
2372 | has_args
2373 , not_fun res_fun
2374 = text "Possible cause:" <+> quotes (ppr fun)
2375 <+> text "is applied to too many arguments"
2376
2377 | otherwise
2378 = Outputable.empty -- Never suggest that a naked variable is -- applied to too many args!
2379 ; return info }
2380 where
2381 not_fun ty -- ty is definitely not an arrow type,
2382 -- and cannot conceivably become one
2383 = case tcSplitTyConApp_maybe ty of
2384 Just (tc, _) -> isAlgTyCon tc
2385 Nothing -> False
2386
2387 badFieldTypes :: [(FieldLabelString,TcType)] -> SDoc
2388 badFieldTypes prs
2389 = hang (text "Record update for insufficiently polymorphic field"
2390 <> plural prs <> colon)
2391 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
2392
2393 badFieldsUpd
2394 :: [LHsRecField' (AmbiguousFieldOcc Id) (LHsExpr Name)] -- Field names that don't belong to a single datacon
2395 -> [ConLike] -- Data cons of the type which the first field name belongs to
2396 -> SDoc
2397 badFieldsUpd rbinds data_cons
2398 = hang (text "No constructor has all these fields:")
2399 2 (pprQuotedList conflictingFields)
2400 -- See Note [Finding the conflicting fields]
2401 where
2402 -- A (preferably small) set of fields such that no constructor contains
2403 -- all of them. See Note [Finding the conflicting fields]
2404 conflictingFields = case nonMembers of
2405 -- nonMember belongs to a different type.
2406 (nonMember, _) : _ -> [aMember, nonMember]
2407 [] -> let
2408 -- All of rbinds belong to one type. In this case, repeatedly add
2409 -- a field to the set until no constructor contains the set.
2410
2411 -- Each field, together with a list indicating which constructors
2412 -- have all the fields so far.
2413 growingSets :: [(FieldLabelString, [Bool])]
2414 growingSets = scanl1 combine membership
2415 combine (_, setMem) (field, fldMem)
2416 = (field, zipWith (&&) setMem fldMem)
2417 in
2418 -- Fields that don't change the membership status of the set
2419 -- are redundant and can be dropped.
2420 map (fst . head) $ groupBy ((==) `on` snd) growingSets
2421
2422 aMember = ASSERT( not (null members) ) fst (head members)
2423 (members, nonMembers) = partition (or . snd) membership
2424
2425 -- For each field, which constructors contain the field?
2426 membership :: [(FieldLabelString, [Bool])]
2427 membership = sortMembership $
2428 map (\fld -> (fld, map (Set.member fld) fieldLabelSets)) $
2429 map (occNameFS . rdrNameOcc . rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) rbinds
2430
2431 fieldLabelSets :: [Set.Set FieldLabelString]
2432 fieldLabelSets = map (Set.fromList . map flLabel . conLikeFieldLabels) data_cons
2433
2434 -- Sort in order of increasing number of True, so that a smaller
2435 -- conflicting set can be found.
2436 sortMembership =
2437 map snd .
2438 sortBy (compare `on` fst) .
2439 map (\ item@(_, membershipRow) -> (countTrue membershipRow, item))
2440
2441 countTrue = length . filter id
2442
2443 {-
2444 Note [Finding the conflicting fields]
2445 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2446 Suppose we have
2447 data A = A {a0, a1 :: Int}
2448 | B {b0, b1 :: Int}
2449 and we see a record update
2450 x { a0 = 3, a1 = 2, b0 = 4, b1 = 5 }
2451 Then we'd like to find the smallest subset of fields that no
2452 constructor has all of. Here, say, {a0,b0}, or {a0,b1}, etc.
2453 We don't really want to report that no constructor has all of
2454 {a0,a1,b0,b1}, because when there are hundreds of fields it's
2455 hard to see what was really wrong.
2456
2457 We may need more than two fields, though; eg
2458 data T = A { x,y :: Int, v::Int }
2459 | B { y,z :: Int, v::Int }
2460 | C { z,x :: Int, v::Int }
2461 with update
2462 r { x=e1, y=e2, z=e3 }, we
2463
2464 Finding the smallest subset is hard, so the code here makes
2465 a decent stab, no more. See Trac #7989.
2466 -}
2467
2468 naughtyRecordSel :: RdrName -> SDoc
2469 naughtyRecordSel sel_id
2470 = text "Cannot use record selector" <+> quotes (ppr sel_id) <+>
2471 text "as a function due to escaped type variables" $$
2472 text "Probable fix: use pattern-matching syntax instead"
2473
2474 notSelector :: Name -> SDoc
2475 notSelector field
2476 = hsep [quotes (ppr field), text "is not a record selector"]
2477
2478 mixedSelectors :: [Id] -> [Id] -> SDoc
2479 mixedSelectors data_sels@(dc_rep_id:_) pat_syn_sels@(ps_rep_id:_)
2480 = ptext
2481 (sLit "Cannot use a mixture of pattern synonym and record selectors") $$
2482 text "Record selectors defined by"
2483 <+> quotes (ppr (tyConName rep_dc))
2484 <> text ":"
2485 <+> pprWithCommas ppr data_sels $$
2486 text "Pattern synonym selectors defined by"
2487 <+> quotes (ppr (patSynName rep_ps))
2488 <> text ":"
2489 <+> pprWithCommas ppr pat_syn_sels
2490 where
2491 RecSelPatSyn rep_ps = recordSelectorTyCon ps_rep_id
2492 RecSelData rep_dc = recordSelectorTyCon dc_rep_id
2493 mixedSelectors _ _ = panic "TcExpr: mixedSelectors emptylists"
2494
2495
2496 missingStrictFields :: ConLike -> [FieldLabelString] -> SDoc
2497 missingStrictFields con fields
2498 = header <> rest
2499 where
2500 rest | null fields = Outputable.empty -- Happens for non-record constructors
2501 -- with strict fields
2502 | otherwise = colon <+> pprWithCommas ppr fields
2503
2504 header = text "Constructor" <+> quotes (ppr con) <+>
2505 text "does not have the required strict field(s)"
2506
2507 missingFields :: ConLike -> [FieldLabelString] -> SDoc
2508 missingFields con fields
2509 = text "Fields of" <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
2510 <+> pprWithCommas ppr fields
2511
2512 -- callCtxt fun args = text "In the call" <+> parens (ppr (foldl mkHsApp fun args))
2513
2514 noPossibleParents :: [LHsRecUpdField Name] -> SDoc
2515 noPossibleParents rbinds
2516 = hang (text "No type has all these fields:")
2517 2 (pprQuotedList fields)
2518 where
2519 fields = map (hsRecFieldLbl . unLoc) rbinds
2520
2521 badOverloadedUpdate :: SDoc
2522 badOverloadedUpdate = text "Record update is ambiguous, and requires a type signature"
2523
2524 fieldNotInType :: RecSelParent -> RdrName -> SDoc
2525 fieldNotInType p rdr
2526 = unknownSubordinateErr (text "field of type" <+> quotes (ppr p)) rdr
2527
2528 {-
2529 ************************************************************************
2530 * *
2531 \subsection{Static Pointers}
2532 * *
2533 ************************************************************************
2534 -}
2535
2536 -- | A data type to describe why a variable is not closed.
2537 data NotClosedReason = NotLetBoundReason
2538 | NotTypeClosed VarSet
2539 | NotClosed Name NotClosedReason
2540
2541 -- | Checks if the given name is closed and emits an error if not.
2542 --
2543 -- See Note [Not-closed error messages].
2544 checkClosedInStaticForm :: Name -> TcM ()
2545 checkClosedInStaticForm name = do
2546 type_env <- getLclTypeEnv
2547 case checkClosed type_env name of
2548 Nothing -> return ()
2549 Just reason -> addErrTc $ explain name reason
2550 where
2551 -- See Note [Checking closedness].
2552 checkClosed :: TcTypeEnv -> Name -> Maybe NotClosedReason
2553 checkClosed type_env n = checkLoop type_env (unitNameSet n) n
2554
2555 checkLoop :: TcTypeEnv -> NameSet -> Name -> Maybe NotClosedReason
2556 checkLoop type_env visited n = do
2557 -- The @visited@ set is an accumulating parameter that contains the set of
2558 -- visited nodes, so we avoid repeating cycles in the traversal.
2559 case lookupNameEnv type_env n of
2560 Just (ATcId { tct_id = tcid, tct_info = info }) -> case info of
2561 ClosedLet -> Nothing
2562 NotLetBound -> Just NotLetBoundReason
2563 NonClosedLet fvs type_closed -> listToMaybe $
2564 -- Look for a non-closed variable in fvs
2565 [ NotClosed n' reason
2566 | n' <- nameSetElemsStable fvs
2567 , not (elemNameSet n' visited)
2568 , Just reason <- [checkLoop type_env (extendNameSet visited n') n']
2569 ] ++
2570 if type_closed then
2571 []
2572 else
2573 -- We consider non-let-bound variables easier to figure out than
2574 -- non-closed types, so we report non-closed types to the user
2575 -- only if we cannot spot the former.
2576 [ NotTypeClosed $ tyCoVarsOfType (idType tcid) ]
2577 -- The binding is closed.
2578 _ -> Nothing
2579
2580 -- Converts a reason into a human-readable sentence.
2581 --
2582 -- @explain name reason@ starts with
2583 --
2584 -- "<name> is used in a static form but it is not closed because it"
2585 --
2586 -- and then follows a list of causes. For each id in the path, the text
2587 --
2588 -- "uses <id> which"
2589 --
2590 -- is appended, yielding something like
2591 --
2592 -- "uses <id> which uses <id1> which uses <id2> which"
2593 --
2594 -- until the end of the path is reached, which is reported as either
2595 --
2596 -- "is not let-bound"
2597 --
2598 -- when the final node is not let-bound, or
2599 --
2600 -- "has a non-closed type because it contains the type variables:
2601 -- v1, v2, v3"
2602 --
2603 -- when the final node has a non-closed type.
2604 --
2605 explain :: Name -> NotClosedReason -> SDoc
2606 explain name reason =
2607 quotes (ppr name) <+> text "is used in a static form but it is not closed"
2608 <+> text "because it"
2609 $$
2610 sep (causes reason)
2611
2612 causes :: NotClosedReason -> [SDoc]
2613 causes NotLetBoundReason = [text "is not let-bound."]
2614 causes (NotTypeClosed vs) =
2615 [ text "has a non-closed type because it contains the"
2616 , text "type variables:" <+>
2617 pprVarSet vs (hsep . punctuate comma . map (quotes . ppr))
2618 ]
2619 causes (NotClosed n reason) =
2620 let msg = text "uses" <+> quotes (ppr n) <+> text "which"
2621 in case reason of
2622 NotClosed _ _ -> msg : causes reason
2623 _ -> let (xs0, xs1) = splitAt 1 $ causes reason
2624 in fmap (msg <+>) xs0 ++ xs1
2625
2626 -- Note [Not-closed error messages]
2627 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2628 --
2629 -- When variables in a static form are not closed, we go through the trouble
2630 -- of explaining why they aren't.
2631 --
2632 -- Thus, the following program
2633 --
2634 -- > {-# LANGUAGE StaticPointers #-}
2635 -- > module M where
2636 -- >
2637 -- > f x = static g
2638 -- > where
2639 -- > g = h
2640 -- > h = x
2641 --
2642 -- produces the error
2643 --
2644 -- 'g' is used in a static form but it is not closed because it
2645 -- uses 'h' which uses 'x' which is not let-bound.
2646 --
2647 -- And a program like
2648 --
2649 -- > {-# LANGUAGE StaticPointers #-}
2650 -- > module M where
2651 -- >
2652 -- > import Data.Typeable
2653 -- > import GHC.StaticPtr
2654 -- >
2655 -- > f :: Typeable a => a -> StaticPtr TypeRep
2656 -- > f x = const (static (g undefined)) (h x)
2657 -- > where
2658 -- > g = h
2659 -- > h = typeOf
2660 --
2661 -- produces the error
2662 --
2663 -- 'g' is used in a static form but it is not closed because it
2664 -- uses 'h' which has a non-closed type because it contains the
2665 -- type variables: 'a'
2666 --
2667
2668 -- Note [Checking closedness]
2669 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~
2670 --
2671 -- @checkClosed@ checks if a binding is closed and returns a reason if it is
2672 -- not.
2673 --
2674 -- The bindings define a graph where the nodes are ids, and there is an edge
2675 -- from @id1@ to @id2@ if the rhs of @id1@ contains @id2@ among its free
2676 -- variables.
2677 --
2678 -- When @n@ is not closed, it has to exist in the graph some node reachable
2679 -- from @n@ that it is not a let-bound variable or that it has a non-closed
2680 -- type. Thus, the "reason" is a path from @n@ to this offending node.
2681 --
2682 -- When @n@ is not closed, we traverse the graph reachable from @n@ to build
2683 -- the reason.
2684 --