Make a smart mkAppTyM
[ghc.git] / compiler / typecheck / Inst.hs
1 {-
2 (c) The University of Glasgow 2006
3 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4
5
6 The @Inst@ type: dictionaries or method instances
7 -}
8
9 {-# LANGUAGE CPP, MultiWayIf, TupleSections #-}
10 {-# LANGUAGE FlexibleContexts #-}
11
12 module Inst (
13 deeplySkolemise,
14 topInstantiate, topInstantiateInferred, deeplyInstantiate,
15 instCall, instDFunType, instStupidTheta, instTyVarsWith,
16 newWanted, newWanteds,
17
18 tcInstInvisibleTyBinders, tcInstInvisibleTyBinder,
19
20 newOverloadedLit, mkOverLit,
21
22 newClsInst,
23 tcGetInsts, tcGetInstEnvs, getOverlapFlag,
24 tcExtendLocalInstEnv,
25 instCallConstraints, newMethodFromName,
26 tcSyntaxName,
27
28 -- Simple functions over evidence variables
29 tyCoVarsOfWC,
30 tyCoVarsOfCt, tyCoVarsOfCts,
31 ) where
32
33 #include "HsVersions.h"
34
35 import GhcPrelude
36
37 import {-# SOURCE #-} TcExpr( tcPolyExpr, tcSyntaxOp )
38 import {-# SOURCE #-} TcUnify( unifyType, unifyKind )
39
40 import BasicTypes ( IntegralLit(..), SourceText(..) )
41 import FastString
42 import HsSyn
43 import TcHsSyn
44 import TcRnMonad
45 import TcEnv
46 import TcEvidence
47 import InstEnv
48 import TysWiredIn ( heqDataCon, eqDataCon )
49 import CoreSyn ( isOrphan )
50 import FunDeps
51 import TcMType
52 import Type
53 import TyCoRep
54 import TcType
55 import HscTypes
56 import Class( Class )
57 import MkId( mkDictFunId )
58 import CoreSyn( Expr(..) ) -- For the Coercion constructor
59 import Id
60 import Name
61 import Var ( EvVar, mkTyVar, tyVarName, VarBndr(..) )
62 import DataCon
63 import VarEnv
64 import PrelNames
65 import SrcLoc
66 import DynFlags
67 import Util
68 import Outputable
69 import qualified GHC.LanguageExtensions as LangExt
70
71 import Control.Monad( unless )
72
73 {-
74 ************************************************************************
75 * *
76 Creating and emittind constraints
77 * *
78 ************************************************************************
79 -}
80
81 newMethodFromName :: CtOrigin -> Name -> TcRhoType -> TcM (HsExpr GhcTcId)
82 -- Used when Name is the wired-in name for a wired-in class method,
83 -- so the caller knows its type for sure, which should be of form
84 -- forall a. C a => <blah>
85 -- newMethodFromName is supposed to instantiate just the outer
86 -- type variable and constraint
87
88 newMethodFromName origin name inst_ty
89 = do { id <- tcLookupId name
90 -- Use tcLookupId not tcLookupGlobalId; the method is almost
91 -- always a class op, but with -XRebindableSyntax GHC is
92 -- meant to find whatever thing is in scope, and that may
93 -- be an ordinary function.
94
95 ; let ty = piResultTy (idType id) inst_ty
96 (theta, _caller_knows_this) = tcSplitPhiTy ty
97 ; wrap <- ASSERT( not (isForAllTy ty) && isSingleton theta )
98 instCall origin [inst_ty] theta
99
100 ; return (mkHsWrap wrap (HsVar noExt (noLoc id))) }
101
102 {-
103 ************************************************************************
104 * *
105 Deep instantiation and skolemisation
106 * *
107 ************************************************************************
108
109 Note [Deep skolemisation]
110 ~~~~~~~~~~~~~~~~~~~~~~~~~
111 deeplySkolemise decomposes and skolemises a type, returning a type
112 with all its arrows visible (ie not buried under foralls)
113
114 Examples:
115
116 deeplySkolemise (Int -> forall a. Ord a => blah)
117 = ( wp, [a], [d:Ord a], Int -> blah )
118 where wp = \x:Int. /\a. \(d:Ord a). <hole> x
119
120 deeplySkolemise (forall a. Ord a => Maybe a -> forall b. Eq b => blah)
121 = ( wp, [a,b], [d1:Ord a,d2:Eq b], Maybe a -> blah )
122 where wp = /\a.\(d1:Ord a).\(x:Maybe a)./\b.\(d2:Ord b). <hole> x
123
124 In general,
125 if deeplySkolemise ty = (wrap, tvs, evs, rho)
126 and e :: rho
127 then wrap e :: ty
128 and 'wrap' binds tvs, evs
129
130 ToDo: this eta-abstraction plays fast and loose with termination,
131 because it can introduce extra lambdas. Maybe add a `seq` to
132 fix this
133 -}
134
135 deeplySkolemise :: TcSigmaType
136 -> TcM ( HsWrapper
137 , [(Name,TyVar)] -- All skolemised variables
138 , [EvVar] -- All "given"s
139 , TcRhoType )
140
141 deeplySkolemise ty
142 = go init_subst ty
143 where
144 init_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ty))
145
146 go subst ty
147 | Just (arg_tys, tvs, theta, ty') <- tcDeepSplitSigmaTy_maybe ty
148 = do { let arg_tys' = substTys subst arg_tys
149 ; ids1 <- newSysLocalIds (fsLit "dk") arg_tys'
150 ; (subst', tvs1) <- tcInstSkolTyVarsX subst tvs
151 ; ev_vars1 <- newEvVars (substTheta subst' theta)
152 ; (wrap, tvs_prs2, ev_vars2, rho) <- go subst' ty'
153 ; let tv_prs1 = map tyVarName tvs `zip` tvs1
154 ; return ( mkWpLams ids1
155 <.> mkWpTyLams tvs1
156 <.> mkWpLams ev_vars1
157 <.> wrap
158 <.> mkWpEvVarApps ids1
159 , tv_prs1 ++ tvs_prs2
160 , ev_vars1 ++ ev_vars2
161 , mkFunTys arg_tys' rho ) }
162
163 | otherwise
164 = return (idHsWrapper, [], [], substTy subst ty)
165 -- substTy is a quick no-op on an empty substitution
166
167 -- | Instantiate all outer type variables
168 -- and any context. Never looks through arrows.
169 topInstantiate :: CtOrigin -> TcSigmaType -> TcM (HsWrapper, TcRhoType)
170 -- if topInstantiate ty = (wrap, rho)
171 -- and e :: ty
172 -- then wrap e :: rho (that is, wrap :: ty "->" rho)
173 topInstantiate = top_instantiate True
174
175 -- | Instantiate all outer 'Inferred' binders
176 -- and any context. Never looks through arrows or specified type variables.
177 -- Used for visible type application.
178 topInstantiateInferred :: CtOrigin -> TcSigmaType
179 -> TcM (HsWrapper, TcSigmaType)
180 -- if topInstantiate ty = (wrap, rho)
181 -- and e :: ty
182 -- then wrap e :: rho
183 topInstantiateInferred = top_instantiate False
184
185 top_instantiate :: Bool -- True <=> instantiate *all* variables
186 -- False <=> instantiate only the inferred ones
187 -> CtOrigin -> TcSigmaType -> TcM (HsWrapper, TcRhoType)
188 top_instantiate inst_all orig ty
189 | not (null binders && null theta)
190 = do { let (inst_bndrs, leave_bndrs) = span should_inst binders
191 (inst_theta, leave_theta)
192 | null leave_bndrs = (theta, [])
193 | otherwise = ([], theta)
194 in_scope = mkInScopeSet (tyCoVarsOfType ty)
195 empty_subst = mkEmptyTCvSubst in_scope
196 inst_tvs = binderVars inst_bndrs
197 ; (subst, inst_tvs') <- mapAccumLM newMetaTyVarX empty_subst inst_tvs
198 ; let inst_theta' = substTheta subst inst_theta
199 sigma' = substTy subst (mkForAllTys leave_bndrs $
200 mkFunTys leave_theta rho)
201 inst_tv_tys' = mkTyVarTys inst_tvs'
202
203 ; wrap1 <- instCall orig inst_tv_tys' inst_theta'
204 ; traceTc "Instantiating"
205 (vcat [ text "all tyvars?" <+> ppr inst_all
206 , text "origin" <+> pprCtOrigin orig
207 , text "type" <+> debugPprType ty
208 , text "theta" <+> ppr theta
209 , text "leave_bndrs" <+> ppr leave_bndrs
210 , text "with" <+> vcat (map debugPprType inst_tv_tys')
211 , text "theta:" <+> ppr inst_theta' ])
212
213 ; (wrap2, rho2) <-
214 if null leave_bndrs
215
216 -- account for types like forall a. Num a => forall b. Ord b => ...
217 then top_instantiate inst_all orig sigma'
218
219 -- but don't loop if there were any un-inst'able tyvars
220 else return (idHsWrapper, sigma')
221
222 ; return (wrap2 <.> wrap1, rho2) }
223
224 | otherwise = return (idHsWrapper, ty)
225 where
226 (binders, phi) = tcSplitForAllVarBndrs ty
227 (theta, rho) = tcSplitPhiTy phi
228
229 should_inst bndr
230 | inst_all = True
231 | otherwise = binderArgFlag bndr == Inferred
232
233 deeplyInstantiate :: CtOrigin -> TcSigmaType -> TcM (HsWrapper, TcRhoType)
234 -- Int -> forall a. a -> a ==> (\x:Int. [] x alpha) :: Int -> alpha
235 -- In general if
236 -- if deeplyInstantiate ty = (wrap, rho)
237 -- and e :: ty
238 -- then wrap e :: rho
239 -- That is, wrap :: ty ~> rho
240 --
241 -- If you don't need the HsWrapper returned from this function, consider
242 -- using tcSplitNestedSigmaTys in TcType, which is a pure alternative that
243 -- only computes the returned TcRhoType.
244
245 deeplyInstantiate orig ty =
246 deeply_instantiate orig
247 (mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ty)))
248 ty
249
250 deeply_instantiate :: CtOrigin
251 -> TCvSubst
252 -> TcSigmaType -> TcM (HsWrapper, TcRhoType)
253 -- Internal function to deeply instantiate that builds on an existing subst.
254 -- It extends the input substitution and applies the final subtitution to
255 -- the types on return. See #12549.
256
257 deeply_instantiate orig subst ty
258 | Just (arg_tys, tvs, theta, rho) <- tcDeepSplitSigmaTy_maybe ty
259 = do { (subst', tvs') <- newMetaTyVarsX subst tvs
260 ; let arg_tys' = substTys subst' arg_tys
261 theta' = substTheta subst' theta
262 ; ids1 <- newSysLocalIds (fsLit "di") arg_tys'
263 ; wrap1 <- instCall orig (mkTyVarTys tvs') theta'
264 ; traceTc "Instantiating (deeply)" (vcat [ text "origin" <+> pprCtOrigin orig
265 , text "type" <+> ppr ty
266 , text "with" <+> ppr tvs'
267 , text "args:" <+> ppr ids1
268 , text "theta:" <+> ppr theta'
269 , text "subst:" <+> ppr subst'])
270 ; (wrap2, rho2) <- deeply_instantiate orig subst' rho
271 ; return (mkWpLams ids1
272 <.> wrap2
273 <.> wrap1
274 <.> mkWpEvVarApps ids1,
275 mkFunTys arg_tys' rho2) }
276
277 | otherwise
278 = do { let ty' = substTy subst ty
279 ; traceTc "deeply_instantiate final subst"
280 (vcat [ text "origin:" <+> pprCtOrigin orig
281 , text "type:" <+> ppr ty
282 , text "new type:" <+> ppr ty'
283 , text "subst:" <+> ppr subst ])
284 ; return (idHsWrapper, ty') }
285
286
287 instTyVarsWith :: CtOrigin -> [TyVar] -> [TcType] -> TcM TCvSubst
288 -- Use this when you want to instantiate (forall a b c. ty) with
289 -- types [ta, tb, tc], but when the kinds of 'a' and 'ta' might
290 -- not yet match (perhaps because there are unsolved constraints; Trac #14154)
291 -- If they don't match, emit a kind-equality to promise that they will
292 -- eventually do so, and thus make a kind-homongeneous substitution.
293 instTyVarsWith orig tvs tys
294 = go empty_subst tvs tys
295 where
296 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfTypes tys))
297
298 go subst [] []
299 = return subst
300 go subst (tv:tvs) (ty:tys)
301 | tv_kind `tcEqType` ty_kind
302 = go (extendTCvSubst subst tv ty) tvs tys
303 | otherwise
304 = do { co <- emitWantedEq orig KindLevel Nominal ty_kind tv_kind
305 ; go (extendTCvSubst subst tv (ty `mkCastTy` co)) tvs tys }
306 where
307 tv_kind = substTy subst (tyVarKind tv)
308 ty_kind = tcTypeKind ty
309
310 go _ _ _ = pprPanic "instTysWith" (ppr tvs $$ ppr tys)
311
312 {-
313 ************************************************************************
314 * *
315 Instantiating a call
316 * *
317 ************************************************************************
318
319 Note [Handling boxed equality]
320 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
321 The solver deals entirely in terms of unboxed (primitive) equality.
322 There should never be a boxed Wanted equality. Ever. But, what if
323 we are calling `foo :: forall a. (F a ~ Bool) => ...`? That equality
324 is boxed, so naive treatment here would emit a boxed Wanted equality.
325
326 So we simply check for this case and make the right boxing of evidence.
327
328 -}
329
330 ----------------
331 instCall :: CtOrigin -> [TcType] -> TcThetaType -> TcM HsWrapper
332 -- Instantiate the constraints of a call
333 -- (instCall o tys theta)
334 -- (a) Makes fresh dictionaries as necessary for the constraints (theta)
335 -- (b) Throws these dictionaries into the LIE
336 -- (c) Returns an HsWrapper ([.] tys dicts)
337
338 instCall orig tys theta
339 = do { dict_app <- instCallConstraints orig theta
340 ; return (dict_app <.> mkWpTyApps tys) }
341
342 ----------------
343 instCallConstraints :: CtOrigin -> TcThetaType -> TcM HsWrapper
344 -- Instantiates the TcTheta, puts all constraints thereby generated
345 -- into the LIE, and returns a HsWrapper to enclose the call site.
346
347 instCallConstraints orig preds
348 | null preds
349 = return idHsWrapper
350 | otherwise
351 = do { evs <- mapM go preds
352 ; traceTc "instCallConstraints" (ppr evs)
353 ; return (mkWpEvApps evs) }
354 where
355 go :: TcPredType -> TcM EvTerm
356 go pred
357 | Just (Nominal, ty1, ty2) <- getEqPredTys_maybe pred -- Try short-cut #1
358 = do { co <- unifyType Nothing ty1 ty2
359 ; return (evCoercion co) }
360
361 -- Try short-cut #2
362 | Just (tc, args@[_, _, ty1, ty2]) <- splitTyConApp_maybe pred
363 , tc `hasKey` heqTyConKey
364 = do { co <- unifyType Nothing ty1 ty2
365 ; return (evDFunApp (dataConWrapId heqDataCon) args [Coercion co]) }
366
367 | otherwise
368 = emitWanted orig pred
369
370 instDFunType :: DFunId -> [DFunInstType]
371 -> TcM ( [TcType] -- instantiated argument types
372 , TcThetaType ) -- instantiated constraint
373 -- See Note [DFunInstType: instantiating types] in InstEnv
374 instDFunType dfun_id dfun_inst_tys
375 = do { (subst, inst_tys) <- go empty_subst dfun_tvs dfun_inst_tys
376 ; return (inst_tys, substTheta subst dfun_theta) }
377 where
378 dfun_ty = idType dfun_id
379 (dfun_tvs, dfun_theta, _) = tcSplitSigmaTy dfun_ty
380 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType dfun_ty))
381 -- With quantified constraints, the
382 -- type of a dfun may not be closed
383
384 go :: TCvSubst -> [TyVar] -> [DFunInstType] -> TcM (TCvSubst, [TcType])
385 go subst [] [] = return (subst, [])
386 go subst (tv:tvs) (Just ty : mb_tys)
387 = do { (subst', tys) <- go (extendTvSubstAndInScope subst tv ty)
388 tvs
389 mb_tys
390 ; return (subst', ty : tys) }
391 go subst (tv:tvs) (Nothing : mb_tys)
392 = do { (subst', tv') <- newMetaTyVarX subst tv
393 ; (subst'', tys) <- go subst' tvs mb_tys
394 ; return (subst'', mkTyVarTy tv' : tys) }
395 go _ _ _ = pprPanic "instDFunTypes" (ppr dfun_id $$ ppr dfun_inst_tys)
396
397 ----------------
398 instStupidTheta :: CtOrigin -> TcThetaType -> TcM ()
399 -- Similar to instCall, but only emit the constraints in the LIE
400 -- Used exclusively for the 'stupid theta' of a data constructor
401 instStupidTheta orig theta
402 = do { _co <- instCallConstraints orig theta -- Discard the coercion
403 ; return () }
404
405 {-
406 ************************************************************************
407 * *
408 Instantiating Kinds
409 * *
410 ************************************************************************
411
412 Note [Constraints handled in types]
413 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
414 Generally, we cannot handle constraints written in types. For example,
415 if we declare
416
417 data C a where
418 MkC :: Show a => a -> C a
419
420 we will not be able to use MkC in types, as we have no way of creating
421 a type-level Show dictionary.
422
423 However, we make an exception for equality types. Consider
424
425 data T1 a where
426 MkT1 :: T1 Bool
427
428 data T2 a where
429 MkT2 :: a ~ Bool => T2 a
430
431 MkT1 has a constrained return type, while MkT2 uses an explicit equality
432 constraint. These two types are often written interchangeably, with a
433 reasonable expectation that they mean the same thing. For this to work --
434 and for us to be able to promote GADTs -- we need to be able to instantiate
435 equality constraints in types.
436
437 One wrinkle is that the equality in MkT2 is *lifted*. But, for proper
438 GADT equalities, GHC produces *unlifted* constraints. (This unlifting comes
439 from DataCon.eqSpecPreds, which uses mkPrimEqPred.) And, perhaps a wily
440 user will use (~~) for a heterogeneous equality. We thus must support
441 all of (~), (~~), and (~#) in types. (See Note [The equality types story]
442 in TysPrim for a primer on these equality types.)
443
444 The get_eq_tys_maybe function recognizes these three forms of equality,
445 returning a suitable type formation function and the two types related
446 by the equality constraint. In the lifted case, it uses mkHEqBoxTy or
447 mkEqBoxTy, which promote the datacons of the (~~) or (~) datatype,
448 respectively.
449
450 One might reasonably wonder who *unpacks* these boxes once they are
451 made. After all, there is no type-level `case` construct. The surprising
452 answer is that no one ever does. Instead, if a GADT constructor is used
453 on the left-hand side of a type family equation, that occurrence forces
454 GHC to unify the types in question. For example:
455
456 data G a where
457 MkG :: G Bool
458
459 type family F (x :: G a) :: a where
460 F MkG = False
461
462 When checking the LHS `F MkG`, GHC sees the MkG constructor and then must
463 unify F's implicit parameter `a` with Bool. This succeeds, making the equation
464
465 F Bool (MkG @Bool <Bool>) = False
466
467 Note that we never need unpack the coercion. This is because type family
468 equations are *not* parametric in their kind variables. That is, we could have
469 just said
470
471 type family H (x :: G a) :: a where
472 H _ = False
473
474 The presence of False on the RHS also forces `a` to become Bool, giving us
475
476 H Bool _ = False
477
478 The fact that any of this works stems from the lack of phase separation between
479 types and kinds (unlike the very present phase separation between terms and types).
480
481 Once we have the ability to pattern-match on types below top-level, this will
482 no longer cut it, but it seems fine for now.
483
484 -}
485
486 ---------------------------
487 -- | Instantiates up to n invisible binders
488 -- Returns the instantiating types, and body kind
489 tcInstInvisibleTyBinders :: Int -> TcKind -> TcM ([TcType], TcKind)
490
491 tcInstInvisibleTyBinders 0 kind
492 = return ([], kind)
493 tcInstInvisibleTyBinders n ty
494 = go n empty_subst ty
495 where
496 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ty))
497
498 go n subst kind
499 | n > 0
500 , Just (bndr, body) <- tcSplitPiTy_maybe kind
501 , isInvisibleBinder bndr
502 = do { (subst', arg) <- tcInstInvisibleTyBinder subst bndr
503 ; (args, inner_ty) <- go (n-1) subst' body
504 ; return (arg:args, inner_ty) }
505 | otherwise
506 = return ([], substTy subst kind)
507
508 -- | Used only in *types*
509 tcInstInvisibleTyBinder :: TCvSubst -> TyBinder -> TcM (TCvSubst, TcType)
510 tcInstInvisibleTyBinder subst (Named (Bndr tv _))
511 = do { (subst', tv') <- newMetaTyVarX subst tv
512 ; return (subst', mkTyVarTy tv') }
513
514 tcInstInvisibleTyBinder subst (Anon ty)
515 -- This is the *only* constraint currently handled in types.
516 | Just (mk, k1, k2) <- get_eq_tys_maybe substed_ty
517 = do { co <- unifyKind Nothing k1 k2
518 ; arg' <- mk co
519 ; return (subst, arg') }
520
521 | isPredTy substed_ty
522 = do { let (env, tidy_ty) = tidyOpenType emptyTidyEnv substed_ty
523 ; addErrTcM (env, text "Illegal constraint in a kind:" <+> ppr tidy_ty)
524
525 -- just invent a new variable so that we can continue
526 ; u <- newUnique
527 ; let name = mkSysTvName u (fsLit "dict")
528 ; return (subst, mkTyVarTy $ mkTyVar name substed_ty) }
529
530
531 | otherwise
532 = do { tv_ty <- newFlexiTyVarTy substed_ty
533 ; return (subst, tv_ty) }
534
535 where
536 substed_ty = substTy subst ty
537
538 -- See Note [Constraints handled in types]
539 get_eq_tys_maybe :: Type
540 -> Maybe ( Coercion -> TcM Type
541 -- given a coercion proving t1 ~# t2, produce the
542 -- right instantiation for the TyBinder at hand
543 , Type -- t1
544 , Type -- t2
545 )
546 get_eq_tys_maybe ty
547 -- unlifted equality (~#)
548 | Just (Nominal, k1, k2) <- getEqPredTys_maybe ty
549 = Just (\co -> return $ mkCoercionTy co, k1, k2)
550
551 -- lifted heterogeneous equality (~~)
552 | Just (tc, [_, _, k1, k2]) <- splitTyConApp_maybe ty
553 = if | tc `hasKey` heqTyConKey
554 -> Just (\co -> mkHEqBoxTy co k1 k2, k1, k2)
555 | otherwise
556 -> Nothing
557
558 -- lifted homogeneous equality (~)
559 | Just (tc, [_, k1, k2]) <- splitTyConApp_maybe ty
560 = if | tc `hasKey` eqTyConKey
561 -> Just (\co -> mkEqBoxTy co k1 k2, k1, k2)
562 | otherwise
563 -> Nothing
564
565 | otherwise
566 = Nothing
567
568 -------------------------------
569 -- | This takes @a ~# b@ and returns @a ~~ b@.
570 mkHEqBoxTy :: TcCoercion -> Type -> Type -> TcM Type
571 -- monadic just for convenience with mkEqBoxTy
572 mkHEqBoxTy co ty1 ty2
573 = return $
574 mkTyConApp (promoteDataCon heqDataCon) [k1, k2, ty1, ty2, mkCoercionTy co]
575 where k1 = tcTypeKind ty1
576 k2 = tcTypeKind ty2
577
578 -- | This takes @a ~# b@ and returns @a ~ b@.
579 mkEqBoxTy :: TcCoercion -> Type -> Type -> TcM Type
580 mkEqBoxTy co ty1 ty2
581 = return $
582 mkTyConApp (promoteDataCon eqDataCon) [k, ty1, ty2, mkCoercionTy co]
583 where k = tcTypeKind ty1
584
585 {-
586 ************************************************************************
587 * *
588 Literals
589 * *
590 ************************************************************************
591
592 -}
593
594 {-
595 In newOverloadedLit we convert directly to an Int or Integer if we
596 know that's what we want. This may save some time, by not
597 temporarily generating overloaded literals, but it won't catch all
598 cases (the rest are caught in lookupInst).
599
600 -}
601
602 newOverloadedLit :: HsOverLit GhcRn
603 -> ExpRhoType
604 -> TcM (HsOverLit GhcTcId)
605 newOverloadedLit
606 lit@(OverLit { ol_val = val, ol_ext = rebindable }) res_ty
607 | not rebindable
608 -- all built-in overloaded lits are tau-types, so we can just
609 -- tauify the ExpType
610 = do { res_ty <- expTypeToType res_ty
611 ; dflags <- getDynFlags
612 ; case shortCutLit dflags val res_ty of
613 -- Do not generate a LitInst for rebindable syntax.
614 -- Reason: If we do, tcSimplify will call lookupInst, which
615 -- will call tcSyntaxName, which does unification,
616 -- which tcSimplify doesn't like
617 Just expr -> return (lit { ol_witness = expr
618 , ol_ext = OverLitTc False res_ty })
619 Nothing -> newNonTrivialOverloadedLit orig lit
620 (mkCheckExpType res_ty) }
621
622 | otherwise
623 = newNonTrivialOverloadedLit orig lit res_ty
624 where
625 orig = LiteralOrigin lit
626 newOverloadedLit XOverLit{} _ = panic "newOverloadedLit"
627
628 -- Does not handle things that 'shortCutLit' can handle. See also
629 -- newOverloadedLit in TcUnify
630 newNonTrivialOverloadedLit :: CtOrigin
631 -> HsOverLit GhcRn
632 -> ExpRhoType
633 -> TcM (HsOverLit GhcTcId)
634 newNonTrivialOverloadedLit orig
635 lit@(OverLit { ol_val = val, ol_witness = HsVar _ (L _ meth_name)
636 , ol_ext = rebindable }) res_ty
637 = do { hs_lit <- mkOverLit val
638 ; let lit_ty = hsLitType hs_lit
639 ; (_, fi') <- tcSyntaxOp orig (mkRnSyntaxExpr meth_name)
640 [synKnownType lit_ty] res_ty $
641 \_ -> return ()
642 ; let L _ witness = nlHsSyntaxApps fi' [nlHsLit hs_lit]
643 ; res_ty <- readExpType res_ty
644 ; return (lit { ol_witness = witness
645 , ol_ext = OverLitTc rebindable res_ty }) }
646 newNonTrivialOverloadedLit _ lit _
647 = pprPanic "newNonTrivialOverloadedLit" (ppr lit)
648
649 ------------
650 mkOverLit ::OverLitVal -> TcM (HsLit GhcTc)
651 mkOverLit (HsIntegral i)
652 = do { integer_ty <- tcMetaTy integerTyConName
653 ; return (HsInteger (il_text i)
654 (il_value i) integer_ty) }
655
656 mkOverLit (HsFractional r)
657 = do { rat_ty <- tcMetaTy rationalTyConName
658 ; return (HsRat noExt r rat_ty) }
659
660 mkOverLit (HsIsString src s) = return (HsString src s)
661
662 {-
663 ************************************************************************
664 * *
665 Re-mappable syntax
666
667 Used only for arrow syntax -- find a way to nuke this
668 * *
669 ************************************************************************
670
671 Suppose we are doing the -XRebindableSyntax thing, and we encounter
672 a do-expression. We have to find (>>) in the current environment, which is
673 done by the rename. Then we have to check that it has the same type as
674 Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
675 this:
676
677 (>>) :: HB m n mn => m a -> n b -> mn b
678
679 So the idea is to generate a local binding for (>>), thus:
680
681 let then72 :: forall a b. m a -> m b -> m b
682 then72 = ...something involving the user's (>>)...
683 in
684 ...the do-expression...
685
686 Now the do-expression can proceed using then72, which has exactly
687 the expected type.
688
689 In fact tcSyntaxName just generates the RHS for then72, because we only
690 want an actual binding in the do-expression case. For literals, we can
691 just use the expression inline.
692 -}
693
694 tcSyntaxName :: CtOrigin
695 -> TcType -- ^ Type to instantiate it at
696 -> (Name, HsExpr GhcRn) -- ^ (Standard name, user name)
697 -> TcM (Name, HsExpr GhcTcId)
698 -- ^ (Standard name, suitable expression)
699 -- USED ONLY FOR CmdTop (sigh) ***
700 -- See Note [CmdSyntaxTable] in HsExpr
701
702 tcSyntaxName orig ty (std_nm, HsVar _ (L _ user_nm))
703 | std_nm == user_nm
704 = do rhs <- newMethodFromName orig std_nm ty
705 return (std_nm, rhs)
706
707 tcSyntaxName orig ty (std_nm, user_nm_expr) = do
708 std_id <- tcLookupId std_nm
709 let
710 -- C.f. newMethodAtLoc
711 ([tv], _, tau) = tcSplitSigmaTy (idType std_id)
712 sigma1 = substTyWith [tv] [ty] tau
713 -- Actually, the "tau-type" might be a sigma-type in the
714 -- case of locally-polymorphic methods.
715
716 addErrCtxtM (syntaxNameCtxt user_nm_expr orig sigma1) $ do
717
718 -- Check that the user-supplied thing has the
719 -- same type as the standard one.
720 -- Tiresome jiggling because tcCheckSigma takes a located expression
721 span <- getSrcSpanM
722 expr <- tcPolyExpr (L span user_nm_expr) sigma1
723 return (std_nm, unLoc expr)
724
725 syntaxNameCtxt :: HsExpr GhcRn -> CtOrigin -> Type -> TidyEnv
726 -> TcRn (TidyEnv, SDoc)
727 syntaxNameCtxt name orig ty tidy_env
728 = do { inst_loc <- getCtLocM orig (Just TypeLevel)
729 ; let msg = vcat [ text "When checking that" <+> quotes (ppr name)
730 <+> text "(needed by a syntactic construct)"
731 , nest 2 (text "has the required type:"
732 <+> ppr (tidyType tidy_env ty))
733 , nest 2 (pprCtLoc inst_loc) ]
734 ; return (tidy_env, msg) }
735
736 {-
737 ************************************************************************
738 * *
739 Instances
740 * *
741 ************************************************************************
742 -}
743
744 getOverlapFlag :: Maybe OverlapMode -> TcM OverlapFlag
745 -- Construct the OverlapFlag from the global module flags,
746 -- but if the overlap_mode argument is (Just m),
747 -- set the OverlapMode to 'm'
748 getOverlapFlag overlap_mode
749 = do { dflags <- getDynFlags
750 ; let overlap_ok = xopt LangExt.OverlappingInstances dflags
751 incoherent_ok = xopt LangExt.IncoherentInstances dflags
752 use x = OverlapFlag { isSafeOverlap = safeLanguageOn dflags
753 , overlapMode = x }
754 default_oflag | incoherent_ok = use (Incoherent NoSourceText)
755 | overlap_ok = use (Overlaps NoSourceText)
756 | otherwise = use (NoOverlap NoSourceText)
757
758 final_oflag = setOverlapModeMaybe default_oflag overlap_mode
759 ; return final_oflag }
760
761 tcGetInsts :: TcM [ClsInst]
762 -- Gets the local class instances.
763 tcGetInsts = fmap tcg_insts getGblEnv
764
765 newClsInst :: Maybe OverlapMode -> Name -> [TyVar] -> ThetaType
766 -> Class -> [Type] -> TcM ClsInst
767 newClsInst overlap_mode dfun_name tvs theta clas tys
768 = do { (subst, tvs') <- freshenTyVarBndrs tvs
769 -- Be sure to freshen those type variables,
770 -- so they are sure not to appear in any lookup
771 ; let tys' = substTys subst tys
772
773 dfun = mkDictFunId dfun_name tvs theta clas tys
774 -- The dfun uses the original 'tvs' because
775 -- (a) they don't need to be fresh
776 -- (b) they may be mentioned in the ib_binds field of
777 -- an InstInfo, and in TcEnv.pprInstInfoDetails it's
778 -- helpful to use the same names
779
780 ; oflag <- getOverlapFlag overlap_mode
781 ; let inst = mkLocalInstance dfun oflag tvs' clas tys'
782 ; warnIfFlag Opt_WarnOrphans
783 (isOrphan (is_orphan inst))
784 (instOrphWarn inst)
785 ; return inst }
786
787 instOrphWarn :: ClsInst -> SDoc
788 instOrphWarn inst
789 = hang (text "Orphan instance:") 2 (pprInstanceHdr inst)
790 $$ text "To avoid this"
791 $$ nest 4 (vcat possibilities)
792 where
793 possibilities =
794 text "move the instance declaration to the module of the class or of the type, or" :
795 text "wrap the type with a newtype and declare the instance on the new type." :
796 []
797
798 tcExtendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a
799 -- Add new locally-defined instances
800 tcExtendLocalInstEnv dfuns thing_inside
801 = do { traceDFuns dfuns
802 ; env <- getGblEnv
803 ; (inst_env', cls_insts') <- foldlM addLocalInst
804 (tcg_inst_env env, tcg_insts env)
805 dfuns
806 ; let env' = env { tcg_insts = cls_insts'
807 , tcg_inst_env = inst_env' }
808 ; setGblEnv env' thing_inside }
809
810 addLocalInst :: (InstEnv, [ClsInst]) -> ClsInst -> TcM (InstEnv, [ClsInst])
811 -- Check that the proposed new instance is OK,
812 -- and then add it to the home inst env
813 -- If overwrite_inst, then we can overwrite a direct match
814 addLocalInst (home_ie, my_insts) ispec
815 = do {
816 -- Load imported instances, so that we report
817 -- duplicates correctly
818
819 -- 'matches' are existing instance declarations that are less
820 -- specific than the new one
821 -- 'dups' are those 'matches' that are equal to the new one
822 ; isGHCi <- getIsGHCi
823 ; eps <- getEps
824 ; tcg_env <- getGblEnv
825
826 -- In GHCi, we *override* any identical instances
827 -- that are also defined in the interactive context
828 -- See Note [Override identical instances in GHCi]
829 ; let home_ie'
830 | isGHCi = deleteFromInstEnv home_ie ispec
831 | otherwise = home_ie
832
833 global_ie = eps_inst_env eps
834 inst_envs = InstEnvs { ie_global = global_ie
835 , ie_local = home_ie'
836 , ie_visible = tcVisibleOrphanMods tcg_env }
837
838 -- Check for inconsistent functional dependencies
839 ; let inconsistent_ispecs = checkFunDeps inst_envs ispec
840 ; unless (null inconsistent_ispecs) $
841 funDepErr ispec inconsistent_ispecs
842
843 -- Check for duplicate instance decls.
844 ; let (_tvs, cls, tys) = instanceHead ispec
845 (matches, _, _) = lookupInstEnv False inst_envs cls tys
846 dups = filter (identicalClsInstHead ispec) (map fst matches)
847 ; unless (null dups) $
848 dupInstErr ispec (head dups)
849
850 ; return (extendInstEnv home_ie' ispec, ispec : my_insts) }
851
852 {-
853 Note [Signature files and type class instances]
854 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
855 Instances in signature files do not have an effect when compiling:
856 when you compile a signature against an implementation, you will
857 see the instances WHETHER OR NOT the instance is declared in
858 the file (this is because the signatures go in the EPS and we
859 can't filter them out easily.) This is also why we cannot
860 place the instance in the hi file: it would show up as a duplicate,
861 and we don't have instance reexports anyway.
862
863 However, you might find them useful when typechecking against
864 a signature: the instance is a way of indicating to GHC that
865 some instance exists, in case downstream code uses it.
866
867 Implementing this is a little tricky. Consider the following
868 situation (sigof03):
869
870 module A where
871 instance C T where ...
872
873 module ASig where
874 instance C T
875
876 When compiling ASig, A.hi is loaded, which brings its instances
877 into the EPS. When we process the instance declaration in ASig,
878 we should ignore it for the purpose of doing a duplicate check,
879 since it's not actually a duplicate. But don't skip the check
880 entirely, we still want this to fail (tcfail221):
881
882 module ASig where
883 instance C T
884 instance C T
885
886 Note that in some situations, the interface containing the type
887 class instances may not have been loaded yet at all. The usual
888 situation when A imports another module which provides the
889 instances (sigof02m):
890
891 module A(module B) where
892 import B
893
894 See also Note [Signature lazy interface loading]. We can't
895 rely on this, however, since sometimes we'll have spurious
896 type class instances in the EPS, see #9422 (sigof02dm)
897
898 ************************************************************************
899 * *
900 Errors and tracing
901 * *
902 ************************************************************************
903 -}
904
905 traceDFuns :: [ClsInst] -> TcRn ()
906 traceDFuns ispecs
907 = traceTc "Adding instances:" (vcat (map pp ispecs))
908 where
909 pp ispec = hang (ppr (instanceDFunId ispec) <+> colon)
910 2 (ppr ispec)
911 -- Print the dfun name itself too
912
913 funDepErr :: ClsInst -> [ClsInst] -> TcRn ()
914 funDepErr ispec ispecs
915 = addClsInstsErr (text "Functional dependencies conflict between instance declarations:")
916 (ispec : ispecs)
917
918 dupInstErr :: ClsInst -> ClsInst -> TcRn ()
919 dupInstErr ispec dup_ispec
920 = addClsInstsErr (text "Duplicate instance declarations:")
921 [ispec, dup_ispec]
922
923 addClsInstsErr :: SDoc -> [ClsInst] -> TcRn ()
924 addClsInstsErr herald ispecs
925 = setSrcSpan (getSrcSpan (head sorted)) $
926 addErr (hang herald 2 (pprInstances sorted))
927 where
928 sorted = sortWith getSrcLoc ispecs
929 -- The sortWith just arranges that instances are dislayed in order
930 -- of source location, which reduced wobbling in error messages,
931 -- and is better for users