2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcPat]{Typechecking patterns}
7 module TcPat ( tcLetPat, tcLamPat, tcLamPats, tcOverloadedLit,
8 addDataConStupidTheta, badFieldCon, polyPatSig ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
13 import HsSyn ( Pat(..), LPat, HsConDetails(..), HsLit(..),
14 HsOverLit(..), HsExpr(..), OutPat, ExprCoFn(..),
16 LHsBinds, emptyLHsBinds, isEmptyLHsBinds,
17 collectPatsBinders, nlHsLit )
18 import TcHsSyn ( TcId, hsLitType )
20 import Inst ( InstOrigin(..), shortCutFracLit, shortCutIntLit,
21 newDictBndrs, instToId, instStupidTheta, isHsVar
23 import Id ( Id, idType, mkLocalId )
24 import CoreFVs ( idFreeTyVars )
25 import Name ( Name, mkSystemVarName )
26 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
27 import TcEnv ( newLocalName, tcExtendIdEnv1, tcExtendTyVarEnv2,
28 tcLookupClass, tcLookupDataCon, refineEnvironment,
29 tcLookupField, tcMetaTy )
30 import TcMType ( newFlexiTyVarTy, arityErr, tcInstSkolTyVars,
31 newCoVars, zonkTcType, tcInstTyVars )
32 import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType, BoxyType,
34 BoxySigmaType, BoxyRhoType, argTypeKind, typeKind,
35 pprSkolTvBinding, isRigidTy, tcTyVarsOfTypes,
36 zipTopTvSubst, isArgTypeKind, isUnboxedTupleType,
37 mkTyVarTys, mkClassPred, isOverloadedTy, substEqSpec,
38 mkFunTy, mkFunTys, tidyOpenType, tidyOpenTypes )
39 import VarSet ( elemVarSet )
40 import {- Kind parts of -}
41 Type ( liftedTypeKind )
42 import TcUnify ( boxySplitTyConApp, boxySplitListTy, unBox,
43 zapToMonotype, boxyUnify, boxyUnifyList,
44 checkSigTyVarsWrt, unifyType )
45 import TcHsType ( UserTypeCtxt(..), tcPatSig )
46 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
47 import Type ( Type, mkTyConApp, substTys, substTheta )
48 import StaticFlags ( opt_IrrefutableTuples )
49 import TyCon ( TyCon, FieldLabel, tyConFamInst_maybe,
50 tyConFamilyCoercion_maybe, tyConTyVars )
51 import DataCon ( DataCon, dataConTyCon, dataConFullSig, dataConName,
52 dataConFieldLabels, dataConSourceArity,
53 dataConStupidTheta, dataConUnivTyVars )
54 import PrelNames ( integralClassName, fromIntegerName, integerTyConName,
55 fromRationalName, rationalTyConName )
56 import BasicTypes ( isBoxed )
57 import SrcLoc ( Located(..), SrcSpan, noLoc )
58 import ErrUtils ( Message )
59 import Util ( zipEqual )
60 import Maybes ( MaybeErr(..) )
66 %************************************************************************
70 %************************************************************************
73 tcLetPat :: (Name -> Maybe TcRhoType)
74 -> LPat Name -> BoxySigmaType
77 tcLetPat sig_fn pat pat_ty thing_inside
78 = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
79 pat_reft = emptyRefinement }
80 ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
82 -- Don't know how to deal with pattern-bound existentials yet
83 ; checkTc (null ex_tvs) (existentialExplode pat)
85 ; return (pat', res) }
88 tcLamPats :: [LPat Name] -- Patterns,
89 -> [BoxySigmaType] -- and their types
90 -> BoxyRhoType -- Result type,
91 -> ((Refinement, BoxyRhoType) -> TcM a) -- and the checker for the body
92 -> TcM ([LPat TcId], a)
94 -- This is the externally-callable wrapper function
95 -- Typecheck the patterns, extend the environment to bind the variables,
96 -- do the thing inside, use any existentially-bound dictionaries to
97 -- discharge parts of the returning LIE, and deal with pattern type
100 -- 1. Initialise the PatState
101 -- 2. Check the patterns
102 -- 3. Apply the refinement to the environment and result type
104 -- 5. Check that no existentials escape
106 tcLamPats pats tys res_ty thing_inside
107 = tc_lam_pats (zipEqual "tcLamPats" pats tys)
108 (emptyRefinement, res_ty) thing_inside
110 tcLamPat :: LPat Name -> BoxySigmaType
111 -> (Refinement,BoxyRhoType) -- Result type
112 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
113 -> TcM (LPat TcId, a)
114 tcLamPat pat pat_ty res_ty thing_inside
115 = do { ([pat'],thing) <- tc_lam_pats [(pat, pat_ty)] res_ty thing_inside
116 ; return (pat', thing) }
119 tc_lam_pats :: [(LPat Name,BoxySigmaType)]
120 -> (Refinement,BoxyRhoType) -- Result type
121 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
122 -> TcM ([LPat TcId], a)
123 tc_lam_pats pat_ty_prs (reft, res_ty) thing_inside
124 = do { let init_state = PS { pat_ctxt = LamPat, pat_reft = reft }
126 ; (pats', ex_tvs, res) <- tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
127 refineEnvironment (pat_reft pstate') $
128 thing_inside (pat_reft pstate', res_ty)
130 ; let tys = map snd pat_ty_prs
131 ; tcCheckExistentialPat pats' ex_tvs tys res_ty
133 ; returnM (pats', res) }
137 tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
138 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
139 -> [BoxySigmaType] -- Types of the patterns
140 -> BoxyRhoType -- Type of the body of the match
141 -- Tyvars in either of these must not escape
143 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
144 -- For example, we must reject this program:
145 -- data C = forall a. C (a -> Int)
147 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
149 tcCheckExistentialPat pats [] pat_tys body_ty
150 = return () -- Short cut for case when there are no existentials
152 tcCheckExistentialPat pats ex_tvs pat_tys body_ty
153 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys body_ty) $
154 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
158 pat_reft :: Refinement -- Binds rigid TcTyVars to their refinements
163 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
165 patSigCtxt :: PatState -> UserTypeCtxt
166 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
167 patSigCtxt other = LamPatSigCtxt
172 %************************************************************************
176 %************************************************************************
179 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
180 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
181 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
182 -- We have an undecorated binder, so we do rule ABS1,
183 -- by unboxing the boxy type, forcing any un-filled-in
184 -- boxes to become monotypes
185 -- NB that pat_ty' can still be a polytype:
186 -- data T = MkT (forall a. a->a)
187 -- f t = case t of { MkT g -> ... }
188 -- Here, the 'g' must get type (forall a. a->a) from the
190 ; return (mkLocalId bndr_name pat_ty') }
192 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
193 | Just mono_ty <- lookup_sig bndr_name
194 = do { mono_name <- newLocalName bndr_name
195 ; boxyUnify mono_ty pat_ty
196 ; return (mkLocalId mono_name mono_ty) }
199 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
200 ; mono_name <- newLocalName bndr_name
201 ; return (mkLocalId mono_name pat_ty') }
205 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
206 bindInstsOfPatId id thing_inside
207 | not (isOverloadedTy (idType id))
208 = do { res <- thing_inside; return (res, emptyLHsBinds) }
210 = do { (res, lie) <- getLIE thing_inside
211 ; binds <- bindInstsOfLocalFuns lie [id]
212 ; return (res, binds) }
215 unBoxPatBndrType ty name = unBoxArgType ty (ptext SLIT("The variable") <+> quotes (ppr name))
216 unBoxWildCardType ty = unBoxArgType ty (ptext SLIT("A wild-card pattern"))
218 unBoxArgType :: BoxyType -> SDoc -> TcM TcType
219 -- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
220 -- that is, it can't be an unboxed tuple. For example,
221 -- case (f x) of r -> ...
222 -- should fail if 'f' returns an unboxed tuple.
223 unBoxArgType ty pp_this
224 = do { ty' <- unBox ty -- Returns a zonked type
226 -- Neither conditional is strictly necesssary (the unify alone will do)
227 -- but they improve error messages, and allocate fewer tyvars
228 ; if isUnboxedTupleType ty' then
230 else if isArgTypeKind (typeKind ty') then
232 else do -- OpenTypeKind, so constrain it
233 { ty2 <- newFlexiTyVarTy argTypeKind
237 msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
241 %************************************************************************
243 The main worker functions
245 %************************************************************************
249 tcPat takes a "thing inside" over which the patter scopes. This is partly
250 so that tcPat can extend the environment for the thing_inside, but also
251 so that constraints arising in the thing_inside can be discharged by the
254 This does not work so well for the ErrCtxt carried by the monad: we don't
255 want the error-context for the pattern to scope over the RHS.
256 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
260 type Checker inp out = forall r.
263 -> (PatState -> TcM r)
264 -> TcM (out, [TcTyVar], r)
266 tcMultiple :: Checker inp out -> Checker [inp] [out]
267 tcMultiple tc_pat args pstate thing_inside
268 = do { err_ctxt <- getErrCtxt
270 = do { res <- thing_inside pstate
271 ; return ([], [], res) }
273 loop pstate (arg:args)
274 = do { (p', p_tvs, (ps', ps_tvs, res))
275 <- tc_pat arg pstate $ \ pstate' ->
276 setErrCtxt err_ctxt $
278 -- setErrCtxt: restore context before doing the next pattern
279 -- See note [Nesting] above
281 ; return (p':ps', p_tvs ++ ps_tvs, res) }
286 tc_lpat_pr :: (LPat Name, BoxySigmaType)
288 -> (PatState -> TcM a)
289 -> TcM (LPat TcId, [TcTyVar], a)
290 tc_lpat_pr (pat, ty) = tc_lpat pat ty
295 -> (PatState -> TcM a)
296 -> TcM (LPat TcId, [TcTyVar], a)
297 tc_lpat (L span pat) pat_ty pstate thing_inside
299 maybeAddErrCtxt (patCtxt pat) $
300 do { let (coercion, pat_ty') = refineType (pat_reft pstate) pat_ty
301 -- Make sure the result type reflects the current refinement
302 -- We must do this here, so that it correctly ``sees'' all
303 -- the refinements to the left. Example:
304 -- Suppose C :: forall a. T a -> a -> Foo
305 -- Pattern C a p1 True
306 -- So p1 might refine 'a' to True, and the True
307 -- pattern had better see it.
309 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
310 ; return (mkCoPat coercion (L span pat') pat_ty, tvs, res) }
314 -> Pat Name -> BoxySigmaType -- Fully refined result type
315 -> (PatState -> TcM a) -- Thing inside
316 -> TcM (Pat TcId, -- Translated pattern
317 [TcTyVar], -- Existential binders
318 a) -- Result of thing inside
320 tc_pat pstate (VarPat name) pat_ty thing_inside
321 = do { id <- tcPatBndr pstate name pat_ty
322 ; (res, binds) <- bindInstsOfPatId id $
323 tcExtendIdEnv1 name id $
324 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
325 >> thing_inside pstate)
326 ; let pat' | isEmptyLHsBinds binds = VarPat id
327 | otherwise = VarPatOut id binds
328 ; return (pat', [], res) }
330 tc_pat pstate (ParPat pat) pat_ty thing_inside
331 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
332 ; return (ParPat pat', tvs, res) }
334 tc_pat pstate (BangPat pat) pat_ty thing_inside
335 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
336 ; return (BangPat pat', tvs, res) }
338 -- There's a wrinkle with irrefutable patterns, namely that we
339 -- must not propagate type refinement from them. For example
340 -- data T a where { T1 :: Int -> T Int; ... }
341 -- f :: T a -> Int -> a
343 -- It's obviously not sound to refine a to Int in the right
344 -- hand side, because the arugment might not match T1 at all!
346 -- Nor should a lazy pattern bind any existential type variables
347 -- because they won't be in scope when we do the desugaring
348 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
349 = do { (pat', pat_tvs, res) <- tc_lpat pat pat_ty pstate $ \ _ ->
351 -- Ignore refined pstate',
353 -- Check no existentials
354 ; if (null pat_tvs) then return ()
355 else lazyPatErr lpat pat_tvs
357 -- Check that the pattern has a lifted type
358 ; pat_tv <- newBoxyTyVar liftedTypeKind
359 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
361 ; return (LazyPat pat', [], res) }
363 tc_pat pstate (WildPat _) pat_ty thing_inside
364 = do { pat_ty' <- unBoxWildCardType pat_ty -- Make sure it's filled in with monotypes
365 ; res <- thing_inside pstate
366 ; return (WildPat pat_ty', [], res) }
368 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
369 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
370 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
371 tc_lpat pat (idType bndr_id) pstate thing_inside
372 -- NB: if we do inference on:
373 -- \ (y@(x::forall a. a->a)) = e
374 -- we'll fail. The as-pattern infers a monotype for 'y', which then
375 -- fails to unify with the polymorphic type for 'x'. This could
376 -- perhaps be fixed, but only with a bit more work.
378 -- If you fix it, don't forget the bindInstsOfPatIds!
379 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
381 -- Type signatures in patterns
382 -- See Note [Pattern coercions] below
383 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
384 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
385 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
386 tc_lpat pat inner_ty pstate thing_inside
387 ; return (SigPatOut pat' inner_ty, tvs, res) }
389 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
390 = failWithTc (badTypePat pat)
392 ------------------------
393 -- Lists, tuples, arrays
394 tc_pat pstate (ListPat pats _) pat_ty thing_inside
395 = do { elt_ty <- boxySplitListTy pat_ty
396 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
397 pats pstate thing_inside
398 ; return (ListPat pats' elt_ty, pats_tvs, res) }
400 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
401 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
402 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
403 pats pstate thing_inside
404 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
405 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
407 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
408 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
409 ; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
412 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
413 -- so that we can experiment with lazy tuple-matching.
414 -- This is a pretty odd place to make the switch, but
415 -- it was easy to do.
416 ; let unmangled_result = TuplePat pats' boxity pat_ty
417 possibly_mangled_result
418 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
419 | otherwise = unmangled_result
421 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
422 return (possibly_mangled_result, pats_tvs, res) }
424 ------------------------
426 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
427 = do { data_con <- tcLookupDataCon con_name
428 ; let tycon = dataConTyCon data_con
429 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
431 ------------------------
433 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
434 = do { boxyUnify (hsLitType simple_lit) pat_ty
435 ; res <- thing_inside pstate
436 ; returnM (LitPat simple_lit, [], res) }
438 ------------------------
439 -- Overloaded patterns: n, and n+k
440 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
441 = do { let orig = LiteralOrigin over_lit
442 ; lit' <- tcOverloadedLit orig over_lit pat_ty
443 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
444 ; mb_neg' <- case mb_neg of
445 Nothing -> return Nothing -- Positive literal
446 Just neg -> -- Negative literal
447 -- The 'negate' is re-mappable syntax
448 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
449 ; return (Just neg') }
450 ; res <- thing_inside pstate
451 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
453 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
454 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
455 ; let pat_ty' = idType bndr_id
456 orig = LiteralOrigin lit
457 ; lit' <- tcOverloadedLit orig lit pat_ty'
459 -- The '>=' and '-' parts are re-mappable syntax
460 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
461 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
463 -- The Report says that n+k patterns must be in Integral
464 -- We may not want this when using re-mappable syntax, though (ToDo?)
465 ; icls <- tcLookupClass integralClassName
466 ; instStupidTheta orig [mkClassPred icls [pat_ty']]
468 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
469 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
471 tc_pat _ _other_pat _ _ = panic "tc_pat" -- DictPat, ConPatOut, SigPatOut, VarPatOut
475 %************************************************************************
477 Most of the work for constructors is here
478 (the rest is in the ConPatIn case of tc_pat)
480 %************************************************************************
482 [Pattern matching indexed data types]
483 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
484 Consider the following declarations:
486 data family Map k :: * -> *
487 data instance Map (a, b) v = MapPair (Map a (Pair b v))
489 and a case expression
491 case x :: Map (Int, c) w of MapPair m -> ...
493 As explained by [Wrappers for data instance tycons] in MkIds.lhs, the
494 worker/wrapper types for MapPair are
496 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
497 $wMapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
499 So, the type of the scrutinee is Map (Int, c) w, but the tycon of MapPair is
500 :R123Map, which means the straight use of boxySplitTyConApp would give a type
501 error. Hence, the smart wrapper function boxySplitTyConAppWithFamily calls
502 boxySplitTyConApp with the family tycon Map instead, which gives us the family
503 type list {(Int, c), w}. To get the correct split for :R123Map, we need to
504 unify the family type list {(Int, c), w} with the instance types {(a, b), v}
505 (provided by tyConFamInst_maybe together with the family tycon). This
506 unification yields the substitution [a -> Int, b -> c, v -> w], which gives us
507 the split arguments for the representation tycon :R123Map as {Int, c, w}
509 In other words, boxySplitTyConAppWithFamily implicitly takes the coercion
511 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
513 moving between representation and family type into account. To produce type
514 correct Core, this coercion needs to be used to case the type of the scrutinee
515 from the family to the representation type. This is achieved by
516 unwrapFamInstScrutinee using a CoPat around the result pattern.
518 Now it might appear seem as if we could have used the existing GADT type
519 refinement infrastructure of refineAlt and friends instead of the explicit
520 unification and CoPat generation. However, that would be wrong. Why? The
521 whole point of GADT refinement is that the refinement is local to the case
522 alternative. In contrast, the substitution generated by the unification of
523 the family type list and instance types needs to be propagated to the outside.
524 Imagine that in the above example, the type of the scrutinee would have been
525 (Map x w), then we would have unified {x, w} with {(a, b), v}, yielding the
526 substitution [x -> (a, b), v -> w]. In contrast to GADT matching, the
527 instantiation of x with (a, b) must be global; ie, it must be valid in *all*
528 alternatives of the case expression, whereas in the GADT case it might vary
529 between alternatives.
531 In fact, if we have a data instance declaration defining a GADT, eq_spec will
532 be non-empty and we will get a mixture of global instantiations and local
533 refinement from a single match. This neatly reflects that, as soon as we
534 have constrained the type of the scrutinee to the required type index, all
535 further type refinement is local to the alternative.
539 -- MkT :: forall a b c. (a:=:[b]) => b -> c -> T a
540 -- with scrutinee of type (T ty)
542 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
543 -> BoxySigmaType -- Type of the pattern
544 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
545 -> TcM (Pat TcId, [TcTyVar], a)
546 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
547 = do { span <- getSrcSpanM -- Span for the whole pattern
548 ; let (univ_tvs, ex_tvs, eq_spec, theta, arg_tys) = dataConFullSig data_con
549 skol_info = PatSkol data_con span
550 origin = SigOrigin skol_info
552 -- Instantiate the constructor type variables [a->ty]
553 ; ctxt_res_tys <- boxySplitTyConAppWithFamily tycon pat_ty
554 ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs
555 ; let tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
556 (ctxt_res_tys ++ mkTyVarTys ex_tvs')
557 eq_spec' = substEqSpec tenv eq_spec
558 theta' = substTheta tenv theta
559 arg_tys' = substTys tenv arg_tys
561 ; co_vars <- newCoVars eq_spec' -- Make coercion variables
562 ; pstate' <- refineAlt data_con pstate ex_tvs co_vars pat_ty
564 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
565 tcConArgs data_con arg_tys' arg_pats pstate' thing_inside
567 ; loc <- getInstLoc origin
568 ; dicts <- newDictBndrs loc theta'
569 ; dict_binds <- tcSimplifyCheck doc ex_tvs' dicts lie_req
571 ; addDataConStupidTheta origin data_con ctxt_res_tys
574 (unwrapFamInstScrutinee tycon ctxt_res_tys $
575 ConPatOut { pat_con = L con_span data_con,
576 pat_tvs = ex_tvs' ++ co_vars,
577 pat_dicts = map instToId dicts,
578 pat_binds = dict_binds,
579 pat_args = arg_pats', pat_ty = pat_ty },
580 ex_tvs' ++ inner_tvs, res)
583 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
585 -- Split against the family tycon if the pattern constructor belongs to a
586 -- representation tycon.
588 boxySplitTyConAppWithFamily tycon pat_ty =
589 case tyConFamInst_maybe tycon of
590 Nothing -> boxySplitTyConApp tycon pat_ty
591 Just (fam_tycon, instTys) ->
592 do { scrutinee_arg_tys <- boxySplitTyConApp fam_tycon pat_ty
593 ; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
594 ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
598 -- Wraps the pattern (which must be a ConPatOut pattern) in a coercion
599 -- pattern if the tycon is an instance of a family.
601 unwrapFamInstScrutinee :: TyCon -> [Type] -> Pat Id -> Pat Id
602 unwrapFamInstScrutinee tycon args pat
603 | Just co_con <- tyConFamilyCoercion_maybe tycon
604 -- NB: We can use CoPat directly, rather than mkCoPat, as we know the
605 -- coercion is not the identity; mkCoPat is inconvenient as it
606 -- wants a located pattern.
607 = CoPat (ExprCoFn $ mkTyConApp co_con args) -- co fam ty to repr ty
608 (pat {pat_ty = mkTyConApp tycon args}) -- representation type
609 pat_ty -- family inst type
614 tcConArgs :: DataCon -> [TcSigmaType]
615 -> Checker (HsConDetails Name (LPat Name))
616 (HsConDetails Id (LPat Id))
618 tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
619 = do { checkTc (con_arity == no_of_args) -- Check correct arity
620 (arityErr "Constructor" data_con con_arity no_of_args)
621 ; let pats_w_tys = zipEqual "tcConArgs" arg_pats arg_tys
622 ; (arg_pats', tvs, res) <- tcMultiple tcConArg pats_w_tys
624 ; return (PrefixCon arg_pats', tvs, res) }
626 con_arity = dataConSourceArity data_con
627 no_of_args = length arg_pats
629 tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
630 = do { checkTc (con_arity == 2) -- Check correct arity
631 (arityErr "Constructor" data_con con_arity 2)
632 ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
634 ; return (InfixCon p1' p2', tvs, res) }
636 con_arity = dataConSourceArity data_con
638 tcConArgs data_con arg_tys (RecCon rpats) pstate thing_inside
639 = do { (rpats', tvs, res) <- tcMultiple tc_field rpats pstate thing_inside
640 ; return (RecCon rpats', tvs, res) }
642 tc_field :: Checker (Located Name, LPat Name) (Located TcId, LPat TcId)
643 tc_field (field_lbl, pat) pstate thing_inside
644 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
645 ; (pat', tvs, res) <- tcConArg (pat, pat_ty) pstate thing_inside
646 ; return ((sel_id, pat'), tvs, res) }
648 find_field_ty :: FieldLabel -> TcM (Id, TcType)
649 find_field_ty field_lbl
650 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
652 -- No matching field; chances are this field label comes from some
653 -- other record type (or maybe none). As well as reporting an
654 -- error we still want to typecheck the pattern, principally to
655 -- make sure that all the variables it binds are put into the
656 -- environment, else the type checker crashes later:
657 -- f (R { foo = (a,b) }) = a+b
658 -- If foo isn't one of R's fields, we don't want to crash when
659 -- typechecking the "a+b".
660 [] -> do { addErrTc (badFieldCon data_con field_lbl)
661 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
662 ; return (error "Bogus selector Id", bogus_ty) }
664 -- The normal case, when the field comes from the right constructor
666 ASSERT( null extras )
667 do { sel_id <- tcLookupField field_lbl
668 ; return (sel_id, pat_ty) }
670 field_tys :: [(FieldLabel, TcType)]
671 field_tys = zip (dataConFieldLabels data_con) arg_tys
672 -- Don't use zipEqual! If the constructor isn't really a record, then
673 -- dataConFieldLabels will be empty (and each field in the pattern
674 -- will generate an error below).
676 tcConArg :: Checker (LPat Name, BoxySigmaType) (LPat Id)
677 tcConArg (arg_pat, arg_ty) pstate thing_inside
678 = tc_lpat arg_pat arg_ty pstate thing_inside
679 -- NB: the tc_lpat will refine pat_ty if necessary
680 -- based on the current pstate, which may include
681 -- refinements from peer argument patterns to the left
685 addDataConStupidTheta :: InstOrigin -> DataCon -> [TcType] -> TcM ()
686 -- Instantiate the "stupid theta" of the data con, and throw
687 -- the constraints into the constraint set
688 addDataConStupidTheta origin data_con inst_tys
689 | null stupid_theta = return ()
690 | otherwise = instStupidTheta origin inst_theta
692 stupid_theta = dataConStupidTheta data_con
693 tenv = zipTopTvSubst (dataConUnivTyVars data_con) inst_tys
694 inst_theta = substTheta tenv stupid_theta
698 %************************************************************************
702 %************************************************************************
705 refineAlt :: DataCon -- For tracing only
707 -> [TcTyVar] -- Existentials
708 -> [CoVar] -- Equational constraints
709 -> BoxySigmaType -- Pattern type
712 refineAlt con pstate ex_tvs [] pat_ty
713 = return pstate -- Common case: no equational constraints
715 refineAlt con pstate ex_tvs co_vars pat_ty
716 | not (isRigidTy pat_ty)
717 = failWithTc (nonRigidMatch con)
718 -- We are matching against a GADT constructor with non-trivial
719 -- constraints, but pattern type is wobbly. For now we fail.
720 -- We can make sense of this, however:
721 -- Suppose MkT :: forall a b. (a:=:[b]) => b -> T a
722 -- (\x -> case x of { MkT v -> v })
723 -- We can infer that x must have type T [c], for some wobbly 'c'
725 -- (\(x::T [c]) -> case x of
726 -- MkT b (g::([c]:=:[b])) (v::b) -> v `cast` sym g
727 -- To implement this, we'd first instantiate the equational
728 -- constraints with *wobbly* type variables for the existentials;
729 -- then unify these constraints to make pat_ty the right shape;
730 -- then proceed exactly as in the rigid case
732 | otherwise -- In the rigid case, we perform type refinement
733 = case gadtRefine (pat_reft pstate) ex_tvs co_vars of {
734 Failed msg -> failWithTc (inaccessibleAlt msg) ;
735 Succeeded reft -> do { traceTc trace_msg
736 ; return (pstate { pat_reft = reft }) }
737 -- DO NOT refine the envt right away, because we
738 -- might be inside a lazy pattern. Instead, refine pstate
741 trace_msg = text "refineAlt:match" <+> ppr con <+> ppr reft
746 %************************************************************************
750 %************************************************************************
752 In tcOverloadedLit we convert directly to an Int or Integer if we
753 know that's what we want. This may save some time, by not
754 temporarily generating overloaded literals, but it won't catch all
755 cases (the rest are caught in lookupInst).
758 tcOverloadedLit :: InstOrigin
761 -> TcM (HsOverLit TcId)
762 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
763 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
764 -- Reason: If we do, tcSimplify will call lookupInst, which
765 -- will call tcSyntaxName, which does unification,
766 -- which tcSimplify doesn't like
767 -- ToDo: noLoc sadness
768 = do { integer_ty <- tcMetaTy integerTyConName
769 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
770 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
772 | Just expr <- shortCutIntLit i res_ty
773 = return (HsIntegral i expr)
776 = do { expr <- newLitInst orig lit res_ty
777 ; return (HsIntegral i expr) }
779 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
780 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
781 = do { rat_ty <- tcMetaTy rationalTyConName
782 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
783 -- Overloaded literals must have liftedTypeKind, because
784 -- we're instantiating an overloaded function here,
785 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
786 -- However this'll be picked up by tcSyntaxOp if necessary
787 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
789 | Just expr <- shortCutFracLit r res_ty
790 = return (HsFractional r expr)
793 = do { expr <- newLitInst orig lit res_ty
794 ; return (HsFractional r expr) }
796 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
797 newLitInst orig lit res_ty -- Make a LitInst
798 = do { loc <- getInstLoc orig
799 ; res_tau <- zapToMonotype res_ty
800 ; new_uniq <- newUnique
801 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
802 lit_inst = LitInst lit_nm lit res_tau loc
804 ; return (HsVar (instToId lit_inst)) }
808 %************************************************************************
810 Note [Pattern coercions]
812 %************************************************************************
814 In principle, these program would be reasonable:
816 f :: (forall a. a->a) -> Int
817 f (x :: Int->Int) = x 3
819 g :: (forall a. [a]) -> Bool
822 In both cases, the function type signature restricts what arguments can be passed
823 in a call (to polymorphic ones). The pattern type signature then instantiates this
824 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
825 generate the translated term
826 f = \x' :: (forall a. a->a). let x = x' Int in x 3
828 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
829 And it requires a significant amount of code to implement, becuase we need to decorate
830 the translated pattern with coercion functions (generated from the subsumption check
833 So for now I'm just insisting on type *equality* in patterns. No subsumption.
835 Old notes about desugaring, at a time when pattern coercions were handled:
837 A SigPat is a type coercion and must be handled one at at time. We can't
838 combine them unless the type of the pattern inside is identical, and we don't
839 bother to check for that. For example:
841 data T = T1 Int | T2 Bool
842 f :: (forall a. a -> a) -> T -> t
843 f (g::Int->Int) (T1 i) = T1 (g i)
844 f (g::Bool->Bool) (T2 b) = T2 (g b)
846 We desugar this as follows:
848 f = \ g::(forall a. a->a) t::T ->
850 in case t of { T1 i -> T1 (gi i)
853 in case t of { T2 b -> T2 (gb b)
856 Note that we do not treat the first column of patterns as a
857 column of variables, because the coerced variables (gi, gb)
858 would be of different types. So we get rather grotty code.
859 But I don't think this is a common case, and if it was we could
860 doubtless improve it.
862 Meanwhile, the strategy is:
863 * treat each SigPat coercion (always non-identity coercions)
865 * deal with the stuff inside, and then wrap a binding round
866 the result to bind the new variable (gi, gb, etc)
869 %************************************************************************
871 \subsection{Errors and contexts}
873 %************************************************************************
876 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
877 patCtxt (VarPat _) = Nothing
878 patCtxt (ParPat _) = Nothing
879 patCtxt (AsPat _ _) = Nothing
880 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
883 -----------------------------------------------
885 existentialExplode pat
886 = hang (vcat [text "My brain just exploded.",
887 text "I can't handle pattern bindings for existentially-quantified constructors.",
888 text "In the binding group for"])
891 sigPatCtxt bound_ids bound_tvs pat_tys body_ty tidy_env
892 = do { pat_tys' <- mapM zonkTcType pat_tys
893 ; body_ty' <- zonkTcType body_ty
894 ; let (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
895 (env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
896 (env3, tidy_body_ty) = tidyOpenType env2 body_ty'
898 sep [ptext SLIT("When checking an existential match that binds"),
899 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
900 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
901 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
904 show_ids = filter is_interesting bound_ids
905 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
907 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
908 -- Don't zonk the types so we get the separate, un-unified versions
910 badFieldCon :: DataCon -> Name -> SDoc
911 badFieldCon con field
912 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
913 ptext SLIT("does not have field"), quotes (ppr field)]
915 polyPatSig :: TcType -> SDoc
917 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
920 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
924 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
925 2 (vcat (map pprSkolTvBinding tvs))
928 = hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
929 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
932 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg