2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 TcPat: Typechecking patterns
9 module TcPat ( tcLetPat, tcLamPat, tcLamPats, tcOverloadedLit,
10 addDataConStupidTheta, badFieldCon, polyPatSig ) where
12 #include "HsVersions.h"
14 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
38 import BasicTypes hiding (SuccessFlag(..))
48 %************************************************************************
52 %************************************************************************
55 tcLetPat :: (Name -> Maybe TcRhoType)
56 -> LPat Name -> BoxySigmaType
59 tcLetPat sig_fn pat pat_ty thing_inside
60 = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
61 pat_reft = emptyRefinement }
62 ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
64 -- Don't know how to deal with pattern-bound existentials yet
65 ; checkTc (null ex_tvs) (existentialExplode pat)
67 ; return (pat', res) }
70 tcLamPats :: [LPat Name] -- Patterns,
71 -> [BoxySigmaType] -- and their types
72 -> BoxyRhoType -- Result type,
73 -> ((Refinement, BoxyRhoType) -> TcM a) -- and the checker for the body
74 -> TcM ([LPat TcId], a)
76 -- This is the externally-callable wrapper function
77 -- Typecheck the patterns, extend the environment to bind the variables,
78 -- do the thing inside, use any existentially-bound dictionaries to
79 -- discharge parts of the returning LIE, and deal with pattern type
82 -- 1. Initialise the PatState
83 -- 2. Check the patterns
84 -- 3. Apply the refinement to the environment and result type
86 -- 5. Check that no existentials escape
88 tcLamPats pats tys res_ty thing_inside
89 = tc_lam_pats (zipEqual "tcLamPats" pats tys)
90 (emptyRefinement, res_ty) thing_inside
92 tcLamPat :: LPat Name -> BoxySigmaType
93 -> (Refinement,BoxyRhoType) -- Result type
94 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
96 tcLamPat pat pat_ty res_ty thing_inside
97 = do { ([pat'],thing) <- tc_lam_pats [(pat, pat_ty)] res_ty thing_inside
98 ; return (pat', thing) }
101 tc_lam_pats :: [(LPat Name,BoxySigmaType)]
102 -> (Refinement,BoxyRhoType) -- Result type
103 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
104 -> TcM ([LPat TcId], a)
105 tc_lam_pats pat_ty_prs (reft, res_ty) thing_inside
106 = do { let init_state = PS { pat_ctxt = LamPat, pat_reft = reft }
108 ; (pats', ex_tvs, res) <- tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
109 refineEnvironment (pat_reft pstate') $
110 thing_inside (pat_reft pstate', res_ty)
112 ; let tys = map snd pat_ty_prs
113 ; tcCheckExistentialPat pats' ex_tvs tys res_ty
115 ; returnM (pats', res) }
119 tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
120 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
121 -> [BoxySigmaType] -- Types of the patterns
122 -> BoxyRhoType -- Type of the body of the match
123 -- Tyvars in either of these must not escape
125 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
126 -- For example, we must reject this program:
127 -- data C = forall a. C (a -> Int)
129 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
131 tcCheckExistentialPat pats [] pat_tys body_ty
132 = return () -- Short cut for case when there are no existentials
134 tcCheckExistentialPat pats ex_tvs pat_tys body_ty
135 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys body_ty) $
136 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
140 pat_reft :: Refinement -- Binds rigid TcTyVars to their refinements
145 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
147 patSigCtxt :: PatState -> UserTypeCtxt
148 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
149 patSigCtxt other = LamPatSigCtxt
154 %************************************************************************
158 %************************************************************************
161 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
162 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
163 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
164 -- We have an undecorated binder, so we do rule ABS1,
165 -- by unboxing the boxy type, forcing any un-filled-in
166 -- boxes to become monotypes
167 -- NB that pat_ty' can still be a polytype:
168 -- data T = MkT (forall a. a->a)
169 -- f t = case t of { MkT g -> ... }
170 -- Here, the 'g' must get type (forall a. a->a) from the
172 ; return (Id.mkLocalId bndr_name pat_ty') }
174 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
175 | Just mono_ty <- lookup_sig bndr_name
176 = do { mono_name <- newLocalName bndr_name
177 ; boxyUnify mono_ty pat_ty
178 ; return (Id.mkLocalId mono_name mono_ty) }
181 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
182 ; mono_name <- newLocalName bndr_name
183 ; return (Id.mkLocalId mono_name pat_ty') }
187 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
188 bindInstsOfPatId id thing_inside
189 | not (isOverloadedTy (idType id))
190 = do { res <- thing_inside; return (res, emptyLHsBinds) }
192 = do { (res, lie) <- getLIE thing_inside
193 ; binds <- bindInstsOfLocalFuns lie [id]
194 ; return (res, binds) }
197 unBoxPatBndrType ty name = unBoxArgType ty (ptext SLIT("The variable") <+> quotes (ppr name))
198 unBoxWildCardType ty = unBoxArgType ty (ptext SLIT("A wild-card pattern"))
200 unBoxArgType :: BoxyType -> SDoc -> TcM TcType
201 -- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
202 -- that is, it can't be an unboxed tuple. For example,
203 -- case (f x) of r -> ...
204 -- should fail if 'f' returns an unboxed tuple.
205 unBoxArgType ty pp_this
206 = do { ty' <- unBox ty -- Returns a zonked type
208 -- Neither conditional is strictly necesssary (the unify alone will do)
209 -- but they improve error messages, and allocate fewer tyvars
210 ; if isUnboxedTupleType ty' then
212 else if isSubArgTypeKind (typeKind ty') then
214 else do -- OpenTypeKind, so constrain it
215 { ty2 <- newFlexiTyVarTy argTypeKind
219 msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
223 %************************************************************************
225 The main worker functions
227 %************************************************************************
231 tcPat takes a "thing inside" over which the patter scopes. This is partly
232 so that tcPat can extend the environment for the thing_inside, but also
233 so that constraints arising in the thing_inside can be discharged by the
236 This does not work so well for the ErrCtxt carried by the monad: we don't
237 want the error-context for the pattern to scope over the RHS.
238 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
242 type Checker inp out = forall r.
245 -> (PatState -> TcM r)
246 -> TcM (out, [TcTyVar], r)
248 tcMultiple :: Checker inp out -> Checker [inp] [out]
249 tcMultiple tc_pat args pstate thing_inside
250 = do { err_ctxt <- getErrCtxt
252 = do { res <- thing_inside pstate
253 ; return ([], [], res) }
255 loop pstate (arg:args)
256 = do { (p', p_tvs, (ps', ps_tvs, res))
257 <- tc_pat arg pstate $ \ pstate' ->
258 setErrCtxt err_ctxt $
260 -- setErrCtxt: restore context before doing the next pattern
261 -- See note [Nesting] above
263 ; return (p':ps', p_tvs ++ ps_tvs, res) }
268 tc_lpat_pr :: (LPat Name, BoxySigmaType)
270 -> (PatState -> TcM a)
271 -> TcM (LPat TcId, [TcTyVar], a)
272 tc_lpat_pr (pat, ty) = tc_lpat pat ty
277 -> (PatState -> TcM a)
278 -> TcM (LPat TcId, [TcTyVar], a)
279 tc_lpat (L span pat) pat_ty pstate thing_inside
281 maybeAddErrCtxt (patCtxt pat) $
282 do { let (coercion, pat_ty') = refineType (pat_reft pstate) pat_ty
283 -- Make sure the result type reflects the current refinement
284 -- We must do this here, so that it correctly ``sees'' all
285 -- the refinements to the left. Example:
286 -- Suppose C :: forall a. T a -> a -> Foo
287 -- Pattern C a p1 True
288 -- So p1 might refine 'a' to True, and the True
289 -- pattern had better see it.
291 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
292 ; return (mkCoPat coercion (L span pat') pat_ty, tvs, res) }
296 -> Pat Name -> BoxySigmaType -- Fully refined result type
297 -> (PatState -> TcM a) -- Thing inside
298 -> TcM (Pat TcId, -- Translated pattern
299 [TcTyVar], -- Existential binders
300 a) -- Result of thing inside
302 tc_pat pstate (VarPat name) pat_ty thing_inside
303 = do { id <- tcPatBndr pstate name pat_ty
304 ; (res, binds) <- bindInstsOfPatId id $
305 tcExtendIdEnv1 name id $
306 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
307 >> thing_inside pstate)
308 ; let pat' | isEmptyLHsBinds binds = VarPat id
309 | otherwise = VarPatOut id binds
310 ; return (pat', [], res) }
312 tc_pat pstate (ParPat pat) pat_ty thing_inside
313 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
314 ; return (ParPat pat', tvs, res) }
316 tc_pat pstate (BangPat pat) pat_ty thing_inside
317 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
318 ; return (BangPat pat', tvs, res) }
320 -- There's a wrinkle with irrefutable patterns, namely that we
321 -- must not propagate type refinement from them. For example
322 -- data T a where { T1 :: Int -> T Int; ... }
323 -- f :: T a -> Int -> a
325 -- It's obviously not sound to refine a to Int in the right
326 -- hand side, because the arugment might not match T1 at all!
328 -- Nor should a lazy pattern bind any existential type variables
329 -- because they won't be in scope when we do the desugaring
330 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
331 = do { (pat', pat_tvs, res) <- tc_lpat pat pat_ty pstate $ \ _ ->
333 -- Ignore refined pstate',
335 -- Check no existentials
336 ; if (null pat_tvs) then return ()
337 else lazyPatErr lpat pat_tvs
339 -- Check that the pattern has a lifted type
340 ; pat_tv <- newBoxyTyVar liftedTypeKind
341 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
343 ; return (LazyPat pat', [], res) }
345 tc_pat pstate (WildPat _) pat_ty thing_inside
346 = do { pat_ty' <- unBoxWildCardType pat_ty -- Make sure it's filled in with monotypes
347 ; res <- thing_inside pstate
348 ; return (WildPat pat_ty', [], res) }
350 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
351 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
352 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
353 tc_lpat pat (idType bndr_id) pstate thing_inside
354 -- NB: if we do inference on:
355 -- \ (y@(x::forall a. a->a)) = e
356 -- we'll fail. The as-pattern infers a monotype for 'y', which then
357 -- fails to unify with the polymorphic type for 'x'. This could
358 -- perhaps be fixed, but only with a bit more work.
360 -- If you fix it, don't forget the bindInstsOfPatIds!
361 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
363 -- Type signatures in patterns
364 -- See Note [Pattern coercions] below
365 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
366 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
367 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
368 tc_lpat pat inner_ty pstate thing_inside
369 ; return (SigPatOut pat' inner_ty, tvs, res) }
371 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
372 = failWithTc (badTypePat pat)
374 ------------------------
375 -- Lists, tuples, arrays
376 tc_pat pstate (ListPat pats _) pat_ty thing_inside
377 = do { elt_ty <- boxySplitListTy pat_ty
378 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
379 pats pstate thing_inside
380 ; return (ListPat pats' elt_ty, pats_tvs, res) }
382 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
383 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
384 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
385 pats pstate thing_inside
386 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
387 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
389 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
390 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
391 ; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
394 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
395 -- so that we can experiment with lazy tuple-matching.
396 -- This is a pretty odd place to make the switch, but
397 -- it was easy to do.
398 ; let unmangled_result = TuplePat pats' boxity pat_ty
399 possibly_mangled_result
400 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
401 | otherwise = unmangled_result
403 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
404 return (possibly_mangled_result, pats_tvs, res) }
406 ------------------------
408 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
409 = do { data_con <- tcLookupDataCon con_name
410 ; let tycon = dataConTyCon data_con
411 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
413 ------------------------
415 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
416 = do { boxyUnify (hsLitType simple_lit) pat_ty
417 ; res <- thing_inside pstate
418 ; returnM (LitPat simple_lit, [], res) }
420 ------------------------
421 -- Overloaded patterns: n, and n+k
422 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
423 = do { let orig = LiteralOrigin over_lit
424 ; lit' <- tcOverloadedLit orig over_lit pat_ty
425 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
426 ; mb_neg' <- case mb_neg of
427 Nothing -> return Nothing -- Positive literal
428 Just neg -> -- Negative literal
429 -- The 'negate' is re-mappable syntax
430 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
431 ; return (Just neg') }
432 ; res <- thing_inside pstate
433 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
435 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
436 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
437 ; let pat_ty' = idType bndr_id
438 orig = LiteralOrigin lit
439 ; lit' <- tcOverloadedLit orig lit pat_ty'
441 -- The '>=' and '-' parts are re-mappable syntax
442 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
443 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
445 -- The Report says that n+k patterns must be in Integral
446 -- We may not want this when using re-mappable syntax, though (ToDo?)
447 ; icls <- tcLookupClass integralClassName
448 ; instStupidTheta orig [mkClassPred icls [pat_ty']]
450 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
451 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
453 tc_pat _ _other_pat _ _ = panic "tc_pat" -- DictPat, ConPatOut, SigPatOut, VarPatOut
457 %************************************************************************
459 Most of the work for constructors is here
460 (the rest is in the ConPatIn case of tc_pat)
462 %************************************************************************
464 [Pattern matching indexed data types]
465 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
466 Consider the following declarations:
468 data family Map k :: * -> *
469 data instance Map (a, b) v = MapPair (Map a (Pair b v))
471 and a case expression
473 case x :: Map (Int, c) w of MapPair m -> ...
475 As explained by [Wrappers for data instance tycons] in MkIds.lhs, the
476 worker/wrapper types for MapPair are
478 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
479 $wMapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
481 So, the type of the scrutinee is Map (Int, c) w, but the tycon of MapPair is
482 :R123Map, which means the straight use of boxySplitTyConApp would give a type
483 error. Hence, the smart wrapper function boxySplitTyConAppWithFamily calls
484 boxySplitTyConApp with the family tycon Map instead, which gives us the family
485 type list {(Int, c), w}. To get the correct split for :R123Map, we need to
486 unify the family type list {(Int, c), w} with the instance types {(a, b), v}
487 (provided by tyConFamInst_maybe together with the family tycon). This
488 unification yields the substitution [a -> Int, b -> c, v -> w], which gives us
489 the split arguments for the representation tycon :R123Map as {Int, c, w}
491 In other words, boxySplitTyConAppWithFamily implicitly takes the coercion
493 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
495 moving between representation and family type into account. To produce type
496 correct Core, this coercion needs to be used to case the type of the scrutinee
497 from the family to the representation type. This is achieved by
498 unwrapFamInstScrutinee using a CoPat around the result pattern.
500 Now it might appear seem as if we could have used the existing GADT type
501 refinement infrastructure of refineAlt and friends instead of the explicit
502 unification and CoPat generation. However, that would be wrong. Why? The
503 whole point of GADT refinement is that the refinement is local to the case
504 alternative. In contrast, the substitution generated by the unification of
505 the family type list and instance types needs to be propagated to the outside.
506 Imagine that in the above example, the type of the scrutinee would have been
507 (Map x w), then we would have unified {x, w} with {(a, b), v}, yielding the
508 substitution [x -> (a, b), v -> w]. In contrast to GADT matching, the
509 instantiation of x with (a, b) must be global; ie, it must be valid in *all*
510 alternatives of the case expression, whereas in the GADT case it might vary
511 between alternatives.
513 In fact, if we have a data instance declaration defining a GADT, eq_spec will
514 be non-empty and we will get a mixture of global instantiations and local
515 refinement from a single match. This neatly reflects that, as soon as we
516 have constrained the type of the scrutinee to the required type index, all
517 further type refinement is local to the alternative.
521 -- MkT :: forall a b c. (a:=:[b]) => b -> c -> T a
522 -- with scrutinee of type (T ty)
524 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
525 -> BoxySigmaType -- Type of the pattern
526 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
527 -> TcM (Pat TcId, [TcTyVar], a)
528 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
529 = do { span <- getSrcSpanM -- Span for the whole pattern
530 ; let (univ_tvs, ex_tvs, eq_spec, theta, arg_tys) = dataConFullSig data_con
531 skol_info = PatSkol data_con span
532 origin = SigOrigin skol_info
534 -- Instantiate the constructor type variables [a->ty]
535 ; ctxt_res_tys <- boxySplitTyConAppWithFamily tycon pat_ty
536 ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs
537 ; let tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
538 (ctxt_res_tys ++ mkTyVarTys ex_tvs')
539 eq_spec' = substEqSpec tenv eq_spec
540 theta' = substTheta tenv theta
541 arg_tys' = substTys tenv arg_tys
543 ; co_vars <- newCoVars eq_spec' -- Make coercion variables
544 ; pstate' <- refineAlt data_con pstate ex_tvs' co_vars pat_ty
546 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
547 tcConArgs data_con arg_tys' arg_pats pstate' thing_inside
549 ; loc <- getInstLoc origin
550 ; dicts <- newDictBndrs loc theta'
551 ; dict_binds <- tcSimplifyCheck doc ex_tvs' dicts lie_req
553 ; addDataConStupidTheta data_con ctxt_res_tys
556 (unwrapFamInstScrutinee tycon ctxt_res_tys $
557 ConPatOut { pat_con = L con_span data_con,
558 pat_tvs = ex_tvs' ++ co_vars,
559 pat_dicts = map instToId dicts,
560 pat_binds = dict_binds,
561 pat_args = arg_pats', pat_ty = pat_ty },
562 ex_tvs' ++ inner_tvs, res)
565 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
567 -- Split against the family tycon if the pattern constructor belongs to a
568 -- representation tycon.
570 boxySplitTyConAppWithFamily tycon pat_ty =
572 case tyConFamInst_maybe tycon of
573 Nothing -> boxySplitTyConApp tycon pat_ty
574 Just (fam_tycon, instTys) ->
575 do { scrutinee_arg_tys <- boxySplitTyConApp fam_tycon pat_ty
576 ; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
577 ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
581 traceMsg = sep [ text "tcConPat:boxySplitTyConAppWithFamily:" <+>
582 ppr tycon <+> ppr pat_ty
583 , text " family instance:" <+>
584 ppr (tyConFamInst_maybe tycon)
587 -- Wraps the pattern (which must be a ConPatOut pattern) in a coercion
588 -- pattern if the tycon is an instance of a family.
590 unwrapFamInstScrutinee :: TyCon -> [Type] -> Pat Id -> Pat Id
591 unwrapFamInstScrutinee tycon args pat
592 | Just co_con <- tyConFamilyCoercion_maybe tycon
593 -- , not (isNewTyCon tycon) -- newtypes are explicitly unwrapped by
595 -- NB: We can use CoPat directly, rather than mkCoPat, as we know the
596 -- coercion is not the identity; mkCoPat is inconvenient as it
597 -- wants a located pattern.
598 = CoPat (WpCo $ mkTyConApp co_con args) -- co fam ty to repr ty
599 (pat {pat_ty = mkTyConApp tycon args}) -- representation type
600 pat_ty -- family inst type
605 tcConArgs :: DataCon -> [TcSigmaType]
606 -> Checker (HsConDetails Name (LPat Name))
607 (HsConDetails Id (LPat Id))
609 tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
610 = do { checkTc (con_arity == no_of_args) -- Check correct arity
611 (arityErr "Constructor" data_con con_arity no_of_args)
612 ; let pats_w_tys = zipEqual "tcConArgs" arg_pats arg_tys
613 ; (arg_pats', tvs, res) <- tcMultiple tcConArg pats_w_tys
615 ; return (PrefixCon arg_pats', tvs, res) }
617 con_arity = dataConSourceArity data_con
618 no_of_args = length arg_pats
620 tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
621 = do { checkTc (con_arity == 2) -- Check correct arity
622 (arityErr "Constructor" data_con con_arity 2)
623 ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
625 ; return (InfixCon p1' p2', tvs, res) }
627 con_arity = dataConSourceArity data_con
629 tcConArgs data_con other_args (InfixCon p1 p2) pstate thing_inside
630 = pprPanic "tcConArgs" (ppr data_con) -- InfixCon always has two arguments
632 tcConArgs data_con arg_tys (RecCon rpats) pstate thing_inside
633 = do { (rpats', tvs, res) <- tcMultiple tc_field rpats pstate thing_inside
634 ; return (RecCon rpats', tvs, res) }
636 -- doc comments are typechecked to Nothing here
637 tc_field :: Checker (HsRecField FieldLabel (LPat Name)) (HsRecField TcId (LPat TcId))
638 tc_field (HsRecField field_lbl pat _) pstate thing_inside
639 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
640 ; (pat', tvs, res) <- tcConArg (pat, pat_ty) pstate thing_inside
641 ; return (mkRecField sel_id pat', tvs, res) }
643 find_field_ty :: FieldLabel -> TcM (Id, TcType)
644 find_field_ty field_lbl
645 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
647 -- No matching field; chances are this field label comes from some
648 -- other record type (or maybe none). As well as reporting an
649 -- error we still want to typecheck the pattern, principally to
650 -- make sure that all the variables it binds are put into the
651 -- environment, else the type checker crashes later:
652 -- f (R { foo = (a,b) }) = a+b
653 -- If foo isn't one of R's fields, we don't want to crash when
654 -- typechecking the "a+b".
655 [] -> do { addErrTc (badFieldCon data_con field_lbl)
656 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
657 ; return (error "Bogus selector Id", bogus_ty) }
659 -- The normal case, when the field comes from the right constructor
661 ASSERT( null extras )
662 do { sel_id <- tcLookupField field_lbl
663 ; return (sel_id, pat_ty) }
665 field_tys :: [(FieldLabel, TcType)]
666 field_tys = zip (dataConFieldLabels data_con) arg_tys
667 -- Don't use zipEqual! If the constructor isn't really a record, then
668 -- dataConFieldLabels will be empty (and each field in the pattern
669 -- will generate an error below).
671 tcConArg :: Checker (LPat Name, BoxySigmaType) (LPat Id)
672 tcConArg (arg_pat, arg_ty) pstate thing_inside
673 = tc_lpat arg_pat arg_ty pstate thing_inside
674 -- NB: the tc_lpat will refine pat_ty if necessary
675 -- based on the current pstate, which may include
676 -- refinements from peer argument patterns to the left
680 addDataConStupidTheta :: DataCon -> [TcType] -> TcM ()
681 -- Instantiate the "stupid theta" of the data con, and throw
682 -- the constraints into the constraint set
683 addDataConStupidTheta data_con inst_tys
684 | null stupid_theta = return ()
685 | otherwise = instStupidTheta origin inst_theta
687 origin = OccurrenceOf (dataConName data_con)
688 -- The origin should always report "occurrence of C"
689 -- even when C occurs in a pattern
690 stupid_theta = dataConStupidTheta data_con
691 tenv = zipTopTvSubst (dataConUnivTyVars data_con) inst_tys
692 inst_theta = substTheta tenv stupid_theta
696 %************************************************************************
700 %************************************************************************
703 refineAlt :: DataCon -- For tracing only
705 -> [TcTyVar] -- Existentials
706 -> [CoVar] -- Equational constraints
707 -> BoxySigmaType -- Pattern type
710 refineAlt con pstate ex_tvs [] pat_ty
711 = return pstate -- Common case: no equational constraints
713 refineAlt con pstate ex_tvs co_vars pat_ty
714 | not (isRigidTy pat_ty)
715 = failWithTc (nonRigidMatch con)
716 -- We are matching against a GADT constructor with non-trivial
717 -- constraints, but pattern type is wobbly. For now we fail.
718 -- We can make sense of this, however:
719 -- Suppose MkT :: forall a b. (a:=:[b]) => b -> T a
720 -- (\x -> case x of { MkT v -> v })
721 -- We can infer that x must have type T [c], for some wobbly 'c'
723 -- (\(x::T [c]) -> case x of
724 -- MkT b (g::([c]:=:[b])) (v::b) -> v `cast` sym g
725 -- To implement this, we'd first instantiate the equational
726 -- constraints with *wobbly* type variables for the existentials;
727 -- then unify these constraints to make pat_ty the right shape;
728 -- then proceed exactly as in the rigid case
730 | otherwise -- In the rigid case, we perform type refinement
731 = case gadtRefine (pat_reft pstate) ex_tvs co_vars of {
732 Failed msg -> failWithTc (inaccessibleAlt msg) ;
733 Succeeded reft -> do { traceTc trace_msg
734 ; return (pstate { pat_reft = reft }) }
735 -- DO NOT refine the envt right away, because we
736 -- might be inside a lazy pattern. Instead, refine pstate
739 trace_msg = text "refineAlt:match" <+>
740 vcat [ ppr con <+> ppr ex_tvs,
741 ppr [(v, tyVarKind v) | v <- co_vars],
747 %************************************************************************
751 %************************************************************************
753 In tcOverloadedLit we convert directly to an Int or Integer if we
754 know that's what we want. This may save some time, by not
755 temporarily generating overloaded literals, but it won't catch all
756 cases (the rest are caught in lookupInst).
759 tcOverloadedLit :: InstOrigin
762 -> TcM (HsOverLit TcId)
763 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
764 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
765 -- Reason: If we do, tcSimplify will call lookupInst, which
766 -- will call tcSyntaxName, which does unification,
767 -- which tcSimplify doesn't like
768 -- ToDo: noLoc sadness
769 = do { integer_ty <- tcMetaTy integerTyConName
770 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
771 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
773 | Just expr <- shortCutIntLit i res_ty
774 = return (HsIntegral i expr)
777 = do { expr <- newLitInst orig lit res_ty
778 ; return (HsIntegral i expr) }
780 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
781 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
782 = do { rat_ty <- tcMetaTy rationalTyConName
783 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
784 -- Overloaded literals must have liftedTypeKind, because
785 -- we're instantiating an overloaded function here,
786 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
787 -- However this'll be picked up by tcSyntaxOp if necessary
788 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
790 | Just expr <- shortCutFracLit r res_ty
791 = return (HsFractional r expr)
794 = do { expr <- newLitInst orig lit res_ty
795 ; return (HsFractional r expr) }
797 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
798 newLitInst orig lit res_ty -- Make a LitInst
799 = do { loc <- getInstLoc orig
800 ; res_tau <- zapToMonotype res_ty
801 ; new_uniq <- newUnique
802 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
803 lit_inst = LitInst {tci_name = lit_nm, tci_lit = lit,
804 tci_ty = res_tau, tci_loc = loc}
806 ; return (HsVar (instToId lit_inst)) }
810 %************************************************************************
812 Note [Pattern coercions]
814 %************************************************************************
816 In principle, these program would be reasonable:
818 f :: (forall a. a->a) -> Int
819 f (x :: Int->Int) = x 3
821 g :: (forall a. [a]) -> Bool
824 In both cases, the function type signature restricts what arguments can be passed
825 in a call (to polymorphic ones). The pattern type signature then instantiates this
826 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
827 generate the translated term
828 f = \x' :: (forall a. a->a). let x = x' Int in x 3
830 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
831 And it requires a significant amount of code to implement, becuase we need to decorate
832 the translated pattern with coercion functions (generated from the subsumption check
835 So for now I'm just insisting on type *equality* in patterns. No subsumption.
837 Old notes about desugaring, at a time when pattern coercions were handled:
839 A SigPat is a type coercion and must be handled one at at time. We can't
840 combine them unless the type of the pattern inside is identical, and we don't
841 bother to check for that. For example:
843 data T = T1 Int | T2 Bool
844 f :: (forall a. a -> a) -> T -> t
845 f (g::Int->Int) (T1 i) = T1 (g i)
846 f (g::Bool->Bool) (T2 b) = T2 (g b)
848 We desugar this as follows:
850 f = \ g::(forall a. a->a) t::T ->
852 in case t of { T1 i -> T1 (gi i)
855 in case t of { T2 b -> T2 (gb b)
858 Note that we do not treat the first column of patterns as a
859 column of variables, because the coerced variables (gi, gb)
860 would be of different types. So we get rather grotty code.
861 But I don't think this is a common case, and if it was we could
862 doubtless improve it.
864 Meanwhile, the strategy is:
865 * treat each SigPat coercion (always non-identity coercions)
867 * deal with the stuff inside, and then wrap a binding round
868 the result to bind the new variable (gi, gb, etc)
871 %************************************************************************
873 \subsection{Errors and contexts}
875 %************************************************************************
878 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
879 patCtxt (VarPat _) = Nothing
880 patCtxt (ParPat _) = Nothing
881 patCtxt (AsPat _ _) = Nothing
882 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
885 -----------------------------------------------
887 existentialExplode pat
888 = hang (vcat [text "My brain just exploded.",
889 text "I can't handle pattern bindings for existentially-quantified constructors.",
890 text "In the binding group for"])
893 sigPatCtxt bound_ids bound_tvs pat_tys body_ty tidy_env
894 = do { pat_tys' <- mapM zonkTcType pat_tys
895 ; body_ty' <- zonkTcType body_ty
896 ; let (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
897 (env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
898 (env3, tidy_body_ty) = tidyOpenType env2 body_ty'
900 sep [ptext SLIT("When checking an existential match that binds"),
901 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
902 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
903 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
906 show_ids = filter is_interesting bound_ids
907 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
909 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
910 -- Don't zonk the types so we get the separate, un-unified versions
912 badFieldCon :: DataCon -> Name -> SDoc
913 badFieldCon con field
914 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
915 ptext SLIT("does not have field"), quotes (ppr field)]
917 polyPatSig :: TcType -> SDoc
919 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
922 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
926 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
927 2 (vcat (map pprSkolTvBinding tvs))
930 = hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
931 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
934 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg