2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 TcPat: Typechecking patterns
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module TcPat ( tcLetPat, tcLamPat, tcLamPats, tcOverloadedLit,
17 addDataConStupidTheta, badFieldCon, polyPatSig ) where
19 #include "HsVersions.h"
21 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
47 import BasicTypes hiding (SuccessFlag(..))
57 %************************************************************************
61 %************************************************************************
64 tcLetPat :: (Name -> Maybe TcRhoType)
65 -> LPat Name -> BoxySigmaType
68 tcLetPat sig_fn pat pat_ty thing_inside
69 = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
70 pat_reft = emptyRefinement,
72 ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
74 -- Don't know how to deal with pattern-bound existentials yet
75 ; checkTc (null ex_tvs) (existentialExplode pat)
77 ; return (pat', res) }
80 tcLamPats :: [LPat Name] -- Patterns,
81 -> [BoxySigmaType] -- and their types
82 -> BoxyRhoType -- Result type,
83 -> ((Refinement, BoxyRhoType) -> TcM a) -- and the checker for the body
84 -> TcM ([LPat TcId], a)
86 -- This is the externally-callable wrapper function
87 -- Typecheck the patterns, extend the environment to bind the variables,
88 -- do the thing inside, use any existentially-bound dictionaries to
89 -- discharge parts of the returning LIE, and deal with pattern type
92 -- 1. Initialise the PatState
93 -- 2. Check the patterns
94 -- 3. Apply the refinement to the environment and result type
96 -- 5. Check that no existentials escape
98 tcLamPats pats tys res_ty thing_inside
99 = tc_lam_pats (zipEqual "tcLamPats" pats tys)
100 (emptyRefinement, res_ty) thing_inside
102 tcLamPat :: LPat Name -> BoxySigmaType
103 -> (Refinement,BoxyRhoType) -- Result type
104 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
105 -> TcM (LPat TcId, a)
106 tcLamPat pat pat_ty res_ty thing_inside
107 = do { ([pat'],thing) <- tc_lam_pats [(pat, pat_ty)] res_ty thing_inside
108 ; return (pat', thing) }
111 tc_lam_pats :: [(LPat Name,BoxySigmaType)]
112 -> (Refinement,BoxyRhoType) -- Result type
113 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
114 -> TcM ([LPat TcId], a)
115 tc_lam_pats pat_ty_prs (reft, res_ty) thing_inside
116 = do { let init_state = PS { pat_ctxt = LamPat, pat_reft = reft, pat_eqs = False }
118 ; (pats', ex_tvs, res) <- tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
119 refineEnvironment (pat_reft pstate') (pat_eqs pstate') $
120 if (pat_eqs pstate' && (not $ isRigidTy res_ty))
121 then failWithTc (nonRigidResult res_ty)
122 else thing_inside (pat_reft pstate', res_ty)
124 ; let tys = map snd pat_ty_prs
125 ; tcCheckExistentialPat pats' ex_tvs tys res_ty
127 ; returnM (pats', res) }
131 tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
132 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
133 -> [BoxySigmaType] -- Types of the patterns
134 -> BoxyRhoType -- Type of the body of the match
135 -- Tyvars in either of these must not escape
137 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
138 -- For example, we must reject this program:
139 -- data C = forall a. C (a -> Int)
141 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
143 tcCheckExistentialPat pats [] pat_tys body_ty
144 = return () -- Short cut for case when there are no existentials
146 tcCheckExistentialPat pats ex_tvs pat_tys body_ty
147 = addErrCtxtM (sigPatCtxt pats ex_tvs pat_tys body_ty) $
148 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
152 pat_reft :: Refinement, -- Binds rigid TcTyVars to their refinements
153 pat_eqs :: Bool -- <=> there are GADT equational constraints
159 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
161 patSigCtxt :: PatState -> UserTypeCtxt
162 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
163 patSigCtxt other = LamPatSigCtxt
168 %************************************************************************
172 %************************************************************************
175 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
176 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
177 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
178 -- We have an undecorated binder, so we do rule ABS1,
179 -- by unboxing the boxy type, forcing any un-filled-in
180 -- boxes to become monotypes
181 -- NB that pat_ty' can still be a polytype:
182 -- data T = MkT (forall a. a->a)
183 -- f t = case t of { MkT g -> ... }
184 -- Here, the 'g' must get type (forall a. a->a) from the
186 ; return (Id.mkLocalId bndr_name pat_ty') }
188 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
189 | Just mono_ty <- lookup_sig bndr_name
190 = do { mono_name <- newLocalName bndr_name
191 ; boxyUnify mono_ty pat_ty
192 ; return (Id.mkLocalId mono_name mono_ty) }
195 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
196 ; mono_name <- newLocalName bndr_name
197 ; return (Id.mkLocalId mono_name pat_ty') }
201 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
202 bindInstsOfPatId id thing_inside
203 | not (isOverloadedTy (idType id))
204 = do { res <- thing_inside; return (res, emptyLHsBinds) }
206 = do { (res, lie) <- getLIE thing_inside
207 ; binds <- bindInstsOfLocalFuns lie [id]
208 ; return (res, binds) }
211 unBoxPatBndrType ty name = unBoxArgType ty (ptext SLIT("The variable") <+> quotes (ppr name))
212 unBoxWildCardType ty = unBoxArgType ty (ptext SLIT("A wild-card pattern"))
214 unBoxArgType :: BoxyType -> SDoc -> TcM TcType
215 -- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
216 -- that is, it can't be an unboxed tuple. For example,
217 -- case (f x) of r -> ...
218 -- should fail if 'f' returns an unboxed tuple.
219 unBoxArgType ty pp_this
220 = do { ty' <- unBox ty -- Returns a zonked type
222 -- Neither conditional is strictly necesssary (the unify alone will do)
223 -- but they improve error messages, and allocate fewer tyvars
224 ; if isUnboxedTupleType ty' then
226 else if isSubArgTypeKind (typeKind ty') then
228 else do -- OpenTypeKind, so constrain it
229 { ty2 <- newFlexiTyVarTy argTypeKind
233 msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
237 %************************************************************************
239 The main worker functions
241 %************************************************************************
245 tcPat takes a "thing inside" over which the pattern scopes. This is partly
246 so that tcPat can extend the environment for the thing_inside, but also
247 so that constraints arising in the thing_inside can be discharged by the
250 This does not work so well for the ErrCtxt carried by the monad: we don't
251 want the error-context for the pattern to scope over the RHS.
252 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
256 type Checker inp out = forall r.
259 -> (PatState -> TcM r)
260 -> TcM (out, [TcTyVar], r)
262 tcMultiple :: Checker inp out -> Checker [inp] [out]
263 tcMultiple tc_pat args pstate thing_inside
264 = do { err_ctxt <- getErrCtxt
266 = do { res <- thing_inside pstate
267 ; return ([], [], res) }
269 loop pstate (arg:args)
270 = do { (p', p_tvs, (ps', ps_tvs, res))
271 <- tc_pat arg pstate $ \ pstate' ->
272 setErrCtxt err_ctxt $
274 -- setErrCtxt: restore context before doing the next pattern
275 -- See note [Nesting] above
277 ; return (p':ps', p_tvs ++ ps_tvs, res) }
282 tc_lpat_pr :: (LPat Name, BoxySigmaType)
284 -> (PatState -> TcM a)
285 -> TcM (LPat TcId, [TcTyVar], a)
286 tc_lpat_pr (pat, ty) = tc_lpat pat ty
291 -> (PatState -> TcM a)
292 -> TcM (LPat TcId, [TcTyVar], a)
293 tc_lpat (L span pat) pat_ty pstate thing_inside
295 maybeAddErrCtxt (patCtxt pat) $
296 do { let mb_reft = refineType (pat_reft pstate) pat_ty
297 pat_ty' = case mb_reft of { Just (_, ty') -> ty'; Nothing -> pat_ty }
299 -- Make sure the result type reflects the current refinement
300 -- We must do this here, so that it correctly ``sees'' all
301 -- the refinements to the left. Example:
302 -- Suppose C :: forall a. T a -> a -> Foo
303 -- Pattern C a p1 True
304 -- So p1 might refine 'a' to True, and the True
305 -- pattern had better see it.
307 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
308 ; let final_pat = case mb_reft of
310 Just (co,_) -> CoPat (WpCo co) pat' pat_ty
311 ; return (L span final_pat, tvs, res) }
315 -> Pat Name -> BoxySigmaType -- Fully refined result type
316 -> (PatState -> TcM a) -- Thing inside
317 -> TcM (Pat TcId, -- Translated pattern
318 [TcTyVar], -- Existential binders
319 a) -- Result of thing inside
321 tc_pat pstate (VarPat name) pat_ty thing_inside
322 = do { id <- tcPatBndr pstate name pat_ty
323 ; (res, binds) <- bindInstsOfPatId id $
324 tcExtendIdEnv1 name id $
325 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
326 >> thing_inside pstate)
327 ; let pat' | isEmptyLHsBinds binds = VarPat id
328 | otherwise = VarPatOut id binds
329 ; return (pat', [], res) }
331 tc_pat pstate (ParPat pat) pat_ty thing_inside
332 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
333 ; return (ParPat pat', tvs, res) }
335 tc_pat pstate (BangPat pat) pat_ty thing_inside
336 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
337 ; return (BangPat pat', tvs, res) }
339 -- There's a wrinkle with irrefutable patterns, namely that we
340 -- must not propagate type refinement from them. For example
341 -- data T a where { T1 :: Int -> T Int; ... }
342 -- f :: T a -> Int -> a
344 -- It's obviously not sound to refine a to Int in the right
345 -- hand side, because the arugment might not match T1 at all!
347 -- Nor should a lazy pattern bind any existential type variables
348 -- because they won't be in scope when we do the desugaring
350 -- Note [Hopping the LIE in lazy patterns]
351 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
352 -- In a lazy pattern, we must *not* discharge constraints from the RHS
353 -- from dictionaries bound in the pattern. E.g.
355 -- We can't discharge the Num constraint from dictionaries bound by
358 -- So we have to make the constraints from thing_inside "hop around"
359 -- the pattern. Hence the getLLE and extendLIEs later.
361 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
362 = do { (pat', pat_tvs, (res,lie))
363 <- tc_lpat pat pat_ty pstate $ \ _ ->
364 getLIE (thing_inside pstate)
365 -- Ignore refined pstate', revert to pstate
367 -- getLIE/extendLIEs: see Note [Hopping the LIE in lazy patterns]
369 -- Check no existentials
370 ; if (null pat_tvs) then return ()
371 else lazyPatErr lpat pat_tvs
373 -- Check that the pattern has a lifted type
374 ; pat_tv <- newBoxyTyVar liftedTypeKind
375 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
377 ; return (LazyPat pat', [], res) }
379 tc_pat pstate (WildPat _) pat_ty thing_inside
380 = do { pat_ty' <- unBoxWildCardType pat_ty -- Make sure it's filled in with monotypes
381 ; res <- thing_inside pstate
382 ; return (WildPat pat_ty', [], res) }
384 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
385 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
386 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
387 tc_lpat pat (idType bndr_id) pstate thing_inside
388 -- NB: if we do inference on:
389 -- \ (y@(x::forall a. a->a)) = e
390 -- we'll fail. The as-pattern infers a monotype for 'y', which then
391 -- fails to unify with the polymorphic type for 'x'. This could
392 -- perhaps be fixed, but only with a bit more work.
394 -- If you fix it, don't forget the bindInstsOfPatIds!
395 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
397 -- Type signatures in patterns
398 -- See Note [Pattern coercions] below
399 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
400 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
401 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
402 tc_lpat pat inner_ty pstate thing_inside
403 ; return (SigPatOut pat' inner_ty, tvs, res) }
405 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
406 = failWithTc (badTypePat pat)
408 ------------------------
409 -- Lists, tuples, arrays
410 tc_pat pstate (ListPat pats _) pat_ty thing_inside
411 = do { (elt_ty, coi) <- boxySplitListTy pat_ty
412 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
413 pats pstate thing_inside
414 ; return (mkCoPatCoI coi (ListPat pats' elt_ty) pat_ty, pats_tvs, res) }
416 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
417 = do { (elt_ty, coi) <- boxySplitPArrTy pat_ty
418 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
419 pats pstate thing_inside
420 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
421 ; return (mkCoPatCoI coi (PArrPat pats' elt_ty) pat_ty, pats_tvs, res) }
423 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
424 = do { let tc = tupleTyCon boxity (length pats)
425 ; (arg_tys, coi) <- boxySplitTyConApp tc pat_ty
426 ; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
429 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
430 -- so that we can experiment with lazy tuple-matching.
431 -- This is a pretty odd place to make the switch, but
432 -- it was easy to do.
433 ; let pat_ty' = mkTyConApp tc arg_tys
434 -- pat_ty /= pat_ty iff coi /= IdCo
435 unmangled_result = TuplePat pats' boxity pat_ty'
436 possibly_mangled_result
437 | opt_IrrefutableTuples &&
438 isBoxed boxity = LazyPat (noLoc unmangled_result)
439 | otherwise = unmangled_result
441 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
442 return (mkCoPatCoI coi possibly_mangled_result pat_ty, pats_tvs, res)
445 ------------------------
447 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
448 = do { data_con <- tcLookupDataCon con_name
449 ; let tycon = dataConTyCon data_con
450 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
452 ------------------------
454 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
455 = do { let lit_ty = hsLitType simple_lit
456 ; coi <- boxyUnify lit_ty pat_ty
457 -- coi is of kind: lit_ty ~ pat_ty
458 ; res <- thing_inside pstate
459 ; span <- getSrcSpanM
460 -- pattern coercions have to
461 -- be of kind: pat_ty ~ lit_ty
463 ; returnM (mkCoPatCoI (mkSymCoI coi) (LitPat simple_lit) pat_ty,
466 ------------------------
467 -- Overloaded patterns: n, and n+k
468 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
469 = do { let orig = LiteralOrigin over_lit
470 ; lit' <- tcOverloadedLit orig over_lit pat_ty
471 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
472 ; mb_neg' <- case mb_neg of
473 Nothing -> return Nothing -- Positive literal
474 Just neg -> -- Negative literal
475 -- The 'negate' is re-mappable syntax
476 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
477 ; return (Just neg') }
478 ; res <- thing_inside pstate
479 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
481 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
482 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
483 ; let pat_ty' = idType bndr_id
484 orig = LiteralOrigin lit
485 ; lit' <- tcOverloadedLit orig lit pat_ty'
487 -- The '>=' and '-' parts are re-mappable syntax
488 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
489 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
491 -- The Report says that n+k patterns must be in Integral
492 -- We may not want this when using re-mappable syntax, though (ToDo?)
493 ; icls <- tcLookupClass integralClassName
494 ; instStupidTheta orig [mkClassPred icls [pat_ty']]
496 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
497 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
499 tc_pat _ _other_pat _ _ = panic "tc_pat" -- ConPatOut, SigPatOut, VarPatOut
503 %************************************************************************
505 Most of the work for constructors is here
506 (the rest is in the ConPatIn case of tc_pat)
508 %************************************************************************
510 [Pattern matching indexed data types]
511 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
512 Consider the following declarations:
514 data family Map k :: * -> *
515 data instance Map (a, b) v = MapPair (Map a (Pair b v))
517 and a case expression
519 case x :: Map (Int, c) w of MapPair m -> ...
521 As explained by [Wrappers for data instance tycons] in MkIds.lhs, the
522 worker/wrapper types for MapPair are
524 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
525 $wMapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
527 So, the type of the scrutinee is Map (Int, c) w, but the tycon of MapPair is
528 :R123Map, which means the straight use of boxySplitTyConApp would give a type
529 error. Hence, the smart wrapper function boxySplitTyConAppWithFamily calls
530 boxySplitTyConApp with the family tycon Map instead, which gives us the family
531 type list {(Int, c), w}. To get the correct split for :R123Map, we need to
532 unify the family type list {(Int, c), w} with the instance types {(a, b), v}
533 (provided by tyConFamInst_maybe together with the family tycon). This
534 unification yields the substitution [a -> Int, b -> c, v -> w], which gives us
535 the split arguments for the representation tycon :R123Map as {Int, c, w}
537 In other words, boxySplitTyConAppWithFamily implicitly takes the coercion
539 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
541 moving between representation and family type into account. To produce type
542 correct Core, this coercion needs to be used to case the type of the scrutinee
543 from the family to the representation type. This is achieved by
544 unwrapFamInstScrutinee using a CoPat around the result pattern.
546 Now it might appear seem as if we could have used the existing GADT type
547 refinement infrastructure of refineAlt and friends instead of the explicit
548 unification and CoPat generation. However, that would be wrong. Why? The
549 whole point of GADT refinement is that the refinement is local to the case
550 alternative. In contrast, the substitution generated by the unification of
551 the family type list and instance types needs to be propagated to the outside.
552 Imagine that in the above example, the type of the scrutinee would have been
553 (Map x w), then we would have unified {x, w} with {(a, b), v}, yielding the
554 substitution [x -> (a, b), v -> w]. In contrast to GADT matching, the
555 instantiation of x with (a, b) must be global; ie, it must be valid in *all*
556 alternatives of the case expression, whereas in the GADT case it might vary
557 between alternatives.
559 In fact, if we have a data instance declaration defining a GADT, eq_spec will
560 be non-empty and we will get a mixture of global instantiations and local
561 refinement from a single match. This neatly reflects that, as soon as we
562 have constrained the type of the scrutinee to the required type index, all
563 further type refinement is local to the alternative.
567 -- MkT :: forall a b c. (a:=:[b]) => b -> c -> T a
568 -- with scrutinee of type (T ty)
570 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
571 -> BoxySigmaType -- Type of the pattern
572 -> HsConPatDetails Name -> (PatState -> TcM a)
573 -> TcM (Pat TcId, [TcTyVar], a)
574 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
575 = do { let (univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _) = dataConFullSig data_con
576 skol_info = PatSkol data_con
577 origin = SigOrigin skol_info
579 -- Instantiate the constructor type variables [a->ty]
580 ; (ctxt_res_tys, coi) <- boxySplitTyConAppWithFamily tycon pat_ty
581 ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs -- Get location from monad,
583 ; let tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
584 (ctxt_res_tys ++ mkTyVarTys ex_tvs')
585 eq_spec' = substEqSpec tenv eq_spec
586 theta' = substTheta tenv (eq_theta ++ dict_theta)
587 arg_tys' = substTys tenv arg_tys
589 ; co_vars <- newCoVars eq_spec' -- Make coercion variables
590 ; traceTc (text "tcConPat: refineAlt")
591 ; pstate' <- refineAlt data_con pstate ex_tvs' co_vars pat_ty
592 ; traceTc (text "tcConPat: refineAlt done!")
594 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
595 tcConArgs data_con arg_tys' arg_pats pstate' thing_inside
597 ; loc <- getInstLoc origin
598 ; dicts <- newDictBndrs loc theta'
599 ; dict_binds <- tcSimplifyCheckPat loc co_vars (pat_reft pstate')
600 ex_tvs' dicts lie_req
602 ; addDataConStupidTheta data_con ctxt_res_tys
604 ; let pat_ty' = mkTyConApp tycon ctxt_res_tys
605 -- pat_ty /= pat_ty iff coi /= IdCo
606 res_pat = ConPatOut { pat_con = L con_span data_con,
607 pat_tvs = ex_tvs' ++ co_vars,
608 pat_dicts = map instToVar dicts,
609 pat_binds = dict_binds,
610 pat_args = arg_pats', pat_ty = pat_ty' }
613 (unwrapFamInstScrutinee tycon ctxt_res_tys res_pat) pat_ty,
614 ex_tvs' ++ inner_tvs, res)
617 -- Split against the family tycon if the pattern constructor
618 -- belongs to a family instance tycon.
619 boxySplitTyConAppWithFamily tycon pat_ty =
621 case tyConFamInst_maybe tycon of
622 Nothing -> boxySplitTyConApp tycon pat_ty
623 Just (fam_tycon, instTys) ->
624 do { (scrutinee_arg_tys, coi) <- boxySplitTyConApp fam_tycon pat_ty
625 ; (_, freshTvs, subst) <- tcInstTyVars (tyConTyVars tycon)
626 ; boxyUnifyList (substTys subst instTys) scrutinee_arg_tys
627 ; return (freshTvs, coi)
630 traceMsg = sep [ text "tcConPat:boxySplitTyConAppWithFamily:" <+>
631 ppr tycon <+> ppr pat_ty
632 , text " family instance:" <+>
633 ppr (tyConFamInst_maybe tycon)
636 -- Wraps the pattern (which must be a ConPatOut pattern) in a coercion
637 -- pattern if the tycon is an instance of a family.
639 unwrapFamInstScrutinee :: TyCon -> [Type] -> Pat Id -> Pat Id
640 unwrapFamInstScrutinee tycon args pat
641 | Just co_con <- tyConFamilyCoercion_maybe tycon
642 -- , not (isNewTyCon tycon) -- newtypes are explicitly unwrapped by
644 -- NB: We can use CoPat directly, rather than mkCoPat, as we know the
645 -- coercion is not the identity; mkCoPat is inconvenient as it
646 -- wants a located pattern.
647 = CoPat (WpCo $ mkTyConApp co_con args) -- co fam ty to repr ty
648 (pat {pat_ty = mkTyConApp tycon args}) -- representation type
649 pat_ty -- family inst type
654 tcConArgs :: DataCon -> [TcSigmaType]
655 -> Checker (HsConPatDetails Name) (HsConPatDetails Id)
657 tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
658 = do { checkTc (con_arity == no_of_args) -- Check correct arity
659 (arityErr "Constructor" data_con con_arity no_of_args)
660 ; let pats_w_tys = zipEqual "tcConArgs" arg_pats arg_tys
661 ; (arg_pats', tvs, res) <- tcMultiple tcConArg pats_w_tys
663 ; return (PrefixCon arg_pats', tvs, res) }
665 con_arity = dataConSourceArity data_con
666 no_of_args = length arg_pats
668 tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
669 = do { checkTc (con_arity == 2) -- Check correct arity
670 (arityErr "Constructor" data_con con_arity 2)
671 ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
673 ; return (InfixCon p1' p2', tvs, res) }
675 con_arity = dataConSourceArity data_con
677 tcConArgs data_con other_args (InfixCon p1 p2) pstate thing_inside
678 = pprPanic "tcConArgs" (ppr data_con) -- InfixCon always has two arguments
680 tcConArgs data_con arg_tys (RecCon (HsRecFields rpats dd)) pstate thing_inside
681 = do { (rpats', tvs, res) <- tcMultiple tc_field rpats pstate thing_inside
682 ; return (RecCon (HsRecFields rpats' dd), tvs, res) }
684 tc_field :: Checker (HsRecField FieldLabel (LPat Name)) (HsRecField TcId (LPat TcId))
685 tc_field (HsRecField field_lbl pat pun) pstate thing_inside
686 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
687 ; (pat', tvs, res) <- tcConArg (pat, pat_ty) pstate thing_inside
688 ; return (HsRecField sel_id pat' pun, tvs, res) }
690 find_field_ty :: FieldLabel -> TcM (Id, TcType)
691 find_field_ty field_lbl
692 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
694 -- No matching field; chances are this field label comes from some
695 -- other record type (or maybe none). As well as reporting an
696 -- error we still want to typecheck the pattern, principally to
697 -- make sure that all the variables it binds are put into the
698 -- environment, else the type checker crashes later:
699 -- f (R { foo = (a,b) }) = a+b
700 -- If foo isn't one of R's fields, we don't want to crash when
701 -- typechecking the "a+b".
702 [] -> do { addErrTc (badFieldCon data_con field_lbl)
703 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
704 ; return (error "Bogus selector Id", bogus_ty) }
706 -- The normal case, when the field comes from the right constructor
708 ASSERT( null extras )
709 do { sel_id <- tcLookupField field_lbl
710 ; return (sel_id, pat_ty) }
712 field_tys :: [(FieldLabel, TcType)]
713 field_tys = zip (dataConFieldLabels data_con) arg_tys
714 -- Don't use zipEqual! If the constructor isn't really a record, then
715 -- dataConFieldLabels will be empty (and each field in the pattern
716 -- will generate an error below).
718 tcConArg :: Checker (LPat Name, BoxySigmaType) (LPat Id)
719 tcConArg (arg_pat, arg_ty) pstate thing_inside
720 = tc_lpat arg_pat arg_ty pstate thing_inside
721 -- NB: the tc_lpat will refine pat_ty if necessary
722 -- based on the current pstate, which may include
723 -- refinements from peer argument patterns to the left
727 addDataConStupidTheta :: DataCon -> [TcType] -> TcM ()
728 -- Instantiate the "stupid theta" of the data con, and throw
729 -- the constraints into the constraint set
730 addDataConStupidTheta data_con inst_tys
731 | null stupid_theta = return ()
732 | otherwise = instStupidTheta origin inst_theta
734 origin = OccurrenceOf (dataConName data_con)
735 -- The origin should always report "occurrence of C"
736 -- even when C occurs in a pattern
737 stupid_theta = dataConStupidTheta data_con
738 tenv = zipTopTvSubst (dataConUnivTyVars data_con) inst_tys
739 inst_theta = substTheta tenv stupid_theta
743 %************************************************************************
747 %************************************************************************
750 refineAlt :: DataCon -- For tracing only
752 -> [TcTyVar] -- Existentials
753 -> [CoVar] -- Equational constraints
754 -> BoxySigmaType -- Pattern type
757 refineAlt con pstate ex_tvs [] pat_ty
758 | null $ dataConEqTheta con
759 = return pstate -- Common case: no equational constraints
761 refineAlt con pstate ex_tvs co_vars pat_ty
762 = do { opt_gadt <- doptM Opt_GADTs -- No type-refinement unless GADTs are on
763 ; if (not opt_gadt) then return pstate
766 { checkTc (isRigidTy pat_ty) (nonRigidMatch con)
767 -- We are matching against a GADT constructor with non-trivial
768 -- constraints, but pattern type is wobbly. For now we fail.
769 -- We can make sense of this, however:
770 -- Suppose MkT :: forall a b. (a:=:[b]) => b -> T a
771 -- (\x -> case x of { MkT v -> v })
772 -- We can infer that x must have type T [c], for some wobbly 'c'
774 -- (\(x::T [c]) -> case x of
775 -- MkT b (g::([c]:=:[b])) (v::b) -> v `cast` sym g
776 -- To implement this, we'd first instantiate the equational
777 -- constraints with *wobbly* type variables for the existentials;
778 -- then unify these constraints to make pat_ty the right shape;
779 -- then proceed exactly as in the rigid case
781 -- In the rigid case, we perform type refinement
782 ; case gadtRefine (pat_reft pstate) ex_tvs co_vars of {
783 Failed msg -> failWithTc (inaccessibleAlt msg) ;
784 Succeeded reft -> do { traceTc trace_msg
785 ; return (pstate { pat_reft = reft, pat_eqs = (pat_eqs pstate || not (null $ dataConEqTheta con)) }) }
786 -- DO NOT refine the envt right away, because we
787 -- might be inside a lazy pattern. Instead, refine pstate
790 trace_msg = text "refineAlt:match" <+>
791 vcat [ ppr con <+> ppr ex_tvs,
792 ppr [(v, tyVarKind v) | v <- co_vars],
798 %************************************************************************
802 %************************************************************************
804 In tcOverloadedLit we convert directly to an Int or Integer if we
805 know that's what we want. This may save some time, by not
806 temporarily generating overloaded literals, but it won't catch all
807 cases (the rest are caught in lookupInst).
810 tcOverloadedLit :: InstOrigin
813 -> TcM (HsOverLit TcId)
814 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
815 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
816 -- Reason: If we do, tcSimplify will call lookupInst, which
817 -- will call tcSyntaxName, which does unification,
818 -- which tcSimplify doesn't like
819 -- ToDo: noLoc sadness
820 = do { integer_ty <- tcMetaTy integerTyConName
821 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
822 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
824 | Just expr <- shortCutIntLit i res_ty
825 = return (HsIntegral i expr)
828 = do { expr <- newLitInst orig lit res_ty
829 ; return (HsIntegral i expr) }
831 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
832 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
833 = do { rat_ty <- tcMetaTy rationalTyConName
834 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
835 -- Overloaded literals must have liftedTypeKind, because
836 -- we're instantiating an overloaded function here,
837 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
838 -- However this'll be picked up by tcSyntaxOp if necessary
839 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
841 | Just expr <- shortCutFracLit r res_ty
842 = return (HsFractional r expr)
845 = do { expr <- newLitInst orig lit res_ty
846 ; return (HsFractional r expr) }
848 tcOverloadedLit orig lit@(HsIsString s fr) res_ty
849 | not (fr `isHsVar` fromStringName) -- c.f. HsIntegral case
850 = do { str_ty <- tcMetaTy stringTyConName
851 ; fr' <- tcSyntaxOp orig fr (mkFunTy str_ty res_ty)
852 ; return (HsIsString s (HsApp (noLoc fr') (nlHsLit (HsString s)))) }
854 | Just expr <- shortCutStringLit s res_ty
855 = return (HsIsString s expr)
858 = do { expr <- newLitInst orig lit res_ty
859 ; return (HsIsString s expr) }
861 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
862 newLitInst orig lit res_ty -- Make a LitInst
863 = do { loc <- getInstLoc orig
864 ; res_tau <- zapToMonotype res_ty
865 ; new_uniq <- newUnique
866 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
867 lit_inst = LitInst {tci_name = lit_nm, tci_lit = lit,
868 tci_ty = res_tau, tci_loc = loc}
870 ; return (HsVar (instToId lit_inst)) }
874 %************************************************************************
876 Note [Pattern coercions]
878 %************************************************************************
880 In principle, these program would be reasonable:
882 f :: (forall a. a->a) -> Int
883 f (x :: Int->Int) = x 3
885 g :: (forall a. [a]) -> Bool
888 In both cases, the function type signature restricts what arguments can be passed
889 in a call (to polymorphic ones). The pattern type signature then instantiates this
890 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
891 generate the translated term
892 f = \x' :: (forall a. a->a). let x = x' Int in x 3
894 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
895 And it requires a significant amount of code to implement, becuase we need to decorate
896 the translated pattern with coercion functions (generated from the subsumption check
899 So for now I'm just insisting on type *equality* in patterns. No subsumption.
901 Old notes about desugaring, at a time when pattern coercions were handled:
903 A SigPat is a type coercion and must be handled one at at time. We can't
904 combine them unless the type of the pattern inside is identical, and we don't
905 bother to check for that. For example:
907 data T = T1 Int | T2 Bool
908 f :: (forall a. a -> a) -> T -> t
909 f (g::Int->Int) (T1 i) = T1 (g i)
910 f (g::Bool->Bool) (T2 b) = T2 (g b)
912 We desugar this as follows:
914 f = \ g::(forall a. a->a) t::T ->
916 in case t of { T1 i -> T1 (gi i)
919 in case t of { T2 b -> T2 (gb b)
922 Note that we do not treat the first column of patterns as a
923 column of variables, because the coerced variables (gi, gb)
924 would be of different types. So we get rather grotty code.
925 But I don't think this is a common case, and if it was we could
926 doubtless improve it.
928 Meanwhile, the strategy is:
929 * treat each SigPat coercion (always non-identity coercions)
931 * deal with the stuff inside, and then wrap a binding round
932 the result to bind the new variable (gi, gb, etc)
935 %************************************************************************
937 \subsection{Errors and contexts}
939 %************************************************************************
942 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
943 patCtxt (VarPat _) = Nothing
944 patCtxt (ParPat _) = Nothing
945 patCtxt (AsPat _ _) = Nothing
946 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
949 -----------------------------------------------
951 existentialExplode pat
952 = hang (vcat [text "My brain just exploded.",
953 text "I can't handle pattern bindings for existentially-quantified constructors.",
954 text "Instead, use a case-expression, or do-notation, to unpack the constructor.",
955 text "In the binding group for"])
958 sigPatCtxt pats bound_tvs pat_tys body_ty tidy_env
959 = do { pat_tys' <- mapM zonkTcType pat_tys
960 ; body_ty' <- zonkTcType body_ty
961 ; let (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
962 (env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
963 (env3, tidy_body_ty) = tidyOpenType env2 body_ty'
965 sep [ptext SLIT("When checking an existential match that binds"),
966 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
967 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
968 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
971 bound_ids = collectPatsBinders pats
972 show_ids = filter is_interesting bound_ids
973 is_interesting id = any (`elemVarSet` varTypeTyVars id) bound_tvs
975 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
976 -- Don't zonk the types so we get the separate, un-unified versions
978 badFieldCon :: DataCon -> Name -> SDoc
979 badFieldCon con field
980 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
981 ptext SLIT("does not have field"), quotes (ppr field)]
983 polyPatSig :: TcType -> SDoc
985 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
988 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
992 hang (ptext SLIT("A lazy (~) pattern cannot bind existential type variables"))
993 2 (vcat (map pprSkolTvBinding tvs))
996 = hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
997 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
999 nonRigidResult res_ty
1000 = hang (ptext SLIT("GADT pattern match with non-rigid result type") <+> quotes (ppr res_ty))
1001 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
1004 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg