2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcPat]{Typechecking patterns}
7 module TcPat ( tcLetPat, tcLamPat, tcLamPats, tcOverloadedLit,
8 badFieldCon, polyPatSig ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
13 import HsSyn ( Pat(..), LPat, HsConDetails(..), HsLit(..), HsOverLit(..), HsExpr(..),
15 LHsBinds, emptyLHsBinds, isEmptyLHsBinds,
16 collectPatsBinders, nlHsLit )
17 import TcHsSyn ( TcId, hsLitType )
19 import Inst ( InstOrigin(..), shortCutFracLit, shortCutIntLit,
20 newDicts, instToId, tcInstStupidTheta, isHsVar
22 import Id ( Id, idType, mkLocalId )
23 import CoreFVs ( idFreeTyVars )
24 import Name ( Name, mkSystemVarName )
25 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
26 import TcEnv ( newLocalName, tcExtendIdEnv1, tcExtendTyVarEnv2,
27 tcLookupClass, tcLookupDataCon, refineEnvironment,
28 tcLookupField, tcMetaTy )
29 import TcMType ( newFlexiTyVarTy, arityErr, tcInstSkolTyVars,
30 + newCoVars, zonkTcType )
31 import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType, BoxyType,
33 BoxySigmaType, BoxyRhoType, argTypeKind, typeKind,
34 pprSkolTvBinding, isRigidTy, tcTyVarsOfTypes,
35 zipTopTvSubst, isArgTypeKind, isUnboxedTupleType,
36 mkTyVarTys, mkClassPred, isOverloadedTy, substEqSpec,
37 mkFunTy, mkFunTys, tidyOpenType, tidyOpenTypes )
38 import VarSet ( elemVarSet )
39 import {- Kind parts of -}
40 Type ( liftedTypeKind )
41 import TcUnify ( boxySplitTyConApp, boxySplitListTy, unBox,
42 zapToMonotype, boxyUnify, checkSigTyVarsWrt,
44 import TcHsType ( UserTypeCtxt(..), tcPatSig )
45 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
46 import Type ( substTys, substTheta )
47 import StaticFlags ( opt_IrrefutableTuples )
48 import TyCon ( TyCon, FieldLabel )
49 import DataCon ( DataCon, dataConTyCon, dataConFullSig, dataConName,
50 dataConFieldLabels, dataConSourceArity )
51 import PrelNames ( integralClassName, fromIntegerName, integerTyConName,
52 fromRationalName, rationalTyConName )
53 import BasicTypes ( isBoxed )
54 import SrcLoc ( Located(..), SrcSpan, noLoc )
55 import ErrUtils ( Message )
56 import Util ( zipEqual )
57 import Maybes ( MaybeErr(..) )
63 %************************************************************************
67 %************************************************************************
70 tcLetPat :: (Name -> Maybe TcRhoType)
71 -> LPat Name -> BoxySigmaType
74 tcLetPat sig_fn pat pat_ty thing_inside
75 = do { let init_state = PS { pat_ctxt = LetPat sig_fn,
76 pat_reft = emptyRefinement }
77 ; (pat', ex_tvs, res) <- tc_lpat pat pat_ty init_state (\ _ -> thing_inside)
79 -- Don't know how to deal with pattern-bound existentials yet
80 ; checkTc (null ex_tvs) (existentialExplode pat)
82 ; return (pat', res) }
85 tcLamPats :: [LPat Name] -- Patterns,
86 -> [BoxySigmaType] -- and their types
87 -> BoxyRhoType -- Result type,
88 -> ((Refinement, BoxyRhoType) -> TcM a) -- and the checker for the body
89 -> TcM ([LPat TcId], a)
91 -- This is the externally-callable wrapper function
92 -- Typecheck the patterns, extend the environment to bind the variables,
93 -- do the thing inside, use any existentially-bound dictionaries to
94 -- discharge parts of the returning LIE, and deal with pattern type
97 -- 1. Initialise the PatState
98 -- 2. Check the patterns
99 -- 3. Apply the refinement to the environment and result type
101 -- 5. Check that no existentials escape
103 tcLamPats pats tys res_ty thing_inside
104 = tc_lam_pats (zipEqual "tcLamPats" pats tys)
105 (emptyRefinement, res_ty) thing_inside
107 tcLamPat :: LPat Name -> BoxySigmaType
108 -> (Refinement,BoxyRhoType) -- Result type
109 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
110 -> TcM (LPat TcId, a)
111 tcLamPat pat pat_ty res_ty thing_inside
112 = do { ([pat'],thing) <- tc_lam_pats [(pat, pat_ty)] res_ty thing_inside
113 ; return (pat', thing) }
116 tc_lam_pats :: [(LPat Name,BoxySigmaType)]
117 -> (Refinement,BoxyRhoType) -- Result type
118 -> ((Refinement,BoxyRhoType) -> TcM a) -- Checker for body, given its result type
119 -> TcM ([LPat TcId], a)
120 tc_lam_pats pat_ty_prs (reft, res_ty) thing_inside
121 = do { let init_state = PS { pat_ctxt = LamPat, pat_reft = reft }
123 ; (pats', ex_tvs, res) <- tcMultiple tc_lpat_pr pat_ty_prs init_state $ \ pstate' ->
124 refineEnvironment (pat_reft pstate') $
125 thing_inside (pat_reft pstate', res_ty)
127 ; let tys = map snd pat_ty_prs
128 ; tcCheckExistentialPat pats' ex_tvs tys res_ty
130 ; returnM (pats', res) }
134 tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
135 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
136 -> [BoxySigmaType] -- Types of the patterns
137 -> BoxyRhoType -- Type of the body of the match
138 -- Tyvars in either of these must not escape
140 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
141 -- For example, we must reject this program:
142 -- data C = forall a. C (a -> Int)
144 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
146 tcCheckExistentialPat pats [] pat_tys body_ty
147 = return () -- Short cut for case when there are no existentials
149 tcCheckExistentialPat pats ex_tvs pat_tys body_ty
150 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys body_ty) $
151 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
155 pat_reft :: Refinement -- Binds rigid TcTyVars to their refinements
160 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
162 patSigCtxt :: PatState -> UserTypeCtxt
163 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
164 patSigCtxt other = LamPatSigCtxt
169 %************************************************************************
173 %************************************************************************
176 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
177 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
178 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
179 -- We have an undecorated binder, so we do rule ABS1,
180 -- by unboxing the boxy type, forcing any un-filled-in
181 -- boxes to become monotypes
182 -- NB that pat_ty' can still be a polytype:
183 -- data T = MkT (forall a. a->a)
184 -- f t = case t of { MkT g -> ... }
185 -- Here, the 'g' must get type (forall a. a->a) from the
187 ; return (mkLocalId bndr_name pat_ty') }
189 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
190 | Just mono_ty <- lookup_sig bndr_name
191 = do { mono_name <- newLocalName bndr_name
192 ; boxyUnify mono_ty pat_ty
193 ; return (mkLocalId mono_name mono_ty) }
196 = do { pat_ty' <- unBoxPatBndrType pat_ty bndr_name
197 ; mono_name <- newLocalName bndr_name
198 ; return (mkLocalId mono_name pat_ty') }
202 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
203 bindInstsOfPatId id thing_inside
204 | not (isOverloadedTy (idType id))
205 = do { res <- thing_inside; return (res, emptyLHsBinds) }
207 = do { (res, lie) <- getLIE thing_inside
208 ; binds <- bindInstsOfLocalFuns lie [id]
209 ; return (res, binds) }
212 unBoxPatBndrType ty name = unBoxArgType ty (ptext SLIT("The variable") <+> quotes (ppr name))
213 unBoxWildCardType ty = unBoxArgType ty (ptext SLIT("A wild-card pattern"))
215 unBoxArgType :: BoxyType -> SDoc -> TcM TcType
216 -- In addition to calling unbox, unBoxArgType ensures that the type is of ArgTypeKind;
217 -- that is, it can't be an unboxed tuple. For example,
218 -- case (f x) of r -> ...
219 -- should fail if 'f' returns an unboxed tuple.
220 unBoxArgType ty pp_this
221 = do { ty' <- unBox ty -- Returns a zonked type
223 -- Neither conditional is strictly necesssary (the unify alone will do)
224 -- but they improve error messages, and allocate fewer tyvars
225 ; if isUnboxedTupleType ty' then
227 else if isArgTypeKind (typeKind ty') then
229 else do -- OpenTypeKind, so constrain it
230 { ty2 <- newFlexiTyVarTy argTypeKind
234 msg = pp_this <+> ptext SLIT("cannot be bound to an unboxed tuple")
238 %************************************************************************
240 The main worker functions
242 %************************************************************************
246 tcPat takes a "thing inside" over which the patter scopes. This is partly
247 so that tcPat can extend the environment for the thing_inside, but also
248 so that constraints arising in the thing_inside can be discharged by the
251 This does not work so well for the ErrCtxt carried by the monad: we don't
252 want the error-context for the pattern to scope over the RHS.
253 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
257 type Checker inp out = forall r.
260 -> (PatState -> TcM r)
261 -> TcM (out, [TcTyVar], r)
263 tcMultiple :: Checker inp out -> Checker [inp] [out]
264 tcMultiple tc_pat args pstate thing_inside
265 = do { err_ctxt <- getErrCtxt
267 = do { res <- thing_inside pstate
268 ; return ([], [], res) }
270 loop pstate (arg:args)
271 = do { (p', p_tvs, (ps', ps_tvs, res))
272 <- tc_pat arg pstate $ \ pstate' ->
273 setErrCtxt err_ctxt $
275 -- setErrCtxt: restore context before doing the next pattern
276 -- See note [Nesting] above
278 ; return (p':ps', p_tvs ++ ps_tvs, res) }
283 tc_lpat_pr :: (LPat Name, BoxySigmaType)
285 -> (PatState -> TcM a)
286 -> TcM (LPat TcId, [TcTyVar], a)
287 tc_lpat_pr (pat, ty) = tc_lpat pat ty
292 -> (PatState -> TcM a)
293 -> TcM (LPat TcId, [TcTyVar], a)
294 tc_lpat (L span pat) pat_ty pstate thing_inside
296 maybeAddErrCtxt (patCtxt pat) $
297 do { let (coercion, pat_ty') = refineType (pat_reft pstate) pat_ty
298 -- Make sure the result type reflects the current refinement
299 -- We must do this here, so that it correctly ``sees'' all
300 -- the refinements to the left. Example:
301 -- Suppose C :: forall a. T a -> a -> Foo
302 -- Pattern C a p1 True
303 -- So p1 might refine 'a' to True, and the True
304 -- pattern had better see it.
306 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
307 ; return (mkCoPat coercion (L span pat') pat_ty, tvs, res) }
311 -> Pat Name -> BoxySigmaType -- Fully refined result type
312 -> (PatState -> TcM a) -- Thing inside
313 -> TcM (Pat TcId, -- Translated pattern
314 [TcTyVar], -- Existential binders
315 a) -- Result of thing inside
317 tc_pat pstate (VarPat name) pat_ty thing_inside
318 = do { id <- tcPatBndr pstate name pat_ty
319 ; (res, binds) <- bindInstsOfPatId id $
320 tcExtendIdEnv1 name id $
321 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
322 >> thing_inside pstate)
323 ; let pat' | isEmptyLHsBinds binds = VarPat id
324 | otherwise = VarPatOut id binds
325 ; return (pat', [], res) }
327 tc_pat pstate (ParPat pat) pat_ty thing_inside
328 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
329 ; return (ParPat pat', tvs, res) }
331 tc_pat pstate (BangPat pat) pat_ty thing_inside
332 = do { (pat', tvs, res) <- tc_lpat pat pat_ty pstate thing_inside
333 ; return (BangPat pat', tvs, res) }
335 -- There's a wrinkle with irrefutable patterns, namely that we
336 -- must not propagate type refinement from them. For example
337 -- data T a where { T1 :: Int -> T Int; ... }
338 -- f :: T a -> Int -> a
340 -- It's obviously not sound to refine a to Int in the right
341 -- hand side, because the arugment might not match T1 at all!
343 -- Nor should a lazy pattern bind any existential type variables
344 -- because they won't be in scope when we do the desugaring
345 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
346 = do { (pat', pat_tvs, res) <- tc_lpat pat pat_ty pstate $ \ _ ->
348 -- Ignore refined pstate',
350 -- Check no existentials
351 ; if (null pat_tvs) then return ()
352 else lazyPatErr lpat pat_tvs
354 -- Check that the pattern has a lifted type
355 ; pat_tv <- newBoxyTyVar liftedTypeKind
356 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
358 ; return (LazyPat pat', [], res) }
360 tc_pat pstate (WildPat _) pat_ty thing_inside
361 = do { pat_ty' <- unBoxWildCardType pat_ty -- Make sure it's filled in with monotypes
362 ; res <- thing_inside pstate
363 ; return (WildPat pat_ty', [], res) }
365 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
366 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
367 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
368 tc_lpat pat (idType bndr_id) pstate thing_inside
369 -- NB: if we do inference on:
370 -- \ (y@(x::forall a. a->a)) = e
371 -- we'll fail. The as-pattern infers a monotype for 'y', which then
372 -- fails to unify with the polymorphic type for 'x'. This could
373 -- perhaps be fixed, but only with a bit more work.
375 -- If you fix it, don't forget the bindInstsOfPatIds!
376 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
378 -- Type signatures in patterns
379 -- See Note [Pattern coercions] below
380 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
381 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
382 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
383 tc_lpat pat inner_ty pstate thing_inside
384 ; return (SigPatOut pat' inner_ty, tvs, res) }
386 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
387 = failWithTc (badTypePat pat)
389 ------------------------
390 -- Lists, tuples, arrays
391 tc_pat pstate (ListPat pats _) pat_ty thing_inside
392 = do { elt_ty <- boxySplitListTy pat_ty
393 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
394 pats pstate thing_inside
395 ; return (ListPat pats' elt_ty, pats_tvs, res) }
397 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
398 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
399 ; (pats', pats_tvs, res) <- tcMultiple (\p -> tc_lpat p elt_ty)
400 pats pstate thing_inside
401 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
402 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
404 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
405 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
406 ; (pats', pats_tvs, res) <- tcMultiple tc_lpat_pr (pats `zip` arg_tys)
409 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
410 -- so that we can experiment with lazy tuple-matching.
411 -- This is a pretty odd place to make the switch, but
412 -- it was easy to do.
413 ; let unmangled_result = TuplePat pats' boxity pat_ty
414 possibly_mangled_result
415 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
416 | otherwise = unmangled_result
418 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
419 return (possibly_mangled_result, pats_tvs, res) }
421 ------------------------
423 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
424 = do { data_con <- tcLookupDataCon con_name
425 ; let tycon = dataConTyCon data_con
426 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
428 ------------------------
430 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
431 = do { boxyUnify (hsLitType simple_lit) pat_ty
432 ; res <- thing_inside pstate
433 ; returnM (LitPat simple_lit, [], res) }
435 ------------------------
436 -- Overloaded patterns: n, and n+k
437 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
438 = do { let orig = LiteralOrigin over_lit
439 ; lit' <- tcOverloadedLit orig over_lit pat_ty
440 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
441 ; mb_neg' <- case mb_neg of
442 Nothing -> return Nothing -- Positive literal
443 Just neg -> -- Negative literal
444 -- The 'negate' is re-mappable syntax
445 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
446 ; return (Just neg') }
447 ; res <- thing_inside pstate
448 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
450 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
451 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
452 ; let pat_ty' = idType bndr_id
453 orig = LiteralOrigin lit
454 ; lit' <- tcOverloadedLit orig lit pat_ty'
456 -- The '>=' and '-' parts are re-mappable syntax
457 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
458 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
460 -- The Report says that n+k patterns must be in Integral
461 -- We may not want this when using re-mappable syntax, though (ToDo?)
462 ; icls <- tcLookupClass integralClassName
463 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
466 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
467 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
469 tc_pat _ _other_pat _ _ = panic "tc_pat" -- DictPat, ConPatOut, SigPatOut, VarPatOut
473 %************************************************************************
475 Most of the work for constructors is here
476 (the rest is in the ConPatIn case of tc_pat)
478 %************************************************************************
482 -- MkT :: forall a b c. (a:=:[b]) => b -> c -> T a
483 -- with scrutinee of type (T ty)
485 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
486 -> BoxySigmaType -- Type of the pattern
487 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
488 -> TcM (Pat TcId, [TcTyVar], a)
489 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
490 = do { span <- getSrcSpanM -- Span for the whole pattern
491 ; let (univ_tvs, ex_tvs, eq_spec, theta, arg_tys) = dataConFullSig data_con
492 skol_info = PatSkol data_con span
494 -- Instantiate the constructor type variables [a->ty]
495 ; ctxt_res_tys <- boxySplitTyConApp tycon pat_ty
496 ; ex_tvs' <- tcInstSkolTyVars skol_info ex_tvs
497 ; let tenv = zipTopTvSubst (univ_tvs ++ ex_tvs)
498 (ctxt_res_tys ++ mkTyVarTys ex_tvs')
499 eq_spec' = substEqSpec tenv eq_spec
500 theta' = substTheta tenv theta
501 arg_tys' = substTys tenv arg_tys
503 ; co_vars <- newCoVars eq_spec' -- Make coercion variables
504 ; pstate' <- refineAlt data_con pstate ex_tvs co_vars pat_ty
506 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
507 tcConArgs data_con arg_tys' arg_pats pstate' thing_inside
509 ; dicts <- newDicts (SigOrigin skol_info) theta'
510 ; dict_binds <- tcSimplifyCheck doc ex_tvs' dicts lie_req
512 ; tcInstStupidTheta data_con ctxt_res_tys
514 ; return (ConPatOut { pat_con = L con_span data_con,
515 pat_tvs = ex_tvs' ++ co_vars,
516 pat_dicts = map instToId dicts, pat_binds = dict_binds,
517 pat_args = arg_pats', pat_ty = pat_ty },
518 ex_tvs' ++ inner_tvs, res)
521 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
523 tcConArgs :: DataCon -> [TcSigmaType]
524 -> Checker (HsConDetails Name (LPat Name)) (HsConDetails Id (LPat Id))
526 tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
527 = do { checkTc (con_arity == no_of_args) -- Check correct arity
528 (arityErr "Constructor" data_con con_arity no_of_args)
529 ; let pats_w_tys = zipEqual "tcConArgs" arg_pats arg_tys
530 ; (arg_pats', tvs, res) <- tcMultiple tcConArg pats_w_tys
532 ; return (PrefixCon arg_pats', tvs, res) }
534 con_arity = dataConSourceArity data_con
535 no_of_args = length arg_pats
537 tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
538 = do { checkTc (con_arity == 2) -- Check correct arity
539 (arityErr "Constructor" data_con con_arity 2)
540 ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
542 ; return (InfixCon p1' p2', tvs, res) }
544 con_arity = dataConSourceArity data_con
546 tcConArgs data_con arg_tys (RecCon rpats) pstate thing_inside
547 = do { (rpats', tvs, res) <- tcMultiple tc_field rpats pstate thing_inside
548 ; return (RecCon rpats', tvs, res) }
550 tc_field :: Checker (Located Name, LPat Name) (Located TcId, LPat TcId)
551 tc_field (field_lbl, pat) pstate thing_inside
552 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
553 ; (pat', tvs, res) <- tcConArg (pat, pat_ty) pstate thing_inside
554 ; return ((sel_id, pat'), tvs, res) }
556 find_field_ty :: FieldLabel -> TcM (Id, TcType)
557 find_field_ty field_lbl
558 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
560 -- No matching field; chances are this field label comes from some
561 -- other record type (or maybe none). As well as reporting an
562 -- error we still want to typecheck the pattern, principally to
563 -- make sure that all the variables it binds are put into the
564 -- environment, else the type checker crashes later:
565 -- f (R { foo = (a,b) }) = a+b
566 -- If foo isn't one of R's fields, we don't want to crash when
567 -- typechecking the "a+b".
568 [] -> do { addErrTc (badFieldCon data_con field_lbl)
569 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
570 ; return (error "Bogus selector Id", bogus_ty) }
572 -- The normal case, when the field comes from the right constructor
574 ASSERT( null extras )
575 do { sel_id <- tcLookupField field_lbl
576 ; return (sel_id, pat_ty) }
578 field_tys :: [(FieldLabel, TcType)]
579 field_tys = zip (dataConFieldLabels data_con) arg_tys
580 -- Don't use zipEqual! If the constructor isn't really a record, then
581 -- dataConFieldLabels will be empty (and each field in the pattern
582 -- will generate an error below).
584 tcConArg :: Checker (LPat Name, BoxySigmaType) (LPat Id)
585 tcConArg (arg_pat, arg_ty) pstate thing_inside
586 = tc_lpat arg_pat arg_ty pstate thing_inside
587 -- NB: the tc_lpat will refine pat_ty if necessary
588 -- based on the current pstate, which may include
589 -- refinements from peer argument patterns to the left
593 %************************************************************************
597 %************************************************************************
600 refineAlt :: DataCon -- For tracing only
602 -> [TcTyVar] -- Existentials
603 -> [CoVar] -- Equational constraints
604 -> BoxySigmaType -- Pattern type
607 refineAlt con pstate ex_tvs [] pat_ty
608 = return pstate -- Common case: no equational constraints
610 refineAlt con pstate ex_tvs co_vars pat_ty
611 | not (isRigidTy pat_ty)
612 = failWithTc (nonRigidMatch con)
613 -- We are matching against a GADT constructor with non-trivial
614 -- constraints, but pattern type is wobbly. For now we fail.
615 -- We can make sense of this, however:
616 -- Suppose MkT :: forall a b. (a:=:[b]) => b -> T a
617 -- (\x -> case x of { MkT v -> v })
618 -- We can infer that x must have type T [c], for some wobbly 'c'
620 -- (\(x::T [c]) -> case x of
621 -- MkT b (g::([c]:=:[b])) (v::b) -> v `cast` sym g
622 -- To implement this, we'd first instantiate the equational
623 -- constraints with *wobbly* type variables for the existentials;
624 -- then unify these constraints to make pat_ty the right shape;
625 -- then proceed exactly as in the rigid case
627 | otherwise -- In the rigid case, we perform type refinement
628 = case gadtRefine (pat_reft pstate) ex_tvs co_vars of {
629 Failed msg -> failWithTc (inaccessibleAlt msg) ;
630 Succeeded reft -> do { traceTc trace_msg
631 ; return (pstate { pat_reft = reft }) }
632 -- DO NOT refine the envt right away, because we
633 -- might be inside a lazy pattern. Instead, refine pstate
636 trace_msg = text "refineAlt:match" <+> ppr con <+> ppr reft
641 %************************************************************************
645 %************************************************************************
647 In tcOverloadedLit we convert directly to an Int or Integer if we
648 know that's what we want. This may save some time, by not
649 temporarily generating overloaded literals, but it won't catch all
650 cases (the rest are caught in lookupInst).
653 tcOverloadedLit :: InstOrigin
656 -> TcM (HsOverLit TcId)
657 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
658 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
659 -- Reason: If we do, tcSimplify will call lookupInst, which
660 -- will call tcSyntaxName, which does unification,
661 -- which tcSimplify doesn't like
662 -- ToDo: noLoc sadness
663 = do { integer_ty <- tcMetaTy integerTyConName
664 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
665 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
667 | Just expr <- shortCutIntLit i res_ty
668 = return (HsIntegral i expr)
671 = do { expr <- newLitInst orig lit res_ty
672 ; return (HsIntegral i expr) }
674 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
675 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
676 = do { rat_ty <- tcMetaTy rationalTyConName
677 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
678 -- Overloaded literals must have liftedTypeKind, because
679 -- we're instantiating an overloaded function here,
680 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
681 -- However this'll be picked up by tcSyntaxOp if necessary
682 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
684 | Just expr <- shortCutFracLit r res_ty
685 = return (HsFractional r expr)
688 = do { expr <- newLitInst orig lit res_ty
689 ; return (HsFractional r expr) }
691 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
692 newLitInst orig lit res_ty -- Make a LitInst
693 = do { loc <- getInstLoc orig
694 ; res_tau <- zapToMonotype res_ty
695 ; new_uniq <- newUnique
696 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
697 lit_inst = LitInst lit_nm lit res_tau loc
699 ; return (HsVar (instToId lit_inst)) }
703 %************************************************************************
705 Note [Pattern coercions]
707 %************************************************************************
709 In principle, these program would be reasonable:
711 f :: (forall a. a->a) -> Int
712 f (x :: Int->Int) = x 3
714 g :: (forall a. [a]) -> Bool
717 In both cases, the function type signature restricts what arguments can be passed
718 in a call (to polymorphic ones). The pattern type signature then instantiates this
719 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
720 generate the translated term
721 f = \x' :: (forall a. a->a). let x = x' Int in x 3
723 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
724 And it requires a significant amount of code to implement, becuase we need to decorate
725 the translated pattern with coercion functions (generated from the subsumption check
728 So for now I'm just insisting on type *equality* in patterns. No subsumption.
730 Old notes about desugaring, at a time when pattern coercions were handled:
732 A SigPat is a type coercion and must be handled one at at time. We can't
733 combine them unless the type of the pattern inside is identical, and we don't
734 bother to check for that. For example:
736 data T = T1 Int | T2 Bool
737 f :: (forall a. a -> a) -> T -> t
738 f (g::Int->Int) (T1 i) = T1 (g i)
739 f (g::Bool->Bool) (T2 b) = T2 (g b)
741 We desugar this as follows:
743 f = \ g::(forall a. a->a) t::T ->
745 in case t of { T1 i -> T1 (gi i)
748 in case t of { T2 b -> T2 (gb b)
751 Note that we do not treat the first column of patterns as a
752 column of variables, because the coerced variables (gi, gb)
753 would be of different types. So we get rather grotty code.
754 But I don't think this is a common case, and if it was we could
755 doubtless improve it.
757 Meanwhile, the strategy is:
758 * treat each SigPat coercion (always non-identity coercions)
760 * deal with the stuff inside, and then wrap a binding round
761 the result to bind the new variable (gi, gb, etc)
764 %************************************************************************
766 \subsection{Errors and contexts}
768 %************************************************************************
771 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
772 patCtxt (VarPat _) = Nothing
773 patCtxt (ParPat _) = Nothing
774 patCtxt (AsPat _ _) = Nothing
775 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
778 -----------------------------------------------
780 existentialExplode pat
781 = hang (vcat [text "My brain just exploded.",
782 text "I can't handle pattern bindings for existentially-quantified constructors.",
783 text "In the binding group for"])
786 sigPatCtxt bound_ids bound_tvs pat_tys body_ty tidy_env
787 = do { pat_tys' <- mapM zonkTcType pat_tys
788 ; body_ty' <- zonkTcType body_ty
789 ; let (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
790 (env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
791 (env3, tidy_body_ty) = tidyOpenType env2 body_ty'
793 sep [ptext SLIT("When checking an existential match that binds"),
794 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
795 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
796 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
799 show_ids = filter is_interesting bound_ids
800 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
802 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
803 -- Don't zonk the types so we get the separate, un-unified versions
805 badFieldCon :: DataCon -> Name -> SDoc
806 badFieldCon con field
807 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
808 ptext SLIT("does not have field"), quotes (ppr field)]
810 polyPatSig :: TcType -> SDoc
812 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
815 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
819 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
820 2 (vcat (map pprSkolTvBinding tvs))
823 = hang (ptext SLIT("GADT pattern match in non-rigid context for") <+> quotes (ppr con))
824 2 (ptext SLIT("Tell GHC HQ if you'd like this to unify the context"))
827 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg