2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcPat]{Typechecking patterns}
7 module TcPat ( tcPat, tcPats, tcOverloadedLit,
8 PatCtxt(..), badFieldCon, polyPatSig ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
13 import HsSyn ( Pat(..), LPat, HsConDetails(..), HsLit(..), HsOverLit(..), HsExpr(..),
14 LHsBinds, emptyLHsBinds, isEmptyLHsBinds,
15 collectPatsBinders, nlHsLit )
16 import TcHsSyn ( TcId, hsLitType )
18 import Inst ( InstOrigin(..), shortCutFracLit, shortCutIntLit,
19 newDicts, instToId, tcInstStupidTheta, isHsVar
21 import Id ( Id, idType, mkLocalId )
22 import CoreFVs ( idFreeTyVars )
23 import Name ( Name, mkSystemVarName )
24 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
25 import TcEnv ( newLocalName, tcExtendIdEnv1, tcExtendTyVarEnv2,
26 tcLookupClass, tcLookupDataCon, tcLookupId, refineEnvironment,
28 import TcMType ( newFlexiTyVarTy, arityErr, tcInstSkolTyVars, newBoxyTyVar, zonkTcType )
29 import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType,
31 BoxySigmaType, BoxyRhoType,
32 pprSkolTvBinding, isRefineableTy, isRigidTy, tcTyVarsOfTypes, mkTyVarTy, lookupTyVar,
33 emptyTvSubst, substTyVar, substTy, mkTopTvSubst, zipTopTvSubst, zipOpenTvSubst,
34 mkTyVarTys, mkClassPred, mkTyConApp, isOverloadedTy,
35 mkFunTy, mkFunTys, exactTyVarsOfTypes,
37 import VarSet ( elemVarSet, mkVarSet )
38 import Kind ( liftedTypeKind, openTypeKind )
39 import TcUnify ( boxySplitTyConApp, boxySplitListTy,
40 unBox, stripBoxyType, zapToMonotype,
41 boxyMatchTypes, boxyUnify, boxyUnifyList, checkSigTyVarsWrt )
42 import TcHsType ( UserTypeCtxt(..), tcPatSig )
43 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
44 import Unify ( MaybeErr(..), gadtRefineTys )
45 import Type ( substTys, substTheta )
46 import StaticFlags ( opt_IrrefutableTuples )
47 import TyCon ( TyCon )
48 import DataCon ( DataCon, dataConTyCon, isVanillaDataCon,
49 dataConFieldLabels, dataConSourceArity, dataConSig )
50 import PrelNames ( integralClassName, fromIntegerName, integerTyConName,
51 fromRationalName, rationalTyConName )
52 import BasicTypes ( isBoxed )
53 import SrcLoc ( Located(..), SrcSpan, noLoc )
54 import ErrUtils ( Message )
55 import Util ( takeList, zipEqual )
61 %************************************************************************
65 %************************************************************************
69 -> [LPat Name] -- Patterns,
70 -> [BoxySigmaType] -- and their types
71 -> BoxyRhoType -- Result type,
72 -> (BoxyRhoType -> TcM a) -- and the checker for the body
73 -> TcM ([LPat TcId], a)
75 -- This is the externally-callable wrapper function
76 -- Typecheck the patterns, extend the environment to bind the variables,
77 -- do the thing inside, use any existentially-bound dictionaries to
78 -- discharge parts of the returning LIE, and deal with pattern type
81 -- 1. Initialise the PatState
82 -- 2. Check the patterns
83 -- 3. Apply the refinement
85 -- 5. Check that no existentials escape
87 tcPats ctxt pats tys res_ty thing_inside
88 = do { let init_state = PS { pat_ctxt = ctxt, pat_reft = emptyTvSubst }
90 ; (pats', ex_tvs, res) <- tc_lpats init_state pats tys $ \ pstate' ->
91 thing_inside (refineType (pat_reft pstate') res_ty)
93 ; tcCheckExistentialPat ctxt pats' ex_tvs tys res_ty
95 ; returnM (pats', res) }
100 -> LPat Name -> TcType
101 -> BoxyRhoType -- Result type
102 -> (BoxyRhoType -> TcM a) -- Checker for body, given its result type
103 -> TcM (LPat TcId, a)
104 tcPat ctxt pat pat_ty res_ty thing_inside
105 = do { ([pat'],thing) <- tcPats ctxt [pat] [pat_ty] res_ty thing_inside
106 ; return (pat', thing) }
110 tcCheckExistentialPat :: PatCtxt
111 -> [LPat TcId] -- Patterns (just for error message)
112 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
113 -> [BoxySigmaType] -- Types of the patterns
114 -> BoxyRhoType -- Type of the body of the match
115 -- Tyvars in either of these must not escape
117 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
118 -- For example, we must reject this program:
119 -- data C = forall a. C (a -> Int)
121 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
123 tcCheckExistentialPat ctxt pats [] pat_tys body_ty
124 = return () -- Short cut for case when there are no existentials
126 tcCheckExistentialPat (LetPat _) pats ex_tvs pat_tys body_ty
127 -- Don't know how to deal with pattern-bound existentials yet
128 = failWithTc (existentialExplode pats)
130 tcCheckExistentialPat ctxt pats ex_tvs pat_tys body_ty
131 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys) $
132 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
136 pat_reft :: GadtRefinement -- Binds rigid TcTyVars to their refinements
141 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
143 patSigCtxt :: PatState -> UserTypeCtxt
144 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
145 patSigCtxt other = LamPatSigCtxt
150 %************************************************************************
154 %************************************************************************
157 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
158 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
159 = do { pat_ty' <- unBox pat_ty
160 -- We have an undecorated binder, so we do rule ABS1,
161 -- by unboxing the boxy type, forcing any un-filled-in
162 -- boxes to become monotypes
163 -- NB that pat_ty' can still be a polytype:
164 -- data T = MkT (forall a. a->a)
165 -- f t = case t of { MkT g -> ... }
166 -- Here, the 'g' must get type (forall a. a->a) from the
168 ; return (mkLocalId bndr_name pat_ty') }
170 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
171 | Just mono_ty <- lookup_sig bndr_name
172 = do { mono_name <- newLocalName bndr_name
173 ; boxyUnify mono_ty pat_ty
174 ; return (mkLocalId mono_name mono_ty) }
177 = do { pat_ty' <- unBox pat_ty
178 ; mono_name <- newLocalName bndr_name
179 ; return (mkLocalId mono_name pat_ty') }
183 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
184 bindInstsOfPatId id thing_inside
185 | not (isOverloadedTy (idType id))
186 = do { res <- thing_inside; return (res, emptyLHsBinds) }
188 = do { (res, lie) <- getLIE thing_inside
189 ; binds <- bindInstsOfLocalFuns lie [id]
190 ; return (res, binds) }
194 %************************************************************************
196 The main worker functions
198 %************************************************************************
202 tcPat takes a "thing inside" over which the patter scopes. This is partly
203 so that tcPat can extend the environment for the thing_inside, but also
204 so that constraints arising in the thing_inside can be discharged by the
207 This does not work so well for the ErrCtxt carried by the monad: we don't
208 want the error-context for the pattern to scope over the RHS.
209 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
216 -> (PatState -> TcM a)
217 -> TcM ([LPat TcId], [TcTyVar], a)
219 tc_lpats pstate pats pat_tys thing_inside
220 = do { err_ctxt <- getErrCtxt
221 ; let loop pstate [] []
222 = do { res <- thing_inside pstate
223 ; return ([], [], res) }
225 loop pstate (p:ps) (ty:tys)
226 = do { (p', p_tvs, (ps', ps_tvs, res))
227 <- tc_lpat pstate p ty $ \ pstate' ->
228 setErrCtxt err_ctxt $
230 -- setErrCtxt: restore context before doing the next pattern
231 -- See note [Nesting] above
233 ; return (p':ps', p_tvs ++ ps_tvs, res) }
235 loop _ _ _ = pprPanic "tc_lpats" (ppr pats $$ ppr pat_tys)
237 ; loop pstate pats pat_tys }
243 -> (PatState -> TcM a)
244 -> TcM (LPat TcId, [TcTyVar], a)
245 tc_lpat pstate (L span pat) pat_ty thing_inside
247 maybeAddErrCtxt (patCtxt pat) $
248 do { let pat_ty' = refineType (pat_reft pstate) pat_ty
249 -- Make sure the result type reflects the current refinement
250 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
251 ; return (L span pat', tvs, res) }
256 -> Pat Name -> BoxySigmaType -- Fully refined result type
257 -> (PatState -> TcM a) -- Thing inside
258 -> TcM (Pat TcId, -- Translated pattern
259 [TcTyVar], -- Existential binders
260 a) -- Result of thing inside
262 tc_pat pstate (VarPat name) pat_ty thing_inside
263 = do { id <- tcPatBndr pstate name pat_ty
264 ; (res, binds) <- bindInstsOfPatId id $
265 tcExtendIdEnv1 name id $
266 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
267 >> thing_inside pstate)
268 ; let pat' | isEmptyLHsBinds binds = VarPat id
269 | otherwise = VarPatOut id binds
270 ; return (pat', [], res) }
272 tc_pat pstate (ParPat pat) pat_ty thing_inside
273 = do { (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
274 ; return (ParPat pat', tvs, res) }
276 -- There's a wrinkle with irrefuatable patterns, namely that we
277 -- must not propagate type refinement from them. For example
278 -- data T a where { T1 :: Int -> T Int; ... }
279 -- f :: T a -> Int -> a
281 -- It's obviously not sound to refine a to Int in the right
282 -- hand side, because the arugment might not match T1 at all!
284 -- Nor should a lazy pattern bind any existential type variables
285 -- because they won't be in scope when we do the desugaring
286 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
287 = do { (pat', pat_tvs, res) <- tc_lpat pstate pat pat_ty $ \ _ ->
289 -- Ignore refined pstate',
291 ; if (null pat_tvs) then return ()
292 else lazyPatErr lpat pat_tvs
293 ; return (LazyPat pat', [], res) }
295 tc_pat pstate (WildPat _) pat_ty thing_inside
296 = do { pat_ty' <- unBox pat_ty -- Make sure it's filled in with monotypes
297 ; res <- thing_inside pstate
298 ; return (WildPat pat_ty', [], res) }
300 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
301 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
302 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
303 tc_lpat pstate pat (idType bndr_id) thing_inside
304 -- NB: if we do inference on:
305 -- \ (y@(x::forall a. a->a)) = e
306 -- we'll fail. The as-pattern infers a monotype for 'y', which then
307 -- fails to unify with the polymorphic type for 'x'. This could
308 -- perhaps be fixed, but only with a bit more work.
310 -- If you fix it, don't forget the bindInstsOfPatIds!
311 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
313 -- Type signatures in patterns
314 -- See Note [Pattern coercions] below
315 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
316 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
317 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
318 tc_lpat pstate pat inner_ty thing_inside
319 ; return (SigPatOut pat' inner_ty, tvs, res) }
321 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
322 = failWithTc (badTypePat pat)
324 ------------------------
325 -- Lists, tuples, arrays
326 tc_pat pstate (ListPat pats _) pat_ty thing_inside
327 = do { elt_ty <- boxySplitListTy pat_ty
328 ; let elt_tys = takeList pats (repeat elt_ty)
329 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
330 ; return (ListPat pats' elt_ty, pats_tvs, res) }
332 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
333 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
334 ; let elt_tys = takeList pats (repeat elt_ty)
335 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
336 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
337 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
339 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
340 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
341 ; (pats', pats_tvs, res) <- tc_lpats pstate pats arg_tys thing_inside
343 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
344 -- so that we can experiment with lazy tuple-matching.
345 -- This is a pretty odd place to make the switch, but
346 -- it was easy to do.
347 ; let unmangled_result = TuplePat pats' boxity pat_ty
348 possibly_mangled_result
349 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
350 | otherwise = unmangled_result
352 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
353 return (possibly_mangled_result, pats_tvs, res) }
355 ------------------------
357 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
358 = do { data_con <- tcLookupDataCon con_name
359 ; let tycon = dataConTyCon data_con
360 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
362 ------------------------
364 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
365 = do { boxyUnify (hsLitType simple_lit) pat_ty
366 ; res <- thing_inside pstate
367 ; returnM (LitPat simple_lit, [], res) }
369 ------------------------
370 -- Overloaded patterns: n, and n+k
371 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
372 = do { let orig = LiteralOrigin over_lit
373 ; lit' <- tcOverloadedLit orig over_lit pat_ty
374 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
375 ; mb_neg' <- case mb_neg of
376 Nothing -> return Nothing -- Positive literal
377 Just neg -> -- Negative literal
378 -- The 'negate' is re-mappable syntax
379 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
380 ; return (Just neg') }
381 ; res <- thing_inside pstate
382 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
384 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
385 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
386 ; let pat_ty' = idType bndr_id
387 orig = LiteralOrigin lit
388 ; lit' <- tcOverloadedLit orig lit pat_ty'
390 -- The '>=' and '-' parts are re-mappable syntax
391 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
392 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
394 -- The Report says that n+k patterns must be in Integral
395 -- We may not want this when using re-mappable syntax, though (ToDo?)
396 ; icls <- tcLookupClass integralClassName
397 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
400 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
401 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
405 %************************************************************************
407 Most of the work for constructors is here
408 (the rest is in the ConPatIn case of tc_pat)
410 %************************************************************************
413 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
414 -> BoxySigmaType -- Type of the pattern
415 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
416 -> TcM (Pat TcId, [TcTyVar], a)
417 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
418 | isVanillaDataCon data_con
419 = do { ty_args <- boxySplitTyConApp tycon pat_ty
420 ; let (tvs, _, arg_tys, _, _) = dataConSig data_con
421 arg_tvs = exactTyVarsOfTypes arg_tys
422 -- See Note [Silly type synonyms in smart-app] in TcExpr
423 -- for why we must use exactTyVarsOfTypes
424 inst_prs = zipEqual "tcConPat" tvs ty_args
425 subst = mkTopTvSubst inst_prs
426 arg_tys' = substTys subst arg_tys
427 unconstrained_ty_args = [ty_arg | (tv,ty_arg) <- inst_prs,
428 not (tv `elemVarSet` arg_tvs)]
429 ; mapM unBox unconstrained_ty_args -- Zap these to monotypes
430 ; tcInstStupidTheta data_con ty_args
431 ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys'])
432 ; (arg_pats', tvs, res) <- tcConArgs pstate data_con arg_pats arg_tys' thing_inside
433 ; return (ConPatOut (L con_span data_con) [] [] emptyLHsBinds
434 arg_pats' (mkTyConApp tycon ty_args),
437 | otherwise -- GADT case
438 = do { ty_args <- boxySplitTyConApp tycon pat_ty
439 ; span <- getSrcSpanM -- The whole pattern
441 -- Instantiate the constructor type variables and result type
442 ; let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
443 arg_tvs = exactTyVarsOfTypes arg_tys
444 -- See Note [Silly type synonyms in smart-app] in TcExpr
445 -- for why we must use exactTyVarsOfTypes
446 skol_info = PatSkol data_con span
447 arg_flags = [ tv `elemVarSet` arg_tvs | tv <- tvs ]
448 ; tvs' <- tcInstSkolTyVars skol_info tvs
449 ; let res_tys' = substTys (zipTopTvSubst tvs (mkTyVarTys tvs')) res_tys
451 -- Do type refinement!
452 ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr res_tys',
453 text "ty-args:" <+> ppr ty_args ])
454 ; refineAlt pstate data_con tvs' arg_flags res_tys' ty_args
455 $ \ pstate' tv_tys' -> do
457 -- ToDo: arg_tys should be boxy, but I don't think theta' should be,
458 -- or the tv_tys' in the call to tcInstStupidTheta
459 { let tenv' = zipTopTvSubst tvs tv_tys'
460 theta' = substTheta tenv' theta
461 arg_tys' = substTys tenv' arg_tys -- Boxy types
463 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
464 do { tcInstStupidTheta data_con tv_tys'
465 -- The stupid-theta mentions the newly-bound tyvars, so
466 -- it must live inside the getLIE, so that the
467 -- tcSimplifyCheck will apply the type refinement to it
468 ; tcConArgs pstate' data_con arg_pats arg_tys' thing_inside }
470 ; dicts <- newDicts (SigOrigin skol_info) theta'
471 ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
473 ; return (ConPatOut (L con_span data_con)
474 tvs' (map instToId dicts) dict_binds
475 arg_pats' (mkTyConApp tycon ty_args),
476 tvs' ++ inner_tvs, res)
479 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
481 tcConArgs :: PatState -> DataCon
482 -> HsConDetails Name (LPat Name) -> [TcSigmaType]
483 -> (PatState -> TcM a)
484 -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
486 tcConArgs pstate data_con (PrefixCon arg_pats) arg_tys thing_inside
487 = do { checkTc (con_arity == no_of_args) -- Check correct arity
488 (arityErr "Constructor" data_con con_arity no_of_args)
489 ; (arg_pats', tvs, res) <- tc_lpats pstate arg_pats arg_tys thing_inside
490 ; return (PrefixCon arg_pats', tvs, res) }
492 con_arity = dataConSourceArity data_con
493 no_of_args = length arg_pats
495 tcConArgs pstate data_con (InfixCon p1 p2) arg_tys thing_inside
496 = do { checkTc (con_arity == 2) -- Check correct arity
497 (arityErr "Constructor" data_con con_arity 2)
498 ; ([p1',p2'], tvs, res) <- tc_lpats pstate [p1,p2] arg_tys thing_inside
499 ; return (InfixCon p1' p2', tvs, res) }
501 con_arity = dataConSourceArity data_con
503 tcConArgs pstate data_con (RecCon rpats) arg_tys thing_inside
504 = do { (rpats', tvs, res) <- tc_fields pstate rpats thing_inside
505 ; return (RecCon rpats', tvs, res) }
507 tc_fields :: PatState -> [(Located Name, LPat Name)]
508 -> (PatState -> TcM a)
509 -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
510 tc_fields pstate [] thing_inside
511 = do { res <- thing_inside pstate
512 ; return ([], [], res) }
514 tc_fields pstate (rpat : rpats) thing_inside
515 = do { (rpat', tvs1, (rpats', tvs2, res))
516 <- tc_field pstate rpat $ \ pstate' ->
517 tc_fields pstate' rpats thing_inside
518 ; return (rpat':rpats', tvs1 ++ tvs2, res) }
520 tc_field pstate (field_lbl, pat) thing_inside
521 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
522 ; (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
523 ; return ((sel_id, pat'), tvs, res) }
525 find_field_ty field_lbl
526 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
528 -- No matching field; chances are this field label comes from some
529 -- other record type (or maybe none). As well as reporting an
530 -- error we still want to typecheck the pattern, principally to
531 -- make sure that all the variables it binds are put into the
532 -- environment, else the type checker crashes later:
533 -- f (R { foo = (a,b) }) = a+b
534 -- If foo isn't one of R's fields, we don't want to crash when
535 -- typechecking the "a+b".
536 [] -> do { addErrTc (badFieldCon data_con field_lbl)
537 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
538 ; return (error "Bogus selector Id", bogus_ty) }
540 -- The normal case, when the field comes from the right constructor
542 ASSERT( null extras )
543 do { sel_id <- tcLookupId field_lbl
544 ; return (sel_id, pat_ty) }
546 field_tys = zip (dataConFieldLabels data_con) arg_tys
547 -- Don't use zipEqual! If the constructor isn't really a record, then
548 -- dataConFieldLabels will be empty (and each field in the pattern
549 -- will generate an error below).
553 %************************************************************************
557 %************************************************************************
560 refineAlt :: PatState
561 -> DataCon -- For tracing only
562 -> [TcTyVar] -- Type variables from pattern
563 -> [Bool] -- Flags indicating which type variables occur
564 -- in the type of at least one argument
565 -> [TcType] -- Result types from the pattern
566 -> [BoxySigmaType] -- Result types from the scrutinee (context)
567 -> (PatState -> [BoxySigmaType] -> TcM a)
568 -- Possibly-refined existentials
570 refineAlt pstate con pat_tvs arg_flags pat_res_tys ctxt_res_tys thing_inside
571 | not (all isRigidTy ctxt_res_tys)
572 -- The context is not a rigid type, so we do no type refinement here.
573 = do { let arg_tvs = mkVarSet [ tv | (tv, True) <- pat_tvs `zip` arg_flags]
574 subst = boxyMatchTypes arg_tvs pat_res_tys ctxt_res_tys
576 res_tvs = tcTyVarsOfTypes pat_res_tys
577 -- The tvs are (already) all fresh skolems. We need a
578 -- fresh skolem for each type variable (to bind in the pattern)
579 -- even if it's refined away by the type refinement
581 | not (tv `elemVarSet` res_tvs) = return (mkTyVarTy tv)
582 | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
583 | otherwise = do { tv <- newBoxyTyVar openTypeKind
584 ; return (mkTyVarTy tv) }
585 ; pat_tys' <- mapM find_inst pat_tvs
587 -- Do the thing inside
588 ; res <- thing_inside pstate pat_tys'
590 -- Unbox the types that have been filled in by the thing_inside
591 -- I.e. the ones whose type variables are mentioned in at least one arg
592 ; let strip ty in_arg_tv | in_arg_tv = stripBoxyType ty
593 | otherwise = return ty
594 ; pat_tys'' <- zipWithM strip pat_tys' arg_flags
595 ; let subst = zipOpenTvSubst pat_tvs pat_tys''
596 ; boxyUnifyList (substTys subst pat_res_tys) ctxt_res_tys
598 ; return res } -- All boxes now filled
600 | otherwise -- The context is rigid, so we can do type refinement
601 = case gadtRefineTys (pat_reft pstate) con pat_tvs pat_res_tys ctxt_res_tys of
602 Failed msg -> failWithTc (inaccessibleAlt msg)
603 Succeeded (new_subst, all_bound_here)
604 | all_bound_here -- All the new bindings are for pat_tvs, so no need
605 -- to refine the environment or pstate
606 -> do { traceTc trace_msg
607 ; thing_inside pstate pat_tvs' }
608 | otherwise -- New bindings affect the context, so refine
609 -- the environment and pstate
610 -> refineEnvironment (pat_reft pstate') $
611 do { traceTc trace_msg
612 ; thing_inside pstate' pat_tvs' }
614 pat_tvs' = map (substTyVar new_subst) pat_tvs
615 pstate' = pstate { pat_reft = new_subst }
616 trace_msg = text "refineTypes:match" <+> ppr con <+> ppr new_subst
618 refineType :: GadtRefinement -> BoxyRhoType -> BoxyRhoType
619 -- Refine the type if it is rigid
621 | isRefineableTy ty = substTy reft ty
626 %************************************************************************
630 %************************************************************************
632 In tcOverloadedLit we convert directly to an Int or Integer if we
633 know that's what we want. This may save some time, by not
634 temporarily generating overloaded literals, but it won't catch all
635 cases (the rest are caught in lookupInst).
638 tcOverloadedLit :: InstOrigin
641 -> TcM (HsOverLit TcId)
642 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
643 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
644 -- Reason: If we do, tcSimplify will call lookupInst, which
645 -- will call tcSyntaxName, which does unification,
646 -- which tcSimplify doesn't like
647 -- ToDo: noLoc sadness
648 = do { integer_ty <- tcMetaTy integerTyConName
649 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
650 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
652 | Just expr <- shortCutIntLit i res_ty
653 = return (HsIntegral i expr)
656 = do { expr <- newLitInst orig lit res_ty
657 ; return (HsIntegral i expr) }
659 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
660 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
661 = do { rat_ty <- tcMetaTy rationalTyConName
662 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
663 -- Overloaded literals must have liftedTypeKind, because
664 -- we're instantiating an overloaded function here,
665 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
666 -- However this'll be picked up by tcSyntaxOp if necessary
667 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
669 | Just expr <- shortCutFracLit r res_ty
670 = return (HsFractional r expr)
673 = do { expr <- newLitInst orig lit res_ty
674 ; return (HsFractional r expr) }
676 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
677 newLitInst orig lit res_ty -- Make a LitInst
678 = do { loc <- getInstLoc orig
679 ; res_tau <- zapToMonotype res_ty
680 ; new_uniq <- newUnique
682 lit_nm = mkSystemVarName new_uniq FSLIT("lit")
683 lit_inst = LitInst lit_nm lit res_tau loc
685 ; return (HsVar (instToId lit_inst)) }
689 %************************************************************************
691 Note [Pattern coercions]
693 %************************************************************************
695 In principle, these program would be reasonable:
697 f :: (forall a. a->a) -> Int
698 f (x :: Int->Int) = x 3
700 g :: (forall a. [a]) -> Bool
703 In both cases, the function type signature restricts what arguments can be passed
704 in a call (to polymorphic ones). The pattern type signature then instantiates this
705 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
706 generate the translated term
707 f = \x' :: (forall a. a->a). let x = x' Int in x 3
709 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
710 And it requires a significant amount of code to implement, becuase we need to decorate
711 the translated pattern with coercion functions (generated from the subsumption check
714 So for now I'm just insisting on type *equality* in patterns. No subsumption.
716 Old notes about desugaring, at a time when pattern coercions were handled:
718 A SigPat is a type coercion and must be handled one at at time. We can't
719 combine them unless the type of the pattern inside is identical, and we don't
720 bother to check for that. For example:
722 data T = T1 Int | T2 Bool
723 f :: (forall a. a -> a) -> T -> t
724 f (g::Int->Int) (T1 i) = T1 (g i)
725 f (g::Bool->Bool) (T2 b) = T2 (g b)
727 We desugar this as follows:
729 f = \ g::(forall a. a->a) t::T ->
731 in case t of { T1 i -> T1 (gi i)
734 in case t of { T2 b -> T2 (gb b)
737 Note that we do not treat the first column of patterns as a
738 column of variables, because the coerced variables (gi, gb)
739 would be of different types. So we get rather grotty code.
740 But I don't think this is a common case, and if it was we could
741 doubtless improve it.
743 Meanwhile, the strategy is:
744 * treat each SigPat coercion (always non-identity coercions)
746 * deal with the stuff inside, and then wrap a binding round
747 the result to bind the new variable (gi, gb, etc)
750 %************************************************************************
752 \subsection{Errors and contexts}
754 %************************************************************************
757 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
758 patCtxt (VarPat _) = Nothing
759 patCtxt (ParPat _) = Nothing
760 patCtxt (AsPat _ _) = Nothing
761 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
764 -----------------------------------------------
766 existentialExplode pats
767 = hang (vcat [text "My brain just exploded.",
768 text "I can't handle pattern bindings for existentially-quantified constructors.",
769 text "In the binding group for"])
770 4 (vcat (map ppr pats))
772 sigPatCtxt bound_ids bound_tvs tys tidy_env
773 = -- tys is (body_ty : pat_tys)
774 mapM zonkTcType tys `thenM` \ tys' ->
776 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
777 (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys'
780 sep [ptext SLIT("When checking an existential match that binds"),
781 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
782 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
783 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
786 show_ids = filter is_interesting bound_ids
787 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
789 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
790 -- Don't zonk the types so we get the separate, un-unified versions
792 badFieldCon :: DataCon -> Name -> SDoc
793 badFieldCon con field
794 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
795 ptext SLIT("does not have field"), quotes (ppr field)]
797 polyPatSig :: TcType -> SDoc
799 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
802 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
806 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
807 2 (vcat (map pprSkolTvBinding tvs))
810 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg