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 refineEnvironment (pat_reft pstate') $
92 thing_inside (refineType (pat_reft pstate') res_ty)
94 ; tcCheckExistentialPat ctxt pats' ex_tvs tys res_ty
96 ; returnM (pats', res) }
101 -> LPat Name -> BoxySigmaType
102 -> BoxyRhoType -- Result type
103 -> (BoxyRhoType -> TcM a) -- Checker for body, given its result type
104 -> TcM (LPat TcId, a)
105 tcPat ctxt pat pat_ty res_ty thing_inside
106 = do { ([pat'],thing) <- tcPats ctxt [pat] [pat_ty] res_ty thing_inside
107 ; return (pat', thing) }
111 tcCheckExistentialPat :: PatCtxt
112 -> [LPat TcId] -- Patterns (just for error message)
113 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
114 -> [BoxySigmaType] -- Types of the patterns
115 -> BoxyRhoType -- Type of the body of the match
116 -- Tyvars in either of these must not escape
118 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
119 -- For example, we must reject this program:
120 -- data C = forall a. C (a -> Int)
122 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
124 tcCheckExistentialPat ctxt pats [] pat_tys body_ty
125 = return () -- Short cut for case when there are no existentials
127 tcCheckExistentialPat (LetPat _) pats ex_tvs pat_tys body_ty
128 -- Don't know how to deal with pattern-bound existentials yet
129 = failWithTc (existentialExplode pats)
131 tcCheckExistentialPat ctxt pats ex_tvs pat_tys body_ty
132 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys) $
133 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
137 pat_reft :: GadtRefinement -- Binds rigid TcTyVars to their refinements
142 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
144 patSigCtxt :: PatState -> UserTypeCtxt
145 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
146 patSigCtxt other = LamPatSigCtxt
151 %************************************************************************
155 %************************************************************************
158 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
159 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
160 = do { pat_ty' <- unBox pat_ty
161 -- We have an undecorated binder, so we do rule ABS1,
162 -- by unboxing the boxy type, forcing any un-filled-in
163 -- boxes to become monotypes
164 -- NB that pat_ty' can still be a polytype:
165 -- data T = MkT (forall a. a->a)
166 -- f t = case t of { MkT g -> ... }
167 -- Here, the 'g' must get type (forall a. a->a) from the
169 ; return (mkLocalId bndr_name pat_ty') }
171 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
172 | Just mono_ty <- lookup_sig bndr_name
173 = do { mono_name <- newLocalName bndr_name
174 ; boxyUnify mono_ty pat_ty
175 ; return (mkLocalId mono_name mono_ty) }
178 = do { pat_ty' <- unBox pat_ty
179 ; mono_name <- newLocalName bndr_name
180 ; return (mkLocalId mono_name pat_ty') }
184 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
185 bindInstsOfPatId id thing_inside
186 | not (isOverloadedTy (idType id))
187 = do { res <- thing_inside; return (res, emptyLHsBinds) }
189 = do { (res, lie) <- getLIE thing_inside
190 ; binds <- bindInstsOfLocalFuns lie [id]
191 ; return (res, binds) }
195 %************************************************************************
197 The main worker functions
199 %************************************************************************
203 tcPat takes a "thing inside" over which the patter scopes. This is partly
204 so that tcPat can extend the environment for the thing_inside, but also
205 so that constraints arising in the thing_inside can be discharged by the
208 This does not work so well for the ErrCtxt carried by the monad: we don't
209 want the error-context for the pattern to scope over the RHS.
210 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
217 -> (PatState -> TcM a)
218 -> TcM ([LPat TcId], [TcTyVar], a)
220 tc_lpats pstate pats pat_tys thing_inside
221 = do { err_ctxt <- getErrCtxt
222 ; let loop pstate [] []
223 = do { res <- thing_inside pstate
224 ; return ([], [], res) }
226 loop pstate (p:ps) (ty:tys)
227 = do { (p', p_tvs, (ps', ps_tvs, res))
228 <- tc_lpat pstate p ty $ \ pstate' ->
229 setErrCtxt err_ctxt $
231 -- setErrCtxt: restore context before doing the next pattern
232 -- See note [Nesting] above
234 ; return (p':ps', p_tvs ++ ps_tvs, res) }
236 loop _ _ _ = pprPanic "tc_lpats" (ppr pats $$ ppr pat_tys)
238 ; loop pstate pats pat_tys }
244 -> (PatState -> TcM a)
245 -> TcM (LPat TcId, [TcTyVar], a)
246 tc_lpat pstate (L span pat) pat_ty thing_inside
248 maybeAddErrCtxt (patCtxt pat) $
249 do { let pat_ty' = refineType (pat_reft pstate) pat_ty
250 -- Make sure the result type reflects the current refinement
251 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
252 ; return (L span pat', tvs, res) }
257 -> Pat Name -> BoxySigmaType -- Fully refined result type
258 -> (PatState -> TcM a) -- Thing inside
259 -> TcM (Pat TcId, -- Translated pattern
260 [TcTyVar], -- Existential binders
261 a) -- Result of thing inside
263 tc_pat pstate (VarPat name) pat_ty thing_inside
264 = do { id <- tcPatBndr pstate name pat_ty
265 ; (res, binds) <- bindInstsOfPatId id $
266 tcExtendIdEnv1 name id $
267 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
268 >> thing_inside pstate)
269 ; let pat' | isEmptyLHsBinds binds = VarPat id
270 | otherwise = VarPatOut id binds
271 ; return (pat', [], res) }
273 tc_pat pstate (ParPat pat) pat_ty thing_inside
274 = do { (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
275 ; return (ParPat pat', tvs, res) }
277 tc_pat pstate (BangPat pat) pat_ty thing_inside
278 = do { (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
279 ; return (BangPat pat', tvs, res) }
281 -- There's a wrinkle with irrefuatable patterns, namely that we
282 -- must not propagate type refinement from them. For example
283 -- data T a where { T1 :: Int -> T Int; ... }
284 -- f :: T a -> Int -> a
286 -- It's obviously not sound to refine a to Int in the right
287 -- hand side, because the arugment might not match T1 at all!
289 -- Nor should a lazy pattern bind any existential type variables
290 -- because they won't be in scope when we do the desugaring
291 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
292 = do { (pat', pat_tvs, res) <- tc_lpat pstate pat pat_ty $ \ _ ->
294 -- Ignore refined pstate',
296 ; if (null pat_tvs) then return ()
297 else lazyPatErr lpat pat_tvs
298 ; return (LazyPat pat', [], res) }
300 tc_pat pstate (WildPat _) pat_ty thing_inside
301 = do { pat_ty' <- unBox pat_ty -- Make sure it's filled in with monotypes
302 ; res <- thing_inside pstate
303 ; return (WildPat pat_ty', [], res) }
305 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
306 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
307 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
308 tc_lpat pstate pat (idType bndr_id) thing_inside
309 -- NB: if we do inference on:
310 -- \ (y@(x::forall a. a->a)) = e
311 -- we'll fail. The as-pattern infers a monotype for 'y', which then
312 -- fails to unify with the polymorphic type for 'x'. This could
313 -- perhaps be fixed, but only with a bit more work.
315 -- If you fix it, don't forget the bindInstsOfPatIds!
316 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
318 -- Type signatures in patterns
319 -- See Note [Pattern coercions] below
320 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
321 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
322 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
323 tc_lpat pstate pat inner_ty thing_inside
324 ; return (SigPatOut pat' inner_ty, tvs, res) }
326 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
327 = failWithTc (badTypePat pat)
329 ------------------------
330 -- Lists, tuples, arrays
331 tc_pat pstate (ListPat pats _) pat_ty thing_inside
332 = do { elt_ty <- boxySplitListTy pat_ty
333 ; let elt_tys = takeList pats (repeat elt_ty)
334 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
335 ; return (ListPat pats' elt_ty, pats_tvs, res) }
337 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
338 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
339 ; let elt_tys = takeList pats (repeat elt_ty)
340 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
341 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
342 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
344 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
345 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
346 ; (pats', pats_tvs, res) <- tc_lpats pstate pats arg_tys thing_inside
348 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
349 -- so that we can experiment with lazy tuple-matching.
350 -- This is a pretty odd place to make the switch, but
351 -- it was easy to do.
352 ; let unmangled_result = TuplePat pats' boxity pat_ty
353 possibly_mangled_result
354 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
355 | otherwise = unmangled_result
357 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
358 return (possibly_mangled_result, pats_tvs, res) }
360 ------------------------
362 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
363 = do { data_con <- tcLookupDataCon con_name
364 ; let tycon = dataConTyCon data_con
365 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
367 ------------------------
369 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
370 = do { boxyUnify (hsLitType simple_lit) pat_ty
371 ; res <- thing_inside pstate
372 ; returnM (LitPat simple_lit, [], res) }
374 ------------------------
375 -- Overloaded patterns: n, and n+k
376 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
377 = do { let orig = LiteralOrigin over_lit
378 ; lit' <- tcOverloadedLit orig over_lit pat_ty
379 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
380 ; mb_neg' <- case mb_neg of
381 Nothing -> return Nothing -- Positive literal
382 Just neg -> -- Negative literal
383 -- The 'negate' is re-mappable syntax
384 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
385 ; return (Just neg') }
386 ; res <- thing_inside pstate
387 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
389 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
390 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
391 ; let pat_ty' = idType bndr_id
392 orig = LiteralOrigin lit
393 ; lit' <- tcOverloadedLit orig lit pat_ty'
395 -- The '>=' and '-' parts are re-mappable syntax
396 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
397 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
399 -- The Report says that n+k patterns must be in Integral
400 -- We may not want this when using re-mappable syntax, though (ToDo?)
401 ; icls <- tcLookupClass integralClassName
402 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
405 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
406 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
410 %************************************************************************
412 Most of the work for constructors is here
413 (the rest is in the ConPatIn case of tc_pat)
415 %************************************************************************
418 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
419 -> BoxySigmaType -- Type of the pattern
420 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
421 -> TcM (Pat TcId, [TcTyVar], a)
422 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
423 | isVanillaDataCon data_con
424 = do { ty_args <- boxySplitTyConApp tycon pat_ty
425 ; let (tvs, _, arg_tys, _, _) = dataConSig data_con
426 arg_tvs = exactTyVarsOfTypes arg_tys
427 -- See Note [Silly type synonyms in smart-app] in TcExpr
428 -- for why we must use exactTyVarsOfTypes
429 inst_prs = zipEqual "tcConPat" tvs ty_args
430 subst = mkTopTvSubst inst_prs
431 arg_tys' = substTys subst arg_tys
432 unconstrained_ty_args = [ty_arg | (tv,ty_arg) <- inst_prs,
433 not (tv `elemVarSet` arg_tvs)]
434 ; mapM unBox unconstrained_ty_args -- Zap these to monotypes
435 ; tcInstStupidTheta data_con ty_args
436 ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys'])
437 ; (arg_pats', tvs, res) <- tcConArgs pstate data_con arg_pats arg_tys' thing_inside
438 ; return (ConPatOut (L con_span data_con) [] [] emptyLHsBinds
439 arg_pats' (mkTyConApp tycon ty_args),
442 | otherwise -- GADT case
443 = do { ty_args <- boxySplitTyConApp tycon pat_ty
444 ; span <- getSrcSpanM -- The whole pattern
446 -- Instantiate the constructor type variables and result type
447 ; let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
448 arg_tvs = exactTyVarsOfTypes arg_tys
449 -- See Note [Silly type synonyms in smart-app] in TcExpr
450 -- for why we must use exactTyVarsOfTypes
451 skol_info = PatSkol data_con span
452 arg_flags = [ tv `elemVarSet` arg_tvs | tv <- tvs ]
453 ; tvs' <- tcInstSkolTyVars skol_info tvs
454 ; let res_tys' = substTys (zipTopTvSubst tvs (mkTyVarTys tvs')) res_tys
456 -- Do type refinement!
457 ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr res_tys',
458 text "ty-args:" <+> ppr ty_args ])
459 ; refineAlt pstate data_con tvs' arg_flags res_tys' ty_args
460 $ \ pstate' tv_tys' -> do
462 -- ToDo: arg_tys should be boxy, but I don't think theta' should be,
463 -- or the tv_tys' in the call to tcInstStupidTheta
464 { let tenv' = zipTopTvSubst tvs tv_tys'
465 theta' = substTheta tenv' theta
466 arg_tys' = substTys tenv' arg_tys -- Boxy types
468 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
469 do { tcInstStupidTheta data_con tv_tys'
470 -- The stupid-theta mentions the newly-bound tyvars, so
471 -- it must live inside the getLIE, so that the
472 -- tcSimplifyCheck will apply the type refinement to it
473 ; tcConArgs pstate' data_con arg_pats arg_tys' thing_inside }
475 ; dicts <- newDicts (SigOrigin skol_info) theta'
476 ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
478 ; return (ConPatOut (L con_span data_con)
479 tvs' (map instToId dicts) dict_binds
480 arg_pats' (mkTyConApp tycon ty_args),
481 tvs' ++ inner_tvs, res)
484 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
486 tcConArgs :: PatState -> DataCon
487 -> HsConDetails Name (LPat Name) -> [TcSigmaType]
488 -> (PatState -> TcM a)
489 -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
491 tcConArgs pstate data_con (PrefixCon arg_pats) arg_tys thing_inside
492 = do { checkTc (con_arity == no_of_args) -- Check correct arity
493 (arityErr "Constructor" data_con con_arity no_of_args)
494 ; (arg_pats', tvs, res) <- tc_lpats pstate arg_pats arg_tys thing_inside
495 ; return (PrefixCon arg_pats', tvs, res) }
497 con_arity = dataConSourceArity data_con
498 no_of_args = length arg_pats
500 tcConArgs pstate data_con (InfixCon p1 p2) arg_tys thing_inside
501 = do { checkTc (con_arity == 2) -- Check correct arity
502 (arityErr "Constructor" data_con con_arity 2)
503 ; ([p1',p2'], tvs, res) <- tc_lpats pstate [p1,p2] arg_tys thing_inside
504 ; return (InfixCon p1' p2', tvs, res) }
506 con_arity = dataConSourceArity data_con
508 tcConArgs pstate data_con (RecCon rpats) arg_tys thing_inside
509 = do { (rpats', tvs, res) <- tc_fields pstate rpats thing_inside
510 ; return (RecCon rpats', tvs, res) }
512 tc_fields :: PatState -> [(Located Name, LPat Name)]
513 -> (PatState -> TcM a)
514 -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
515 tc_fields pstate [] thing_inside
516 = do { res <- thing_inside pstate
517 ; return ([], [], res) }
519 tc_fields pstate (rpat : rpats) thing_inside
520 = do { (rpat', tvs1, (rpats', tvs2, res))
521 <- tc_field pstate rpat $ \ pstate' ->
522 tc_fields pstate' rpats thing_inside
523 ; return (rpat':rpats', tvs1 ++ tvs2, res) }
525 tc_field pstate (field_lbl, pat) thing_inside
526 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
527 ; (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
528 ; return ((sel_id, pat'), tvs, res) }
530 find_field_ty field_lbl
531 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
533 -- No matching field; chances are this field label comes from some
534 -- other record type (or maybe none). As well as reporting an
535 -- error we still want to typecheck the pattern, principally to
536 -- make sure that all the variables it binds are put into the
537 -- environment, else the type checker crashes later:
538 -- f (R { foo = (a,b) }) = a+b
539 -- If foo isn't one of R's fields, we don't want to crash when
540 -- typechecking the "a+b".
541 [] -> do { addErrTc (badFieldCon data_con field_lbl)
542 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
543 ; return (error "Bogus selector Id", bogus_ty) }
545 -- The normal case, when the field comes from the right constructor
547 ASSERT( null extras )
548 do { sel_id <- tcLookupId field_lbl
549 ; return (sel_id, pat_ty) }
551 field_tys = zip (dataConFieldLabels data_con) arg_tys
552 -- Don't use zipEqual! If the constructor isn't really a record, then
553 -- dataConFieldLabels will be empty (and each field in the pattern
554 -- will generate an error below).
558 %************************************************************************
562 %************************************************************************
565 refineAlt :: PatState
566 -> DataCon -- For tracing only
567 -> [TcTyVar] -- Type variables from pattern
568 -> [Bool] -- Flags indicating which type variables occur
569 -- in the type of at least one argument
570 -> [TcType] -- Result types from the pattern
571 -> [BoxySigmaType] -- Result types from the scrutinee (context)
572 -> (PatState -> [BoxySigmaType] -> TcM a)
573 -- Possibly-refined existentials
575 refineAlt pstate con pat_tvs arg_flags pat_res_tys ctxt_res_tys thing_inside
576 | not (all isRigidTy ctxt_res_tys)
577 -- The context is not a rigid type, so we do no type refinement here.
578 = do { let arg_tvs = mkVarSet [ tv | (tv, True) <- pat_tvs `zip` arg_flags]
579 subst = boxyMatchTypes arg_tvs pat_res_tys ctxt_res_tys
581 res_tvs = tcTyVarsOfTypes pat_res_tys
582 -- The tvs are (already) all fresh skolems. We need a
583 -- fresh skolem for each type variable (to bind in the pattern)
584 -- even if it's refined away by the type refinement
586 | not (tv `elemVarSet` res_tvs) = return (mkTyVarTy tv)
587 | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
588 | otherwise = do { tv <- newBoxyTyVar openTypeKind
589 ; return (mkTyVarTy tv) }
590 ; pat_tys' <- mapM find_inst pat_tvs
592 -- Do the thing inside
593 ; res <- thing_inside pstate pat_tys'
595 -- Unbox the types that have been filled in by the thing_inside
596 -- I.e. the ones whose type variables are mentioned in at least one arg
597 ; let strip ty in_arg_tv | in_arg_tv = stripBoxyType ty
598 | otherwise = return ty
599 ; pat_tys'' <- zipWithM strip pat_tys' arg_flags
600 ; let subst = zipOpenTvSubst pat_tvs pat_tys''
601 ; boxyUnifyList (substTys subst pat_res_tys) ctxt_res_tys
603 ; return res } -- All boxes now filled
605 | otherwise -- The context is rigid, so we can do type refinement
606 = case gadtRefineTys (pat_reft pstate) con pat_tvs pat_res_tys ctxt_res_tys of
607 Failed msg -> failWithTc (inaccessibleAlt msg)
608 Succeeded (new_subst, all_bound_here)
609 | all_bound_here -- All the new bindings are for pat_tvs, so no need
610 -- to refine the environment or pstate
611 -> do { traceTc trace_msg
612 ; thing_inside pstate pat_tvs' }
613 | otherwise -- New bindings affect the context, so pass down pstate'.
614 -- DO NOT refine the envt, because we might be inside a
616 -> do { traceTc trace_msg
617 ; thing_inside pstate' pat_tvs' }
619 pat_tvs' = map (substTyVar new_subst) pat_tvs
620 pstate' = pstate { pat_reft = new_subst }
621 trace_msg = text "refineTypes:match" <+> ppr con <+> ppr new_subst
623 refineType :: GadtRefinement -> BoxyRhoType -> BoxyRhoType
624 -- Refine the type if it is rigid
626 | isRefineableTy ty = substTy reft ty
631 %************************************************************************
635 %************************************************************************
637 In tcOverloadedLit we convert directly to an Int or Integer if we
638 know that's what we want. This may save some time, by not
639 temporarily generating overloaded literals, but it won't catch all
640 cases (the rest are caught in lookupInst).
643 tcOverloadedLit :: InstOrigin
646 -> TcM (HsOverLit TcId)
647 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
648 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
649 -- Reason: If we do, tcSimplify will call lookupInst, which
650 -- will call tcSyntaxName, which does unification,
651 -- which tcSimplify doesn't like
652 -- ToDo: noLoc sadness
653 = do { integer_ty <- tcMetaTy integerTyConName
654 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
655 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
657 | Just expr <- shortCutIntLit i res_ty
658 = return (HsIntegral i expr)
661 = do { expr <- newLitInst orig lit res_ty
662 ; return (HsIntegral i expr) }
664 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
665 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
666 = do { rat_ty <- tcMetaTy rationalTyConName
667 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
668 -- Overloaded literals must have liftedTypeKind, because
669 -- we're instantiating an overloaded function here,
670 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
671 -- However this'll be picked up by tcSyntaxOp if necessary
672 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
674 | Just expr <- shortCutFracLit r res_ty
675 = return (HsFractional r expr)
678 = do { expr <- newLitInst orig lit res_ty
679 ; return (HsFractional r expr) }
681 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
682 newLitInst orig lit res_ty -- Make a LitInst
683 = do { loc <- getInstLoc orig
684 ; res_tau <- zapToMonotype res_ty
685 ; new_uniq <- newUnique
687 lit_nm = mkSystemVarName new_uniq FSLIT("lit")
688 lit_inst = LitInst lit_nm lit res_tau loc
690 ; return (HsVar (instToId lit_inst)) }
694 %************************************************************************
696 Note [Pattern coercions]
698 %************************************************************************
700 In principle, these program would be reasonable:
702 f :: (forall a. a->a) -> Int
703 f (x :: Int->Int) = x 3
705 g :: (forall a. [a]) -> Bool
708 In both cases, the function type signature restricts what arguments can be passed
709 in a call (to polymorphic ones). The pattern type signature then instantiates this
710 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
711 generate the translated term
712 f = \x' :: (forall a. a->a). let x = x' Int in x 3
714 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
715 And it requires a significant amount of code to implement, becuase we need to decorate
716 the translated pattern with coercion functions (generated from the subsumption check
719 So for now I'm just insisting on type *equality* in patterns. No subsumption.
721 Old notes about desugaring, at a time when pattern coercions were handled:
723 A SigPat is a type coercion and must be handled one at at time. We can't
724 combine them unless the type of the pattern inside is identical, and we don't
725 bother to check for that. For example:
727 data T = T1 Int | T2 Bool
728 f :: (forall a. a -> a) -> T -> t
729 f (g::Int->Int) (T1 i) = T1 (g i)
730 f (g::Bool->Bool) (T2 b) = T2 (g b)
732 We desugar this as follows:
734 f = \ g::(forall a. a->a) t::T ->
736 in case t of { T1 i -> T1 (gi i)
739 in case t of { T2 b -> T2 (gb b)
742 Note that we do not treat the first column of patterns as a
743 column of variables, because the coerced variables (gi, gb)
744 would be of different types. So we get rather grotty code.
745 But I don't think this is a common case, and if it was we could
746 doubtless improve it.
748 Meanwhile, the strategy is:
749 * treat each SigPat coercion (always non-identity coercions)
751 * deal with the stuff inside, and then wrap a binding round
752 the result to bind the new variable (gi, gb, etc)
755 %************************************************************************
757 \subsection{Errors and contexts}
759 %************************************************************************
762 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
763 patCtxt (VarPat _) = Nothing
764 patCtxt (ParPat _) = Nothing
765 patCtxt (AsPat _ _) = Nothing
766 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
769 -----------------------------------------------
771 existentialExplode pats
772 = hang (vcat [text "My brain just exploded.",
773 text "I can't handle pattern bindings for existentially-quantified constructors.",
774 text "In the binding group for"])
775 4 (vcat (map ppr pats))
777 sigPatCtxt bound_ids bound_tvs tys tidy_env
778 = -- tys is (body_ty : pat_tys)
779 mapM zonkTcType tys `thenM` \ tys' ->
781 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
782 (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys'
785 sep [ptext SLIT("When checking an existential match that binds"),
786 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
787 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
788 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
791 show_ids = filter is_interesting bound_ids
792 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
794 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
795 -- Don't zonk the types so we get the separate, un-unified versions
797 badFieldCon :: DataCon -> Name -> SDoc
798 badFieldCon con field
799 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
800 ptext SLIT("does not have field"), quotes (ppr field)]
802 polyPatSig :: TcType -> SDoc
804 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
807 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
811 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
812 2 (vcat (map pprSkolTvBinding tvs))
815 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg