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,
36 tidyOpenType, tidyOpenTypes )
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 body_ty) $
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 irrefutable 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 -- Check no existentials
297 ; if (null pat_tvs) then return ()
298 else lazyPatErr lpat pat_tvs
300 -- Check that the pattern has a lifted type
301 ; pat_tv <- newBoxyTyVar liftedTypeKind
302 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
304 ; return (LazyPat pat', [], res) }
306 tc_pat pstate (WildPat _) pat_ty thing_inside
307 = do { pat_ty' <- unBox pat_ty -- Make sure it's filled in with monotypes
308 ; res <- thing_inside pstate
309 ; return (WildPat pat_ty', [], res) }
311 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
312 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
313 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
314 tc_lpat pstate pat (idType bndr_id) thing_inside
315 -- NB: if we do inference on:
316 -- \ (y@(x::forall a. a->a)) = e
317 -- we'll fail. The as-pattern infers a monotype for 'y', which then
318 -- fails to unify with the polymorphic type for 'x'. This could
319 -- perhaps be fixed, but only with a bit more work.
321 -- If you fix it, don't forget the bindInstsOfPatIds!
322 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
324 -- Type signatures in patterns
325 -- See Note [Pattern coercions] below
326 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
327 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
328 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
329 tc_lpat pstate pat inner_ty thing_inside
330 ; return (SigPatOut pat' inner_ty, tvs, res) }
332 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
333 = failWithTc (badTypePat pat)
335 ------------------------
336 -- Lists, tuples, arrays
337 tc_pat pstate (ListPat pats _) pat_ty thing_inside
338 = do { elt_ty <- boxySplitListTy 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 ; return (ListPat pats' elt_ty, pats_tvs, res) }
343 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
344 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
345 ; let elt_tys = takeList pats (repeat elt_ty)
346 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
347 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
348 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
350 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
351 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
352 ; (pats', pats_tvs, res) <- tc_lpats pstate pats arg_tys thing_inside
354 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
355 -- so that we can experiment with lazy tuple-matching.
356 -- This is a pretty odd place to make the switch, but
357 -- it was easy to do.
358 ; let unmangled_result = TuplePat pats' boxity pat_ty
359 possibly_mangled_result
360 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
361 | otherwise = unmangled_result
363 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
364 return (possibly_mangled_result, pats_tvs, res) }
366 ------------------------
368 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
369 = do { data_con <- tcLookupDataCon con_name
370 ; let tycon = dataConTyCon data_con
371 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
373 ------------------------
375 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
376 = do { boxyUnify (hsLitType simple_lit) pat_ty
377 ; res <- thing_inside pstate
378 ; returnM (LitPat simple_lit, [], res) }
380 ------------------------
381 -- Overloaded patterns: n, and n+k
382 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
383 = do { let orig = LiteralOrigin over_lit
384 ; lit' <- tcOverloadedLit orig over_lit pat_ty
385 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
386 ; mb_neg' <- case mb_neg of
387 Nothing -> return Nothing -- Positive literal
388 Just neg -> -- Negative literal
389 -- The 'negate' is re-mappable syntax
390 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
391 ; return (Just neg') }
392 ; res <- thing_inside pstate
393 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
395 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
396 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
397 ; let pat_ty' = idType bndr_id
398 orig = LiteralOrigin lit
399 ; lit' <- tcOverloadedLit orig lit pat_ty'
401 -- The '>=' and '-' parts are re-mappable syntax
402 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
403 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
405 -- The Report says that n+k patterns must be in Integral
406 -- We may not want this when using re-mappable syntax, though (ToDo?)
407 ; icls <- tcLookupClass integralClassName
408 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
411 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
412 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
414 tc_pat _ _other_pat _ _ = panic "tc_pat" -- DictPat, ConPatOut, SigPatOut, VarPatOut
418 %************************************************************************
420 Most of the work for constructors is here
421 (the rest is in the ConPatIn case of tc_pat)
423 %************************************************************************
426 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
427 -> BoxySigmaType -- Type of the pattern
428 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
429 -> TcM (Pat TcId, [TcTyVar], a)
430 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
431 | isVanillaDataCon data_con
432 = do { ty_args <- boxySplitTyConApp tycon pat_ty
433 ; let (tvs, _, arg_tys, _, _) = dataConSig data_con
434 arg_tvs = exactTyVarsOfTypes arg_tys
435 -- See Note [Silly type synonyms in smart-app] in TcExpr
436 -- for why we must use exactTyVarsOfTypes
437 inst_prs = zipEqual "tcConPat" tvs ty_args
438 subst = mkTopTvSubst inst_prs
439 arg_tys' = substTys subst arg_tys
440 unconstrained_ty_args = [ty_arg | (tv,ty_arg) <- inst_prs,
441 not (tv `elemVarSet` arg_tvs)]
442 ; mapM unBox unconstrained_ty_args -- Zap these to monotypes
443 ; tcInstStupidTheta data_con ty_args
444 ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys'])
445 ; (arg_pats', tvs, res) <- tcConArgs pstate data_con arg_pats arg_tys' thing_inside
446 ; return (ConPatOut (L con_span data_con) [] [] emptyLHsBinds
447 arg_pats' (mkTyConApp tycon ty_args),
450 | otherwise -- GADT case
451 = do { ty_args <- boxySplitTyConApp tycon pat_ty
452 ; span <- getSrcSpanM -- The whole pattern
454 -- Instantiate the constructor type variables and result type
455 ; let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
456 arg_tvs = exactTyVarsOfTypes arg_tys
457 -- See Note [Silly type synonyms in smart-app] in TcExpr
458 -- for why we must use exactTyVarsOfTypes
459 skol_info = PatSkol data_con span
460 arg_flags = [ tv `elemVarSet` arg_tvs | tv <- tvs ]
461 ; tvs' <- tcInstSkolTyVars skol_info tvs
462 ; let res_tys' = substTys (zipTopTvSubst tvs (mkTyVarTys tvs')) res_tys
464 -- Do type refinement!
465 ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr res_tys',
466 text "ty-args:" <+> ppr ty_args ])
467 ; refineAlt pstate data_con tvs' arg_flags res_tys' ty_args
468 $ \ pstate' tv_tys' -> do
470 -- ToDo: arg_tys should be boxy, but I don't think theta' should be,
471 -- or the tv_tys' in the call to tcInstStupidTheta
472 { let tenv' = zipTopTvSubst tvs tv_tys'
473 theta' = substTheta tenv' theta
474 arg_tys' = substTys tenv' arg_tys -- Boxy types
476 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
477 do { tcInstStupidTheta data_con tv_tys'
478 -- The stupid-theta mentions the newly-bound tyvars, so
479 -- it must live inside the getLIE, so that the
480 -- tcSimplifyCheck will apply the type refinement to it
481 ; tcConArgs pstate' data_con arg_pats arg_tys' thing_inside }
483 ; dicts <- newDicts (SigOrigin skol_info) theta'
484 ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
486 ; return (ConPatOut (L con_span data_con)
487 tvs' (map instToId dicts) dict_binds
488 arg_pats' (mkTyConApp tycon ty_args),
489 tvs' ++ inner_tvs, res)
492 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
494 tcConArgs :: PatState -> DataCon
495 -> HsConDetails Name (LPat Name) -> [TcSigmaType]
496 -> (PatState -> TcM a)
497 -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
499 tcConArgs pstate data_con (PrefixCon arg_pats) arg_tys thing_inside
500 = do { checkTc (con_arity == no_of_args) -- Check correct arity
501 (arityErr "Constructor" data_con con_arity no_of_args)
502 ; (arg_pats', tvs, res) <- tc_lpats pstate arg_pats arg_tys thing_inside
503 ; return (PrefixCon arg_pats', tvs, res) }
505 con_arity = dataConSourceArity data_con
506 no_of_args = length arg_pats
508 tcConArgs pstate data_con (InfixCon p1 p2) arg_tys thing_inside
509 = do { checkTc (con_arity == 2) -- Check correct arity
510 (arityErr "Constructor" data_con con_arity 2)
511 ; ([p1',p2'], tvs, res) <- tc_lpats pstate [p1,p2] arg_tys thing_inside
512 ; return (InfixCon p1' p2', tvs, res) }
514 con_arity = dataConSourceArity data_con
516 tcConArgs pstate data_con (RecCon rpats) arg_tys thing_inside
517 = do { (rpats', tvs, res) <- tc_fields pstate rpats thing_inside
518 ; return (RecCon rpats', tvs, res) }
520 tc_fields :: PatState -> [(Located Name, LPat Name)]
521 -> (PatState -> TcM a)
522 -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
523 tc_fields pstate [] thing_inside
524 = do { res <- thing_inside pstate
525 ; return ([], [], res) }
527 tc_fields pstate (rpat : rpats) thing_inside
528 = do { (rpat', tvs1, (rpats', tvs2, res))
529 <- tc_field pstate rpat $ \ pstate' ->
530 tc_fields pstate' rpats thing_inside
531 ; return (rpat':rpats', tvs1 ++ tvs2, res) }
533 tc_field pstate (field_lbl, pat) thing_inside
534 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
535 ; (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
536 ; return ((sel_id, pat'), tvs, res) }
538 find_field_ty field_lbl
539 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
541 -- No matching field; chances are this field label comes from some
542 -- other record type (or maybe none). As well as reporting an
543 -- error we still want to typecheck the pattern, principally to
544 -- make sure that all the variables it binds are put into the
545 -- environment, else the type checker crashes later:
546 -- f (R { foo = (a,b) }) = a+b
547 -- If foo isn't one of R's fields, we don't want to crash when
548 -- typechecking the "a+b".
549 [] -> do { addErrTc (badFieldCon data_con field_lbl)
550 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
551 ; return (error "Bogus selector Id", bogus_ty) }
553 -- The normal case, when the field comes from the right constructor
555 ASSERT( null extras )
556 do { sel_id <- tcLookupId field_lbl
557 ; return (sel_id, pat_ty) }
559 field_tys = zip (dataConFieldLabels data_con) arg_tys
560 -- Don't use zipEqual! If the constructor isn't really a record, then
561 -- dataConFieldLabels will be empty (and each field in the pattern
562 -- will generate an error below).
566 %************************************************************************
570 %************************************************************************
573 refineAlt :: PatState
574 -> DataCon -- For tracing only
575 -> [TcTyVar] -- Type variables from pattern
576 -> [Bool] -- Flags indicating which type variables occur
577 -- in the type of at least one argument
578 -> [TcType] -- Result types from the pattern
579 -> [BoxySigmaType] -- Result types from the scrutinee (context)
580 -> (PatState -> [BoxySigmaType] -> TcM a)
581 -- Possibly-refined existentials
583 refineAlt pstate con pat_tvs arg_flags pat_res_tys ctxt_res_tys thing_inside
584 | not (all isRigidTy ctxt_res_tys)
585 -- The context is not a rigid type, so we do no type refinement here.
586 = do { let arg_tvs = mkVarSet [ tv | (tv, True) <- pat_tvs `zip` arg_flags]
587 subst = boxyMatchTypes arg_tvs pat_res_tys ctxt_res_tys
589 res_tvs = tcTyVarsOfTypes pat_res_tys
590 -- The tvs are (already) all fresh skolems. We need a
591 -- fresh skolem for each type variable (to bind in the pattern)
592 -- even if it's refined away by the type refinement
594 | not (tv `elemVarSet` res_tvs) = return (mkTyVarTy tv)
595 | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
596 | otherwise = do { tv <- newBoxyTyVar openTypeKind
597 ; return (mkTyVarTy tv) }
598 ; pat_tys' <- mapM find_inst pat_tvs
600 -- Do the thing inside
601 ; res <- thing_inside pstate pat_tys'
603 -- Unbox the types that have been filled in by the thing_inside
604 -- I.e. the ones whose type variables are mentioned in at least one arg
605 ; let strip ty in_arg_tv | in_arg_tv = stripBoxyType ty
606 | otherwise = return ty
607 ; pat_tys'' <- zipWithM strip pat_tys' arg_flags
608 ; let subst = zipOpenTvSubst pat_tvs pat_tys''
609 ; boxyUnifyList (substTys subst pat_res_tys) ctxt_res_tys
611 ; return res } -- All boxes now filled
613 | otherwise -- The context is rigid, so we can do type refinement
614 = case gadtRefineTys (pat_reft pstate) con pat_tvs pat_res_tys ctxt_res_tys of
615 Failed msg -> failWithTc (inaccessibleAlt msg)
616 Succeeded (new_subst, all_bound_here)
617 | all_bound_here -- All the new bindings are for pat_tvs, so no need
618 -- to refine the environment or pstate
619 -> do { traceTc trace_msg
620 ; thing_inside pstate pat_tvs' }
621 | otherwise -- New bindings affect the context, so pass down pstate'.
622 -- DO NOT refine the envt, because we might be inside a
624 -> do { traceTc trace_msg
625 ; thing_inside pstate' pat_tvs' }
627 pat_tvs' = map (substTyVar new_subst) pat_tvs
628 pstate' = pstate { pat_reft = new_subst }
629 trace_msg = text "refineTypes:match" <+> ppr con <+> ppr new_subst
631 refineType :: GadtRefinement -> BoxyRhoType -> BoxyRhoType
632 -- Refine the type if it is rigid
634 | isRefineableTy ty = substTy reft ty
639 %************************************************************************
643 %************************************************************************
645 In tcOverloadedLit we convert directly to an Int or Integer if we
646 know that's what we want. This may save some time, by not
647 temporarily generating overloaded literals, but it won't catch all
648 cases (the rest are caught in lookupInst).
651 tcOverloadedLit :: InstOrigin
654 -> TcM (HsOverLit TcId)
655 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
656 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
657 -- Reason: If we do, tcSimplify will call lookupInst, which
658 -- will call tcSyntaxName, which does unification,
659 -- which tcSimplify doesn't like
660 -- ToDo: noLoc sadness
661 = do { integer_ty <- tcMetaTy integerTyConName
662 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
663 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
665 | Just expr <- shortCutIntLit i res_ty
666 = return (HsIntegral i expr)
669 = do { expr <- newLitInst orig lit res_ty
670 ; return (HsIntegral i expr) }
672 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
673 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
674 = do { rat_ty <- tcMetaTy rationalTyConName
675 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
676 -- Overloaded literals must have liftedTypeKind, because
677 -- we're instantiating an overloaded function here,
678 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
679 -- However this'll be picked up by tcSyntaxOp if necessary
680 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
682 | Just expr <- shortCutFracLit r res_ty
683 = return (HsFractional r expr)
686 = do { expr <- newLitInst orig lit res_ty
687 ; return (HsFractional r expr) }
689 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
690 newLitInst orig lit res_ty -- Make a LitInst
691 = do { loc <- getInstLoc orig
692 ; res_tau <- zapToMonotype res_ty
693 ; new_uniq <- newUnique
694 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
695 lit_inst = LitInst lit_nm lit res_tau loc
697 ; return (HsVar (instToId lit_inst)) }
701 %************************************************************************
703 Note [Pattern coercions]
705 %************************************************************************
707 In principle, these program would be reasonable:
709 f :: (forall a. a->a) -> Int
710 f (x :: Int->Int) = x 3
712 g :: (forall a. [a]) -> Bool
715 In both cases, the function type signature restricts what arguments can be passed
716 in a call (to polymorphic ones). The pattern type signature then instantiates this
717 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
718 generate the translated term
719 f = \x' :: (forall a. a->a). let x = x' Int in x 3
721 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
722 And it requires a significant amount of code to implement, becuase we need to decorate
723 the translated pattern with coercion functions (generated from the subsumption check
726 So for now I'm just insisting on type *equality* in patterns. No subsumption.
728 Old notes about desugaring, at a time when pattern coercions were handled:
730 A SigPat is a type coercion and must be handled one at at time. We can't
731 combine them unless the type of the pattern inside is identical, and we don't
732 bother to check for that. For example:
734 data T = T1 Int | T2 Bool
735 f :: (forall a. a -> a) -> T -> t
736 f (g::Int->Int) (T1 i) = T1 (g i)
737 f (g::Bool->Bool) (T2 b) = T2 (g b)
739 We desugar this as follows:
741 f = \ g::(forall a. a->a) t::T ->
743 in case t of { T1 i -> T1 (gi i)
746 in case t of { T2 b -> T2 (gb b)
749 Note that we do not treat the first column of patterns as a
750 column of variables, because the coerced variables (gi, gb)
751 would be of different types. So we get rather grotty code.
752 But I don't think this is a common case, and if it was we could
753 doubtless improve it.
755 Meanwhile, the strategy is:
756 * treat each SigPat coercion (always non-identity coercions)
758 * deal with the stuff inside, and then wrap a binding round
759 the result to bind the new variable (gi, gb, etc)
762 %************************************************************************
764 \subsection{Errors and contexts}
766 %************************************************************************
769 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
770 patCtxt (VarPat _) = Nothing
771 patCtxt (ParPat _) = Nothing
772 patCtxt (AsPat _ _) = Nothing
773 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
776 -----------------------------------------------
778 existentialExplode pats
779 = hang (vcat [text "My brain just exploded.",
780 text "I can't handle pattern bindings for existentially-quantified constructors.",
781 text "In the binding group for"])
782 4 (vcat (map ppr pats))
784 sigPatCtxt bound_ids bound_tvs pat_tys body_ty tidy_env
785 = do { pat_tys' <- mapM zonkTcType pat_tys
786 ; body_ty' <- zonkTcType body_ty
787 ; let (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
788 (env2, tidy_pat_tys) = tidyOpenTypes env1 pat_tys'
789 (env3, tidy_body_ty) = tidyOpenType env2 body_ty'
791 sep [ptext SLIT("When checking an existential match that binds"),
792 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
793 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
794 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
797 show_ids = filter is_interesting bound_ids
798 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
800 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
801 -- Don't zonk the types so we get the separate, un-unified versions
803 badFieldCon :: DataCon -> Name -> SDoc
804 badFieldCon con field
805 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
806 ptext SLIT("does not have field"), quotes (ppr field)]
808 polyPatSig :: TcType -> SDoc
810 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
813 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
817 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
818 2 (vcat (map pprSkolTvBinding tvs))
821 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg