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 -> TcType
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 -- There's a wrinkle with irrefuatable patterns, namely that we
278 -- must not propagate type refinement from them. For example
279 -- data T a where { T1 :: Int -> T Int; ... }
280 -- f :: T a -> Int -> a
282 -- It's obviously not sound to refine a to Int in the right
283 -- hand side, because the arugment might not match T1 at all!
285 -- Nor should a lazy pattern bind any existential type variables
286 -- because they won't be in scope when we do the desugaring
287 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
288 = do { (pat', pat_tvs, res) <- tc_lpat pstate pat pat_ty $ \ _ ->
290 -- Ignore refined pstate',
292 ; if (null pat_tvs) then return ()
293 else lazyPatErr lpat pat_tvs
294 ; return (LazyPat pat', [], res) }
296 tc_pat pstate (WildPat _) pat_ty thing_inside
297 = do { pat_ty' <- unBox pat_ty -- Make sure it's filled in with monotypes
298 ; res <- thing_inside pstate
299 ; return (WildPat pat_ty', [], res) }
301 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
302 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
303 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
304 tc_lpat pstate pat (idType bndr_id) thing_inside
305 -- NB: if we do inference on:
306 -- \ (y@(x::forall a. a->a)) = e
307 -- we'll fail. The as-pattern infers a monotype for 'y', which then
308 -- fails to unify with the polymorphic type for 'x'. This could
309 -- perhaps be fixed, but only with a bit more work.
311 -- If you fix it, don't forget the bindInstsOfPatIds!
312 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
314 -- Type signatures in patterns
315 -- See Note [Pattern coercions] below
316 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
317 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
318 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
319 tc_lpat pstate pat inner_ty thing_inside
320 ; return (SigPatOut pat' inner_ty, tvs, res) }
322 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
323 = failWithTc (badTypePat pat)
325 ------------------------
326 -- Lists, tuples, arrays
327 tc_pat pstate (ListPat pats _) pat_ty thing_inside
328 = do { elt_ty <- boxySplitListTy pat_ty
329 ; let elt_tys = takeList pats (repeat elt_ty)
330 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
331 ; return (ListPat pats' elt_ty, pats_tvs, res) }
333 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
334 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
335 ; let elt_tys = takeList pats (repeat elt_ty)
336 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
337 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
338 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
340 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
341 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
342 ; (pats', pats_tvs, res) <- tc_lpats pstate pats arg_tys thing_inside
344 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
345 -- so that we can experiment with lazy tuple-matching.
346 -- This is a pretty odd place to make the switch, but
347 -- it was easy to do.
348 ; let unmangled_result = TuplePat pats' boxity pat_ty
349 possibly_mangled_result
350 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
351 | otherwise = unmangled_result
353 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
354 return (possibly_mangled_result, pats_tvs, res) }
356 ------------------------
358 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
359 = do { data_con <- tcLookupDataCon con_name
360 ; let tycon = dataConTyCon data_con
361 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
363 ------------------------
365 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
366 = do { boxyUnify (hsLitType simple_lit) pat_ty
367 ; res <- thing_inside pstate
368 ; returnM (LitPat simple_lit, [], res) }
370 ------------------------
371 -- Overloaded patterns: n, and n+k
372 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
373 = do { let orig = LiteralOrigin over_lit
374 ; lit' <- tcOverloadedLit orig over_lit pat_ty
375 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
376 ; mb_neg' <- case mb_neg of
377 Nothing -> return Nothing -- Positive literal
378 Just neg -> -- Negative literal
379 -- The 'negate' is re-mappable syntax
380 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
381 ; return (Just neg') }
382 ; res <- thing_inside pstate
383 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
385 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
386 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
387 ; let pat_ty' = idType bndr_id
388 orig = LiteralOrigin lit
389 ; lit' <- tcOverloadedLit orig lit pat_ty'
391 -- The '>=' and '-' parts are re-mappable syntax
392 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
393 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
395 -- The Report says that n+k patterns must be in Integral
396 -- We may not want this when using re-mappable syntax, though (ToDo?)
397 ; icls <- tcLookupClass integralClassName
398 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
401 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
402 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
406 %************************************************************************
408 Most of the work for constructors is here
409 (the rest is in the ConPatIn case of tc_pat)
411 %************************************************************************
414 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
415 -> BoxySigmaType -- Type of the pattern
416 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
417 -> TcM (Pat TcId, [TcTyVar], a)
418 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
419 | isVanillaDataCon data_con
420 = do { ty_args <- boxySplitTyConApp tycon pat_ty
421 ; let (tvs, _, arg_tys, _, _) = dataConSig data_con
422 arg_tvs = exactTyVarsOfTypes arg_tys
423 -- See Note [Silly type synonyms in smart-app] in TcExpr
424 -- for why we must use exactTyVarsOfTypes
425 inst_prs = zipEqual "tcConPat" tvs ty_args
426 subst = mkTopTvSubst inst_prs
427 arg_tys' = substTys subst arg_tys
428 unconstrained_ty_args = [ty_arg | (tv,ty_arg) <- inst_prs,
429 not (tv `elemVarSet` arg_tvs)]
430 ; mapM unBox unconstrained_ty_args -- Zap these to monotypes
431 ; tcInstStupidTheta data_con ty_args
432 ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys'])
433 ; (arg_pats', tvs, res) <- tcConArgs pstate data_con arg_pats arg_tys' thing_inside
434 ; return (ConPatOut (L con_span data_con) [] [] emptyLHsBinds
435 arg_pats' (mkTyConApp tycon ty_args),
438 | otherwise -- GADT case
439 = do { ty_args <- boxySplitTyConApp tycon pat_ty
440 ; span <- getSrcSpanM -- The whole pattern
442 -- Instantiate the constructor type variables and result type
443 ; let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
444 arg_tvs = exactTyVarsOfTypes arg_tys
445 -- See Note [Silly type synonyms in smart-app] in TcExpr
446 -- for why we must use exactTyVarsOfTypes
447 skol_info = PatSkol data_con span
448 arg_flags = [ tv `elemVarSet` arg_tvs | tv <- tvs ]
449 ; tvs' <- tcInstSkolTyVars skol_info tvs
450 ; let res_tys' = substTys (zipTopTvSubst tvs (mkTyVarTys tvs')) res_tys
452 -- Do type refinement!
453 ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr res_tys',
454 text "ty-args:" <+> ppr ty_args ])
455 ; refineAlt pstate data_con tvs' arg_flags res_tys' ty_args
456 $ \ pstate' tv_tys' -> do
458 -- ToDo: arg_tys should be boxy, but I don't think theta' should be,
459 -- or the tv_tys' in the call to tcInstStupidTheta
460 { let tenv' = zipTopTvSubst tvs tv_tys'
461 theta' = substTheta tenv' theta
462 arg_tys' = substTys tenv' arg_tys -- Boxy types
464 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
465 do { tcInstStupidTheta data_con tv_tys'
466 -- The stupid-theta mentions the newly-bound tyvars, so
467 -- it must live inside the getLIE, so that the
468 -- tcSimplifyCheck will apply the type refinement to it
469 ; tcConArgs pstate' data_con arg_pats arg_tys' thing_inside }
471 ; dicts <- newDicts (SigOrigin skol_info) theta'
472 ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
474 ; return (ConPatOut (L con_span data_con)
475 tvs' (map instToId dicts) dict_binds
476 arg_pats' (mkTyConApp tycon ty_args),
477 tvs' ++ inner_tvs, res)
480 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
482 tcConArgs :: PatState -> DataCon
483 -> HsConDetails Name (LPat Name) -> [TcSigmaType]
484 -> (PatState -> TcM a)
485 -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
487 tcConArgs pstate data_con (PrefixCon arg_pats) arg_tys thing_inside
488 = do { checkTc (con_arity == no_of_args) -- Check correct arity
489 (arityErr "Constructor" data_con con_arity no_of_args)
490 ; (arg_pats', tvs, res) <- tc_lpats pstate arg_pats arg_tys thing_inside
491 ; return (PrefixCon arg_pats', tvs, res) }
493 con_arity = dataConSourceArity data_con
494 no_of_args = length arg_pats
496 tcConArgs pstate data_con (InfixCon p1 p2) arg_tys thing_inside
497 = do { checkTc (con_arity == 2) -- Check correct arity
498 (arityErr "Constructor" data_con con_arity 2)
499 ; ([p1',p2'], tvs, res) <- tc_lpats pstate [p1,p2] arg_tys thing_inside
500 ; return (InfixCon p1' p2', tvs, res) }
502 con_arity = dataConSourceArity data_con
504 tcConArgs pstate data_con (RecCon rpats) arg_tys thing_inside
505 = do { (rpats', tvs, res) <- tc_fields pstate rpats thing_inside
506 ; return (RecCon rpats', tvs, res) }
508 tc_fields :: PatState -> [(Located Name, LPat Name)]
509 -> (PatState -> TcM a)
510 -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
511 tc_fields pstate [] thing_inside
512 = do { res <- thing_inside pstate
513 ; return ([], [], res) }
515 tc_fields pstate (rpat : rpats) thing_inside
516 = do { (rpat', tvs1, (rpats', tvs2, res))
517 <- tc_field pstate rpat $ \ pstate' ->
518 tc_fields pstate' rpats thing_inside
519 ; return (rpat':rpats', tvs1 ++ tvs2, res) }
521 tc_field pstate (field_lbl, pat) thing_inside
522 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
523 ; (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
524 ; return ((sel_id, pat'), tvs, res) }
526 find_field_ty field_lbl
527 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
529 -- No matching field; chances are this field label comes from some
530 -- other record type (or maybe none). As well as reporting an
531 -- error we still want to typecheck the pattern, principally to
532 -- make sure that all the variables it binds are put into the
533 -- environment, else the type checker crashes later:
534 -- f (R { foo = (a,b) }) = a+b
535 -- If foo isn't one of R's fields, we don't want to crash when
536 -- typechecking the "a+b".
537 [] -> do { addErrTc (badFieldCon data_con field_lbl)
538 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
539 ; return (error "Bogus selector Id", bogus_ty) }
541 -- The normal case, when the field comes from the right constructor
543 ASSERT( null extras )
544 do { sel_id <- tcLookupId field_lbl
545 ; return (sel_id, pat_ty) }
547 field_tys = zip (dataConFieldLabels data_con) arg_tys
548 -- Don't use zipEqual! If the constructor isn't really a record, then
549 -- dataConFieldLabels will be empty (and each field in the pattern
550 -- will generate an error below).
554 %************************************************************************
558 %************************************************************************
561 refineAlt :: PatState
562 -> DataCon -- For tracing only
563 -> [TcTyVar] -- Type variables from pattern
564 -> [Bool] -- Flags indicating which type variables occur
565 -- in the type of at least one argument
566 -> [TcType] -- Result types from the pattern
567 -> [BoxySigmaType] -- Result types from the scrutinee (context)
568 -> (PatState -> [BoxySigmaType] -> TcM a)
569 -- Possibly-refined existentials
571 refineAlt pstate con pat_tvs arg_flags pat_res_tys ctxt_res_tys thing_inside
572 | not (all isRigidTy ctxt_res_tys)
573 -- The context is not a rigid type, so we do no type refinement here.
574 = do { let arg_tvs = mkVarSet [ tv | (tv, True) <- pat_tvs `zip` arg_flags]
575 subst = boxyMatchTypes arg_tvs pat_res_tys ctxt_res_tys
577 res_tvs = tcTyVarsOfTypes pat_res_tys
578 -- The tvs are (already) all fresh skolems. We need a
579 -- fresh skolem for each type variable (to bind in the pattern)
580 -- even if it's refined away by the type refinement
582 | not (tv `elemVarSet` res_tvs) = return (mkTyVarTy tv)
583 | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
584 | otherwise = do { tv <- newBoxyTyVar openTypeKind
585 ; return (mkTyVarTy tv) }
586 ; pat_tys' <- mapM find_inst pat_tvs
588 -- Do the thing inside
589 ; res <- thing_inside pstate pat_tys'
591 -- Unbox the types that have been filled in by the thing_inside
592 -- I.e. the ones whose type variables are mentioned in at least one arg
593 ; let strip ty in_arg_tv | in_arg_tv = stripBoxyType ty
594 | otherwise = return ty
595 ; pat_tys'' <- zipWithM strip pat_tys' arg_flags
596 ; let subst = zipOpenTvSubst pat_tvs pat_tys''
597 ; boxyUnifyList (substTys subst pat_res_tys) ctxt_res_tys
599 ; return res } -- All boxes now filled
601 | otherwise -- The context is rigid, so we can do type refinement
602 = case gadtRefineTys (pat_reft pstate) con pat_tvs pat_res_tys ctxt_res_tys of
603 Failed msg -> failWithTc (inaccessibleAlt msg)
604 Succeeded (new_subst, all_bound_here)
605 | all_bound_here -- All the new bindings are for pat_tvs, so no need
606 -- to refine the environment or pstate
607 -> do { traceTc trace_msg
608 ; thing_inside pstate pat_tvs' }
609 | otherwise -- New bindings affect the context, so pass down pstate'.
610 -- DO NOT refine the envt, because we might be inside a
612 -> do { traceTc trace_msg
613 ; thing_inside pstate' pat_tvs' }
615 pat_tvs' = map (substTyVar new_subst) pat_tvs
616 pstate' = pstate { pat_reft = new_subst }
617 trace_msg = text "refineTypes:match" <+> ppr con <+> ppr new_subst
619 refineType :: GadtRefinement -> BoxyRhoType -> BoxyRhoType
620 -- Refine the type if it is rigid
622 | isRefineableTy ty = substTy reft ty
627 %************************************************************************
631 %************************************************************************
633 In tcOverloadedLit we convert directly to an Int or Integer if we
634 know that's what we want. This may save some time, by not
635 temporarily generating overloaded literals, but it won't catch all
636 cases (the rest are caught in lookupInst).
639 tcOverloadedLit :: InstOrigin
642 -> TcM (HsOverLit TcId)
643 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
644 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
645 -- Reason: If we do, tcSimplify will call lookupInst, which
646 -- will call tcSyntaxName, which does unification,
647 -- which tcSimplify doesn't like
648 -- ToDo: noLoc sadness
649 = do { integer_ty <- tcMetaTy integerTyConName
650 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
651 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
653 | Just expr <- shortCutIntLit i res_ty
654 = return (HsIntegral i expr)
657 = do { expr <- newLitInst orig lit res_ty
658 ; return (HsIntegral i expr) }
660 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
661 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
662 = do { rat_ty <- tcMetaTy rationalTyConName
663 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
664 -- Overloaded literals must have liftedTypeKind, because
665 -- we're instantiating an overloaded function here,
666 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
667 -- However this'll be picked up by tcSyntaxOp if necessary
668 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
670 | Just expr <- shortCutFracLit r res_ty
671 = return (HsFractional r expr)
674 = do { expr <- newLitInst orig lit res_ty
675 ; return (HsFractional r expr) }
677 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
678 newLitInst orig lit res_ty -- Make a LitInst
679 = do { loc <- getInstLoc orig
680 ; res_tau <- zapToMonotype res_ty
681 ; new_uniq <- newUnique
683 lit_nm = mkSystemVarName new_uniq FSLIT("lit")
684 lit_inst = LitInst lit_nm lit res_tau loc
686 ; return (HsVar (instToId lit_inst)) }
690 %************************************************************************
692 Note [Pattern coercions]
694 %************************************************************************
696 In principle, these program would be reasonable:
698 f :: (forall a. a->a) -> Int
699 f (x :: Int->Int) = x 3
701 g :: (forall a. [a]) -> Bool
704 In both cases, the function type signature restricts what arguments can be passed
705 in a call (to polymorphic ones). The pattern type signature then instantiates this
706 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
707 generate the translated term
708 f = \x' :: (forall a. a->a). let x = x' Int in x 3
710 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
711 And it requires a significant amount of code to implement, becuase we need to decorate
712 the translated pattern with coercion functions (generated from the subsumption check
715 So for now I'm just insisting on type *equality* in patterns. No subsumption.
717 Old notes about desugaring, at a time when pattern coercions were handled:
719 A SigPat is a type coercion and must be handled one at at time. We can't
720 combine them unless the type of the pattern inside is identical, and we don't
721 bother to check for that. For example:
723 data T = T1 Int | T2 Bool
724 f :: (forall a. a -> a) -> T -> t
725 f (g::Int->Int) (T1 i) = T1 (g i)
726 f (g::Bool->Bool) (T2 b) = T2 (g b)
728 We desugar this as follows:
730 f = \ g::(forall a. a->a) t::T ->
732 in case t of { T1 i -> T1 (gi i)
735 in case t of { T2 b -> T2 (gb b)
738 Note that we do not treat the first column of patterns as a
739 column of variables, because the coerced variables (gi, gb)
740 would be of different types. So we get rather grotty code.
741 But I don't think this is a common case, and if it was we could
742 doubtless improve it.
744 Meanwhile, the strategy is:
745 * treat each SigPat coercion (always non-identity coercions)
747 * deal with the stuff inside, and then wrap a binding round
748 the result to bind the new variable (gi, gb, etc)
751 %************************************************************************
753 \subsection{Errors and contexts}
755 %************************************************************************
758 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
759 patCtxt (VarPat _) = Nothing
760 patCtxt (ParPat _) = Nothing
761 patCtxt (AsPat _ _) = Nothing
762 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
765 -----------------------------------------------
767 existentialExplode pats
768 = hang (vcat [text "My brain just exploded.",
769 text "I can't handle pattern bindings for existentially-quantified constructors.",
770 text "In the binding group for"])
771 4 (vcat (map ppr pats))
773 sigPatCtxt bound_ids bound_tvs tys tidy_env
774 = -- tys is (body_ty : pat_tys)
775 mapM zonkTcType tys `thenM` \ tys' ->
777 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
778 (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys'
781 sep [ptext SLIT("When checking an existential match that binds"),
782 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
783 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
784 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
787 show_ids = filter is_interesting bound_ids
788 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
790 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
791 -- Don't zonk the types so we get the separate, un-unified versions
793 badFieldCon :: DataCon -> Name -> SDoc
794 badFieldCon con field
795 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
796 ptext SLIT("does not have field"), quotes (ppr field)]
798 polyPatSig :: TcType -> SDoc
800 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
803 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
807 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
808 2 (vcat (map pprSkolTvBinding tvs))
811 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg