2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcPat]{Typechecking patterns}
7 module TcPat ( tcPat, tcMonoPatBndr, tcSubPat,
8 badFieldCon, polyPatSig
11 #include "HsVersions.h"
13 import HsSyn ( InPat(..), OutPat(..), HsLit(..), HsOverLit(..), HsExpr(..) )
14 import RnHsSyn ( RenamedPat )
15 import TcHsSyn ( TcPat, TcId, simpleHsLitTy )
18 import Inst ( InstOrigin(..),
19 emptyLIE, plusLIE, LIE, mkLIE, unitLIE, instToId, isEmptyLIE,
20 newMethod, newMethodFromName, newOverloadedLit, newDicts, tcInstDataCon
22 import Id ( mkLocalId, mkSysLocal )
24 import FieldLabel ( fieldLabelName )
25 import TcEnv ( tcLookupClass, tcLookupDataCon, tcLookupGlobalId, tcLookupId )
26 import TcMType ( newTyVarTy, zapToType )
27 import TcType ( TcType, TcTyVar, TcSigmaType,
28 mkClassPred, liftedTypeKind )
29 import TcUnify ( tcSubOff, TcHoleType,
30 unifyTauTy, unifyListTy, unifyPArrTy, unifyTupleTy,
31 mkCoercion, idCoercion, isIdCoercion,
33 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
35 import TysWiredIn ( stringTy )
36 import CmdLineOpts ( opt_IrrefutableTuples )
37 import DataCon ( dataConFieldLabels, dataConSourceArity )
38 import PrelNames ( eqStringName, eqName, geName, cCallableClassName )
39 import BasicTypes ( isBoxed )
45 %************************************************************************
47 \subsection{Variable patterns}
49 %************************************************************************
52 type BinderChecker = Name -> TcSigmaType -> TcM (PatCoFn, LIE, TcId)
53 -- How to construct a suitable (monomorphic)
54 -- Id for variables found in the pattern
55 -- The TcSigmaType is the expected type
56 -- from the pattern context
58 -- The Id may have a sigma type (e.g. f (x::forall a. a->a))
59 -- so we want to *create* it during pattern type checking.
60 -- We don't want to make Ids first with a type-variable type
61 -- and then unify... becuase we can't unify a sigma type with a type variable.
63 tcMonoPatBndr :: BinderChecker
64 -- This is the right function to pass to tcPat when
65 -- we're looking at a lambda-bound pattern,
66 -- so there's no polymorphic guy to worry about
68 tcMonoPatBndr binder_name pat_ty
69 = zapToType pat_ty `thenNF_Tc` \ pat_ty' ->
70 -- If there are *no constraints* on the pattern type, we
71 -- revert to good old H-M typechecking, making
72 -- the type of the binder into an *ordinary*
73 -- type variable. We find out if there are no constraints
74 -- by seeing if we are given an "open hole" as our info.
75 -- What we are trying to avoid here is giving a binder
76 -- a type that is a 'hole'. The only place holes should
77 -- appear is as an argument to tcPat and tcExpr/tcMonoExpr.
79 returnTc (idCoercion, emptyLIE, mkLocalId binder_name pat_ty')
83 %************************************************************************
85 \subsection{Typechecking patterns}
87 %************************************************************************
90 tcPat :: BinderChecker
93 -> TcHoleType -- Expected type derived from the context
94 -- In the case of a function with a rank-2 signature,
95 -- this type might be a forall type.
98 LIE, -- Required by n+k and literal pats
99 Bag TcTyVar, -- TyVars bound by the pattern
100 -- These are just the existentially-bound ones.
101 -- Any tyvars bound by *type signatures* in the
102 -- patterns are brought into scope before we begin.
103 Bag (Name, TcId), -- Ids bound by the pattern, along with the Name under
104 -- which it occurs in the pattern
105 -- The two aren't the same because we conjure up a new
106 -- local name for each variable.
107 LIE) -- Dicts or methods [see below] bound by the pattern
108 -- from existential constructor patterns
112 %************************************************************************
114 \subsection{Variables, wildcards, lazy pats, as-pats}
116 %************************************************************************
119 tcPat tc_bndr pat@(TypePatIn ty) pat_ty
120 = failWithTc (badTypePat pat)
122 tcPat tc_bndr (VarPatIn name) pat_ty
123 = tc_bndr name pat_ty `thenTc` \ (co_fn, lie_req, bndr_id) ->
124 returnTc (co_fn <$> VarPat bndr_id, lie_req,
125 emptyBag, unitBag (name, bndr_id), emptyLIE)
127 tcPat tc_bndr (LazyPatIn pat) pat_ty
128 = tcPat tc_bndr pat pat_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
129 returnTc (LazyPat pat', lie_req, tvs, ids, lie_avail)
131 tcPat tc_bndr pat_in@(AsPatIn name pat) pat_ty
132 = tc_bndr name pat_ty `thenTc` \ (co_fn, lie_req1, bndr_id) ->
133 tcPat tc_bndr pat pat_ty `thenTc` \ (pat', lie_req2, tvs, ids, lie_avail) ->
134 returnTc (co_fn <$> (AsPat bndr_id pat'), lie_req1 `plusLIE` lie_req2,
135 tvs, (name, bndr_id) `consBag` ids, lie_avail)
137 tcPat tc_bndr WildPatIn pat_ty
138 = zapToType pat_ty `thenNF_Tc` \ pat_ty' ->
139 -- We might have an incoming 'hole' type variable; no annotation
140 -- so zap it to a type. Rather like tcMonoPatBndr.
141 returnTc (WildPat pat_ty', emptyLIE, emptyBag, emptyBag, emptyLIE)
143 tcPat tc_bndr (ParPatIn parend_pat) pat_ty
144 = tcPat tc_bndr parend_pat pat_ty
146 tcPat tc_bndr pat_in@(SigPatIn pat sig) pat_ty
147 = tcAddErrCtxt (patCtxt pat_in) $
148 tcHsSigType PatSigCtxt sig `thenTc` \ sig_ty ->
149 tcSubPat sig_ty pat_ty `thenTc` \ (co_fn, lie_sig) ->
150 tcPat tc_bndr pat sig_ty `thenTc` \ (pat', lie_req, tvs, ids, lie_avail) ->
151 returnTc (co_fn <$> pat', lie_req `plusLIE` lie_sig, tvs, ids, lie_avail)
155 %************************************************************************
157 \subsection{Explicit lists, parallel arrays, and tuples}
159 %************************************************************************
162 tcPat tc_bndr pat_in@(ListPatIn pats) pat_ty
163 = tcAddErrCtxt (patCtxt pat_in) $
164 unifyListTy pat_ty `thenTc` \ elem_ty ->
165 tcPats tc_bndr pats (repeat elem_ty) `thenTc` \ (pats', lie_req, tvs, ids, lie_avail) ->
166 returnTc (ListPat elem_ty pats', lie_req, tvs, ids, lie_avail)
168 tcPat tc_bndr pat_in@(PArrPatIn pats) pat_ty
169 = tcAddErrCtxt (patCtxt pat_in) $
170 unifyPArrTy pat_ty `thenTc` \ elem_ty ->
171 tcPats tc_bndr pats (repeat elem_ty) `thenTc` \ (pats', lie_req, tvs, ids, lie_avail) ->
172 returnTc (PArrPat elem_ty pats', lie_req, tvs, ids, lie_avail)
174 tcPat tc_bndr pat_in@(TuplePatIn pats boxity) pat_ty
175 = tcAddErrCtxt (patCtxt pat_in) $
177 unifyTupleTy boxity arity pat_ty `thenTc` \ arg_tys ->
178 tcPats tc_bndr pats arg_tys `thenTc` \ (pats', lie_req, tvs, ids, lie_avail) ->
180 -- possibly do the "make all tuple-pats irrefutable" test:
182 unmangled_result = TuplePat pats' boxity
184 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
185 -- so that we can experiment with lazy tuple-matching.
186 -- This is a pretty odd place to make the switch, but
187 -- it was easy to do.
189 possibly_mangled_result
190 | opt_IrrefutableTuples && isBoxed boxity = LazyPat unmangled_result
191 | otherwise = unmangled_result
193 returnTc (possibly_mangled_result, lie_req, tvs, ids, lie_avail)
199 %************************************************************************
201 \subsection{Other constructors}
204 %************************************************************************
207 tcPat tc_bndr pat@(ConPatIn name arg_pats) pat_ty
208 = tcConPat tc_bndr pat name arg_pats pat_ty
210 tcPat tc_bndr pat@(ConOpPatIn pat1 op _ pat2) pat_ty
211 = tcConPat tc_bndr pat op [pat1, pat2] pat_ty
215 %************************************************************************
219 %************************************************************************
222 tcPat tc_bndr pat@(RecPatIn name rpats) pat_ty
223 = tcAddErrCtxt (patCtxt pat) $
225 -- Check the constructor itself
226 tcConstructor pat name `thenTc` \ (data_con, lie_req1, ex_tvs, ex_dicts, lie_avail1, arg_tys, con_res_ty) ->
228 -- Check overall type matches (c.f. tcConPat)
229 tcSubPat con_res_ty pat_ty `thenTc` \ (co_fn, lie_req2) ->
231 -- Don't use zipEqual! If the constructor isn't really a record, then
232 -- dataConFieldLabels will be empty (and each field in the pattern
233 -- will generate an error below).
234 field_tys = zip (map fieldLabelName (dataConFieldLabels data_con))
239 tc_fields field_tys rpats `thenTc` \ (rpats', lie_req3, tvs, ids, lie_avail2) ->
241 returnTc (RecPat data_con pat_ty ex_tvs ex_dicts rpats',
242 lie_req1 `plusLIE` lie_req2 `plusLIE` lie_req3,
243 listToBag ex_tvs `unionBags` tvs,
245 lie_avail1 `plusLIE` lie_avail2)
248 tc_fields field_tys []
249 = returnTc ([], emptyLIE, emptyBag, emptyBag, emptyLIE)
251 tc_fields field_tys ((field_label, rhs_pat, pun_flag) : rpats)
252 = tc_fields field_tys rpats `thenTc` \ (rpats', lie_req1, tvs1, ids1, lie_avail1) ->
254 (case [ty | (f,ty) <- field_tys, f == field_label] of
256 -- No matching field; chances are this field label comes from some
257 -- other record type (or maybe none). As well as reporting an
258 -- error we still want to typecheck the pattern, principally to
259 -- make sure that all the variables it binds are put into the
260 -- environment, else the type checker crashes later:
261 -- f (R { foo = (a,b) }) = a+b
262 -- If foo isn't one of R's fields, we don't want to crash when
263 -- typechecking the "a+b".
264 [] -> addErrTc (badFieldCon name field_label) `thenNF_Tc_`
265 newTyVarTy liftedTypeKind `thenNF_Tc_`
266 returnTc (error "Bogus selector Id", pat_ty)
268 -- The normal case, when the field comes from the right constructor
270 ASSERT( null extras )
271 tcLookupGlobalId field_label `thenNF_Tc` \ sel_id ->
272 returnTc (sel_id, pat_ty)
273 ) `thenTc` \ (sel_id, pat_ty) ->
275 tcPat tc_bndr rhs_pat pat_ty `thenTc` \ (rhs_pat', lie_req2, tvs2, ids2, lie_avail2) ->
277 returnTc ((sel_id, rhs_pat', pun_flag) : rpats',
278 lie_req1 `plusLIE` lie_req2,
279 tvs1 `unionBags` tvs2,
280 ids1 `unionBags` ids2,
281 lie_avail1 `plusLIE` lie_avail2)
284 %************************************************************************
286 \subsection{Literals}
288 %************************************************************************
291 tcPat tc_bndr (LitPatIn lit@(HsLitLit s _)) pat_ty
292 -- cf tcExpr on LitLits
293 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
294 newDicts (LitLitOrigin (_UNPK_ s))
295 [mkClassPred cCallableClass [pat_ty]] `thenNF_Tc` \ dicts ->
296 returnTc (LitPat (HsLitLit s pat_ty) pat_ty, mkLIE dicts, emptyBag, emptyBag, emptyLIE)
298 tcPat tc_bndr pat@(LitPatIn lit@(HsString _)) pat_ty
299 = unifyTauTy pat_ty stringTy `thenTc_`
300 tcLookupGlobalId eqStringName `thenNF_Tc` \ eq_id ->
301 returnTc (NPat lit stringTy (HsVar eq_id `HsApp` HsLit lit),
302 emptyLIE, emptyBag, emptyBag, emptyLIE)
304 tcPat tc_bndr (LitPatIn simple_lit) pat_ty
305 = unifyTauTy pat_ty (simpleHsLitTy simple_lit) `thenTc_`
306 returnTc (LitPat simple_lit pat_ty, emptyLIE, emptyBag, emptyBag, emptyLIE)
308 tcPat tc_bndr pat@(NPatIn over_lit) pat_ty
309 = newOverloadedLit origin over_lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie1) ->
310 newMethodFromName origin pat_ty eqName `thenNF_Tc` \ eq ->
312 returnTc (NPat lit' pat_ty (HsApp (HsVar (instToId eq)) over_lit_expr),
313 lie1 `plusLIE` unitLIE eq,
314 emptyBag, emptyBag, emptyLIE)
316 origin = PatOrigin pat
317 lit' = case over_lit of
318 HsIntegral i _ -> HsInteger i
319 HsFractional f _ -> HsRat f pat_ty
322 %************************************************************************
324 \subsection{n+k patterns}
326 %************************************************************************
329 tcPat tc_bndr pat@(NPlusKPatIn name lit@(HsIntegral i _) minus_name) pat_ty
330 = tc_bndr name pat_ty `thenTc` \ (co_fn, lie1, bndr_id) ->
331 newOverloadedLit origin lit pat_ty `thenNF_Tc` \ (over_lit_expr, lie2) ->
332 newMethodFromName origin pat_ty geName `thenNF_Tc` \ ge ->
334 -- The '-' part is re-mappable syntax
335 tcLookupId minus_name `thenNF_Tc` \ minus_sel_id ->
336 newMethod origin minus_sel_id [pat_ty] `thenNF_Tc` \ minus ->
338 returnTc (NPlusKPat bndr_id i pat_ty
339 (SectionR (HsVar (instToId ge)) over_lit_expr)
340 (SectionR (HsVar (instToId minus)) over_lit_expr),
341 lie1 `plusLIE` lie2 `plusLIE` mkLIE [ge,minus],
342 emptyBag, unitBag (name, bndr_id), emptyLIE)
344 origin = PatOrigin pat
347 %************************************************************************
349 \subsection{Lists of patterns}
351 %************************************************************************
356 tcPats :: BinderChecker -- How to deal with variables
357 -> [RenamedPat] -> [TcType] -- Excess 'expected types' discarded
359 LIE, -- Required by n+k and literal pats
361 Bag (Name, TcId), -- Ids bound by the pattern
362 LIE) -- Dicts bound by the pattern
364 tcPats tc_bndr [] tys = returnTc ([], emptyLIE, emptyBag, emptyBag, emptyLIE)
366 tcPats tc_bndr (ty:tys) (pat:pats)
367 = tcPat tc_bndr ty pat `thenTc` \ (pat', lie_req1, tvs1, ids1, lie_avail1) ->
368 tcPats tc_bndr tys pats `thenTc` \ (pats', lie_req2, tvs2, ids2, lie_avail2) ->
370 returnTc (pat':pats', lie_req1 `plusLIE` lie_req2,
371 tvs1 `unionBags` tvs2, ids1 `unionBags` ids2,
372 lie_avail1 `plusLIE` lie_avail2)
375 ------------------------------------------------------
377 tcConstructor pat con_name
378 = -- Check that it's a constructor
379 tcLookupDataCon con_name `thenNF_Tc` \ data_con ->
382 tcInstDataCon (PatOrigin pat) data_con `thenNF_Tc` \ (_, ex_dicts, arg_tys, result_ty, lie_req, ex_lie, ex_tvs) ->
384 returnTc (data_con, lie_req, ex_tvs, ex_dicts, ex_lie, arg_tys, result_ty)
387 ------------------------------------------------------
389 tcConPat tc_bndr pat con_name arg_pats pat_ty
390 = tcAddErrCtxt (patCtxt pat) $
392 -- Check the constructor itself
393 tcConstructor pat con_name `thenTc` \ (data_con, lie_req1, ex_tvs, ex_dicts, lie_avail1, arg_tys, con_res_ty) ->
395 -- Check overall type matches.
396 -- The pat_ty might be a for-all type, in which
397 -- case we must instantiate to match
398 tcSubPat con_res_ty pat_ty `thenTc` \ (co_fn, lie_req2) ->
400 -- Check correct arity
402 con_arity = dataConSourceArity data_con
403 no_of_args = length arg_pats
405 checkTc (con_arity == no_of_args)
406 (arityErr "Constructor" data_con con_arity no_of_args) `thenTc_`
409 tcPats tc_bndr arg_pats arg_tys `thenTc` \ (arg_pats', lie_req3, tvs, ids, lie_avail2) ->
411 returnTc (co_fn <$> ConPat data_con pat_ty ex_tvs ex_dicts arg_pats',
412 lie_req1 `plusLIE` lie_req2 `plusLIE` lie_req3,
413 listToBag ex_tvs `unionBags` tvs,
415 lie_avail1 `plusLIE` lie_avail2)
419 %************************************************************************
421 \subsection{Subsumption}
423 %************************************************************************
426 f :: (forall a. a->a) -> Int -> Int
427 f (g::Int->Int) y = g y
428 This is ok: the type signature allows fewer callers than
429 the (more general) signature f :: (Int->Int) -> Int -> Int
430 I.e. (forall a. a->a) <= Int -> Int
431 We end up translating this to:
432 f = \g' :: (forall a. a->a). let g = g' Int in g' y
434 tcSubPat does the work
435 sig_ty is the signature on the pattern itself
436 (Int->Int in the example)
437 expected_ty is the type passed inwards from the context
438 (forall a. a->a in the example)
441 tcSubPat :: TcSigmaType -> TcHoleType -> TcM (PatCoFn, LIE)
443 tcSubPat sig_ty exp_ty
444 = tcSubOff sig_ty exp_ty `thenTc` \ (co_fn, lie) ->
445 -- co_fn is a coercion on *expressions*, and we
446 -- need to make a coercion on *patterns*
447 if isIdCoercion co_fn then
448 ASSERT( isEmptyLIE lie )
449 returnNF_Tc (idCoercion, emptyLIE)
451 tcGetUnique `thenNF_Tc` \ uniq ->
453 arg_id = mkSysLocal FSLIT("sub") uniq exp_ty
454 the_fn = DictLam [arg_id] (co_fn <$> HsVar arg_id)
455 pat_co_fn p = SigPat p exp_ty the_fn
457 returnNF_Tc (mkCoercion pat_co_fn, lie)
461 %************************************************************************
463 \subsection{Errors and contexts}
465 %************************************************************************
468 patCtxt pat = hang (ptext SLIT("When checking the pattern:"))
471 badFieldCon :: Name -> Name -> SDoc
472 badFieldCon con field
473 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
474 ptext SLIT("does not have field"), quotes (ppr field)]
476 polyPatSig :: TcType -> SDoc
478 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
481 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat