2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcApp, tcExpr, tcMonoExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsMatchContext(..), HsDoContext(..), mkMonoBind
14 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
15 import TcHsSyn ( TcExpr, TcRecordBinds, mkHsLet )
18 import BasicTypes ( RecFlag(..) )
20 import Inst ( InstOrigin(..),
21 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
22 newOverloadedLit, newMethod, newIPDict,
26 import TcBinds ( tcBindsAndThen )
27 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
28 tcLookupTyCon, tcLookupDataCon, tcLookupId,
29 tcExtendGlobalTyVars, tcLookupSyntaxName
31 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
32 import TcMonoType ( tcHsSigType, checkSigTyVars, sigCtxt )
33 import TcPat ( badFieldCon, simpleHsLitTy )
34 import TcSimplify ( tcSimplifyCheck, tcSimplifyIPs )
35 import TcMType ( tcInstTyVars, tcInstType,
36 newTyVarTy, newTyVarTys, zonkTcType,
37 unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy
39 import TcType ( tcSplitFunTys, tcSplitTyConApp,
41 mkFunTy, mkAppTy, mkTyConTy,
42 mkTyConApp, mkClassPred, tcFunArgTy,
43 isTauTy, tyVarsOfType, tyVarsOfTypes,
44 liftedTypeKind, openTypeKind, mkArrowKind,
45 tcSplitSigmaTy, tcTyConAppTyCon,
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
49 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
50 import DataCon ( dataConFieldLabels, dataConSig,
53 import Demand ( isMarkedStrict )
55 import TyCon ( TyCon, tyConTyVars, isAlgTyCon, tyConDataCons )
56 import Subst ( mkTopTyVarSubst, substTheta, substTy )
57 import VarSet ( elemVarSet )
58 import TysWiredIn ( boolTy, mkListTy, listTyCon )
59 import PrelNames ( cCallableClassName,
61 enumFromName, enumFromThenName, negateName,
62 enumFromToName, enumFromThenToName,
63 thenMName, failMName, returnMName, ioTyConName
66 import ListSetOps ( minusList )
69 import HscTypes ( TyThing(..) )
73 %************************************************************************
75 \subsection{Main wrappers}
77 %************************************************************************
80 tcExpr :: RenamedHsExpr -- Expession to type check
81 -> TcType -- Expected type (could be a polytpye)
84 tcExpr expr ty | isQualifiedTy ty = -- Polymorphic case
85 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
88 | otherwise = -- Monomorphic case
93 %************************************************************************
95 \subsection{@tcPolyExpr@ typchecks an application}
97 %************************************************************************
100 -- tcPolyExpr is like tcMonoExpr, except that the expected type
101 -- can be a polymorphic one.
102 tcPolyExpr :: RenamedHsExpr
103 -> TcType -- Expected type
104 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
105 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
107 tcPolyExpr arg expected_arg_ty
108 = -- Ha! The argument type of the function is a for-all type,
109 -- An example of rank-2 polymorphism.
111 -- To ensure that the forall'd type variables don't get unified with each
112 -- other or any other types, we make fresh copy of the alleged type
113 tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
115 free_tvs = tyVarsOfType expected_arg_ty
117 -- Type-check the arg and unify with expected type
118 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
120 -- Check that the sig_tyvars havn't been constrained
121 -- The interesting bit here is that we must include the free variables
122 -- of the expected arg ty. Here's an example:
123 -- runST (newVar True)
124 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
125 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
126 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
127 -- So now s' isn't unconstrained because it's linked to a.
128 -- Conclusion: include the free vars of the expected arg type in the
129 -- list of "free vars" for the signature check.
131 tcExtendGlobalTyVars free_tvs $
132 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
134 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
136 (text "the type signature of an expression")
138 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
140 checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
143 -- This HsLet binds any Insts which came out of the simplification.
144 -- It's a bit out of place here, but using AbsBind involves inventing
145 -- a couple of new names which seems worse.
146 generalised_arg = TyLam zonked_sig_tyvars $
147 DictLam (map instToId sig_dicts) $
151 returnTc ( generalised_arg, free_insts,
152 arg', sig_tau, lie_arg )
154 sig_msg = ptext SLIT("When checking an expression type signature")
157 %************************************************************************
159 \subsection{The TAUT rules for variables}
161 %************************************************************************
164 tcMonoExpr :: RenamedHsExpr -- Expession to type check
165 -> TcTauType -- Expected type (could be a type variable)
168 tcMonoExpr (HsVar name) res_ty
169 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
170 unifyTauTy res_ty id_ty `thenTc_`
172 -- Check that the result type doesn't have any nested for-alls.
173 -- For example, a "build" on its own is no good; it must be
174 -- applied to something.
175 checkTc (isTauTy id_ty)
176 (lurkingRank2Err name id_ty) `thenTc_`
178 returnTc (expr', lie)
182 tcMonoExpr (HsIPVar name) res_ty
183 = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
184 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
187 %************************************************************************
189 \subsection{Other expression forms}
191 %************************************************************************
194 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
195 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
196 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
198 tcMonoExpr (NegApp expr) res_ty
199 = tcLookupSyntaxName negateName `thenNF_Tc` \ neg ->
200 tcMonoExpr (HsApp (HsVar neg) expr) res_ty
202 tcMonoExpr (HsLam match) res_ty
203 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
204 returnTc (HsLam match', lie)
206 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
208 accum (HsApp e1 e2) args = accum e1 (e2:args)
210 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
211 returnTc (foldl HsApp fun' args', lie)
213 -- equivalent to (op e1) e2:
214 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
215 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
216 returnTc (OpApp arg1' op' fix arg2', lie)
219 Note that the operators in sections are expected to be binary, and
220 a type error will occur if they aren't.
223 -- Left sections, equivalent to
230 tcMonoExpr in_expr@(SectionL arg op) res_ty
231 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
233 -- Check that res_ty is a function type
234 -- Without this check we barf in the desugarer on
236 -- because it tries to desugar to
237 -- f op = \r -> 3 op r
238 -- so (3 `op`) had better be a function!
239 tcAddErrCtxt (sectionLAppCtxt in_expr) $
240 unifyFunTy res_ty `thenTc_`
242 returnTc (SectionL arg' op', lie)
244 -- Right sections, equivalent to \ x -> x op expr, or
247 tcMonoExpr in_expr@(SectionR op expr) res_ty
248 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
249 tcAddErrCtxt (sectionRAppCtxt in_expr) $
250 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
251 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
252 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
253 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
256 The interesting thing about @ccall@ is that it is just a template
257 which we instantiate by filling in details about the types of its
258 argument and result (ie minimal typechecking is performed). So, the
259 basic story is that we allocate a load of type variables (to hold the
260 arg/result types); unify them with the args/result; and store them for
264 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
265 = -- Get the callable and returnable classes.
266 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
267 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
268 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
270 new_arg_dict (arg, arg_ty)
271 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
272 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
273 returnNF_Tc arg_dicts -- Actually a singleton bag
275 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
279 let n_args = length args
280 tv_idxs | n_args == 0 = []
281 | otherwise = [1..n_args]
283 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
284 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
286 -- The argument types can be unlifted or lifted; the result
287 -- type must, however, be lifted since it's an argument to the IO
289 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
291 io_result_ty = mkTyConApp ioTyCon [result_ty]
293 unifyTauTy res_ty io_result_ty `thenTc_`
295 -- Construct the extra insts, which encode the
296 -- constraints on the argument and result types.
297 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
298 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
299 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
300 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
304 tcMonoExpr (HsSCC lbl expr) res_ty
305 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
306 returnTc (HsSCC lbl expr', lie)
308 tcMonoExpr (HsLet binds expr) res_ty
311 binds -- Bindings to check
312 tc_expr `thenTc` \ (expr', lie) ->
313 returnTc (expr', lie)
315 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
316 returnTc (expr', lie)
317 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
319 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
320 = tcAddSrcLoc src_loc $
321 tcAddErrCtxt (caseCtxt in_expr) $
323 -- Typecheck the case alternatives first.
324 -- The case patterns tend to give good type info to use
325 -- when typechecking the scrutinee. For example
328 -- will report that map is applied to too few arguments
330 -- Not only that, but it's better to check the matches on their
331 -- own, so that we get the expected results for scoped type variables.
333 -- (p::a, q::b) -> (q,p)
334 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
335 -- claimed by the pattern signatures. But if we typechecked the
336 -- match with x in scope and x's type as the expected type, we'd be hosed.
338 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
340 tcAddErrCtxt (caseScrutCtxt scrut) (
341 tcMonoExpr scrut scrut_ty
342 ) `thenTc` \ (scrut',lie1) ->
344 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
346 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
347 = tcAddSrcLoc src_loc $
348 tcAddErrCtxt (predCtxt pred) (
349 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
351 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
352 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
353 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
357 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
358 = tcDoStmts do_or_lc stmts src_loc res_ty
362 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
363 = unifyListTy res_ty `thenTc` \ elt_ty ->
364 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
365 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
368 = tcAddErrCtxt (listCtxt expr) $
369 tcMonoExpr expr elt_ty
371 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
372 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
373 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
374 (exprs `zip` arg_tys) -- we know they're of equal length.
375 `thenTc` \ (exprs', lies) ->
376 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
378 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
379 = tcAddErrCtxt (recordConCtxt expr) $
380 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
382 (_, record_ty) = tcSplitFunTys con_tau
383 (tycon, ty_args) = tcSplitTyConApp record_ty
385 ASSERT( isAlgTyCon tycon )
386 unifyTauTy res_ty record_ty `thenTc_`
388 -- Check that the record bindings match the constructor
389 -- con_name is syntactically constrained to be a data constructor
390 tcLookupDataCon con_name `thenTc` \ data_con ->
392 bad_fields = badFields rbinds data_con
394 if not (null bad_fields) then
395 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
396 failTc -- Fail now, because tcRecordBinds will crash on a bad field
399 -- Typecheck the record bindings
400 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
403 (missing_s_fields, missing_fields) = missingFields rbinds data_con
405 checkTcM (null missing_s_fields)
406 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
407 returnNF_Tc ()) `thenNF_Tc_`
408 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
409 checkTcM (not (warn && not (null missing_fields)))
410 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
411 returnNF_Tc ()) `thenNF_Tc_`
413 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
415 -- The main complication with RecordUpd is that we need to explicitly
416 -- handle the *non-updated* fields. Consider:
418 -- data T a b = MkT1 { fa :: a, fb :: b }
419 -- | MkT2 { fa :: a, fc :: Int -> Int }
420 -- | MkT3 { fd :: a }
422 -- upd :: T a b -> c -> T a c
423 -- upd t x = t { fb = x}
425 -- The type signature on upd is correct (i.e. the result should not be (T a b))
426 -- because upd should be equivalent to:
428 -- upd t x = case t of
429 -- MkT1 p q -> MkT1 p x
430 -- MkT2 a b -> MkT2 p b
431 -- MkT3 d -> error ...
433 -- So we need to give a completely fresh type to the result record,
434 -- and then constrain it by the fields that are *not* updated ("p" above).
436 -- Note that because MkT3 doesn't contain all the fields being updated,
437 -- its RHS is simply an error, so it doesn't impose any type constraints
439 -- All this is done in STEP 4 below.
441 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
442 = tcAddErrCtxt (recordUpdCtxt expr) $
445 -- Check that the field names are really field names
446 ASSERT( not (null rbinds) )
448 field_names = [field_name | (field_name, _, _) <- rbinds]
450 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
452 bad_guys = [ addErrTc (notSelector field_name)
453 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
455 Just (AnId sel_id) -> not (isRecordSelector sel_id)
459 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
462 -- Figure out the tycon and data cons from the first field name
464 -- It's OK to use the non-tc splitters here (for a selector)
465 (Just (AnId sel_id) : _) = maybe_sel_ids
466 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
467 -- when the data type has a context
468 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
469 tycon = tcTyConAppTyCon data_ty
470 data_cons = tyConDataCons tycon
471 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
473 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
476 -- Check that at least one constructor has all the named fields
477 -- i.e. has an empty set of bad fields returned by badFields
478 checkTc (any (null . badFields rbinds) data_cons)
479 (badFieldsUpd rbinds) `thenTc_`
482 -- Typecheck the update bindings.
483 -- (Do this after checking for bad fields in case there's a field that
484 -- doesn't match the constructor.)
486 result_record_ty = mkTyConApp tycon result_inst_tys
488 unifyTauTy res_ty result_record_ty `thenTc_`
489 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
492 -- Use the un-updated fields to find a vector of booleans saying
493 -- which type arguments must be the same in updatee and result.
495 -- WARNING: this code assumes that all data_cons in a common tycon
496 -- have FieldLabels abstracted over the same tyvars.
498 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
499 con_field_lbls_s = map dataConFieldLabels data_cons
501 -- A constructor is only relevant to this process if
502 -- it contains all the fields that are being updated
503 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
504 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
506 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
507 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
509 mk_inst_ty (tyvar, result_inst_ty)
510 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
511 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
513 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
516 -- Typecheck the expression to be updated
518 record_ty = mkTyConApp tycon inst_tys
520 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
523 -- Figure out the LIE we need. We have to generate some
524 -- dictionaries for the data type context, since we are going to
525 -- do some construction.
527 -- What dictionaries do we need? For the moment we assume that all
528 -- data constructors have the same context, and grab it from the first
529 -- constructor. If they have varying contexts then we'd have to
530 -- union the ones that could participate in the update.
532 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
533 inst_env = mkTopTyVarSubst tyvars result_inst_tys
534 theta' = substTheta inst_env theta
536 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
539 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
540 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
542 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
543 = unifyListTy res_ty `thenTc` \ elt_ty ->
544 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
546 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
547 newMethod (ArithSeqOrigin seq)
548 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
550 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
551 lie1 `plusLIE` unitLIE enum_from)
553 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
554 = tcAddErrCtxt (arithSeqCtxt in_expr) $
555 unifyListTy res_ty `thenTc` \ elt_ty ->
556 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
557 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
558 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
559 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
561 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
562 (FromThen expr1' expr2'),
563 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
565 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
566 = tcAddErrCtxt (arithSeqCtxt in_expr) $
567 unifyListTy res_ty `thenTc` \ elt_ty ->
568 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
569 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
570 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
571 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
573 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
574 (FromTo expr1' expr2'),
575 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
577 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
578 = tcAddErrCtxt (arithSeqCtxt in_expr) $
579 unifyListTy res_ty `thenTc` \ elt_ty ->
580 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
581 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
582 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
583 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
584 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
586 returnTc (ArithSeqOut (HsVar (instToId eft))
587 (FromThenTo expr1' expr2' expr3'),
588 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
591 %************************************************************************
593 \subsection{Expressions type signatures}
595 %************************************************************************
598 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
599 = tcAddErrCtxt (exprSigCtxt in_expr) $
600 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
602 if not (isQualifiedTy sig_tc_ty) then
604 unifyTauTy sig_tc_ty res_ty `thenTc_`
605 tcMonoExpr expr sig_tc_ty
607 else -- Signature is polymorphic
608 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
610 -- Now match the signature type with res_ty.
611 -- We must not do this earlier, because res_ty might well
612 -- mention variables free in the environment, and we'd get
613 -- bogus complaints about not being able to for-all the
615 unifyTauTy res_ty expr_ty `thenTc_`
617 -- If everything is ok, return the stuff unchanged, except for
618 -- the effect of any substutions etc. We simply discard the
619 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
620 -- resolution it may have done, which is recorded in the
625 Implicit Parameter bindings.
628 tcMonoExpr (HsWith expr binds) res_ty
629 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
630 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
632 -- If the binding binds ?x = E, we must now
633 -- discharge any ?x constraints in expr_lie
634 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
636 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
637 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
639 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
641 tcIPBind (name, expr)
642 = newTyVarTy openTypeKind `thenTc` \ ty ->
643 tcGetSrcLoc `thenTc` \ loc ->
644 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
645 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
646 returnTc ((ip, expr'), lie)
649 %************************************************************************
651 \subsection{@tcApp@ typchecks an application}
653 %************************************************************************
657 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
658 -> TcType -- Expected result type of application
659 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
662 tcApp fun args res_ty
663 = -- First type-check the function
664 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
666 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
667 split_fun_ty fun_ty (length args)
668 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
670 -- Unify with expected result before type-checking the args
671 -- This is when we might detect a too-few args situation
672 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
673 unifyTauTy res_ty actual_result_ty
676 -- Now typecheck the args
677 mapAndUnzipTc (tcArg fun)
678 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
680 -- Check that the result type doesn't have any nested for-alls.
681 -- For example, a "build" on its own is no good; it must be applied to something.
682 checkTc (isTauTy actual_result_ty)
683 (lurkingRank2Err fun actual_result_ty) `thenTc_`
685 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
688 -- If an error happens we try to figure out whether the
689 -- function has been given too many or too few arguments,
691 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
692 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
693 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
695 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
696 (env2, act_ty'') = tidyOpenType env1 act_ty'
697 (exp_args, _) = tcSplitFunTys exp_ty''
698 (act_args, _) = tcSplitFunTys act_ty''
700 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
701 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
702 | otherwise = appCtxt fun args
704 returnNF_Tc (env2, message)
707 split_fun_ty :: TcType -- The type of the function
708 -> Int -- Number of arguments
709 -> TcM ([TcType], -- Function argument types
710 TcType) -- Function result types
712 split_fun_ty fun_ty 0
713 = returnTc ([], fun_ty)
715 split_fun_ty fun_ty n
716 = -- Expect the function to have type A->B
717 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
718 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
719 returnTc (arg_ty:arg_tys, final_res_ty)
723 tcArg :: RenamedHsExpr -- The function (for error messages)
724 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
725 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
727 tcArg the_fun (arg, expected_arg_ty, arg_no)
728 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
729 tcExpr arg expected_arg_ty
733 %************************************************************************
735 \subsection{@tcId@ typchecks an identifier occurrence}
737 %************************************************************************
740 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
741 tcId name -- Look up the Id and instantiate its type
742 = tcLookupId name `thenNF_Tc` \ id ->
746 Typecheck expression which in most cases will be an Id.
749 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
750 tcExpr_id (HsVar name) = tcId name
751 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
752 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
753 returnTc (expr', lie_id, id_ty)
757 %************************************************************************
759 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
761 %************************************************************************
764 tcDoStmts do_or_lc stmts src_loc res_ty
765 = -- get the Monad and MonadZero classes
766 -- create type consisting of a fresh monad tyvar
767 ASSERT( not (null stmts) )
768 tcAddSrcLoc src_loc $
770 -- If it's a comprehension we're dealing with,
771 -- force it to be a list comprehension.
772 -- (as of Haskell 98, monad comprehensions are no more.)
774 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
775 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
777 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
778 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
779 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
780 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
781 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
783 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
785 -- Build the then and zero methods in case we need them
786 -- It's important that "then" and "return" appear just once in the final LIE,
787 -- not only for typechecker efficiency, but also because otherwise during
788 -- simplification we end up with silly stuff like
789 -- then = case d of (t,r) -> t
791 -- where the second "then" sees that it already exists in the "available" stuff.
793 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
794 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
795 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
796 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
797 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
798 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
800 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
802 returnTc (HsDoOut do_or_lc stmts'
803 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
805 stmts_lie `plusLIE` monad_lie)
809 %************************************************************************
811 \subsection{Record bindings}
813 %************************************************************************
815 Game plan for record bindings
816 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
817 1. Find the TyCon for the bindings, from the first field label.
819 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
821 For each binding field = value
823 3. Instantiate the field type (from the field label) using the type
826 4 Type check the value using tcArg, passing the field type as
827 the expected argument type.
829 This extends OK when the field types are universally quantified.
834 :: TyCon -- Type constructor for the record
835 -> [TcType] -- Args of this type constructor
836 -> RenamedRecordBinds
837 -> TcM (TcRecordBinds, LIE)
839 tcRecordBinds tycon ty_args rbinds
840 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
841 returnTc (rbinds', plusLIEs lies)
843 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
845 do_bind (field_lbl_name, rhs, pun_flag)
846 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
848 field_lbl = recordSelectorFieldLabel sel_id
849 field_ty = substTy tenv (fieldLabelType field_lbl)
851 ASSERT( isRecordSelector sel_id )
852 -- This lookup and assertion will surely succeed, because
853 -- we check that the fields are indeed record selectors
854 -- before calling tcRecordBinds
855 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
856 -- The caller of tcRecordBinds has already checked
857 -- that all the fields come from the same type
859 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
861 returnTc ((sel_id, rhs', pun_flag), lie)
863 badFields rbinds data_con
864 = [field_name | (field_name, _, _) <- rbinds,
865 not (field_name `elem` field_names)
868 field_names = map fieldLabelName (dataConFieldLabels data_con)
870 missingFields rbinds data_con
871 | null field_labels = ([], []) -- Not declared as a record;
872 -- But C{} is still valid
874 = (missing_strict_fields, other_missing_fields)
876 missing_strict_fields
877 = [ fl | (fl, str) <- field_info,
879 not (fieldLabelName fl `elem` field_names_used)
882 = [ fl | (fl, str) <- field_info,
883 not (isMarkedStrict str),
884 not (fieldLabelName fl `elem` field_names_used)
887 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
888 field_labels = dataConFieldLabels data_con
890 field_info = zipEqual "missingFields"
892 (drop (length ex_theta) (dataConStrictMarks data_con))
893 -- The 'drop' is because dataConStrictMarks
894 -- includes the existential dictionaries
895 (_, _, _, ex_theta, _, _) = dataConSig data_con
898 %************************************************************************
900 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
902 %************************************************************************
905 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
907 tcMonoExprs [] [] = returnTc ([], emptyLIE)
908 tcMonoExprs (expr:exprs) (ty:tys)
909 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
910 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
911 returnTc (expr':exprs', lie1 `plusLIE` lie2)
915 %************************************************************************
917 \subsection{Literals}
919 %************************************************************************
924 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
925 tcLit (HsLitLit s _) res_ty
926 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
927 newDicts (LitLitOrigin (_UNPK_ s))
928 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
929 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
932 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
933 returnTc (HsLit lit, emptyLIE)
937 %************************************************************************
939 \subsection{Errors and contexts}
941 %************************************************************************
945 Boring and alphabetical:
948 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
951 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
954 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
957 = hang (ptext SLIT("In an expression with a type signature:"))
961 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
964 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
967 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
970 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
972 funAppCtxt fun arg arg_no
973 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
974 quotes (ppr fun) <> text ", namely"])
977 wrongArgsCtxt too_many_or_few fun args
978 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
979 <+> ptext SLIT("is applied to") <+> text too_many_or_few
980 <+> ptext SLIT("arguments in the call"))
981 4 (parens (ppr the_app))
983 the_app = foldl HsApp fun args -- Used in error messages
986 = ptext SLIT("In the application") <+> quotes (ppr the_app)
988 the_app = foldl HsApp fun args -- Used in error messages
990 lurkingRank2Err fun fun_ty
991 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
992 4 (vcat [ptext SLIT("It is applied to too few arguments"),
993 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
996 = hang (ptext SLIT("No constructor has all these fields:"))
997 4 (pprQuotedList fields)
999 fields = [field | (field, _, _) <- rbinds]
1001 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1002 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1005 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1007 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1008 missingStrictFieldCon con field
1009 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1010 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1012 missingFieldCon :: Name -> FieldLabel -> SDoc
1013 missingFieldCon con field
1014 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1015 ptext SLIT("is not initialised")]