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(..), isMarkedStrict )
19 import Inst ( InstOrigin(..),
20 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
21 newOverloadedLit, newMethod, newIPDict,
25 import TcBinds ( tcBindsAndThen )
26 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
27 tcLookupTyCon, tcLookupDataCon, tcLookupId,
30 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
31 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), checkSigTyVars, sigCtxt )
32 import TcPat ( badFieldCon, simpleHsLitTy )
33 import TcSimplify ( tcSimplifyCheck, tcSimplifyIPs )
34 import TcMType ( tcInstTyVars, tcInstType,
35 newTyVarTy, newTyVarTys, zonkTcType,
36 unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy
38 import TcType ( tcSplitFunTys, tcSplitTyConApp,
40 mkFunTy, mkAppTy, mkTyConTy,
41 mkTyConApp, mkClassPred, tcFunArgTy,
42 isTauTy, tyVarsOfType, tyVarsOfTypes,
43 liftedTypeKind, openTypeKind, mkArrowKind,
44 tcSplitSigmaTy, tcTyConAppTyCon,
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
48 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
49 import DataCon ( dataConFieldLabels, dataConSig,
53 import TyCon ( TyCon, tyConTyVars, isAlgTyCon, tyConDataCons )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( elemVarSet )
56 import TysWiredIn ( boolTy, mkListTy, listTyCon )
57 import PrelNames ( cCallableClassName,
59 enumFromName, enumFromThenName,
60 enumFromToName, enumFromThenToName,
61 thenMName, failMName, returnMName, ioTyConName
64 import ListSetOps ( minusList )
67 import HscTypes ( TyThing(..) )
71 %************************************************************************
73 \subsection{Main wrappers}
75 %************************************************************************
78 tcExpr :: RenamedHsExpr -- Expession to type check
79 -> TcType -- Expected type (could be a polytpye)
82 tcExpr expr ty | isQualifiedTy ty = -- Polymorphic case
83 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
86 | otherwise = -- Monomorphic case
91 %************************************************************************
93 \subsection{@tcPolyExpr@ typchecks an application}
95 %************************************************************************
98 -- tcPolyExpr is like tcMonoExpr, except that the expected type
99 -- can be a polymorphic one.
100 tcPolyExpr :: RenamedHsExpr
101 -> TcType -- Expected type
102 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
103 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
105 tcPolyExpr arg expected_arg_ty
106 = -- Ha! The argument type of the function is a for-all type,
107 -- An example of rank-2 polymorphism.
109 -- To ensure that the forall'd type variables don't get unified with each
110 -- other or any other types, we make fresh copy of the alleged type
111 tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
113 free_tvs = tyVarsOfType expected_arg_ty
115 -- Type-check the arg and unify with expected type
116 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
118 -- Check that the sig_tyvars havn't been constrained
119 -- The interesting bit here is that we must include the free variables
120 -- of the expected arg ty. Here's an example:
121 -- runST (newVar True)
122 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
123 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
124 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
125 -- So now s' isn't unconstrained because it's linked to a.
126 -- Conclusion: include the free vars of the expected arg type in the
127 -- list of "free vars" for the signature check.
129 tcExtendGlobalTyVars free_tvs $
130 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
132 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
134 (text "the type signature of an expression")
136 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
138 checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
141 -- This HsLet binds any Insts which came out of the simplification.
142 -- It's a bit out of place here, but using AbsBind involves inventing
143 -- a couple of new names which seems worse.
144 generalised_arg = TyLam zonked_sig_tyvars $
145 DictLam (map instToId sig_dicts) $
149 returnTc ( generalised_arg, free_insts,
150 arg', sig_tau, lie_arg )
152 sig_msg = ptext SLIT("When checking an expression type signature")
155 %************************************************************************
157 \subsection{The TAUT rules for variables}
159 %************************************************************************
162 tcMonoExpr :: RenamedHsExpr -- Expession to type check
163 -> TcTauType -- Expected type (could be a type variable)
166 tcMonoExpr (HsVar name) res_ty
167 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
168 unifyTauTy res_ty id_ty `thenTc_`
170 -- Check that the result type doesn't have any nested for-alls.
171 -- For example, a "build" on its own is no good; it must be
172 -- applied to something.
173 checkTc (isTauTy id_ty)
174 (lurkingRank2Err name id_ty) `thenTc_`
176 returnTc (expr', lie)
180 tcMonoExpr (HsIPVar name) res_ty
181 = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
182 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
185 %************************************************************************
187 \subsection{Other expression forms}
189 %************************************************************************
192 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
193 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
194 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
196 tcMonoExpr (NegApp expr neg_name) res_ty
197 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
199 tcMonoExpr (HsLam match) res_ty
200 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
201 returnTc (HsLam match', lie)
203 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
205 accum (HsApp e1 e2) args = accum e1 (e2:args)
207 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
208 returnTc (foldl HsApp fun' args', lie)
210 -- equivalent to (op e1) e2:
211 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
212 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
213 returnTc (OpApp arg1' op' fix arg2', lie)
216 Note that the operators in sections are expected to be binary, and
217 a type error will occur if they aren't.
220 -- Left sections, equivalent to
227 tcMonoExpr in_expr@(SectionL arg op) res_ty
228 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
230 -- Check that res_ty is a function type
231 -- Without this check we barf in the desugarer on
233 -- because it tries to desugar to
234 -- f op = \r -> 3 op r
235 -- so (3 `op`) had better be a function!
236 tcAddErrCtxt (sectionLAppCtxt in_expr) $
237 unifyFunTy res_ty `thenTc_`
239 returnTc (SectionL arg' op', lie)
241 -- Right sections, equivalent to \ x -> x op expr, or
244 tcMonoExpr in_expr@(SectionR op expr) res_ty
245 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
246 tcAddErrCtxt (sectionRAppCtxt in_expr) $
247 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
248 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
249 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
250 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
253 The interesting thing about @ccall@ is that it is just a template
254 which we instantiate by filling in details about the types of its
255 argument and result (ie minimal typechecking is performed). So, the
256 basic story is that we allocate a load of type variables (to hold the
257 arg/result types); unify them with the args/result; and store them for
261 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
262 = -- Get the callable and returnable classes.
263 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
264 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
265 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
267 new_arg_dict (arg, arg_ty)
268 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
269 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
270 returnNF_Tc arg_dicts -- Actually a singleton bag
272 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
276 let n_args = length args
277 tv_idxs | n_args == 0 = []
278 | otherwise = [1..n_args]
280 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
281 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
283 -- The argument types can be unlifted or lifted; the result
284 -- type must, however, be lifted since it's an argument to the IO
286 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
288 io_result_ty = mkTyConApp ioTyCon [result_ty]
290 unifyTauTy res_ty io_result_ty `thenTc_`
292 -- Construct the extra insts, which encode the
293 -- constraints on the argument and result types.
294 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
295 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
296 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
297 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
301 tcMonoExpr (HsSCC lbl expr) res_ty
302 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
303 returnTc (HsSCC lbl expr', lie)
305 tcMonoExpr (HsLet binds expr) res_ty
308 binds -- Bindings to check
309 tc_expr `thenTc` \ (expr', lie) ->
310 returnTc (expr', lie)
312 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
313 returnTc (expr', lie)
314 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
316 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
317 = tcAddSrcLoc src_loc $
318 tcAddErrCtxt (caseCtxt in_expr) $
320 -- Typecheck the case alternatives first.
321 -- The case patterns tend to give good type info to use
322 -- when typechecking the scrutinee. For example
325 -- will report that map is applied to too few arguments
327 -- Not only that, but it's better to check the matches on their
328 -- own, so that we get the expected results for scoped type variables.
330 -- (p::a, q::b) -> (q,p)
331 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
332 -- claimed by the pattern signatures. But if we typechecked the
333 -- match with x in scope and x's type as the expected type, we'd be hosed.
335 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
337 tcAddErrCtxt (caseScrutCtxt scrut) (
338 tcMonoExpr scrut scrut_ty
339 ) `thenTc` \ (scrut',lie1) ->
341 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
343 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
344 = tcAddSrcLoc src_loc $
345 tcAddErrCtxt (predCtxt pred) (
346 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
348 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
349 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
350 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
354 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
355 = tcDoStmts do_or_lc stmts src_loc res_ty
359 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
360 = unifyListTy res_ty `thenTc` \ elt_ty ->
361 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
362 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
365 = tcAddErrCtxt (listCtxt expr) $
366 tcMonoExpr expr elt_ty
368 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
369 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
370 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
371 (exprs `zip` arg_tys) -- we know they're of equal length.
372 `thenTc` \ (exprs', lies) ->
373 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
375 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
376 = tcAddErrCtxt (recordConCtxt expr) $
377 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
379 (_, record_ty) = tcSplitFunTys con_tau
380 (tycon, ty_args) = tcSplitTyConApp record_ty
382 ASSERT( isAlgTyCon tycon )
383 unifyTauTy res_ty record_ty `thenTc_`
385 -- Check that the record bindings match the constructor
386 -- con_name is syntactically constrained to be a data constructor
387 tcLookupDataCon con_name `thenTc` \ data_con ->
389 bad_fields = badFields rbinds data_con
391 if not (null bad_fields) then
392 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
393 failTc -- Fail now, because tcRecordBinds will crash on a bad field
396 -- Typecheck the record bindings
397 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
400 (missing_s_fields, missing_fields) = missingFields rbinds data_con
402 checkTcM (null missing_s_fields)
403 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
404 returnNF_Tc ()) `thenNF_Tc_`
405 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
406 checkTcM (not (warn && not (null missing_fields)))
407 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
408 returnNF_Tc ()) `thenNF_Tc_`
410 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
412 -- The main complication with RecordUpd is that we need to explicitly
413 -- handle the *non-updated* fields. Consider:
415 -- data T a b = MkT1 { fa :: a, fb :: b }
416 -- | MkT2 { fa :: a, fc :: Int -> Int }
417 -- | MkT3 { fd :: a }
419 -- upd :: T a b -> c -> T a c
420 -- upd t x = t { fb = x}
422 -- The type signature on upd is correct (i.e. the result should not be (T a b))
423 -- because upd should be equivalent to:
425 -- upd t x = case t of
426 -- MkT1 p q -> MkT1 p x
427 -- MkT2 a b -> MkT2 p b
428 -- MkT3 d -> error ...
430 -- So we need to give a completely fresh type to the result record,
431 -- and then constrain it by the fields that are *not* updated ("p" above).
433 -- Note that because MkT3 doesn't contain all the fields being updated,
434 -- its RHS is simply an error, so it doesn't impose any type constraints
436 -- All this is done in STEP 4 below.
438 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
439 = tcAddErrCtxt (recordUpdCtxt expr) $
442 -- Check that the field names are really field names
443 ASSERT( not (null rbinds) )
445 field_names = [field_name | (field_name, _, _) <- rbinds]
447 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
449 bad_guys = [ addErrTc (notSelector field_name)
450 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
452 Just (AnId sel_id) -> not (isRecordSelector sel_id)
456 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
459 -- Figure out the tycon and data cons from the first field name
461 -- It's OK to use the non-tc splitters here (for a selector)
462 (Just (AnId sel_id) : _) = maybe_sel_ids
463 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
464 -- when the data type has a context
465 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
466 tycon = tcTyConAppTyCon data_ty
467 data_cons = tyConDataCons tycon
468 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
470 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
473 -- Check that at least one constructor has all the named fields
474 -- i.e. has an empty set of bad fields returned by badFields
475 checkTc (any (null . badFields rbinds) data_cons)
476 (badFieldsUpd rbinds) `thenTc_`
479 -- Typecheck the update bindings.
480 -- (Do this after checking for bad fields in case there's a field that
481 -- doesn't match the constructor.)
483 result_record_ty = mkTyConApp tycon result_inst_tys
485 unifyTauTy res_ty result_record_ty `thenTc_`
486 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
489 -- Use the un-updated fields to find a vector of booleans saying
490 -- which type arguments must be the same in updatee and result.
492 -- WARNING: this code assumes that all data_cons in a common tycon
493 -- have FieldLabels abstracted over the same tyvars.
495 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
496 con_field_lbls_s = map dataConFieldLabels data_cons
498 -- A constructor is only relevant to this process if
499 -- it contains all the fields that are being updated
500 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
501 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
503 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
504 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
506 mk_inst_ty (tyvar, result_inst_ty)
507 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
508 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
510 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
513 -- Typecheck the expression to be updated
515 record_ty = mkTyConApp tycon inst_tys
517 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
520 -- Figure out the LIE we need. We have to generate some
521 -- dictionaries for the data type context, since we are going to
522 -- do some construction.
524 -- What dictionaries do we need? For the moment we assume that all
525 -- data constructors have the same context, and grab it from the first
526 -- constructor. If they have varying contexts then we'd have to
527 -- union the ones that could participate in the update.
529 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
530 inst_env = mkTopTyVarSubst tyvars result_inst_tys
531 theta' = substTheta inst_env theta
533 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
536 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
537 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
539 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
540 = unifyListTy res_ty `thenTc` \ elt_ty ->
541 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
543 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
544 newMethod (ArithSeqOrigin seq)
545 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
547 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
548 lie1 `plusLIE` unitLIE enum_from)
550 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
551 = tcAddErrCtxt (arithSeqCtxt in_expr) $
552 unifyListTy res_ty `thenTc` \ elt_ty ->
553 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
554 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
555 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
556 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
558 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
559 (FromThen expr1' expr2'),
560 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
562 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
563 = tcAddErrCtxt (arithSeqCtxt in_expr) $
564 unifyListTy res_ty `thenTc` \ elt_ty ->
565 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
566 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
567 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
568 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
570 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
571 (FromTo expr1' expr2'),
572 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
574 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
575 = tcAddErrCtxt (arithSeqCtxt in_expr) $
576 unifyListTy res_ty `thenTc` \ elt_ty ->
577 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
578 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
579 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
580 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
581 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
583 returnTc (ArithSeqOut (HsVar (instToId eft))
584 (FromThenTo expr1' expr2' expr3'),
585 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
588 %************************************************************************
590 \subsection{Expressions type signatures}
592 %************************************************************************
595 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
596 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
598 tcAddErrCtxt (exprSigCtxt in_expr) $
599 if not (isQualifiedTy sig_tc_ty) then
601 unifyTauTy sig_tc_ty res_ty `thenTc_`
602 tcMonoExpr expr sig_tc_ty
604 else -- Signature is polymorphic
605 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
607 -- Now match the signature type with res_ty.
608 -- We must not do this earlier, because res_ty might well
609 -- mention variables free in the environment, and we'd get
610 -- bogus complaints about not being able to for-all the
612 unifyTauTy res_ty expr_ty `thenTc_`
614 -- If everything is ok, return the stuff unchanged, except for
615 -- the effect of any substutions etc. We simply discard the
616 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
617 -- resolution it may have done, which is recorded in the
622 Implicit Parameter bindings.
625 tcMonoExpr (HsWith expr binds) res_ty
626 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
627 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
629 -- If the binding binds ?x = E, we must now
630 -- discharge any ?x constraints in expr_lie
631 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
633 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
634 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
636 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
638 tcIPBind (name, expr)
639 = newTyVarTy openTypeKind `thenTc` \ ty ->
640 tcGetSrcLoc `thenTc` \ loc ->
641 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
642 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
643 returnTc ((ip, expr'), lie)
646 %************************************************************************
648 \subsection{@tcApp@ typchecks an application}
650 %************************************************************************
654 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
655 -> TcType -- Expected result type of application
656 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
659 tcApp fun args res_ty
660 = -- First type-check the function
661 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
663 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
664 split_fun_ty fun_ty (length args)
665 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
667 -- Unify with expected result before type-checking the args
668 -- This is when we might detect a too-few args situation
669 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
670 unifyTauTy res_ty actual_result_ty
673 -- Now typecheck the args
674 mapAndUnzipTc (tcArg fun)
675 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
677 -- Check that the result type doesn't have any nested for-alls.
678 -- For example, a "build" on its own is no good; it must be applied to something.
679 checkTc (isTauTy actual_result_ty)
680 (lurkingRank2Err fun actual_result_ty) `thenTc_`
682 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
685 -- If an error happens we try to figure out whether the
686 -- function has been given too many or too few arguments,
688 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
689 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
690 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
692 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
693 (env2, act_ty'') = tidyOpenType env1 act_ty'
694 (exp_args, _) = tcSplitFunTys exp_ty''
695 (act_args, _) = tcSplitFunTys act_ty''
697 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
698 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
699 | otherwise = appCtxt fun args
701 returnNF_Tc (env2, message)
704 split_fun_ty :: TcType -- The type of the function
705 -> Int -- Number of arguments
706 -> TcM ([TcType], -- Function argument types
707 TcType) -- Function result types
709 split_fun_ty fun_ty 0
710 = returnTc ([], fun_ty)
712 split_fun_ty fun_ty n
713 = -- Expect the function to have type A->B
714 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
715 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
716 returnTc (arg_ty:arg_tys, final_res_ty)
720 tcArg :: RenamedHsExpr -- The function (for error messages)
721 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
722 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
724 tcArg the_fun (arg, expected_arg_ty, arg_no)
725 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
726 tcExpr arg expected_arg_ty
730 %************************************************************************
732 \subsection{@tcId@ typchecks an identifier occurrence}
734 %************************************************************************
737 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
738 tcId name -- Look up the Id and instantiate its type
739 = tcLookupId name `thenNF_Tc` \ id ->
743 Typecheck expression which in most cases will be an Id.
746 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
747 tcExpr_id (HsVar name) = tcId name
748 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
749 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
750 returnTc (expr', lie_id, id_ty)
754 %************************************************************************
756 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
758 %************************************************************************
761 tcDoStmts do_or_lc stmts src_loc res_ty
762 = -- get the Monad and MonadZero classes
763 -- create type consisting of a fresh monad tyvar
764 ASSERT( not (null stmts) )
765 tcAddSrcLoc src_loc $
767 -- If it's a comprehension we're dealing with,
768 -- force it to be a list comprehension.
769 -- (as of Haskell 98, monad comprehensions are no more.)
771 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
772 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
774 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
775 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
776 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
777 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
778 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
780 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
782 -- Build the then and zero methods in case we need them
783 -- It's important that "then" and "return" appear just once in the final LIE,
784 -- not only for typechecker efficiency, but also because otherwise during
785 -- simplification we end up with silly stuff like
786 -- then = case d of (t,r) -> t
788 -- where the second "then" sees that it already exists in the "available" stuff.
790 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
791 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
792 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
793 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
794 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
795 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
797 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
799 returnTc (HsDoOut do_or_lc stmts'
800 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
802 stmts_lie `plusLIE` monad_lie)
806 %************************************************************************
808 \subsection{Record bindings}
810 %************************************************************************
812 Game plan for record bindings
813 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
814 1. Find the TyCon for the bindings, from the first field label.
816 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
818 For each binding field = value
820 3. Instantiate the field type (from the field label) using the type
823 4 Type check the value using tcArg, passing the field type as
824 the expected argument type.
826 This extends OK when the field types are universally quantified.
831 :: TyCon -- Type constructor for the record
832 -> [TcType] -- Args of this type constructor
833 -> RenamedRecordBinds
834 -> TcM (TcRecordBinds, LIE)
836 tcRecordBinds tycon ty_args rbinds
837 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
838 returnTc (rbinds', plusLIEs lies)
840 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
842 do_bind (field_lbl_name, rhs, pun_flag)
843 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
845 field_lbl = recordSelectorFieldLabel sel_id
846 field_ty = substTy tenv (fieldLabelType field_lbl)
848 ASSERT( isRecordSelector sel_id )
849 -- This lookup and assertion will surely succeed, because
850 -- we check that the fields are indeed record selectors
851 -- before calling tcRecordBinds
852 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
853 -- The caller of tcRecordBinds has already checked
854 -- that all the fields come from the same type
856 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
858 returnTc ((sel_id, rhs', pun_flag), lie)
860 badFields rbinds data_con
861 = [field_name | (field_name, _, _) <- rbinds,
862 not (field_name `elem` field_names)
865 field_names = map fieldLabelName (dataConFieldLabels data_con)
867 missingFields rbinds data_con
868 | null field_labels = ([], []) -- Not declared as a record;
869 -- But C{} is still valid
871 = (missing_strict_fields, other_missing_fields)
873 missing_strict_fields
874 = [ fl | (fl, str) <- field_info,
876 not (fieldLabelName fl `elem` field_names_used)
879 = [ fl | (fl, str) <- field_info,
880 not (isMarkedStrict str),
881 not (fieldLabelName fl `elem` field_names_used)
884 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
885 field_labels = dataConFieldLabels data_con
887 field_info = zipEqual "missingFields"
889 (drop (length ex_theta) (dataConStrictMarks data_con))
890 -- The 'drop' is because dataConStrictMarks
891 -- includes the existential dictionaries
892 (_, _, _, ex_theta, _, _) = dataConSig data_con
895 %************************************************************************
897 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
899 %************************************************************************
902 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
904 tcMonoExprs [] [] = returnTc ([], emptyLIE)
905 tcMonoExprs (expr:exprs) (ty:tys)
906 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
907 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
908 returnTc (expr':exprs', lie1 `plusLIE` lie2)
912 %************************************************************************
914 \subsection{Literals}
916 %************************************************************************
921 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
922 tcLit (HsLitLit s _) res_ty
923 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
924 newDicts (LitLitOrigin (_UNPK_ s))
925 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
926 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
929 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
930 returnTc (HsLit lit, emptyLIE)
934 %************************************************************************
936 \subsection{Errors and contexts}
938 %************************************************************************
942 Boring and alphabetical:
945 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
948 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
951 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
954 = hang (ptext SLIT("In an expression with a type signature:"))
958 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
961 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
964 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
967 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
969 funAppCtxt fun arg arg_no
970 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
971 quotes (ppr fun) <> text ", namely"])
974 wrongArgsCtxt too_many_or_few fun args
975 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
976 <+> ptext SLIT("is applied to") <+> text too_many_or_few
977 <+> ptext SLIT("arguments in the call"))
978 4 (parens (ppr the_app))
980 the_app = foldl HsApp fun args -- Used in error messages
983 = ptext SLIT("In the application") <+> quotes (ppr the_app)
985 the_app = foldl HsApp fun args -- Used in error messages
987 lurkingRank2Err fun fun_ty
988 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
989 4 (vcat [ptext SLIT("It is applied to too few arguments"),
990 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
993 = hang (ptext SLIT("No constructor has all these fields:"))
994 4 (pprQuotedList fields)
996 fields = [field | (field, _, _) <- rbinds]
998 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
999 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1002 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1004 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1005 missingStrictFieldCon con field
1006 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1007 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1009 missingFieldCon :: Name -> FieldLabel -> SDoc
1010 missingFieldCon con field
1011 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1012 ptext SLIT("is not initialised")]