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(..), 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 TcType ( TcType, TcTauType,
36 tcInstTyVars, tcInstType,
37 newTyVarTy, newTyVarTys, zonkTcType )
39 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
40 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
41 import DataCon ( dataConFieldLabels, dataConSig,
44 import Demand ( isMarkedStrict )
46 import Type ( mkFunTy, mkAppTy, mkTyConTy,
47 splitFunTy_maybe, splitFunTys,
48 mkTyConApp, splitSigmaTy, mkClassPred,
49 isTauTy, tyVarsOfType, tyVarsOfTypes,
50 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
51 liftedTypeKind, openTypeKind, mkArrowKind,
54 import TyCon ( TyCon, tyConTyVars )
55 import Subst ( mkTopTyVarSubst, substTheta, substTy )
56 import VarSet ( elemVarSet )
57 import TysWiredIn ( boolTy, mkListTy, listTyCon )
58 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
59 import PrelNames ( cCallableClassName,
61 enumFromName, enumFromThenName, negateName,
62 enumFromToName, enumFromThenToName,
63 thenMName, failMName, returnMName, ioTyConName
66 import Maybes ( maybeToBool )
67 import ListSetOps ( minusList )
70 import HscTypes ( TyThing(..) )
74 %************************************************************************
76 \subsection{Main wrappers}
78 %************************************************************************
81 tcExpr :: RenamedHsExpr -- Expession to type check
82 -> TcType -- Expected type (could be a polytpye)
85 tcExpr expr ty | isSigmaTy ty = -- Polymorphic case
86 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
89 | otherwise = -- Monomorphic case
94 %************************************************************************
96 \subsection{@tcPolyExpr@ typchecks an application}
98 %************************************************************************
101 -- tcPolyExpr is like tcMonoExpr, except that the expected type
102 -- can be a polymorphic one.
103 tcPolyExpr :: RenamedHsExpr
104 -> TcType -- Expected type
105 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
106 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
108 tcPolyExpr arg expected_arg_ty
109 = -- Ha! The argument type of the function is a for-all type,
110 -- An example of rank-2 polymorphism.
112 -- To ensure that the forall'd type variables don't get unified with each
113 -- other or any other types, we make fresh copy of the alleged type
114 tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
116 free_tvs = tyVarsOfType expected_arg_ty
118 -- Type-check the arg and unify with expected type
119 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
121 -- Check that the sig_tyvars havn't been constrained
122 -- The interesting bit here is that we must include the free variables
123 -- of the expected arg ty. Here's an example:
124 -- runST (newVar True)
125 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
126 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
127 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
128 -- So now s' isn't unconstrained because it's linked to a.
129 -- Conclusion: include the free vars of the expected arg type in the
130 -- list of "free vars" for the signature check.
132 tcExtendGlobalTyVars free_tvs $
133 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
135 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
137 (text "the type signature of an expression")
139 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
141 checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
144 -- This HsLet binds any Insts which came out of the simplification.
145 -- It's a bit out of place here, but using AbsBind involves inventing
146 -- a couple of new names which seems worse.
147 generalised_arg = TyLam zonked_sig_tyvars $
148 DictLam (map instToId sig_dicts) $
152 returnTc ( generalised_arg, free_insts,
153 arg', sig_tau, lie_arg )
155 sig_msg = ptext SLIT("When checking an expression type signature")
158 %************************************************************************
160 \subsection{The TAUT rules for variables}
162 %************************************************************************
165 tcMonoExpr :: RenamedHsExpr -- Expession to type check
166 -> TcTauType -- Expected type (could be a type variable)
169 tcMonoExpr (HsVar name) res_ty
170 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
171 unifyTauTy res_ty id_ty `thenTc_`
173 -- Check that the result type doesn't have any nested for-alls.
174 -- For example, a "build" on its own is no good; it must be
175 -- applied to something.
176 checkTc (isTauTy id_ty)
177 (lurkingRank2Err name id_ty) `thenTc_`
179 returnTc (expr', lie)
183 tcMonoExpr (HsIPVar name) res_ty
184 = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
185 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
188 %************************************************************************
190 \subsection{Other expression forms}
192 %************************************************************************
195 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
196 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
197 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
199 tcMonoExpr (NegApp expr) res_ty
200 = tcLookupSyntaxName negateName `thenNF_Tc` \ neg ->
201 tcMonoExpr (HsApp (HsVar neg) expr) res_ty
203 tcMonoExpr (HsLam match) res_ty
204 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
205 returnTc (HsLam match', lie)
207 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
209 accum (HsApp e1 e2) args = accum e1 (e2:args)
211 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
212 returnTc (foldl HsApp fun' args', lie)
214 -- equivalent to (op e1) e2:
215 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
216 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
217 returnTc (OpApp arg1' op' fix arg2', lie)
220 Note that the operators in sections are expected to be binary, and
221 a type error will occur if they aren't.
224 -- Left sections, equivalent to
231 tcMonoExpr in_expr@(SectionL arg op) res_ty
232 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
234 -- Check that res_ty is a function type
235 -- Without this check we barf in the desugarer on
237 -- because it tries to desugar to
238 -- f op = \r -> 3 op r
239 -- so (3 `op`) had better be a function!
240 tcAddErrCtxt (sectionLAppCtxt in_expr) $
241 unifyFunTy res_ty `thenTc_`
243 returnTc (SectionL arg' op', lie)
245 -- Right sections, equivalent to \ x -> x op expr, or
248 tcMonoExpr in_expr@(SectionR op expr) res_ty
249 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
250 tcAddErrCtxt (sectionRAppCtxt in_expr) $
251 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
252 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
253 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
254 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
257 The interesting thing about @ccall@ is that it is just a template
258 which we instantiate by filling in details about the types of its
259 argument and result (ie minimal typechecking is performed). So, the
260 basic story is that we allocate a load of type variables (to hold the
261 arg/result types); unify them with the args/result; and store them for
265 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
266 = -- Get the callable and returnable classes.
267 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
268 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
269 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
271 new_arg_dict (arg, arg_ty)
272 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
273 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
274 returnNF_Tc arg_dicts -- Actually a singleton bag
276 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
280 let n_args = length args
281 tv_idxs | n_args == 0 = []
282 | otherwise = [1..n_args]
284 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
285 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
287 -- The argument types can be unlifted or lifted; the result
288 -- type must, however, be lifted since it's an argument to the IO
290 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
292 io_result_ty = mkTyConApp ioTyCon [result_ty]
294 unifyTauTy res_ty io_result_ty `thenTc_`
296 -- Construct the extra insts, which encode the
297 -- constraints on the argument and result types.
298 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
299 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
300 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
301 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
305 tcMonoExpr (HsSCC lbl expr) res_ty
306 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
307 returnTc (HsSCC lbl expr', lie)
309 tcMonoExpr (HsLet binds expr) res_ty
312 binds -- Bindings to check
313 tc_expr `thenTc` \ (expr', lie) ->
314 returnTc (expr', lie)
316 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
317 returnTc (expr', lie)
318 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
320 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
321 = tcAddSrcLoc src_loc $
322 tcAddErrCtxt (caseCtxt in_expr) $
324 -- Typecheck the case alternatives first.
325 -- The case patterns tend to give good type info to use
326 -- when typechecking the scrutinee. For example
329 -- will report that map is applied to too few arguments
331 -- Not only that, but it's better to check the matches on their
332 -- own, so that we get the expected results for scoped type variables.
334 -- (p::a, q::b) -> (q,p)
335 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
336 -- claimed by the pattern signatures. But if we typechecked the
337 -- match with x in scope and x's type as the expected type, we'd be hosed.
339 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
341 tcAddErrCtxt (caseScrutCtxt scrut) (
342 tcMonoExpr scrut scrut_ty
343 ) `thenTc` \ (scrut',lie1) ->
345 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
347 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
348 = tcAddSrcLoc src_loc $
349 tcAddErrCtxt (predCtxt pred) (
350 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
352 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
353 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
354 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
358 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
359 = tcDoStmts do_or_lc stmts src_loc res_ty
363 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
364 = unifyListTy res_ty `thenTc` \ elt_ty ->
365 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
366 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
369 = tcAddErrCtxt (listCtxt expr) $
370 tcMonoExpr expr elt_ty
372 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
373 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
374 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
375 (exprs `zip` arg_tys) -- we know they're of equal length.
376 `thenTc` \ (exprs', lies) ->
377 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
379 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
380 = tcAddErrCtxt (recordConCtxt expr) $
381 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
383 (_, record_ty) = splitFunTys con_tau
384 (tycon, ty_args, _) = splitAlgTyConApp record_ty
386 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
387 unifyTauTy res_ty record_ty `thenTc_`
389 -- Check that the record bindings match the constructor
390 -- con_name is syntactically constrained to be a data constructor
391 tcLookupDataCon con_name `thenTc` \ data_con ->
393 bad_fields = badFields rbinds data_con
395 if not (null bad_fields) then
396 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
397 failTc -- Fail now, because tcRecordBinds will crash on a bad field
400 -- Typecheck the record bindings
401 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
404 (missing_s_fields, missing_fields) = missingFields rbinds data_con
406 checkTcM (null missing_s_fields)
407 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
408 returnNF_Tc ()) `thenNF_Tc_`
409 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
410 checkTcM (not (warn && not (null missing_fields)))
411 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
412 returnNF_Tc ()) `thenNF_Tc_`
414 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
416 -- The main complication with RecordUpd is that we need to explicitly
417 -- handle the *non-updated* fields. Consider:
419 -- data T a b = MkT1 { fa :: a, fb :: b }
420 -- | MkT2 { fa :: a, fc :: Int -> Int }
421 -- | MkT3 { fd :: a }
423 -- upd :: T a b -> c -> T a c
424 -- upd t x = t { fb = x}
426 -- The type signature on upd is correct (i.e. the result should not be (T a b))
427 -- because upd should be equivalent to:
429 -- upd t x = case t of
430 -- MkT1 p q -> MkT1 p x
431 -- MkT2 a b -> MkT2 p b
432 -- MkT3 d -> error ...
434 -- So we need to give a completely fresh type to the result record,
435 -- and then constrain it by the fields that are *not* updated ("p" above).
437 -- Note that because MkT3 doesn't contain all the fields being updated,
438 -- its RHS is simply an error, so it doesn't impose any type constraints
440 -- All this is done in STEP 4 below.
442 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
443 = tcAddErrCtxt (recordUpdCtxt expr) $
446 -- Check that the field names are really field names
447 ASSERT( not (null rbinds) )
449 field_names = [field_name | (field_name, _, _) <- rbinds]
451 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
453 bad_guys = [ addErrTc (notSelector field_name)
454 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
456 Just (AnId sel_id) -> not (isRecordSelector sel_id)
460 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
463 -- Figure out the tycon and data cons from the first field name
465 (Just (AnId sel_id) : _) = maybe_sel_ids
466 (_, _, tau) = splitSigmaTy (idType sel_id) -- Selectors can be overloaded
467 -- when the data type has a context
468 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
469 (tycon, _, data_cons) = splitAlgTyConApp data_ty
470 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
472 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
475 -- Check that at least one constructor has all the named fields
476 -- i.e. has an empty set of bad fields returned by badFields
477 checkTc (any (null . badFields rbinds) data_cons)
478 (badFieldsUpd rbinds) `thenTc_`
481 -- Typecheck the update bindings.
482 -- (Do this after checking for bad fields in case there's a field that
483 -- doesn't match the constructor.)
485 result_record_ty = mkTyConApp tycon result_inst_tys
487 unifyTauTy res_ty result_record_ty `thenTc_`
488 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
491 -- Use the un-updated fields to find a vector of booleans saying
492 -- which type arguments must be the same in updatee and result.
494 -- WARNING: this code assumes that all data_cons in a common tycon
495 -- have FieldLabels abstracted over the same tyvars.
497 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
498 con_field_lbls_s = map dataConFieldLabels data_cons
500 -- A constructor is only relevant to this process if
501 -- it contains all the fields that are being updated
502 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
503 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
505 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
506 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
508 mk_inst_ty (tyvar, result_inst_ty)
509 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
510 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
512 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
515 -- Typecheck the expression to be updated
517 record_ty = mkTyConApp tycon inst_tys
519 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
522 -- Figure out the LIE we need. We have to generate some
523 -- dictionaries for the data type context, since we are going to
524 -- do some construction.
526 -- What dictionaries do we need? For the moment we assume that all
527 -- data constructors have the same context, and grab it from the first
528 -- constructor. If they have varying contexts then we'd have to
529 -- union the ones that could participate in the update.
531 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
532 inst_env = mkTopTyVarSubst tyvars result_inst_tys
533 theta' = substTheta inst_env theta
535 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
538 returnTc (RecordUpdOut record_expr' result_record_ty (map instToId dicts) rbinds',
539 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
541 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
542 = unifyListTy res_ty `thenTc` \ elt_ty ->
543 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
545 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
546 newMethod (ArithSeqOrigin seq)
547 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
549 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
550 lie1 `plusLIE` unitLIE enum_from)
552 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
553 = tcAddErrCtxt (arithSeqCtxt in_expr) $
554 unifyListTy res_ty `thenTc` \ elt_ty ->
555 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
556 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
557 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
558 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
560 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
561 (FromThen expr1' expr2'),
562 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
564 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
565 = tcAddErrCtxt (arithSeqCtxt in_expr) $
566 unifyListTy res_ty `thenTc` \ elt_ty ->
567 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
568 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
569 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
570 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
572 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
573 (FromTo expr1' expr2'),
574 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
576 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
577 = tcAddErrCtxt (arithSeqCtxt in_expr) $
578 unifyListTy res_ty `thenTc` \ elt_ty ->
579 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
580 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
581 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
582 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
583 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
585 returnTc (ArithSeqOut (HsVar (instToId eft))
586 (FromThenTo expr1' expr2' expr3'),
587 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
590 %************************************************************************
592 \subsection{Expressions type signatures}
594 %************************************************************************
597 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
598 = tcAddErrCtxt (exprSigCtxt in_expr) $
599 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
601 if not (isSigmaTy sig_tc_ty) then
603 unifyTauTy sig_tc_ty res_ty `thenTc_`
604 tcMonoExpr expr sig_tc_ty
606 else -- Signature is polymorphic
607 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
609 -- Now match the signature type with res_ty.
610 -- We must not do this earlier, because res_ty might well
611 -- mention variables free in the environment, and we'd get
612 -- bogus complaints about not being able to for-all the
614 unifyTauTy res_ty expr_ty `thenTc_`
616 -- If everything is ok, return the stuff unchanged, except for
617 -- the effect of any substutions etc. We simply discard the
618 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
619 -- resolution it may have done, which is recorded in the
624 Implicit Parameter bindings.
627 tcMonoExpr (HsWith expr binds) res_ty
628 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
629 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
631 -- If the binding binds ?x = E, we must now
632 -- discharge any ?x constraints in expr_lie
633 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
635 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
636 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
638 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
640 tcIPBind (name, expr)
641 = newTyVarTy openTypeKind `thenTc` \ ty ->
642 tcGetSrcLoc `thenTc` \ loc ->
643 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
644 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
645 returnTc ((ip, expr'), lie)
648 %************************************************************************
650 \subsection{@tcApp@ typchecks an application}
652 %************************************************************************
656 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
657 -> TcType -- Expected result type of application
658 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
661 tcApp fun args res_ty
662 = -- First type-check the function
663 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
665 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
666 split_fun_ty fun_ty (length args)
667 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
669 -- Unify with expected result before type-checking the args
670 -- This is when we might detect a too-few args situation
671 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
672 unifyTauTy res_ty actual_result_ty
675 -- Now typecheck the args
676 mapAndUnzipTc (tcArg fun)
677 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
679 -- Check that the result type doesn't have any nested for-alls.
680 -- For example, a "build" on its own is no good; it must be applied to something.
681 checkTc (isTauTy actual_result_ty)
682 (lurkingRank2Err fun actual_result_ty) `thenTc_`
684 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
687 -- If an error happens we try to figure out whether the
688 -- function has been given too many or too few arguments,
690 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
691 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
692 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
694 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
695 (env2, act_ty'') = tidyOpenType env1 act_ty'
696 (exp_args, _) = splitFunTys exp_ty''
697 (act_args, _) = splitFunTys act_ty''
699 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
700 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
701 | otherwise = appCtxt fun args
703 returnNF_Tc (env2, message)
706 split_fun_ty :: TcType -- The type of the function
707 -> Int -- Number of arguments
708 -> TcM ([TcType], -- Function argument types
709 TcType) -- Function result types
711 split_fun_ty fun_ty 0
712 = returnTc ([], fun_ty)
714 split_fun_ty fun_ty n
715 = -- Expect the function to have type A->B
716 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
717 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
718 returnTc (arg_ty:arg_tys, final_res_ty)
722 tcArg :: RenamedHsExpr -- The function (for error messages)
723 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
724 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
726 tcArg the_fun (arg, expected_arg_ty, arg_no)
727 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
728 tcExpr arg expected_arg_ty
732 %************************************************************************
734 \subsection{@tcId@ typchecks an identifier occurrence}
736 %************************************************************************
739 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
740 tcId name -- Look up the Id and instantiate its type
741 = tcLookupId name `thenNF_Tc` \ id ->
745 Typecheck expression which in most cases will be an Id.
748 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
749 tcExpr_id (HsVar name) = tcId name
750 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
751 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
752 returnTc (expr', lie_id, id_ty)
756 %************************************************************************
758 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
760 %************************************************************************
763 tcDoStmts do_or_lc stmts src_loc res_ty
764 = -- get the Monad and MonadZero classes
765 -- create type consisting of a fresh monad tyvar
766 ASSERT( not (null stmts) )
767 tcAddSrcLoc src_loc $
769 -- If it's a comprehension we're dealing with,
770 -- force it to be a list comprehension.
771 -- (as of Haskell 98, monad comprehensions are no more.)
773 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
774 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
776 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
777 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
778 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
779 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
780 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
782 tcStmts do_or_lc m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
784 -- Build the then and zero methods in case we need them
785 -- It's important that "then" and "return" appear just once in the final LIE,
786 -- not only for typechecker efficiency, but also because otherwise during
787 -- simplification we end up with silly stuff like
788 -- then = case d of (t,r) -> t
790 -- where the second "then" sees that it already exists in the "available" stuff.
792 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
793 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
794 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
795 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
796 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
797 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
799 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
801 returnTc (HsDoOut do_or_lc stmts'
802 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
804 stmts_lie `plusLIE` monad_lie)
808 %************************************************************************
810 \subsection{Record bindings}
812 %************************************************************************
814 Game plan for record bindings
815 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
816 1. Find the TyCon for the bindings, from the first field label.
818 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
820 For each binding field = value
822 3. Instantiate the field type (from the field label) using the type
825 4 Type check the value using tcArg, passing the field type as
826 the expected argument type.
828 This extends OK when the field types are universally quantified.
833 :: TyCon -- Type constructor for the record
834 -> [TcType] -- Args of this type constructor
835 -> RenamedRecordBinds
836 -> TcM (TcRecordBinds, LIE)
838 tcRecordBinds tycon ty_args rbinds
839 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
840 returnTc (rbinds', plusLIEs lies)
842 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
844 do_bind (field_lbl_name, rhs, pun_flag)
845 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
847 field_lbl = recordSelectorFieldLabel sel_id
848 field_ty = substTy tenv (fieldLabelType field_lbl)
850 ASSERT( isRecordSelector sel_id )
851 -- This lookup and assertion will surely succeed, because
852 -- we check that the fields are indeed record selectors
853 -- before calling tcRecordBinds
854 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
855 -- The caller of tcRecordBinds has already checked
856 -- that all the fields come from the same type
858 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
860 returnTc ((sel_id, rhs', pun_flag), lie)
862 badFields rbinds data_con
863 = [field_name | (field_name, _, _) <- rbinds,
864 not (field_name `elem` field_names)
867 field_names = map fieldLabelName (dataConFieldLabels data_con)
869 missingFields rbinds data_con
870 | null field_labels = ([], []) -- Not declared as a record;
871 -- But C{} is still valid
873 = (missing_strict_fields, other_missing_fields)
875 missing_strict_fields
876 = [ fl | (fl, str) <- field_info,
878 not (fieldLabelName fl `elem` field_names_used)
881 = [ fl | (fl, str) <- field_info,
882 not (isMarkedStrict str),
883 not (fieldLabelName fl `elem` field_names_used)
886 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
887 field_labels = dataConFieldLabels data_con
889 field_info = zipEqual "missingFields"
891 (drop (length ex_theta) (dataConStrictMarks data_con))
892 -- The 'drop' is because dataConStrictMarks
893 -- includes the existential dictionaries
894 (_, _, _, ex_theta, _, _) = dataConSig data_con
897 %************************************************************************
899 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
901 %************************************************************************
904 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
906 tcMonoExprs [] [] = returnTc ([], emptyLIE)
907 tcMonoExprs (expr:exprs) (ty:tys)
908 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
909 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
910 returnTc (expr':exprs', lie1 `plusLIE` lie2)
914 %************************************************************************
916 \subsection{Literals}
918 %************************************************************************
923 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
924 tcLit (HsLitLit s _) res_ty
925 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
926 newDicts (LitLitOrigin (_UNPK_ s))
927 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
928 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
931 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
932 returnTc (HsLit lit, emptyLIE)
936 %************************************************************************
938 \subsection{Errors and contexts}
940 %************************************************************************
944 Boring and alphabetical:
947 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
950 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
953 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
956 = hang (ptext SLIT("In an expression with a type signature:"))
960 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
963 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
966 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
969 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
971 funAppCtxt fun arg arg_no
972 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
973 quotes (ppr fun) <> text ", namely"])
976 wrongArgsCtxt too_many_or_few fun args
977 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
978 <+> ptext SLIT("is applied to") <+> text too_many_or_few
979 <+> ptext SLIT("arguments in the call"))
980 4 (parens (ppr the_app))
982 the_app = foldl HsApp fun args -- Used in error messages
985 = ptext SLIT("In the application") <+> quotes (ppr the_app)
987 the_app = foldl HsApp fun args -- Used in error messages
989 lurkingRank2Err fun fun_ty
990 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
991 4 (vcat [ptext SLIT("It is applied to too few arguments"),
992 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
995 = hang (ptext SLIT("No constructor has all these fields:"))
996 4 (pprQuotedList fields)
998 fields = [field | (field, _, _) <- rbinds]
1000 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1001 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1004 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1006 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1007 missingStrictFieldCon con field
1008 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1009 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1011 missingFieldCon :: Name -> FieldLabel -> SDoc
1012 missingFieldCon con field
1013 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1014 ptext SLIT("is not initialised")]