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 e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
263 = getDOptsTc `thenNF_Tc` \ dflags ->
265 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
266 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
267 text "Either compile with -fvia-C, or, better, rewrite your code",
268 text "to use the foreign function interface. _casm_s are deprecated",
269 text "and support for them may one day disappear."])
272 -- Get the callable and returnable classes.
273 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
274 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
275 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
277 new_arg_dict (arg, arg_ty)
278 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
279 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
280 returnNF_Tc arg_dicts -- Actually a singleton bag
282 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
286 let tv_idxs | null args = []
287 | otherwise = [1..length args]
289 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
290 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
292 -- The argument types can be unlifted or lifted; the result
293 -- type must, however, be lifted since it's an argument to the IO
295 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
297 io_result_ty = mkTyConApp ioTyCon [result_ty]
299 unifyTauTy res_ty io_result_ty `thenTc_`
301 -- Construct the extra insts, which encode the
302 -- constraints on the argument and result types.
303 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
304 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
305 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
306 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
310 tcMonoExpr (HsSCC lbl expr) res_ty
311 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
312 returnTc (HsSCC lbl expr', lie)
314 tcMonoExpr (HsLet binds expr) res_ty
317 binds -- Bindings to check
318 tc_expr `thenTc` \ (expr', lie) ->
319 returnTc (expr', lie)
321 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
322 returnTc (expr', lie)
323 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
325 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
326 = tcAddSrcLoc src_loc $
327 tcAddErrCtxt (caseCtxt in_expr) $
329 -- Typecheck the case alternatives first.
330 -- The case patterns tend to give good type info to use
331 -- when typechecking the scrutinee. For example
334 -- will report that map is applied to too few arguments
336 -- Not only that, but it's better to check the matches on their
337 -- own, so that we get the expected results for scoped type variables.
339 -- (p::a, q::b) -> (q,p)
340 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
341 -- claimed by the pattern signatures. But if we typechecked the
342 -- match with x in scope and x's type as the expected type, we'd be hosed.
344 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
346 tcAddErrCtxt (caseScrutCtxt scrut) (
347 tcMonoExpr scrut scrut_ty
348 ) `thenTc` \ (scrut',lie1) ->
350 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
352 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
353 = tcAddSrcLoc src_loc $
354 tcAddErrCtxt (predCtxt pred) (
355 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
357 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
358 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
359 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
363 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
364 = tcDoStmts do_or_lc stmts src_loc res_ty
368 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
369 = unifyListTy res_ty `thenTc` \ elt_ty ->
370 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
371 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
374 = tcAddErrCtxt (listCtxt expr) $
375 tcMonoExpr expr elt_ty
377 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
378 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
379 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
380 (exprs `zip` arg_tys) -- we know they're of equal length.
381 `thenTc` \ (exprs', lies) ->
382 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
384 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
385 = tcAddErrCtxt (recordConCtxt expr) $
386 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
388 (_, record_ty) = tcSplitFunTys con_tau
389 (tycon, ty_args) = tcSplitTyConApp record_ty
391 ASSERT( isAlgTyCon tycon )
392 unifyTauTy res_ty record_ty `thenTc_`
394 -- Check that the record bindings match the constructor
395 -- con_name is syntactically constrained to be a data constructor
396 tcLookupDataCon con_name `thenTc` \ data_con ->
398 bad_fields = badFields rbinds data_con
400 if not (null bad_fields) then
401 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
402 failTc -- Fail now, because tcRecordBinds will crash on a bad field
405 -- Typecheck the record bindings
406 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
409 (missing_s_fields, missing_fields) = missingFields rbinds data_con
411 checkTcM (null missing_s_fields)
412 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
413 returnNF_Tc ()) `thenNF_Tc_`
414 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
415 checkTcM (not (warn && not (null missing_fields)))
416 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
417 returnNF_Tc ()) `thenNF_Tc_`
419 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
421 -- The main complication with RecordUpd is that we need to explicitly
422 -- handle the *non-updated* fields. Consider:
424 -- data T a b = MkT1 { fa :: a, fb :: b }
425 -- | MkT2 { fa :: a, fc :: Int -> Int }
426 -- | MkT3 { fd :: a }
428 -- upd :: T a b -> c -> T a c
429 -- upd t x = t { fb = x}
431 -- The type signature on upd is correct (i.e. the result should not be (T a b))
432 -- because upd should be equivalent to:
434 -- upd t x = case t of
435 -- MkT1 p q -> MkT1 p x
436 -- MkT2 a b -> MkT2 p b
437 -- MkT3 d -> error ...
439 -- So we need to give a completely fresh type to the result record,
440 -- and then constrain it by the fields that are *not* updated ("p" above).
442 -- Note that because MkT3 doesn't contain all the fields being updated,
443 -- its RHS is simply an error, so it doesn't impose any type constraints
445 -- All this is done in STEP 4 below.
447 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
448 = tcAddErrCtxt (recordUpdCtxt expr) $
451 -- Check that the field names are really field names
452 ASSERT( not (null rbinds) )
454 field_names = [field_name | (field_name, _, _) <- rbinds]
456 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
458 bad_guys = [ addErrTc (notSelector field_name)
459 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
461 Just (AnId sel_id) -> not (isRecordSelector sel_id)
465 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
468 -- Figure out the tycon and data cons from the first field name
470 -- It's OK to use the non-tc splitters here (for a selector)
471 (Just (AnId sel_id) : _) = maybe_sel_ids
472 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
473 -- when the data type has a context
474 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
475 tycon = tcTyConAppTyCon data_ty
476 data_cons = tyConDataCons tycon
477 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
479 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
482 -- Check that at least one constructor has all the named fields
483 -- i.e. has an empty set of bad fields returned by badFields
484 checkTc (any (null . badFields rbinds) data_cons)
485 (badFieldsUpd rbinds) `thenTc_`
488 -- Typecheck the update bindings.
489 -- (Do this after checking for bad fields in case there's a field that
490 -- doesn't match the constructor.)
492 result_record_ty = mkTyConApp tycon result_inst_tys
494 unifyTauTy res_ty result_record_ty `thenTc_`
495 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
498 -- Use the un-updated fields to find a vector of booleans saying
499 -- which type arguments must be the same in updatee and result.
501 -- WARNING: this code assumes that all data_cons in a common tycon
502 -- have FieldLabels abstracted over the same tyvars.
504 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
505 con_field_lbls_s = map dataConFieldLabels data_cons
507 -- A constructor is only relevant to this process if
508 -- it contains all the fields that are being updated
509 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
510 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
512 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
513 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
515 mk_inst_ty (tyvar, result_inst_ty)
516 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
517 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
519 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
522 -- Typecheck the expression to be updated
524 record_ty = mkTyConApp tycon inst_tys
526 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
529 -- Figure out the LIE we need. We have to generate some
530 -- dictionaries for the data type context, since we are going to
531 -- do some construction.
533 -- What dictionaries do we need? For the moment we assume that all
534 -- data constructors have the same context, and grab it from the first
535 -- constructor. If they have varying contexts then we'd have to
536 -- union the ones that could participate in the update.
538 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
539 inst_env = mkTopTyVarSubst tyvars result_inst_tys
540 theta' = substTheta inst_env theta
542 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
545 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
546 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
548 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
549 = unifyListTy res_ty `thenTc` \ elt_ty ->
550 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
552 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
553 newMethod (ArithSeqOrigin seq)
554 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
556 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
557 lie1 `plusLIE` unitLIE enum_from)
559 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
560 = tcAddErrCtxt (arithSeqCtxt in_expr) $
561 unifyListTy res_ty `thenTc` \ elt_ty ->
562 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
563 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
564 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
565 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
567 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
568 (FromThen expr1' expr2'),
569 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
571 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
572 = tcAddErrCtxt (arithSeqCtxt in_expr) $
573 unifyListTy res_ty `thenTc` \ elt_ty ->
574 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
575 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
576 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
577 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
579 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
580 (FromTo expr1' expr2'),
581 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
583 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
584 = tcAddErrCtxt (arithSeqCtxt in_expr) $
585 unifyListTy res_ty `thenTc` \ elt_ty ->
586 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
587 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
588 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
589 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
590 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
592 returnTc (ArithSeqOut (HsVar (instToId eft))
593 (FromThenTo expr1' expr2' expr3'),
594 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
597 %************************************************************************
599 \subsection{Expressions type signatures}
601 %************************************************************************
604 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
605 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
607 tcAddErrCtxt (exprSigCtxt in_expr) $
608 if not (isQualifiedTy sig_tc_ty) then
610 unifyTauTy sig_tc_ty res_ty `thenTc_`
611 tcMonoExpr expr sig_tc_ty
613 else -- Signature is polymorphic
614 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
616 -- Now match the signature type with res_ty.
617 -- We must not do this earlier, because res_ty might well
618 -- mention variables free in the environment, and we'd get
619 -- bogus complaints about not being able to for-all the
621 unifyTauTy res_ty expr_ty `thenTc_`
623 -- If everything is ok, return the stuff unchanged, except for
624 -- the effect of any substutions etc. We simply discard the
625 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
626 -- resolution it may have done, which is recorded in the
631 Implicit Parameter bindings.
634 tcMonoExpr (HsWith expr binds) res_ty
635 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
636 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
638 -- If the binding binds ?x = E, we must now
639 -- discharge any ?x constraints in expr_lie
640 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
642 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
643 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
645 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
647 tcIPBind (name, expr)
648 = newTyVarTy openTypeKind `thenTc` \ ty ->
649 tcGetSrcLoc `thenTc` \ loc ->
650 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
651 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
652 returnTc ((ip, expr'), lie)
655 %************************************************************************
657 \subsection{@tcApp@ typchecks an application}
659 %************************************************************************
663 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
664 -> TcType -- Expected result type of application
665 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
668 tcApp fun args res_ty
669 = -- First type-check the function
670 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
672 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
673 split_fun_ty fun_ty (length args)
674 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
676 -- Unify with expected result before type-checking the args
677 -- This is when we might detect a too-few args situation
678 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
679 unifyTauTy res_ty actual_result_ty
682 -- Now typecheck the args
683 mapAndUnzipTc (tcArg fun)
684 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
686 -- Check that the result type doesn't have any nested for-alls.
687 -- For example, a "build" on its own is no good; it must be applied to something.
688 checkTc (isTauTy actual_result_ty)
689 (lurkingRank2Err fun actual_result_ty) `thenTc_`
691 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
694 -- If an error happens we try to figure out whether the
695 -- function has been given too many or too few arguments,
697 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
698 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
699 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
701 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
702 (env2, act_ty'') = tidyOpenType env1 act_ty'
703 (exp_args, _) = tcSplitFunTys exp_ty''
704 (act_args, _) = tcSplitFunTys act_ty''
706 len_act_args = length act_args
707 len_exp_args = length exp_args
709 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
710 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
711 | otherwise = appCtxt fun args
713 returnNF_Tc (env2, message)
716 split_fun_ty :: TcType -- The type of the function
717 -> Int -- Number of arguments
718 -> TcM ([TcType], -- Function argument types
719 TcType) -- Function result types
721 split_fun_ty fun_ty 0
722 = returnTc ([], fun_ty)
724 split_fun_ty fun_ty n
725 = -- Expect the function to have type A->B
726 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
727 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
728 returnTc (arg_ty:arg_tys, final_res_ty)
732 tcArg :: RenamedHsExpr -- The function (for error messages)
733 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
734 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
736 tcArg the_fun (arg, expected_arg_ty, arg_no)
737 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
738 tcExpr arg expected_arg_ty
742 %************************************************************************
744 \subsection{@tcId@ typchecks an identifier occurrence}
746 %************************************************************************
749 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
750 tcId name -- Look up the Id and instantiate its type
751 = tcLookupId name `thenNF_Tc` \ id ->
755 Typecheck expression which in most cases will be an Id.
758 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
759 tcExpr_id (HsVar name) = tcId name
760 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
761 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
762 returnTc (expr', lie_id, id_ty)
766 %************************************************************************
768 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
770 %************************************************************************
773 tcDoStmts do_or_lc stmts src_loc res_ty
774 = -- get the Monad and MonadZero classes
775 -- create type consisting of a fresh monad tyvar
776 ASSERT( not (null stmts) )
777 tcAddSrcLoc src_loc $
779 -- If it's a comprehension we're dealing with,
780 -- force it to be a list comprehension.
781 -- (as of Haskell 98, monad comprehensions are no more.)
783 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
784 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
786 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
787 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
788 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
789 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
790 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
792 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
794 -- Build the then and zero methods in case we need them
795 -- It's important that "then" and "return" appear just once in the final LIE,
796 -- not only for typechecker efficiency, but also because otherwise during
797 -- simplification we end up with silly stuff like
798 -- then = case d of (t,r) -> t
800 -- where the second "then" sees that it already exists in the "available" stuff.
802 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
803 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
804 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
805 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
806 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
807 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
809 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
811 returnTc (HsDoOut do_or_lc stmts'
812 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
814 stmts_lie `plusLIE` monad_lie)
818 %************************************************************************
820 \subsection{Record bindings}
822 %************************************************************************
824 Game plan for record bindings
825 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
826 1. Find the TyCon for the bindings, from the first field label.
828 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
830 For each binding field = value
832 3. Instantiate the field type (from the field label) using the type
835 4 Type check the value using tcArg, passing the field type as
836 the expected argument type.
838 This extends OK when the field types are universally quantified.
843 :: TyCon -- Type constructor for the record
844 -> [TcType] -- Args of this type constructor
845 -> RenamedRecordBinds
846 -> TcM (TcRecordBinds, LIE)
848 tcRecordBinds tycon ty_args rbinds
849 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
850 returnTc (rbinds', plusLIEs lies)
852 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
854 do_bind (field_lbl_name, rhs, pun_flag)
855 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
857 field_lbl = recordSelectorFieldLabel sel_id
858 field_ty = substTy tenv (fieldLabelType field_lbl)
860 ASSERT( isRecordSelector sel_id )
861 -- This lookup and assertion will surely succeed, because
862 -- we check that the fields are indeed record selectors
863 -- before calling tcRecordBinds
864 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
865 -- The caller of tcRecordBinds has already checked
866 -- that all the fields come from the same type
868 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
870 returnTc ((sel_id, rhs', pun_flag), lie)
872 badFields rbinds data_con
873 = [field_name | (field_name, _, _) <- rbinds,
874 not (field_name `elem` field_names)
877 field_names = map fieldLabelName (dataConFieldLabels data_con)
879 missingFields rbinds data_con
880 | null field_labels = ([], []) -- Not declared as a record;
881 -- But C{} is still valid
883 = (missing_strict_fields, other_missing_fields)
885 missing_strict_fields
886 = [ fl | (fl, str) <- field_info,
888 not (fieldLabelName fl `elem` field_names_used)
891 = [ fl | (fl, str) <- field_info,
892 not (isMarkedStrict str),
893 not (fieldLabelName fl `elem` field_names_used)
896 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
897 field_labels = dataConFieldLabels data_con
899 field_info = zipEqual "missingFields"
901 (dropList ex_theta (dataConStrictMarks data_con))
902 -- The 'drop' is because dataConStrictMarks
903 -- includes the existential dictionaries
904 (_, _, _, ex_theta, _, _) = dataConSig data_con
907 %************************************************************************
909 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
911 %************************************************************************
914 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
916 tcMonoExprs [] [] = returnTc ([], emptyLIE)
917 tcMonoExprs (expr:exprs) (ty:tys)
918 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
919 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
920 returnTc (expr':exprs', lie1 `plusLIE` lie2)
924 %************************************************************************
926 \subsection{Literals}
928 %************************************************************************
933 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
934 tcLit (HsLitLit s _) res_ty
935 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
936 newDicts (LitLitOrigin (_UNPK_ s))
937 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
938 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
941 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
942 returnTc (HsLit lit, emptyLIE)
946 %************************************************************************
948 \subsection{Errors and contexts}
950 %************************************************************************
954 Boring and alphabetical:
957 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
960 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
963 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
966 = hang (ptext SLIT("In an expression with a type signature:"))
970 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
973 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
976 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
979 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
981 funAppCtxt fun arg arg_no
982 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
983 quotes (ppr fun) <> text ", namely"])
986 wrongArgsCtxt too_many_or_few fun args
987 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
988 <+> ptext SLIT("is applied to") <+> text too_many_or_few
989 <+> ptext SLIT("arguments in the call"))
990 4 (parens (ppr the_app))
992 the_app = foldl HsApp fun args -- Used in error messages
995 = ptext SLIT("In the application") <+> quotes (ppr the_app)
997 the_app = foldl HsApp fun args -- Used in error messages
999 lurkingRank2Err fun fun_ty
1000 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1001 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1002 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1005 = hang (ptext SLIT("No constructor has all these fields:"))
1006 4 (pprQuotedList fields)
1008 fields = [field | (field, _, _) <- rbinds]
1010 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1011 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1014 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1016 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1017 missingStrictFieldCon con field
1018 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1019 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1021 missingFieldCon :: Name -> FieldLabel -> SDoc
1022 missingFieldCon con field
1023 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1024 ptext SLIT("is not initialised")]