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 ( fieldLabelName, fieldLabelType, fieldLabelTyCon )
40 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
41 import DataCon ( dataConFieldLabels, dataConSig,
42 dataConStrictMarks, StrictnessMark(..)
45 import Type ( mkFunTy, mkAppTy, mkTyConTy,
46 splitFunTy_maybe, splitFunTys,
47 mkTyConApp, splitSigmaTy, mkClassPred,
48 isTauTy, tyVarsOfType, tyVarsOfTypes,
49 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
50 liftedTypeKind, openTypeKind, mkArrowKind,
53 import TyCon ( TyCon, tyConTyVars )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( elemVarSet )
56 import TysWiredIn ( boolTy, mkListTy, listTyCon )
57 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
58 import PrelNames ( cCallableClassName,
60 enumFromName, enumFromThenName, negateName,
61 enumFromToName, enumFromThenToName,
62 thenMName, failMName, returnMName, ioTyConName
65 import Maybes ( maybeToBool, mapMaybe )
66 import ListSetOps ( minusList )
69 import HscTypes ( TyThing(..) )
73 %************************************************************************
75 \subsection{Main wrappers}
77 %************************************************************************
80 tcExpr :: RenamedHsExpr -- Expession to type check
81 -> TcType -- Expected type (could be a polytpye)
84 tcExpr expr ty | isSigmaTy ty = -- Polymorphic case
85 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
88 | otherwise = -- Monomorphic case
93 %************************************************************************
95 \subsection{@tcPolyExpr@ typchecks an application}
97 %************************************************************************
100 -- tcPolyExpr is like tcMonoExpr, except that the expected type
101 -- can be a polymorphic one.
102 tcPolyExpr :: RenamedHsExpr
103 -> TcType -- Expected type
104 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
105 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
107 tcPolyExpr arg expected_arg_ty
108 = -- Ha! The argument type of the function is a for-all type,
109 -- An example of rank-2 polymorphism.
111 -- To ensure that the forall'd type variables don't get unified with each
112 -- other or any other types, we make fresh copy of the alleged type
113 tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
115 free_tvs = tyVarsOfType expected_arg_ty
117 -- Type-check the arg and unify with expected type
118 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
120 -- Check that the sig_tyvars havn't been constrained
121 -- The interesting bit here is that we must include the free variables
122 -- of the expected arg ty. Here's an example:
123 -- runST (newVar True)
124 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
125 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
126 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
127 -- So now s' isn't unconstrained because it's linked to a.
128 -- Conclusion: include the free vars of the expected arg type in the
129 -- list of "free vars" for the signature check.
131 tcExtendGlobalTyVars free_tvs $
132 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
134 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
136 (text "the type signature of an expression")
138 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
140 checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
143 -- This HsLet binds any Insts which came out of the simplification.
144 -- It's a bit out of place here, but using AbsBind involves inventing
145 -- a couple of new names which seems worse.
146 generalised_arg = TyLam zonked_sig_tyvars $
147 DictLam (map instToId sig_dicts) $
151 returnTc ( generalised_arg, free_insts,
152 arg', sig_tau, lie_arg )
154 sig_msg = ptext SLIT("When checking an expression type signature")
157 %************************************************************************
159 \subsection{The TAUT rules for variables}
161 %************************************************************************
164 tcMonoExpr :: RenamedHsExpr -- Expession to type check
165 -> TcTauType -- Expected type (could be a type variable)
168 tcMonoExpr (HsVar name) res_ty
169 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
170 unifyTauTy res_ty id_ty `thenTc_`
172 -- Check that the result type doesn't have any nested for-alls.
173 -- For example, a "build" on its own is no good; it must be
174 -- applied to something.
175 checkTc (isTauTy id_ty)
176 (lurkingRank2Err name id_ty) `thenTc_`
178 returnTc (expr', lie)
182 tcMonoExpr (HsIPVar name) res_ty
183 = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
184 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
187 %************************************************************************
189 \subsection{Other expression forms}
191 %************************************************************************
194 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
195 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
196 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
198 tcMonoExpr (NegApp expr) res_ty
199 = tcLookupSyntaxName negateName `thenNF_Tc` \ neg ->
200 tcMonoExpr (HsApp (HsVar neg) expr) res_ty
202 tcMonoExpr (HsLam match) res_ty
203 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
204 returnTc (HsLam match', lie)
206 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
208 accum (HsApp e1 e2) args = accum e1 (e2:args)
210 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
211 returnTc (foldl HsApp fun' args', lie)
213 -- equivalent to (op e1) e2:
214 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
215 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
216 returnTc (OpApp arg1' op' fix arg2', lie)
219 Note that the operators in sections are expected to be binary, and
220 a type error will occur if they aren't.
223 -- Left sections, equivalent to
230 tcMonoExpr in_expr@(SectionL arg op) res_ty
231 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
233 -- Check that res_ty is a function type
234 -- Without this check we barf in the desugarer on
236 -- because it tries to desugar to
237 -- f op = \r -> 3 op r
238 -- so (3 `op`) had better be a function!
239 tcAddErrCtxt (sectionLAppCtxt in_expr) $
240 unifyFunTy res_ty `thenTc_`
242 returnTc (SectionL arg' op', lie)
244 -- Right sections, equivalent to \ x -> x op expr, or
247 tcMonoExpr in_expr@(SectionR op expr) res_ty
248 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
249 tcAddErrCtxt (sectionRAppCtxt in_expr) $
250 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
251 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
252 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
253 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
256 The interesting thing about @ccall@ is that it is just a template
257 which we instantiate by filling in details about the types of its
258 argument and result (ie minimal typechecking is performed). So, the
259 basic story is that we allocate a load of type variables (to hold the
260 arg/result types); unify them with the args/result; and store them for
264 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
265 = -- Get the callable and returnable classes.
266 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
267 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
268 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
270 new_arg_dict (arg, arg_ty)
271 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
272 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
273 returnNF_Tc arg_dicts -- Actually a singleton bag
275 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
279 let n_args = length args
280 tv_idxs | n_args == 0 = []
281 | otherwise = [1..n_args]
283 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
284 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
286 -- The argument types can be unlifted or lifted; the result
287 -- type must, however, be lifted since it's an argument to the IO
289 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
291 io_result_ty = mkTyConApp ioTyCon [result_ty]
293 unifyTauTy res_ty io_result_ty `thenTc_`
295 -- Construct the extra insts, which encode the
296 -- constraints on the argument and result types.
297 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
298 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
299 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
300 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
304 tcMonoExpr (HsSCC lbl expr) res_ty
305 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
306 returnTc (HsSCC lbl expr', lie)
308 tcMonoExpr (HsLet binds expr) res_ty
311 binds -- Bindings to check
312 tc_expr `thenTc` \ (expr', lie) ->
313 returnTc (expr', lie)
315 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
316 returnTc (expr', lie)
317 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
319 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
320 = tcAddSrcLoc src_loc $
321 tcAddErrCtxt (caseCtxt in_expr) $
323 -- Typecheck the case alternatives first.
324 -- The case patterns tend to give good type info to use
325 -- when typechecking the scrutinee. For example
328 -- will report that map is applied to too few arguments
330 -- Not only that, but it's better to check the matches on their
331 -- own, so that we get the expected results for scoped type variables.
333 -- (p::a, q::b) -> (q,p)
334 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
335 -- claimed by the pattern signatures. But if we typechecked the
336 -- match with x in scope and x's type as the expected type, we'd be hosed.
338 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
340 tcAddErrCtxt (caseScrutCtxt scrut) (
341 tcMonoExpr scrut scrut_ty
342 ) `thenTc` \ (scrut',lie1) ->
344 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
346 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
347 = tcAddSrcLoc src_loc $
348 tcAddErrCtxt (predCtxt pred) (
349 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
351 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
352 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
353 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
357 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
358 = tcDoStmts do_or_lc stmts src_loc res_ty
362 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
363 = unifyListTy res_ty `thenTc` \ elt_ty ->
364 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
365 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
368 = tcAddErrCtxt (listCtxt expr) $
369 tcMonoExpr expr elt_ty
371 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
372 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
373 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
374 (exprs `zip` arg_tys) -- we know they're of equal length.
375 `thenTc` \ (exprs', lies) ->
376 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
378 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
379 = tcAddErrCtxt (recordConCtxt expr) $
380 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
382 (_, record_ty) = splitFunTys con_tau
383 (tycon, ty_args, _) = splitAlgTyConApp record_ty
385 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
386 unifyTauTy res_ty record_ty `thenTc_`
388 -- Check that the record bindings match the constructor
389 -- con_name is syntactically constrained to be a data constructor
390 tcLookupDataCon con_name `thenTc` \ data_con ->
392 bad_fields = badFields rbinds data_con
394 if not (null bad_fields) then
395 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
396 failTc -- Fail now, because tcRecordBinds will crash on a bad field
399 -- Typecheck the record bindings
400 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
403 missing_s_fields = missingStrictFields rbinds data_con
405 checkTcM (null missing_s_fields)
406 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
407 returnNF_Tc ()) `thenNF_Tc_`
409 missing_fields = missingFields rbinds data_con
411 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
412 checkTcM (not (warn && not (null missing_fields)))
413 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
414 returnNF_Tc ()) `thenNF_Tc_`
416 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
418 -- The main complication with RecordUpd is that we need to explicitly
419 -- handle the *non-updated* fields. Consider:
421 -- data T a b = MkT1 { fa :: a, fb :: b }
422 -- | MkT2 { fa :: a, fc :: Int -> Int }
423 -- | MkT3 { fd :: a }
425 -- upd :: T a b -> c -> T a c
426 -- upd t x = t { fb = x}
428 -- The type signature on upd is correct (i.e. the result should not be (T a b))
429 -- because upd should be equivalent to:
431 -- upd t x = case t of
432 -- MkT1 p q -> MkT1 p x
433 -- MkT2 a b -> MkT2 p b
434 -- MkT3 d -> error ...
436 -- So we need to give a completely fresh type to the result record,
437 -- and then constrain it by the fields that are *not* updated ("p" above).
439 -- Note that because MkT3 doesn't contain all the fields being updated,
440 -- its RHS is simply an error, so it doesn't impose any type constraints
442 -- All this is done in STEP 4 below.
444 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
445 = tcAddErrCtxt (recordUpdCtxt expr) $
448 -- Check that the field names are really field names
449 ASSERT( not (null rbinds) )
451 field_names = [field_name | (field_name, _, _) <- rbinds]
453 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
455 bad_guys = [ addErrTc (notSelector field_name)
456 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
458 Just (AnId sel_id) -> not (isRecordSelector sel_id)
462 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
465 -- Figure out the tycon and data cons from the first field name
467 (Just (AnId sel_id) : _) = maybe_sel_ids
468 (_, _, tau) = splitSigmaTy (idType sel_id) -- Selectors can be overloaded
469 -- when the data type has a context
470 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
471 (tycon, _, data_cons) = splitAlgTyConApp data_ty
472 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
474 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
477 -- Check that at least one constructor has all the named fields
478 -- i.e. has an empty set of bad fields returned by badFields
479 checkTc (any (null . badFields rbinds) data_cons)
480 (badFieldsUpd rbinds) `thenTc_`
483 -- Typecheck the update bindings.
484 -- (Do this after checking for bad fields in case there's a field that
485 -- doesn't match the constructor.)
487 result_record_ty = mkTyConApp tycon result_inst_tys
489 unifyTauTy res_ty result_record_ty `thenTc_`
490 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
493 -- Use the un-updated fields to find a vector of booleans saying
494 -- which type arguments must be the same in updatee and result.
496 -- WARNING: this code assumes that all data_cons in a common tycon
497 -- have FieldLabels abstracted over the same tyvars.
499 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
500 con_field_lbls_s = map dataConFieldLabels data_cons
502 -- A constructor is only relevant to this process if
503 -- it contains all the fields that are being updated
504 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
505 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
507 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
508 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
510 mk_inst_ty (tyvar, result_inst_ty)
511 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
512 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
514 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
517 -- Typecheck the expression to be updated
519 record_ty = mkTyConApp tycon inst_tys
521 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
524 -- Figure out the LIE we need. We have to generate some
525 -- dictionaries for the data type context, since we are going to
526 -- do some construction.
528 -- What dictionaries do we need? For the moment we assume that all
529 -- data constructors have the same context, and grab it from the first
530 -- constructor. If they have varying contexts then we'd have to
531 -- union the ones that could participate in the update.
533 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
534 inst_env = mkTopTyVarSubst tyvars result_inst_tys
535 theta' = substTheta inst_env theta
537 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
540 returnTc (RecordUpdOut record_expr' result_record_ty (map instToId dicts) rbinds',
541 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
543 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
544 = unifyListTy res_ty `thenTc` \ elt_ty ->
545 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
547 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
548 newMethod (ArithSeqOrigin seq)
549 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
551 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
552 lie1 `plusLIE` unitLIE enum_from)
554 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
555 = tcAddErrCtxt (arithSeqCtxt in_expr) $
556 unifyListTy res_ty `thenTc` \ elt_ty ->
557 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
558 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
559 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
560 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
562 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
563 (FromThen expr1' expr2'),
564 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
566 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
567 = tcAddErrCtxt (arithSeqCtxt in_expr) $
568 unifyListTy res_ty `thenTc` \ elt_ty ->
569 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
570 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
571 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
572 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
574 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
575 (FromTo expr1' expr2'),
576 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
578 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
579 = tcAddErrCtxt (arithSeqCtxt in_expr) $
580 unifyListTy res_ty `thenTc` \ elt_ty ->
581 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
582 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
583 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
584 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
585 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
587 returnTc (ArithSeqOut (HsVar (instToId eft))
588 (FromThenTo expr1' expr2' expr3'),
589 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
592 %************************************************************************
594 \subsection{Expressions type signatures}
596 %************************************************************************
599 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
600 = tcSetErrCtxt (exprSigCtxt in_expr) $
601 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
603 if not (isSigmaTy sig_tc_ty) then
605 unifyTauTy sig_tc_ty res_ty `thenTc_`
606 tcMonoExpr expr sig_tc_ty
608 else -- Signature is polymorphic
609 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
611 -- Now match the signature type with res_ty.
612 -- We must not do this earlier, because res_ty might well
613 -- mention variables free in the environment, and we'd get
614 -- bogus complaints about not being able to for-all the
616 unifyTauTy res_ty expr_ty `thenTc_`
618 -- If everything is ok, return the stuff unchanged, except for
619 -- the effect of any substutions etc. We simply discard the
620 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
621 -- resolution it may have done, which is recorded in the
626 Implicit Parameter bindings.
629 tcMonoExpr (HsWith expr binds) res_ty
630 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
631 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
633 -- If the binding binds ?x = E, we must now
634 -- discharge any ?x constraints in expr_lie
635 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
637 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
638 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
640 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
642 tcIPBind (name, expr)
643 = newTyVarTy openTypeKind `thenTc` \ ty ->
644 tcGetSrcLoc `thenTc` \ loc ->
645 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
646 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
647 returnTc ((ip, expr'), lie)
650 %************************************************************************
652 \subsection{@tcApp@ typchecks an application}
654 %************************************************************************
658 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
659 -> TcType -- Expected result type of application
660 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
663 tcApp fun args res_ty
664 = -- First type-check the function
665 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
667 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
668 split_fun_ty fun_ty (length args)
669 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
671 -- Unify with expected result before type-checking the args
672 -- This is when we might detect a too-few args situation
673 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
674 unifyTauTy res_ty actual_result_ty
677 -- Now typecheck the args
678 mapAndUnzipTc (tcArg fun)
679 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
681 -- Check that the result type doesn't have any nested for-alls.
682 -- For example, a "build" on its own is no good; it must be applied to something.
683 checkTc (isTauTy actual_result_ty)
684 (lurkingRank2Err fun actual_result_ty) `thenTc_`
686 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
689 -- If an error happens we try to figure out whether the
690 -- function has been given too many or too few arguments,
692 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
693 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
694 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
696 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
697 (env2, act_ty'') = tidyOpenType env1 act_ty'
698 (exp_args, _) = splitFunTys exp_ty''
699 (act_args, _) = splitFunTys act_ty''
701 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
702 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
703 | otherwise = appCtxt fun args
705 returnNF_Tc (env2, message)
708 split_fun_ty :: TcType -- The type of the function
709 -> Int -- Number of arguments
710 -> TcM ([TcType], -- Function argument types
711 TcType) -- Function result types
713 split_fun_ty fun_ty 0
714 = returnTc ([], fun_ty)
716 split_fun_ty fun_ty n
717 = -- Expect the function to have type A->B
718 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
719 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
720 returnTc (arg_ty:arg_tys, final_res_ty)
724 tcArg :: RenamedHsExpr -- The function (for error messages)
725 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
726 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
728 tcArg the_fun (arg, expected_arg_ty, arg_no)
729 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
730 tcExpr arg expected_arg_ty
734 %************************************************************************
736 \subsection{@tcId@ typchecks an identifier occurrence}
738 %************************************************************************
741 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
742 tcId name -- Look up the Id and instantiate its type
743 = tcLookupId name `thenNF_Tc` \ id ->
747 Typecheck expression which in most cases will be an Id.
750 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
751 tcExpr_id (HsVar name) = tcId name
752 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
753 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
754 returnTc (expr', lie_id, id_ty)
758 %************************************************************************
760 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
762 %************************************************************************
765 tcDoStmts do_or_lc stmts src_loc res_ty
766 = -- get the Monad and MonadZero classes
767 -- create type consisting of a fresh monad tyvar
768 ASSERT( not (null stmts) )
769 tcAddSrcLoc src_loc $
771 -- If it's a comprehension we're dealing with,
772 -- force it to be a list comprehension.
773 -- (as of Haskell 98, monad comprehensions are no more.)
775 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
776 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
778 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
779 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
780 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
781 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
782 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
784 tcStmts do_or_lc m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
786 -- Build the then and zero methods in case we need them
787 -- It's important that "then" and "return" appear just once in the final LIE,
788 -- not only for typechecker efficiency, but also because otherwise during
789 -- simplification we end up with silly stuff like
790 -- then = case d of (t,r) -> t
792 -- where the second "then" sees that it already exists in the "available" stuff.
794 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
795 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
796 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
797 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
798 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
799 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
801 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
803 returnTc (HsDoOut do_or_lc stmts'
804 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
806 stmts_lie `plusLIE` monad_lie)
810 %************************************************************************
812 \subsection{Record bindings}
814 %************************************************************************
816 Game plan for record bindings
817 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
818 1. Find the TyCon for the bindings, from the first field label.
820 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
822 For each binding field = value
824 3. Instantiate the field type (from the field label) using the type
827 4 Type check the value using tcArg, passing the field type as
828 the expected argument type.
830 This extends OK when the field types are universally quantified.
835 :: TyCon -- Type constructor for the record
836 -> [TcType] -- Args of this type constructor
837 -> RenamedRecordBinds
838 -> TcM (TcRecordBinds, LIE)
840 tcRecordBinds tycon ty_args rbinds
841 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
842 returnTc (rbinds', plusLIEs lies)
844 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
846 do_bind (field_lbl_name, rhs, pun_flag)
847 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
849 field_lbl = recordSelectorFieldLabel sel_id
850 field_ty = substTy tenv (fieldLabelType field_lbl)
852 ASSERT( isRecordSelector sel_id )
853 -- This lookup and assertion will surely succeed, because
854 -- we check that the fields are indeed record selectors
855 -- before calling tcRecordBinds
856 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
857 -- The caller of tcRecordBinds has already checked
858 -- that all the fields come from the same type
860 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
862 returnTc ((sel_id, rhs', pun_flag), lie)
864 badFields rbinds data_con
865 = [field_name | (field_name, _, _) <- rbinds,
866 not (field_name `elem` field_names)
869 field_names = map fieldLabelName (dataConFieldLabels data_con)
871 missingStrictFields rbinds data_con
872 = [ fn | fn <- strict_field_names,
873 not (fn `elem` field_names_used)
876 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
877 strict_field_names = mapMaybe isStrict field_info
879 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
882 field_info = zip (dataConFieldLabels data_con)
883 (dataConStrictMarks data_con)
885 missingFields rbinds data_con
886 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
888 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
890 -- missing strict fields have already been flagged as
891 -- being so, so leave them out here.
892 non_strict_field_names = mapMaybe isn'tStrict field_info
894 isn'tStrict (fl, MarkedStrict) = Nothing
895 isn'tStrict (fl, _) = Just (fieldLabelName fl)
897 field_info = zip (dataConFieldLabels data_con)
898 (dataConStrictMarks data_con)
902 %************************************************************************
904 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
906 %************************************************************************
909 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
911 tcMonoExprs [] [] = returnTc ([], emptyLIE)
912 tcMonoExprs (expr:exprs) (ty:tys)
913 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
914 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
915 returnTc (expr':exprs', lie1 `plusLIE` lie2)
919 %************************************************************************
921 \subsection{Literals}
923 %************************************************************************
928 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
929 tcLit (HsLitLit s _) res_ty
930 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
931 newDicts (LitLitOrigin (_UNPK_ s))
932 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
933 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
936 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
937 returnTc (HsLit lit, emptyLIE)
941 %************************************************************************
943 \subsection{Errors and contexts}
945 %************************************************************************
950 pp_nest_hang :: String -> SDoc -> SDoc
951 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
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 -> Name -> 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 -> Name -> SDoc
1022 missingFieldCon con field
1023 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1024 ptext SLIT("is not initialised")]