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 n_args = length args
287 tv_idxs | n_args == 0 = []
288 | otherwise = [1..n_args]
290 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
291 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
293 -- The argument types can be unlifted or lifted; the result
294 -- type must, however, be lifted since it's an argument to the IO
296 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
298 io_result_ty = mkTyConApp ioTyCon [result_ty]
300 unifyTauTy res_ty io_result_ty `thenTc_`
302 -- Construct the extra insts, which encode the
303 -- constraints on the argument and result types.
304 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
305 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
306 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
307 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
311 tcMonoExpr (HsSCC lbl expr) res_ty
312 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
313 returnTc (HsSCC lbl expr', lie)
315 tcMonoExpr (HsLet binds expr) res_ty
318 binds -- Bindings to check
319 tc_expr `thenTc` \ (expr', lie) ->
320 returnTc (expr', lie)
322 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
323 returnTc (expr', lie)
324 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
326 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
327 = tcAddSrcLoc src_loc $
328 tcAddErrCtxt (caseCtxt in_expr) $
330 -- Typecheck the case alternatives first.
331 -- The case patterns tend to give good type info to use
332 -- when typechecking the scrutinee. For example
335 -- will report that map is applied to too few arguments
337 -- Not only that, but it's better to check the matches on their
338 -- own, so that we get the expected results for scoped type variables.
340 -- (p::a, q::b) -> (q,p)
341 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
342 -- claimed by the pattern signatures. But if we typechecked the
343 -- match with x in scope and x's type as the expected type, we'd be hosed.
345 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
347 tcAddErrCtxt (caseScrutCtxt scrut) (
348 tcMonoExpr scrut scrut_ty
349 ) `thenTc` \ (scrut',lie1) ->
351 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
353 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
354 = tcAddSrcLoc src_loc $
355 tcAddErrCtxt (predCtxt pred) (
356 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
358 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
359 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
360 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
364 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
365 = tcDoStmts do_or_lc stmts src_loc res_ty
369 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
370 = unifyListTy res_ty `thenTc` \ elt_ty ->
371 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
372 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
375 = tcAddErrCtxt (listCtxt expr) $
376 tcMonoExpr expr elt_ty
378 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
379 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
380 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
381 (exprs `zip` arg_tys) -- we know they're of equal length.
382 `thenTc` \ (exprs', lies) ->
383 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
385 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
386 = tcAddErrCtxt (recordConCtxt expr) $
387 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
389 (_, record_ty) = tcSplitFunTys con_tau
390 (tycon, ty_args) = tcSplitTyConApp record_ty
392 ASSERT( isAlgTyCon tycon )
393 unifyTauTy res_ty record_ty `thenTc_`
395 -- Check that the record bindings match the constructor
396 -- con_name is syntactically constrained to be a data constructor
397 tcLookupDataCon con_name `thenTc` \ data_con ->
399 bad_fields = badFields rbinds data_con
401 if not (null bad_fields) then
402 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
403 failTc -- Fail now, because tcRecordBinds will crash on a bad field
406 -- Typecheck the record bindings
407 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
410 (missing_s_fields, missing_fields) = missingFields rbinds data_con
412 checkTcM (null missing_s_fields)
413 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
414 returnNF_Tc ()) `thenNF_Tc_`
415 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
416 checkTcM (not (warn && not (null missing_fields)))
417 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
418 returnNF_Tc ()) `thenNF_Tc_`
420 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
422 -- The main complication with RecordUpd is that we need to explicitly
423 -- handle the *non-updated* fields. Consider:
425 -- data T a b = MkT1 { fa :: a, fb :: b }
426 -- | MkT2 { fa :: a, fc :: Int -> Int }
427 -- | MkT3 { fd :: a }
429 -- upd :: T a b -> c -> T a c
430 -- upd t x = t { fb = x}
432 -- The type signature on upd is correct (i.e. the result should not be (T a b))
433 -- because upd should be equivalent to:
435 -- upd t x = case t of
436 -- MkT1 p q -> MkT1 p x
437 -- MkT2 a b -> MkT2 p b
438 -- MkT3 d -> error ...
440 -- So we need to give a completely fresh type to the result record,
441 -- and then constrain it by the fields that are *not* updated ("p" above).
443 -- Note that because MkT3 doesn't contain all the fields being updated,
444 -- its RHS is simply an error, so it doesn't impose any type constraints
446 -- All this is done in STEP 4 below.
448 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
449 = tcAddErrCtxt (recordUpdCtxt expr) $
452 -- Check that the field names are really field names
453 ASSERT( not (null rbinds) )
455 field_names = [field_name | (field_name, _, _) <- rbinds]
457 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
459 bad_guys = [ addErrTc (notSelector field_name)
460 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
462 Just (AnId sel_id) -> not (isRecordSelector sel_id)
466 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
469 -- Figure out the tycon and data cons from the first field name
471 -- It's OK to use the non-tc splitters here (for a selector)
472 (Just (AnId sel_id) : _) = maybe_sel_ids
473 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
474 -- when the data type has a context
475 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
476 tycon = tcTyConAppTyCon data_ty
477 data_cons = tyConDataCons tycon
478 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
480 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
483 -- Check that at least one constructor has all the named fields
484 -- i.e. has an empty set of bad fields returned by badFields
485 checkTc (any (null . badFields rbinds) data_cons)
486 (badFieldsUpd rbinds) `thenTc_`
489 -- Typecheck the update bindings.
490 -- (Do this after checking for bad fields in case there's a field that
491 -- doesn't match the constructor.)
493 result_record_ty = mkTyConApp tycon result_inst_tys
495 unifyTauTy res_ty result_record_ty `thenTc_`
496 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
499 -- Use the un-updated fields to find a vector of booleans saying
500 -- which type arguments must be the same in updatee and result.
502 -- WARNING: this code assumes that all data_cons in a common tycon
503 -- have FieldLabels abstracted over the same tyvars.
505 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
506 con_field_lbls_s = map dataConFieldLabels data_cons
508 -- A constructor is only relevant to this process if
509 -- it contains all the fields that are being updated
510 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
511 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
513 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
514 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
516 mk_inst_ty (tyvar, result_inst_ty)
517 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
518 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
520 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
523 -- Typecheck the expression to be updated
525 record_ty = mkTyConApp tycon inst_tys
527 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
530 -- Figure out the LIE we need. We have to generate some
531 -- dictionaries for the data type context, since we are going to
532 -- do some construction.
534 -- What dictionaries do we need? For the moment we assume that all
535 -- data constructors have the same context, and grab it from the first
536 -- constructor. If they have varying contexts then we'd have to
537 -- union the ones that could participate in the update.
539 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
540 inst_env = mkTopTyVarSubst tyvars result_inst_tys
541 theta' = substTheta inst_env theta
543 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
546 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
547 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
549 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
550 = unifyListTy res_ty `thenTc` \ elt_ty ->
551 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
553 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
554 newMethod (ArithSeqOrigin seq)
555 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
557 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
558 lie1 `plusLIE` unitLIE enum_from)
560 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
561 = tcAddErrCtxt (arithSeqCtxt in_expr) $
562 unifyListTy res_ty `thenTc` \ elt_ty ->
563 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
564 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
565 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
566 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
568 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
569 (FromThen expr1' expr2'),
570 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
572 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
573 = tcAddErrCtxt (arithSeqCtxt in_expr) $
574 unifyListTy res_ty `thenTc` \ elt_ty ->
575 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
576 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
577 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
578 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
580 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
581 (FromTo expr1' expr2'),
582 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
584 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
585 = tcAddErrCtxt (arithSeqCtxt in_expr) $
586 unifyListTy res_ty `thenTc` \ elt_ty ->
587 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
588 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
589 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
590 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
591 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
593 returnTc (ArithSeqOut (HsVar (instToId eft))
594 (FromThenTo expr1' expr2' expr3'),
595 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
598 %************************************************************************
600 \subsection{Expressions type signatures}
602 %************************************************************************
605 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
606 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
608 tcAddErrCtxt (exprSigCtxt in_expr) $
609 if not (isQualifiedTy sig_tc_ty) then
611 unifyTauTy sig_tc_ty res_ty `thenTc_`
612 tcMonoExpr expr sig_tc_ty
614 else -- Signature is polymorphic
615 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
617 -- Now match the signature type with res_ty.
618 -- We must not do this earlier, because res_ty might well
619 -- mention variables free in the environment, and we'd get
620 -- bogus complaints about not being able to for-all the
622 unifyTauTy res_ty expr_ty `thenTc_`
624 -- If everything is ok, return the stuff unchanged, except for
625 -- the effect of any substutions etc. We simply discard the
626 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
627 -- resolution it may have done, which is recorded in the
632 Implicit Parameter bindings.
635 tcMonoExpr (HsWith expr binds) res_ty
636 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
637 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
639 -- If the binding binds ?x = E, we must now
640 -- discharge any ?x constraints in expr_lie
641 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
643 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
644 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
646 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
648 tcIPBind (name, expr)
649 = newTyVarTy openTypeKind `thenTc` \ ty ->
650 tcGetSrcLoc `thenTc` \ loc ->
651 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
652 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
653 returnTc ((ip, expr'), lie)
656 %************************************************************************
658 \subsection{@tcApp@ typchecks an application}
660 %************************************************************************
664 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
665 -> TcType -- Expected result type of application
666 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
669 tcApp fun args res_ty
670 = -- First type-check the function
671 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
673 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
674 split_fun_ty fun_ty (length args)
675 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
677 -- Unify with expected result before type-checking the args
678 -- This is when we might detect a too-few args situation
679 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
680 unifyTauTy res_ty actual_result_ty
683 -- Now typecheck the args
684 mapAndUnzipTc (tcArg fun)
685 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
687 -- Check that the result type doesn't have any nested for-alls.
688 -- For example, a "build" on its own is no good; it must be applied to something.
689 checkTc (isTauTy actual_result_ty)
690 (lurkingRank2Err fun actual_result_ty) `thenTc_`
692 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
695 -- If an error happens we try to figure out whether the
696 -- function has been given too many or too few arguments,
698 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
699 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
700 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
702 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
703 (env2, act_ty'') = tidyOpenType env1 act_ty'
704 (exp_args, _) = tcSplitFunTys exp_ty''
705 (act_args, _) = tcSplitFunTys act_ty''
707 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
708 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
709 | otherwise = appCtxt fun args
711 returnNF_Tc (env2, message)
714 split_fun_ty :: TcType -- The type of the function
715 -> Int -- Number of arguments
716 -> TcM ([TcType], -- Function argument types
717 TcType) -- Function result types
719 split_fun_ty fun_ty 0
720 = returnTc ([], fun_ty)
722 split_fun_ty fun_ty n
723 = -- Expect the function to have type A->B
724 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
725 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
726 returnTc (arg_ty:arg_tys, final_res_ty)
730 tcArg :: RenamedHsExpr -- The function (for error messages)
731 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
732 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
734 tcArg the_fun (arg, expected_arg_ty, arg_no)
735 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
736 tcExpr arg expected_arg_ty
740 %************************************************************************
742 \subsection{@tcId@ typchecks an identifier occurrence}
744 %************************************************************************
747 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
748 tcId name -- Look up the Id and instantiate its type
749 = tcLookupId name `thenNF_Tc` \ id ->
753 Typecheck expression which in most cases will be an Id.
756 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
757 tcExpr_id (HsVar name) = tcId name
758 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
759 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
760 returnTc (expr', lie_id, id_ty)
764 %************************************************************************
766 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
768 %************************************************************************
771 tcDoStmts do_or_lc stmts src_loc res_ty
772 = -- get the Monad and MonadZero classes
773 -- create type consisting of a fresh monad tyvar
774 ASSERT( not (null stmts) )
775 tcAddSrcLoc src_loc $
777 -- If it's a comprehension we're dealing with,
778 -- force it to be a list comprehension.
779 -- (as of Haskell 98, monad comprehensions are no more.)
781 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
782 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
784 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
785 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
786 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
787 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
788 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
790 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
792 -- Build the then and zero methods in case we need them
793 -- It's important that "then" and "return" appear just once in the final LIE,
794 -- not only for typechecker efficiency, but also because otherwise during
795 -- simplification we end up with silly stuff like
796 -- then = case d of (t,r) -> t
798 -- where the second "then" sees that it already exists in the "available" stuff.
800 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
801 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
802 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
803 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
804 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
805 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
807 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
809 returnTc (HsDoOut do_or_lc stmts'
810 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
812 stmts_lie `plusLIE` monad_lie)
816 %************************************************************************
818 \subsection{Record bindings}
820 %************************************************************************
822 Game plan for record bindings
823 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
824 1. Find the TyCon for the bindings, from the first field label.
826 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
828 For each binding field = value
830 3. Instantiate the field type (from the field label) using the type
833 4 Type check the value using tcArg, passing the field type as
834 the expected argument type.
836 This extends OK when the field types are universally quantified.
841 :: TyCon -- Type constructor for the record
842 -> [TcType] -- Args of this type constructor
843 -> RenamedRecordBinds
844 -> TcM (TcRecordBinds, LIE)
846 tcRecordBinds tycon ty_args rbinds
847 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
848 returnTc (rbinds', plusLIEs lies)
850 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
852 do_bind (field_lbl_name, rhs, pun_flag)
853 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
855 field_lbl = recordSelectorFieldLabel sel_id
856 field_ty = substTy tenv (fieldLabelType field_lbl)
858 ASSERT( isRecordSelector sel_id )
859 -- This lookup and assertion will surely succeed, because
860 -- we check that the fields are indeed record selectors
861 -- before calling tcRecordBinds
862 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
863 -- The caller of tcRecordBinds has already checked
864 -- that all the fields come from the same type
866 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
868 returnTc ((sel_id, rhs', pun_flag), lie)
870 badFields rbinds data_con
871 = [field_name | (field_name, _, _) <- rbinds,
872 not (field_name `elem` field_names)
875 field_names = map fieldLabelName (dataConFieldLabels data_con)
877 missingFields rbinds data_con
878 | null field_labels = ([], []) -- Not declared as a record;
879 -- But C{} is still valid
881 = (missing_strict_fields, other_missing_fields)
883 missing_strict_fields
884 = [ fl | (fl, str) <- field_info,
886 not (fieldLabelName fl `elem` field_names_used)
889 = [ fl | (fl, str) <- field_info,
890 not (isMarkedStrict str),
891 not (fieldLabelName fl `elem` field_names_used)
894 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
895 field_labels = dataConFieldLabels data_con
897 field_info = zipEqual "missingFields"
899 (drop (length ex_theta) (dataConStrictMarks data_con))
900 -- The 'drop' is because dataConStrictMarks
901 -- includes the existential dictionaries
902 (_, _, _, ex_theta, _, _) = dataConSig data_con
905 %************************************************************************
907 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
909 %************************************************************************
912 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
914 tcMonoExprs [] [] = returnTc ([], emptyLIE)
915 tcMonoExprs (expr:exprs) (ty:tys)
916 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
917 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
918 returnTc (expr':exprs', lie1 `plusLIE` lie2)
922 %************************************************************************
924 \subsection{Literals}
926 %************************************************************************
931 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
932 tcLit (HsLitLit s _) res_ty
933 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
934 newDicts (LitLitOrigin (_UNPK_ s))
935 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
936 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
939 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
940 returnTc (HsLit lit, emptyLIE)
944 %************************************************************************
946 \subsection{Errors and contexts}
948 %************************************************************************
952 Boring and alphabetical:
955 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
958 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
961 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
964 = hang (ptext SLIT("In an expression with a type signature:"))
968 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
971 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
974 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
977 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
979 funAppCtxt fun arg arg_no
980 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
981 quotes (ppr fun) <> text ", namely"])
984 wrongArgsCtxt too_many_or_few fun args
985 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
986 <+> ptext SLIT("is applied to") <+> text too_many_or_few
987 <+> ptext SLIT("arguments in the call"))
988 4 (parens (ppr the_app))
990 the_app = foldl HsApp fun args -- Used in error messages
993 = ptext SLIT("In the application") <+> quotes (ppr the_app)
995 the_app = foldl HsApp fun args -- Used in error messages
997 lurkingRank2Err fun fun_ty
998 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
999 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1000 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1003 = hang (ptext SLIT("No constructor has all these fields:"))
1004 4 (pprQuotedList fields)
1006 fields = [field | (field, _, _) <- rbinds]
1008 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1009 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1012 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1014 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1015 missingStrictFieldCon con field
1016 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1017 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1019 missingFieldCon :: Name -> FieldLabel -> SDoc
1020 missingFieldCon con field
1021 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1022 ptext SLIT("is not initialised")]