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 ( TcType, TcTauType, tcSplitFunTys, tcSplitTyConApp,
39 isQualifiedTy, mkFunTy, mkAppTy, mkTyConTy,
40 mkTyConApp, mkClassPred, tcFunArgTy,
41 isTauTy, tyVarsOfType, tyVarsOfTypes,
42 liftedTypeKind, openTypeKind, mkArrowKind,
43 tcSplitSigmaTy, tcTyConAppTyCon,
46 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
47 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
48 import DataCon ( dataConFieldLabels, dataConSig,
52 import TyCon ( TyCon, tyConTyVars, isAlgTyCon, tyConDataCons )
53 import Subst ( mkTopTyVarSubst, substTheta, substTy )
54 import VarSet ( elemVarSet )
55 import TysWiredIn ( boolTy, mkListTy, listTyCon )
56 import PrelNames ( cCallableClassName,
58 enumFromName, enumFromThenName,
59 enumFromToName, enumFromThenToName,
60 thenMName, failMName, returnMName, ioTyConName
63 import ListSetOps ( minusList )
66 import HscTypes ( TyThing(..) )
70 %************************************************************************
72 \subsection{Main wrappers}
74 %************************************************************************
77 tcExpr :: RenamedHsExpr -- Expession to type check
78 -> TcType -- Expected type (could be a polytpye)
81 tcExpr expr ty | isQualifiedTy ty = -- Polymorphic case
82 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
85 | otherwise = -- Monomorphic case
90 %************************************************************************
92 \subsection{@tcPolyExpr@ typchecks an application}
94 %************************************************************************
97 -- tcPolyExpr is like tcMonoExpr, except that the expected type
98 -- can be a polymorphic one.
99 tcPolyExpr :: RenamedHsExpr
100 -> TcType -- Expected type
101 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
102 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
104 tcPolyExpr arg expected_arg_ty
105 = -- Ha! The argument type of the function is a for-all type,
106 -- An example of rank-2 polymorphism.
108 -- To ensure that the forall'd type variables don't get unified with each
109 -- other or any other types, we make fresh copy of the alleged type
110 tcInstType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_theta, sig_tau) ->
112 free_tvs = tyVarsOfType expected_arg_ty
114 -- Type-check the arg and unify with expected type
115 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
117 -- Check that the sig_tyvars havn't been constrained
118 -- The interesting bit here is that we must include the free variables
119 -- of the expected arg ty. Here's an example:
120 -- runST (newVar True)
121 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
122 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
123 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
124 -- So now s' isn't unconstrained because it's linked to a.
125 -- Conclusion: include the free vars of the expected arg type in the
126 -- list of "free vars" for the signature check.
128 tcExtendGlobalTyVars free_tvs $
129 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
131 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ sig_dicts ->
133 (text "the type signature of an expression")
135 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
137 checkSigTyVars sig_tyvars free_tvs `thenTc` \ zonked_sig_tyvars ->
140 -- This HsLet binds any Insts which came out of the simplification.
141 -- It's a bit out of place here, but using AbsBind involves inventing
142 -- a couple of new names which seems worse.
143 generalised_arg = TyLam zonked_sig_tyvars $
144 DictLam (map instToId sig_dicts) $
148 returnTc ( generalised_arg, free_insts,
149 arg', sig_tau, lie_arg )
151 sig_msg = ptext SLIT("When checking an expression type signature")
154 %************************************************************************
156 \subsection{The TAUT rules for variables}
158 %************************************************************************
161 tcMonoExpr :: RenamedHsExpr -- Expession to type check
162 -> TcTauType -- Expected type (could be a type variable)
165 tcMonoExpr (HsVar name) res_ty
166 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
167 unifyTauTy res_ty id_ty `thenTc_`
169 -- Check that the result type doesn't have any nested for-alls.
170 -- For example, a "build" on its own is no good; it must be
171 -- applied to something.
172 checkTc (isTauTy id_ty)
173 (lurkingRank2Err name id_ty) `thenTc_`
175 returnTc (expr', lie)
179 tcMonoExpr (HsIPVar name) res_ty
180 = newIPDict (IPOcc name) name res_ty `thenNF_Tc` \ ip ->
181 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
184 %************************************************************************
186 \subsection{Other expression forms}
188 %************************************************************************
191 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
192 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
193 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
195 tcMonoExpr (NegApp expr neg_name) res_ty
196 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
198 tcMonoExpr (HsLam match) res_ty
199 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
200 returnTc (HsLam match', lie)
202 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
204 accum (HsApp e1 e2) args = accum e1 (e2:args)
206 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
207 returnTc (foldl HsApp fun' args', lie)
209 -- equivalent to (op e1) e2:
210 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
211 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
212 returnTc (OpApp arg1' op' fix arg2', lie)
215 Note that the operators in sections are expected to be binary, and
216 a type error will occur if they aren't.
219 -- Left sections, equivalent to
226 tcMonoExpr in_expr@(SectionL arg op) res_ty
227 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
229 -- Check that res_ty is a function type
230 -- Without this check we barf in the desugarer on
232 -- because it tries to desugar to
233 -- f op = \r -> 3 op r
234 -- so (3 `op`) had better be a function!
235 tcAddErrCtxt (sectionLAppCtxt in_expr) $
236 unifyFunTy res_ty `thenTc_`
238 returnTc (SectionL arg' op', lie)
240 -- Right sections, equivalent to \ x -> x op expr, or
243 tcMonoExpr in_expr@(SectionR op expr) res_ty
244 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
245 tcAddErrCtxt (sectionRAppCtxt in_expr) $
246 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
247 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
248 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
249 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
252 The interesting thing about @ccall@ is that it is just a template
253 which we instantiate by filling in details about the types of its
254 argument and result (ie minimal typechecking is performed). So, the
255 basic story is that we allocate a load of type variables (to hold the
256 arg/result types); unify them with the args/result; and store them for
260 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
262 = getDOptsTc `thenNF_Tc` \ dflags ->
264 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
265 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
266 text "Either compile with -fvia-C, or, better, rewrite your code",
267 text "to use the foreign function interface. _casm_s are deprecated",
268 text "and support for them may one day disappear."])
271 -- Get the callable and returnable classes.
272 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
273 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
274 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
276 new_arg_dict (arg, arg_ty)
277 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
278 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
279 returnNF_Tc arg_dicts -- Actually a singleton bag
281 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
285 let tv_idxs | null args = []
286 | otherwise = [1..length args]
288 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
289 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
291 -- The argument types can be unlifted or lifted; the result
292 -- type must, however, be lifted since it's an argument to the IO
294 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
296 io_result_ty = mkTyConApp ioTyCon [result_ty]
298 unifyTauTy res_ty io_result_ty `thenTc_`
300 -- Construct the extra insts, which encode the
301 -- constraints on the argument and result types.
302 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
303 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
304 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
305 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
309 tcMonoExpr (HsSCC lbl expr) res_ty
310 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
311 returnTc (HsSCC lbl expr', lie)
313 tcMonoExpr (HsLet binds expr) res_ty
316 binds -- Bindings to check
317 tc_expr `thenTc` \ (expr', lie) ->
318 returnTc (expr', lie)
320 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
321 returnTc (expr', lie)
322 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
324 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
325 = tcAddSrcLoc src_loc $
326 tcAddErrCtxt (caseCtxt in_expr) $
328 -- Typecheck the case alternatives first.
329 -- The case patterns tend to give good type info to use
330 -- when typechecking the scrutinee. For example
333 -- will report that map is applied to too few arguments
335 -- Not only that, but it's better to check the matches on their
336 -- own, so that we get the expected results for scoped type variables.
338 -- (p::a, q::b) -> (q,p)
339 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
340 -- claimed by the pattern signatures. But if we typechecked the
341 -- match with x in scope and x's type as the expected type, we'd be hosed.
343 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
345 tcAddErrCtxt (caseScrutCtxt scrut) (
346 tcMonoExpr scrut scrut_ty
347 ) `thenTc` \ (scrut',lie1) ->
349 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
351 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
352 = tcAddSrcLoc src_loc $
353 tcAddErrCtxt (predCtxt pred) (
354 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
356 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
357 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
358 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
362 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
363 = tcDoStmts do_or_lc stmts src_loc res_ty
367 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
368 = unifyListTy res_ty `thenTc` \ elt_ty ->
369 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
370 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
373 = tcAddErrCtxt (listCtxt expr) $
374 tcMonoExpr expr elt_ty
376 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
377 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
378 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
379 (exprs `zip` arg_tys) -- we know they're of equal length.
380 `thenTc` \ (exprs', lies) ->
381 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
383 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
384 = tcAddErrCtxt (recordConCtxt expr) $
385 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
387 (_, record_ty) = tcSplitFunTys con_tau
388 (tycon, ty_args) = tcSplitTyConApp record_ty
390 ASSERT( isAlgTyCon tycon )
391 unifyTauTy res_ty record_ty `thenTc_`
393 -- Check that the record bindings match the constructor
394 -- con_name is syntactically constrained to be a data constructor
395 tcLookupDataCon con_name `thenTc` \ data_con ->
397 bad_fields = badFields rbinds data_con
399 if not (null bad_fields) then
400 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
401 failTc -- Fail now, because tcRecordBinds will crash on a bad field
404 -- Typecheck the record bindings
405 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
408 (missing_s_fields, missing_fields) = missingFields rbinds data_con
410 checkTcM (null missing_s_fields)
411 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
412 returnNF_Tc ()) `thenNF_Tc_`
413 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
414 checkTcM (not (warn && not (null missing_fields)))
415 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
416 returnNF_Tc ()) `thenNF_Tc_`
418 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
420 -- The main complication with RecordUpd is that we need to explicitly
421 -- handle the *non-updated* fields. Consider:
423 -- data T a b = MkT1 { fa :: a, fb :: b }
424 -- | MkT2 { fa :: a, fc :: Int -> Int }
425 -- | MkT3 { fd :: a }
427 -- upd :: T a b -> c -> T a c
428 -- upd t x = t { fb = x}
430 -- The type signature on upd is correct (i.e. the result should not be (T a b))
431 -- because upd should be equivalent to:
433 -- upd t x = case t of
434 -- MkT1 p q -> MkT1 p x
435 -- MkT2 a b -> MkT2 p b
436 -- MkT3 d -> error ...
438 -- So we need to give a completely fresh type to the result record,
439 -- and then constrain it by the fields that are *not* updated ("p" above).
441 -- Note that because MkT3 doesn't contain all the fields being updated,
442 -- its RHS is simply an error, so it doesn't impose any type constraints
444 -- All this is done in STEP 4 below.
446 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
447 = tcAddErrCtxt (recordUpdCtxt expr) $
450 -- Check that the field names are really field names
451 ASSERT( not (null rbinds) )
453 field_names = [field_name | (field_name, _, _) <- rbinds]
455 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
457 bad_guys = [ addErrTc (notSelector field_name)
458 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
460 Just (AnId sel_id) -> not (isRecordSelector sel_id)
464 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
467 -- Figure out the tycon and data cons from the first field name
469 -- It's OK to use the non-tc splitters here (for a selector)
470 (Just (AnId sel_id) : _) = maybe_sel_ids
471 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
472 -- when the data type has a context
473 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
474 tycon = tcTyConAppTyCon data_ty
475 data_cons = tyConDataCons tycon
476 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
478 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
481 -- Check that at least one constructor has all the named fields
482 -- i.e. has an empty set of bad fields returned by badFields
483 checkTc (any (null . badFields rbinds) data_cons)
484 (badFieldsUpd rbinds) `thenTc_`
487 -- Typecheck the update bindings.
488 -- (Do this after checking for bad fields in case there's a field that
489 -- doesn't match the constructor.)
491 result_record_ty = mkTyConApp tycon result_inst_tys
493 unifyTauTy res_ty result_record_ty `thenTc_`
494 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
497 -- Use the un-updated fields to find a vector of booleans saying
498 -- which type arguments must be the same in updatee and result.
500 -- WARNING: this code assumes that all data_cons in a common tycon
501 -- have FieldLabels abstracted over the same tyvars.
503 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
504 con_field_lbls_s = map dataConFieldLabels data_cons
506 -- A constructor is only relevant to this process if
507 -- it contains all the fields that are being updated
508 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
509 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
511 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
512 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
514 mk_inst_ty (tyvar, result_inst_ty)
515 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
516 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
518 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
521 -- Typecheck the expression to be updated
523 record_ty = mkTyConApp tycon inst_tys
525 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
528 -- Figure out the LIE we need. We have to generate some
529 -- dictionaries for the data type context, since we are going to
530 -- do some construction.
532 -- What dictionaries do we need? For the moment we assume that all
533 -- data constructors have the same context, and grab it from the first
534 -- constructor. If they have varying contexts then we'd have to
535 -- union the ones that could participate in the update.
537 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
538 inst_env = mkTopTyVarSubst tyvars result_inst_tys
539 theta' = substTheta inst_env theta
541 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
544 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
545 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
547 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
548 = unifyListTy res_ty `thenTc` \ elt_ty ->
549 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
551 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
552 newMethod (ArithSeqOrigin seq)
553 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
555 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
556 lie1 `plusLIE` unitLIE enum_from)
558 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
559 = tcAddErrCtxt (arithSeqCtxt in_expr) $
560 unifyListTy res_ty `thenTc` \ elt_ty ->
561 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
562 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
563 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
564 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
566 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
567 (FromThen expr1' expr2'),
568 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
570 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
571 = tcAddErrCtxt (arithSeqCtxt in_expr) $
572 unifyListTy res_ty `thenTc` \ elt_ty ->
573 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
574 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
575 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
576 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
578 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
579 (FromTo expr1' expr2'),
580 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
582 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
583 = tcAddErrCtxt (arithSeqCtxt in_expr) $
584 unifyListTy res_ty `thenTc` \ elt_ty ->
585 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
586 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
587 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
588 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
589 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
591 returnTc (ArithSeqOut (HsVar (instToId eft))
592 (FromThenTo expr1' expr2' expr3'),
593 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
596 %************************************************************************
598 \subsection{Expressions type signatures}
600 %************************************************************************
603 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
604 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
606 tcAddErrCtxt (exprSigCtxt in_expr) $
607 if not (isQualifiedTy sig_tc_ty) then
609 unifyTauTy sig_tc_ty res_ty `thenTc_`
610 tcMonoExpr expr sig_tc_ty
612 else -- Signature is polymorphic
613 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
615 -- Now match the signature type with res_ty.
616 -- We must not do this earlier, because res_ty might well
617 -- mention variables free in the environment, and we'd get
618 -- bogus complaints about not being able to for-all the
620 unifyTauTy res_ty expr_ty `thenTc_`
622 -- If everything is ok, return the stuff unchanged, except for
623 -- the effect of any substutions etc. We simply discard the
624 -- result of the tcSimplifyCheck (inside tcPolyExpr), except for any default
625 -- resolution it may have done, which is recorded in the
630 Implicit Parameter bindings.
633 tcMonoExpr (HsWith expr binds) res_ty
634 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
635 mapAndUnzipTc tcIPBind binds `thenTc` \ (pairs, bind_lies) ->
637 -- If the binding binds ?x = E, we must now
638 -- discharge any ?x constraints in expr_lie
639 tcSimplifyIPs (map fst pairs) expr_lie `thenTc` \ (expr_lie', dict_binds) ->
641 binds' = [(instToId ip, rhs) | (ip,rhs) <- pairs]
642 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
644 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
646 tcIPBind (name, expr)
647 = newTyVarTy openTypeKind `thenTc` \ ty ->
648 tcGetSrcLoc `thenTc` \ loc ->
649 newIPDict (IPBind name) name ty `thenNF_Tc` \ ip ->
650 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
651 returnTc ((ip, expr'), lie)
654 %************************************************************************
656 \subsection{@tcApp@ typchecks an application}
658 %************************************************************************
662 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
663 -> TcType -- Expected result type of application
664 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
667 tcApp fun args res_ty
668 = -- First type-check the function
669 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
671 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
672 split_fun_ty fun_ty (length args)
673 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
675 -- Unify with expected result before type-checking the args
676 -- This is when we might detect a too-few args situation
677 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
678 unifyTauTy res_ty actual_result_ty
681 -- Now typecheck the args
682 mapAndUnzipTc (tcArg fun)
683 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
685 -- Check that the result type doesn't have any nested for-alls.
686 -- For example, a "build" on its own is no good; it must be applied to something.
687 checkTc (isTauTy actual_result_ty)
688 (lurkingRank2Err fun actual_result_ty) `thenTc_`
690 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
693 -- If an error happens we try to figure out whether the
694 -- function has been given too many or too few arguments,
696 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
697 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
698 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
700 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
701 (env2, act_ty'') = tidyOpenType env1 act_ty'
702 (exp_args, _) = tcSplitFunTys exp_ty''
703 (act_args, _) = tcSplitFunTys act_ty''
705 len_act_args = length act_args
706 len_exp_args = length exp_args
708 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
709 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
710 | otherwise = appCtxt fun args
712 returnNF_Tc (env2, message)
715 split_fun_ty :: TcType -- The type of the function
716 -> Int -- Number of arguments
717 -> TcM ([TcType], -- Function argument types
718 TcType) -- Function result types
720 split_fun_ty fun_ty 0
721 = returnTc ([], fun_ty)
723 split_fun_ty fun_ty n
724 = -- Expect the function to have type A->B
725 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
726 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
727 returnTc (arg_ty:arg_tys, final_res_ty)
731 tcArg :: RenamedHsExpr -- The function (for error messages)
732 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
733 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
735 tcArg the_fun (arg, expected_arg_ty, arg_no)
736 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
737 tcExpr arg expected_arg_ty
741 %************************************************************************
743 \subsection{@tcId@ typchecks an identifier occurrence}
745 %************************************************************************
748 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
749 tcId name -- Look up the Id and instantiate its type
750 = tcLookupId name `thenNF_Tc` \ id ->
754 Typecheck expression which in most cases will be an Id.
757 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
758 tcExpr_id (HsVar name) = tcId name
759 tcExpr_id expr = newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
760 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
761 returnTc (expr', lie_id, id_ty)
765 %************************************************************************
767 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
769 %************************************************************************
772 tcDoStmts do_or_lc stmts src_loc res_ty
773 = -- get the Monad and MonadZero classes
774 -- create type consisting of a fresh monad tyvar
775 ASSERT( not (null stmts) )
776 tcAddSrcLoc src_loc $
778 -- If it's a comprehension we're dealing with,
779 -- force it to be a list comprehension.
780 -- (as of Haskell 98, monad comprehensions are no more.)
782 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
783 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
785 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
786 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
787 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
788 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
789 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
791 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
793 -- Build the then and zero methods in case we need them
794 -- It's important that "then" and "return" appear just once in the final LIE,
795 -- not only for typechecker efficiency, but also because otherwise during
796 -- simplification we end up with silly stuff like
797 -- then = case d of (t,r) -> t
799 -- where the second "then" sees that it already exists in the "available" stuff.
801 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
802 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
803 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
804 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
805 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
806 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
808 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
810 returnTc (HsDoOut do_or_lc stmts'
811 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
813 stmts_lie `plusLIE` monad_lie)
817 %************************************************************************
819 \subsection{Record bindings}
821 %************************************************************************
823 Game plan for record bindings
824 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
825 1. Find the TyCon for the bindings, from the first field label.
827 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
829 For each binding field = value
831 3. Instantiate the field type (from the field label) using the type
834 4 Type check the value using tcArg, passing the field type as
835 the expected argument type.
837 This extends OK when the field types are universally quantified.
842 :: TyCon -- Type constructor for the record
843 -> [TcType] -- Args of this type constructor
844 -> RenamedRecordBinds
845 -> TcM (TcRecordBinds, LIE)
847 tcRecordBinds tycon ty_args rbinds
848 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
849 returnTc (rbinds', plusLIEs lies)
851 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
853 do_bind (field_lbl_name, rhs, pun_flag)
854 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
856 field_lbl = recordSelectorFieldLabel sel_id
857 field_ty = substTy tenv (fieldLabelType field_lbl)
859 ASSERT( isRecordSelector sel_id )
860 -- This lookup and assertion will surely succeed, because
861 -- we check that the fields are indeed record selectors
862 -- before calling tcRecordBinds
863 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
864 -- The caller of tcRecordBinds has already checked
865 -- that all the fields come from the same type
867 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
869 returnTc ((sel_id, rhs', pun_flag), lie)
871 badFields rbinds data_con
872 = [field_name | (field_name, _, _) <- rbinds,
873 not (field_name `elem` field_names)
876 field_names = map fieldLabelName (dataConFieldLabels data_con)
878 missingFields rbinds data_con
879 | null field_labels = ([], []) -- Not declared as a record;
880 -- But C{} is still valid
882 = (missing_strict_fields, other_missing_fields)
884 missing_strict_fields
885 = [ fl | (fl, str) <- field_info,
887 not (fieldLabelName fl `elem` field_names_used)
890 = [ fl | (fl, str) <- field_info,
891 not (isMarkedStrict str),
892 not (fieldLabelName fl `elem` field_names_used)
895 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
896 field_labels = dataConFieldLabels data_con
898 field_info = zipEqual "missingFields"
900 (dropList ex_theta (dataConStrictMarks data_con))
901 -- The 'drop' is because dataConStrictMarks
902 -- includes the existential dictionaries
903 (_, _, _, ex_theta, _, _) = dataConSig data_con
906 %************************************************************************
908 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
910 %************************************************************************
913 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
915 tcMonoExprs [] [] = returnTc ([], emptyLIE)
916 tcMonoExprs (expr:exprs) (ty:tys)
917 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
918 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
919 returnTc (expr':exprs', lie1 `plusLIE` lie2)
923 %************************************************************************
925 \subsection{Literals}
927 %************************************************************************
932 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
933 tcLit (HsLitLit s _) res_ty
934 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
935 newDicts (LitLitOrigin (_UNPK_ s))
936 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
937 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
940 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
941 returnTc (HsLit lit, emptyLIE)
945 %************************************************************************
947 \subsection{Errors and contexts}
949 %************************************************************************
953 Boring and alphabetical:
956 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
959 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
962 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
965 = hang (ptext SLIT("In an expression with a type signature:"))
969 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
972 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
975 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
978 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
980 funAppCtxt fun arg arg_no
981 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
982 quotes (ppr fun) <> text ", namely"])
985 wrongArgsCtxt too_many_or_few fun args
986 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
987 <+> ptext SLIT("is applied to") <+> text too_many_or_few
988 <+> ptext SLIT("arguments in the call"))
989 4 (parens (ppr the_app))
991 the_app = foldl HsApp fun args -- Used in error messages
994 = ptext SLIT("In the application") <+> quotes (ppr the_app)
996 the_app = foldl HsApp fun args -- Used in error messages
998 lurkingRank2Err fun fun_ty
999 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1000 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1001 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1004 = hang (ptext SLIT("No constructor has all these fields:"))
1005 4 (pprQuotedList fields)
1007 fields = [field | (field, _, _) <- rbinds]
1009 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1010 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1013 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1015 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1016 missingStrictFieldCon con field
1017 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1018 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1020 missingFieldCon :: Name -> FieldLabel -> SDoc
1021 missingFieldCon con field
1022 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1023 ptext SLIT("is not initialised")]