2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcApp, tcExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), MonoBinds(..), Stmt(..), StmtCtxt(..),
13 mkMonoBind, nullMonoBinds
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds, mkHsConApp,
21 import BasicTypes ( RecFlag(..) )
23 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
24 LIE, emptyLIE, unitLIE, consLIE, plusLIE, plusLIEs,
26 newOverloadedLit, newMethod, newIPDict,
27 instOverloadedFun, newDicts, newClassDicts,
28 getIPsOfLIE, instToId, ipToId
30 import TcBinds ( tcBindsAndThen )
31 import TcEnv ( tcInstId,
32 tcLookupValue, tcLookupClassByKey,
34 tcExtendGlobalTyVars, tcLookupValueMaybe,
35 tcLookupTyCon, tcLookupDataCon
37 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
38 import TcMonoType ( tcHsSigType, checkSigTyVars, sigCtxt )
39 import TcPat ( badFieldCon )
40 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, partitionPredsOfLIE )
41 import TcType ( TcType, TcTauType,
43 tcInstTcType, tcSplitRhoTy,
44 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
46 import Class ( Class )
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType
49 import Id ( idType, recordSelectorFieldLabel,
53 import DataCon ( dataConFieldLabels, dataConSig,
54 dataConStrictMarks, StrictnessMark(..)
56 import Name ( Name, getName )
57 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
59 splitFunTy_maybe, splitFunTys, isNotUsgTy,
60 mkTyConApp, splitSigmaTy,
62 isTauTy, tyVarsOfType, tyVarsOfTypes,
63 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
64 boxedTypeKind, mkArrowKind,
67 import Subst ( mkTopTyVarSubst, substClasses )
68 import UsageSPUtils ( unannotTy )
69 import VarSet ( emptyVarSet, unionVarSet, elemVarSet, mkVarSet )
70 import TyCon ( tyConDataCons )
71 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
72 floatPrimTy, addrPrimTy
74 import TysWiredIn ( boolTy, charTy, stringTy )
75 import PrelInfo ( ioTyCon_NAME )
76 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
78 import Unique ( cCallableClassKey, cReturnableClassKey,
79 enumFromClassOpKey, enumFromThenClassOpKey,
80 enumFromToClassOpKey, enumFromThenToClassOpKey,
81 thenMClassOpKey, failMClassOpKey, returnMClassOpKey
84 import Maybes ( maybeToBool, mapMaybe )
85 import ListSetOps ( minusList )
87 import CmdLineOpts ( opt_WarnMissingFields )
91 %************************************************************************
93 \subsection{Main wrappers}
95 %************************************************************************
98 tcExpr :: RenamedHsExpr -- Expession to type check
99 -> TcType -- Expected type (could be a polytpye)
100 -> TcM s (TcExpr, LIE)
102 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
103 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
104 returnTc (expr', lie)
106 | otherwise = -- Monomorphic case
111 %************************************************************************
113 \subsection{@tcPolyExpr@ typchecks an application}
115 %************************************************************************
118 -- tcPolyExpr is like tcMonoExpr, except that the expected type
119 -- can be a polymorphic one.
120 tcPolyExpr :: RenamedHsExpr
121 -> TcType -- Expected type
122 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
123 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
125 tcPolyExpr arg expected_arg_ty
126 = -- Ha! The argument type of the function is a for-all type,
127 -- An example of rank-2 polymorphism.
129 -- To ensure that the forall'd type variables don't get unified with each
130 -- other or any other types, we make fresh copy of the alleged type
131 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
133 (sig_theta, sig_tau) = splitRhoTy sig_rho
134 free_tyvars = tyVarsOfType expected_arg_ty
136 -- Type-check the arg and unify with expected type
137 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
139 -- Check that the sig_tyvars havn't been constrained
140 -- The interesting bit here is that we must include the free variables
141 -- of the expected arg ty. Here's an example:
142 -- runST (newVar True)
143 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
144 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
145 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
146 -- So now s' isn't unconstrained because it's linked to a.
147 -- Conclusion: include the free vars of the expected arg type in the
148 -- list of "free vars" for the signature check.
150 tcExtendGlobalTyVars free_tyvars $
151 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
153 checkSigTyVars sig_tyvars free_tyvars `thenTc` \ zonked_sig_tyvars ->
155 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
156 -- ToDo: better origin
158 (text "the type signature of an expression")
159 (mkVarSet zonked_sig_tyvars)
160 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
163 -- This HsLet binds any Insts which came out of the simplification.
164 -- It's a bit out of place here, but using AbsBind involves inventing
165 -- a couple of new names which seems worse.
166 generalised_arg = TyLam zonked_sig_tyvars $
171 returnTc ( generalised_arg, free_insts,
172 arg', sig_tau, lie_arg )
174 sig_msg = ptext SLIT("When checking an expression type signature")
177 %************************************************************************
179 \subsection{The TAUT rules for variables}
181 %************************************************************************
184 tcMonoExpr :: RenamedHsExpr -- Expession to type check
185 -> TcTauType -- Expected type (could be a type variable)
186 -> TcM s (TcExpr, LIE)
188 tcMonoExpr (HsVar name) res_ty
189 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
190 unifyTauTy res_ty id_ty `thenTc_`
192 -- Check that the result type doesn't have any nested for-alls.
193 -- For example, a "build" on its own is no good; it must be
194 -- applied to something.
195 checkTc (isTauTy id_ty)
196 (lurkingRank2Err name id_ty) `thenTc_`
198 returnTc (expr', lie)
202 tcMonoExpr (HsIPVar name) res_ty
203 -- ZZ What's the `id' used for here...
204 = let id = mkVanillaId name res_ty in
205 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
206 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
207 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
210 %************************************************************************
212 \subsection{Literals}
214 %************************************************************************
219 tcMonoExpr (HsLit (HsInt i)) res_ty
220 = newOverloadedLit (LiteralOrigin (HsInt i))
221 (OverloadedIntegral i)
222 res_ty `thenNF_Tc` \ stuff ->
225 tcMonoExpr (HsLit (HsFrac f)) res_ty
226 = newOverloadedLit (LiteralOrigin (HsFrac f))
227 (OverloadedFractional f)
228 res_ty `thenNF_Tc` \ stuff ->
232 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
233 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
234 newClassDicts (LitLitOrigin (_UNPK_ s))
235 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
236 returnTc (HsLitOut lit res_ty, dicts)
242 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
243 = unifyTauTy res_ty charPrimTy `thenTc_`
244 returnTc (HsLitOut lit charPrimTy, emptyLIE)
246 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
247 = unifyTauTy res_ty addrPrimTy `thenTc_`
248 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
250 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
251 = unifyTauTy res_ty intPrimTy `thenTc_`
252 returnTc (HsLitOut lit intPrimTy, emptyLIE)
254 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
255 = unifyTauTy res_ty floatPrimTy `thenTc_`
256 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
258 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
259 = unifyTauTy res_ty doublePrimTy `thenTc_`
260 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
263 Unoverloaded literals:
266 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
267 = unifyTauTy res_ty charTy `thenTc_`
268 returnTc (HsLitOut lit charTy, emptyLIE)
270 tcMonoExpr (HsLit lit@(HsString str)) res_ty
271 = unifyTauTy res_ty stringTy `thenTc_`
272 returnTc (HsLitOut lit stringTy, emptyLIE)
275 %************************************************************************
277 \subsection{Other expression forms}
279 %************************************************************************
282 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
283 = tcMonoExpr expr res_ty
285 -- perform the negate *before* overloading the integer, since the case
286 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
287 -- convenient to do it here.
289 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
290 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
292 tcMonoExpr (NegApp expr neg) res_ty
293 = tcMonoExpr (HsApp neg expr) res_ty
295 tcMonoExpr (HsLam match) res_ty
296 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
297 returnTc (HsLam match', lie)
299 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
301 accum (HsApp e1 e2) args = accum e1 (e2:args)
303 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
304 returnTc (foldl HsApp fun' args', lie)
306 -- equivalent to (op e1) e2:
307 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
308 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
309 returnTc (OpApp arg1' op' fix arg2', lie)
312 Note that the operators in sections are expected to be binary, and
313 a type error will occur if they aren't.
316 -- Left sections, equivalent to
323 tcMonoExpr in_expr@(SectionL arg op) res_ty
324 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
326 -- Check that res_ty is a function type
327 -- Without this check we barf in the desugarer on
329 -- because it tries to desugar to
330 -- f op = \r -> 3 op r
331 -- so (3 `op`) had better be a function!
332 tcAddErrCtxt (sectionLAppCtxt in_expr) $
333 unifyFunTy res_ty `thenTc_`
335 returnTc (SectionL arg' op', lie)
337 -- Right sections, equivalent to \ x -> x op expr, or
340 tcMonoExpr in_expr@(SectionR op expr) res_ty
341 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
342 tcAddErrCtxt (sectionRAppCtxt in_expr) $
343 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
344 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
345 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
346 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
349 The interesting thing about @ccall@ is that it is just a template
350 which we instantiate by filling in details about the types of its
351 argument and result (ie minimal typechecking is performed). So, the
352 basic story is that we allocate a load of type variables (to hold the
353 arg/result types); unify them with the args/result; and store them for
357 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
358 = -- Get the callable and returnable classes.
359 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
360 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
361 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
363 new_arg_dict (arg, arg_ty)
364 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
365 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
366 returnNF_Tc arg_dicts -- Actually a singleton bag
368 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
372 let n_args = length args
373 tv_idxs | n_args == 0 = []
374 | otherwise = [1..n_args]
376 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
377 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
379 -- The argument types can be unboxed or boxed; the result
380 -- type must, however, be boxed since it's an argument to the IO
382 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
384 io_result_ty = mkTyConApp ioTyCon [result_ty]
385 [ioDataCon] = tyConDataCons ioTyCon
387 unifyTauTy res_ty io_result_ty `thenTc_`
389 -- Construct the extra insts, which encode the
390 -- constraints on the argument and result types.
391 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
392 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
393 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
394 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
398 tcMonoExpr (HsSCC lbl expr) res_ty
399 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
400 returnTc (HsSCC lbl expr', lie)
402 tcMonoExpr (HsLet binds expr) res_ty
405 binds -- Bindings to check
406 tc_expr `thenTc` \ (expr', lie) ->
407 returnTc (expr', lie)
409 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
410 returnTc (expr', lie)
411 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
413 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
414 = tcAddSrcLoc src_loc $
415 tcAddErrCtxt (caseCtxt in_expr) $
417 -- Typecheck the case alternatives first.
418 -- The case patterns tend to give good type info to use
419 -- when typechecking the scrutinee. For example
422 -- will report that map is applied to too few arguments
424 -- Not only that, but it's better to check the matches on their
425 -- own, so that we get the expected results for scoped type variables.
427 -- (p::a, q::b) -> (q,p)
428 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
429 -- claimed by the pattern signatures. But if we typechecked the
430 -- match with x in scope and x's type as the expected type, we'd be hosed.
432 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
434 tcAddErrCtxt (caseScrutCtxt scrut) (
435 tcMonoExpr scrut scrut_ty
436 ) `thenTc` \ (scrut',lie1) ->
438 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
440 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
441 = tcAddSrcLoc src_loc $
442 tcAddErrCtxt (predCtxt pred) (
443 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
445 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
446 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
447 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
451 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
452 = tcDoStmts do_or_lc stmts src_loc res_ty
456 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
457 = unifyListTy res_ty `thenTc` \ elt_ty ->
458 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
459 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
462 = tcAddErrCtxt (listCtxt expr) $
463 tcMonoExpr expr elt_ty
465 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
467 then unifyTupleTy (length exprs) res_ty
468 else unifyUnboxedTupleTy (length exprs) res_ty
469 ) `thenTc` \ arg_tys ->
470 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
471 (exprs `zip` arg_tys) -- we know they're of equal length.
472 `thenTc` \ (exprs', lies) ->
473 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
475 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
476 = tcAddErrCtxt (recordConCtxt expr) $
477 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
479 (_, record_ty) = splitFunTys con_tau
481 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
482 unifyTauTy res_ty record_ty `thenTc_`
484 -- Check that the record bindings match the constructor
485 -- con_name is syntactically constrained to be a data constructor
486 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
488 bad_fields = badFields rbinds data_con
490 if not (null bad_fields) then
491 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
492 failTc -- Fail now, because tcRecordBinds will crash on a bad field
495 -- Typecheck the record bindings
496 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
499 missing_s_fields = missingStrictFields rbinds data_con
501 checkTcM (null missing_s_fields)
502 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
503 returnNF_Tc ()) `thenNF_Tc_`
505 missing_fields = missingFields rbinds data_con
507 checkTcM (not (opt_WarnMissingFields && not (null missing_fields)))
508 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
509 returnNF_Tc ()) `thenNF_Tc_`
511 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
513 -- The main complication with RecordUpd is that we need to explicitly
514 -- handle the *non-updated* fields. Consider:
516 -- data T a b = MkT1 { fa :: a, fb :: b }
517 -- | MkT2 { fa :: a, fc :: Int -> Int }
518 -- | MkT3 { fd :: a }
520 -- upd :: T a b -> c -> T a c
521 -- upd t x = t { fb = x}
523 -- The type signature on upd is correct (i.e. the result should not be (T a b))
524 -- because upd should be equivalent to:
526 -- upd t x = case t of
527 -- MkT1 p q -> MkT1 p x
528 -- MkT2 a b -> MkT2 p b
529 -- MkT3 d -> error ...
531 -- So we need to give a completely fresh type to the result record,
532 -- and then constrain it by the fields that are *not* updated ("p" above).
534 -- Note that because MkT3 doesn't contain all the fields being updated,
535 -- its RHS is simply an error, so it doesn't impose any type constraints
537 -- All this is done in STEP 4 below.
539 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
540 = tcAddErrCtxt (recordUpdCtxt expr) $
543 -- Check that the field names are really field names
544 ASSERT( not (null rbinds) )
546 field_names = [field_name | (field_name, _, _) <- rbinds]
548 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
550 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
553 Just sel_id -> not (isRecordSelector sel_id)
556 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
557 if not (null bad_guys) then
562 -- Figure out the tycon and data cons from the first field name
564 (Just sel_id : _) = maybe_sel_ids
565 (_, _, tau) = ASSERT( isNotUsgTy (idType sel_id) )
566 splitSigmaTy (idType sel_id) -- Selectors can be overloaded
567 -- when the data type has a context
568 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
569 (tycon, _, data_cons) = splitAlgTyConApp data_ty
570 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
572 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
575 -- Check that at least one constructor has all the named fields
576 -- i.e. has an empty set of bad fields returned by badFields
577 checkTc (any (null . badFields rbinds) data_cons)
578 (badFieldsUpd rbinds) `thenTc_`
581 -- Typecheck the update bindings.
582 -- (Do this after checking for bad fields in case there's a field that
583 -- doesn't match the constructor.)
585 result_record_ty = mkTyConApp tycon result_inst_tys
587 unifyTauTy res_ty result_record_ty `thenTc_`
588 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
591 -- Use the un-updated fields to find a vector of booleans saying
592 -- which type arguments must be the same in updatee and result.
594 -- WARNING: this code assumes that all data_cons in a common tycon
595 -- have FieldLabels abstracted over the same tyvars.
597 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
598 con_field_lbls_s = map dataConFieldLabels data_cons
600 -- A constructor is only relevant to this process if
601 -- it contains all the fields that are being updated
602 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
603 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
605 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
606 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
608 mk_inst_ty (tyvar, result_inst_ty)
609 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
610 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
612 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
615 -- Typecheck the expression to be updated
617 record_ty = mkTyConApp tycon inst_tys
619 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
622 -- Figure out the LIE we need. We have to generate some
623 -- dictionaries for the data type context, since we are going to
624 -- do some construction.
626 -- What dictionaries do we need? For the moment we assume that all
627 -- data constructors have the same context, and grab it from the first
628 -- constructor. If they have varying contexts then we'd have to
629 -- union the ones that could participate in the update.
631 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
632 inst_env = mkTopTyVarSubst tyvars result_inst_tys
633 theta' = substClasses inst_env theta
635 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
638 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
639 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
641 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
642 = unifyListTy res_ty `thenTc` \ elt_ty ->
643 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
645 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
646 newMethod (ArithSeqOrigin seq)
647 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
649 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
652 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
653 = tcAddErrCtxt (arithSeqCtxt in_expr) $
654 unifyListTy res_ty `thenTc` \ elt_ty ->
655 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
656 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
657 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
658 newMethod (ArithSeqOrigin seq)
659 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
661 returnTc (ArithSeqOut (HsVar enum_from_then_id)
662 (FromThen expr1' expr2'),
663 lie1 `plusLIE` lie2 `plusLIE` lie3)
665 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
666 = tcAddErrCtxt (arithSeqCtxt in_expr) $
667 unifyListTy res_ty `thenTc` \ elt_ty ->
668 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
669 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
670 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
671 newMethod (ArithSeqOrigin seq)
672 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
674 returnTc (ArithSeqOut (HsVar enum_from_to_id)
675 (FromTo expr1' expr2'),
676 lie1 `plusLIE` lie2 `plusLIE` lie3)
678 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
679 = tcAddErrCtxt (arithSeqCtxt in_expr) $
680 unifyListTy res_ty `thenTc` \ elt_ty ->
681 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
682 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
683 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
684 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
685 newMethod (ArithSeqOrigin seq)
686 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
688 returnTc (ArithSeqOut (HsVar eft_id)
689 (FromThenTo expr1' expr2' expr3'),
690 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
693 %************************************************************************
695 \subsection{Expressions type signatures}
697 %************************************************************************
700 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
701 = tcSetErrCtxt (exprSigCtxt in_expr) $
702 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
704 if not (isForAllTy sig_tc_ty) then
706 unifyTauTy sig_tc_ty res_ty `thenTc_`
707 tcMonoExpr expr sig_tc_ty
709 else -- Signature is polymorphic
710 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
712 -- Now match the signature type with res_ty.
713 -- We must not do this earlier, because res_ty might well
714 -- mention variables free in the environment, and we'd get
715 -- bogus complaints about not being able to for-all the
717 unifyTauTy res_ty expr_ty `thenTc_`
719 -- If everything is ok, return the stuff unchanged, except for
720 -- the effect of any substutions etc. We simply discard the
721 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
722 -- resolution it may have done, which is recorded in the
727 Implicit Parameter bindings.
730 tcMonoExpr (HsWith expr binds) res_ty
731 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
732 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
733 partitionPredsOfLIE isBound lie `thenTc` \ (ips, lie', dict_binds) ->
734 pprTrace "tcMonoExpr With" (ppr (ips, lie', dict_binds)) $
735 let expr'' = if nullMonoBinds dict_binds
737 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
740 tcCheckIPBinds binds' types ips `thenTc_`
741 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
743 = case ipName_maybe p of
744 Just n -> n `elem` names
746 names = map fst binds
747 -- revBinds is used because tcSimplify outputs the bindings
748 -- out-of-order. it's not a problem elsewhere because these
749 -- bindings are normally used in a recursive let
750 -- ZZ probably need to find a better solution
751 revBinds (b1 `AndMonoBinds` b2) =
752 (revBinds b2) `AndMonoBinds` (revBinds b1)
755 tcIPBinds ((name, expr) : binds)
756 = newTyVarTy_OpenKind `thenTc` \ ty ->
757 tcGetSrcLoc `thenTc` \ loc ->
758 let id = ipToId name ty loc in
759 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
760 zonkTcType ty `thenTc` \ ty' ->
761 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
762 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
763 tcIPBinds [] = returnTc ([], [], emptyLIE)
765 tcCheckIPBinds binds types ips
766 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
768 -- ZZ how do we use the loc?
769 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
770 = unifyTauTy t1 t2 `thenTc_`
771 tcCheckIPBind bt ips `thenTc` \ ips' ->
773 tcCheckIPBind bt (ip : ips)
774 = tcCheckIPBind bt ips `thenTc` \ ips' ->
780 Typecheck expression which in most cases will be an Id.
783 tcExpr_id :: RenamedHsExpr
789 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
791 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
792 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
793 returnTc (id_expr', lie_id, id_ty)
796 %************************************************************************
798 \subsection{@tcApp@ typchecks an application}
800 %************************************************************************
804 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
805 -> TcType -- Expected result type of application
806 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
809 tcApp fun args res_ty
810 = -- First type-check the function
811 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
813 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
814 split_fun_ty fun_ty (length args)
815 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
817 -- Unify with expected result before type-checking the args
818 -- This is when we might detect a too-few args situation
819 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
820 unifyTauTy res_ty actual_result_ty
823 -- Now typecheck the args
824 mapAndUnzipTc (tcArg fun)
825 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
827 -- Check that the result type doesn't have any nested for-alls.
828 -- For example, a "build" on its own is no good; it must be applied to something.
829 checkTc (isTauTy actual_result_ty)
830 (lurkingRank2Err fun fun_ty) `thenTc_`
832 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
835 -- If an error happens we try to figure out whether the
836 -- function has been given too many or too few arguments,
838 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
839 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
840 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
842 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
843 (env2, act_ty'') = tidyOpenType env1 act_ty'
844 (exp_args, _) = splitFunTys exp_ty''
845 (act_args, _) = splitFunTys act_ty''
847 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
848 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
849 | otherwise = appCtxt fun args
851 returnNF_Tc (env2, message)
854 split_fun_ty :: TcType -- The type of the function
855 -> Int -- Number of arguments
856 -> TcM s ([TcType], -- Function argument types
857 TcType) -- Function result types
859 split_fun_ty fun_ty 0
860 = returnTc ([], fun_ty)
862 split_fun_ty fun_ty n
863 = -- Expect the function to have type A->B
864 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
865 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
866 returnTc (arg_ty:arg_tys, final_res_ty)
870 tcArg :: RenamedHsExpr -- The function (for error messages)
871 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
872 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
874 tcArg the_fun (arg, expected_arg_ty, arg_no)
875 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
876 tcExpr arg expected_arg_ty
880 %************************************************************************
882 \subsection{@tcId@ typchecks an identifier occurrence}
884 %************************************************************************
886 Between the renamer and the first invocation of the UsageSP inference,
887 identifiers read from interface files will have usage information in
888 their types, whereas other identifiers will not. The unannotTy here
889 in @tcId@ prevents this information from pointlessly propagating
890 further prior to the first usage inference.
893 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
896 = -- Look up the Id and instantiate its type
897 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
900 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
902 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
903 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
904 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
907 -- The instantiate_it loop runs round instantiating the Id.
908 -- It has to be a loop because we are now prepared to entertain
910 -- f:: forall a. Eq a => forall b. Baz b => tau
911 -- We want to instantiate this to
912 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
913 instantiate_it orig fun ty
914 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
915 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
916 instantiate_it2 orig fun tyvars theta tau
918 instantiate_it2 orig fun tyvars theta tau
919 = if null theta then -- Is it overloaded?
920 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
922 -- Yes, it's overloaded
923 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
924 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
925 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
928 arg_tys = mkTyVarTys tyvars
931 %************************************************************************
933 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
935 %************************************************************************
938 tcDoStmts do_or_lc stmts src_loc res_ty
939 = -- get the Monad and MonadZero classes
940 -- create type consisting of a fresh monad tyvar
941 ASSERT( not (null stmts) )
942 tcAddSrcLoc src_loc $
944 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
945 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
946 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
948 -- If it's a comprehension we're dealing with,
949 -- force it to be a list comprehension.
950 -- (as of Haskell 98, monad comprehensions are no more.)
952 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
953 _ -> returnTc ()) `thenTc_`
955 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
957 -- Build the then and zero methods in case we need them
958 -- It's important that "then" and "return" appear just once in the final LIE,
959 -- not only for typechecker efficiency, but also because otherwise during
960 -- simplification we end up with silly stuff like
961 -- then = case d of (t,r) -> t
963 -- where the second "then" sees that it already exists in the "available" stuff.
965 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
966 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
967 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
968 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
969 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
970 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
972 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
974 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
975 stmts_lie `plusLIE` monad_lie)
979 %************************************************************************
981 \subsection{Record bindings}
983 %************************************************************************
985 Game plan for record bindings
986 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
989 1. look up "field", to find its selector Id, which must have type
990 forall a1..an. T a1 .. an -> tau
991 where tau is the type of the field.
993 2. Instantiate this type
995 3. Unify the (T a1 .. an) part with the "expected result type", which
996 is passed in. This checks that all the field labels come from the
999 4. Type check the value using tcArg, passing tau as the expected
1002 This extends OK when the field types are universally quantified.
1004 Actually, to save excessive creation of fresh type variables,
1009 :: TcType -- Expected type of whole record
1010 -> RenamedRecordBinds
1011 -> TcM s (TcRecordBinds, LIE)
1013 tcRecordBinds expected_record_ty rbinds
1014 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
1015 returnTc (rbinds', plusLIEs lies)
1017 do_bind (field_label, rhs, pun_flag)
1018 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
1019 ASSERT( isRecordSelector sel_id )
1020 -- This lookup and assertion will surely succeed, because
1021 -- we check that the fields are indeed record selectors
1022 -- before calling tcRecordBinds
1024 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
1026 -- Record selectors all have type
1027 -- forall a1..an. T a1 .. an -> tau
1028 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1030 -- Selector must have type RecordType -> FieldType
1031 Just (record_ty, field_ty) = splitFunTy_maybe tau
1033 unifyTauTy expected_record_ty record_ty `thenTc_`
1034 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1035 returnTc ((sel_id, rhs', pun_flag), lie)
1037 badFields rbinds data_con
1038 = [field_name | (field_name, _, _) <- rbinds,
1039 not (field_name `elem` field_names)
1042 field_names = map fieldLabelName (dataConFieldLabels data_con)
1044 missingStrictFields rbinds data_con
1045 = [ fn | fn <- strict_field_names,
1046 not (fn `elem` field_names_used)
1049 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1050 strict_field_names = mapMaybe isStrict field_info
1052 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1053 isStrict _ = Nothing
1055 field_info = zip (dataConFieldLabels data_con)
1056 (dataConStrictMarks data_con)
1058 missingFields rbinds data_con
1059 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1061 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1063 -- missing strict fields have already been flagged as
1064 -- being so, so leave them out here.
1065 non_strict_field_names = mapMaybe isn'tStrict field_info
1067 isn'tStrict (fl, MarkedStrict) = Nothing
1068 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1070 field_info = zip (dataConFieldLabels data_con)
1071 (dataConStrictMarks data_con)
1075 %************************************************************************
1077 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1079 %************************************************************************
1082 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1084 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1085 tcMonoExprs (expr:exprs) (ty:tys)
1086 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1087 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1088 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1092 % =================================================
1099 pp_nest_hang :: String -> SDoc -> SDoc
1100 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1103 Boring and alphabetical:
1106 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1109 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1112 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1115 = hang (ptext SLIT("In an expression with a type signature:"))
1119 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1122 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1124 sectionRAppCtxt expr
1125 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1127 sectionLAppCtxt expr
1128 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1130 funAppCtxt fun arg arg_no
1131 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1132 quotes (ppr fun) <> text ", namely"])
1133 4 (quotes (ppr arg))
1135 wrongArgsCtxt too_many_or_few fun args
1136 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1137 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1138 <+> ptext SLIT("arguments in the call"))
1139 4 (parens (ppr the_app))
1141 the_app = foldl HsApp fun args -- Used in error messages
1144 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1146 the_app = foldl HsApp fun args -- Used in error messages
1148 lurkingRank2Err fun fun_ty
1149 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1150 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1151 ptext SLIT("so that the result type has for-alls in it")])
1153 rank2ArgCtxt arg expected_arg_ty
1154 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1157 = hang (ptext SLIT("No constructor has all these fields:"))
1158 4 (pprQuotedList fields)
1160 fields = [field | (field, _, _) <- rbinds]
1162 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1163 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1166 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1168 illegalCcallTyErr isArg ty
1169 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1173 | isArg = ptext SLIT("argument")
1174 | otherwise = ptext SLIT("result")
1177 missingStrictFieldCon :: Name -> Name -> SDoc
1178 missingStrictFieldCon con field
1179 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1180 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1182 missingFieldCon :: Name -> Name -> SDoc
1183 missingFieldCon con field
1184 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1185 ptext SLIT("is not initialised")]