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(..), Stmt(..), StmtCtxt(..)
14 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
15 import TcHsSyn ( TcExpr, TcRecordBinds,
16 mkHsTyApp, mkHsLet, maybeBoxedPrimType
20 import BasicTypes ( RecFlag(..) )
22 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
23 LIE, emptyLIE, unitLIE, plusLIE, plusLIEs, newOverloadedLit,
24 newMethod, instOverloadedFun, newDicts, instToId )
25 import TcBinds ( tcBindsAndThen )
26 import TcEnv ( tcInstId,
27 tcLookupValue, tcLookupClassByKey,
29 tcExtendGlobalTyVars, tcLookupValueMaybe,
30 tcLookupTyCon, tcLookupDataCon
32 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
33 import TcMonoType ( tcHsType, checkSigTyVars, sigCtxt )
34 import TcPat ( badFieldCon )
35 import TcSimplify ( tcSimplifyAndCheck )
36 import TcType ( TcType, TcTauType,
38 tcInstTcType, tcSplitRhoTy,
39 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
41 import Class ( Class )
42 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType )
43 import Id ( idType, recordSelectorFieldLabel,
47 import DataCon ( dataConFieldLabels, dataConSig, dataConId )
49 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
50 splitFunTy_maybe, splitFunTys, isNotUsgTy,
52 splitForAllTys, splitRhoTy,
53 isTauTy, tyVarsOfType, tyVarsOfTypes,
54 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
55 boxedTypeKind, mkArrowKind,
58 import Subst ( mkTopTyVarSubst, substTheta )
59 import UsageSPUtils ( unannotTy )
60 import VarSet ( elemVarSet, mkVarSet )
61 import TyCon ( tyConDataCons )
62 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
63 floatPrimTy, addrPrimTy
65 import TysWiredIn ( boolTy, charTy, stringTy )
66 import PrelInfo ( ioTyCon_NAME )
67 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
69 import Unique ( cCallableClassKey, cReturnableClassKey,
70 enumFromClassOpKey, enumFromThenClassOpKey,
71 enumFromToClassOpKey, enumFromThenToClassOpKey,
72 thenMClassOpKey, failMClassOpKey, returnMClassOpKey
75 import Maybes ( maybeToBool )
76 import ListSetOps ( minusList )
80 %************************************************************************
82 \subsection{Main wrappers}
84 %************************************************************************
87 tcExpr :: RenamedHsExpr -- Expession to type check
88 -> TcType -- Expected type (could be a polytpye)
89 -> TcM s (TcExpr, LIE)
91 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
92 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
95 | otherwise = -- Monomorphic case
100 %************************************************************************
102 \subsection{@tcPolyExpr@ typchecks an application}
104 %************************************************************************
107 -- tcPolyExpr is like tcMonoExpr, except that the expected type
108 -- can be a polymorphic one.
109 tcPolyExpr :: RenamedHsExpr
110 -> TcType -- Expected type
111 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
112 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
114 tcPolyExpr arg expected_arg_ty
115 = -- Ha! The argument type of the function is a for-all type,
116 -- An example of rank-2 polymorphism.
118 -- To ensure that the forall'd type variables don't get unified with each
119 -- other or any other types, we make fresh copy of the alleged type
120 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
122 (sig_theta, sig_tau) = splitRhoTy sig_rho
124 -- Type-check the arg and unify with expected type
125 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
127 -- Check that the sig_tyvars havn't been constrained
128 -- The interesting bit here is that we must include the free variables
129 -- of the expected arg ty. Here's an example:
130 -- runST (newVar True)
131 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
132 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
133 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
134 -- So now s' isn't unconstrained because it's linked to a.
135 -- Conclusion: include the free vars of the expected arg type in the
136 -- list of "free vars" for the signature check.
138 tcExtendGlobalTyVars (tyVarsOfType expected_arg_ty) $
139 tcAddErrCtxtM (sigCtxt sig_msg expected_arg_ty) $
141 checkSigTyVars sig_tyvars `thenTc` \ zonked_sig_tyvars ->
143 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
144 -- ToDo: better origin
147 (mkVarSet zonked_sig_tyvars)
148 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
151 -- This HsLet binds any Insts which came out of the simplification.
152 -- It's a bit out of place here, but using AbsBind involves inventing
153 -- a couple of new names which seems worse.
154 generalised_arg = TyLam zonked_sig_tyvars $
159 returnTc ( generalised_arg, free_insts,
160 arg', sig_tau, lie_arg )
162 sig_msg ty = sep [ptext SLIT("In an expression with expected type:"),
166 %************************************************************************
168 \subsection{The TAUT rules for variables}
170 %************************************************************************
173 tcMonoExpr :: RenamedHsExpr -- Expession to type check
174 -> TcTauType -- Expected type (could be a type variable)
175 -> TcM s (TcExpr, LIE)
177 tcMonoExpr (HsVar name) res_ty
178 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
179 unifyTauTy res_ty id_ty `thenTc_`
181 -- Check that the result type doesn't have any nested for-alls.
182 -- For example, a "build" on its own is no good; it must be
183 -- applied to something.
184 checkTc (isTauTy id_ty)
185 (lurkingRank2Err name id_ty) `thenTc_`
187 returnTc (expr', lie)
190 %************************************************************************
192 \subsection{Literals}
194 %************************************************************************
199 tcMonoExpr (HsLit (HsInt i)) res_ty
200 = newOverloadedLit (LiteralOrigin (HsInt i))
201 (OverloadedIntegral i)
202 res_ty `thenNF_Tc` \ stuff ->
205 tcMonoExpr (HsLit (HsFrac f)) res_ty
206 = newOverloadedLit (LiteralOrigin (HsFrac f))
207 (OverloadedFractional f)
208 res_ty `thenNF_Tc` \ stuff ->
212 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
213 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
214 newDicts (LitLitOrigin (_UNPK_ s))
215 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
216 returnTc (HsLitOut lit res_ty, dicts)
222 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
223 = unifyTauTy res_ty charPrimTy `thenTc_`
224 returnTc (HsLitOut lit charPrimTy, emptyLIE)
226 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
227 = unifyTauTy res_ty addrPrimTy `thenTc_`
228 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
230 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
231 = unifyTauTy res_ty intPrimTy `thenTc_`
232 returnTc (HsLitOut lit intPrimTy, emptyLIE)
234 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
235 = unifyTauTy res_ty floatPrimTy `thenTc_`
236 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
238 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
239 = unifyTauTy res_ty doublePrimTy `thenTc_`
240 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
243 Unoverloaded literals:
246 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
247 = unifyTauTy res_ty charTy `thenTc_`
248 returnTc (HsLitOut lit charTy, emptyLIE)
250 tcMonoExpr (HsLit lit@(HsString str)) res_ty
251 = unifyTauTy res_ty stringTy `thenTc_`
252 returnTc (HsLitOut lit stringTy, emptyLIE)
255 %************************************************************************
257 \subsection{Other expression forms}
259 %************************************************************************
262 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
263 = tcMonoExpr expr res_ty
265 -- perform the negate *before* overloading the integer, since the case
266 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
267 -- convenient to do it here.
269 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
270 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
272 tcMonoExpr (NegApp expr neg) res_ty
273 = tcMonoExpr (HsApp neg expr) res_ty
275 tcMonoExpr (HsLam match) res_ty
276 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
277 returnTc (HsLam match', lie)
279 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
281 accum (HsApp e1 e2) args = accum e1 (e2:args)
283 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
284 returnTc (foldl HsApp fun' args', lie)
286 -- equivalent to (op e1) e2:
287 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
288 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
289 returnTc (OpApp arg1' op' fix arg2', lie)
292 Note that the operators in sections are expected to be binary, and
293 a type error will occur if they aren't.
296 -- Left sections, equivalent to
303 tcMonoExpr in_expr@(SectionL arg op) res_ty
304 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
306 -- Check that res_ty is a function type
307 -- Without this check we barf in the desugarer on
309 -- because it tries to desugar to
310 -- f op = \r -> 3 op r
311 -- so (3 `op`) had better be a function!
312 tcAddErrCtxt (sectionLAppCtxt in_expr) $
313 unifyFunTy res_ty `thenTc_`
315 returnTc (SectionL arg' op', lie)
317 -- Right sections, equivalent to \ x -> x op expr, or
320 tcMonoExpr in_expr@(SectionR op expr) res_ty
321 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
322 tcAddErrCtxt (sectionRAppCtxt in_expr) $
323 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
324 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
325 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
326 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
329 The interesting thing about @ccall@ is that it is just a template
330 which we instantiate by filling in details about the types of its
331 argument and result (ie minimal typechecking is performed). So, the
332 basic story is that we allocate a load of type variables (to hold the
333 arg/result types); unify them with the args/result; and store them for
337 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
338 = -- Get the callable and returnable classes.
339 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
340 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
341 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
343 new_arg_dict (arg, arg_ty)
344 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
345 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
346 returnNF_Tc arg_dicts -- Actually a singleton bag
348 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
352 let n_args = length args
353 tv_idxs | n_args == 0 = []
354 | otherwise = [1..n_args]
356 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
357 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
359 -- The argument types can be unboxed or boxed; the result
360 -- type must, however, be boxed since it's an argument to the IO
362 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
364 io_result_ty = mkTyConApp ioTyCon [result_ty]
365 [ioDataCon] = tyConDataCons ioTyCon
367 unifyTauTy res_ty io_result_ty `thenTc_`
369 -- Construct the extra insts, which encode the
370 -- constraints on the argument and result types.
371 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
372 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
373 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
374 (CCall lbl args' may_gc is_asm result_ty),
375 -- do the wrapping in the newtype constructor here
376 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
380 tcMonoExpr (HsSCC lbl expr) res_ty
381 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
382 returnTc (HsSCC lbl expr', lie)
384 tcMonoExpr (HsLet binds expr) res_ty
387 binds -- Bindings to check
388 tc_expr `thenTc` \ (expr', lie) ->
389 returnTc (expr', lie)
391 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
392 returnTc (expr', lie)
393 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
395 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
396 = tcAddSrcLoc src_loc $
397 tcAddErrCtxt (caseCtxt in_expr) $
399 -- Typecheck the case alternatives first.
400 -- The case patterns tend to give good type info to use
401 -- when typechecking the scrutinee. For example
404 -- will report that map is applied to too few arguments
406 -- Not only that, but it's better to check the matches on their
407 -- own, so that we get the expected results for scoped type variables.
409 -- (p::a, q::b) -> (q,p)
410 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
411 -- claimed by the pattern signatures. But if we typechecked the
412 -- match with x in scope and x's type as the expected type, we'd be hosed.
414 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
416 tcAddErrCtxt (caseScrutCtxt scrut) (
417 tcMonoExpr scrut scrut_ty
418 ) `thenTc` \ (scrut',lie1) ->
420 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
422 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
423 = tcAddSrcLoc src_loc $
424 tcAddErrCtxt (predCtxt pred) (
425 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
427 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
428 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
429 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
433 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
434 = tcDoStmts do_or_lc stmts src_loc res_ty
438 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
439 = unifyListTy res_ty `thenTc` \ elt_ty ->
440 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
441 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
444 = tcAddErrCtxt (listCtxt expr) $
445 tcMonoExpr expr elt_ty
447 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
449 then unifyTupleTy (length exprs) res_ty
450 else unifyUnboxedTupleTy (length exprs) res_ty
451 ) `thenTc` \ arg_tys ->
452 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
453 (exprs `zip` arg_tys) -- we know they're of equal length.
454 `thenTc` \ (exprs', lies) ->
455 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
457 tcMonoExpr (RecordCon con_name rbinds) res_ty
458 = tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
460 (_, record_ty) = splitFunTys con_tau
462 -- Con is syntactically constrained to be a data constructor
463 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
464 unifyTauTy res_ty record_ty `thenTc_`
466 -- Check that the record bindings match the constructor
467 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
469 bad_fields = badFields rbinds data_con
471 if not (null bad_fields) then
472 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
473 failTc -- Fail now, because tcRecordBinds will crash on a bad field
476 -- Typecheck the record bindings
477 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
479 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
482 -- The main complication with RecordUpd is that we need to explicitly
483 -- handle the *non-updated* fields. Consider:
485 -- data T a b = MkT1 { fa :: a, fb :: b }
486 -- | MkT2 { fa :: a, fc :: Int -> Int }
487 -- | MkT3 { fd :: a }
489 -- upd :: T a b -> c -> T a c
490 -- upd t x = t { fb = x}
492 -- The type signature on upd is correct (i.e. the result should not be (T a b))
493 -- because upd should be equivalent to:
495 -- upd t x = case t of
496 -- MkT1 p q -> MkT1 p x
497 -- MkT2 a b -> MkT2 p b
498 -- MkT3 d -> error ...
500 -- So we need to give a completely fresh type to the result record,
501 -- and then constrain it by the fields that are *not* updated ("p" above).
503 -- Note that because MkT3 doesn't contain all the fields being updated,
504 -- its RHS is simply an error, so it doesn't impose any type constraints
506 -- All this is done in STEP 4 below.
508 tcMonoExpr (RecordUpd record_expr rbinds) res_ty
509 = tcAddErrCtxt recordUpdCtxt $
512 -- Check that the field names are really field names
513 ASSERT( not (null rbinds) )
515 field_names = [field_name | (field_name, _, _) <- rbinds]
517 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
519 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
522 Just sel_id -> not (isRecordSelector sel_id)
525 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
526 if not (null bad_guys) then
531 -- Figure out the tycon and data cons from the first field name
533 (Just sel_id : _) = maybe_sel_ids
534 (_, tau) = ASSERT( isNotUsgTy (idType sel_id) )
535 splitForAllTys (idType sel_id)
536 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
537 (tycon, _, data_cons) = splitAlgTyConApp data_ty
538 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
540 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
543 -- Check that at least one constructor has all the named fields
544 -- i.e. has an empty set of bad fields returned by badFields
545 checkTc (any (null . badFields rbinds) data_cons)
546 (badFieldsUpd rbinds) `thenTc_`
549 -- Typecheck the update bindings.
550 -- (Do this after checking for bad fields in case there's a field that
551 -- doesn't match the constructor.)
553 result_record_ty = mkTyConApp tycon result_inst_tys
555 unifyTauTy res_ty result_record_ty `thenTc_`
556 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
559 -- Use the un-updated fields to find a vector of booleans saying
560 -- which type arguments must be the same in updatee and result.
562 -- WARNING: this code assumes that all data_cons in a common tycon
563 -- have FieldLabels abstracted over the same tyvars.
565 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
566 con_field_lbls_s = map dataConFieldLabels data_cons
568 -- A constructor is only relevant to this process if
569 -- it contains all the fields that are being updated
570 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
571 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
573 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
574 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
576 mk_inst_ty (tyvar, result_inst_ty)
577 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
578 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
580 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
583 -- Typecheck the expression to be updated
585 record_ty = mkTyConApp tycon inst_tys
587 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
590 -- Figure out the LIE we need. We have to generate some
591 -- dictionaries for the data type context, since we are going to
592 -- do some construction.
594 -- What dictionaries do we need? For the moment we assume that all
595 -- data constructors have the same context, and grab it from the first
596 -- constructor. If they have varying contexts then we'd have to
597 -- union the ones that could participate in the update.
599 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
600 inst_env = mkTopTyVarSubst tyvars result_inst_tys
601 theta' = substTheta inst_env theta
603 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
606 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
607 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
609 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
610 = unifyListTy res_ty `thenTc` \ elt_ty ->
611 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
613 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
614 newMethod (ArithSeqOrigin seq)
615 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
617 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
620 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
621 = tcAddErrCtxt (arithSeqCtxt in_expr) $
622 unifyListTy res_ty `thenTc` \ elt_ty ->
623 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
624 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
625 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
626 newMethod (ArithSeqOrigin seq)
627 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
629 returnTc (ArithSeqOut (HsVar enum_from_then_id)
630 (FromThen expr1' expr2'),
631 lie1 `plusLIE` lie2 `plusLIE` lie3)
633 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
634 = tcAddErrCtxt (arithSeqCtxt in_expr) $
635 unifyListTy res_ty `thenTc` \ elt_ty ->
636 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
637 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
638 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
639 newMethod (ArithSeqOrigin seq)
640 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
642 returnTc (ArithSeqOut (HsVar enum_from_to_id)
643 (FromTo expr1' expr2'),
644 lie1 `plusLIE` lie2 `plusLIE` lie3)
646 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
647 = tcAddErrCtxt (arithSeqCtxt in_expr) $
648 unifyListTy res_ty `thenTc` \ elt_ty ->
649 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
650 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
651 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
652 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
653 newMethod (ArithSeqOrigin seq)
654 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
656 returnTc (ArithSeqOut (HsVar eft_id)
657 (FromThenTo expr1' expr2' expr3'),
658 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
661 %************************************************************************
663 \subsection{Expressions type signatures}
665 %************************************************************************
668 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
669 = tcSetErrCtxt (exprSigCtxt in_expr) $
670 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
672 if not (isForAllTy sig_tc_ty) then
674 unifyTauTy sig_tc_ty res_ty `thenTc_`
675 tcMonoExpr expr sig_tc_ty
677 else -- Signature is polymorphic
678 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
680 -- Now match the signature type with res_ty.
681 -- We must not do this earlier, because res_ty might well
682 -- mention variables free in the environment, and we'd get
683 -- bogus complaints about not being able to for-all the
685 unifyTauTy res_ty expr_ty `thenTc_`
687 -- If everything is ok, return the stuff unchanged, except for
688 -- the effect of any substutions etc. We simply discard the
689 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
690 -- resolution it may have done, which is recorded in the
695 Typecheck expression which in most cases will be an Id.
698 tcExpr_id :: RenamedHsExpr
704 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
706 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
707 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
708 returnTc (id_expr', lie_id, id_ty)
711 %************************************************************************
713 \subsection{@tcApp@ typchecks an application}
715 %************************************************************************
719 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
720 -> TcType -- Expected result type of application
721 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
724 tcApp fun args res_ty
725 = -- First type-check the function
726 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
728 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
729 split_fun_ty fun_ty (length args)
730 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
732 -- Unify with expected result before type-checking the args
733 -- This is when we might detect a too-few args situation
734 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
735 unifyTauTy res_ty actual_result_ty
738 -- Now typecheck the args
739 mapAndUnzipTc (tcArg fun)
740 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
742 -- Check that the result type doesn't have any nested for-alls.
743 -- For example, a "build" on its own is no good; it must be applied to something.
744 checkTc (isTauTy actual_result_ty)
745 (lurkingRank2Err fun fun_ty) `thenTc_`
747 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
750 -- If an error happens we try to figure out whether the
751 -- function has been given too many or too few arguments,
753 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
754 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
755 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
757 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
758 (env2, act_ty'') = tidyOpenType env1 act_ty'
759 (exp_args, _) = splitFunTys exp_ty''
760 (act_args, _) = splitFunTys act_ty''
762 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
763 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
764 | otherwise = appCtxt fun args
766 returnNF_Tc (env2, message)
769 split_fun_ty :: TcType -- The type of the function
770 -> Int -- Number of arguments
771 -> TcM s ([TcType], -- Function argument types
772 TcType) -- Function result types
774 split_fun_ty fun_ty 0
775 = returnTc ([], fun_ty)
777 split_fun_ty fun_ty n
778 = -- Expect the function to have type A->B
779 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
780 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
781 returnTc (arg_ty:arg_tys, final_res_ty)
785 tcArg :: RenamedHsExpr -- The function (for error messages)
786 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
787 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
789 tcArg the_fun (arg, expected_arg_ty, arg_no)
790 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
791 tcExpr arg expected_arg_ty
795 %************************************************************************
797 \subsection{@tcId@ typchecks an identifier occurrence}
799 %************************************************************************
801 Between the renamer and the first invocation of the UsageSP inference,
802 identifiers read from interface files will have usage information in
803 their types, whereas other identifiers will not. The unannotTy here
804 in @tcId@ prevents this information from pointlessly propagating
805 further prior to the first usage inference.
808 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
811 = -- Look up the Id and instantiate its type
812 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
815 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
817 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
818 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
819 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
822 -- The instantiate_it loop runs round instantiating the Id.
823 -- It has to be a loop because we are now prepared to entertain
825 -- f:: forall a. Eq a => forall b. Baz b => tau
826 -- We want to instantiate this to
827 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
828 instantiate_it orig fun ty
829 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
830 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
831 instantiate_it2 orig fun tyvars theta tau
833 instantiate_it2 orig fun tyvars theta tau
834 = if null theta then -- Is it overloaded?
835 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
837 -- Yes, it's overloaded
838 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
839 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
840 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
843 arg_tys = mkTyVarTys tyvars
846 %************************************************************************
848 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
850 %************************************************************************
853 tcDoStmts do_or_lc stmts src_loc res_ty
854 = -- get the Monad and MonadZero classes
855 -- create type consisting of a fresh monad tyvar
856 ASSERT( not (null stmts) )
857 tcAddSrcLoc src_loc $
859 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
860 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
861 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
863 -- If it's a comprehension we're dealing with,
864 -- force it to be a list comprehension.
865 -- (as of Haskell 98, monad comprehensions are no more.)
867 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
868 _ -> returnTc ()) `thenTc_`
870 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
872 -- Build the then and zero methods in case we need them
873 -- It's important that "then" and "return" appear just once in the final LIE,
874 -- not only for typechecker efficiency, but also because otherwise during
875 -- simplification we end up with silly stuff like
876 -- then = case d of (t,r) -> t
878 -- where the second "then" sees that it already exists in the "available" stuff.
880 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
881 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
882 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
883 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
884 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
885 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
887 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
889 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
890 stmts_lie `plusLIE` monad_lie)
894 %************************************************************************
896 \subsection{Record bindings}
898 %************************************************************************
900 Game plan for record bindings
901 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
904 1. look up "field", to find its selector Id, which must have type
905 forall a1..an. T a1 .. an -> tau
906 where tau is the type of the field.
908 2. Instantiate this type
910 3. Unify the (T a1 .. an) part with the "expected result type", which
911 is passed in. This checks that all the field labels come from the
914 4. Type check the value using tcArg, passing tau as the expected
917 This extends OK when the field types are universally quantified.
919 Actually, to save excessive creation of fresh type variables,
924 :: TcType -- Expected type of whole record
925 -> RenamedRecordBinds
926 -> TcM s (TcRecordBinds, LIE)
928 tcRecordBinds expected_record_ty rbinds
929 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
930 returnTc (rbinds', plusLIEs lies)
932 do_bind (field_label, rhs, pun_flag)
933 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
934 ASSERT( isRecordSelector sel_id )
935 -- This lookup and assertion will surely succeed, because
936 -- we check that the fields are indeed record selectors
937 -- before calling tcRecordBinds
939 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
941 -- Record selectors all have type
942 -- forall a1..an. T a1 .. an -> tau
943 ASSERT( maybeToBool (splitFunTy_maybe tau) )
945 -- Selector must have type RecordType -> FieldType
946 Just (record_ty, field_ty) = splitFunTy_maybe tau
948 unifyTauTy expected_record_ty record_ty `thenTc_`
949 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
950 returnTc ((sel_id, rhs', pun_flag), lie)
952 badFields rbinds data_con
953 = [field_name | (field_name, _, _) <- rbinds,
954 not (field_name `elem` field_names)
957 field_names = map fieldLabelName (dataConFieldLabels data_con)
960 %************************************************************************
962 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
964 %************************************************************************
967 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
969 tcMonoExprs [] [] = returnTc ([], emptyLIE)
970 tcMonoExprs (expr:exprs) (ty:tys)
971 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
972 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
973 returnTc (expr':exprs', lie1 `plusLIE` lie2)
977 % =================================================
984 pp_nest_hang :: String -> SDoc -> SDoc
985 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
988 Boring and alphabetical:
991 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
994 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
997 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1000 = hang (ptext SLIT("In an expression with a type signature:"))
1004 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1007 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1009 sectionRAppCtxt expr
1010 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1012 sectionLAppCtxt expr
1013 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1015 funAppCtxt fun arg arg_no
1016 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1017 quotes (ppr fun) <> text ", namely"])
1018 4 (quotes (ppr arg))
1020 wrongArgsCtxt too_many_or_few fun args
1021 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1022 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1023 <+> ptext SLIT("arguments in the call"))
1024 4 (parens (ppr the_app))
1026 the_app = foldl HsApp fun args -- Used in error messages
1029 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1031 the_app = foldl HsApp fun args -- Used in error messages
1033 lurkingRank2Err fun fun_ty
1034 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1035 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1036 ptext SLIT("so that the result type has for-alls in it")])
1038 rank2ArgCtxt arg expected_arg_ty
1039 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1042 = hang (ptext SLIT("No constructor has all these fields:"))
1043 4 (pprQuotedList fields)
1045 fields = [field | (field, _, _) <- rbinds]
1047 recordUpdCtxt = ptext SLIT("In a record update construct")
1050 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1052 illegalCcallTyErr isArg ty
1053 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1057 | isArg = ptext SLIT("argument")
1058 | otherwise = ptext SLIT("result")