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 TcImprove ( tcImprove )
42 import TcType ( TcType, TcTauType,
44 tcInstTcType, tcSplitRhoTy,
45 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
47 import Class ( Class )
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
49 import Id ( idType, recordSelectorFieldLabel, isRecordSelector,
52 import DataCon ( dataConFieldLabels, dataConSig,
53 dataConStrictMarks, StrictnessMark(..)
55 import Name ( Name, getName )
56 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
58 splitFunTy_maybe, splitFunTys, isNotUsgTy,
59 mkTyConApp, splitSigmaTy,
61 isTauTy, tyVarsOfType, tyVarsOfTypes,
62 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
63 boxedTypeKind, mkArrowKind,
66 import TyCon ( tyConTyVars )
67 import Subst ( mkTopTyVarSubst, substClasses, substTy )
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 | isSigmaTy 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 tcImprove (sig_dicts `plusLIE` lie_arg) `thenTc_`
157 -- ToDo: better origin
159 (text "the type signature of an expression")
160 (mkVarSet zonked_sig_tyvars)
161 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
164 -- This HsLet binds any Insts which came out of the simplification.
165 -- It's a bit out of place here, but using AbsBind involves inventing
166 -- a couple of new names which seems worse.
167 generalised_arg = TyLam zonked_sig_tyvars $
172 returnTc ( generalised_arg, free_insts,
173 arg', sig_tau, lie_arg )
175 sig_msg = ptext SLIT("When checking an expression type signature")
178 %************************************************************************
180 \subsection{The TAUT rules for variables}
182 %************************************************************************
185 tcMonoExpr :: RenamedHsExpr -- Expession to type check
186 -> TcTauType -- Expected type (could be a type variable)
187 -> TcM s (TcExpr, LIE)
189 tcMonoExpr (HsVar name) res_ty
190 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
191 unifyTauTy res_ty id_ty `thenTc_`
193 -- Check that the result type doesn't have any nested for-alls.
194 -- For example, a "build" on its own is no good; it must be
195 -- applied to something.
196 checkTc (isTauTy id_ty)
197 (lurkingRank2Err name id_ty) `thenTc_`
199 returnTc (expr', lie)
203 tcMonoExpr (HsIPVar name) res_ty
204 -- ZZ What's the `id' used for here...
205 = let id = mkVanillaId name res_ty in
206 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
207 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
208 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
211 %************************************************************************
213 \subsection{Literals}
215 %************************************************************************
220 tcMonoExpr (HsLit (HsInt i)) res_ty
221 = newOverloadedLit (LiteralOrigin (HsInt i))
222 (OverloadedIntegral i)
223 res_ty `thenNF_Tc` \ stuff ->
226 tcMonoExpr (HsLit (HsFrac f)) res_ty
227 = newOverloadedLit (LiteralOrigin (HsFrac f))
228 (OverloadedFractional f)
229 res_ty `thenNF_Tc` \ stuff ->
233 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
234 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
235 newClassDicts (LitLitOrigin (_UNPK_ s))
236 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
237 returnTc (HsLitOut lit res_ty, dicts)
243 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
244 = unifyTauTy res_ty charPrimTy `thenTc_`
245 returnTc (HsLitOut lit charPrimTy, emptyLIE)
247 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
248 = unifyTauTy res_ty addrPrimTy `thenTc_`
249 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
251 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
252 = unifyTauTy res_ty intPrimTy `thenTc_`
253 returnTc (HsLitOut lit intPrimTy, emptyLIE)
255 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
256 = unifyTauTy res_ty floatPrimTy `thenTc_`
257 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
259 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
260 = unifyTauTy res_ty doublePrimTy `thenTc_`
261 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
264 Unoverloaded literals:
267 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
268 = unifyTauTy res_ty charTy `thenTc_`
269 returnTc (HsLitOut lit charTy, emptyLIE)
271 tcMonoExpr (HsLit lit@(HsString str)) res_ty
272 = unifyTauTy res_ty stringTy `thenTc_`
273 returnTc (HsLitOut lit stringTy, emptyLIE)
276 %************************************************************************
278 \subsection{Other expression forms}
280 %************************************************************************
283 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
284 = tcMonoExpr expr res_ty
286 -- perform the negate *before* overloading the integer, since the case
287 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
288 -- convenient to do it here.
290 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
291 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
293 tcMonoExpr (NegApp expr neg) res_ty
294 = tcMonoExpr (HsApp neg expr) res_ty
296 tcMonoExpr (HsLam match) res_ty
297 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
298 returnTc (HsLam match', lie)
300 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
302 accum (HsApp e1 e2) args = accum e1 (e2:args)
304 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
305 returnTc (foldl HsApp fun' args', lie)
307 -- equivalent to (op e1) e2:
308 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
309 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
310 returnTc (OpApp arg1' op' fix arg2', lie)
313 Note that the operators in sections are expected to be binary, and
314 a type error will occur if they aren't.
317 -- Left sections, equivalent to
324 tcMonoExpr in_expr@(SectionL arg op) res_ty
325 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
327 -- Check that res_ty is a function type
328 -- Without this check we barf in the desugarer on
330 -- because it tries to desugar to
331 -- f op = \r -> 3 op r
332 -- so (3 `op`) had better be a function!
333 tcAddErrCtxt (sectionLAppCtxt in_expr) $
334 unifyFunTy res_ty `thenTc_`
336 returnTc (SectionL arg' op', lie)
338 -- Right sections, equivalent to \ x -> x op expr, or
341 tcMonoExpr in_expr@(SectionR op expr) res_ty
342 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
343 tcAddErrCtxt (sectionRAppCtxt in_expr) $
344 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
345 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
346 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
347 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
350 The interesting thing about @ccall@ is that it is just a template
351 which we instantiate by filling in details about the types of its
352 argument and result (ie minimal typechecking is performed). So, the
353 basic story is that we allocate a load of type variables (to hold the
354 arg/result types); unify them with the args/result; and store them for
358 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
359 = -- Get the callable and returnable classes.
360 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
361 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
362 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
364 new_arg_dict (arg, arg_ty)
365 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
366 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
367 returnNF_Tc arg_dicts -- Actually a singleton bag
369 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
373 let n_args = length args
374 tv_idxs | n_args == 0 = []
375 | otherwise = [1..n_args]
377 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
378 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
380 -- The argument types can be unboxed or boxed; the result
381 -- type must, however, be boxed since it's an argument to the IO
383 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
385 io_result_ty = mkTyConApp ioTyCon [result_ty]
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, _, _, _, _, _) = 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 (isSigmaTy 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 let expr'' = if nullMonoBinds dict_binds
736 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
739 tcCheckIPBinds binds' types ips `thenTc_`
740 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
742 = case ipName_maybe p of
743 Just n -> n `elem` names
745 names = map fst binds
746 -- revBinds is used because tcSimplify outputs the bindings
747 -- out-of-order. it's not a problem elsewhere because these
748 -- bindings are normally used in a recursive let
749 -- ZZ probably need to find a better solution
750 revBinds (b1 `AndMonoBinds` b2) =
751 (revBinds b2) `AndMonoBinds` (revBinds b1)
754 tcIPBinds ((name, expr) : binds)
755 = newTyVarTy_OpenKind `thenTc` \ ty ->
756 tcGetSrcLoc `thenTc` \ loc ->
757 let id = ipToId name ty loc in
758 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
759 zonkTcType ty `thenTc` \ ty' ->
760 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
761 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
762 tcIPBinds [] = returnTc ([], [], emptyLIE)
764 tcCheckIPBinds binds types ips
765 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
767 -- ZZ how do we use the loc?
768 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
769 = unifyTauTy t1 t2 `thenTc_`
770 tcCheckIPBind bt ips `thenTc` \ ips' ->
772 tcCheckIPBind bt (ip : ips)
773 = tcCheckIPBind bt ips `thenTc` \ ips' ->
779 Typecheck expression which in most cases will be an Id.
782 tcExpr_id :: RenamedHsExpr
788 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
790 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
791 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
792 returnTc (id_expr', lie_id, id_ty)
795 %************************************************************************
797 \subsection{@tcApp@ typchecks an application}
799 %************************************************************************
803 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
804 -> TcType -- Expected result type of application
805 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
808 tcApp fun args res_ty
809 = -- First type-check the function
810 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
812 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
813 split_fun_ty fun_ty (length args)
814 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
816 -- Unify with expected result before type-checking the args
817 -- This is when we might detect a too-few args situation
818 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
819 unifyTauTy res_ty actual_result_ty
822 -- Now typecheck the args
823 mapAndUnzipTc (tcArg fun)
824 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
826 -- Check that the result type doesn't have any nested for-alls.
827 -- For example, a "build" on its own is no good; it must be applied to something.
828 checkTc (isTauTy actual_result_ty)
829 (lurkingRank2Err fun fun_ty) `thenTc_`
831 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
834 -- If an error happens we try to figure out whether the
835 -- function has been given too many or too few arguments,
837 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
838 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
839 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
841 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
842 (env2, act_ty'') = tidyOpenType env1 act_ty'
843 (exp_args, _) = splitFunTys exp_ty''
844 (act_args, _) = splitFunTys act_ty''
846 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
847 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
848 | otherwise = appCtxt fun args
850 returnNF_Tc (env2, message)
853 split_fun_ty :: TcType -- The type of the function
854 -> Int -- Number of arguments
855 -> TcM s ([TcType], -- Function argument types
856 TcType) -- Function result types
858 split_fun_ty fun_ty 0
859 = returnTc ([], fun_ty)
861 split_fun_ty fun_ty n
862 = -- Expect the function to have type A->B
863 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
864 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
865 returnTc (arg_ty:arg_tys, final_res_ty)
869 tcArg :: RenamedHsExpr -- The function (for error messages)
870 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
871 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
873 tcArg the_fun (arg, expected_arg_ty, arg_no)
874 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
875 tcExpr arg expected_arg_ty
879 %************************************************************************
881 \subsection{@tcId@ typchecks an identifier occurrence}
883 %************************************************************************
885 Between the renamer and the first invocation of the UsageSP inference,
886 identifiers read from interface files will have usage information in
887 their types, whereas other identifiers will not. The unannotTy here
888 in @tcId@ prevents this information from pointlessly propagating
889 further prior to the first usage inference.
892 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
895 = -- Look up the Id and instantiate its type
896 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
899 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
901 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
902 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
903 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
906 -- The instantiate_it loop runs round instantiating the Id.
907 -- It has to be a loop because we are now prepared to entertain
909 -- f:: forall a. Eq a => forall b. Baz b => tau
910 -- We want to instantiate this to
911 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
912 instantiate_it orig fun ty
913 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
914 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
915 instantiate_it2 orig fun tyvars theta tau
917 instantiate_it2 orig fun tyvars theta tau
918 = if null theta then -- Is it overloaded?
919 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
921 -- Yes, it's overloaded
922 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
923 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
924 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
927 arg_tys = mkTyVarTys tyvars
930 %************************************************************************
932 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
934 %************************************************************************
937 tcDoStmts do_or_lc stmts src_loc res_ty
938 = -- get the Monad and MonadZero classes
939 -- create type consisting of a fresh monad tyvar
940 ASSERT( not (null stmts) )
941 tcAddSrcLoc src_loc $
943 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
944 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
945 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
947 -- If it's a comprehension we're dealing with,
948 -- force it to be a list comprehension.
949 -- (as of Haskell 98, monad comprehensions are no more.)
951 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
952 _ -> returnTc ()) `thenTc_`
954 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
956 -- Build the then and zero methods in case we need them
957 -- It's important that "then" and "return" appear just once in the final LIE,
958 -- not only for typechecker efficiency, but also because otherwise during
959 -- simplification we end up with silly stuff like
960 -- then = case d of (t,r) -> t
962 -- where the second "then" sees that it already exists in the "available" stuff.
964 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
965 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
966 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
967 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
968 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
969 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
971 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
973 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
974 stmts_lie `plusLIE` monad_lie)
978 %************************************************************************
980 \subsection{Record bindings}
982 %************************************************************************
984 Game plan for record bindings
985 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
986 1. Find the TyCon for the bindings, from the first field label.
988 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
990 For each binding field = value
992 3. Instantiate the field type (from the field label) using the type
995 4 Type check the value using tcArg, passing the field type as
996 the expected argument type.
998 This extends OK when the field types are universally quantified.
1003 :: TcType -- Expected type of whole record
1004 -> RenamedRecordBinds
1005 -> TcM s (TcRecordBinds, LIE)
1007 tcRecordBinds expected_record_ty rbinds
1008 = tcLookupValue first_field_lbl_name `thenNF_Tc` \ first_sel_id ->
1010 tycon = fieldLabelTyCon (recordSelectorFieldLabel first_sel_id)
1012 tcInstTyVars (tyConTyVars tycon) `thenTc` \ (_, arg_tys, tenv) ->
1013 unifyTauTy expected_record_ty
1014 (mkTyConApp tycon arg_tys) `thenTc_`
1015 mapAndUnzipTc (do_bind tycon tenv) rbinds `thenTc` \ (rbinds', lies) ->
1016 returnTc (rbinds', plusLIEs lies)
1018 (first_field_lbl_name, _, _) = head rbinds
1020 do_bind tycon tenv (field_lbl_name, rhs, pun_flag)
1021 = tcLookupValue field_lbl_name `thenNF_Tc` \ sel_id ->
1023 field_lbl = recordSelectorFieldLabel sel_id
1024 field_ty = substTy tenv (fieldLabelType field_lbl)
1026 ASSERT( isRecordSelector sel_id )
1027 -- This lookup and assertion will surely succeed, because
1028 -- we check that the fields are indeed record selectors
1029 -- before calling tcRecordBinds
1030 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
1031 -- The caller of tcRecordBinds has already checked
1032 -- that all the fields come from the same type
1034 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1036 returnTc ((sel_id, rhs', pun_flag), lie)
1038 badFields rbinds data_con
1039 = [field_name | (field_name, _, _) <- rbinds,
1040 not (field_name `elem` field_names)
1043 field_names = map fieldLabelName (dataConFieldLabels data_con)
1045 missingStrictFields rbinds data_con
1046 = [ fn | fn <- strict_field_names,
1047 not (fn `elem` field_names_used)
1050 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1051 strict_field_names = mapMaybe isStrict field_info
1053 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1054 isStrict _ = Nothing
1056 field_info = zip (dataConFieldLabels data_con)
1057 (dataConStrictMarks data_con)
1059 missingFields rbinds data_con
1060 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1062 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1064 -- missing strict fields have already been flagged as
1065 -- being so, so leave them out here.
1066 non_strict_field_names = mapMaybe isn'tStrict field_info
1068 isn'tStrict (fl, MarkedStrict) = Nothing
1069 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1071 field_info = zip (dataConFieldLabels data_con)
1072 (dataConStrictMarks data_con)
1076 %************************************************************************
1078 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1080 %************************************************************************
1083 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1085 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1086 tcMonoExprs (expr:exprs) (ty:tys)
1087 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1088 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1089 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1093 % =================================================
1100 pp_nest_hang :: String -> SDoc -> SDoc
1101 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1104 Boring and alphabetical:
1107 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1110 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1113 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1116 = hang (ptext SLIT("In an expression with a type signature:"))
1120 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1123 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1125 sectionRAppCtxt expr
1126 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1128 sectionLAppCtxt expr
1129 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1131 funAppCtxt fun arg arg_no
1132 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1133 quotes (ppr fun) <> text ", namely"])
1134 4 (quotes (ppr arg))
1136 wrongArgsCtxt too_many_or_few fun args
1137 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1138 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1139 <+> ptext SLIT("arguments in the call"))
1140 4 (parens (ppr the_app))
1142 the_app = foldl HsApp fun args -- Used in error messages
1145 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1147 the_app = foldl HsApp fun args -- Used in error messages
1149 lurkingRank2Err fun fun_ty
1150 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1151 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1152 ptext SLIT("so that the result type has for-alls in it")])
1154 rank2ArgCtxt arg expected_arg_ty
1155 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1158 = hang (ptext SLIT("No constructor has all these fields:"))
1159 4 (pprQuotedList fields)
1161 fields = [field | (field, _, _) <- rbinds]
1163 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1164 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1167 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1169 illegalCcallTyErr isArg ty
1170 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1174 | isArg = ptext SLIT("argument")
1175 | otherwise = ptext SLIT("result")
1178 missingStrictFieldCon :: Name -> Name -> SDoc
1179 missingStrictFieldCon con field
1180 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1181 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1183 missingFieldCon :: Name -> Name -> SDoc
1184 missingFieldCon con field
1185 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1186 ptext SLIT("is not initialised")]