2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), DoOrListComp(..),
13 failureFreePat, collectPatBinders
15 import RnHsSyn ( RenamedHsExpr,
16 RenamedStmt, RenamedRecordBinds
18 import TcHsSyn ( TcExpr, TcStmt,
24 import BasicTypes ( RecFlag(..) )
26 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
27 LIE, emptyLIE, plusLIE, plusLIEs, newOverloadedLit,
28 newMethod, newMethodWithGivenTy, newDicts )
29 import TcBinds ( tcBindsAndThen, checkSigTyVars )
30 import TcEnv ( TcIdOcc(..), tcInstId,
31 tcLookupLocalValue, tcLookupGlobalValue, tcLookupClassByKey,
32 tcLookupGlobalValueByKey, newMonoIds,
33 tcExtendGlobalTyVars, tcLookupGlobalValueMaybe,
36 import TcMatches ( tcMatchesCase, tcMatchExpected )
37 import TcGRHSs ( tcStmt )
38 import TcMonoType ( tcHsType )
39 import TcPat ( tcPat )
40 import TcSimplify ( tcSimplifyAndCheck )
41 import TcType ( TcType, TcTauType, TcMaybe(..),
42 tcInstType, tcInstSigTcType, tcInstTyVars,
43 tcInstSigType, tcInstTcType, tcInstTheta, tcSplitRhoTy,
44 newTyVarTy, newTyVarTys, zonkTcType )
45 import TcKind ( TcKind )
47 import Class ( Class )
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType )
49 import Id ( idType, dataConFieldLabels, dataConSig, recordSelectorFieldLabel,
53 import Kind ( Kind, mkBoxedTypeKind, mkTypeKind, mkArrowKind )
54 import Name ( Name{-instance Eq-} )
55 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
56 splitFunTy_maybe, splitFunTys,
58 splitForAllTys, splitRhoTy, splitSigmaTy,
59 isTauTy, tyVarsOfType, tyVarsOfTypes,
60 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe
62 import TyVar ( emptyTyVarEnv, zipTyVarEnv,
63 elementOfTyVarSet, mkTyVarSet, tyVarSetToList
65 import TyCon ( tyConDataCons )
66 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
67 floatPrimTy, addrPrimTy
69 import TysWiredIn ( boolTy, charTy, stringTy )
70 import PrelInfo ( ioTyCon_NAME )
71 import Unify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
72 import Unique ( Unique, cCallableClassKey, cReturnableClassKey,
73 enumFromClassOpKey, enumFromThenClassOpKey,
74 enumFromToClassOpKey, enumFromThenToClassOpKey,
75 thenMClassOpKey, zeroClassOpKey, returnMClassOpKey
78 import Maybes ( maybeToBool )
79 import ListSetOps ( minusList )
83 %************************************************************************
85 \subsection{Main wrappers}
87 %************************************************************************
90 tcExpr :: RenamedHsExpr -- Expession to type check
91 -> TcType s -- Expected type (could be a polytpye)
92 -> TcM s (TcExpr s, LIE s)
94 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
95 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
98 | otherwise = -- Monomorphic case
103 %************************************************************************
105 \subsection{@tcPolyExpr@ typchecks an application}
107 %************************************************************************
110 -- tcPolyExpr is like tcMonoExpr, except that the expected type
111 -- can be a polymorphic one.
112 tcPolyExpr :: RenamedHsExpr
113 -> TcType s -- Expected type
114 -> TcM s (TcExpr s, LIE s, -- Generalised expr with expected type, and LIE
115 TcExpr s, TcTauType s, LIE s) -- Same thing, but instantiated; tau-type returned
117 tcPolyExpr arg expected_arg_ty
118 = -- Ha! The argument type of the function is a for-all type,
119 -- An example of rank-2 polymorphism.
121 -- To ensure that the forall'd type variables don't get unified with each
122 -- other or any other types, we make fresh copy of the alleged type
123 tcInstSigTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
125 (sig_theta, sig_tau) = splitRhoTy sig_rho
127 -- Type-check the arg and unify with expected type
128 tcExtendGlobalTyVars sig_tyvars (
129 tcMonoExpr arg sig_tau
130 ) `thenTc` \ (arg', lie_arg) ->
132 -- Check that the arg_tyvars havn't been constrained
133 -- The interesting bit here is that we must include the free variables
134 -- of the expected arg ty. Here's an example:
135 -- runST (newVar True)
136 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
137 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
138 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
139 -- So now s' isn't unconstrained because it's linked to a.
140 -- Conclusion: include the free vars of the expected arg type in the
141 -- list of "free vars" for the signature check.
143 tcExtendGlobalTyVars (tyVarSetToList (tyVarsOfType expected_arg_ty)) $
145 checkSigTyVars sig_tyvars sig_tau `thenTc` \ zonked_sig_tyvars ->
146 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
147 -- ToDo: better origin
151 (mkTyVarSet zonked_sig_tyvars)
152 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
155 -- This HsLet binds any Insts which came out of the simplification.
156 -- It's a bit out of place here, but using AbsBind involves inventing
157 -- a couple of new names which seems worse.
158 generalised_arg = TyLam zonked_sig_tyvars $
160 HsLet (MonoBind inst_binds [] Recursive)
163 returnTc ( generalised_arg, free_insts,
164 arg', sig_tau, lie_arg )
167 %************************************************************************
169 \subsection{The TAUT rules for variables}
171 %************************************************************************
174 tcMonoExpr :: RenamedHsExpr -- Expession to type check
175 -> TcTauType s -- Expected type (could be a type variable)
176 -> TcM s (TcExpr s, LIE s)
178 tcMonoExpr (HsVar name) res_ty
179 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
180 unifyTauTy res_ty id_ty `thenTc_`
182 -- Check that the result type doesn't have any nested for-alls.
183 -- For example, a "build" on its own is no good; it must be
184 -- applied to something.
185 checkTc (isTauTy id_ty)
186 (lurkingRank2Err name id_ty) `thenTc_`
188 returnTc (expr', lie)
191 %************************************************************************
193 \subsection{Literals}
195 %************************************************************************
200 tcMonoExpr (HsLit (HsInt i)) res_ty
201 = newOverloadedLit (LiteralOrigin (HsInt i))
202 (OverloadedIntegral i)
203 res_ty `thenNF_Tc` \ stuff ->
206 tcMonoExpr (HsLit (HsFrac f)) res_ty
207 = newOverloadedLit (LiteralOrigin (HsFrac f))
208 (OverloadedFractional f)
209 res_ty `thenNF_Tc` \ stuff ->
213 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
214 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
215 newDicts (LitLitOrigin (_UNPK_ s))
216 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
217 returnTc (HsLitOut lit res_ty, dicts)
223 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
224 = unifyTauTy res_ty charPrimTy `thenTc_`
225 returnTc (HsLitOut lit charPrimTy, emptyLIE)
227 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
228 = unifyTauTy res_ty addrPrimTy `thenTc_`
229 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
231 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
232 = unifyTauTy res_ty intPrimTy `thenTc_`
233 returnTc (HsLitOut lit intPrimTy, emptyLIE)
235 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
236 = unifyTauTy res_ty floatPrimTy `thenTc_`
237 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
239 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
240 = unifyTauTy res_ty doublePrimTy `thenTc_`
241 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
244 Unoverloaded literals:
247 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
248 = unifyTauTy res_ty charTy `thenTc_`
249 returnTc (HsLitOut lit charTy, emptyLIE)
251 tcMonoExpr (HsLit lit@(HsString str)) res_ty
252 = unifyTauTy res_ty stringTy `thenTc_`
253 returnTc (HsLitOut lit stringTy, emptyLIE)
256 %************************************************************************
258 \subsection{Other expression forms}
260 %************************************************************************
263 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
264 = tcMonoExpr expr res_ty
266 -- perform the negate *before* overloading the integer, since the case
267 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
268 -- convenient to do it here.
270 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
271 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
273 tcMonoExpr (NegApp expr neg) res_ty
274 = tcMonoExpr (HsApp neg expr) res_ty
276 tcMonoExpr (HsLam match) res_ty
277 = tcMatchExpected [] res_ty match `thenTc` \ (match',lie) ->
278 returnTc (HsLam match', lie)
280 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
282 accum (HsApp e1 e2) args = accum e1 (e2:args)
284 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
285 returnTc (foldl HsApp fun' args', lie)
287 -- equivalent to (op e1) e2:
288 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
289 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
290 returnTc (OpApp arg1' op' fix arg2', lie)
293 Note that the operators in sections are expected to be binary, and
294 a type error will occur if they aren't.
297 -- Left sections, equivalent to
304 tcMonoExpr in_expr@(SectionL arg op) res_ty
305 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
307 -- Check that res_ty is a function type
308 -- Without this check we barf in the desugarer on
310 -- because it tries to desugar to
311 -- f op = \r -> 3 op r
312 -- so (3 `op`) had better be a function!
313 tcAddErrCtxt (sectionLAppCtxt in_expr) $
314 unifyFunTy res_ty `thenTc_`
316 returnTc (SectionL arg' op', lie)
318 -- Right sections, equivalent to \ x -> x op expr, or
321 tcMonoExpr in_expr@(SectionR op expr) res_ty
322 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
323 tcAddErrCtxt (sectionRAppCtxt in_expr) $
324 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
325 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
326 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
327 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
330 The interesting thing about @ccall@ is that it is just a template
331 which we instantiate by filling in details about the types of its
332 argument and result (ie minimal typechecking is performed). So, the
333 basic story is that we allocate a load of type variables (to hold the
334 arg/result types); unify them with the args/result; and store them for
338 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
339 = -- Get the callable and returnable classes.
340 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
341 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
342 tcLookupTyCon ioTyCon_NAME `thenTc` \ (_,_,ioTyCon) ->
345 new_arg_dict (arg, arg_ty)
346 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
347 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
348 returnNF_Tc arg_dicts -- Actually a singleton bag
350 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
354 mapNF_Tc (\ _ -> newTyVarTy mkTypeKind) [1..(length args)] `thenNF_Tc` \ ty_vars ->
355 tcMonoExprs args ty_vars `thenTc` \ (args', args_lie) ->
357 -- The argument types can be unboxed or boxed; the result
358 -- type must, however, be boxed since it's an argument to the IO
360 newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ result_ty ->
362 io_result_ty = mkTyConApp ioTyCon [result_ty]
364 case tyConDataCons ioTyCon of { [ioDataCon] ->
365 unifyTauTy res_ty io_result_ty `thenTc_`
367 -- Construct the extra insts, which encode the
368 -- constraints on the argument and result types.
369 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args ty_vars) `thenNF_Tc` \ ccarg_dicts_s ->
370 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
372 returnTc (HsApp (HsVar (RealId ioDataCon) `TyApp` [result_ty])
373 (CCall lbl args' may_gc is_asm io_result_ty),
374 -- do the wrapping in the newtype constructor here
375 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
380 tcMonoExpr (HsSCC label expr) res_ty
381 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
382 returnTc (HsSCC label 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 tcMatchesCase res_ty matches `thenTc` \ (scrut_ty, matches', lie2) ->
408 tcAddErrCtxt (caseScrutCtxt scrut) (
409 tcMonoExpr scrut scrut_ty
410 ) `thenTc` \ (scrut',lie1) ->
412 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
414 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
415 = tcAddSrcLoc src_loc $
416 tcAddErrCtxt (predCtxt pred) (
417 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
419 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
420 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
421 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
425 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
426 = tcDoStmts do_or_lc stmts src_loc res_ty
430 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
431 = unifyListTy res_ty `thenTc` \ elt_ty ->
432 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
433 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
436 = tcAddErrCtxt (listCtxt expr) $
437 tcMonoExpr expr elt_ty
439 tcMonoExpr (ExplicitTuple exprs) res_ty
440 = unifyTupleTy (length exprs) res_ty `thenTc` \ arg_tys ->
441 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
442 (exprs `zip` arg_tys) -- we know they're of equal length.
443 `thenTc` \ (exprs', lies) ->
444 returnTc (ExplicitTuple exprs', plusLIEs lies)
446 tcMonoExpr (RecordCon con_name _ rbinds) res_ty
447 = tcLookupGlobalValue con_name `thenNF_Tc` \ con_id ->
448 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
450 (_, record_ty) = splitFunTys con_tau
452 -- Con is syntactically constrained to be a data constructor
453 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
454 unifyTauTy res_ty record_ty `thenTc_`
456 -- Check that the record bindings match the constructor
458 bad_fields = badFields rbinds con_id
460 checkTc (null bad_fields) (badFieldsCon con_id bad_fields) `thenTc_`
462 -- Typecheck the record bindings
463 -- (Do this after checkRecordFields in case there's a field that
464 -- doesn't match the constructor.)
465 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
467 returnTc (RecordCon (RealId con_id) con_expr rbinds', con_lie `plusLIE` rbinds_lie)
470 -- The main complication with RecordUpd is that we need to explicitly
471 -- handle the *non-updated* fields. Consider:
473 -- data T a b = MkT1 { fa :: a, fb :: b }
474 -- | MkT2 { fa :: a, fc :: Int -> Int }
475 -- | MkT3 { fd :: a }
477 -- upd :: T a b -> c -> T a c
478 -- upd t x = t { fb = x}
480 -- The type signature on upd is correct (i.e. the result should not be (T a b))
481 -- because upd should be equivalent to:
483 -- upd t x = case t of
484 -- MkT1 p q -> MkT1 p x
485 -- MkT2 a b -> MkT2 p b
486 -- MkT3 d -> error ...
488 -- So we need to give a completely fresh type to the result record,
489 -- and then constrain it by the fields that are *not* updated ("p" above).
491 -- Note that because MkT3 doesn't contain all the fields being updated,
492 -- its RHS is simply an error, so it doesn't impose any type constraints
494 -- All this is done in STEP 4 below.
496 tcMonoExpr (RecordUpd record_expr rbinds) res_ty
497 = tcAddErrCtxt recordUpdCtxt $
500 -- Figure out the tycon and data cons from the first field name
501 ASSERT( not (null rbinds) )
503 ((first_field_name, _, _) : rest) = rbinds
505 tcLookupGlobalValueMaybe first_field_name `thenNF_Tc` \ maybe_sel_id ->
506 (case maybe_sel_id of
507 Just sel_id | isRecordSelector sel_id -> returnTc sel_id
508 other -> failWithTc (notSelector first_field_name)
509 ) `thenTc` \ sel_id ->
511 (_, tau) = splitForAllTys (idType sel_id)
512 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
513 (tycon, _, data_cons) = splitAlgTyConApp data_ty
514 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
516 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
519 -- Check for bad fields
520 checkTc (any (null . badFields rbinds) data_cons)
521 (badFieldsUpd rbinds) `thenTc_`
523 -- Typecheck the update bindings.
524 -- (Do this after checking for bad fields in case there's a field that
525 -- doesn't match the constructor.)
527 result_record_ty = mkTyConApp tycon result_inst_tys
529 unifyTauTy res_ty result_record_ty `thenTc_`
530 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
533 -- Use the un-updated fields to find a vector of booleans saying
534 -- which type arguments must be the same in updatee and result.
536 -- WARNING: this code assumes that all data_cons in a common tycon
537 -- have FieldLabels abstracted over the same tyvars.
539 upd_field_lbls = [recordSelectorFieldLabel sel_id | (RealId sel_id, _, _) <- rbinds']
540 con_field_lbls_s = map dataConFieldLabels data_cons
542 -- A constructor is only relevant to this process if
543 -- it contains all the fields that are being updated
544 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
545 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
547 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
548 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
550 mk_inst_ty (tyvar, result_inst_ty)
551 | tyvar `elementOfTyVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
552 | otherwise = newTyVarTy mkBoxedTypeKind -- Fresh type
554 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
557 -- Typecheck the expression to be updated
559 record_ty = mkTyConApp tycon inst_tys
561 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
564 -- Figure out the LIE we need. We have to generate some
565 -- dictionaries for the data type context, since we are going to
566 -- do some construction.
568 -- What dictionaries do we need? For the moment we assume that all
569 -- data constructors have the same context, and grab it from the first
570 -- constructor. If they have varying contexts then we'd have to
571 -- union the ones that could participate in the update.
573 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
574 inst_env = zipTyVarEnv tyvars result_inst_tys
576 tcInstTheta inst_env theta `thenNF_Tc` \ theta' ->
577 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
580 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
581 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
583 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
584 = unifyListTy res_ty `thenTc` \ elt_ty ->
585 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
587 tcLookupGlobalValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
588 newMethod (ArithSeqOrigin seq)
589 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
591 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
594 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
595 = tcAddErrCtxt (arithSeqCtxt in_expr) $
596 unifyListTy res_ty `thenTc` \ elt_ty ->
597 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
598 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
599 tcLookupGlobalValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
600 newMethod (ArithSeqOrigin seq)
601 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
603 returnTc (ArithSeqOut (HsVar enum_from_then_id)
604 (FromThen expr1' expr2'),
605 lie1 `plusLIE` lie2 `plusLIE` lie3)
607 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
608 = tcAddErrCtxt (arithSeqCtxt in_expr) $
609 unifyListTy res_ty `thenTc` \ elt_ty ->
610 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
611 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
612 tcLookupGlobalValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
613 newMethod (ArithSeqOrigin seq)
614 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
616 returnTc (ArithSeqOut (HsVar enum_from_to_id)
617 (FromTo expr1' expr2'),
618 lie1 `plusLIE` lie2 `plusLIE` lie3)
620 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) 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 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
626 tcLookupGlobalValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
627 newMethod (ArithSeqOrigin seq)
628 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
630 returnTc (ArithSeqOut (HsVar eft_id)
631 (FromThenTo expr1' expr2' expr3'),
632 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
635 %************************************************************************
637 \subsection{Expressions type signatures}
639 %************************************************************************
642 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
643 = tcSetErrCtxt (exprSigCtxt in_expr) $
644 tcHsType poly_ty `thenTc` \ sig_ty ->
645 tcInstSigType sig_ty `thenNF_Tc` \ sig_tc_ty ->
647 if not (isForAllTy sig_tc_ty) then
649 unifyTauTy sig_tc_ty res_ty `thenTc_`
650 tcMonoExpr expr sig_tc_ty
652 else -- Signature is polymorphic
653 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
655 -- Now match the signature type with res_ty.
656 -- We must not do this earlier, because res_ty might well
657 -- mention variables free in the environment, and we'd get
658 -- bogus complaints about not being able to for-all the
660 unifyTauTy res_ty expr_ty `thenTc_`
662 -- If everything is ok, return the stuff unchanged, except for
663 -- the effect of any substutions etc. We simply discard the
664 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
665 -- resolution it may have done, which is recorded in the
670 Typecheck expression which in most cases will be an Id.
673 tcExpr_id :: RenamedHsExpr
679 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
681 other -> newTyVarTy mkTypeKind `thenNF_Tc` \ id_ty ->
682 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
683 returnTc (id_expr', lie_id, id_ty)
686 %************************************************************************
688 \subsection{@tcApp@ typchecks an application}
690 %************************************************************************
694 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
695 -> TcType s -- Expected result type of application
696 -> TcM s (TcExpr s, [TcExpr s], -- Translated fun and args
699 tcApp fun args res_ty
700 = -- First type-check the function
701 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
703 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
704 split_fun_ty fun_ty (length args)
705 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
707 -- Unify with expected result before type-checking the args
708 -- This is when we might detect a too-few args situation
709 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
710 unifyTauTy res_ty actual_result_ty
713 -- Now typecheck the args
714 mapAndUnzipTc (tcArg fun)
715 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
717 -- Check that the result type doesn't have any nested for-alls.
718 -- For example, a "build" on its own is no good; it must be applied to something.
719 checkTc (isTauTy actual_result_ty)
720 (lurkingRank2Err fun fun_ty) `thenTc_`
722 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
725 -- If an error happens we try to figure out whether the
726 -- function has been given too many or too few arguments,
728 checkArgsCtxt fun args expected_res_ty actual_res_ty
729 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
730 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
732 (exp_args, _) = splitFunTys exp_ty'
733 (act_args, _) = splitFunTys act_ty'
734 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
735 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
736 | otherwise = appCtxt fun args
741 split_fun_ty :: TcType s -- The type of the function
742 -> Int -- Number of arguments
743 -> TcM s ([TcType s], -- Function argument types
744 TcType s) -- Function result types
746 split_fun_ty fun_ty 0
747 = returnTc ([], fun_ty)
749 split_fun_ty fun_ty n
750 = -- Expect the function to have type A->B
751 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
752 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
753 returnTc (arg_ty:arg_tys, final_res_ty)
757 tcArg :: RenamedHsExpr -- The function (for error messages)
758 -> (RenamedHsExpr, TcType s, Int) -- Actual argument and expected arg type
759 -> TcM s (TcExpr s, LIE s) -- Resulting argument and LIE
761 tcArg the_fun (arg, expected_arg_ty, arg_no)
762 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
763 tcExpr arg expected_arg_ty
767 %************************************************************************
769 \subsection{@tcId@ typchecks an identifier occurrence}
771 %************************************************************************
774 tcId :: Name -> NF_TcM s (TcExpr s, LIE s, TcType s)
777 = -- Look up the Id and instantiate its type
778 tcLookupLocalValue name `thenNF_Tc` \ maybe_local ->
781 Just tc_id -> instantiate_it (TcId tc_id) (idType tc_id)
783 Nothing -> tcLookupGlobalValue name `thenNF_Tc` \ id ->
784 tcInstType emptyTyVarEnv (idType id) `thenNF_Tc` \ inst_ty ->
786 (tyvars, rho) = splitForAllTys inst_ty
788 instantiate_it2 (RealId id) tyvars rho
791 -- The instantiate_it loop runs round instantiating the Id.
792 -- It has to be a loop because we are now prepared to entertain
794 -- f:: forall a. Eq a => forall b. Baz b => tau
795 -- We want to instantiate this to
796 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
797 instantiate_it tc_id_occ ty
798 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
799 instantiate_it2 tc_id_occ tyvars rho
801 instantiate_it2 tc_id_occ tyvars rho
802 = tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
803 if null theta then -- Is it overloaded?
804 returnNF_Tc (mkHsTyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau)
806 -- Yes, it's overloaded
807 newMethodWithGivenTy (OccurrenceOf tc_id_occ)
808 tc_id_occ arg_tys theta tau `thenNF_Tc` \ (lie1, meth_id) ->
809 instantiate_it meth_id tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
810 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
813 arg_tys = mkTyVarTys tyvars
816 %************************************************************************
818 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
820 %************************************************************************
823 tcDoStmts do_or_lc stmts src_loc res_ty
824 = -- get the Monad and MonadZero classes
825 -- create type consisting of a fresh monad tyvar
826 ASSERT( not (null stmts) )
827 tcAddSrcLoc src_loc $
828 newTyVarTy (mkArrowKind mkBoxedTypeKind mkBoxedTypeKind) `thenNF_Tc` \ m ->
831 tc_stmts [] = returnTc (([], error "tc_stmts"), emptyLIE)
832 tc_stmts (stmt:stmts) = tcStmt do_or_lc (mkAppTy m) combine_stmts stmt $
835 combine_stmts stmt@(ReturnStmt _) (Just ty) ([], _) = ([stmt], ty)
836 combine_stmts stmt@(ExprStmt e _) (Just ty) ([], _) = ([stmt], ty)
837 combine_stmts stmt _ ([], _) = panic "Bad last stmt tcDoStmts"
838 combine_stmts stmt _ (stmts, ty) = (stmt:stmts, ty)
840 tc_stmts stmts `thenTc` \ ((stmts', result_ty), final_lie) ->
841 unifyTauTy res_ty result_ty `thenTc_`
843 -- Build the then and zero methods in case we need them
844 -- It's important that "then" and "return" appear just once in the final LIE,
845 -- not only for typechecker efficiency, but also because otherwise during
846 -- simplification we end up with silly stuff like
847 -- then = case d of (t,r) -> t
849 -- where the second "then" sees that it already exists in the "available" stuff.
851 tcLookupGlobalValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
852 tcLookupGlobalValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
853 tcLookupGlobalValueByKey zeroClassOpKey `thenNF_Tc` \ zero_sel_id ->
855 (RealId return_sel_id) [m] `thenNF_Tc` \ (return_lie, return_id) ->
857 (RealId then_sel_id) [m] `thenNF_Tc` \ (then_lie, then_id) ->
859 (RealId zero_sel_id) [m] `thenNF_Tc` \ (zero_lie, zero_id) ->
861 monad_lie = then_lie `plusLIE` return_lie `plusLIE` perhaps_zero_lie
862 perhaps_zero_lie | all failure_free stmts' = emptyLIE
863 | otherwise = zero_lie
865 failure_free (BindStmt pat _ _) = failureFreePat pat
866 failure_free (GuardStmt _ _) = False
867 failure_free other_stmt = True
869 returnTc (HsDoOut do_or_lc stmts' return_id then_id zero_id res_ty src_loc,
870 final_lie `plusLIE` monad_lie)
875 %************************************************************************
877 \subsection{Record bindings}
879 %************************************************************************
881 Game plan for record bindings
882 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885 1. look up "field", to find its selector Id, which must have type
886 forall a1..an. T a1 .. an -> tau
887 where tau is the type of the field.
889 2. Instantiate this type
891 3. Unify the (T a1 .. an) part with the "expected result type", which
892 is passed in. This checks that all the field labels come from the
895 4. Type check the value using tcArg, passing tau as the expected
898 This extends OK when the field types are universally quantified.
900 Actually, to save excessive creation of fresh type variables,
905 :: TcType s -- Expected type of whole record
906 -> RenamedRecordBinds
907 -> TcM s (TcRecordBinds s, LIE s)
909 tcRecordBinds expected_record_ty rbinds
910 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
911 returnTc (rbinds', plusLIEs lies)
913 do_bind (field_label, rhs, pun_flag)
914 = tcLookupGlobalValue field_label `thenNF_Tc` \ sel_id ->
915 ASSERT( isRecordSelector sel_id )
916 -- This lookup and assertion will surely succeed, because
917 -- we check that the fields are indeed record selectors
918 -- before calling tcRecordBinds
920 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
922 -- Record selectors all have type
923 -- forall a1..an. T a1 .. an -> tau
924 ASSERT( maybeToBool (splitFunTy_maybe tau) )
926 -- Selector must have type RecordType -> FieldType
927 Just (record_ty, field_ty) = splitFunTy_maybe tau
929 unifyTauTy expected_record_ty record_ty `thenTc_`
930 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
931 returnTc ((RealId sel_id, rhs', pun_flag), lie)
933 badFields rbinds data_con
934 = [field_name | (field_name, _, _) <- rbinds,
935 not (field_name `elem` field_names)
938 field_names = map fieldLabelName (dataConFieldLabels data_con)
941 %************************************************************************
943 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
945 %************************************************************************
948 tcMonoExprs :: [RenamedHsExpr] -> [TcType s] -> TcM s ([TcExpr s], LIE s)
950 tcMonoExprs [] [] = returnTc ([], emptyLIE)
951 tcMonoExprs (expr:exprs) (ty:tys)
952 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
953 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
954 returnTc (expr':exprs', lie1 `plusLIE` lie2)
958 % =================================================
965 pp_nest_hang :: String -> SDoc -> SDoc
966 pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff)
969 Boring and alphabetical:
972 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
975 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
978 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
981 = hang (ptext SLIT("In an expression with a type signature:"))
985 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
988 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
991 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
994 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
996 funAppCtxt fun arg arg_no
997 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
998 quotes (ppr fun) <> text ", namely"])
1001 wrongArgsCtxt too_many_or_few fun args
1002 = hang (ptext SLIT("Probable cause:") <+> ppr fun
1003 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1004 <+> ptext SLIT("arguments in the call"))
1005 4 (parens (ppr the_app))
1007 the_app = foldl HsApp fun args -- Used in error messages
1010 = ptext SLIT("In the application") <+> (ppr the_app)
1012 the_app = foldl HsApp fun args -- Used in error messages
1014 lurkingRank2Err fun fun_ty
1015 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1016 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1017 ptext SLIT("so that the result type has for-alls in it")])
1019 rank2ArgCtxt arg expected_arg_ty
1020 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1023 = hang (ptext SLIT("No constructor has all these fields:"))
1024 4 (pprQuotedList fields)
1026 fields = [field | (field, _, _) <- rbinds]
1028 recordUpdCtxt = ptext SLIT("In a record update construct")
1030 badFieldsCon con fields
1031 = hsep [ptext SLIT("Constructor"), ppr con,
1032 ptext SLIT("does not have field(s):"), pprQuotedList fields]
1035 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]