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 MonoBinds(..), StmtCtxt(..),
13 mkMonoBind, nullMonoBinds
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds, mkHsTyApp, mkHsLet )
19 import BasicTypes ( RecFlag(..) )
21 import Inst ( InstOrigin(..),
22 LIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
23 newOverloadedLit, newMethod, newIPDict,
24 instOverloadedFun, newDicts, newClassDicts,
25 getIPsOfLIE, instToId, ipToId
27 import TcBinds ( tcBindsAndThen )
28 import TcEnv ( tcInstId,
29 tcLookupValue, tcLookupClass, tcLookupGlobalId,
30 tcLookupTyCon, tcLookupDataCon,
31 tcExtendGlobalTyVars, tcLookupValueMaybe,
33 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
34 import TcMonoType ( tcHsSigType, checkSigTyVars, sigCtxt )
35 import TcPat ( badFieldCon, simpleHsLitTy )
36 import TcSimplify ( tcSimplifyAndCheck, partitionPredsOfLIE )
37 import TcImprove ( tcImprove )
38 import TcType ( TcType, TcTauType,
40 tcInstTcType, tcSplitRhoTy,
41 newTyVarTy, newTyVarTys, zonkTcType )
43 import FieldLabel ( fieldLabelName, fieldLabelType, fieldLabelTyCon )
44 import Id ( idType, recordSelectorFieldLabel, isRecordSelector, mkVanillaId )
45 import DataCon ( dataConFieldLabels, dataConSig,
46 dataConStrictMarks, StrictnessMark(..)
48 import Name ( Name, getName )
49 import Type ( mkFunTy, mkAppTy, mkTyVarTys, ipName_maybe,
50 splitFunTy_maybe, splitFunTys, isNotUsgTy,
51 mkTyConApp, splitSigmaTy,
53 isTauTy, tyVarsOfType, tyVarsOfTypes,
54 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
55 boxedTypeKind, openTypeKind, mkArrowKind,
58 import TyCon ( TyCon, tyConTyVars )
59 import Subst ( mkTopTyVarSubst, substClasses, substTy )
60 import UsageSPUtils ( unannotTy )
61 import VarSet ( elemVarSet, mkVarSet )
62 import TysWiredIn ( boolTy )
63 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
64 import PrelNames ( cCallableClassKey, cReturnableClassKey,
65 enumFromClassOpKey, enumFromThenClassOpKey,
66 enumFromToClassOpKey, enumFromThenToClassOpKey,
67 thenMClassOpKey, failMClassOpKey, returnMClassOpKey, ioTyConKey
70 import Maybes ( maybeToBool, mapMaybe )
71 import ListSetOps ( minusList )
73 import CmdLineOpts ( opt_WarnMissingFields )
77 %************************************************************************
79 \subsection{Main wrappers}
81 %************************************************************************
84 tcExpr :: RenamedHsExpr -- Expession to type check
85 -> TcType -- Expected type (could be a polytpye)
88 tcExpr expr ty | isSigmaTy ty = -- Polymorphic case
89 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
92 | otherwise = -- Monomorphic case
97 %************************************************************************
99 \subsection{@tcPolyExpr@ typchecks an application}
101 %************************************************************************
104 -- tcPolyExpr is like tcMonoExpr, except that the expected type
105 -- can be a polymorphic one.
106 tcPolyExpr :: RenamedHsExpr
107 -> TcType -- Expected type
108 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
109 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
111 tcPolyExpr arg expected_arg_ty
112 = -- Ha! The argument type of the function is a for-all type,
113 -- An example of rank-2 polymorphism.
115 -- To ensure that the forall'd type variables don't get unified with each
116 -- other or any other types, we make fresh copy of the alleged type
117 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
119 (sig_theta, sig_tau) = splitRhoTy sig_rho
120 free_tyvars = tyVarsOfType expected_arg_ty
122 -- Type-check the arg and unify with expected type
123 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
125 -- Check that the sig_tyvars havn't been constrained
126 -- The interesting bit here is that we must include the free variables
127 -- of the expected arg ty. Here's an example:
128 -- runST (newVar True)
129 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
130 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
131 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
132 -- So now s' isn't unconstrained because it's linked to a.
133 -- Conclusion: include the free vars of the expected arg type in the
134 -- list of "free vars" for the signature check.
136 tcExtendGlobalTyVars free_tyvars $
137 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
139 checkSigTyVars sig_tyvars free_tyvars `thenTc` \ zonked_sig_tyvars ->
141 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
142 tcImprove (sig_dicts `plusLIE` lie_arg) `thenTc_`
143 -- ToDo: better origin
145 (text "the type signature of an expression")
146 (mkVarSet zonked_sig_tyvars)
147 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
150 -- This HsLet binds any Insts which came out of the simplification.
151 -- It's a bit out of place here, but using AbsBind involves inventing
152 -- a couple of new names which seems worse.
153 generalised_arg = TyLam zonked_sig_tyvars $
158 returnTc ( generalised_arg, free_insts,
159 arg', sig_tau, lie_arg )
161 sig_msg = ptext SLIT("When checking an expression type signature")
164 %************************************************************************
166 \subsection{The TAUT rules for variables}
168 %************************************************************************
171 tcMonoExpr :: RenamedHsExpr -- Expession to type check
172 -> TcTauType -- Expected type (could be a type variable)
175 tcMonoExpr (HsVar name) res_ty
176 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
177 unifyTauTy res_ty id_ty `thenTc_`
179 -- Check that the result type doesn't have any nested for-alls.
180 -- For example, a "build" on its own is no good; it must be
181 -- applied to something.
182 checkTc (isTauTy id_ty)
183 (lurkingRank2Err name id_ty) `thenTc_`
185 returnTc (expr', lie)
189 tcMonoExpr (HsIPVar name) res_ty
190 -- ZZ What's the `id' used for here...
191 = let id = mkVanillaId name res_ty in
192 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
193 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
194 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
197 %************************************************************************
199 \subsection{Other expression forms}
201 %************************************************************************
204 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
205 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
206 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
208 tcMonoExpr (NegApp expr neg) res_ty
209 = tcMonoExpr (HsApp (HsVar neg) expr) res_ty
211 tcMonoExpr (HsLam match) res_ty
212 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
213 returnTc (HsLam match', lie)
215 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
217 accum (HsApp e1 e2) args = accum e1 (e2:args)
219 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
220 returnTc (foldl HsApp fun' args', lie)
222 -- equivalent to (op e1) e2:
223 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
224 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
225 returnTc (OpApp arg1' op' fix arg2', lie)
228 Note that the operators in sections are expected to be binary, and
229 a type error will occur if they aren't.
232 -- Left sections, equivalent to
239 tcMonoExpr in_expr@(SectionL arg op) res_ty
240 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
242 -- Check that res_ty is a function type
243 -- Without this check we barf in the desugarer on
245 -- because it tries to desugar to
246 -- f op = \r -> 3 op r
247 -- so (3 `op`) had better be a function!
248 tcAddErrCtxt (sectionLAppCtxt in_expr) $
249 unifyFunTy res_ty `thenTc_`
251 returnTc (SectionL arg' op', lie)
253 -- Right sections, equivalent to \ x -> x op expr, or
256 tcMonoExpr in_expr@(SectionR op expr) res_ty
257 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
258 tcAddErrCtxt (sectionRAppCtxt in_expr) $
259 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
260 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
261 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
262 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
265 The interesting thing about @ccall@ is that it is just a template
266 which we instantiate by filling in details about the types of its
267 argument and result (ie minimal typechecking is performed). So, the
268 basic story is that we allocate a load of type variables (to hold the
269 arg/result types); unify them with the args/result; and store them for
273 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
274 = -- Get the callable and returnable classes.
275 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
276 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
277 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
279 new_arg_dict (arg, arg_ty)
280 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
281 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
282 returnNF_Tc arg_dicts -- Actually a singleton bag
284 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
288 let n_args = length args
289 tv_idxs | n_args == 0 = []
290 | otherwise = [1..n_args]
292 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
293 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
295 -- The argument types can be unboxed or boxed; the result
296 -- type must, however, be boxed since it's an argument to the IO
298 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
300 io_result_ty = mkTyConApp ioTyCon [result_ty]
302 unifyTauTy res_ty io_result_ty `thenTc_`
304 -- Construct the extra insts, which encode the
305 -- constraints on the argument and result types.
306 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
307 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
308 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
309 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
313 tcMonoExpr (HsSCC lbl expr) res_ty
314 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
315 returnTc (HsSCC lbl expr', lie)
317 tcMonoExpr (HsLet binds expr) res_ty
320 binds -- Bindings to check
321 tc_expr `thenTc` \ (expr', lie) ->
322 returnTc (expr', lie)
324 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
325 returnTc (expr', lie)
326 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
328 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
329 = tcAddSrcLoc src_loc $
330 tcAddErrCtxt (caseCtxt in_expr) $
332 -- Typecheck the case alternatives first.
333 -- The case patterns tend to give good type info to use
334 -- when typechecking the scrutinee. For example
337 -- will report that map is applied to too few arguments
339 -- Not only that, but it's better to check the matches on their
340 -- own, so that we get the expected results for scoped type variables.
342 -- (p::a, q::b) -> (q,p)
343 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
344 -- claimed by the pattern signatures. But if we typechecked the
345 -- match with x in scope and x's type as the expected type, we'd be hosed.
347 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
349 tcAddErrCtxt (caseScrutCtxt scrut) (
350 tcMonoExpr scrut scrut_ty
351 ) `thenTc` \ (scrut',lie1) ->
353 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
355 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
356 = tcAddSrcLoc src_loc $
357 tcAddErrCtxt (predCtxt pred) (
358 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
360 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
361 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
362 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
366 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
367 = tcDoStmts do_or_lc stmts src_loc res_ty
371 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
372 = unifyListTy res_ty `thenTc` \ elt_ty ->
373 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
374 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
377 = tcAddErrCtxt (listCtxt expr) $
378 tcMonoExpr expr elt_ty
380 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
381 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
382 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
383 (exprs `zip` arg_tys) -- we know they're of equal length.
384 `thenTc` \ (exprs', lies) ->
385 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
387 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
388 = tcAddErrCtxt (recordConCtxt expr) $
389 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
391 (_, record_ty) = splitFunTys con_tau
392 (tycon, ty_args, _) = splitAlgTyConApp record_ty
394 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
395 unifyTauTy res_ty record_ty `thenTc_`
397 -- Check that the record bindings match the constructor
398 -- con_name is syntactically constrained to be a data constructor
399 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
401 bad_fields = badFields rbinds data_con
403 if not (null bad_fields) then
404 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
405 failTc -- Fail now, because tcRecordBinds will crash on a bad field
408 -- Typecheck the record bindings
409 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
412 missing_s_fields = missingStrictFields rbinds data_con
414 checkTcM (null missing_s_fields)
415 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
416 returnNF_Tc ()) `thenNF_Tc_`
418 missing_fields = missingFields rbinds data_con
420 checkTcM (not (opt_WarnMissingFields && not (null missing_fields)))
421 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
422 returnNF_Tc ()) `thenNF_Tc_`
424 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
426 -- The main complication with RecordUpd is that we need to explicitly
427 -- handle the *non-updated* fields. Consider:
429 -- data T a b = MkT1 { fa :: a, fb :: b }
430 -- | MkT2 { fa :: a, fc :: Int -> Int }
431 -- | MkT3 { fd :: a }
433 -- upd :: T a b -> c -> T a c
434 -- upd t x = t { fb = x}
436 -- The type signature on upd is correct (i.e. the result should not be (T a b))
437 -- because upd should be equivalent to:
439 -- upd t x = case t of
440 -- MkT1 p q -> MkT1 p x
441 -- MkT2 a b -> MkT2 p b
442 -- MkT3 d -> error ...
444 -- So we need to give a completely fresh type to the result record,
445 -- and then constrain it by the fields that are *not* updated ("p" above).
447 -- Note that because MkT3 doesn't contain all the fields being updated,
448 -- its RHS is simply an error, so it doesn't impose any type constraints
450 -- All this is done in STEP 4 below.
452 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
453 = tcAddErrCtxt (recordUpdCtxt expr) $
456 -- Check that the field names are really field names
457 ASSERT( not (null rbinds) )
459 field_names = [field_name | (field_name, _, _) <- rbinds]
461 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
463 bad_guys = [ addErrTc (notSelector field_name)
464 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
466 Just (AnId sel_id) -> not (isRecordSelector sel_id)
470 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
473 -- Figure out the tycon and data cons from the first field name
475 (Just sel_id : _) = maybe_sel_ids
476 (_, _, tau) = ASSERT( isNotUsgTy (idType sel_id) )
477 splitSigmaTy (idType sel_id) -- Selectors can be overloaded
478 -- when the data type has a context
479 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
480 (tycon, _, data_cons) = splitAlgTyConApp data_ty
481 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
483 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
486 -- Check that at least one constructor has all the named fields
487 -- i.e. has an empty set of bad fields returned by badFields
488 checkTc (any (null . badFields rbinds) data_cons)
489 (badFieldsUpd rbinds) `thenTc_`
492 -- Typecheck the update bindings.
493 -- (Do this after checking for bad fields in case there's a field that
494 -- doesn't match the constructor.)
496 result_record_ty = mkTyConApp tycon result_inst_tys
498 unifyTauTy res_ty result_record_ty `thenTc_`
499 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
502 -- Use the un-updated fields to find a vector of booleans saying
503 -- which type arguments must be the same in updatee and result.
505 -- WARNING: this code assumes that all data_cons in a common tycon
506 -- have FieldLabels abstracted over the same tyvars.
508 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
509 con_field_lbls_s = map dataConFieldLabels data_cons
511 -- A constructor is only relevant to this process if
512 -- it contains all the fields that are being updated
513 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
514 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
516 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
517 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
519 mk_inst_ty (tyvar, result_inst_ty)
520 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
521 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
523 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
526 -- Typecheck the expression to be updated
528 record_ty = mkTyConApp tycon inst_tys
530 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
533 -- Figure out the LIE we need. We have to generate some
534 -- dictionaries for the data type context, since we are going to
535 -- do some construction.
537 -- What dictionaries do we need? For the moment we assume that all
538 -- data constructors have the same context, and grab it from the first
539 -- constructor. If they have varying contexts then we'd have to
540 -- union the ones that could participate in the update.
542 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
543 inst_env = mkTopTyVarSubst tyvars result_inst_tys
544 theta' = substClasses inst_env theta
546 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
549 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
550 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
552 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
553 = unifyListTy res_ty `thenTc` \ elt_ty ->
554 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
556 tcLookupGlobalId enumFromClassOpName `thenNF_Tc` \ sel_id ->
557 newMethod (ArithSeqOrigin seq)
558 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
560 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
563 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
564 = tcAddErrCtxt (arithSeqCtxt in_expr) $
565 unifyListTy res_ty `thenTc` \ elt_ty ->
566 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
567 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
568 tcLookupGlobalId enumFromThenClassOpName `thenNF_Tc` \ sel_id ->
569 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
571 returnTc (ArithSeqOut (HsVar enum_from_then_id)
572 (FromThen expr1' expr2'),
573 lie1 `plusLIE` lie2 `plusLIE` lie3)
575 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
576 = tcAddErrCtxt (arithSeqCtxt in_expr) $
577 unifyListTy res_ty `thenTc` \ elt_ty ->
578 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
579 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
580 tcLookupGlobalId enumFromToClassOpName `thenNF_Tc` \ sel_id ->
581 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
583 returnTc (ArithSeqOut (HsVar enum_from_to_id)
584 (FromTo expr1' expr2'),
585 lie1 `plusLIE` lie2 `plusLIE` lie3)
587 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
588 = tcAddErrCtxt (arithSeqCtxt in_expr) $
589 unifyListTy res_ty `thenTc` \ elt_ty ->
590 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
591 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
592 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
593 tcLookupGlobalId enumFromThenToClassOpName `thenNF_Tc` \ sel_id ->
594 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
596 returnTc (ArithSeqOut (HsVar eft_id)
597 (FromThenTo expr1' expr2' expr3'),
598 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
601 %************************************************************************
603 \subsection{Expressions type signatures}
605 %************************************************************************
608 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
609 = tcSetErrCtxt (exprSigCtxt in_expr) $
610 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
612 if not (isSigmaTy sig_tc_ty) then
614 unifyTauTy sig_tc_ty res_ty `thenTc_`
615 tcMonoExpr expr sig_tc_ty
617 else -- Signature is polymorphic
618 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
620 -- Now match the signature type with res_ty.
621 -- We must not do this earlier, because res_ty might well
622 -- mention variables free in the environment, and we'd get
623 -- bogus complaints about not being able to for-all the
625 unifyTauTy res_ty expr_ty `thenTc_`
627 -- If everything is ok, return the stuff unchanged, except for
628 -- the effect of any substutions etc. We simply discard the
629 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
630 -- resolution it may have done, which is recorded in the
635 Implicit Parameter bindings.
638 tcMonoExpr (HsWith expr binds) res_ty
639 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
640 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
641 partitionPredsOfLIE isBound lie `thenTc` \ (ips, lie', dict_binds) ->
642 let expr'' = if nullMonoBinds dict_binds
644 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
647 tcCheckIPBinds binds' types ips `thenTc_`
648 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
650 = case ipName_maybe p of
651 Just n -> n `elem` names
653 names = map fst binds
654 -- revBinds is used because tcSimplify outputs the bindings
655 -- out-of-order. it's not a problem elsewhere because these
656 -- bindings are normally used in a recursive let
657 -- ZZ probably need to find a better solution
658 revBinds (b1 `AndMonoBinds` b2) =
659 (revBinds b2) `AndMonoBinds` (revBinds b1)
662 tcIPBinds ((name, expr) : binds)
663 = newTyVarTy openTypeKind `thenTc` \ ty ->
664 tcGetSrcLoc `thenTc` \ loc ->
665 let id = ipToId name ty loc in
666 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
667 zonkTcType ty `thenTc` \ ty' ->
668 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
669 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
670 tcIPBinds [] = returnTc ([], [], emptyLIE)
672 tcCheckIPBinds binds types ips
673 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
675 -- ZZ how do we use the loc?
676 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
677 = unifyTauTy t1 t2 `thenTc_`
678 tcCheckIPBind bt ips `thenTc` \ ips' ->
680 tcCheckIPBind bt (ip : ips)
681 = tcCheckIPBind bt ips `thenTc` \ ips' ->
687 Typecheck expression which in most cases will be an Id.
690 tcExpr_id :: RenamedHsExpr
696 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
698 other -> newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
699 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
700 returnTc (id_expr', lie_id, id_ty)
703 %************************************************************************
705 \subsection{@tcApp@ typchecks an application}
707 %************************************************************************
711 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
712 -> TcType -- Expected result type of application
713 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
716 tcApp fun args res_ty
717 = -- First type-check the function
718 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
720 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
721 split_fun_ty fun_ty (length args)
722 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
724 -- Unify with expected result before type-checking the args
725 -- This is when we might detect a too-few args situation
726 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
727 unifyTauTy res_ty actual_result_ty
730 -- Now typecheck the args
731 mapAndUnzipTc (tcArg fun)
732 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
734 -- Check that the result type doesn't have any nested for-alls.
735 -- For example, a "build" on its own is no good; it must be applied to something.
736 checkTc (isTauTy actual_result_ty)
737 (lurkingRank2Err fun actual_result_ty) `thenTc_`
739 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
742 -- If an error happens we try to figure out whether the
743 -- function has been given too many or too few arguments,
745 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
746 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
747 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
749 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
750 (env2, act_ty'') = tidyOpenType env1 act_ty'
751 (exp_args, _) = splitFunTys exp_ty''
752 (act_args, _) = splitFunTys act_ty''
754 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
755 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
756 | otherwise = appCtxt fun args
758 returnNF_Tc (env2, message)
761 split_fun_ty :: TcType -- The type of the function
762 -> Int -- Number of arguments
763 -> TcM ([TcType], -- Function argument types
764 TcType) -- Function result types
766 split_fun_ty fun_ty 0
767 = returnTc ([], fun_ty)
769 split_fun_ty fun_ty n
770 = -- Expect the function to have type A->B
771 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
772 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
773 returnTc (arg_ty:arg_tys, final_res_ty)
777 tcArg :: RenamedHsExpr -- The function (for error messages)
778 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
779 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
781 tcArg the_fun (arg, expected_arg_ty, arg_no)
782 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
783 tcExpr arg expected_arg_ty
787 %************************************************************************
789 \subsection{@tcId@ typchecks an identifier occurrence}
791 %************************************************************************
793 Between the renamer and the first invocation of the UsageSP inference,
794 identifiers read from interface files will have usage information in
795 their types, whereas other identifiers will not. The unannotTy here
796 in @tcId@ prevents this information from pointlessly propagating
797 further prior to the first usage inference.
800 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
803 = -- Look up the Id and instantiate its type
804 tcLookup name `thenNF_Tc` \ thing ->
806 ATcId tc_id -> instantiate_it (OccurrenceOf tc_id) tc_id (idType tc_id)
807 AGlobal (AnId id) -> tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
808 instantiate_it2 (OccurrenceOf id) id tyvars theta tau
811 -- The instantiate_it loop runs round instantiating the Id.
812 -- It has to be a loop because we are now prepared to entertain
814 -- f:: forall a. Eq a => forall b. Baz b => tau
815 -- We want to instantiate this to
816 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
817 instantiate_it orig fun ty
818 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
819 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
820 instantiate_it2 orig fun tyvars theta tau
822 instantiate_it2 orig fun tyvars theta tau
823 = if null theta then -- Is it overloaded?
824 returnNF_Tc (mkHsTyApp (HsVar fun) arg_tys, emptyLIE, tau)
826 -- Yes, it's overloaded
827 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
828 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
829 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
832 arg_tys = mkTyVarTys tyvars
835 %************************************************************************
837 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
839 %************************************************************************
842 tcDoStmts do_or_lc stmts src_loc res_ty
843 = -- get the Monad and MonadZero classes
844 -- create type consisting of a fresh monad tyvar
845 ASSERT( not (null stmts) )
846 tcAddSrcLoc src_loc $
848 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
849 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
850 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
852 -- If it's a comprehension we're dealing with,
853 -- force it to be a list comprehension.
854 -- (as of Haskell 98, monad comprehensions are no more.)
856 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
857 _ -> returnTc ()) `thenTc_`
859 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
861 -- Build the then and zero methods in case we need them
862 -- It's important that "then" and "return" appear just once in the final LIE,
863 -- not only for typechecker efficiency, but also because otherwise during
864 -- simplification we end up with silly stuff like
865 -- then = case d of (t,r) -> t
867 -- where the second "then" sees that it already exists in the "available" stuff.
869 tcLookupGlobalId returnMClassOpName `thenNF_Tc` \ return_sel_id ->
870 tcLookupGlobalId thenMClassOpName `thenNF_Tc` \ then_sel_id ->
871 tcLookupGlobalId failMClassOpName `thenNF_Tc` \ fail_sel_id ->
872 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
873 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
874 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
876 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
878 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
879 stmts_lie `plusLIE` monad_lie)
883 %************************************************************************
885 \subsection{Record bindings}
887 %************************************************************************
889 Game plan for record bindings
890 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
891 1. Find the TyCon for the bindings, from the first field label.
893 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
895 For each binding field = value
897 3. Instantiate the field type (from the field label) using the type
900 4 Type check the value using tcArg, passing the field type as
901 the expected argument type.
903 This extends OK when the field types are universally quantified.
908 :: TyCon -- Type constructor for the record
909 -> [TcType] -- Args of this type constructor
910 -> RenamedRecordBinds
911 -> TcM (TcRecordBinds, LIE)
913 tcRecordBinds tycon ty_args rbinds
914 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
915 returnTc (rbinds', plusLIEs lies)
917 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
919 do_bind (field_lbl_name, rhs, pun_flag)
920 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
922 field_lbl = recordSelectorFieldLabel sel_id
923 field_ty = substTy tenv (fieldLabelType field_lbl)
925 ASSERT( isRecordSelector sel_id )
926 -- This lookup and assertion will surely succeed, because
927 -- we check that the fields are indeed record selectors
928 -- before calling tcRecordBinds
929 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
930 -- The caller of tcRecordBinds has already checked
931 -- that all the fields come from the same type
933 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
935 returnTc ((sel_id, rhs', pun_flag), lie)
937 badFields rbinds data_con
938 = [field_name | (field_name, _, _) <- rbinds,
939 not (field_name `elem` field_names)
942 field_names = map fieldLabelName (dataConFieldLabels data_con)
944 missingStrictFields rbinds data_con
945 = [ fn | fn <- strict_field_names,
946 not (fn `elem` field_names_used)
949 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
950 strict_field_names = mapMaybe isStrict field_info
952 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
955 field_info = zip (dataConFieldLabels data_con)
956 (dataConStrictMarks data_con)
958 missingFields rbinds data_con
959 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
961 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
963 -- missing strict fields have already been flagged as
964 -- being so, so leave them out here.
965 non_strict_field_names = mapMaybe isn'tStrict field_info
967 isn'tStrict (fl, MarkedStrict) = Nothing
968 isn'tStrict (fl, _) = Just (fieldLabelName fl)
970 field_info = zip (dataConFieldLabels data_con)
971 (dataConStrictMarks data_con)
975 %************************************************************************
977 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
979 %************************************************************************
982 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
984 tcMonoExprs [] [] = returnTc ([], emptyLIE)
985 tcMonoExprs (expr:exprs) (ty:tys)
986 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
987 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
988 returnTc (expr':exprs', lie1 `plusLIE` lie2)
992 %************************************************************************
994 \subsection{Literals}
996 %************************************************************************
1001 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
1002 tcLit (HsLitLit s _) res_ty
1003 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
1004 newClassDicts (LitLitOrigin (_UNPK_ s))
1005 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
1006 returnTc (HsLit (HsLitLit s res_ty), dicts)
1009 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
1010 returnTc (HsLit lit, emptyLIE)
1014 %************************************************************************
1016 \subsection{Errors and contexts}
1018 %************************************************************************
1023 pp_nest_hang :: String -> SDoc -> SDoc
1024 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1027 Boring and alphabetical:
1030 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1033 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1036 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1039 = hang (ptext SLIT("In an expression with a type signature:"))
1043 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1046 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1048 sectionRAppCtxt expr
1049 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1051 sectionLAppCtxt expr
1052 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1054 funAppCtxt fun arg arg_no
1055 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1056 quotes (ppr fun) <> text ", namely"])
1057 4 (quotes (ppr arg))
1059 wrongArgsCtxt too_many_or_few fun args
1060 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1061 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1062 <+> ptext SLIT("arguments in the call"))
1063 4 (parens (ppr the_app))
1065 the_app = foldl HsApp fun args -- Used in error messages
1068 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1070 the_app = foldl HsApp fun args -- Used in error messages
1072 lurkingRank2Err fun fun_ty
1073 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1074 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1075 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1078 = hang (ptext SLIT("No constructor has all these fields:"))
1079 4 (pprQuotedList fields)
1081 fields = [field | (field, _, _) <- rbinds]
1083 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1084 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1087 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1089 missingStrictFieldCon :: Name -> Name -> SDoc
1090 missingStrictFieldCon con field
1091 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1092 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1094 missingFieldCon :: Name -> Name -> SDoc
1095 missingFieldCon con field
1096 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1097 ptext SLIT("is not initialised")]