2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcApp, tcExpr, tcMonoExpr, 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 ( TcTyThing(..), tcInstId,
29 tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
30 tcLookupTyCon, tcLookupDataCon, tcLookup,
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,
51 mkTyConApp, splitSigmaTy,
53 isTauTy, tyVarsOfType, tyVarsOfTypes,
54 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
55 liftedTypeKind, openTypeKind, mkArrowKind,
58 import TyCon ( TyCon, tyConTyVars )
59 import Subst ( mkTopTyVarSubst, substClasses, substTy )
60 import VarSet ( elemVarSet, mkVarSet )
61 import TysWiredIn ( boolTy )
62 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
63 import PrelNames ( cCallableClassName,
65 enumFromName, enumFromThenName,
66 enumFromToName, enumFromThenToName,
67 thenMName, failMName, returnMName, ioTyConName
70 import Maybes ( maybeToBool, mapMaybe )
71 import ListSetOps ( minusList )
74 import HscTypes ( TyThing(..) )
78 %************************************************************************
80 \subsection{Main wrappers}
82 %************************************************************************
85 tcExpr :: RenamedHsExpr -- Expession to type check
86 -> TcType -- Expected type (could be a polytpye)
89 tcExpr expr ty | isSigmaTy ty = -- Polymorphic case
90 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
93 | otherwise = -- Monomorphic case
98 %************************************************************************
100 \subsection{@tcPolyExpr@ typchecks an application}
102 %************************************************************************
105 -- tcPolyExpr is like tcMonoExpr, except that the expected type
106 -- can be a polymorphic one.
107 tcPolyExpr :: RenamedHsExpr
108 -> TcType -- Expected type
109 -> TcM (TcExpr, LIE, -- Generalised expr with expected type, and LIE
110 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
112 tcPolyExpr arg expected_arg_ty
113 = -- Ha! The argument type of the function is a for-all type,
114 -- An example of rank-2 polymorphism.
116 -- To ensure that the forall'd type variables don't get unified with each
117 -- other or any other types, we make fresh copy of the alleged type
118 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
120 (sig_theta, sig_tau) = splitRhoTy sig_rho
121 free_tyvars = tyVarsOfType expected_arg_ty
123 -- Type-check the arg and unify with expected type
124 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
126 -- Check that the sig_tyvars havn't been constrained
127 -- The interesting bit here is that we must include the free variables
128 -- of the expected arg ty. Here's an example:
129 -- runST (newVar True)
130 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
131 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
132 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
133 -- So now s' isn't unconstrained because it's linked to a.
134 -- Conclusion: include the free vars of the expected arg type in the
135 -- list of "free vars" for the signature check.
137 tcExtendGlobalTyVars free_tyvars $
138 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
140 checkSigTyVars sig_tyvars free_tyvars `thenTc` \ zonked_sig_tyvars ->
142 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
143 tcImprove (sig_dicts `plusLIE` lie_arg) `thenTc_`
144 -- ToDo: better origin
146 (text "the type signature of an expression")
147 (mkVarSet zonked_sig_tyvars)
148 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
151 -- This HsLet binds any Insts which came out of the simplification.
152 -- It's a bit out of place here, but using AbsBind involves inventing
153 -- a couple of new names which seems worse.
154 generalised_arg = TyLam zonked_sig_tyvars $
159 returnTc ( generalised_arg, free_insts,
160 arg', sig_tau, lie_arg )
162 sig_msg = ptext SLIT("When checking an expression type signature")
165 %************************************************************************
167 \subsection{The TAUT rules for variables}
169 %************************************************************************
172 tcMonoExpr :: RenamedHsExpr -- Expession to type check
173 -> TcTauType -- Expected type (could be a type variable)
176 tcMonoExpr (HsVar name) res_ty
177 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
178 unifyTauTy res_ty id_ty `thenTc_`
180 -- Check that the result type doesn't have any nested for-alls.
181 -- For example, a "build" on its own is no good; it must be
182 -- applied to something.
183 checkTc (isTauTy id_ty)
184 (lurkingRank2Err name id_ty) `thenTc_`
186 returnTc (expr', lie)
190 tcMonoExpr (HsIPVar name) res_ty
191 -- ZZ What's the `id' used for here...
192 = let id = mkVanillaId name res_ty in
193 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
194 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
195 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
198 %************************************************************************
200 \subsection{Other expression forms}
202 %************************************************************************
205 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
206 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
207 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
209 tcMonoExpr (NegApp expr neg) res_ty
210 = tcMonoExpr (HsApp (HsVar neg) expr) res_ty
212 tcMonoExpr (HsLam match) res_ty
213 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
214 returnTc (HsLam match', lie)
216 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
218 accum (HsApp e1 e2) args = accum e1 (e2:args)
220 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
221 returnTc (foldl HsApp fun' args', lie)
223 -- equivalent to (op e1) e2:
224 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
225 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
226 returnTc (OpApp arg1' op' fix arg2', lie)
229 Note that the operators in sections are expected to be binary, and
230 a type error will occur if they aren't.
233 -- Left sections, equivalent to
240 tcMonoExpr in_expr@(SectionL arg op) res_ty
241 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
243 -- Check that res_ty is a function type
244 -- Without this check we barf in the desugarer on
246 -- because it tries to desugar to
247 -- f op = \r -> 3 op r
248 -- so (3 `op`) had better be a function!
249 tcAddErrCtxt (sectionLAppCtxt in_expr) $
250 unifyFunTy res_ty `thenTc_`
252 returnTc (SectionL arg' op', lie)
254 -- Right sections, equivalent to \ x -> x op expr, or
257 tcMonoExpr in_expr@(SectionR op expr) res_ty
258 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
259 tcAddErrCtxt (sectionRAppCtxt in_expr) $
260 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
261 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
262 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
263 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
266 The interesting thing about @ccall@ is that it is just a template
267 which we instantiate by filling in details about the types of its
268 argument and result (ie minimal typechecking is performed). So, the
269 basic story is that we allocate a load of type variables (to hold the
270 arg/result types); unify them with the args/result; and store them for
274 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
275 = -- Get the callable and returnable classes.
276 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
277 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
278 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
280 new_arg_dict (arg, arg_ty)
281 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
282 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
283 returnNF_Tc arg_dicts -- Actually a singleton bag
285 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
289 let n_args = length args
290 tv_idxs | n_args == 0 = []
291 | otherwise = [1..n_args]
293 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
294 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
296 -- The argument types can be unlifted or lifted; the result
297 -- type must, however, be lifted since it's an argument to the IO
299 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
301 io_result_ty = mkTyConApp ioTyCon [result_ty]
303 unifyTauTy res_ty io_result_ty `thenTc_`
305 -- Construct the extra insts, which encode the
306 -- constraints on the argument and result types.
307 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
308 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
309 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
310 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
314 tcMonoExpr (HsSCC lbl expr) res_ty
315 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
316 returnTc (HsSCC lbl expr', lie)
318 tcMonoExpr (HsLet binds expr) res_ty
321 binds -- Bindings to check
322 tc_expr `thenTc` \ (expr', lie) ->
323 returnTc (expr', lie)
325 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
326 returnTc (expr', lie)
327 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
329 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
330 = tcAddSrcLoc src_loc $
331 tcAddErrCtxt (caseCtxt in_expr) $
333 -- Typecheck the case alternatives first.
334 -- The case patterns tend to give good type info to use
335 -- when typechecking the scrutinee. For example
338 -- will report that map is applied to too few arguments
340 -- Not only that, but it's better to check the matches on their
341 -- own, so that we get the expected results for scoped type variables.
343 -- (p::a, q::b) -> (q,p)
344 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
345 -- claimed by the pattern signatures. But if we typechecked the
346 -- match with x in scope and x's type as the expected type, we'd be hosed.
348 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
350 tcAddErrCtxt (caseScrutCtxt scrut) (
351 tcMonoExpr scrut scrut_ty
352 ) `thenTc` \ (scrut',lie1) ->
354 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
356 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
357 = tcAddSrcLoc src_loc $
358 tcAddErrCtxt (predCtxt pred) (
359 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
361 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
362 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
363 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
367 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
368 = tcDoStmts do_or_lc stmts src_loc res_ty
372 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
373 = unifyListTy res_ty `thenTc` \ elt_ty ->
374 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
375 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
378 = tcAddErrCtxt (listCtxt expr) $
379 tcMonoExpr expr elt_ty
381 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
382 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
383 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
384 (exprs `zip` arg_tys) -- we know they're of equal length.
385 `thenTc` \ (exprs', lies) ->
386 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
388 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
389 = tcAddErrCtxt (recordConCtxt expr) $
390 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
392 (_, record_ty) = splitFunTys con_tau
393 (tycon, ty_args, _) = splitAlgTyConApp record_ty
395 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
396 unifyTauTy res_ty record_ty `thenTc_`
398 -- Check that the record bindings match the constructor
399 -- con_name is syntactically constrained to be a data constructor
400 tcLookupDataCon con_name `thenTc` \ data_con ->
402 bad_fields = badFields rbinds data_con
404 if not (null bad_fields) then
405 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
406 failTc -- Fail now, because tcRecordBinds will crash on a bad field
409 -- Typecheck the record bindings
410 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
413 missing_s_fields = missingStrictFields rbinds data_con
415 checkTcM (null missing_s_fields)
416 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
417 returnNF_Tc ()) `thenNF_Tc_`
419 missing_fields = missingFields rbinds data_con
421 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
422 checkTcM (not (warn && not (null missing_fields)))
423 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
424 returnNF_Tc ()) `thenNF_Tc_`
426 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
428 -- The main complication with RecordUpd is that we need to explicitly
429 -- handle the *non-updated* fields. Consider:
431 -- data T a b = MkT1 { fa :: a, fb :: b }
432 -- | MkT2 { fa :: a, fc :: Int -> Int }
433 -- | MkT3 { fd :: a }
435 -- upd :: T a b -> c -> T a c
436 -- upd t x = t { fb = x}
438 -- The type signature on upd is correct (i.e. the result should not be (T a b))
439 -- because upd should be equivalent to:
441 -- upd t x = case t of
442 -- MkT1 p q -> MkT1 p x
443 -- MkT2 a b -> MkT2 p b
444 -- MkT3 d -> error ...
446 -- So we need to give a completely fresh type to the result record,
447 -- and then constrain it by the fields that are *not* updated ("p" above).
449 -- Note that because MkT3 doesn't contain all the fields being updated,
450 -- its RHS is simply an error, so it doesn't impose any type constraints
452 -- All this is done in STEP 4 below.
454 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
455 = tcAddErrCtxt (recordUpdCtxt expr) $
458 -- Check that the field names are really field names
459 ASSERT( not (null rbinds) )
461 field_names = [field_name | (field_name, _, _) <- rbinds]
463 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
465 bad_guys = [ addErrTc (notSelector field_name)
466 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
468 Just (AnId sel_id) -> not (isRecordSelector sel_id)
472 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
475 -- Figure out the tycon and data cons from the first field name
477 (Just (AnId sel_id) : _) = maybe_sel_ids
478 (_, _, tau) = splitSigmaTy (idType sel_id) -- Selectors can be overloaded
479 -- when the data type has a context
480 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
481 (tycon, _, data_cons) = splitAlgTyConApp data_ty
482 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
484 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
487 -- Check that at least one constructor has all the named fields
488 -- i.e. has an empty set of bad fields returned by badFields
489 checkTc (any (null . badFields rbinds) data_cons)
490 (badFieldsUpd rbinds) `thenTc_`
493 -- Typecheck the update bindings.
494 -- (Do this after checking for bad fields in case there's a field that
495 -- doesn't match the constructor.)
497 result_record_ty = mkTyConApp tycon result_inst_tys
499 unifyTauTy res_ty result_record_ty `thenTc_`
500 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
503 -- Use the un-updated fields to find a vector of booleans saying
504 -- which type arguments must be the same in updatee and result.
506 -- WARNING: this code assumes that all data_cons in a common tycon
507 -- have FieldLabels abstracted over the same tyvars.
509 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
510 con_field_lbls_s = map dataConFieldLabels data_cons
512 -- A constructor is only relevant to this process if
513 -- it contains all the fields that are being updated
514 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
515 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
517 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
518 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
520 mk_inst_ty (tyvar, result_inst_ty)
521 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
522 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
524 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
527 -- Typecheck the expression to be updated
529 record_ty = mkTyConApp tycon inst_tys
531 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
534 -- Figure out the LIE we need. We have to generate some
535 -- dictionaries for the data type context, since we are going to
536 -- do some construction.
538 -- What dictionaries do we need? For the moment we assume that all
539 -- data constructors have the same context, and grab it from the first
540 -- constructor. If they have varying contexts then we'd have to
541 -- union the ones that could participate in the update.
543 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
544 inst_env = mkTopTyVarSubst tyvars result_inst_tys
545 theta' = substClasses inst_env theta
547 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
550 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
551 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
553 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
554 = unifyListTy res_ty `thenTc` \ elt_ty ->
555 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
557 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
558 newMethod (ArithSeqOrigin seq)
559 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
561 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
564 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
565 = tcAddErrCtxt (arithSeqCtxt in_expr) $
566 unifyListTy res_ty `thenTc` \ elt_ty ->
567 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
568 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
569 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
570 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
572 returnTc (ArithSeqOut (HsVar enum_from_then_id)
573 (FromThen expr1' expr2'),
574 lie1 `plusLIE` lie2 `plusLIE` lie3)
576 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
577 = tcAddErrCtxt (arithSeqCtxt in_expr) $
578 unifyListTy res_ty `thenTc` \ elt_ty ->
579 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
580 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
581 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
582 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
584 returnTc (ArithSeqOut (HsVar enum_from_to_id)
585 (FromTo expr1' expr2'),
586 lie1 `plusLIE` lie2 `plusLIE` lie3)
588 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
589 = tcAddErrCtxt (arithSeqCtxt in_expr) $
590 unifyListTy res_ty `thenTc` \ elt_ty ->
591 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
592 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
593 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
594 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
595 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
597 returnTc (ArithSeqOut (HsVar eft_id)
598 (FromThenTo expr1' expr2' expr3'),
599 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
602 %************************************************************************
604 \subsection{Expressions type signatures}
606 %************************************************************************
609 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
610 = tcSetErrCtxt (exprSigCtxt in_expr) $
611 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
613 if not (isSigmaTy sig_tc_ty) then
615 unifyTauTy sig_tc_ty res_ty `thenTc_`
616 tcMonoExpr expr sig_tc_ty
618 else -- Signature is polymorphic
619 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
621 -- Now match the signature type with res_ty.
622 -- We must not do this earlier, because res_ty might well
623 -- mention variables free in the environment, and we'd get
624 -- bogus complaints about not being able to for-all the
626 unifyTauTy res_ty expr_ty `thenTc_`
628 -- If everything is ok, return the stuff unchanged, except for
629 -- the effect of any substutions etc. We simply discard the
630 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
631 -- resolution it may have done, which is recorded in the
636 Implicit Parameter bindings.
639 tcMonoExpr (HsWith expr binds) res_ty
640 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
641 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
642 partitionPredsOfLIE isBound lie `thenTc` \ (ips, lie', dict_binds) ->
643 let expr'' = if nullMonoBinds dict_binds
645 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
648 tcCheckIPBinds binds' types ips `thenTc_`
649 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
651 = case ipName_maybe p of
652 Just n -> n `elem` names
654 names = map fst binds
655 -- revBinds is used because tcSimplify outputs the bindings
656 -- out-of-order. it's not a problem elsewhere because these
657 -- bindings are normally used in a recursive let
658 -- ZZ probably need to find a better solution
659 revBinds (b1 `AndMonoBinds` b2) =
660 (revBinds b2) `AndMonoBinds` (revBinds b1)
663 tcIPBinds ((name, expr) : binds)
664 = newTyVarTy openTypeKind `thenTc` \ ty ->
665 tcGetSrcLoc `thenTc` \ loc ->
666 let id = ipToId name ty loc in
667 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
668 zonkTcType ty `thenTc` \ ty' ->
669 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
670 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
671 tcIPBinds [] = returnTc ([], [], emptyLIE)
673 tcCheckIPBinds binds types ips
674 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
676 -- ZZ how do we use the loc?
677 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
678 = unifyTauTy t1 t2 `thenTc_`
679 tcCheckIPBind bt ips `thenTc` \ ips' ->
681 tcCheckIPBind bt (ip : ips)
682 = tcCheckIPBind bt ips `thenTc` \ ips' ->
688 Typecheck expression which in most cases will be an Id.
691 tcExpr_id :: RenamedHsExpr
697 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
699 other -> newTyVarTy openTypeKind `thenNF_Tc` \ id_ty ->
700 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
701 returnTc (id_expr', lie_id, id_ty)
704 %************************************************************************
706 \subsection{@tcApp@ typchecks an application}
708 %************************************************************************
712 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
713 -> TcType -- Expected result type of application
714 -> TcM (TcExpr, [TcExpr], -- Translated fun and args
717 tcApp fun args res_ty
718 = -- First type-check the function
719 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
721 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
722 split_fun_ty fun_ty (length args)
723 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
725 -- Unify with expected result before type-checking the args
726 -- This is when we might detect a too-few args situation
727 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
728 unifyTauTy res_ty actual_result_ty
731 -- Now typecheck the args
732 mapAndUnzipTc (tcArg fun)
733 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
735 -- Check that the result type doesn't have any nested for-alls.
736 -- For example, a "build" on its own is no good; it must be applied to something.
737 checkTc (isTauTy actual_result_ty)
738 (lurkingRank2Err fun actual_result_ty) `thenTc_`
740 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
743 -- If an error happens we try to figure out whether the
744 -- function has been given too many or too few arguments,
746 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
747 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
748 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
750 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
751 (env2, act_ty'') = tidyOpenType env1 act_ty'
752 (exp_args, _) = splitFunTys exp_ty''
753 (act_args, _) = splitFunTys act_ty''
755 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
756 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
757 | otherwise = appCtxt fun args
759 returnNF_Tc (env2, message)
762 split_fun_ty :: TcType -- The type of the function
763 -> Int -- Number of arguments
764 -> TcM ([TcType], -- Function argument types
765 TcType) -- Function result types
767 split_fun_ty fun_ty 0
768 = returnTc ([], fun_ty)
770 split_fun_ty fun_ty n
771 = -- Expect the function to have type A->B
772 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
773 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
774 returnTc (arg_ty:arg_tys, final_res_ty)
778 tcArg :: RenamedHsExpr -- The function (for error messages)
779 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
780 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
782 tcArg the_fun (arg, expected_arg_ty, arg_no)
783 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
784 tcExpr arg expected_arg_ty
788 %************************************************************************
790 \subsection{@tcId@ typchecks an identifier occurrence}
792 %************************************************************************
795 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
798 = -- Look up the Id and instantiate its type
799 tcLookup name `thenNF_Tc` \ thing ->
801 ATcId tc_id -> instantiate_it (OccurrenceOf tc_id) tc_id (idType tc_id)
802 AGlobal (AnId id) -> tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
803 instantiate_it2 (OccurrenceOf id) id tyvars theta tau
805 -- The instantiate_it loop runs round instantiating the Id.
806 -- It has to be a loop because we are now prepared to entertain
808 -- f:: forall a. Eq a => forall b. Baz b => tau
809 -- We want to instantiate this to
810 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
811 instantiate_it orig fun ty
812 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
813 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
814 instantiate_it2 orig fun tyvars theta tau
816 instantiate_it2 orig fun tyvars theta tau
817 = if null theta then -- Is it overloaded?
818 returnNF_Tc (mkHsTyApp (HsVar fun) arg_tys, emptyLIE, tau)
820 -- Yes, it's overloaded
821 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
822 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
823 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
826 arg_tys = mkTyVarTys tyvars
829 %************************************************************************
831 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
833 %************************************************************************
836 tcDoStmts do_or_lc stmts src_loc res_ty
837 = -- get the Monad and MonadZero classes
838 -- create type consisting of a fresh monad tyvar
839 ASSERT( not (null stmts) )
840 tcAddSrcLoc src_loc $
842 newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m ->
843 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
844 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
846 -- If it's a comprehension we're dealing with,
847 -- force it to be a list comprehension.
848 -- (as of Haskell 98, monad comprehensions are no more.)
850 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
851 _ -> returnTc ()) `thenTc_`
853 tcStmts do_or_lc (mkAppTy m) elt_ty src_loc stmts `thenTc` \ ((stmts', _), stmts_lie) ->
855 -- Build the then and zero methods in case we need them
856 -- It's important that "then" and "return" appear just once in the final LIE,
857 -- not only for typechecker efficiency, but also because otherwise during
858 -- simplification we end up with silly stuff like
859 -- then = case d of (t,r) -> t
861 -- where the second "then" sees that it already exists in the "available" stuff.
863 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
864 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
865 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
866 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
867 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
868 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
870 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
872 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
873 stmts_lie `plusLIE` monad_lie)
877 %************************************************************************
879 \subsection{Record bindings}
881 %************************************************************************
883 Game plan for record bindings
884 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885 1. Find the TyCon for the bindings, from the first field label.
887 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
889 For each binding field = value
891 3. Instantiate the field type (from the field label) using the type
894 4 Type check the value using tcArg, passing the field type as
895 the expected argument type.
897 This extends OK when the field types are universally quantified.
902 :: TyCon -- Type constructor for the record
903 -> [TcType] -- Args of this type constructor
904 -> RenamedRecordBinds
905 -> TcM (TcRecordBinds, LIE)
907 tcRecordBinds tycon ty_args rbinds
908 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
909 returnTc (rbinds', plusLIEs lies)
911 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
913 do_bind (field_lbl_name, rhs, pun_flag)
914 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
916 field_lbl = recordSelectorFieldLabel sel_id
917 field_ty = substTy tenv (fieldLabelType field_lbl)
919 ASSERT( isRecordSelector sel_id )
920 -- This lookup and assertion will surely succeed, because
921 -- we check that the fields are indeed record selectors
922 -- before calling tcRecordBinds
923 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
924 -- The caller of tcRecordBinds has already checked
925 -- that all the fields come from the same type
927 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
929 returnTc ((sel_id, rhs', pun_flag), lie)
931 badFields rbinds data_con
932 = [field_name | (field_name, _, _) <- rbinds,
933 not (field_name `elem` field_names)
936 field_names = map fieldLabelName (dataConFieldLabels data_con)
938 missingStrictFields rbinds data_con
939 = [ fn | fn <- strict_field_names,
940 not (fn `elem` field_names_used)
943 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
944 strict_field_names = mapMaybe isStrict field_info
946 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
949 field_info = zip (dataConFieldLabels data_con)
950 (dataConStrictMarks data_con)
952 missingFields rbinds data_con
953 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
955 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
957 -- missing strict fields have already been flagged as
958 -- being so, so leave them out here.
959 non_strict_field_names = mapMaybe isn'tStrict field_info
961 isn'tStrict (fl, MarkedStrict) = Nothing
962 isn'tStrict (fl, _) = Just (fieldLabelName fl)
964 field_info = zip (dataConFieldLabels data_con)
965 (dataConStrictMarks data_con)
969 %************************************************************************
971 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
973 %************************************************************************
976 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
978 tcMonoExprs [] [] = returnTc ([], emptyLIE)
979 tcMonoExprs (expr:exprs) (ty:tys)
980 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
981 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
982 returnTc (expr':exprs', lie1 `plusLIE` lie2)
986 %************************************************************************
988 \subsection{Literals}
990 %************************************************************************
995 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
996 tcLit (HsLitLit s _) res_ty
997 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
998 newClassDicts (LitLitOrigin (_UNPK_ s))
999 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
1000 returnTc (HsLit (HsLitLit s res_ty), dicts)
1003 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
1004 returnTc (HsLit lit, emptyLIE)
1008 %************************************************************************
1010 \subsection{Errors and contexts}
1012 %************************************************************************
1017 pp_nest_hang :: String -> SDoc -> SDoc
1018 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1021 Boring and alphabetical:
1024 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1027 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1030 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1033 = hang (ptext SLIT("In an expression with a type signature:"))
1037 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1040 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1042 sectionRAppCtxt expr
1043 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1045 sectionLAppCtxt expr
1046 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1048 funAppCtxt fun arg arg_no
1049 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1050 quotes (ppr fun) <> text ", namely"])
1051 4 (quotes (ppr arg))
1053 wrongArgsCtxt too_many_or_few fun args
1054 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1055 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1056 <+> ptext SLIT("arguments in the call"))
1057 4 (parens (ppr the_app))
1059 the_app = foldl HsApp fun args -- Used in error messages
1062 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1064 the_app = foldl HsApp fun args -- Used in error messages
1066 lurkingRank2Err fun fun_ty
1067 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1068 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1069 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1072 = hang (ptext SLIT("No constructor has all these fields:"))
1073 4 (pprQuotedList fields)
1075 fields = [field | (field, _, _) <- rbinds]
1077 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1078 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1081 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1083 missingStrictFieldCon :: Name -> Name -> SDoc
1084 missingStrictFieldCon con field
1085 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1086 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1088 missingFieldCon :: Name -> Name -> SDoc
1089 missingFieldCon con field
1090 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1091 ptext SLIT("is not initialised")]