2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), StmtCtxt(..),
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds,
21 import BasicTypes ( RecFlag(..) )
23 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
24 LIE, emptyLIE, unitLIE, plusLIE, plusLIEs, newOverloadedLit,
25 newMethod, newMethodWithGivenTy, newDicts, instToId )
26 import TcBinds ( tcBindsAndThen )
27 import TcEnv ( tcInstId,
28 tcLookupValue, tcLookupClassByKey,
30 tcExtendGlobalTyVars, tcLookupValueMaybe,
31 tcLookupTyCon, tcLookupDataCon
33 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
34 import TcMonoType ( tcHsType, checkSigTyVars, sigCtxt )
35 import TcPat ( badFieldCon )
36 import TcSimplify ( tcSimplifyAndCheck )
37 import TcType ( TcType, TcTauType,
39 tcInstTcType, tcSplitRhoTy,
40 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
42 import Class ( Class )
43 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType )
44 import Id ( idType, recordSelectorFieldLabel,
48 import DataCon ( dataConFieldLabels, dataConSig, dataConId )
50 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
51 splitFunTy_maybe, splitFunTys,
53 splitForAllTys, splitRhoTy,
54 isTauTy, tyVarsOfType, tyVarsOfTypes,
55 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
56 boxedTypeKind, mkArrowKind,
57 substTopTheta, tidyOpenType
59 import VarEnv ( zipVarEnv )
60 import VarSet ( elemVarSet, mkVarSet )
61 import TyCon ( tyConDataCons )
62 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
63 floatPrimTy, addrPrimTy
65 import TysWiredIn ( boolTy, charTy, stringTy )
66 import PrelInfo ( ioTyCon_NAME )
67 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
69 import Unique ( cCallableClassKey, cReturnableClassKey,
70 enumFromClassOpKey, enumFromThenClassOpKey,
71 enumFromToClassOpKey, enumFromThenToClassOpKey,
72 thenMClassOpKey, zeroClassOpKey, returnMClassOpKey
75 import Maybes ( maybeToBool )
76 import ListSetOps ( minusList )
80 %************************************************************************
82 \subsection{Main wrappers}
84 %************************************************************************
87 tcExpr :: RenamedHsExpr -- Expession to type check
88 -> TcType -- Expected type (could be a polytpye)
89 -> TcM s (TcExpr, LIE)
91 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
92 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
95 | otherwise = -- Monomorphic case
100 %************************************************************************
102 \subsection{@tcPolyExpr@ typchecks an application}
104 %************************************************************************
107 -- tcPolyExpr is like tcMonoExpr, except that the expected type
108 -- can be a polymorphic one.
109 tcPolyExpr :: RenamedHsExpr
110 -> TcType -- Expected type
111 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
112 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
114 tcPolyExpr arg expected_arg_ty
115 = -- Ha! The argument type of the function is a for-all type,
116 -- An example of rank-2 polymorphism.
118 -- To ensure that the forall'd type variables don't get unified with each
119 -- other or any other types, we make fresh copy of the alleged type
120 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
122 (sig_theta, sig_tau) = splitRhoTy sig_rho
124 -- Type-check the arg and unify with expected type
125 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
127 -- Check that the sig_tyvars havn't been constrained
128 -- The interesting bit here is that we must include the free variables
129 -- of the expected arg ty. Here's an example:
130 -- runST (newVar True)
131 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
132 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
133 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
134 -- So now s' isn't unconstrained because it's linked to a.
135 -- Conclusion: include the free vars of the expected arg type in the
136 -- list of "free vars" for the signature check.
138 tcExtendGlobalTyVars (tyVarsOfType expected_arg_ty) $
139 tcAddErrCtxtM (sigCtxt sig_msg expected_arg_ty) $
141 checkSigTyVars sig_tyvars `thenTc` \ zonked_sig_tyvars ->
143 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
144 -- ToDo: better origin
147 (mkVarSet zonked_sig_tyvars)
148 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
151 -- This HsLet binds any Insts which came out of the simplification.
152 -- It's a bit out of place here, but using AbsBind involves inventing
153 -- a couple of new names which seems worse.
154 generalised_arg = TyLam zonked_sig_tyvars $
156 HsLet (MonoBind inst_binds [] Recursive)
159 returnTc ( generalised_arg, free_insts,
160 arg', sig_tau, lie_arg )
162 sig_msg ty = ptext SLIT("In an expression with expected type:") <+> ppr ty
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)
174 -> TcM s (TcExpr, LIE)
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)
189 %************************************************************************
191 \subsection{Literals}
193 %************************************************************************
198 tcMonoExpr (HsLit (HsInt i)) res_ty
199 = newOverloadedLit (LiteralOrigin (HsInt i))
200 (OverloadedIntegral i)
201 res_ty `thenNF_Tc` \ stuff ->
204 tcMonoExpr (HsLit (HsFrac f)) res_ty
205 = newOverloadedLit (LiteralOrigin (HsFrac f))
206 (OverloadedFractional f)
207 res_ty `thenNF_Tc` \ stuff ->
211 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
212 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
213 newDicts (LitLitOrigin (_UNPK_ s))
214 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
215 returnTc (HsLitOut lit res_ty, dicts)
221 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
222 = unifyTauTy res_ty charPrimTy `thenTc_`
223 returnTc (HsLitOut lit charPrimTy, emptyLIE)
225 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
226 = unifyTauTy res_ty addrPrimTy `thenTc_`
227 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
229 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
230 = unifyTauTy res_ty intPrimTy `thenTc_`
231 returnTc (HsLitOut lit intPrimTy, emptyLIE)
233 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
234 = unifyTauTy res_ty floatPrimTy `thenTc_`
235 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
237 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
238 = unifyTauTy res_ty doublePrimTy `thenTc_`
239 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
242 Unoverloaded literals:
245 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
246 = unifyTauTy res_ty charTy `thenTc_`
247 returnTc (HsLitOut lit charTy, emptyLIE)
249 tcMonoExpr (HsLit lit@(HsString str)) res_ty
250 = unifyTauTy res_ty stringTy `thenTc_`
251 returnTc (HsLitOut lit stringTy, emptyLIE)
254 %************************************************************************
256 \subsection{Other expression forms}
258 %************************************************************************
261 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
262 = tcMonoExpr expr res_ty
264 -- perform the negate *before* overloading the integer, since the case
265 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
266 -- convenient to do it here.
268 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
269 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
271 tcMonoExpr (NegApp expr neg) res_ty
272 = tcMonoExpr (HsApp neg expr) res_ty
274 tcMonoExpr (HsLam match) res_ty
275 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
276 returnTc (HsLam match', lie)
278 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
280 accum (HsApp e1 e2) args = accum e1 (e2:args)
282 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
283 returnTc (foldl HsApp fun' args', lie)
285 -- equivalent to (op e1) e2:
286 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
287 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
288 returnTc (OpApp arg1' op' fix arg2', lie)
291 Note that the operators in sections are expected to be binary, and
292 a type error will occur if they aren't.
295 -- Left sections, equivalent to
302 tcMonoExpr in_expr@(SectionL arg op) res_ty
303 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
305 -- Check that res_ty is a function type
306 -- Without this check we barf in the desugarer on
308 -- because it tries to desugar to
309 -- f op = \r -> 3 op r
310 -- so (3 `op`) had better be a function!
311 tcAddErrCtxt (sectionLAppCtxt in_expr) $
312 unifyFunTy res_ty `thenTc_`
314 returnTc (SectionL arg' op', lie)
316 -- Right sections, equivalent to \ x -> x op expr, or
319 tcMonoExpr in_expr@(SectionR op expr) res_ty
320 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
321 tcAddErrCtxt (sectionRAppCtxt in_expr) $
322 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
323 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
324 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
325 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
328 The interesting thing about @ccall@ is that it is just a template
329 which we instantiate by filling in details about the types of its
330 argument and result (ie minimal typechecking is performed). So, the
331 basic story is that we allocate a load of type variables (to hold the
332 arg/result types); unify them with the args/result; and store them for
336 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
337 = -- Get the callable and returnable classes.
338 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
339 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
340 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
342 new_arg_dict (arg, arg_ty)
343 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
344 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
345 returnNF_Tc arg_dicts -- Actually a singleton bag
347 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
351 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) [1..(length args)] `thenNF_Tc` \ arg_tys ->
352 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
354 -- The argument types can be unboxed or boxed; the result
355 -- type must, however, be boxed since it's an argument to the IO
357 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
359 io_result_ty = mkTyConApp ioTyCon [result_ty]
360 [ioDataCon] = tyConDataCons ioTyCon
362 unifyTauTy res_ty io_result_ty `thenTc_`
364 -- Construct the extra insts, which encode the
365 -- constraints on the argument and result types.
366 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
367 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
369 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
370 (CCall lbl args' may_gc is_asm result_ty),
371 -- do the wrapping in the newtype constructor here
372 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
376 tcMonoExpr (HsSCC label expr) res_ty
377 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
378 returnTc (HsSCC label expr', lie)
380 tcMonoExpr (HsLet binds expr) res_ty
383 binds -- Bindings to check
384 tc_expr `thenTc` \ (expr', lie) ->
385 returnTc (expr', lie)
387 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
388 returnTc (expr', lie)
389 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
391 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
392 = tcAddSrcLoc src_loc $
393 tcAddErrCtxt (caseCtxt in_expr) $
395 -- Typecheck the case alternatives first.
396 -- The case patterns tend to give good type info to use
397 -- when typechecking the scrutinee. For example
400 -- will report that map is applied to too few arguments
402 -- Not only that, but it's better to check the matches on their
403 -- own, so that we get the expected results for scoped type variables.
405 -- (p::a, q::b) -> (q,p)
406 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
407 -- claimed by the pattern signatures. But if we typechecked the
408 -- match with x in scope and x's type as the expected type, we'd be hosed.
410 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
412 tcAddErrCtxt (caseScrutCtxt scrut) (
413 tcMonoExpr scrut scrut_ty
414 ) `thenTc` \ (scrut',lie1) ->
416 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
418 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
419 = tcAddSrcLoc src_loc $
420 tcAddErrCtxt (predCtxt pred) (
421 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
423 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
424 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
425 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
429 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
430 = tcDoStmts do_or_lc stmts src_loc res_ty
434 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
435 = unifyListTy res_ty `thenTc` \ elt_ty ->
436 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
437 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
440 = tcAddErrCtxt (listCtxt expr) $
441 tcMonoExpr expr elt_ty
443 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
445 then unifyTupleTy (length exprs) res_ty
446 else unifyUnboxedTupleTy (length exprs) res_ty
447 ) `thenTc` \ arg_tys ->
448 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
449 (exprs `zip` arg_tys) -- we know they're of equal length.
450 `thenTc` \ (exprs', lies) ->
451 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
453 tcMonoExpr (RecordCon con_name rbinds) res_ty
454 = tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
456 (_, record_ty) = splitFunTys con_tau
458 -- Con is syntactically constrained to be a data constructor
459 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
460 unifyTauTy res_ty record_ty `thenTc_`
462 -- Check that the record bindings match the constructor
463 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
465 bad_fields = badFields rbinds data_con
467 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
469 -- Typecheck the record bindings
470 -- (Do this after checkRecordFields in case there's a field that
471 -- doesn't match the constructor.)
472 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
474 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
477 -- The main complication with RecordUpd is that we need to explicitly
478 -- handle the *non-updated* fields. Consider:
480 -- data T a b = MkT1 { fa :: a, fb :: b }
481 -- | MkT2 { fa :: a, fc :: Int -> Int }
482 -- | MkT3 { fd :: a }
484 -- upd :: T a b -> c -> T a c
485 -- upd t x = t { fb = x}
487 -- The type signature on upd is correct (i.e. the result should not be (T a b))
488 -- because upd should be equivalent to:
490 -- upd t x = case t of
491 -- MkT1 p q -> MkT1 p x
492 -- MkT2 a b -> MkT2 p b
493 -- MkT3 d -> error ...
495 -- So we need to give a completely fresh type to the result record,
496 -- and then constrain it by the fields that are *not* updated ("p" above).
498 -- Note that because MkT3 doesn't contain all the fields being updated,
499 -- its RHS is simply an error, so it doesn't impose any type constraints
501 -- All this is done in STEP 4 below.
503 tcMonoExpr (RecordUpd record_expr rbinds) res_ty
504 = tcAddErrCtxt recordUpdCtxt $
507 -- Figure out the tycon and data cons from the first field name
508 ASSERT( not (null rbinds) )
510 ((first_field_name, _, _) : rest) = rbinds
512 tcLookupValueMaybe first_field_name `thenNF_Tc` \ maybe_sel_id ->
513 (case maybe_sel_id of
514 Just sel_id | isRecordSelector sel_id -> returnTc sel_id
515 other -> failWithTc (notSelector first_field_name)
516 ) `thenTc` \ sel_id ->
518 (_, tau) = splitForAllTys (idType sel_id)
519 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
520 (tycon, _, data_cons) = splitAlgTyConApp data_ty
521 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
523 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
526 -- Check for bad fields
527 checkTc (any (null . badFields rbinds) data_cons)
528 (badFieldsUpd rbinds) `thenTc_`
530 -- Typecheck the update bindings.
531 -- (Do this after checking for bad fields in case there's a field that
532 -- doesn't match the constructor.)
534 result_record_ty = mkTyConApp tycon result_inst_tys
536 unifyTauTy res_ty result_record_ty `thenTc_`
537 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
540 -- Use the un-updated fields to find a vector of booleans saying
541 -- which type arguments must be the same in updatee and result.
543 -- WARNING: this code assumes that all data_cons in a common tycon
544 -- have FieldLabels abstracted over the same tyvars.
546 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
547 con_field_lbls_s = map dataConFieldLabels data_cons
549 -- A constructor is only relevant to this process if
550 -- it contains all the fields that are being updated
551 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
552 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
554 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
555 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
557 mk_inst_ty (tyvar, result_inst_ty)
558 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
559 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
561 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
564 -- Typecheck the expression to be updated
566 record_ty = mkTyConApp tycon inst_tys
568 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
571 -- Figure out the LIE we need. We have to generate some
572 -- dictionaries for the data type context, since we are going to
573 -- do some construction.
575 -- What dictionaries do we need? For the moment we assume that all
576 -- data constructors have the same context, and grab it from the first
577 -- constructor. If they have varying contexts then we'd have to
578 -- union the ones that could participate in the update.
580 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
581 inst_env = zipVarEnv tyvars result_inst_tys
582 theta' = substTopTheta inst_env theta
584 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
587 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
588 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
590 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
591 = unifyListTy res_ty `thenTc` \ elt_ty ->
592 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
594 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
595 newMethod (ArithSeqOrigin seq)
596 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
598 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
601 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
602 = tcAddErrCtxt (arithSeqCtxt in_expr) $
603 unifyListTy res_ty `thenTc` \ elt_ty ->
604 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
605 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
606 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
607 newMethod (ArithSeqOrigin seq)
608 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
610 returnTc (ArithSeqOut (HsVar enum_from_then_id)
611 (FromThen expr1' expr2'),
612 lie1 `plusLIE` lie2 `plusLIE` lie3)
614 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
615 = tcAddErrCtxt (arithSeqCtxt in_expr) $
616 unifyListTy res_ty `thenTc` \ elt_ty ->
617 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
618 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
619 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
620 newMethod (ArithSeqOrigin seq)
621 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
623 returnTc (ArithSeqOut (HsVar enum_from_to_id)
624 (FromTo expr1' expr2'),
625 lie1 `plusLIE` lie2 `plusLIE` lie3)
627 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
628 = tcAddErrCtxt (arithSeqCtxt in_expr) $
629 unifyListTy res_ty `thenTc` \ elt_ty ->
630 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
631 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
632 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
633 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
634 newMethod (ArithSeqOrigin seq)
635 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
637 returnTc (ArithSeqOut (HsVar eft_id)
638 (FromThenTo expr1' expr2' expr3'),
639 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
642 %************************************************************************
644 \subsection{Expressions type signatures}
646 %************************************************************************
649 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
650 = tcSetErrCtxt (exprSigCtxt in_expr) $
651 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
653 if not (isForAllTy sig_tc_ty) then
655 unifyTauTy sig_tc_ty res_ty `thenTc_`
656 tcMonoExpr expr sig_tc_ty
658 else -- Signature is polymorphic
659 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
661 -- Now match the signature type with res_ty.
662 -- We must not do this earlier, because res_ty might well
663 -- mention variables free in the environment, and we'd get
664 -- bogus complaints about not being able to for-all the
666 unifyTauTy res_ty expr_ty `thenTc_`
668 -- If everything is ok, return the stuff unchanged, except for
669 -- the effect of any substutions etc. We simply discard the
670 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
671 -- resolution it may have done, which is recorded in the
676 Typecheck expression which in most cases will be an Id.
679 tcExpr_id :: RenamedHsExpr
685 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
687 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
688 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
689 returnTc (id_expr', lie_id, id_ty)
692 %************************************************************************
694 \subsection{@tcApp@ typchecks an application}
696 %************************************************************************
700 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
701 -> TcType -- Expected result type of application
702 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
705 tcApp fun args res_ty
706 = -- First type-check the function
707 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
709 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
710 split_fun_ty fun_ty (length args)
711 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
713 -- Unify with expected result before type-checking the args
714 -- This is when we might detect a too-few args situation
715 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
716 unifyTauTy res_ty actual_result_ty
719 -- Now typecheck the args
720 mapAndUnzipTc (tcArg fun)
721 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
723 -- Check that the result type doesn't have any nested for-alls.
724 -- For example, a "build" on its own is no good; it must be applied to something.
725 checkTc (isTauTy actual_result_ty)
726 (lurkingRank2Err fun fun_ty) `thenTc_`
728 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
731 -- If an error happens we try to figure out whether the
732 -- function has been given too many or too few arguments,
734 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
735 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
736 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
738 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
739 (env2, act_ty'') = tidyOpenType env1 act_ty'
740 (exp_args, _) = splitFunTys exp_ty''
741 (act_args, _) = splitFunTys act_ty''
743 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
744 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
745 | otherwise = appCtxt fun args
747 returnNF_Tc (env2, message)
750 split_fun_ty :: TcType -- The type of the function
751 -> Int -- Number of arguments
752 -> TcM s ([TcType], -- Function argument types
753 TcType) -- Function result types
755 split_fun_ty fun_ty 0
756 = returnTc ([], fun_ty)
758 split_fun_ty fun_ty n
759 = -- Expect the function to have type A->B
760 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
761 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
762 returnTc (arg_ty:arg_tys, final_res_ty)
766 tcArg :: RenamedHsExpr -- The function (for error messages)
767 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
768 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
770 tcArg the_fun (arg, expected_arg_ty, arg_no)
771 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
772 tcExpr arg expected_arg_ty
776 %************************************************************************
778 \subsection{@tcId@ typchecks an identifier occurrence}
780 %************************************************************************
783 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
786 = -- Look up the Id and instantiate its type
787 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
790 Just tc_id -> instantiate_it tc_id (idType tc_id)
792 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
793 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
794 instantiate_it2 id tyvars theta tau
797 -- The instantiate_it loop runs round instantiating the Id.
798 -- It has to be a loop because we are now prepared to entertain
800 -- f:: forall a. Eq a => forall b. Baz b => tau
801 -- We want to instantiate this to
802 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
803 instantiate_it tc_id_occ ty
804 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
805 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
806 instantiate_it2 tc_id_occ tyvars theta tau
808 instantiate_it2 tc_id_occ tyvars theta tau
809 = if null theta then -- Is it overloaded?
810 returnNF_Tc (mkHsTyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau)
812 -- Yes, it's overloaded
813 newMethodWithGivenTy (OccurrenceOf tc_id_occ)
814 tc_id_occ arg_tys theta tau `thenNF_Tc` \ inst ->
815 instantiate_it (instToId inst) tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
816 returnNF_Tc (expr, unitLIE inst `plusLIE` lie2, final_tau)
819 arg_tys = mkTyVarTys tyvars
822 %************************************************************************
824 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
826 %************************************************************************
829 tcDoStmts do_or_lc stmts src_loc res_ty
830 = -- get the Monad and MonadZero classes
831 -- create type consisting of a fresh monad tyvar
832 ASSERT( not (null stmts) )
833 tcAddSrcLoc src_loc $
835 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
836 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
837 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
839 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
841 -- Build the then and zero methods in case we need them
842 -- It's important that "then" and "return" appear just once in the final LIE,
843 -- not only for typechecker efficiency, but also because otherwise during
844 -- simplification we end up with silly stuff like
845 -- then = case d of (t,r) -> t
847 -- where the second "then" sees that it already exists in the "available" stuff.
849 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
850 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
851 tcLookupValueByKey zeroClassOpKey `thenNF_Tc` \ zero_sel_id ->
852 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
853 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
854 newMethod DoOrigin zero_sel_id [m] `thenNF_Tc` \ (zero_lie, zero_id) ->
856 monad_lie = then_lie `plusLIE` return_lie `plusLIE` perhaps_zero_lie
857 perhaps_zero_lie | all failure_free stmts' = emptyLIE
858 | otherwise = zero_lie
860 failure_free (BindStmt pat _ _) = failureFreePat pat
861 failure_free (GuardStmt _ _) = False
862 failure_free other_stmt = True
864 returnTc (HsDoOut do_or_lc stmts' return_id then_id zero_id res_ty src_loc,
865 stmts_lie `plusLIE` monad_lie)
869 %************************************************************************
871 \subsection{Record bindings}
873 %************************************************************************
875 Game plan for record bindings
876 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
879 1. look up "field", to find its selector Id, which must have type
880 forall a1..an. T a1 .. an -> tau
881 where tau is the type of the field.
883 2. Instantiate this type
885 3. Unify the (T a1 .. an) part with the "expected result type", which
886 is passed in. This checks that all the field labels come from the
889 4. Type check the value using tcArg, passing tau as the expected
892 This extends OK when the field types are universally quantified.
894 Actually, to save excessive creation of fresh type variables,
899 :: TcType -- Expected type of whole record
900 -> RenamedRecordBinds
901 -> TcM s (TcRecordBinds, LIE)
903 tcRecordBinds expected_record_ty rbinds
904 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
905 returnTc (rbinds', plusLIEs lies)
907 do_bind (field_label, rhs, pun_flag)
908 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
909 ASSERT( isRecordSelector sel_id )
910 -- This lookup and assertion will surely succeed, because
911 -- we check that the fields are indeed record selectors
912 -- before calling tcRecordBinds
914 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
916 -- Record selectors all have type
917 -- forall a1..an. T a1 .. an -> tau
918 ASSERT( maybeToBool (splitFunTy_maybe tau) )
920 -- Selector must have type RecordType -> FieldType
921 Just (record_ty, field_ty) = splitFunTy_maybe tau
923 unifyTauTy expected_record_ty record_ty `thenTc_`
924 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
925 returnTc ((sel_id, rhs', pun_flag), lie)
927 badFields rbinds data_con
928 = [field_name | (field_name, _, _) <- rbinds,
929 not (field_name `elem` field_names)
932 field_names = map fieldLabelName (dataConFieldLabels data_con)
935 %************************************************************************
937 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
939 %************************************************************************
942 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
944 tcMonoExprs [] [] = returnTc ([], emptyLIE)
945 tcMonoExprs (expr:exprs) (ty:tys)
946 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
947 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
948 returnTc (expr':exprs', lie1 `plusLIE` lie2)
952 % =================================================
959 pp_nest_hang :: String -> SDoc -> SDoc
960 pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff)
963 Boring and alphabetical:
966 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
969 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
972 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
975 = hang (ptext SLIT("In an expression with a type signature:"))
979 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
982 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
985 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
988 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
990 funAppCtxt fun arg arg_no
991 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
992 quotes (ppr fun) <> text ", namely"])
995 wrongArgsCtxt too_many_or_few fun args
996 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
997 <+> ptext SLIT("is applied to") <+> text too_many_or_few
998 <+> ptext SLIT("arguments in the call"))
999 4 (parens (ppr the_app))
1001 the_app = foldl HsApp fun args -- Used in error messages
1004 = ptext SLIT("In the application") <+> (ppr the_app)
1006 the_app = foldl HsApp fun args -- Used in error messages
1008 lurkingRank2Err fun fun_ty
1009 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1010 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1011 ptext SLIT("so that the result type has for-alls in it")])
1013 rank2ArgCtxt arg expected_arg_ty
1014 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1017 = hang (ptext SLIT("No constructor has all these fields:"))
1018 4 (pprQuotedList fields)
1020 fields = [field | (field, _, _) <- rbinds]
1022 recordUpdCtxt = ptext SLIT("In a record update construct")
1025 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]