2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcStmt, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), DoOrListComp(..),
13 failureFreePat, collectPatBinders
15 import RnHsSyn ( RenamedHsExpr,
16 RenamedStmt, RenamedRecordBinds
18 import TcHsSyn ( TcExpr, TcStmt,
24 import BasicTypes ( RecFlag(..) )
26 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
27 LIE, emptyLIE, plusLIE, plusLIEs, newOverloadedLit,
28 newMethod, newMethodWithGivenTy, newDicts )
29 import TcBinds ( tcBindsAndThen, checkSigTyVars )
30 import TcEnv ( TcIdOcc(..), tcInstId,
31 tcLookupLocalValue, tcLookupGlobalValue, tcLookupClassByKey,
32 tcLookupGlobalValueByKey, newMonoIds,
33 tcExtendGlobalTyVars, tcLookupGlobalValueMaybe,
36 import TcMatches ( tcMatchesCase, tcMatchExpected )
37 import TcMonoType ( tcHsType )
38 import TcPat ( tcPat )
39 import TcSimplify ( tcSimplifyAndCheck )
40 import TcType ( TcType, TcMaybe(..),
41 tcInstType, tcInstSigTcType, tcInstTyVars,
42 tcInstSigType, tcInstTcType, tcInstTheta, tcSplitRhoTy,
43 newTyVarTy, newTyVarTys, zonkTcType )
44 import TcKind ( TcKind )
46 import Class ( Class )
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType )
48 import Id ( idType, dataConFieldLabels, dataConSig, recordSelectorFieldLabel,
52 import Kind ( Kind, mkBoxedTypeKind, mkTypeKind, mkArrowKind )
53 import Name ( Name{-instance Eq-} )
54 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
55 splitFunTy_maybe, splitFunTys,
57 splitForAllTys, splitRhoTy, splitSigmaTy,
58 isTauTy, tyVarsOfType, tyVarsOfTypes,
59 splitForAllTy_maybe, splitAlgTyConApp, splitAlgTyConApp_maybe
61 import TyVar ( emptyTyVarEnv, zipTyVarEnv,
62 elementOfTyVarSet, mkTyVarSet, tyVarSetToList
64 import TyCon ( tyConDataCons )
65 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
66 floatPrimTy, addrPrimTy
68 import TysWiredIn ( boolTy, charTy, stringTy )
69 import PrelInfo ( ioTyCon_NAME )
70 import Unify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy )
71 import Unique ( Unique, cCallableClassKey, cReturnableClassKey,
72 enumFromClassOpKey, enumFromThenClassOpKey,
73 enumFromToClassOpKey, enumFromThenToClassOpKey,
74 thenMClassOpKey, zeroClassOpKey, returnMClassOpKey
77 import Maybes ( maybeToBool )
78 import ListSetOps ( minusList )
83 tcExpr :: RenamedHsExpr -- Expession to type check
84 -> TcType s -- Expected type (could be a type variable)
85 -> TcM s (TcExpr s, LIE s)
88 %************************************************************************
90 \subsection{The TAUT rules for variables}
92 %************************************************************************
95 tcExpr (HsVar name) res_ty
96 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
97 unifyTauTy res_ty id_ty `thenTc_`
99 -- Check that the result type doesn't have any nested for-alls.
100 -- For example, a "build" on its own is no good; it must be
101 -- applied to something.
102 checkTc (isTauTy id_ty)
103 (lurkingRank2Err name id_ty) `thenTc_`
105 returnTc (expr', lie)
108 %************************************************************************
110 \subsection{Literals}
112 %************************************************************************
117 tcExpr (HsLit (HsInt i)) res_ty
118 = newOverloadedLit (LiteralOrigin (HsInt i))
119 (OverloadedIntegral i)
120 res_ty `thenNF_Tc` \ stuff ->
123 tcExpr (HsLit (HsFrac f)) res_ty
124 = newOverloadedLit (LiteralOrigin (HsFrac f))
125 (OverloadedFractional f)
126 res_ty `thenNF_Tc` \ stuff ->
130 tcExpr (HsLit lit@(HsLitLit s)) res_ty
131 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
132 newDicts (LitLitOrigin (_UNPK_ s))
133 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
134 returnTc (HsLitOut lit res_ty, dicts)
140 tcExpr (HsLit lit@(HsCharPrim c)) res_ty
141 = unifyTauTy res_ty charPrimTy `thenTc_`
142 returnTc (HsLitOut lit charPrimTy, emptyLIE)
144 tcExpr (HsLit lit@(HsStringPrim s)) res_ty
145 = unifyTauTy res_ty addrPrimTy `thenTc_`
146 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
148 tcExpr (HsLit lit@(HsIntPrim i)) res_ty
149 = unifyTauTy res_ty intPrimTy `thenTc_`
150 returnTc (HsLitOut lit intPrimTy, emptyLIE)
152 tcExpr (HsLit lit@(HsFloatPrim f)) res_ty
153 = unifyTauTy res_ty floatPrimTy `thenTc_`
154 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
156 tcExpr (HsLit lit@(HsDoublePrim d)) res_ty
157 = unifyTauTy res_ty doublePrimTy `thenTc_`
158 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
161 Unoverloaded literals:
164 tcExpr (HsLit lit@(HsChar c)) res_ty
165 = unifyTauTy res_ty charTy `thenTc_`
166 returnTc (HsLitOut lit charTy, emptyLIE)
168 tcExpr (HsLit lit@(HsString str)) res_ty
169 = unifyTauTy res_ty stringTy `thenTc_`
170 returnTc (HsLitOut lit stringTy, emptyLIE)
173 %************************************************************************
175 \subsection{Other expression forms}
177 %************************************************************************
180 tcExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
183 -- perform the negate *before* overloading the integer, since the case
184 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
185 -- convenient to do it here.
187 tcExpr (NegApp (HsLit (HsInt i)) neg) res_ty
188 = tcExpr (HsLit (HsInt (-i))) res_ty
190 tcExpr (NegApp expr neg) res_ty
191 = tcExpr (HsApp neg expr) res_ty
193 tcExpr (HsLam match) res_ty
194 = tcMatchExpected [] res_ty match `thenTc` \ (match',lie) ->
195 returnTc (HsLam match', lie)
197 tcExpr (HsApp e1 e2) res_ty = accum e1 [e2]
199 accum (HsApp e1 e2) args = accum e1 (e2:args)
201 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
202 returnTc (foldl HsApp fun' args', lie)
204 -- equivalent to (op e1) e2:
205 tcExpr (OpApp arg1 op fix arg2) res_ty
206 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
207 returnTc (OpApp arg1' op' fix arg2', lie)
210 Note that the operators in sections are expected to be binary, and
211 a type error will occur if they aren't.
214 -- Left sections, equivalent to
221 tcExpr in_expr@(SectionL arg op) res_ty
222 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
224 -- Check that res_ty is a function type
225 -- Without this check we barf in the desugarer on
227 -- because it tries to desugar to
228 -- f op = \r -> 3 op r
229 -- so (3 `op`) had better be a function!
230 tcAddErrCtxt (sectionLAppCtxt in_expr) $
231 unifyFunTy res_ty `thenTc_`
233 returnTc (SectionL arg' op', lie)
235 -- Right sections, equivalent to \ x -> x op expr, or
238 tcExpr in_expr@(SectionR op expr) res_ty
239 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
240 tcAddErrCtxt (sectionRAppCtxt in_expr) $
241 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
242 tcExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
243 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
244 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
247 The interesting thing about @ccall@ is that it is just a template
248 which we instantiate by filling in details about the types of its
249 argument and result (ie minimal typechecking is performed). So, the
250 basic story is that we allocate a load of type variables (to hold the
251 arg/result types); unify them with the args/result; and store them for
255 tcExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
256 = -- Get the callable and returnable classes.
257 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
258 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
259 tcLookupTyCon ioTyCon_NAME `thenTc` \ (_,_,ioTyCon) ->
262 new_arg_dict (arg, arg_ty)
263 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
264 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
265 returnNF_Tc arg_dicts -- Actually a singleton bag
267 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
271 mapNF_Tc (\ _ -> newTyVarTy mkTypeKind) [1..(length args)] `thenNF_Tc` \ ty_vars ->
272 tcExprs args ty_vars `thenTc` \ (args', args_lie) ->
274 -- The argument types can be unboxed or boxed; the result
275 -- type must, however, be boxed since it's an argument to the IO
277 newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ result_ty ->
279 io_result_ty = mkTyConApp ioTyCon [result_ty]
281 case tyConDataCons ioTyCon of { [ioDataCon] ->
282 unifyTauTy res_ty io_result_ty `thenTc_`
284 -- Construct the extra insts, which encode the
285 -- constraints on the argument and result types.
286 mapNF_Tc new_arg_dict (zipEqual "tcExpr:CCall" args ty_vars) `thenNF_Tc` \ ccarg_dicts_s ->
287 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
289 returnTc (HsApp (HsVar (RealId ioDataCon) `TyApp` [result_ty])
290 (CCall lbl args' may_gc is_asm io_result_ty),
291 -- do the wrapping in the newtype constructor here
292 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
297 tcExpr (HsSCC label expr) res_ty
298 = tcExpr expr res_ty `thenTc` \ (expr', lie) ->
299 returnTc (HsSCC label expr', lie)
301 tcExpr (HsLet binds expr) res_ty
304 binds -- Bindings to check
305 (tc_expr) `thenTc` \ (expr', lie) ->
306 returnTc (expr', lie)
308 tc_expr = tcExpr expr res_ty `thenTc` \ (expr', lie) ->
309 returnTc (expr', lie)
310 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
312 tcExpr in_expr@(HsCase scrut matches src_loc) res_ty
313 = tcAddSrcLoc src_loc $
314 tcAddErrCtxt (caseCtxt in_expr) $
316 -- Typecheck the case alternatives first.
317 -- The case patterns tend to give good type info to use
318 -- when typechecking the scrutinee. For example
321 -- will report that map is applied to too few arguments
323 tcMatchesCase res_ty matches `thenTc` \ (scrut_ty, matches', lie2) ->
325 tcAddErrCtxt (caseScrutCtxt scrut) (
326 tcExpr scrut scrut_ty
327 ) `thenTc` \ (scrut',lie1) ->
329 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
331 tcExpr (HsIf pred b1 b2 src_loc) res_ty
332 = tcAddSrcLoc src_loc $
333 tcAddErrCtxt (predCtxt pred) (
334 tcExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
336 tcExpr b1 res_ty `thenTc` \ (b1',lie2) ->
337 tcExpr b2 res_ty `thenTc` \ (b2',lie3) ->
338 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
342 tcExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
343 = tcDoStmts do_or_lc stmts src_loc res_ty
347 tcExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
348 = unifyListTy res_ty `thenTc` \ elt_ty ->
349 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
350 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
353 = tcAddErrCtxt (listCtxt expr) $
356 tcExpr (ExplicitTuple exprs) res_ty
357 = unifyTupleTy (length exprs) res_ty `thenTc` \ arg_tys ->
358 mapAndUnzipTc (\ (expr, arg_ty) -> tcExpr expr arg_ty)
359 (exprs `zip` arg_tys) -- we know they're of equal length.
360 `thenTc` \ (exprs', lies) ->
361 returnTc (ExplicitTuple exprs', plusLIEs lies)
363 tcExpr (RecordCon con_name _ rbinds) res_ty
364 = tcLookupGlobalValue con_name `thenNF_Tc` \ con_id ->
365 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
367 (_, record_ty) = splitFunTys con_tau
369 -- Con is syntactically constrained to be a data constructor
370 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
371 unifyTauTy res_ty record_ty `thenTc_`
373 -- Check that the record bindings match the constructor
375 bad_fields = badFields rbinds con_id
377 checkTc (null bad_fields) (badFieldsCon con_id bad_fields) `thenTc_`
379 -- Typecheck the record bindings
380 -- (Do this after checkRecordFields in case there's a field that
381 -- doesn't match the constructor.)
382 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
384 returnTc (RecordCon (RealId con_id) con_expr rbinds', con_lie `plusLIE` rbinds_lie)
387 -- The main complication with RecordUpd is that we need to explicitly
388 -- handle the *non-updated* fields. Consider:
390 -- data T a b = MkT1 { fa :: a, fb :: b }
391 -- | MkT2 { fa :: a, fc :: Int -> Int }
392 -- | MkT3 { fd :: a }
394 -- upd :: T a b -> c -> T a c
395 -- upd t x = t { fb = x}
397 -- The type signature on upd is correct (i.e. the result should not be (T a b))
398 -- because upd should be equivalent to:
400 -- upd t x = case t of
401 -- MkT1 p q -> MkT1 p x
402 -- MkT2 a b -> MkT2 p b
403 -- MkT3 d -> error ...
405 -- So we need to give a completely fresh type to the result record,
406 -- and then constrain it by the fields that are *not* updated ("p" above).
408 -- Note that because MkT3 doesn't contain all the fields being updated,
409 -- its RHS is simply an error, so it doesn't impose any type constraints
411 -- All this is done in STEP 4 below.
413 tcExpr (RecordUpd record_expr rbinds) res_ty
414 = tcAddErrCtxt recordUpdCtxt $
417 -- Figure out the tycon and data cons from the first field name
418 ASSERT( not (null rbinds) )
420 ((first_field_name, _, _) : rest) = rbinds
422 tcLookupGlobalValueMaybe first_field_name `thenNF_Tc` \ maybe_sel_id ->
423 (case maybe_sel_id of
424 Just sel_id | isRecordSelector sel_id -> returnTc sel_id
425 other -> failWithTc (notSelector first_field_name)
426 ) `thenTc` \ sel_id ->
428 (_, tau) = splitForAllTys (idType sel_id)
429 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
430 (tycon, _, data_cons) = splitAlgTyConApp data_ty
431 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
433 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
436 -- Check for bad fields
437 checkTc (any (null . badFields rbinds) data_cons)
438 (badFieldsUpd rbinds) `thenTc_`
440 -- Typecheck the update bindings.
441 -- (Do this after checking for bad fields in case there's a field that
442 -- doesn't match the constructor.)
444 result_record_ty = mkTyConApp tycon result_inst_tys
446 unifyTauTy res_ty result_record_ty `thenTc_`
447 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
450 -- Use the un-updated fields to find a vector of booleans saying
451 -- which type arguments must be the same in updatee and result.
453 -- WARNING: this code assumes that all data_cons in a common tycon
454 -- have FieldLabels abstracted over the same tyvars.
456 upd_field_lbls = [recordSelectorFieldLabel sel_id | (RealId sel_id, _, _) <- rbinds']
457 con_field_lbls_s = map dataConFieldLabels data_cons
459 -- A constructor is only relevant to this process if
460 -- it contains all the fields that are being updated
461 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
462 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
464 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
465 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
467 mk_inst_ty (tyvar, result_inst_ty)
468 | tyvar `elementOfTyVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
469 | otherwise = newTyVarTy mkBoxedTypeKind -- Fresh type
471 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
474 -- Typecheck the expression to be updated
476 record_ty = mkTyConApp tycon inst_tys
478 tcExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
481 -- Figure out the LIE we need. We have to generate some
482 -- dictionaries for the data type context, since we are going to
483 -- do some construction.
485 -- What dictionaries do we need? For the moment we assume that all
486 -- data constructors have the same context, and grab it from the first
487 -- constructor. If they have varying contexts then we'd have to
488 -- union the ones that could participate in the update.
490 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
491 inst_env = zipTyVarEnv tyvars result_inst_tys
493 tcInstTheta inst_env theta `thenNF_Tc` \ theta' ->
494 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
497 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
498 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
500 tcExpr (ArithSeqIn seq@(From expr)) res_ty
501 = unifyListTy res_ty `thenTc` \ elt_ty ->
502 tcExpr expr elt_ty `thenTc` \ (expr', lie1) ->
504 tcLookupGlobalValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
505 newMethod (ArithSeqOrigin seq)
506 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
508 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
511 tcExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
512 = tcAddErrCtxt (arithSeqCtxt in_expr) $
513 unifyListTy res_ty `thenTc` \ elt_ty ->
514 tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
515 tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
516 tcLookupGlobalValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
517 newMethod (ArithSeqOrigin seq)
518 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
520 returnTc (ArithSeqOut (HsVar enum_from_then_id)
521 (FromThen expr1' expr2'),
522 lie1 `plusLIE` lie2 `plusLIE` lie3)
524 tcExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
525 = tcAddErrCtxt (arithSeqCtxt in_expr) $
526 unifyListTy res_ty `thenTc` \ elt_ty ->
527 tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
528 tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
529 tcLookupGlobalValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
530 newMethod (ArithSeqOrigin seq)
531 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
533 returnTc (ArithSeqOut (HsVar enum_from_to_id)
534 (FromTo expr1' expr2'),
535 lie1 `plusLIE` lie2 `plusLIE` lie3)
537 tcExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
538 = tcAddErrCtxt (arithSeqCtxt in_expr) $
539 unifyListTy res_ty `thenTc` \ elt_ty ->
540 tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
541 tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
542 tcExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
543 tcLookupGlobalValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
544 newMethod (ArithSeqOrigin seq)
545 (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
547 returnTc (ArithSeqOut (HsVar eft_id)
548 (FromThenTo expr1' expr2' expr3'),
549 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
552 %************************************************************************
554 \subsection{Expressions type signatures}
556 %************************************************************************
559 tcExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
560 = tcSetErrCtxt (exprSigCtxt in_expr) $
561 tcHsType poly_ty `thenTc` \ sigma_sig ->
563 -- Check the tau-type part
564 tcInstSigType sigma_sig `thenNF_Tc` \ sigma_sig' ->
566 (sig_tyvars', sig_theta', sig_tau') = splitSigmaTy sigma_sig'
569 -- Type check the expression, expecting the signature type
570 tcExtendGlobalTyVars sig_tyvars' (
572 ) `thenTc` \ (texpr, lie) ->
574 -- Check the type variables of the signature,
575 -- *after* typechecking the expression
576 checkSigTyVars sig_tyvars' sig_tau' `thenTc` \ zonked_sig_tyvars ->
578 -- Check overloading constraints
579 newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (sig_dicts, _) ->
581 (ptext SLIT("the type signature") <+> quotes (ppr sigma_sig))
582 (mkTyVarSet zonked_sig_tyvars)
586 -- Now match the signature type with res_ty.
587 -- We must not do this earlier, because res_ty might well
588 -- mention variables free in the environment, and we'd get
589 -- bogus complaints about not being able to for-all the
591 unifyTauTy res_ty sig_tau' `thenTc_`
593 -- If everything is ok, return the stuff unchanged, except for
594 -- the effect of any substutions etc. We simply discard the
595 -- result of the tcSimplifyAndCheck, except for any default
596 -- resolution it may have done, which is recorded in the
598 returnTc (texpr, lie)
602 Typecheck expression which in most cases will be an Id.
605 tcExpr_id :: RenamedHsExpr
611 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
613 other -> newTyVarTy mkTypeKind `thenNF_Tc` \ id_ty ->
614 tcExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
615 returnTc (id_expr', lie_id, id_ty)
618 %************************************************************************
620 \subsection{@tcApp@ typchecks an application}
622 %************************************************************************
626 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
627 -> TcType s -- Expected result type of application
628 -> TcM s (TcExpr s, [TcExpr s], -- Translated fun and args
631 tcApp fun args res_ty
632 = -- First type-check the function
633 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
635 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
636 split_fun_ty fun_ty (length args)
637 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
639 -- Unify with expected result before type-checking the args
640 -- This is when we might detect a too-few args situation
641 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
642 unifyTauTy res_ty actual_result_ty
645 -- Now typecheck the args
646 mapAndUnzipTc (tcArg fun)
647 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
649 -- Check that the result type doesn't have any nested for-alls.
650 -- For example, a "build" on its own is no good; it must be applied to something.
651 checkTc (isTauTy actual_result_ty)
652 (lurkingRank2Err fun fun_ty) `thenTc_`
654 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
657 -- If an error happens we try to figure out whether the
658 -- function has been given too many or too few arguments,
660 checkArgsCtxt fun args expected_res_ty actual_res_ty
661 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
662 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
664 (exp_args, _) = splitFunTys exp_ty'
665 (act_args, _) = splitFunTys act_ty'
666 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
667 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
668 | otherwise = appCtxt fun args
673 split_fun_ty :: TcType s -- The type of the function
674 -> Int -- Number of arguments
675 -> TcM s ([TcType s], -- Function argument types
676 TcType s) -- Function result types
678 split_fun_ty fun_ty 0
679 = returnTc ([], fun_ty)
681 split_fun_ty fun_ty n
682 = -- Expect the function to have type A->B
683 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
684 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
685 returnTc (arg_ty:arg_tys, final_res_ty)
689 tcArg :: RenamedHsExpr -- The function (for error messages)
690 -> (RenamedHsExpr, TcType s, Int) -- Actual argument and expected arg type
691 -> TcM s (TcExpr s, LIE s) -- Resulting argument and LIE
693 tcArg the_fun (arg, expected_arg_ty, arg_no)
694 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
695 tcPolyExpr (ptext SLIT("argument type of") <+> quotes (ppr the_fun))
699 -- tcPolyExpr is like tcExpr, except that the expected type
700 -- can be a polymorphic one.
701 tcPolyExpr :: SDoc -- Just for error messages
703 -> TcType s -- Expected type
704 -> TcM s (TcExpr s, LIE s) -- Resulting type and LIE
706 tcPolyExpr str arg expected_arg_ty
707 | not (maybeToBool (splitForAllTy_maybe expected_arg_ty))
708 = -- The ordinary, non-rank-2 polymorphic case
709 tcExpr arg expected_arg_ty
712 = -- Ha! The argument type of the function is a for-all type,
713 -- An example of rank-2 polymorphism.
715 -- No need to instantiate the argument type... it's must be the result
716 -- of instantiating a function involving rank-2 polymorphism, so there
717 -- isn't any danger of using the same tyvars twice
718 -- The argument type shouldn't be overloaded type (hence ASSERT)
720 -- To ensure that the forall'd type variables don't get unified with each
721 -- other or any other types, we make fresh *signature* type variables
722 -- and unify them with the tyvars.
723 tcInstSigTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
725 (sig_theta, sig_tau) = splitRhoTy sig_rho
727 -- Type-check the arg and unify with expected type
728 tcExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
730 -- Check that the arg_tyvars havn't been constrained
731 -- The interesting bit here is that we must include the free variables
732 -- of the expected arg ty. Here's an example:
733 -- runST (newVar True)
734 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
735 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
736 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
737 -- So now s' isn't unconstrained because it's linked to a.
738 -- Conclusion: include the free vars of the expected arg type in the
739 -- list of "free vars" for the signature check.
741 tcExtendGlobalTyVars (tyVarSetToList (tyVarsOfType expected_arg_ty)) $
743 checkSigTyVars sig_tyvars sig_tau `thenTc` \ zonked_sig_tyvars ->
744 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
745 -- ToDo: better origin
749 (mkTyVarSet zonked_sig_tyvars)
750 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
752 -- This HsLet binds any Insts which came out of the simplification.
753 -- It's a bit out of place here, but using AbsBind involves inventing
754 -- a couple of new names which seems worse.
755 returnTc ( TyLam zonked_sig_tyvars $
757 HsLet (MonoBind inst_binds [] Recursive)
763 %************************************************************************
765 \subsection{@tcId@ typchecks an identifier occurrence}
767 %************************************************************************
770 tcId :: Name -> NF_TcM s (TcExpr s, LIE s, TcType s)
773 = -- Look up the Id and instantiate its type
774 tcLookupLocalValue name `thenNF_Tc` \ maybe_local ->
777 Just tc_id -> instantiate_it (TcId tc_id) (idType tc_id)
779 Nothing -> tcLookupGlobalValue name `thenNF_Tc` \ id ->
780 tcInstType emptyTyVarEnv (idType id) `thenNF_Tc` \ inst_ty ->
782 (tyvars, rho) = splitForAllTys inst_ty
784 instantiate_it2 (RealId id) tyvars rho
787 -- The instantiate_it loop runs round instantiating the Id.
788 -- It has to be a loop because we are now prepared to entertain
790 -- f:: forall a. Eq a => forall b. Baz b => tau
791 -- We want to instantiate this to
792 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
793 instantiate_it tc_id_occ ty
794 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
795 instantiate_it2 tc_id_occ tyvars rho
797 instantiate_it2 tc_id_occ tyvars rho
798 = tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
799 if null theta then -- Is it overloaded?
800 returnNF_Tc (mkHsTyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau)
802 -- Yes, it's overloaded
803 newMethodWithGivenTy (OccurrenceOf tc_id_occ)
804 tc_id_occ arg_tys theta tau `thenNF_Tc` \ (lie1, meth_id) ->
805 instantiate_it meth_id tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
806 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
809 arg_tys = mkTyVarTys tyvars
812 %************************************************************************
814 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
816 %************************************************************************
819 tcDoStmts do_or_lc stmts src_loc res_ty
820 = -- get the Monad and MonadZero classes
821 -- create type consisting of a fresh monad tyvar
822 ASSERT( not (null stmts) )
823 tcAddSrcLoc src_loc $
824 newTyVarTy (mkArrowKind mkBoxedTypeKind mkBoxedTypeKind) `thenNF_Tc` \ m ->
827 tc_stmts [] = returnTc (([], error "tc_stmts"), emptyLIE)
828 tc_stmts (stmt:stmts) = tcStmt tcExpr do_or_lc (mkAppTy m) combine_stmts stmt $
831 combine_stmts stmt@(ReturnStmt _) (Just ty) ([], _) = ([stmt], ty)
832 combine_stmts stmt@(ExprStmt e _) (Just ty) ([], _) = ([stmt], ty)
833 combine_stmts stmt _ ([], _) = panic "Bad last stmt tcDoStmts"
834 combine_stmts stmt _ (stmts, ty) = (stmt:stmts, ty)
836 tc_stmts stmts `thenTc` \ ((stmts', result_ty), final_lie) ->
837 unifyTauTy res_ty result_ty `thenTc_`
839 -- Build the then and zero methods in case we need them
840 -- It's important that "then" and "return" appear just once in the final LIE,
841 -- not only for typechecker efficiency, but also because otherwise during
842 -- simplification we end up with silly stuff like
843 -- then = case d of (t,r) -> t
845 -- where the second "then" sees that it already exists in the "available" stuff.
847 tcLookupGlobalValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
848 tcLookupGlobalValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
849 tcLookupGlobalValueByKey zeroClassOpKey `thenNF_Tc` \ zero_sel_id ->
851 (RealId return_sel_id) [m] `thenNF_Tc` \ (return_lie, return_id) ->
853 (RealId then_sel_id) [m] `thenNF_Tc` \ (then_lie, then_id) ->
855 (RealId zero_sel_id) [m] `thenNF_Tc` \ (zero_lie, zero_id) ->
857 monad_lie = then_lie `plusLIE` return_lie `plusLIE` perhaps_zero_lie
858 perhaps_zero_lie | all failure_free stmts' = emptyLIE
859 | otherwise = zero_lie
861 failure_free (BindStmt pat _ _) = failureFreePat pat
862 failure_free (GuardStmt _ _) = False
863 failure_free other_stmt = True
865 returnTc (HsDoOut do_or_lc stmts' return_id then_id zero_id res_ty src_loc,
866 final_lie `plusLIE` monad_lie)
871 tcStmt :: (RenamedHsExpr -> TcType s -> TcM s (TcExpr s, LIE s)) -- This is tcExpr
872 -- The sole, disgusting, reason for this parameter
873 -- is to get the effect of polymorphic recursion
874 -- ToDo: rm when booting with Haskell 1.3
876 -> (TcType s -> TcType s) -- Relationship type of pat and rhs in pat <- rhs
877 -> (TcStmt s -> Maybe (TcType s) -> thing -> thing)
879 -> TcM s (thing, LIE s)
880 -> TcM s (thing, LIE s)
882 tcStmt tc_expr do_or_lc m combine stmt@(ReturnStmt exp) do_next
883 = ASSERT( case do_or_lc of { DoStmt -> False; ListComp -> True; Guard -> True } )
884 tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
885 newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty ->
886 tc_expr exp exp_ty `thenTc` \ (exp', exp_lie) ->
887 returnTc (ReturnStmt exp', exp_lie, m exp_ty)
888 ) `thenTc` \ (stmt', stmt_lie, stmt_ty) ->
889 do_next `thenTc` \ (thing', thing_lie) ->
890 returnTc (combine stmt' (Just stmt_ty) thing',
891 stmt_lie `plusLIE` thing_lie)
893 tcStmt tc_expr do_or_lc m combine stmt@(GuardStmt exp src_loc) do_next
894 = ASSERT( case do_or_lc of { DoStmt -> False; ListComp -> True; Guard -> True } )
895 newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty ->
896 tcAddSrcLoc src_loc (
897 tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
898 tc_expr exp boolTy `thenTc` \ (exp', exp_lie) ->
899 returnTc (GuardStmt exp' src_loc, exp_lie)
900 )) `thenTc` \ (stmt', stmt_lie) ->
901 do_next `thenTc` \ (thing', thing_lie) ->
902 returnTc (combine stmt' Nothing thing',
903 stmt_lie `plusLIE` thing_lie)
905 tcStmt tc_expr do_or_lc m combine stmt@(ExprStmt exp src_loc) do_next
906 = ASSERT( case do_or_lc of { DoStmt -> True; ListComp -> False; Guard -> False } )
907 newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty ->
908 tcAddSrcLoc src_loc (
909 tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
910 newTyVarTy mkTypeKind `thenNF_Tc` \ tau ->
912 -- exp has type (m tau) for some tau (doesn't matter what)
915 tc_expr exp exp_ty `thenTc` \ (exp', exp_lie) ->
916 returnTc (ExprStmt exp' src_loc, exp_lie, exp_ty)
917 )) `thenTc` \ (stmt', stmt_lie, stmt_ty) ->
918 do_next `thenTc` \ (thing', thing_lie) ->
919 returnTc (combine stmt' (Just stmt_ty) thing',
920 stmt_lie `plusLIE` thing_lie)
922 tcStmt tc_expr do_or_lc m combine stmt@(BindStmt pat exp src_loc) do_next
923 = newMonoIds (collectPatBinders pat) mkBoxedTypeKind $ \ _ ->
924 tcAddSrcLoc src_loc (
925 tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
926 tcPat pat `thenTc` \ (pat', pat_lie, pat_ty) ->
927 tc_expr exp (m pat_ty) `thenTc` \ (exp', exp_lie) ->
929 -- NB: the environment has been extended with the new binders
930 -- which the rhs can't "see", but the renamer should have made
931 -- sure that everything is distinct by now, so there's no problem.
932 -- Putting the tcExpr before the newMonoIds messes up the nesting
933 -- of error contexts, so I didn't bother
935 returnTc (BindStmt pat' exp' src_loc, pat_lie `plusLIE` exp_lie)
936 )) `thenTc` \ (stmt', stmt_lie) ->
937 do_next `thenTc` \ (thing', thing_lie) ->
938 returnTc (combine stmt' Nothing thing',
939 stmt_lie `plusLIE` thing_lie)
941 tcStmt tc_expr do_or_lc m combine (LetStmt binds) do_next
942 = tcBindsAndThen -- No error context, but a binding group is
943 combine' -- rather a large thing for an error context anyway
947 combine' is_rec binds' thing' = combine (LetStmt (MonoBind binds' [] is_rec)) Nothing thing'
950 %************************************************************************
952 \subsection{Record bindings}
954 %************************************************************************
956 Game plan for record bindings
957 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
960 1. look up "field", to find its selector Id, which must have type
961 forall a1..an. T a1 .. an -> tau
962 where tau is the type of the field.
964 2. Instantiate this type
966 3. Unify the (T a1 .. an) part with the "expected result type", which
967 is passed in. This checks that all the field labels come from the
970 4. Type check the value using tcArg, passing tau as the expected
973 This extends OK when the field types are universally quantified.
975 Actually, to save excessive creation of fresh type variables,
980 :: TcType s -- Expected type of whole record
981 -> RenamedRecordBinds
982 -> TcM s (TcRecordBinds s, LIE s)
984 tcRecordBinds expected_record_ty rbinds
985 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
986 returnTc (rbinds', plusLIEs lies)
988 do_bind (field_label, rhs, pun_flag)
989 = tcLookupGlobalValue field_label `thenNF_Tc` \ sel_id ->
990 ASSERT( isRecordSelector sel_id )
991 -- This lookup and assertion will surely succeed, because
992 -- we check that the fields are indeed record selectors
993 -- before calling tcRecordBinds
995 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
997 -- Record selectors all have type
998 -- forall a1..an. T a1 .. an -> tau
999 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1001 -- Selector must have type RecordType -> FieldType
1002 Just (record_ty, field_ty) = splitFunTy_maybe tau
1004 unifyTauTy expected_record_ty record_ty `thenTc_`
1005 tcPolyExpr (ptext SLIT("type of field") <+> quotes (ppr field_label))
1006 rhs field_ty `thenTc` \ (rhs', lie) ->
1007 returnTc ((RealId sel_id, rhs', pun_flag), lie)
1009 badFields rbinds data_con
1010 = [field_name | (field_name, _, _) <- rbinds,
1011 not (field_name `elem` field_names)
1014 field_names = map fieldLabelName (dataConFieldLabels data_con)
1017 %************************************************************************
1019 \subsection{@tcExprs@ typechecks a {\em list} of expressions}
1021 %************************************************************************
1024 tcExprs :: [RenamedHsExpr] -> [TcType s] -> TcM s ([TcExpr s], LIE s)
1026 tcExprs [] [] = returnTc ([], emptyLIE)
1027 tcExprs (expr:exprs) (ty:tys)
1028 = tcExpr expr ty `thenTc` \ (expr', lie1) ->
1029 tcExprs exprs tys `thenTc` \ (exprs', lie2) ->
1030 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1034 % =================================================
1041 pp_nest_hang :: String -> SDoc -> SDoc
1042 pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff)
1045 Boring and alphabetical:
1048 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1051 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1054 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1057 = hang (ptext SLIT("In an expression with a type signature:"))
1061 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1064 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1066 sectionRAppCtxt expr
1067 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1069 sectionLAppCtxt expr
1070 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1072 funAppCtxt fun arg arg_no
1073 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1074 quotes (ppr fun) <> text ", namely"])
1075 4 (quotes (ppr arg))
1077 stmtCtxt do_or_lc stmt
1078 = hang (ptext SLIT("In a") <+> whatever <> colon)
1081 whatever = case do_or_lc of
1082 ListComp -> ptext SLIT("list-comprehension qualifier")
1083 DoStmt -> ptext SLIT("do statement")
1084 Guard -> ptext SLIT("guard")
1086 wrongArgsCtxt too_many_or_few fun args
1087 = hang (ptext SLIT("Probable cause:") <+> ppr fun
1088 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1089 <+> ptext SLIT("arguments in the call"))
1090 4 (parens (ppr the_app))
1092 the_app = foldl HsApp fun args -- Used in error messages
1095 = ptext SLIT("In the application") <+> (ppr the_app)
1097 the_app = foldl HsApp fun args -- Used in error messages
1099 lurkingRank2Err fun fun_ty
1100 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1101 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1102 ptext SLIT("so that the result type has for-alls in it")])
1104 rank2ArgCtxt arg expected_arg_ty
1105 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1108 = hang (ptext SLIT("No constructor has all these fields:"))
1109 4 (pprQuotedList fields)
1111 fields = [field | (field, _, _) <- rbinds]
1113 recordUpdCtxt = ptext SLIT("In a record update construct")
1115 badFieldsCon con fields
1116 = hsep [ptext SLIT("Constructor"), ppr con,
1117 ptext SLIT("does not have field(s):"), pprQuotedList fields]
1120 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]