2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcApp, tcExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), StmtCtxt(..)
14 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
15 import TcHsSyn ( TcExpr, TcRecordBinds,
16 mkHsTyApp, mkHsLet, maybeBoxedPrimType
20 import BasicTypes ( RecFlag(..) )
22 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
23 LIE, emptyLIE, unitLIE, plusLIE, plusLIEs, newOverloadedLit,
24 newMethod, instOverloadedFun, newDicts, instToId )
25 import TcBinds ( tcBindsAndThen )
26 import TcEnv ( tcInstId,
27 tcLookupValue, tcLookupClassByKey,
29 tcExtendGlobalTyVars, tcLookupValueMaybe,
30 tcLookupTyCon, tcLookupDataCon
32 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
33 import TcMonoType ( tcHsType, checkSigTyVars, sigCtxt )
34 import TcPat ( badFieldCon )
35 import TcSimplify ( tcSimplifyAndCheck )
36 import TcType ( TcType, TcTauType,
38 tcInstTcType, tcSplitRhoTy,
39 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
41 import Class ( Class )
42 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType
44 import Id ( idType, recordSelectorFieldLabel,
48 import DataCon ( dataConFieldLabels, dataConSig, dataConId,
49 dataConStrictMarks, StrictnessMark(..)
52 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
53 splitFunTy_maybe, splitFunTys, isNotUsgTy,
55 splitForAllTys, splitRhoTy,
56 isTauTy, tyVarsOfType, tyVarsOfTypes,
57 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
58 boxedTypeKind, mkArrowKind,
61 import Subst ( mkTopTyVarSubst, substTheta )
62 import UsageSPUtils ( unannotTy )
63 import VarSet ( elemVarSet, mkVarSet )
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 TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
72 import Unique ( cCallableClassKey, cReturnableClassKey,
73 enumFromClassOpKey, enumFromThenClassOpKey,
74 enumFromToClassOpKey, enumFromThenToClassOpKey,
75 thenMClassOpKey, failMClassOpKey, returnMClassOpKey
78 import Maybes ( maybeToBool, mapMaybe )
79 import ListSetOps ( minusList )
81 import CmdLineOpts ( opt_WarnMissingFields )
85 %************************************************************************
87 \subsection{Main wrappers}
89 %************************************************************************
92 tcExpr :: RenamedHsExpr -- Expession to type check
93 -> TcType -- Expected type (could be a polytpye)
94 -> TcM s (TcExpr, LIE)
96 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
97 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
100 | otherwise = -- Monomorphic case
105 %************************************************************************
107 \subsection{@tcPolyExpr@ typchecks an application}
109 %************************************************************************
112 -- tcPolyExpr is like tcMonoExpr, except that the expected type
113 -- can be a polymorphic one.
114 tcPolyExpr :: RenamedHsExpr
115 -> TcType -- Expected type
116 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
117 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
119 tcPolyExpr arg expected_arg_ty
120 = -- Ha! The argument type of the function is a for-all type,
121 -- An example of rank-2 polymorphism.
123 -- To ensure that the forall'd type variables don't get unified with each
124 -- other or any other types, we make fresh copy of the alleged type
125 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
127 (sig_theta, sig_tau) = splitRhoTy sig_rho
129 -- Type-check the arg and unify with expected type
130 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
132 -- Check that the sig_tyvars havn't been constrained
133 -- The interesting bit here is that we must include the free variables
134 -- of the expected arg ty. Here's an example:
135 -- runST (newVar True)
136 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
137 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
138 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
139 -- So now s' isn't unconstrained because it's linked to a.
140 -- Conclusion: include the free vars of the expected arg type in the
141 -- list of "free vars" for the signature check.
143 tcExtendGlobalTyVars (tyVarsOfType expected_arg_ty) $
144 tcAddErrCtxtM (sigCtxt sig_msg expected_arg_ty) $
146 checkSigTyVars sig_tyvars `thenTc` \ zonked_sig_tyvars ->
148 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
149 -- ToDo: better origin
151 (text "the type signature of an expression")
152 (mkVarSet zonked_sig_tyvars)
153 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
156 -- This HsLet binds any Insts which came out of the simplification.
157 -- It's a bit out of place here, but using AbsBind involves inventing
158 -- a couple of new names which seems worse.
159 generalised_arg = TyLam zonked_sig_tyvars $
164 returnTc ( generalised_arg, free_insts,
165 arg', sig_tau, lie_arg )
167 sig_msg ty = sep [ptext SLIT("In an expression with expected type:"),
171 %************************************************************************
173 \subsection{The TAUT rules for variables}
175 %************************************************************************
178 tcMonoExpr :: RenamedHsExpr -- Expession to type check
179 -> TcTauType -- Expected type (could be a type variable)
180 -> TcM s (TcExpr, LIE)
182 tcMonoExpr (HsVar name) res_ty
183 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
184 unifyTauTy res_ty id_ty `thenTc_`
186 -- Check that the result type doesn't have any nested for-alls.
187 -- For example, a "build" on its own is no good; it must be
188 -- applied to something.
189 checkTc (isTauTy id_ty)
190 (lurkingRank2Err name id_ty) `thenTc_`
192 returnTc (expr', lie)
195 %************************************************************************
197 \subsection{Literals}
199 %************************************************************************
204 tcMonoExpr (HsLit (HsInt i)) res_ty
205 = newOverloadedLit (LiteralOrigin (HsInt i))
206 (OverloadedIntegral i)
207 res_ty `thenNF_Tc` \ stuff ->
210 tcMonoExpr (HsLit (HsFrac f)) res_ty
211 = newOverloadedLit (LiteralOrigin (HsFrac f))
212 (OverloadedFractional f)
213 res_ty `thenNF_Tc` \ stuff ->
217 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
218 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
219 newDicts (LitLitOrigin (_UNPK_ s))
220 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
221 returnTc (HsLitOut lit res_ty, dicts)
227 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
228 = unifyTauTy res_ty charPrimTy `thenTc_`
229 returnTc (HsLitOut lit charPrimTy, emptyLIE)
231 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
232 = unifyTauTy res_ty addrPrimTy `thenTc_`
233 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
235 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
236 = unifyTauTy res_ty intPrimTy `thenTc_`
237 returnTc (HsLitOut lit intPrimTy, emptyLIE)
239 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
240 = unifyTauTy res_ty floatPrimTy `thenTc_`
241 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
243 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
244 = unifyTauTy res_ty doublePrimTy `thenTc_`
245 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
248 Unoverloaded literals:
251 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
252 = unifyTauTy res_ty charTy `thenTc_`
253 returnTc (HsLitOut lit charTy, emptyLIE)
255 tcMonoExpr (HsLit lit@(HsString str)) res_ty
256 = unifyTauTy res_ty stringTy `thenTc_`
257 returnTc (HsLitOut lit stringTy, emptyLIE)
260 %************************************************************************
262 \subsection{Other expression forms}
264 %************************************************************************
267 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
268 = tcMonoExpr expr res_ty
270 -- perform the negate *before* overloading the integer, since the case
271 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
272 -- convenient to do it here.
274 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
275 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
277 tcMonoExpr (NegApp expr neg) res_ty
278 = tcMonoExpr (HsApp neg expr) res_ty
280 tcMonoExpr (HsLam match) res_ty
281 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
282 returnTc (HsLam match', lie)
284 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
286 accum (HsApp e1 e2) args = accum e1 (e2:args)
288 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
289 returnTc (foldl HsApp fun' args', lie)
291 -- equivalent to (op e1) e2:
292 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
293 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
294 returnTc (OpApp arg1' op' fix arg2', lie)
297 Note that the operators in sections are expected to be binary, and
298 a type error will occur if they aren't.
301 -- Left sections, equivalent to
308 tcMonoExpr in_expr@(SectionL arg op) res_ty
309 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
311 -- Check that res_ty is a function type
312 -- Without this check we barf in the desugarer on
314 -- because it tries to desugar to
315 -- f op = \r -> 3 op r
316 -- so (3 `op`) had better be a function!
317 tcAddErrCtxt (sectionLAppCtxt in_expr) $
318 unifyFunTy res_ty `thenTc_`
320 returnTc (SectionL arg' op', lie)
322 -- Right sections, equivalent to \ x -> x op expr, or
325 tcMonoExpr in_expr@(SectionR op expr) res_ty
326 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
327 tcAddErrCtxt (sectionRAppCtxt in_expr) $
328 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
329 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
330 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
331 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
334 The interesting thing about @ccall@ is that it is just a template
335 which we instantiate by filling in details about the types of its
336 argument and result (ie minimal typechecking is performed). So, the
337 basic story is that we allocate a load of type variables (to hold the
338 arg/result types); unify them with the args/result; and store them for
342 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
343 = -- Get the callable and returnable classes.
344 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
345 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
346 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
348 new_arg_dict (arg, arg_ty)
349 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
350 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
351 returnNF_Tc arg_dicts -- Actually a singleton bag
353 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
357 let n_args = length args
358 tv_idxs | n_args == 0 = []
359 | otherwise = [1..n_args]
361 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
362 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
364 -- The argument types can be unboxed or boxed; the result
365 -- type must, however, be boxed since it's an argument to the IO
367 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
369 io_result_ty = mkTyConApp ioTyCon [result_ty]
370 [ioDataCon] = tyConDataCons ioTyCon
372 unifyTauTy res_ty io_result_ty `thenTc_`
374 -- Construct the extra insts, which encode the
375 -- constraints on the argument and result types.
376 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
377 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
378 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
379 (CCall lbl args' may_gc is_asm result_ty),
380 -- do the wrapping in the newtype constructor here
381 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
385 tcMonoExpr (HsSCC lbl expr) res_ty
386 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
387 returnTc (HsSCC lbl expr', lie)
389 tcMonoExpr (HsLet binds expr) res_ty
392 binds -- Bindings to check
393 tc_expr `thenTc` \ (expr', lie) ->
394 returnTc (expr', lie)
396 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
397 returnTc (expr', lie)
398 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
400 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
401 = tcAddSrcLoc src_loc $
402 tcAddErrCtxt (caseCtxt in_expr) $
404 -- Typecheck the case alternatives first.
405 -- The case patterns tend to give good type info to use
406 -- when typechecking the scrutinee. For example
409 -- will report that map is applied to too few arguments
411 -- Not only that, but it's better to check the matches on their
412 -- own, so that we get the expected results for scoped type variables.
414 -- (p::a, q::b) -> (q,p)
415 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
416 -- claimed by the pattern signatures. But if we typechecked the
417 -- match with x in scope and x's type as the expected type, we'd be hosed.
419 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
421 tcAddErrCtxt (caseScrutCtxt scrut) (
422 tcMonoExpr scrut scrut_ty
423 ) `thenTc` \ (scrut',lie1) ->
425 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
427 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
428 = tcAddSrcLoc src_loc $
429 tcAddErrCtxt (predCtxt pred) (
430 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
432 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
433 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
434 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
438 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
439 = tcDoStmts do_or_lc stmts src_loc res_ty
443 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
444 = unifyListTy res_ty `thenTc` \ elt_ty ->
445 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
446 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
449 = tcAddErrCtxt (listCtxt expr) $
450 tcMonoExpr expr elt_ty
452 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
454 then unifyTupleTy (length exprs) res_ty
455 else unifyUnboxedTupleTy (length exprs) res_ty
456 ) `thenTc` \ arg_tys ->
457 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
458 (exprs `zip` arg_tys) -- we know they're of equal length.
459 `thenTc` \ (exprs', lies) ->
460 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
462 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
463 = tcAddErrCtxt (recordConCtxt expr) $
464 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
466 (_, record_ty) = splitFunTys con_tau
468 -- Con is syntactically constrained to be a data constructor
469 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
470 unifyTauTy res_ty record_ty `thenTc_`
472 -- Check that the record bindings match the constructor
473 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
475 bad_fields = badFields rbinds data_con
477 if not (null bad_fields) then
478 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
479 failTc -- Fail now, because tcRecordBinds will crash on a bad field
482 -- Typecheck the record bindings
483 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
486 missing_s_fields = missingStrictFields rbinds data_con
488 checkTcM (null missing_s_fields)
489 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
490 returnNF_Tc ()) `thenNF_Tc_`
492 missing_fields = missingFields rbinds data_con
494 checkTcM (not (opt_WarnMissingFields && not (null missing_fields)))
495 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
496 returnNF_Tc ()) `thenNF_Tc_`
498 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
500 -- The main complication with RecordUpd is that we need to explicitly
501 -- handle the *non-updated* fields. Consider:
503 -- data T a b = MkT1 { fa :: a, fb :: b }
504 -- | MkT2 { fa :: a, fc :: Int -> Int }
505 -- | MkT3 { fd :: a }
507 -- upd :: T a b -> c -> T a c
508 -- upd t x = t { fb = x}
510 -- The type signature on upd is correct (i.e. the result should not be (T a b))
511 -- because upd should be equivalent to:
513 -- upd t x = case t of
514 -- MkT1 p q -> MkT1 p x
515 -- MkT2 a b -> MkT2 p b
516 -- MkT3 d -> error ...
518 -- So we need to give a completely fresh type to the result record,
519 -- and then constrain it by the fields that are *not* updated ("p" above).
521 -- Note that because MkT3 doesn't contain all the fields being updated,
522 -- its RHS is simply an error, so it doesn't impose any type constraints
524 -- All this is done in STEP 4 below.
526 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
527 = tcAddErrCtxt (recordUpdCtxt expr) $
530 -- Check that the field names are really field names
531 ASSERT( not (null rbinds) )
533 field_names = [field_name | (field_name, _, _) <- rbinds]
535 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
537 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
540 Just sel_id -> not (isRecordSelector sel_id)
543 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
544 if not (null bad_guys) then
549 -- Figure out the tycon and data cons from the first field name
551 (Just sel_id : _) = maybe_sel_ids
552 (_, tau) = ASSERT( isNotUsgTy (idType sel_id) )
553 splitForAllTys (idType sel_id)
554 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
555 (tycon, _, data_cons) = splitAlgTyConApp data_ty
556 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
558 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
561 -- Check that at least one constructor has all the named fields
562 -- i.e. has an empty set of bad fields returned by badFields
563 checkTc (any (null . badFields rbinds) data_cons)
564 (badFieldsUpd rbinds) `thenTc_`
567 -- Typecheck the update bindings.
568 -- (Do this after checking for bad fields in case there's a field that
569 -- doesn't match the constructor.)
571 result_record_ty = mkTyConApp tycon result_inst_tys
573 unifyTauTy res_ty result_record_ty `thenTc_`
574 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
577 -- Use the un-updated fields to find a vector of booleans saying
578 -- which type arguments must be the same in updatee and result.
580 -- WARNING: this code assumes that all data_cons in a common tycon
581 -- have FieldLabels abstracted over the same tyvars.
583 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
584 con_field_lbls_s = map dataConFieldLabels data_cons
586 -- A constructor is only relevant to this process if
587 -- it contains all the fields that are being updated
588 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
589 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
591 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
592 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
594 mk_inst_ty (tyvar, result_inst_ty)
595 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
596 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
598 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
601 -- Typecheck the expression to be updated
603 record_ty = mkTyConApp tycon inst_tys
605 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
608 -- Figure out the LIE we need. We have to generate some
609 -- dictionaries for the data type context, since we are going to
610 -- do some construction.
612 -- What dictionaries do we need? For the moment we assume that all
613 -- data constructors have the same context, and grab it from the first
614 -- constructor. If they have varying contexts then we'd have to
615 -- union the ones that could participate in the update.
617 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
618 inst_env = mkTopTyVarSubst tyvars result_inst_tys
619 theta' = substTheta inst_env theta
621 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
624 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
625 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
627 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
628 = unifyListTy res_ty `thenTc` \ elt_ty ->
629 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
631 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
632 newMethod (ArithSeqOrigin seq)
633 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
635 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
638 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
639 = tcAddErrCtxt (arithSeqCtxt in_expr) $
640 unifyListTy res_ty `thenTc` \ elt_ty ->
641 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
642 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
643 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
644 newMethod (ArithSeqOrigin seq)
645 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
647 returnTc (ArithSeqOut (HsVar enum_from_then_id)
648 (FromThen expr1' expr2'),
649 lie1 `plusLIE` lie2 `plusLIE` lie3)
651 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
652 = tcAddErrCtxt (arithSeqCtxt in_expr) $
653 unifyListTy res_ty `thenTc` \ elt_ty ->
654 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
655 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
656 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
657 newMethod (ArithSeqOrigin seq)
658 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
660 returnTc (ArithSeqOut (HsVar enum_from_to_id)
661 (FromTo expr1' expr2'),
662 lie1 `plusLIE` lie2 `plusLIE` lie3)
664 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
665 = tcAddErrCtxt (arithSeqCtxt in_expr) $
666 unifyListTy res_ty `thenTc` \ elt_ty ->
667 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
668 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
669 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
670 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
671 newMethod (ArithSeqOrigin seq)
672 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
674 returnTc (ArithSeqOut (HsVar eft_id)
675 (FromThenTo expr1' expr2' expr3'),
676 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
679 %************************************************************************
681 \subsection{Expressions type signatures}
683 %************************************************************************
686 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
687 = tcSetErrCtxt (exprSigCtxt in_expr) $
688 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
690 if not (isForAllTy sig_tc_ty) then
692 unifyTauTy sig_tc_ty res_ty `thenTc_`
693 tcMonoExpr expr sig_tc_ty
695 else -- Signature is polymorphic
696 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
698 -- Now match the signature type with res_ty.
699 -- We must not do this earlier, because res_ty might well
700 -- mention variables free in the environment, and we'd get
701 -- bogus complaints about not being able to for-all the
703 unifyTauTy res_ty expr_ty `thenTc_`
705 -- If everything is ok, return the stuff unchanged, except for
706 -- the effect of any substutions etc. We simply discard the
707 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
708 -- resolution it may have done, which is recorded in the
713 Typecheck expression which in most cases will be an Id.
716 tcExpr_id :: RenamedHsExpr
722 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
724 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
725 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
726 returnTc (id_expr', lie_id, id_ty)
729 %************************************************************************
731 \subsection{@tcApp@ typchecks an application}
733 %************************************************************************
737 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
738 -> TcType -- Expected result type of application
739 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
742 tcApp fun args res_ty
743 = -- First type-check the function
744 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
746 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
747 split_fun_ty fun_ty (length args)
748 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
750 -- Unify with expected result before type-checking the args
751 -- This is when we might detect a too-few args situation
752 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
753 unifyTauTy res_ty actual_result_ty
756 -- Now typecheck the args
757 mapAndUnzipTc (tcArg fun)
758 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
760 -- Check that the result type doesn't have any nested for-alls.
761 -- For example, a "build" on its own is no good; it must be applied to something.
762 checkTc (isTauTy actual_result_ty)
763 (lurkingRank2Err fun fun_ty) `thenTc_`
765 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
768 -- If an error happens we try to figure out whether the
769 -- function has been given too many or too few arguments,
771 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
772 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
773 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
775 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
776 (env2, act_ty'') = tidyOpenType env1 act_ty'
777 (exp_args, _) = splitFunTys exp_ty''
778 (act_args, _) = splitFunTys act_ty''
780 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
781 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
782 | otherwise = appCtxt fun args
784 returnNF_Tc (env2, message)
787 split_fun_ty :: TcType -- The type of the function
788 -> Int -- Number of arguments
789 -> TcM s ([TcType], -- Function argument types
790 TcType) -- Function result types
792 split_fun_ty fun_ty 0
793 = returnTc ([], fun_ty)
795 split_fun_ty fun_ty n
796 = -- Expect the function to have type A->B
797 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
798 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
799 returnTc (arg_ty:arg_tys, final_res_ty)
803 tcArg :: RenamedHsExpr -- The function (for error messages)
804 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
805 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
807 tcArg the_fun (arg, expected_arg_ty, arg_no)
808 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
809 tcExpr arg expected_arg_ty
813 %************************************************************************
815 \subsection{@tcId@ typchecks an identifier occurrence}
817 %************************************************************************
819 Between the renamer and the first invocation of the UsageSP inference,
820 identifiers read from interface files will have usage information in
821 their types, whereas other identifiers will not. The unannotTy here
822 in @tcId@ prevents this information from pointlessly propagating
823 further prior to the first usage inference.
826 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
829 = -- Look up the Id and instantiate its type
830 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
833 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
835 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
836 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
837 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
840 -- The instantiate_it loop runs round instantiating the Id.
841 -- It has to be a loop because we are now prepared to entertain
843 -- f:: forall a. Eq a => forall b. Baz b => tau
844 -- We want to instantiate this to
845 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
846 instantiate_it orig fun ty
847 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
848 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
849 instantiate_it2 orig fun tyvars theta tau
851 instantiate_it2 orig fun tyvars theta tau
852 = if null theta then -- Is it overloaded?
853 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
855 -- Yes, it's overloaded
856 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
857 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
858 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
861 arg_tys = mkTyVarTys tyvars
864 %************************************************************************
866 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
868 %************************************************************************
871 tcDoStmts do_or_lc stmts src_loc res_ty
872 = -- get the Monad and MonadZero classes
873 -- create type consisting of a fresh monad tyvar
874 ASSERT( not (null stmts) )
875 tcAddSrcLoc src_loc $
877 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
878 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
879 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
881 -- If it's a comprehension we're dealing with,
882 -- force it to be a list comprehension.
883 -- (as of Haskell 98, monad comprehensions are no more.)
885 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
886 _ -> returnTc ()) `thenTc_`
888 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
890 -- Build the then and zero methods in case we need them
891 -- It's important that "then" and "return" appear just once in the final LIE,
892 -- not only for typechecker efficiency, but also because otherwise during
893 -- simplification we end up with silly stuff like
894 -- then = case d of (t,r) -> t
896 -- where the second "then" sees that it already exists in the "available" stuff.
898 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
899 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
900 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
901 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
902 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
903 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
905 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
907 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
908 stmts_lie `plusLIE` monad_lie)
912 %************************************************************************
914 \subsection{Record bindings}
916 %************************************************************************
918 Game plan for record bindings
919 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
922 1. look up "field", to find its selector Id, which must have type
923 forall a1..an. T a1 .. an -> tau
924 where tau is the type of the field.
926 2. Instantiate this type
928 3. Unify the (T a1 .. an) part with the "expected result type", which
929 is passed in. This checks that all the field labels come from the
932 4. Type check the value using tcArg, passing tau as the expected
935 This extends OK when the field types are universally quantified.
937 Actually, to save excessive creation of fresh type variables,
942 :: TcType -- Expected type of whole record
943 -> RenamedRecordBinds
944 -> TcM s (TcRecordBinds, LIE)
946 tcRecordBinds expected_record_ty rbinds
947 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
948 returnTc (rbinds', plusLIEs lies)
950 do_bind (field_label, rhs, pun_flag)
951 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
952 ASSERT( isRecordSelector sel_id )
953 -- This lookup and assertion will surely succeed, because
954 -- we check that the fields are indeed record selectors
955 -- before calling tcRecordBinds
957 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
959 -- Record selectors all have type
960 -- forall a1..an. T a1 .. an -> tau
961 ASSERT( maybeToBool (splitFunTy_maybe tau) )
963 -- Selector must have type RecordType -> FieldType
964 Just (record_ty, field_ty) = splitFunTy_maybe tau
966 unifyTauTy expected_record_ty record_ty `thenTc_`
967 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
968 returnTc ((sel_id, rhs', pun_flag), lie)
970 badFields rbinds data_con
971 = [field_name | (field_name, _, _) <- rbinds,
972 not (field_name `elem` field_names)
975 field_names = map fieldLabelName (dataConFieldLabels data_con)
977 missingStrictFields rbinds data_con
978 = [ fn | fn <- strict_field_names,
979 not (fn `elem` field_names_used)
982 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
983 strict_field_names = mapMaybe isStrict field_info
985 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
988 field_info = zip (dataConFieldLabels data_con)
989 (dataConStrictMarks data_con)
991 missingFields rbinds data_con
992 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
994 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
996 -- missing strict fields have already been flagged as
997 -- being so, so leave them out here.
998 non_strict_field_names = mapMaybe isn'tStrict field_info
1000 isn'tStrict (fl, MarkedStrict) = Nothing
1001 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1003 field_info = zip (dataConFieldLabels data_con)
1004 (dataConStrictMarks data_con)
1008 %************************************************************************
1010 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1012 %************************************************************************
1015 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1017 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1018 tcMonoExprs (expr:exprs) (ty:tys)
1019 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1020 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1021 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1025 % =================================================
1032 pp_nest_hang :: String -> SDoc -> SDoc
1033 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1036 Boring and alphabetical:
1039 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1042 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1045 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1048 = hang (ptext SLIT("In an expression with a type signature:"))
1052 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1055 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1057 sectionRAppCtxt expr
1058 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1060 sectionLAppCtxt expr
1061 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1063 funAppCtxt fun arg arg_no
1064 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1065 quotes (ppr fun) <> text ", namely"])
1066 4 (quotes (ppr arg))
1068 wrongArgsCtxt too_many_or_few fun args
1069 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1070 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1071 <+> ptext SLIT("arguments in the call"))
1072 4 (parens (ppr the_app))
1074 the_app = foldl HsApp fun args -- Used in error messages
1077 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1079 the_app = foldl HsApp fun args -- Used in error messages
1081 lurkingRank2Err fun fun_ty
1082 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1083 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1084 ptext SLIT("so that the result type has for-alls in it")])
1086 rank2ArgCtxt arg expected_arg_ty
1087 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1090 = hang (ptext SLIT("No constructor has all these fields:"))
1091 4 (pprQuotedList fields)
1093 fields = [field | (field, _, _) <- rbinds]
1095 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1096 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1099 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1101 illegalCcallTyErr isArg ty
1102 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1106 | isArg = ptext SLIT("argument")
1107 | otherwise = ptext SLIT("result")
1110 missingStrictFieldCon :: Name -> Name -> SDoc
1111 missingStrictFieldCon con field
1112 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1113 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1115 missingFieldCon :: Name -> Name -> SDoc
1116 missingFieldCon con field
1117 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1118 ptext SLIT("is not initialised")]