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 )
43 import Id ( idType, recordSelectorFieldLabel,
47 import DataCon ( dataConFieldLabels, dataConSig, dataConId )
49 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
50 splitFunTy_maybe, splitFunTys, isNotUsgTy,
52 splitForAllTys, splitRhoTy,
53 isTauTy, tyVarsOfType, tyVarsOfTypes,
54 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
55 boxedTypeKind, mkArrowKind,
58 import Subst ( mkTopTyVarSubst, substTheta )
59 import UsageSPUtils ( unannotTy )
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, failMClassOpKey, 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 $
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 let n_args = length args
352 tv_idxs | n_args == 0 = []
353 | otherwise = [1..n_args]
355 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
356 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
358 -- The argument types can be unboxed or boxed; the result
359 -- type must, however, be boxed since it's an argument to the IO
361 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
363 io_result_ty = mkTyConApp ioTyCon [result_ty]
364 [ioDataCon] = tyConDataCons ioTyCon
366 unifyTauTy res_ty io_result_ty `thenTc_`
368 -- Construct the extra insts, which encode the
369 -- constraints on the argument and result types.
370 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
371 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
372 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
373 (CCall lbl args' may_gc is_asm result_ty),
374 -- do the wrapping in the newtype constructor here
375 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
379 tcMonoExpr (HsSCC label expr) res_ty
380 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
381 returnTc (HsSCC label expr', lie)
383 tcMonoExpr (HsLet binds expr) res_ty
386 binds -- Bindings to check
387 tc_expr `thenTc` \ (expr', lie) ->
388 returnTc (expr', lie)
390 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
391 returnTc (expr', lie)
392 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
394 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
395 = tcAddSrcLoc src_loc $
396 tcAddErrCtxt (caseCtxt in_expr) $
398 -- Typecheck the case alternatives first.
399 -- The case patterns tend to give good type info to use
400 -- when typechecking the scrutinee. For example
403 -- will report that map is applied to too few arguments
405 -- Not only that, but it's better to check the matches on their
406 -- own, so that we get the expected results for scoped type variables.
408 -- (p::a, q::b) -> (q,p)
409 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
410 -- claimed by the pattern signatures. But if we typechecked the
411 -- match with x in scope and x's type as the expected type, we'd be hosed.
413 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
415 tcAddErrCtxt (caseScrutCtxt scrut) (
416 tcMonoExpr scrut scrut_ty
417 ) `thenTc` \ (scrut',lie1) ->
419 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
421 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
422 = tcAddSrcLoc src_loc $
423 tcAddErrCtxt (predCtxt pred) (
424 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
426 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
427 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
428 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
432 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
433 = tcDoStmts do_or_lc stmts src_loc res_ty
437 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
438 = unifyListTy res_ty `thenTc` \ elt_ty ->
439 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
440 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
443 = tcAddErrCtxt (listCtxt expr) $
444 tcMonoExpr expr elt_ty
446 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
448 then unifyTupleTy (length exprs) res_ty
449 else unifyUnboxedTupleTy (length exprs) res_ty
450 ) `thenTc` \ arg_tys ->
451 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
452 (exprs `zip` arg_tys) -- we know they're of equal length.
453 `thenTc` \ (exprs', lies) ->
454 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
456 tcMonoExpr (RecordCon con_name rbinds) res_ty
457 = tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
459 (_, record_ty) = splitFunTys con_tau
461 -- Con is syntactically constrained to be a data constructor
462 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
463 unifyTauTy res_ty record_ty `thenTc_`
465 -- Check that the record bindings match the constructor
466 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
468 bad_fields = badFields rbinds data_con
470 if not (null bad_fields) then
471 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
472 failTc -- Fail now, because tcRecordBinds will crash on a bad field
475 -- Typecheck the record bindings
476 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
478 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
481 -- The main complication with RecordUpd is that we need to explicitly
482 -- handle the *non-updated* fields. Consider:
484 -- data T a b = MkT1 { fa :: a, fb :: b }
485 -- | MkT2 { fa :: a, fc :: Int -> Int }
486 -- | MkT3 { fd :: a }
488 -- upd :: T a b -> c -> T a c
489 -- upd t x = t { fb = x}
491 -- The type signature on upd is correct (i.e. the result should not be (T a b))
492 -- because upd should be equivalent to:
494 -- upd t x = case t of
495 -- MkT1 p q -> MkT1 p x
496 -- MkT2 a b -> MkT2 p b
497 -- MkT3 d -> error ...
499 -- So we need to give a completely fresh type to the result record,
500 -- and then constrain it by the fields that are *not* updated ("p" above).
502 -- Note that because MkT3 doesn't contain all the fields being updated,
503 -- its RHS is simply an error, so it doesn't impose any type constraints
505 -- All this is done in STEP 4 below.
507 tcMonoExpr (RecordUpd record_expr rbinds) res_ty
508 = tcAddErrCtxt recordUpdCtxt $
511 -- Check that the field names are really field names
512 ASSERT( not (null rbinds) )
514 field_names = [field_name | (field_name, _, _) <- rbinds]
516 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
518 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
521 Just sel_id -> not (isRecordSelector sel_id)
524 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
525 if not (null bad_guys) then
530 -- Figure out the tycon and data cons from the first field name
532 (Just sel_id : _) = maybe_sel_ids
533 (_, tau) = ASSERT( isNotUsgTy (idType sel_id) )
534 splitForAllTys (idType sel_id)
535 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
536 (tycon, _, data_cons) = splitAlgTyConApp data_ty
537 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
539 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
542 -- Check that at least one constructor has all the named fields
543 -- i.e. has an empty set of bad fields returned by badFields
544 checkTc (any (null . badFields rbinds) data_cons)
545 (badFieldsUpd rbinds) `thenTc_`
548 -- Typecheck the update bindings.
549 -- (Do this after checking for bad fields in case there's a field that
550 -- doesn't match the constructor.)
552 result_record_ty = mkTyConApp tycon result_inst_tys
554 unifyTauTy res_ty result_record_ty `thenTc_`
555 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
558 -- Use the un-updated fields to find a vector of booleans saying
559 -- which type arguments must be the same in updatee and result.
561 -- WARNING: this code assumes that all data_cons in a common tycon
562 -- have FieldLabels abstracted over the same tyvars.
564 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
565 con_field_lbls_s = map dataConFieldLabels data_cons
567 -- A constructor is only relevant to this process if
568 -- it contains all the fields that are being updated
569 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
570 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
572 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
573 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
575 mk_inst_ty (tyvar, result_inst_ty)
576 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
577 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
579 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
582 -- Typecheck the expression to be updated
584 record_ty = mkTyConApp tycon inst_tys
586 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
589 -- Figure out the LIE we need. We have to generate some
590 -- dictionaries for the data type context, since we are going to
591 -- do some construction.
593 -- What dictionaries do we need? For the moment we assume that all
594 -- data constructors have the same context, and grab it from the first
595 -- constructor. If they have varying contexts then we'd have to
596 -- union the ones that could participate in the update.
598 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
599 inst_env = mkTopTyVarSubst tyvars result_inst_tys
600 theta' = substTheta inst_env theta
602 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
605 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
606 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
608 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
609 = unifyListTy res_ty `thenTc` \ elt_ty ->
610 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
612 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
613 newMethod (ArithSeqOrigin seq)
614 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
616 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
619 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
620 = tcAddErrCtxt (arithSeqCtxt in_expr) $
621 unifyListTy res_ty `thenTc` \ elt_ty ->
622 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
623 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
624 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
625 newMethod (ArithSeqOrigin seq)
626 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
628 returnTc (ArithSeqOut (HsVar enum_from_then_id)
629 (FromThen expr1' expr2'),
630 lie1 `plusLIE` lie2 `plusLIE` lie3)
632 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
633 = tcAddErrCtxt (arithSeqCtxt in_expr) $
634 unifyListTy res_ty `thenTc` \ elt_ty ->
635 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
636 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
637 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
638 newMethod (ArithSeqOrigin seq)
639 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
641 returnTc (ArithSeqOut (HsVar enum_from_to_id)
642 (FromTo expr1' expr2'),
643 lie1 `plusLIE` lie2 `plusLIE` lie3)
645 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
646 = tcAddErrCtxt (arithSeqCtxt in_expr) $
647 unifyListTy res_ty `thenTc` \ elt_ty ->
648 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
649 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
650 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
651 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
652 newMethod (ArithSeqOrigin seq)
653 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
655 returnTc (ArithSeqOut (HsVar eft_id)
656 (FromThenTo expr1' expr2' expr3'),
657 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
660 %************************************************************************
662 \subsection{Expressions type signatures}
664 %************************************************************************
667 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
668 = tcSetErrCtxt (exprSigCtxt in_expr) $
669 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
671 if not (isForAllTy sig_tc_ty) then
673 unifyTauTy sig_tc_ty res_ty `thenTc_`
674 tcMonoExpr expr sig_tc_ty
676 else -- Signature is polymorphic
677 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
679 -- Now match the signature type with res_ty.
680 -- We must not do this earlier, because res_ty might well
681 -- mention variables free in the environment, and we'd get
682 -- bogus complaints about not being able to for-all the
684 unifyTauTy res_ty expr_ty `thenTc_`
686 -- If everything is ok, return the stuff unchanged, except for
687 -- the effect of any substutions etc. We simply discard the
688 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
689 -- resolution it may have done, which is recorded in the
694 Typecheck expression which in most cases will be an Id.
697 tcExpr_id :: RenamedHsExpr
703 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
705 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
706 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
707 returnTc (id_expr', lie_id, id_ty)
710 %************************************************************************
712 \subsection{@tcApp@ typchecks an application}
714 %************************************************************************
718 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
719 -> TcType -- Expected result type of application
720 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
723 tcApp fun args res_ty
724 = -- First type-check the function
725 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
727 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
728 split_fun_ty fun_ty (length args)
729 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
731 -- Unify with expected result before type-checking the args
732 -- This is when we might detect a too-few args situation
733 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
734 unifyTauTy res_ty actual_result_ty
737 -- Now typecheck the args
738 mapAndUnzipTc (tcArg fun)
739 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
741 -- Check that the result type doesn't have any nested for-alls.
742 -- For example, a "build" on its own is no good; it must be applied to something.
743 checkTc (isTauTy actual_result_ty)
744 (lurkingRank2Err fun fun_ty) `thenTc_`
746 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
749 -- If an error happens we try to figure out whether the
750 -- function has been given too many or too few arguments,
752 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
753 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
754 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
756 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
757 (env2, act_ty'') = tidyOpenType env1 act_ty'
758 (exp_args, _) = splitFunTys exp_ty''
759 (act_args, _) = splitFunTys act_ty''
761 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
762 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
763 | otherwise = appCtxt fun args
765 returnNF_Tc (env2, message)
768 split_fun_ty :: TcType -- The type of the function
769 -> Int -- Number of arguments
770 -> TcM s ([TcType], -- Function argument types
771 TcType) -- Function result types
773 split_fun_ty fun_ty 0
774 = returnTc ([], fun_ty)
776 split_fun_ty fun_ty n
777 = -- Expect the function to have type A->B
778 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
779 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
780 returnTc (arg_ty:arg_tys, final_res_ty)
784 tcArg :: RenamedHsExpr -- The function (for error messages)
785 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
786 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
788 tcArg the_fun (arg, expected_arg_ty, arg_no)
789 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
790 tcExpr arg expected_arg_ty
794 %************************************************************************
796 \subsection{@tcId@ typchecks an identifier occurrence}
798 %************************************************************************
800 Between the renamer and the first invocation of the UsageSP inference,
801 identifiers read from interface files will have usage information in
802 their types, whereas other identifiers will not. The unannotTy here
803 in @tcId@ prevents this information from pointlessly propagating
804 further prior to the first usage inference.
807 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
810 = -- Look up the Id and instantiate its type
811 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
814 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
816 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
817 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
818 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
821 -- The instantiate_it loop runs round instantiating the Id.
822 -- It has to be a loop because we are now prepared to entertain
824 -- f:: forall a. Eq a => forall b. Baz b => tau
825 -- We want to instantiate this to
826 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
827 instantiate_it orig fun ty
828 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
829 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
830 instantiate_it2 orig fun tyvars theta tau
832 instantiate_it2 orig fun tyvars theta tau
833 = if null theta then -- Is it overloaded?
834 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
836 -- Yes, it's overloaded
837 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
838 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
839 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
842 arg_tys = mkTyVarTys tyvars
845 %************************************************************************
847 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
849 %************************************************************************
852 tcDoStmts do_or_lc stmts src_loc res_ty
853 = -- get the Monad and MonadZero classes
854 -- create type consisting of a fresh monad tyvar
855 ASSERT( not (null stmts) )
856 tcAddSrcLoc src_loc $
858 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
859 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
860 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
862 -- If it's a comprehension we're dealing with,
863 -- force it to be a list comprehension.
864 -- (as of Haskell 98, monad comprehensions are no more.)
866 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
867 _ -> returnTc ()) `thenTc_`
869 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
871 -- Build the then and zero methods in case we need them
872 -- It's important that "then" and "return" appear just once in the final LIE,
873 -- not only for typechecker efficiency, but also because otherwise during
874 -- simplification we end up with silly stuff like
875 -- then = case d of (t,r) -> t
877 -- where the second "then" sees that it already exists in the "available" stuff.
879 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
880 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
881 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
882 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
883 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
884 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
886 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
888 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
889 stmts_lie `plusLIE` monad_lie)
893 %************************************************************************
895 \subsection{Record bindings}
897 %************************************************************************
899 Game plan for record bindings
900 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
903 1. look up "field", to find its selector Id, which must have type
904 forall a1..an. T a1 .. an -> tau
905 where tau is the type of the field.
907 2. Instantiate this type
909 3. Unify the (T a1 .. an) part with the "expected result type", which
910 is passed in. This checks that all the field labels come from the
913 4. Type check the value using tcArg, passing tau as the expected
916 This extends OK when the field types are universally quantified.
918 Actually, to save excessive creation of fresh type variables,
923 :: TcType -- Expected type of whole record
924 -> RenamedRecordBinds
925 -> TcM s (TcRecordBinds, LIE)
927 tcRecordBinds expected_record_ty rbinds
928 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
929 returnTc (rbinds', plusLIEs lies)
931 do_bind (field_label, rhs, pun_flag)
932 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
933 ASSERT( isRecordSelector sel_id )
934 -- This lookup and assertion will surely succeed, because
935 -- we check that the fields are indeed record selectors
936 -- before calling tcRecordBinds
938 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
940 -- Record selectors all have type
941 -- forall a1..an. T a1 .. an -> tau
942 ASSERT( maybeToBool (splitFunTy_maybe tau) )
944 -- Selector must have type RecordType -> FieldType
945 Just (record_ty, field_ty) = splitFunTy_maybe tau
947 unifyTauTy expected_record_ty record_ty `thenTc_`
948 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
949 returnTc ((sel_id, rhs', pun_flag), lie)
951 badFields rbinds data_con
952 = [field_name | (field_name, _, _) <- rbinds,
953 not (field_name `elem` field_names)
956 field_names = map fieldLabelName (dataConFieldLabels data_con)
959 %************************************************************************
961 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
963 %************************************************************************
966 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
968 tcMonoExprs [] [] = returnTc ([], emptyLIE)
969 tcMonoExprs (expr:exprs) (ty:tys)
970 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
971 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
972 returnTc (expr':exprs', lie1 `plusLIE` lie2)
976 % =================================================
983 pp_nest_hang :: String -> SDoc -> SDoc
984 pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff)
987 Boring and alphabetical:
990 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
993 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
996 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
999 = hang (ptext SLIT("In an expression with a type signature:"))
1003 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1006 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1008 sectionRAppCtxt expr
1009 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1011 sectionLAppCtxt expr
1012 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1014 funAppCtxt fun arg arg_no
1015 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1016 quotes (ppr fun) <> text ", namely"])
1017 4 (quotes (ppr arg))
1019 wrongArgsCtxt too_many_or_few fun args
1020 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1021 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1022 <+> ptext SLIT("arguments in the call"))
1023 4 (parens (ppr the_app))
1025 the_app = foldl HsApp fun args -- Used in error messages
1028 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1030 the_app = foldl HsApp fun args -- Used in error messages
1032 lurkingRank2Err fun fun_ty
1033 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1034 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1035 ptext SLIT("so that the result type has for-alls in it")])
1037 rank2ArgCtxt arg expected_arg_ty
1038 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1041 = hang (ptext SLIT("No constructor has all these fields:"))
1042 4 (pprQuotedList fields)
1044 fields = [field | (field, _, _) <- rbinds]
1046 recordUpdCtxt = ptext SLIT("In a record update construct")
1049 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1051 illegalCcallTyErr isArg ty
1052 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1056 | isArg = ptext SLIT("argument")
1057 | otherwise = ptext SLIT("result")