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(..), MonoBinds(..), Stmt(..), StmtCtxt(..),
13 mkMonoBind, nullMonoBinds
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds,
17 mkHsTyApp, mkHsLet, maybeBoxedPrimType
21 import BasicTypes ( RecFlag(..) )
23 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
24 LIE, emptyLIE, unitLIE, consLIE, plusLIE, plusLIEs,
25 lieToList, listToLIE, tyVarsOfLIE, zonkLIE,
26 newOverloadedLit, newMethod, newIPDict,
27 instOverloadedFun, newDicts, newClassDicts,
28 partitionLIEbyMeth, getIPsOfLIE, instToId, ipToId
30 import TcBinds ( tcBindsAndThen )
31 import TcEnv ( tcInstId,
32 tcLookupValue, tcLookupClassByKey,
34 tcExtendGlobalTyVars, tcLookupValueMaybe,
35 tcLookupTyCon, tcLookupDataCon
37 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
38 import TcMonoType ( tcHsType, checkSigTyVars, sigCtxt )
39 import TcPat ( badFieldCon )
40 import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
41 import TcType ( TcType, TcTauType,
43 tcInstTcType, tcSplitRhoTy,
44 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
46 import Class ( Class )
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType
49 import Id ( idType, recordSelectorFieldLabel,
53 import DataCon ( dataConFieldLabels, dataConSig, dataConId,
54 dataConStrictMarks, StrictnessMark(..)
56 import Name ( Name, getName )
57 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
59 splitFunTy_maybe, splitFunTys, isNotUsgTy,
61 splitForAllTys, splitRhoTy,
62 isTauTy, tyVarsOfType, tyVarsOfTypes,
63 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
64 boxedTypeKind, mkArrowKind,
67 import Subst ( mkTopTyVarSubst, substClasses )
68 import UsageSPUtils ( unannotTy )
69 import VarSet ( emptyVarSet, unionVarSet, elemVarSet, mkVarSet )
70 import TyCon ( tyConDataCons )
71 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
72 floatPrimTy, addrPrimTy
74 import TysWiredIn ( boolTy, charTy, stringTy )
75 import PrelInfo ( ioTyCon_NAME )
76 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
78 import Unique ( cCallableClassKey, cReturnableClassKey,
79 enumFromClassOpKey, enumFromThenClassOpKey,
80 enumFromToClassOpKey, enumFromThenToClassOpKey,
81 thenMClassOpKey, failMClassOpKey, returnMClassOpKey
84 import Maybes ( maybeToBool, mapMaybe )
85 import ListSetOps ( minusList )
87 import CmdLineOpts ( opt_WarnMissingFields )
91 %************************************************************************
93 \subsection{Main wrappers}
95 %************************************************************************
98 tcExpr :: RenamedHsExpr -- Expession to type check
99 -> TcType -- Expected type (could be a polytpye)
100 -> TcM s (TcExpr, LIE)
102 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
103 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
104 returnTc (expr', lie)
106 | otherwise = -- Monomorphic case
111 %************************************************************************
113 \subsection{@tcPolyExpr@ typchecks an application}
115 %************************************************************************
118 -- tcPolyExpr is like tcMonoExpr, except that the expected type
119 -- can be a polymorphic one.
120 tcPolyExpr :: RenamedHsExpr
121 -> TcType -- Expected type
122 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
123 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
125 tcPolyExpr arg expected_arg_ty
126 = -- Ha! The argument type of the function is a for-all type,
127 -- An example of rank-2 polymorphism.
129 -- To ensure that the forall'd type variables don't get unified with each
130 -- other or any other types, we make fresh copy of the alleged type
131 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
133 (sig_theta, sig_tau) = splitRhoTy sig_rho
135 -- Type-check the arg and unify with expected type
136 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
138 -- Check that the sig_tyvars havn't been constrained
139 -- The interesting bit here is that we must include the free variables
140 -- of the expected arg ty. Here's an example:
141 -- runST (newVar True)
142 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
143 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
144 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
145 -- So now s' isn't unconstrained because it's linked to a.
146 -- Conclusion: include the free vars of the expected arg type in the
147 -- list of "free vars" for the signature check.
149 tcExtendGlobalTyVars (tyVarsOfType expected_arg_ty) $
150 tcAddErrCtxtM (sigCtxt sig_msg expected_arg_ty) $
152 checkSigTyVars sig_tyvars `thenTc` \ zonked_sig_tyvars ->
154 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
155 -- ToDo: better origin
157 (text "the type signature of an expression")
158 (mkVarSet zonked_sig_tyvars)
159 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
162 -- This HsLet binds any Insts which came out of the simplification.
163 -- It's a bit out of place here, but using AbsBind involves inventing
164 -- a couple of new names which seems worse.
165 generalised_arg = TyLam zonked_sig_tyvars $
170 returnTc ( generalised_arg, free_insts,
171 arg', sig_tau, lie_arg )
173 sig_msg ty = sep [ptext SLIT("In an expression with expected type:"),
177 %************************************************************************
179 \subsection{The TAUT rules for variables}
181 %************************************************************************
184 tcMonoExpr :: RenamedHsExpr -- Expession to type check
185 -> TcTauType -- Expected type (could be a type variable)
186 -> TcM s (TcExpr, LIE)
188 tcMonoExpr (HsVar name) res_ty
189 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
190 unifyTauTy res_ty id_ty `thenTc_`
192 -- Check that the result type doesn't have any nested for-alls.
193 -- For example, a "build" on its own is no good; it must be
194 -- applied to something.
195 checkTc (isTauTy id_ty)
196 (lurkingRank2Err name id_ty) `thenTc_`
198 returnTc (expr', lie)
202 tcMonoExpr (HsIPVar name) res_ty
203 -- ZZ What's the `id' used for here...
204 = let id = mkVanillaId name res_ty in
205 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
206 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
207 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
210 %************************************************************************
212 \subsection{Literals}
214 %************************************************************************
219 tcMonoExpr (HsLit (HsInt i)) res_ty
220 = newOverloadedLit (LiteralOrigin (HsInt i))
221 (OverloadedIntegral i)
222 res_ty `thenNF_Tc` \ stuff ->
225 tcMonoExpr (HsLit (HsFrac f)) res_ty
226 = newOverloadedLit (LiteralOrigin (HsFrac f))
227 (OverloadedFractional f)
228 res_ty `thenNF_Tc` \ stuff ->
232 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
233 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
234 newClassDicts (LitLitOrigin (_UNPK_ s))
235 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
236 returnTc (HsLitOut lit res_ty, dicts)
242 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
243 = unifyTauTy res_ty charPrimTy `thenTc_`
244 returnTc (HsLitOut lit charPrimTy, emptyLIE)
246 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
247 = unifyTauTy res_ty addrPrimTy `thenTc_`
248 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
250 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
251 = unifyTauTy res_ty intPrimTy `thenTc_`
252 returnTc (HsLitOut lit intPrimTy, emptyLIE)
254 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
255 = unifyTauTy res_ty floatPrimTy `thenTc_`
256 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
258 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
259 = unifyTauTy res_ty doublePrimTy `thenTc_`
260 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
263 Unoverloaded literals:
266 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
267 = unifyTauTy res_ty charTy `thenTc_`
268 returnTc (HsLitOut lit charTy, emptyLIE)
270 tcMonoExpr (HsLit lit@(HsString str)) res_ty
271 = unifyTauTy res_ty stringTy `thenTc_`
272 returnTc (HsLitOut lit stringTy, emptyLIE)
275 %************************************************************************
277 \subsection{Other expression forms}
279 %************************************************************************
282 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
283 = tcMonoExpr expr res_ty
285 -- perform the negate *before* overloading the integer, since the case
286 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
287 -- convenient to do it here.
289 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
290 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
292 tcMonoExpr (NegApp expr neg) res_ty
293 = tcMonoExpr (HsApp neg expr) res_ty
295 tcMonoExpr (HsLam match) res_ty
296 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
297 returnTc (HsLam match', lie)
299 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
301 accum (HsApp e1 e2) args = accum e1 (e2:args)
303 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
304 returnTc (foldl HsApp fun' args', lie)
306 -- equivalent to (op e1) e2:
307 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
308 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
309 returnTc (OpApp arg1' op' fix arg2', lie)
312 Note that the operators in sections are expected to be binary, and
313 a type error will occur if they aren't.
316 -- Left sections, equivalent to
323 tcMonoExpr in_expr@(SectionL arg op) res_ty
324 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
326 -- Check that res_ty is a function type
327 -- Without this check we barf in the desugarer on
329 -- because it tries to desugar to
330 -- f op = \r -> 3 op r
331 -- so (3 `op`) had better be a function!
332 tcAddErrCtxt (sectionLAppCtxt in_expr) $
333 unifyFunTy res_ty `thenTc_`
335 returnTc (SectionL arg' op', lie)
337 -- Right sections, equivalent to \ x -> x op expr, or
340 tcMonoExpr in_expr@(SectionR op expr) res_ty
341 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
342 tcAddErrCtxt (sectionRAppCtxt in_expr) $
343 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
344 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
345 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
346 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
349 The interesting thing about @ccall@ is that it is just a template
350 which we instantiate by filling in details about the types of its
351 argument and result (ie minimal typechecking is performed). So, the
352 basic story is that we allocate a load of type variables (to hold the
353 arg/result types); unify them with the args/result; and store them for
357 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
358 = -- Get the callable and returnable classes.
359 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
360 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
361 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
363 new_arg_dict (arg, arg_ty)
364 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
365 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
366 returnNF_Tc arg_dicts -- Actually a singleton bag
368 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
372 let n_args = length args
373 tv_idxs | n_args == 0 = []
374 | otherwise = [1..n_args]
376 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
377 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
379 -- The argument types can be unboxed or boxed; the result
380 -- type must, however, be boxed since it's an argument to the IO
382 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
384 io_result_ty = mkTyConApp ioTyCon [result_ty]
385 [ioDataCon] = tyConDataCons ioTyCon
387 unifyTauTy res_ty io_result_ty `thenTc_`
389 -- Construct the extra insts, which encode the
390 -- constraints on the argument and result types.
391 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
392 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
393 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
394 (CCall lbl args' may_gc is_asm result_ty),
395 -- do the wrapping in the newtype constructor here
396 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
400 tcMonoExpr (HsSCC lbl expr) res_ty
401 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
402 returnTc (HsSCC lbl expr', lie)
404 tcMonoExpr (HsLet binds expr) res_ty
407 binds -- Bindings to check
408 tc_expr `thenTc` \ (expr', lie) ->
409 returnTc (expr', lie)
411 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
412 returnTc (expr', lie)
413 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
415 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
416 = tcAddSrcLoc src_loc $
417 tcAddErrCtxt (caseCtxt in_expr) $
419 -- Typecheck the case alternatives first.
420 -- The case patterns tend to give good type info to use
421 -- when typechecking the scrutinee. For example
424 -- will report that map is applied to too few arguments
426 -- Not only that, but it's better to check the matches on their
427 -- own, so that we get the expected results for scoped type variables.
429 -- (p::a, q::b) -> (q,p)
430 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
431 -- claimed by the pattern signatures. But if we typechecked the
432 -- match with x in scope and x's type as the expected type, we'd be hosed.
434 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
436 tcAddErrCtxt (caseScrutCtxt scrut) (
437 tcMonoExpr scrut scrut_ty
438 ) `thenTc` \ (scrut',lie1) ->
440 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
442 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
443 = tcAddSrcLoc src_loc $
444 tcAddErrCtxt (predCtxt pred) (
445 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
447 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
448 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
449 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
453 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
454 = tcDoStmts do_or_lc stmts src_loc res_ty
458 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
459 = unifyListTy res_ty `thenTc` \ elt_ty ->
460 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
461 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
464 = tcAddErrCtxt (listCtxt expr) $
465 tcMonoExpr expr elt_ty
467 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
469 then unifyTupleTy (length exprs) res_ty
470 else unifyUnboxedTupleTy (length exprs) res_ty
471 ) `thenTc` \ arg_tys ->
472 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
473 (exprs `zip` arg_tys) -- we know they're of equal length.
474 `thenTc` \ (exprs', lies) ->
475 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
477 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
478 = tcAddErrCtxt (recordConCtxt expr) $
479 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
481 (_, record_ty) = splitFunTys con_tau
483 -- Con is syntactically constrained to be a data constructor
484 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
485 unifyTauTy res_ty record_ty `thenTc_`
487 -- Check that the record bindings match the constructor
488 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
490 bad_fields = badFields rbinds data_con
492 if not (null bad_fields) then
493 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
494 failTc -- Fail now, because tcRecordBinds will crash on a bad field
497 -- Typecheck the record bindings
498 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
501 missing_s_fields = missingStrictFields rbinds data_con
503 checkTcM (null missing_s_fields)
504 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
505 returnNF_Tc ()) `thenNF_Tc_`
507 missing_fields = missingFields rbinds data_con
509 checkTcM (not (opt_WarnMissingFields && not (null missing_fields)))
510 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
511 returnNF_Tc ()) `thenNF_Tc_`
513 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
515 -- The main complication with RecordUpd is that we need to explicitly
516 -- handle the *non-updated* fields. Consider:
518 -- data T a b = MkT1 { fa :: a, fb :: b }
519 -- | MkT2 { fa :: a, fc :: Int -> Int }
520 -- | MkT3 { fd :: a }
522 -- upd :: T a b -> c -> T a c
523 -- upd t x = t { fb = x}
525 -- The type signature on upd is correct (i.e. the result should not be (T a b))
526 -- because upd should be equivalent to:
528 -- upd t x = case t of
529 -- MkT1 p q -> MkT1 p x
530 -- MkT2 a b -> MkT2 p b
531 -- MkT3 d -> error ...
533 -- So we need to give a completely fresh type to the result record,
534 -- and then constrain it by the fields that are *not* updated ("p" above).
536 -- Note that because MkT3 doesn't contain all the fields being updated,
537 -- its RHS is simply an error, so it doesn't impose any type constraints
539 -- All this is done in STEP 4 below.
541 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
542 = tcAddErrCtxt (recordUpdCtxt expr) $
545 -- Check that the field names are really field names
546 ASSERT( not (null rbinds) )
548 field_names = [field_name | (field_name, _, _) <- rbinds]
550 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
552 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
555 Just sel_id -> not (isRecordSelector sel_id)
558 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
559 if not (null bad_guys) then
564 -- Figure out the tycon and data cons from the first field name
566 (Just sel_id : _) = maybe_sel_ids
567 (_, tau) = ASSERT( isNotUsgTy (idType sel_id) )
568 splitForAllTys (idType sel_id)
569 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
570 (tycon, _, data_cons) = splitAlgTyConApp data_ty
571 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
573 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
576 -- Check that at least one constructor has all the named fields
577 -- i.e. has an empty set of bad fields returned by badFields
578 checkTc (any (null . badFields rbinds) data_cons)
579 (badFieldsUpd rbinds) `thenTc_`
582 -- Typecheck the update bindings.
583 -- (Do this after checking for bad fields in case there's a field that
584 -- doesn't match the constructor.)
586 result_record_ty = mkTyConApp tycon result_inst_tys
588 unifyTauTy res_ty result_record_ty `thenTc_`
589 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
592 -- Use the un-updated fields to find a vector of booleans saying
593 -- which type arguments must be the same in updatee and result.
595 -- WARNING: this code assumes that all data_cons in a common tycon
596 -- have FieldLabels abstracted over the same tyvars.
598 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
599 con_field_lbls_s = map dataConFieldLabels data_cons
601 -- A constructor is only relevant to this process if
602 -- it contains all the fields that are being updated
603 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
604 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
606 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
607 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
609 mk_inst_ty (tyvar, result_inst_ty)
610 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
611 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
613 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
616 -- Typecheck the expression to be updated
618 record_ty = mkTyConApp tycon inst_tys
620 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
623 -- Figure out the LIE we need. We have to generate some
624 -- dictionaries for the data type context, since we are going to
625 -- do some construction.
627 -- What dictionaries do we need? For the moment we assume that all
628 -- data constructors have the same context, and grab it from the first
629 -- constructor. If they have varying contexts then we'd have to
630 -- union the ones that could participate in the update.
632 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
633 inst_env = mkTopTyVarSubst tyvars result_inst_tys
634 theta' = substClasses inst_env theta
636 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
639 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
640 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
642 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
643 = unifyListTy res_ty `thenTc` \ elt_ty ->
644 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
646 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
647 newMethod (ArithSeqOrigin seq)
648 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
650 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
653 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
654 = tcAddErrCtxt (arithSeqCtxt in_expr) $
655 unifyListTy res_ty `thenTc` \ elt_ty ->
656 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
657 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
658 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
659 newMethod (ArithSeqOrigin seq)
660 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
662 returnTc (ArithSeqOut (HsVar enum_from_then_id)
663 (FromThen expr1' expr2'),
664 lie1 `plusLIE` lie2 `plusLIE` lie3)
666 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
667 = tcAddErrCtxt (arithSeqCtxt in_expr) $
668 unifyListTy res_ty `thenTc` \ elt_ty ->
669 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
670 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
671 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
672 newMethod (ArithSeqOrigin seq)
673 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
675 returnTc (ArithSeqOut (HsVar enum_from_to_id)
676 (FromTo expr1' expr2'),
677 lie1 `plusLIE` lie2 `plusLIE` lie3)
679 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
680 = tcAddErrCtxt (arithSeqCtxt in_expr) $
681 unifyListTy res_ty `thenTc` \ elt_ty ->
682 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
683 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
684 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
685 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
686 newMethod (ArithSeqOrigin seq)
687 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
689 returnTc (ArithSeqOut (HsVar eft_id)
690 (FromThenTo expr1' expr2' expr3'),
691 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
694 %************************************************************************
696 \subsection{Expressions type signatures}
698 %************************************************************************
701 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
702 = tcSetErrCtxt (exprSigCtxt in_expr) $
703 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
705 if not (isForAllTy sig_tc_ty) then
707 unifyTauTy sig_tc_ty res_ty `thenTc_`
708 tcMonoExpr expr sig_tc_ty
710 else -- Signature is polymorphic
711 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
713 -- Now match the signature type with res_ty.
714 -- We must not do this earlier, because res_ty might well
715 -- mention variables free in the environment, and we'd get
716 -- bogus complaints about not being able to for-all the
718 unifyTauTy res_ty expr_ty `thenTc_`
720 -- If everything is ok, return the stuff unchanged, except for
721 -- the effect of any substutions etc. We simply discard the
722 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
723 -- resolution it may have done, which is recorded in the
728 Implicit Parameter bindings.
731 tcMonoExpr (HsWith expr binds) res_ty
732 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
733 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
734 partitionLIEbyMeth isBound lie `thenTc` \ (ips, lie') ->
735 zonkLIE ips `thenTc` \ ips' ->
736 tcSimplify (text "tcMonoExpr With") (tyVarsOfLIE ips') ips'
737 `thenTc` \ res@(_, dict_binds, _) ->
738 let expr'' = if nullMonoBinds dict_binds
740 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
743 tcCheckIPBinds binds' types ips' `thenTc_`
744 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
746 = case ipName_maybe p of
747 Just n -> n `elem` names
749 names = map fst binds
750 -- revBinds is used because tcSimplify outputs the bindings
751 -- out-of-order. it's not a problem elsewhere because these
752 -- bindings are normally used in a recursive let
753 -- ZZ probably need to find a better solution
754 revBinds (b1 `AndMonoBinds` b2) =
755 (revBinds b2) `AndMonoBinds` (revBinds b1)
758 tcIPBinds ((name, expr) : binds)
759 = newTyVarTy_OpenKind `thenTc` \ ty ->
760 tcGetSrcLoc `thenTc` \ loc ->
761 let id = ipToId name ty loc in
762 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
763 zonkTcType ty `thenTc` \ ty' ->
764 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
765 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
766 tcIPBinds [] = returnTc ([], [], emptyLIE)
768 tcCheckIPBinds binds types ips
769 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
771 -- ZZ how do we use the loc?
772 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
773 = unifyTauTy t1 t2 `thenTc_`
774 tcCheckIPBind bt ips `thenTc` \ ips' ->
776 tcCheckIPBind bt (ip : ips)
777 = tcCheckIPBind bt ips `thenTc` \ ips' ->
783 Typecheck expression which in most cases will be an Id.
786 tcExpr_id :: RenamedHsExpr
792 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
794 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
795 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
796 returnTc (id_expr', lie_id, id_ty)
799 %************************************************************************
801 \subsection{@tcApp@ typchecks an application}
803 %************************************************************************
807 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
808 -> TcType -- Expected result type of application
809 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
812 tcApp fun args res_ty
813 = -- First type-check the function
814 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
816 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
817 split_fun_ty fun_ty (length args)
818 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
820 -- Unify with expected result before type-checking the args
821 -- This is when we might detect a too-few args situation
822 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
823 unifyTauTy res_ty actual_result_ty
826 -- Now typecheck the args
827 mapAndUnzipTc (tcArg fun)
828 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
830 -- Check that the result type doesn't have any nested for-alls.
831 -- For example, a "build" on its own is no good; it must be applied to something.
832 checkTc (isTauTy actual_result_ty)
833 (lurkingRank2Err fun fun_ty) `thenTc_`
835 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
838 -- If an error happens we try to figure out whether the
839 -- function has been given too many or too few arguments,
841 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
842 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
843 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
845 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
846 (env2, act_ty'') = tidyOpenType env1 act_ty'
847 (exp_args, _) = splitFunTys exp_ty''
848 (act_args, _) = splitFunTys act_ty''
850 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
851 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
852 | otherwise = appCtxt fun args
854 returnNF_Tc (env2, message)
857 split_fun_ty :: TcType -- The type of the function
858 -> Int -- Number of arguments
859 -> TcM s ([TcType], -- Function argument types
860 TcType) -- Function result types
862 split_fun_ty fun_ty 0
863 = returnTc ([], fun_ty)
865 split_fun_ty fun_ty n
866 = -- Expect the function to have type A->B
867 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
868 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
869 returnTc (arg_ty:arg_tys, final_res_ty)
873 tcArg :: RenamedHsExpr -- The function (for error messages)
874 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
875 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
877 tcArg the_fun (arg, expected_arg_ty, arg_no)
878 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
879 tcExpr arg expected_arg_ty
883 %************************************************************************
885 \subsection{@tcId@ typchecks an identifier occurrence}
887 %************************************************************************
889 Between the renamer and the first invocation of the UsageSP inference,
890 identifiers read from interface files will have usage information in
891 their types, whereas other identifiers will not. The unannotTy here
892 in @tcId@ prevents this information from pointlessly propagating
893 further prior to the first usage inference.
896 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
899 = -- Look up the Id and instantiate its type
900 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
903 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
905 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
906 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
907 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
910 -- The instantiate_it loop runs round instantiating the Id.
911 -- It has to be a loop because we are now prepared to entertain
913 -- f:: forall a. Eq a => forall b. Baz b => tau
914 -- We want to instantiate this to
915 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
916 instantiate_it orig fun ty
917 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
918 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
919 instantiate_it2 orig fun tyvars theta tau
921 instantiate_it2 orig fun tyvars theta tau
922 = if null theta then -- Is it overloaded?
923 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
925 -- Yes, it's overloaded
926 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
927 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
928 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
931 arg_tys = mkTyVarTys tyvars
934 %************************************************************************
936 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
938 %************************************************************************
941 tcDoStmts do_or_lc stmts src_loc res_ty
942 = -- get the Monad and MonadZero classes
943 -- create type consisting of a fresh monad tyvar
944 ASSERT( not (null stmts) )
945 tcAddSrcLoc src_loc $
947 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
948 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
949 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
951 -- If it's a comprehension we're dealing with,
952 -- force it to be a list comprehension.
953 -- (as of Haskell 98, monad comprehensions are no more.)
955 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
956 _ -> returnTc ()) `thenTc_`
958 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
960 -- Build the then and zero methods in case we need them
961 -- It's important that "then" and "return" appear just once in the final LIE,
962 -- not only for typechecker efficiency, but also because otherwise during
963 -- simplification we end up with silly stuff like
964 -- then = case d of (t,r) -> t
966 -- where the second "then" sees that it already exists in the "available" stuff.
968 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
969 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
970 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
971 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
972 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
973 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
975 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
977 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
978 stmts_lie `plusLIE` monad_lie)
982 %************************************************************************
984 \subsection{Record bindings}
986 %************************************************************************
988 Game plan for record bindings
989 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
992 1. look up "field", to find its selector Id, which must have type
993 forall a1..an. T a1 .. an -> tau
994 where tau is the type of the field.
996 2. Instantiate this type
998 3. Unify the (T a1 .. an) part with the "expected result type", which
999 is passed in. This checks that all the field labels come from the
1002 4. Type check the value using tcArg, passing tau as the expected
1005 This extends OK when the field types are universally quantified.
1007 Actually, to save excessive creation of fresh type variables,
1012 :: TcType -- Expected type of whole record
1013 -> RenamedRecordBinds
1014 -> TcM s (TcRecordBinds, LIE)
1016 tcRecordBinds expected_record_ty rbinds
1017 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
1018 returnTc (rbinds', plusLIEs lies)
1020 do_bind (field_label, rhs, pun_flag)
1021 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
1022 ASSERT( isRecordSelector sel_id )
1023 -- This lookup and assertion will surely succeed, because
1024 -- we check that the fields are indeed record selectors
1025 -- before calling tcRecordBinds
1027 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
1029 -- Record selectors all have type
1030 -- forall a1..an. T a1 .. an -> tau
1031 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1033 -- Selector must have type RecordType -> FieldType
1034 Just (record_ty, field_ty) = splitFunTy_maybe tau
1036 unifyTauTy expected_record_ty record_ty `thenTc_`
1037 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1038 returnTc ((sel_id, rhs', pun_flag), lie)
1040 badFields rbinds data_con
1041 = [field_name | (field_name, _, _) <- rbinds,
1042 not (field_name `elem` field_names)
1045 field_names = map fieldLabelName (dataConFieldLabels data_con)
1047 missingStrictFields rbinds data_con
1048 = [ fn | fn <- strict_field_names,
1049 not (fn `elem` field_names_used)
1052 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1053 strict_field_names = mapMaybe isStrict field_info
1055 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1056 isStrict _ = Nothing
1058 field_info = zip (dataConFieldLabels data_con)
1059 (dataConStrictMarks data_con)
1061 missingFields rbinds data_con
1062 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1064 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1066 -- missing strict fields have already been flagged as
1067 -- being so, so leave them out here.
1068 non_strict_field_names = mapMaybe isn'tStrict field_info
1070 isn'tStrict (fl, MarkedStrict) = Nothing
1071 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1073 field_info = zip (dataConFieldLabels data_con)
1074 (dataConStrictMarks data_con)
1078 %************************************************************************
1080 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1082 %************************************************************************
1085 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1087 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1088 tcMonoExprs (expr:exprs) (ty:tys)
1089 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1090 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1091 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1095 % =================================================
1102 pp_nest_hang :: String -> SDoc -> SDoc
1103 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1106 Boring and alphabetical:
1109 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1112 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1115 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1118 = hang (ptext SLIT("In an expression with a type signature:"))
1122 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1125 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1127 sectionRAppCtxt expr
1128 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1130 sectionLAppCtxt expr
1131 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1133 funAppCtxt fun arg arg_no
1134 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1135 quotes (ppr fun) <> text ", namely"])
1136 4 (quotes (ppr arg))
1138 wrongArgsCtxt too_many_or_few fun args
1139 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1140 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1141 <+> ptext SLIT("arguments in the call"))
1142 4 (parens (ppr the_app))
1144 the_app = foldl HsApp fun args -- Used in error messages
1147 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1149 the_app = foldl HsApp fun args -- Used in error messages
1151 lurkingRank2Err fun fun_ty
1152 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1153 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1154 ptext SLIT("so that the result type has for-alls in it")])
1156 rank2ArgCtxt arg expected_arg_ty
1157 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1160 = hang (ptext SLIT("No constructor has all these fields:"))
1161 4 (pprQuotedList fields)
1163 fields = [field | (field, _, _) <- rbinds]
1165 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1166 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1169 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1171 illegalCcallTyErr isArg ty
1172 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1176 | isArg = ptext SLIT("argument")
1177 | otherwise = ptext SLIT("result")
1180 missingStrictFieldCon :: Name -> Name -> SDoc
1181 missingStrictFieldCon con field
1182 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1183 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1185 missingFieldCon :: Name -> Name -> SDoc
1186 missingFieldCon con field
1187 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1188 ptext SLIT("is not initialised")]