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, mkHsConApp,
21 import BasicTypes ( RecFlag(..) )
23 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
24 LIE, emptyLIE, unitLIE, consLIE, plusLIE, plusLIEs,
26 newOverloadedLit, newMethod, newIPDict,
27 instOverloadedFun, newDicts, newClassDicts,
28 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 ( tcHsSigType, checkSigTyVars, sigCtxt )
39 import TcPat ( badFieldCon )
40 import TcSimplify ( tcSimplify, tcSimplifyAndCheck, partitionPredsOfLIE )
41 import TcImprove ( tcImprove )
42 import TcType ( TcType, TcTauType,
44 tcInstTcType, tcSplitRhoTy,
45 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
47 import Class ( Class )
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType
50 import Id ( idType, recordSelectorFieldLabel,
54 import DataCon ( dataConFieldLabels, dataConSig,
55 dataConStrictMarks, StrictnessMark(..)
57 import Name ( Name, getName )
58 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
60 splitFunTy_maybe, splitFunTys, isNotUsgTy,
61 mkTyConApp, splitSigmaTy,
63 isTauTy, tyVarsOfType, tyVarsOfTypes,
64 isSigmaTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
65 boxedTypeKind, mkArrowKind,
68 import Subst ( mkTopTyVarSubst, substClasses )
69 import UsageSPUtils ( unannotTy )
70 import VarSet ( emptyVarSet, unionVarSet, elemVarSet, mkVarSet )
71 import TyCon ( tyConDataCons )
72 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
73 floatPrimTy, addrPrimTy
75 import TysWiredIn ( boolTy, charTy, stringTy )
76 import PrelInfo ( ioTyCon_NAME )
77 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
79 import Unique ( cCallableClassKey, cReturnableClassKey,
80 enumFromClassOpKey, enumFromThenClassOpKey,
81 enumFromToClassOpKey, enumFromThenToClassOpKey,
82 thenMClassOpKey, failMClassOpKey, returnMClassOpKey
85 import Maybes ( maybeToBool, mapMaybe )
86 import ListSetOps ( minusList )
88 import CmdLineOpts ( opt_WarnMissingFields )
92 %************************************************************************
94 \subsection{Main wrappers}
96 %************************************************************************
99 tcExpr :: RenamedHsExpr -- Expession to type check
100 -> TcType -- Expected type (could be a polytpye)
101 -> TcM s (TcExpr, LIE)
103 tcExpr expr ty | isSigmaTy ty = -- Polymorphic case
104 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
105 returnTc (expr', lie)
107 | otherwise = -- Monomorphic case
112 %************************************************************************
114 \subsection{@tcPolyExpr@ typchecks an application}
116 %************************************************************************
119 -- tcPolyExpr is like tcMonoExpr, except that the expected type
120 -- can be a polymorphic one.
121 tcPolyExpr :: RenamedHsExpr
122 -> TcType -- Expected type
123 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
124 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
126 tcPolyExpr arg expected_arg_ty
127 = -- Ha! The argument type of the function is a for-all type,
128 -- An example of rank-2 polymorphism.
130 -- To ensure that the forall'd type variables don't get unified with each
131 -- other or any other types, we make fresh copy of the alleged type
132 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
134 (sig_theta, sig_tau) = splitRhoTy sig_rho
135 free_tyvars = tyVarsOfType expected_arg_ty
137 -- Type-check the arg and unify with expected type
138 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
140 -- Check that the sig_tyvars havn't been constrained
141 -- The interesting bit here is that we must include the free variables
142 -- of the expected arg ty. Here's an example:
143 -- runST (newVar True)
144 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
145 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
146 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
147 -- So now s' isn't unconstrained because it's linked to a.
148 -- Conclusion: include the free vars of the expected arg type in the
149 -- list of "free vars" for the signature check.
151 tcExtendGlobalTyVars free_tyvars $
152 tcAddErrCtxtM (sigCtxt sig_msg sig_tyvars sig_theta sig_tau) $
154 checkSigTyVars sig_tyvars free_tyvars `thenTc` \ zonked_sig_tyvars ->
156 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
157 tcImprove (sig_dicts `plusLIE` lie_arg) `thenTc_`
158 -- ToDo: better origin
160 (text "the type signature of an expression")
161 (mkVarSet zonked_sig_tyvars)
162 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
165 -- This HsLet binds any Insts which came out of the simplification.
166 -- It's a bit out of place here, but using AbsBind involves inventing
167 -- a couple of new names which seems worse.
168 generalised_arg = TyLam zonked_sig_tyvars $
173 returnTc ( generalised_arg, free_insts,
174 arg', sig_tau, lie_arg )
176 sig_msg = ptext SLIT("When checking an expression type signature")
179 %************************************************************************
181 \subsection{The TAUT rules for variables}
183 %************************************************************************
186 tcMonoExpr :: RenamedHsExpr -- Expession to type check
187 -> TcTauType -- Expected type (could be a type variable)
188 -> TcM s (TcExpr, LIE)
190 tcMonoExpr (HsVar name) res_ty
191 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
192 unifyTauTy res_ty id_ty `thenTc_`
194 -- Check that the result type doesn't have any nested for-alls.
195 -- For example, a "build" on its own is no good; it must be
196 -- applied to something.
197 checkTc (isTauTy id_ty)
198 (lurkingRank2Err name id_ty) `thenTc_`
200 returnTc (expr', lie)
204 tcMonoExpr (HsIPVar name) res_ty
205 -- ZZ What's the `id' used for here...
206 = let id = mkVanillaId name res_ty in
207 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
208 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
209 returnNF_Tc (HsIPVar (instToId ip), unitLIE ip)
212 %************************************************************************
214 \subsection{Literals}
216 %************************************************************************
221 tcMonoExpr (HsLit (HsInt i)) res_ty
222 = newOverloadedLit (LiteralOrigin (HsInt i))
223 (OverloadedIntegral i)
224 res_ty `thenNF_Tc` \ stuff ->
227 tcMonoExpr (HsLit (HsFrac f)) res_ty
228 = newOverloadedLit (LiteralOrigin (HsFrac f))
229 (OverloadedFractional f)
230 res_ty `thenNF_Tc` \ stuff ->
234 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
235 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
236 newClassDicts (LitLitOrigin (_UNPK_ s))
237 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
238 returnTc (HsLitOut lit res_ty, dicts)
244 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
245 = unifyTauTy res_ty charPrimTy `thenTc_`
246 returnTc (HsLitOut lit charPrimTy, emptyLIE)
248 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
249 = unifyTauTy res_ty addrPrimTy `thenTc_`
250 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
252 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
253 = unifyTauTy res_ty intPrimTy `thenTc_`
254 returnTc (HsLitOut lit intPrimTy, emptyLIE)
256 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
257 = unifyTauTy res_ty floatPrimTy `thenTc_`
258 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
260 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
261 = unifyTauTy res_ty doublePrimTy `thenTc_`
262 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
265 Unoverloaded literals:
268 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
269 = unifyTauTy res_ty charTy `thenTc_`
270 returnTc (HsLitOut lit charTy, emptyLIE)
272 tcMonoExpr (HsLit lit@(HsString str)) res_ty
273 = unifyTauTy res_ty stringTy `thenTc_`
274 returnTc (HsLitOut lit stringTy, emptyLIE)
277 %************************************************************************
279 \subsection{Other expression forms}
281 %************************************************************************
284 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
285 = tcMonoExpr expr res_ty
287 -- perform the negate *before* overloading the integer, since the case
288 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
289 -- convenient to do it here.
291 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
292 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
294 tcMonoExpr (NegApp expr neg) res_ty
295 = tcMonoExpr (HsApp neg expr) res_ty
297 tcMonoExpr (HsLam match) res_ty
298 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
299 returnTc (HsLam match', lie)
301 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
303 accum (HsApp e1 e2) args = accum e1 (e2:args)
305 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
306 returnTc (foldl HsApp fun' args', lie)
308 -- equivalent to (op e1) e2:
309 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
310 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
311 returnTc (OpApp arg1' op' fix arg2', lie)
314 Note that the operators in sections are expected to be binary, and
315 a type error will occur if they aren't.
318 -- Left sections, equivalent to
325 tcMonoExpr in_expr@(SectionL arg op) res_ty
326 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
328 -- Check that res_ty is a function type
329 -- Without this check we barf in the desugarer on
331 -- because it tries to desugar to
332 -- f op = \r -> 3 op r
333 -- so (3 `op`) had better be a function!
334 tcAddErrCtxt (sectionLAppCtxt in_expr) $
335 unifyFunTy res_ty `thenTc_`
337 returnTc (SectionL arg' op', lie)
339 -- Right sections, equivalent to \ x -> x op expr, or
342 tcMonoExpr in_expr@(SectionR op expr) res_ty
343 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
344 tcAddErrCtxt (sectionRAppCtxt in_expr) $
345 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
346 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
347 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
348 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
351 The interesting thing about @ccall@ is that it is just a template
352 which we instantiate by filling in details about the types of its
353 argument and result (ie minimal typechecking is performed). So, the
354 basic story is that we allocate a load of type variables (to hold the
355 arg/result types); unify them with the args/result; and store them for
359 tcMonoExpr (HsCCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
360 = -- Get the callable and returnable classes.
361 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
362 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
363 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
365 new_arg_dict (arg, arg_ty)
366 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
367 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
368 returnNF_Tc arg_dicts -- Actually a singleton bag
370 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
374 let n_args = length args
375 tv_idxs | n_args == 0 = []
376 | otherwise = [1..n_args]
378 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
379 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
381 -- The argument types can be unboxed or boxed; the result
382 -- type must, however, be boxed since it's an argument to the IO
384 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
386 io_result_ty = mkTyConApp ioTyCon [result_ty]
387 [ioDataCon] = tyConDataCons ioTyCon
389 unifyTauTy res_ty io_result_ty `thenTc_`
391 -- Construct the extra insts, which encode the
392 -- constraints on the argument and result types.
393 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
394 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
395 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
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 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
484 unifyTauTy res_ty record_ty `thenTc_`
486 -- Check that the record bindings match the constructor
487 -- con_name is syntactically constrained to be a data 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 splitSigmaTy (idType sel_id) -- Selectors can be overloaded
569 -- when the data type has a context
570 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
571 (tycon, _, data_cons) = splitAlgTyConApp data_ty
572 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
574 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
577 -- Check that at least one constructor has all the named fields
578 -- i.e. has an empty set of bad fields returned by badFields
579 checkTc (any (null . badFields rbinds) data_cons)
580 (badFieldsUpd rbinds) `thenTc_`
583 -- Typecheck the update bindings.
584 -- (Do this after checking for bad fields in case there's a field that
585 -- doesn't match the constructor.)
587 result_record_ty = mkTyConApp tycon result_inst_tys
589 unifyTauTy res_ty result_record_ty `thenTc_`
590 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
593 -- Use the un-updated fields to find a vector of booleans saying
594 -- which type arguments must be the same in updatee and result.
596 -- WARNING: this code assumes that all data_cons in a common tycon
597 -- have FieldLabels abstracted over the same tyvars.
599 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
600 con_field_lbls_s = map dataConFieldLabels data_cons
602 -- A constructor is only relevant to this process if
603 -- it contains all the fields that are being updated
604 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
605 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
607 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
608 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
610 mk_inst_ty (tyvar, result_inst_ty)
611 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
612 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
614 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
617 -- Typecheck the expression to be updated
619 record_ty = mkTyConApp tycon inst_tys
621 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
624 -- Figure out the LIE we need. We have to generate some
625 -- dictionaries for the data type context, since we are going to
626 -- do some construction.
628 -- What dictionaries do we need? For the moment we assume that all
629 -- data constructors have the same context, and grab it from the first
630 -- constructor. If they have varying contexts then we'd have to
631 -- union the ones that could participate in the update.
633 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
634 inst_env = mkTopTyVarSubst tyvars result_inst_tys
635 theta' = substClasses inst_env theta
637 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
640 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
641 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
643 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
644 = unifyListTy res_ty `thenTc` \ elt_ty ->
645 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
647 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
648 newMethod (ArithSeqOrigin seq)
649 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
651 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
654 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
655 = tcAddErrCtxt (arithSeqCtxt in_expr) $
656 unifyListTy res_ty `thenTc` \ elt_ty ->
657 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
658 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
659 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
660 newMethod (ArithSeqOrigin seq)
661 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
663 returnTc (ArithSeqOut (HsVar enum_from_then_id)
664 (FromThen expr1' expr2'),
665 lie1 `plusLIE` lie2 `plusLIE` lie3)
667 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
668 = tcAddErrCtxt (arithSeqCtxt in_expr) $
669 unifyListTy res_ty `thenTc` \ elt_ty ->
670 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
671 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
672 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
673 newMethod (ArithSeqOrigin seq)
674 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
676 returnTc (ArithSeqOut (HsVar enum_from_to_id)
677 (FromTo expr1' expr2'),
678 lie1 `plusLIE` lie2 `plusLIE` lie3)
680 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
681 = tcAddErrCtxt (arithSeqCtxt in_expr) $
682 unifyListTy res_ty `thenTc` \ elt_ty ->
683 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
684 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
685 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
686 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
687 newMethod (ArithSeqOrigin seq)
688 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
690 returnTc (ArithSeqOut (HsVar eft_id)
691 (FromThenTo expr1' expr2' expr3'),
692 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
695 %************************************************************************
697 \subsection{Expressions type signatures}
699 %************************************************************************
702 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
703 = tcSetErrCtxt (exprSigCtxt in_expr) $
704 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
706 if not (isSigmaTy sig_tc_ty) then
708 unifyTauTy sig_tc_ty res_ty `thenTc_`
709 tcMonoExpr expr sig_tc_ty
711 else -- Signature is polymorphic
712 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
714 -- Now match the signature type with res_ty.
715 -- We must not do this earlier, because res_ty might well
716 -- mention variables free in the environment, and we'd get
717 -- bogus complaints about not being able to for-all the
719 unifyTauTy res_ty expr_ty `thenTc_`
721 -- If everything is ok, return the stuff unchanged, except for
722 -- the effect of any substutions etc. We simply discard the
723 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
724 -- resolution it may have done, which is recorded in the
729 Implicit Parameter bindings.
732 tcMonoExpr (HsWith expr binds) res_ty
733 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
734 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
735 partitionPredsOfLIE isBound lie `thenTc` \ (ips, lie', dict_binds) ->
736 let expr'' = if nullMonoBinds dict_binds
738 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
741 tcCheckIPBinds binds' types ips `thenTc_`
742 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
744 = case ipName_maybe p of
745 Just n -> n `elem` names
747 names = map fst binds
748 -- revBinds is used because tcSimplify outputs the bindings
749 -- out-of-order. it's not a problem elsewhere because these
750 -- bindings are normally used in a recursive let
751 -- ZZ probably need to find a better solution
752 revBinds (b1 `AndMonoBinds` b2) =
753 (revBinds b2) `AndMonoBinds` (revBinds b1)
756 tcIPBinds ((name, expr) : binds)
757 = newTyVarTy_OpenKind `thenTc` \ ty ->
758 tcGetSrcLoc `thenTc` \ loc ->
759 let id = ipToId name ty loc in
760 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
761 zonkTcType ty `thenTc` \ ty' ->
762 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
763 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
764 tcIPBinds [] = returnTc ([], [], emptyLIE)
766 tcCheckIPBinds binds types ips
767 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
769 -- ZZ how do we use the loc?
770 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
771 = unifyTauTy t1 t2 `thenTc_`
772 tcCheckIPBind bt ips `thenTc` \ ips' ->
774 tcCheckIPBind bt (ip : ips)
775 = tcCheckIPBind bt ips `thenTc` \ ips' ->
781 Typecheck expression which in most cases will be an Id.
784 tcExpr_id :: RenamedHsExpr
790 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
792 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
793 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
794 returnTc (id_expr', lie_id, id_ty)
797 %************************************************************************
799 \subsection{@tcApp@ typchecks an application}
801 %************************************************************************
805 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
806 -> TcType -- Expected result type of application
807 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
810 tcApp fun args res_ty
811 = -- First type-check the function
812 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
814 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
815 split_fun_ty fun_ty (length args)
816 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
818 -- Unify with expected result before type-checking the args
819 -- This is when we might detect a too-few args situation
820 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
821 unifyTauTy res_ty actual_result_ty
824 -- Now typecheck the args
825 mapAndUnzipTc (tcArg fun)
826 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
828 -- Check that the result type doesn't have any nested for-alls.
829 -- For example, a "build" on its own is no good; it must be applied to something.
830 checkTc (isTauTy actual_result_ty)
831 (lurkingRank2Err fun fun_ty) `thenTc_`
833 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
836 -- If an error happens we try to figure out whether the
837 -- function has been given too many or too few arguments,
839 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
840 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
841 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
843 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
844 (env2, act_ty'') = tidyOpenType env1 act_ty'
845 (exp_args, _) = splitFunTys exp_ty''
846 (act_args, _) = splitFunTys act_ty''
848 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
849 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
850 | otherwise = appCtxt fun args
852 returnNF_Tc (env2, message)
855 split_fun_ty :: TcType -- The type of the function
856 -> Int -- Number of arguments
857 -> TcM s ([TcType], -- Function argument types
858 TcType) -- Function result types
860 split_fun_ty fun_ty 0
861 = returnTc ([], fun_ty)
863 split_fun_ty fun_ty n
864 = -- Expect the function to have type A->B
865 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
866 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
867 returnTc (arg_ty:arg_tys, final_res_ty)
871 tcArg :: RenamedHsExpr -- The function (for error messages)
872 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
873 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
875 tcArg the_fun (arg, expected_arg_ty, arg_no)
876 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
877 tcExpr arg expected_arg_ty
881 %************************************************************************
883 \subsection{@tcId@ typchecks an identifier occurrence}
885 %************************************************************************
887 Between the renamer and the first invocation of the UsageSP inference,
888 identifiers read from interface files will have usage information in
889 their types, whereas other identifiers will not. The unannotTy here
890 in @tcId@ prevents this information from pointlessly propagating
891 further prior to the first usage inference.
894 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
897 = -- Look up the Id and instantiate its type
898 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
901 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
903 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
904 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
905 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
908 -- The instantiate_it loop runs round instantiating the Id.
909 -- It has to be a loop because we are now prepared to entertain
911 -- f:: forall a. Eq a => forall b. Baz b => tau
912 -- We want to instantiate this to
913 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
914 instantiate_it orig fun ty
915 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
916 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
917 instantiate_it2 orig fun tyvars theta tau
919 instantiate_it2 orig fun tyvars theta tau
920 = if null theta then -- Is it overloaded?
921 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
923 -- Yes, it's overloaded
924 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
925 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
926 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
929 arg_tys = mkTyVarTys tyvars
932 %************************************************************************
934 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
936 %************************************************************************
939 tcDoStmts do_or_lc stmts src_loc res_ty
940 = -- get the Monad and MonadZero classes
941 -- create type consisting of a fresh monad tyvar
942 ASSERT( not (null stmts) )
943 tcAddSrcLoc src_loc $
945 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
946 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
947 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
949 -- If it's a comprehension we're dealing with,
950 -- force it to be a list comprehension.
951 -- (as of Haskell 98, monad comprehensions are no more.)
953 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
954 _ -> returnTc ()) `thenTc_`
956 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
958 -- Build the then and zero methods in case we need them
959 -- It's important that "then" and "return" appear just once in the final LIE,
960 -- not only for typechecker efficiency, but also because otherwise during
961 -- simplification we end up with silly stuff like
962 -- then = case d of (t,r) -> t
964 -- where the second "then" sees that it already exists in the "available" stuff.
966 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
967 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
968 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
969 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
970 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
971 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
973 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
975 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
976 stmts_lie `plusLIE` monad_lie)
980 %************************************************************************
982 \subsection{Record bindings}
984 %************************************************************************
986 Game plan for record bindings
987 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
990 1. look up "field", to find its selector Id, which must have type
991 forall a1..an. T a1 .. an -> tau
992 where tau is the type of the field.
994 2. Instantiate this type
996 3. Unify the (T a1 .. an) part with the "expected result type", which
997 is passed in. This checks that all the field labels come from the
1000 4. Type check the value using tcArg, passing tau as the expected
1003 This extends OK when the field types are universally quantified.
1005 Actually, to save excessive creation of fresh type variables,
1010 :: TcType -- Expected type of whole record
1011 -> RenamedRecordBinds
1012 -> TcM s (TcRecordBinds, LIE)
1014 tcRecordBinds expected_record_ty rbinds
1015 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
1016 returnTc (rbinds', plusLIEs lies)
1018 do_bind (field_label, rhs, pun_flag)
1019 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
1020 ASSERT( isRecordSelector sel_id )
1021 -- This lookup and assertion will surely succeed, because
1022 -- we check that the fields are indeed record selectors
1023 -- before calling tcRecordBinds
1025 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
1027 -- Record selectors all have type
1028 -- forall a1..an. T a1 .. an -> tau
1029 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1031 -- Selector must have type RecordType -> FieldType
1032 Just (record_ty, field_ty) = splitFunTy_maybe tau
1034 unifyTauTy expected_record_ty record_ty `thenTc_`
1035 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1036 returnTc ((sel_id, rhs', pun_flag), lie)
1038 badFields rbinds data_con
1039 = [field_name | (field_name, _, _) <- rbinds,
1040 not (field_name `elem` field_names)
1043 field_names = map fieldLabelName (dataConFieldLabels data_con)
1045 missingStrictFields rbinds data_con
1046 = [ fn | fn <- strict_field_names,
1047 not (fn `elem` field_names_used)
1050 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1051 strict_field_names = mapMaybe isStrict field_info
1053 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1054 isStrict _ = Nothing
1056 field_info = zip (dataConFieldLabels data_con)
1057 (dataConStrictMarks data_con)
1059 missingFields rbinds data_con
1060 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1062 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1064 -- missing strict fields have already been flagged as
1065 -- being so, so leave them out here.
1066 non_strict_field_names = mapMaybe isn'tStrict field_info
1068 isn'tStrict (fl, MarkedStrict) = Nothing
1069 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1071 field_info = zip (dataConFieldLabels data_con)
1072 (dataConStrictMarks data_con)
1076 %************************************************************************
1078 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1080 %************************************************************************
1083 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1085 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1086 tcMonoExprs (expr:exprs) (ty:tys)
1087 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1088 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1089 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1093 % =================================================
1100 pp_nest_hang :: String -> SDoc -> SDoc
1101 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1104 Boring and alphabetical:
1107 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1110 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1113 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1116 = hang (ptext SLIT("In an expression with a type signature:"))
1120 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1123 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1125 sectionRAppCtxt expr
1126 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1128 sectionLAppCtxt expr
1129 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1131 funAppCtxt fun arg arg_no
1132 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1133 quotes (ppr fun) <> text ", namely"])
1134 4 (quotes (ppr arg))
1136 wrongArgsCtxt too_many_or_few fun args
1137 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1138 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1139 <+> ptext SLIT("arguments in the call"))
1140 4 (parens (ppr the_app))
1142 the_app = foldl HsApp fun args -- Used in error messages
1145 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1147 the_app = foldl HsApp fun args -- Used in error messages
1149 lurkingRank2Err fun fun_ty
1150 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1151 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1152 ptext SLIT("so that the result type has for-alls in it")])
1154 rank2ArgCtxt arg expected_arg_ty
1155 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1158 = hang (ptext SLIT("No constructor has all these fields:"))
1159 4 (pprQuotedList fields)
1161 fields = [field | (field, _, _) <- rbinds]
1163 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1164 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1167 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1169 illegalCcallTyErr isArg ty
1170 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1174 | isArg = ptext SLIT("argument")
1175 | otherwise = ptext SLIT("result")
1178 missingStrictFieldCon :: Name -> Name -> SDoc
1179 missingStrictFieldCon con field
1180 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1181 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1183 missingFieldCon :: Name -> Name -> SDoc
1184 missingFieldCon con field
1185 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1186 ptext SLIT("is not initialised")]