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]
388 unifyTauTy res_ty io_result_ty `thenTc_`
390 -- Construct the extra insts, which encode the
391 -- constraints on the argument and result types.
392 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
393 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
394 returnTc (HsCCall lbl args' may_gc is_asm io_result_ty,
395 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
399 tcMonoExpr (HsSCC lbl expr) res_ty
400 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
401 returnTc (HsSCC lbl expr', lie)
403 tcMonoExpr (HsLet binds expr) res_ty
406 binds -- Bindings to check
407 tc_expr `thenTc` \ (expr', lie) ->
408 returnTc (expr', lie)
410 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
411 returnTc (expr', lie)
412 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
414 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
415 = tcAddSrcLoc src_loc $
416 tcAddErrCtxt (caseCtxt in_expr) $
418 -- Typecheck the case alternatives first.
419 -- The case patterns tend to give good type info to use
420 -- when typechecking the scrutinee. For example
423 -- will report that map is applied to too few arguments
425 -- Not only that, but it's better to check the matches on their
426 -- own, so that we get the expected results for scoped type variables.
428 -- (p::a, q::b) -> (q,p)
429 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
430 -- claimed by the pattern signatures. But if we typechecked the
431 -- match with x in scope and x's type as the expected type, we'd be hosed.
433 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
435 tcAddErrCtxt (caseScrutCtxt scrut) (
436 tcMonoExpr scrut scrut_ty
437 ) `thenTc` \ (scrut',lie1) ->
439 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
441 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
442 = tcAddSrcLoc src_loc $
443 tcAddErrCtxt (predCtxt pred) (
444 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
446 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
447 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
448 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
452 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
453 = tcDoStmts do_or_lc stmts src_loc res_ty
457 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
458 = unifyListTy res_ty `thenTc` \ elt_ty ->
459 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
460 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
463 = tcAddErrCtxt (listCtxt expr) $
464 tcMonoExpr expr elt_ty
466 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
468 then unifyTupleTy (length exprs) res_ty
469 else unifyUnboxedTupleTy (length exprs) res_ty
470 ) `thenTc` \ arg_tys ->
471 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
472 (exprs `zip` arg_tys) -- we know they're of equal length.
473 `thenTc` \ (exprs', lies) ->
474 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
476 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
477 = tcAddErrCtxt (recordConCtxt expr) $
478 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
480 (_, record_ty) = splitFunTys con_tau
482 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
483 unifyTauTy res_ty record_ty `thenTc_`
485 -- Check that the record bindings match the constructor
486 -- con_name is syntactically constrained to be a data constructor
487 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
489 bad_fields = badFields rbinds data_con
491 if not (null bad_fields) then
492 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
493 failTc -- Fail now, because tcRecordBinds will crash on a bad field
496 -- Typecheck the record bindings
497 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
500 missing_s_fields = missingStrictFields rbinds data_con
502 checkTcM (null missing_s_fields)
503 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
504 returnNF_Tc ()) `thenNF_Tc_`
506 missing_fields = missingFields rbinds data_con
508 checkTcM (not (opt_WarnMissingFields && not (null missing_fields)))
509 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
510 returnNF_Tc ()) `thenNF_Tc_`
512 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
514 -- The main complication with RecordUpd is that we need to explicitly
515 -- handle the *non-updated* fields. Consider:
517 -- data T a b = MkT1 { fa :: a, fb :: b }
518 -- | MkT2 { fa :: a, fc :: Int -> Int }
519 -- | MkT3 { fd :: a }
521 -- upd :: T a b -> c -> T a c
522 -- upd t x = t { fb = x}
524 -- The type signature on upd is correct (i.e. the result should not be (T a b))
525 -- because upd should be equivalent to:
527 -- upd t x = case t of
528 -- MkT1 p q -> MkT1 p x
529 -- MkT2 a b -> MkT2 p b
530 -- MkT3 d -> error ...
532 -- So we need to give a completely fresh type to the result record,
533 -- and then constrain it by the fields that are *not* updated ("p" above).
535 -- Note that because MkT3 doesn't contain all the fields being updated,
536 -- its RHS is simply an error, so it doesn't impose any type constraints
538 -- All this is done in STEP 4 below.
540 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
541 = tcAddErrCtxt (recordUpdCtxt expr) $
544 -- Check that the field names are really field names
545 ASSERT( not (null rbinds) )
547 field_names = [field_name | (field_name, _, _) <- rbinds]
549 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
551 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
554 Just sel_id -> not (isRecordSelector sel_id)
557 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
558 if not (null bad_guys) then
563 -- Figure out the tycon and data cons from the first field name
565 (Just sel_id : _) = maybe_sel_ids
566 (_, _, tau) = ASSERT( isNotUsgTy (idType sel_id) )
567 splitSigmaTy (idType sel_id) -- Selectors can be overloaded
568 -- when the data type has a context
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, _, _, _, _, _) = 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 tcHsSigType poly_ty `thenTc` \ sig_tc_ty ->
705 if not (isSigmaTy 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 partitionPredsOfLIE isBound lie `thenTc` \ (ips, lie', dict_binds) ->
735 let expr'' = if nullMonoBinds dict_binds
737 else HsLet (mkMonoBind (revBinds dict_binds) [] NonRecursive)
740 tcCheckIPBinds binds' types ips `thenTc_`
741 returnTc (HsWith expr'' binds', lie' `plusLIE` lie2)
743 = case ipName_maybe p of
744 Just n -> n `elem` names
746 names = map fst binds
747 -- revBinds is used because tcSimplify outputs the bindings
748 -- out-of-order. it's not a problem elsewhere because these
749 -- bindings are normally used in a recursive let
750 -- ZZ probably need to find a better solution
751 revBinds (b1 `AndMonoBinds` b2) =
752 (revBinds b2) `AndMonoBinds` (revBinds b1)
755 tcIPBinds ((name, expr) : binds)
756 = newTyVarTy_OpenKind `thenTc` \ ty ->
757 tcGetSrcLoc `thenTc` \ loc ->
758 let id = ipToId name ty loc in
759 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
760 zonkTcType ty `thenTc` \ ty' ->
761 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
762 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
763 tcIPBinds [] = returnTc ([], [], emptyLIE)
765 tcCheckIPBinds binds types ips
766 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
768 -- ZZ how do we use the loc?
769 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
770 = unifyTauTy t1 t2 `thenTc_`
771 tcCheckIPBind bt ips `thenTc` \ ips' ->
773 tcCheckIPBind bt (ip : ips)
774 = tcCheckIPBind bt ips `thenTc` \ ips' ->
780 Typecheck expression which in most cases will be an Id.
783 tcExpr_id :: RenamedHsExpr
789 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
791 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
792 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
793 returnTc (id_expr', lie_id, id_ty)
796 %************************************************************************
798 \subsection{@tcApp@ typchecks an application}
800 %************************************************************************
804 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
805 -> TcType -- Expected result type of application
806 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
809 tcApp fun args res_ty
810 = -- First type-check the function
811 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
813 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
814 split_fun_ty fun_ty (length args)
815 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
817 -- Unify with expected result before type-checking the args
818 -- This is when we might detect a too-few args situation
819 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
820 unifyTauTy res_ty actual_result_ty
823 -- Now typecheck the args
824 mapAndUnzipTc (tcArg fun)
825 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
827 -- Check that the result type doesn't have any nested for-alls.
828 -- For example, a "build" on its own is no good; it must be applied to something.
829 checkTc (isTauTy actual_result_ty)
830 (lurkingRank2Err fun fun_ty) `thenTc_`
832 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
835 -- If an error happens we try to figure out whether the
836 -- function has been given too many or too few arguments,
838 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
839 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
840 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
842 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
843 (env2, act_ty'') = tidyOpenType env1 act_ty'
844 (exp_args, _) = splitFunTys exp_ty''
845 (act_args, _) = splitFunTys act_ty''
847 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
848 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
849 | otherwise = appCtxt fun args
851 returnNF_Tc (env2, message)
854 split_fun_ty :: TcType -- The type of the function
855 -> Int -- Number of arguments
856 -> TcM s ([TcType], -- Function argument types
857 TcType) -- Function result types
859 split_fun_ty fun_ty 0
860 = returnTc ([], fun_ty)
862 split_fun_ty fun_ty n
863 = -- Expect the function to have type A->B
864 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
865 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
866 returnTc (arg_ty:arg_tys, final_res_ty)
870 tcArg :: RenamedHsExpr -- The function (for error messages)
871 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
872 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
874 tcArg the_fun (arg, expected_arg_ty, arg_no)
875 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
876 tcExpr arg expected_arg_ty
880 %************************************************************************
882 \subsection{@tcId@ typchecks an identifier occurrence}
884 %************************************************************************
886 Between the renamer and the first invocation of the UsageSP inference,
887 identifiers read from interface files will have usage information in
888 their types, whereas other identifiers will not. The unannotTy here
889 in @tcId@ prevents this information from pointlessly propagating
890 further prior to the first usage inference.
893 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
896 = -- Look up the Id and instantiate its type
897 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
900 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
902 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
903 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
904 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
907 -- The instantiate_it loop runs round instantiating the Id.
908 -- It has to be a loop because we are now prepared to entertain
910 -- f:: forall a. Eq a => forall b. Baz b => tau
911 -- We want to instantiate this to
912 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
913 instantiate_it orig fun ty
914 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
915 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
916 instantiate_it2 orig fun tyvars theta tau
918 instantiate_it2 orig fun tyvars theta tau
919 = if null theta then -- Is it overloaded?
920 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
922 -- Yes, it's overloaded
923 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
924 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
925 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
928 arg_tys = mkTyVarTys tyvars
931 %************************************************************************
933 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
935 %************************************************************************
938 tcDoStmts do_or_lc stmts src_loc res_ty
939 = -- get the Monad and MonadZero classes
940 -- create type consisting of a fresh monad tyvar
941 ASSERT( not (null stmts) )
942 tcAddSrcLoc src_loc $
944 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
945 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
946 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
948 -- If it's a comprehension we're dealing with,
949 -- force it to be a list comprehension.
950 -- (as of Haskell 98, monad comprehensions are no more.)
952 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
953 _ -> returnTc ()) `thenTc_`
955 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
957 -- Build the then and zero methods in case we need them
958 -- It's important that "then" and "return" appear just once in the final LIE,
959 -- not only for typechecker efficiency, but also because otherwise during
960 -- simplification we end up with silly stuff like
961 -- then = case d of (t,r) -> t
963 -- where the second "then" sees that it already exists in the "available" stuff.
965 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
966 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
967 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
968 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
969 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
970 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
972 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
974 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
975 stmts_lie `plusLIE` monad_lie)
979 %************************************************************************
981 \subsection{Record bindings}
983 %************************************************************************
985 Game plan for record bindings
986 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
989 1. look up "field", to find its selector Id, which must have type
990 forall a1..an. T a1 .. an -> tau
991 where tau is the type of the field.
993 2. Instantiate this type
995 3. Unify the (T a1 .. an) part with the "expected result type", which
996 is passed in. This checks that all the field labels come from the
999 4. Type check the value using tcArg, passing tau as the expected
1002 This extends OK when the field types are universally quantified.
1004 Actually, to save excessive creation of fresh type variables,
1009 :: TcType -- Expected type of whole record
1010 -> RenamedRecordBinds
1011 -> TcM s (TcRecordBinds, LIE)
1013 tcRecordBinds expected_record_ty rbinds
1014 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
1015 returnTc (rbinds', plusLIEs lies)
1017 do_bind (field_label, rhs, pun_flag)
1018 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
1019 ASSERT( isRecordSelector sel_id )
1020 -- This lookup and assertion will surely succeed, because
1021 -- we check that the fields are indeed record selectors
1022 -- before calling tcRecordBinds
1024 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
1026 -- Record selectors all have type
1027 -- forall a1..an. T a1 .. an -> tau
1028 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1030 -- Selector must have type RecordType -> FieldType
1031 Just (record_ty, field_ty) = splitFunTy_maybe tau
1033 unifyTauTy expected_record_ty record_ty `thenTc_`
1034 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1035 returnTc ((sel_id, rhs', pun_flag), lie)
1037 badFields rbinds data_con
1038 = [field_name | (field_name, _, _) <- rbinds,
1039 not (field_name `elem` field_names)
1042 field_names = map fieldLabelName (dataConFieldLabels data_con)
1044 missingStrictFields rbinds data_con
1045 = [ fn | fn <- strict_field_names,
1046 not (fn `elem` field_names_used)
1049 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1050 strict_field_names = mapMaybe isStrict field_info
1052 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1053 isStrict _ = Nothing
1055 field_info = zip (dataConFieldLabels data_con)
1056 (dataConStrictMarks data_con)
1058 missingFields rbinds data_con
1059 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1061 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1063 -- missing strict fields have already been flagged as
1064 -- being so, so leave them out here.
1065 non_strict_field_names = mapMaybe isn'tStrict field_info
1067 isn'tStrict (fl, MarkedStrict) = Nothing
1068 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1070 field_info = zip (dataConFieldLabels data_con)
1071 (dataConStrictMarks data_con)
1075 %************************************************************************
1077 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1079 %************************************************************************
1082 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1084 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1085 tcMonoExprs (expr:exprs) (ty:tys)
1086 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1087 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1088 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1092 % =================================================
1099 pp_nest_hang :: String -> SDoc -> SDoc
1100 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1103 Boring and alphabetical:
1106 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1109 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1112 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1115 = hang (ptext SLIT("In an expression with a type signature:"))
1119 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1122 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1124 sectionRAppCtxt expr
1125 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1127 sectionLAppCtxt expr
1128 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1130 funAppCtxt fun arg arg_no
1131 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1132 quotes (ppr fun) <> text ", namely"])
1133 4 (quotes (ppr arg))
1135 wrongArgsCtxt too_many_or_few fun args
1136 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1137 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1138 <+> ptext SLIT("arguments in the call"))
1139 4 (parens (ppr the_app))
1141 the_app = foldl HsApp fun args -- Used in error messages
1144 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1146 the_app = foldl HsApp fun args -- Used in error messages
1148 lurkingRank2Err fun fun_ty
1149 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1150 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1151 ptext SLIT("so that the result type has for-alls in it")])
1153 rank2ArgCtxt arg expected_arg_ty
1154 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1157 = hang (ptext SLIT("No constructor has all these fields:"))
1158 4 (pprQuotedList fields)
1160 fields = [field | (field, _, _) <- rbinds]
1162 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1163 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1166 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1168 illegalCcallTyErr isArg ty
1169 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1173 | isArg = ptext SLIT("argument")
1174 | otherwise = ptext SLIT("result")
1177 missingStrictFieldCon :: Name -> Name -> SDoc
1178 missingStrictFieldCon con field
1179 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1180 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1182 missingFieldCon :: Name -> Name -> SDoc
1183 missingFieldCon con field
1184 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1185 ptext SLIT("is not initialised")]