2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcApp, tcExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), StmtCtxt(..),
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
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 = let id = mkVanillaId name res_ty in
204 tcGetInstLoc (OccurrenceOf id) `thenNF_Tc` \ loc ->
205 newIPDict name res_ty loc `thenNF_Tc` \ ip ->
206 returnNF_Tc (HsIPVar id, unitLIE ip)
209 %************************************************************************
211 \subsection{Literals}
213 %************************************************************************
218 tcMonoExpr (HsLit (HsInt i)) res_ty
219 = newOverloadedLit (LiteralOrigin (HsInt i))
220 (OverloadedIntegral i)
221 res_ty `thenNF_Tc` \ stuff ->
224 tcMonoExpr (HsLit (HsFrac f)) res_ty
225 = newOverloadedLit (LiteralOrigin (HsFrac f))
226 (OverloadedFractional f)
227 res_ty `thenNF_Tc` \ stuff ->
231 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
232 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
233 newClassDicts (LitLitOrigin (_UNPK_ s))
234 [(cCallableClass,[res_ty])] `thenNF_Tc` \ (dicts, _) ->
235 returnTc (HsLitOut lit res_ty, dicts)
241 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
242 = unifyTauTy res_ty charPrimTy `thenTc_`
243 returnTc (HsLitOut lit charPrimTy, emptyLIE)
245 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
246 = unifyTauTy res_ty addrPrimTy `thenTc_`
247 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
249 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
250 = unifyTauTy res_ty intPrimTy `thenTc_`
251 returnTc (HsLitOut lit intPrimTy, emptyLIE)
253 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
254 = unifyTauTy res_ty floatPrimTy `thenTc_`
255 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
257 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
258 = unifyTauTy res_ty doublePrimTy `thenTc_`
259 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
262 Unoverloaded literals:
265 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
266 = unifyTauTy res_ty charTy `thenTc_`
267 returnTc (HsLitOut lit charTy, emptyLIE)
269 tcMonoExpr (HsLit lit@(HsString str)) res_ty
270 = unifyTauTy res_ty stringTy `thenTc_`
271 returnTc (HsLitOut lit stringTy, emptyLIE)
274 %************************************************************************
276 \subsection{Other expression forms}
278 %************************************************************************
281 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
282 = tcMonoExpr expr res_ty
284 -- perform the negate *before* overloading the integer, since the case
285 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
286 -- convenient to do it here.
288 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
289 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
291 tcMonoExpr (NegApp expr neg) res_ty
292 = tcMonoExpr (HsApp neg expr) res_ty
294 tcMonoExpr (HsLam match) res_ty
295 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
296 returnTc (HsLam match', lie)
298 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
300 accum (HsApp e1 e2) args = accum e1 (e2:args)
302 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
303 returnTc (foldl HsApp fun' args', lie)
305 -- equivalent to (op e1) e2:
306 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
307 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
308 returnTc (OpApp arg1' op' fix arg2', lie)
311 Note that the operators in sections are expected to be binary, and
312 a type error will occur if they aren't.
315 -- Left sections, equivalent to
322 tcMonoExpr in_expr@(SectionL arg op) res_ty
323 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
325 -- Check that res_ty is a function type
326 -- Without this check we barf in the desugarer on
328 -- because it tries to desugar to
329 -- f op = \r -> 3 op r
330 -- so (3 `op`) had better be a function!
331 tcAddErrCtxt (sectionLAppCtxt in_expr) $
332 unifyFunTy res_ty `thenTc_`
334 returnTc (SectionL arg' op', lie)
336 -- Right sections, equivalent to \ x -> x op expr, or
339 tcMonoExpr in_expr@(SectionR op expr) res_ty
340 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
341 tcAddErrCtxt (sectionRAppCtxt in_expr) $
342 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
343 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
344 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
345 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
348 The interesting thing about @ccall@ is that it is just a template
349 which we instantiate by filling in details about the types of its
350 argument and result (ie minimal typechecking is performed). So, the
351 basic story is that we allocate a load of type variables (to hold the
352 arg/result types); unify them with the args/result; and store them for
356 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
357 = -- Get the callable and returnable classes.
358 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
359 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
360 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
362 new_arg_dict (arg, arg_ty)
363 = newClassDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
364 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
365 returnNF_Tc arg_dicts -- Actually a singleton bag
367 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
371 let n_args = length args
372 tv_idxs | n_args == 0 = []
373 | otherwise = [1..n_args]
375 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) tv_idxs `thenNF_Tc` \ arg_tys ->
376 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
378 -- The argument types can be unboxed or boxed; the result
379 -- type must, however, be boxed since it's an argument to the IO
381 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
383 io_result_ty = mkTyConApp ioTyCon [result_ty]
384 [ioDataCon] = tyConDataCons ioTyCon
386 unifyTauTy res_ty io_result_ty `thenTc_`
388 -- Construct the extra insts, which encode the
389 -- constraints on the argument and result types.
390 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
391 newClassDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
392 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
393 (CCall lbl args' may_gc is_asm result_ty),
394 -- do the wrapping in the newtype constructor here
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 -- Con is syntactically constrained to be a data constructor
483 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
484 unifyTauTy res_ty record_ty `thenTc_`
486 -- Check that the record bindings match the 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 splitForAllTys (idType sel_id)
568 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
569 (tycon, _, data_cons) = splitAlgTyConApp data_ty
570 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
572 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
575 -- Check that at least one constructor has all the named fields
576 -- i.e. has an empty set of bad fields returned by badFields
577 checkTc (any (null . badFields rbinds) data_cons)
578 (badFieldsUpd rbinds) `thenTc_`
581 -- Typecheck the update bindings.
582 -- (Do this after checking for bad fields in case there's a field that
583 -- doesn't match the constructor.)
585 result_record_ty = mkTyConApp tycon result_inst_tys
587 unifyTauTy res_ty result_record_ty `thenTc_`
588 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
591 -- Use the un-updated fields to find a vector of booleans saying
592 -- which type arguments must be the same in updatee and result.
594 -- WARNING: this code assumes that all data_cons in a common tycon
595 -- have FieldLabels abstracted over the same tyvars.
597 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
598 con_field_lbls_s = map dataConFieldLabels data_cons
600 -- A constructor is only relevant to this process if
601 -- it contains all the fields that are being updated
602 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
603 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
605 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
606 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
608 mk_inst_ty (tyvar, result_inst_ty)
609 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
610 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
612 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
615 -- Typecheck the expression to be updated
617 record_ty = mkTyConApp tycon inst_tys
619 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
622 -- Figure out the LIE we need. We have to generate some
623 -- dictionaries for the data type context, since we are going to
624 -- do some construction.
626 -- What dictionaries do we need? For the moment we assume that all
627 -- data constructors have the same context, and grab it from the first
628 -- constructor. If they have varying contexts then we'd have to
629 -- union the ones that could participate in the update.
631 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
632 inst_env = mkTopTyVarSubst tyvars result_inst_tys
633 theta' = substClasses inst_env theta
635 newClassDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
638 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
639 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
641 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
642 = unifyListTy res_ty `thenTc` \ elt_ty ->
643 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
645 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
646 newMethod (ArithSeqOrigin seq)
647 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
649 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
652 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
653 = tcAddErrCtxt (arithSeqCtxt in_expr) $
654 unifyListTy res_ty `thenTc` \ elt_ty ->
655 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
656 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
657 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
658 newMethod (ArithSeqOrigin seq)
659 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
661 returnTc (ArithSeqOut (HsVar enum_from_then_id)
662 (FromThen expr1' expr2'),
663 lie1 `plusLIE` lie2 `plusLIE` lie3)
665 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
666 = tcAddErrCtxt (arithSeqCtxt in_expr) $
667 unifyListTy res_ty `thenTc` \ elt_ty ->
668 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
669 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
670 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
671 newMethod (ArithSeqOrigin seq)
672 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
674 returnTc (ArithSeqOut (HsVar enum_from_to_id)
675 (FromTo expr1' expr2'),
676 lie1 `plusLIE` lie2 `plusLIE` lie3)
678 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
679 = tcAddErrCtxt (arithSeqCtxt in_expr) $
680 unifyListTy res_ty `thenTc` \ elt_ty ->
681 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
682 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
683 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
684 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
685 newMethod (ArithSeqOrigin seq)
686 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
688 returnTc (ArithSeqOut (HsVar eft_id)
689 (FromThenTo expr1' expr2' expr3'),
690 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
693 %************************************************************************
695 \subsection{Expressions type signatures}
697 %************************************************************************
700 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
701 = tcSetErrCtxt (exprSigCtxt in_expr) $
702 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
704 if not (isForAllTy sig_tc_ty) then
706 unifyTauTy sig_tc_ty res_ty `thenTc_`
707 tcMonoExpr expr sig_tc_ty
709 else -- Signature is polymorphic
710 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
712 -- Now match the signature type with res_ty.
713 -- We must not do this earlier, because res_ty might well
714 -- mention variables free in the environment, and we'd get
715 -- bogus complaints about not being able to for-all the
717 unifyTauTy res_ty expr_ty `thenTc_`
719 -- If everything is ok, return the stuff unchanged, except for
720 -- the effect of any substutions etc. We simply discard the
721 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
722 -- resolution it may have done, which is recorded in the
727 Implicit Parameter bindings.
730 tcMonoExpr (HsWith expr binds) res_ty
731 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
732 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
733 partitionLIEbyMeth isBound lie `thenTc` \ (ips, lie') ->
734 zonkLIE ips `thenTc` \ ips' ->
735 tcSimplify (text "With!") (tyVarsOfLIE ips') ips' `thenTc` \ res@(_, dict_binds, _) ->
736 let expr'' = if nullMonoBinds dict_binds
738 else HsLet (MonoBind dict_binds [] NonRecursive) expr' in
739 tcCheckIPBinds binds' types ips' `thenTc_`
740 returnTc (HsWith expr'' binds', lie')
742 = case ipName_maybe p of
743 Just n -> n `elem` names
745 names = map fst binds
747 tcIPBinds ((name, expr) : binds)
748 = newTyVarTy_OpenKind `thenTc` \ ty ->
749 let id = mkVanillaId name ty in
750 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
751 zonkTcType ty `thenTc` \ ty' ->
752 tcIPBinds binds `thenTc` \ (binds', types, lie2) ->
753 returnTc ((id, expr') : binds', ty : types, lie `plusLIE` lie2)
754 tcIPBinds [] = returnTc ([], [], emptyLIE)
756 tcCheckIPBinds binds types ips
757 = foldrTc tcCheckIPBind (getIPsOfLIE ips) (zip binds types)
759 -- ZZ how do we use the loc?
760 tcCheckIPBind bt@((v, _), t1) ((n, t2) : ips) | getName v == n
761 = unifyTauTy t1 t2 `thenTc_`
762 tcCheckIPBind bt ips `thenTc` \ ips' ->
764 tcCheckIPBind bt (ip : ips)
765 = tcCheckIPBind bt ips `thenTc` \ ips' ->
771 Typecheck expression which in most cases will be an Id.
774 tcExpr_id :: RenamedHsExpr
780 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
782 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
783 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
784 returnTc (id_expr', lie_id, id_ty)
787 %************************************************************************
789 \subsection{@tcApp@ typchecks an application}
791 %************************************************************************
795 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
796 -> TcType -- Expected result type of application
797 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
800 tcApp fun args res_ty
801 = -- First type-check the function
802 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
804 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
805 split_fun_ty fun_ty (length args)
806 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
808 -- Unify with expected result before type-checking the args
809 -- This is when we might detect a too-few args situation
810 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
811 unifyTauTy res_ty actual_result_ty
814 -- Now typecheck the args
815 mapAndUnzipTc (tcArg fun)
816 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
818 -- Check that the result type doesn't have any nested for-alls.
819 -- For example, a "build" on its own is no good; it must be applied to something.
820 checkTc (isTauTy actual_result_ty)
821 (lurkingRank2Err fun fun_ty) `thenTc_`
823 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
826 -- If an error happens we try to figure out whether the
827 -- function has been given too many or too few arguments,
829 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
830 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
831 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
833 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
834 (env2, act_ty'') = tidyOpenType env1 act_ty'
835 (exp_args, _) = splitFunTys exp_ty''
836 (act_args, _) = splitFunTys act_ty''
838 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
839 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
840 | otherwise = appCtxt fun args
842 returnNF_Tc (env2, message)
845 split_fun_ty :: TcType -- The type of the function
846 -> Int -- Number of arguments
847 -> TcM s ([TcType], -- Function argument types
848 TcType) -- Function result types
850 split_fun_ty fun_ty 0
851 = returnTc ([], fun_ty)
853 split_fun_ty fun_ty n
854 = -- Expect the function to have type A->B
855 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
856 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
857 returnTc (arg_ty:arg_tys, final_res_ty)
861 tcArg :: RenamedHsExpr -- The function (for error messages)
862 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
863 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
865 tcArg the_fun (arg, expected_arg_ty, arg_no)
866 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
867 tcExpr arg expected_arg_ty
871 %************************************************************************
873 \subsection{@tcId@ typchecks an identifier occurrence}
875 %************************************************************************
877 Between the renamer and the first invocation of the UsageSP inference,
878 identifiers read from interface files will have usage information in
879 their types, whereas other identifiers will not. The unannotTy here
880 in @tcId@ prevents this information from pointlessly propagating
881 further prior to the first usage inference.
884 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
887 = -- Look up the Id and instantiate its type
888 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
891 Just tc_id -> instantiate_it (OccurrenceOf tc_id) (HsVar tc_id) (unannotTy (idType tc_id))
893 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
894 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
895 instantiate_it2 (OccurrenceOf id) (HsVar id) tyvars theta tau
898 -- The instantiate_it loop runs round instantiating the Id.
899 -- It has to be a loop because we are now prepared to entertain
901 -- f:: forall a. Eq a => forall b. Baz b => tau
902 -- We want to instantiate this to
903 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
904 instantiate_it orig fun ty
905 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
906 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
907 instantiate_it2 orig fun tyvars theta tau
909 instantiate_it2 orig fun tyvars theta tau
910 = if null theta then -- Is it overloaded?
911 returnNF_Tc (mkHsTyApp fun arg_tys, emptyLIE, tau)
913 -- Yes, it's overloaded
914 instOverloadedFun orig fun arg_tys theta tau `thenNF_Tc` \ (fun', lie1) ->
915 instantiate_it orig fun' tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
916 returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau)
919 arg_tys = mkTyVarTys tyvars
922 %************************************************************************
924 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
926 %************************************************************************
929 tcDoStmts do_or_lc stmts src_loc res_ty
930 = -- get the Monad and MonadZero classes
931 -- create type consisting of a fresh monad tyvar
932 ASSERT( not (null stmts) )
933 tcAddSrcLoc src_loc $
935 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
936 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
937 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
939 -- If it's a comprehension we're dealing with,
940 -- force it to be a list comprehension.
941 -- (as of Haskell 98, monad comprehensions are no more.)
943 ListComp -> unifyListTy res_ty `thenTc_` returnTc ()
944 _ -> returnTc ()) `thenTc_`
946 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
948 -- Build the then and zero methods in case we need them
949 -- It's important that "then" and "return" appear just once in the final LIE,
950 -- not only for typechecker efficiency, but also because otherwise during
951 -- simplification we end up with silly stuff like
952 -- then = case d of (t,r) -> t
954 -- where the second "then" sees that it already exists in the "available" stuff.
956 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
957 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
958 tcLookupValueByKey failMClassOpKey `thenNF_Tc` \ fail_sel_id ->
959 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
960 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
961 newMethod DoOrigin fail_sel_id [m] `thenNF_Tc` \ (fail_lie, fail_id) ->
963 monad_lie = then_lie `plusLIE` return_lie `plusLIE` fail_lie
965 returnTc (HsDoOut do_or_lc stmts' return_id then_id fail_id res_ty src_loc,
966 stmts_lie `plusLIE` monad_lie)
970 %************************************************************************
972 \subsection{Record bindings}
974 %************************************************************************
976 Game plan for record bindings
977 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
980 1. look up "field", to find its selector Id, which must have type
981 forall a1..an. T a1 .. an -> tau
982 where tau is the type of the field.
984 2. Instantiate this type
986 3. Unify the (T a1 .. an) part with the "expected result type", which
987 is passed in. This checks that all the field labels come from the
990 4. Type check the value using tcArg, passing tau as the expected
993 This extends OK when the field types are universally quantified.
995 Actually, to save excessive creation of fresh type variables,
1000 :: TcType -- Expected type of whole record
1001 -> RenamedRecordBinds
1002 -> TcM s (TcRecordBinds, LIE)
1004 tcRecordBinds expected_record_ty rbinds
1005 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
1006 returnTc (rbinds', plusLIEs lies)
1008 do_bind (field_label, rhs, pun_flag)
1009 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
1010 ASSERT( isRecordSelector sel_id )
1011 -- This lookup and assertion will surely succeed, because
1012 -- we check that the fields are indeed record selectors
1013 -- before calling tcRecordBinds
1015 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
1017 -- Record selectors all have type
1018 -- forall a1..an. T a1 .. an -> tau
1019 ASSERT( maybeToBool (splitFunTy_maybe tau) )
1021 -- Selector must have type RecordType -> FieldType
1022 Just (record_ty, field_ty) = splitFunTy_maybe tau
1024 unifyTauTy expected_record_ty record_ty `thenTc_`
1025 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
1026 returnTc ((sel_id, rhs', pun_flag), lie)
1028 badFields rbinds data_con
1029 = [field_name | (field_name, _, _) <- rbinds,
1030 not (field_name `elem` field_names)
1033 field_names = map fieldLabelName (dataConFieldLabels data_con)
1035 missingStrictFields rbinds data_con
1036 = [ fn | fn <- strict_field_names,
1037 not (fn `elem` field_names_used)
1040 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1041 strict_field_names = mapMaybe isStrict field_info
1043 isStrict (fl, MarkedStrict) = Just (fieldLabelName fl)
1044 isStrict _ = Nothing
1046 field_info = zip (dataConFieldLabels data_con)
1047 (dataConStrictMarks data_con)
1049 missingFields rbinds data_con
1050 = [ fn | fn <- non_strict_field_names, not (fn `elem` field_names_used) ]
1052 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
1054 -- missing strict fields have already been flagged as
1055 -- being so, so leave them out here.
1056 non_strict_field_names = mapMaybe isn'tStrict field_info
1058 isn'tStrict (fl, MarkedStrict) = Nothing
1059 isn'tStrict (fl, _) = Just (fieldLabelName fl)
1061 field_info = zip (dataConFieldLabels data_con)
1062 (dataConStrictMarks data_con)
1066 %************************************************************************
1068 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1070 %************************************************************************
1073 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
1075 tcMonoExprs [] [] = returnTc ([], emptyLIE)
1076 tcMonoExprs (expr:exprs) (ty:tys)
1077 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
1078 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
1079 returnTc (expr':exprs', lie1 `plusLIE` lie2)
1083 % =================================================
1090 pp_nest_hang :: String -> SDoc -> SDoc
1091 pp_nest_hang lbl stuff = nest 2 (hang (text lbl) 4 stuff)
1094 Boring and alphabetical:
1097 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1100 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1103 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1106 = hang (ptext SLIT("In an expression with a type signature:"))
1110 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1113 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1115 sectionRAppCtxt expr
1116 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1118 sectionLAppCtxt expr
1119 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1121 funAppCtxt fun arg arg_no
1122 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1123 quotes (ppr fun) <> text ", namely"])
1124 4 (quotes (ppr arg))
1126 wrongArgsCtxt too_many_or_few fun args
1127 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1128 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1129 <+> ptext SLIT("arguments in the call"))
1130 4 (parens (ppr the_app))
1132 the_app = foldl HsApp fun args -- Used in error messages
1135 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1137 the_app = foldl HsApp fun args -- Used in error messages
1139 lurkingRank2Err fun fun_ty
1140 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1141 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1142 ptext SLIT("so that the result type has for-alls in it")])
1144 rank2ArgCtxt arg expected_arg_ty
1145 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1148 = hang (ptext SLIT("No constructor has all these fields:"))
1149 4 (pprQuotedList fields)
1151 fields = [field | (field, _, _) <- rbinds]
1153 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1154 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1157 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1159 illegalCcallTyErr isArg ty
1160 = hang (hsep [ptext SLIT("Unacceptable"), arg_or_res, ptext SLIT("type in _ccall_ or _casm_:")])
1164 | isArg = ptext SLIT("argument")
1165 | otherwise = ptext SLIT("result")
1168 missingStrictFieldCon :: Name -> Name -> SDoc
1169 missingStrictFieldCon con field
1170 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1171 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1173 missingFieldCon :: Name -> Name -> SDoc
1174 missingFieldCon con field
1175 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1176 ptext SLIT("is not initialised")]