2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcPolyExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsBinds(..), Stmt(..), StmtCtxt(..),
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds,
21 import BasicTypes ( RecFlag(..) )
23 import Inst ( Inst, InstOrigin(..), OverloadedLit(..),
24 LIE, emptyLIE, unitLIE, plusLIE, plusLIEs, newOverloadedLit,
25 newMethod, newMethodWithGivenTy, newDicts, instToId )
26 import TcBinds ( tcBindsAndThen )
27 import TcEnv ( tcInstId,
28 tcLookupValue, tcLookupClassByKey,
30 tcExtendGlobalTyVars, tcLookupValueMaybe,
31 tcLookupTyCon, tcLookupDataCon
33 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
34 import TcMonoType ( tcHsType, checkSigTyVars, sigCtxt )
35 import TcPat ( badFieldCon )
36 import TcSimplify ( tcSimplifyAndCheck )
37 import TcType ( TcType, TcTauType,
39 tcInstTcType, tcSplitRhoTy,
40 newTyVarTy, newTyVarTy_OpenKind, zonkTcType )
42 import Class ( Class )
43 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType )
44 import Id ( idType, recordSelectorFieldLabel,
48 import DataCon ( dataConFieldLabels, dataConSig, dataConId )
50 import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys,
51 splitFunTy_maybe, splitFunTys,
53 splitForAllTys, splitRhoTy,
54 isTauTy, tyVarsOfType, tyVarsOfTypes,
55 isForAllTy, splitAlgTyConApp, splitAlgTyConApp_maybe,
56 boxedTypeKind, mkArrowKind,
57 substTopTheta, tidyOpenType
59 import VarEnv ( zipVarEnv )
60 import VarSet ( elemVarSet, mkVarSet )
61 import TyCon ( tyConDataCons )
62 import TysPrim ( intPrimTy, charPrimTy, doublePrimTy,
63 floatPrimTy, addrPrimTy
65 import TysWiredIn ( boolTy, charTy, stringTy )
66 import PrelInfo ( ioTyCon_NAME )
67 import TcUnify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy,
69 import Unique ( cCallableClassKey, cReturnableClassKey,
70 enumFromClassOpKey, enumFromThenClassOpKey,
71 enumFromToClassOpKey, enumFromThenToClassOpKey,
72 thenMClassOpKey, zeroClassOpKey, returnMClassOpKey
75 import Maybes ( maybeToBool )
76 import ListSetOps ( minusList )
80 %************************************************************************
82 \subsection{Main wrappers}
84 %************************************************************************
87 tcExpr :: RenamedHsExpr -- Expession to type check
88 -> TcType -- Expected type (could be a polytpye)
89 -> TcM s (TcExpr, LIE)
91 tcExpr expr ty | isForAllTy ty = -- Polymorphic case
92 tcPolyExpr expr ty `thenTc` \ (expr', lie, _, _, _) ->
95 | otherwise = -- Monomorphic case
100 %************************************************************************
102 \subsection{@tcPolyExpr@ typchecks an application}
104 %************************************************************************
107 -- tcPolyExpr is like tcMonoExpr, except that the expected type
108 -- can be a polymorphic one.
109 tcPolyExpr :: RenamedHsExpr
110 -> TcType -- Expected type
111 -> TcM s (TcExpr, LIE, -- Generalised expr with expected type, and LIE
112 TcExpr, TcTauType, LIE) -- Same thing, but instantiated; tau-type returned
114 tcPolyExpr arg expected_arg_ty
115 = -- Ha! The argument type of the function is a for-all type,
116 -- An example of rank-2 polymorphism.
118 -- To ensure that the forall'd type variables don't get unified with each
119 -- other or any other types, we make fresh copy of the alleged type
120 tcInstTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) ->
122 (sig_theta, sig_tau) = splitRhoTy sig_rho
124 -- Type-check the arg and unify with expected type
125 tcMonoExpr arg sig_tau `thenTc` \ (arg', lie_arg) ->
127 -- Check that the sig_tyvars havn't been constrained
128 -- The interesting bit here is that we must include the free variables
129 -- of the expected arg ty. Here's an example:
130 -- runST (newVar True)
131 -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool))
132 -- for (newVar True), with s fresh. Then we unify with the runST's arg type
133 -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool.
134 -- So now s' isn't unconstrained because it's linked to a.
135 -- Conclusion: include the free vars of the expected arg type in the
136 -- list of "free vars" for the signature check.
138 tcExtendGlobalTyVars (tyVarsOfType expected_arg_ty) $
139 tcAddErrCtxtM (sigCtxt sig_msg expected_arg_ty) $
141 checkSigTyVars sig_tyvars `thenTc` \ zonked_sig_tyvars ->
143 newDicts SignatureOrigin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) ->
144 -- ToDo: better origin
147 (mkVarSet zonked_sig_tyvars)
148 sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) ->
151 -- This HsLet binds any Insts which came out of the simplification.
152 -- It's a bit out of place here, but using AbsBind involves inventing
153 -- a couple of new names which seems worse.
154 generalised_arg = TyLam zonked_sig_tyvars $
156 HsLet (MonoBind inst_binds [] Recursive)
159 returnTc ( generalised_arg, free_insts,
160 arg', sig_tau, lie_arg )
162 sig_msg ty = ptext SLIT("In an expression with expected type:") <+> ppr ty
165 %************************************************************************
167 \subsection{The TAUT rules for variables}
169 %************************************************************************
172 tcMonoExpr :: RenamedHsExpr -- Expession to type check
173 -> TcTauType -- Expected type (could be a type variable)
174 -> TcM s (TcExpr, LIE)
176 tcMonoExpr (HsVar name) res_ty
177 = tcId name `thenNF_Tc` \ (expr', lie, id_ty) ->
178 unifyTauTy res_ty id_ty `thenTc_`
180 -- Check that the result type doesn't have any nested for-alls.
181 -- For example, a "build" on its own is no good; it must be
182 -- applied to something.
183 checkTc (isTauTy id_ty)
184 (lurkingRank2Err name id_ty) `thenTc_`
186 returnTc (expr', lie)
189 %************************************************************************
191 \subsection{Literals}
193 %************************************************************************
198 tcMonoExpr (HsLit (HsInt i)) res_ty
199 = newOverloadedLit (LiteralOrigin (HsInt i))
200 (OverloadedIntegral i)
201 res_ty `thenNF_Tc` \ stuff ->
204 tcMonoExpr (HsLit (HsFrac f)) res_ty
205 = newOverloadedLit (LiteralOrigin (HsFrac f))
206 (OverloadedFractional f)
207 res_ty `thenNF_Tc` \ stuff ->
211 tcMonoExpr (HsLit lit@(HsLitLit s)) res_ty
212 = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
213 newDicts (LitLitOrigin (_UNPK_ s))
214 [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) ->
215 returnTc (HsLitOut lit res_ty, dicts)
221 tcMonoExpr (HsLit lit@(HsCharPrim c)) res_ty
222 = unifyTauTy res_ty charPrimTy `thenTc_`
223 returnTc (HsLitOut lit charPrimTy, emptyLIE)
225 tcMonoExpr (HsLit lit@(HsStringPrim s)) res_ty
226 = unifyTauTy res_ty addrPrimTy `thenTc_`
227 returnTc (HsLitOut lit addrPrimTy, emptyLIE)
229 tcMonoExpr (HsLit lit@(HsIntPrim i)) res_ty
230 = unifyTauTy res_ty intPrimTy `thenTc_`
231 returnTc (HsLitOut lit intPrimTy, emptyLIE)
233 tcMonoExpr (HsLit lit@(HsFloatPrim f)) res_ty
234 = unifyTauTy res_ty floatPrimTy `thenTc_`
235 returnTc (HsLitOut lit floatPrimTy, emptyLIE)
237 tcMonoExpr (HsLit lit@(HsDoublePrim d)) res_ty
238 = unifyTauTy res_ty doublePrimTy `thenTc_`
239 returnTc (HsLitOut lit doublePrimTy, emptyLIE)
242 Unoverloaded literals:
245 tcMonoExpr (HsLit lit@(HsChar c)) res_ty
246 = unifyTauTy res_ty charTy `thenTc_`
247 returnTc (HsLitOut lit charTy, emptyLIE)
249 tcMonoExpr (HsLit lit@(HsString str)) res_ty
250 = unifyTauTy res_ty stringTy `thenTc_`
251 returnTc (HsLitOut lit stringTy, emptyLIE)
254 %************************************************************************
256 \subsection{Other expression forms}
258 %************************************************************************
261 tcMonoExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go
262 = tcMonoExpr expr res_ty
264 -- perform the negate *before* overloading the integer, since the case
265 -- of minBound on Ints fails otherwise. Could be done elsewhere, but
266 -- convenient to do it here.
268 tcMonoExpr (NegApp (HsLit (HsInt i)) neg) res_ty
269 = tcMonoExpr (HsLit (HsInt (-i))) res_ty
271 tcMonoExpr (NegApp expr neg) res_ty
272 = tcMonoExpr (HsApp neg expr) res_ty
274 tcMonoExpr (HsLam match) res_ty
275 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
276 returnTc (HsLam match', lie)
278 tcMonoExpr (HsApp e1 e2) res_ty = accum e1 [e2]
280 accum (HsApp e1 e2) args = accum e1 (e2:args)
282 = tcApp fun args res_ty `thenTc` \ (fun', args', lie) ->
283 returnTc (foldl HsApp fun' args', lie)
285 -- equivalent to (op e1) e2:
286 tcMonoExpr (OpApp arg1 op fix arg2) res_ty
287 = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) ->
288 returnTc (OpApp arg1' op' fix arg2', lie)
291 Note that the operators in sections are expected to be binary, and
292 a type error will occur if they aren't.
295 -- Left sections, equivalent to
302 tcMonoExpr in_expr@(SectionL arg op) res_ty
303 = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) ->
305 -- Check that res_ty is a function type
306 -- Without this check we barf in the desugarer on
308 -- because it tries to desugar to
309 -- f op = \r -> 3 op r
310 -- so (3 `op`) had better be a function!
311 tcAddErrCtxt (sectionLAppCtxt in_expr) $
312 unifyFunTy res_ty `thenTc_`
314 returnTc (SectionL arg' op', lie)
316 -- Right sections, equivalent to \ x -> x op expr, or
319 tcMonoExpr in_expr@(SectionR op expr) res_ty
320 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
321 tcAddErrCtxt (sectionRAppCtxt in_expr) $
322 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
323 tcMonoExpr expr arg2_ty `thenTc` \ (expr',lie2) ->
324 unifyTauTy res_ty (mkFunTy arg1_ty op_res_ty) `thenTc_`
325 returnTc (SectionR op' expr', lie1 `plusLIE` lie2)
328 The interesting thing about @ccall@ is that it is just a template
329 which we instantiate by filling in details about the types of its
330 argument and result (ie minimal typechecking is performed). So, the
331 basic story is that we allocate a load of type variables (to hold the
332 arg/result types); unify them with the args/result; and store them for
336 tcMonoExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty
337 = -- Get the callable and returnable classes.
338 tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass ->
339 tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass ->
340 tcLookupTyCon ioTyCon_NAME `thenNF_Tc` \ ioTyCon ->
342 new_arg_dict (arg, arg_ty)
343 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
344 [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) ->
345 returnNF_Tc arg_dicts -- Actually a singleton bag
347 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
351 mapNF_Tc (\ _ -> newTyVarTy_OpenKind) [1..(length args)] `thenNF_Tc` \ arg_tys ->
352 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
354 -- The argument types can be unboxed or boxed; the result
355 -- type must, however, be boxed since it's an argument to the IO
357 newTyVarTy boxedTypeKind `thenNF_Tc` \ result_ty ->
359 io_result_ty = mkTyConApp ioTyCon [result_ty]
360 [ioDataCon] = tyConDataCons ioTyCon
362 unifyTauTy res_ty io_result_ty `thenTc_`
364 -- Construct the extra insts, which encode the
365 -- constraints on the argument and result types.
366 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
367 newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) ->
369 returnTc (HsApp (HsVar (dataConId ioDataCon) `TyApp` [result_ty])
370 (CCall lbl args' may_gc is_asm result_ty),
371 -- do the wrapping in the newtype constructor here
372 foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie)
376 tcMonoExpr (HsSCC label expr) res_ty
377 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
378 returnTc (HsSCC label expr', lie)
380 tcMonoExpr (HsLet binds expr) res_ty
383 binds -- Bindings to check
384 tc_expr `thenTc` \ (expr', lie) ->
385 returnTc (expr', lie)
387 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
388 returnTc (expr', lie)
389 combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr
391 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
392 = tcAddSrcLoc src_loc $
393 tcAddErrCtxt (caseCtxt in_expr) $
395 -- Typecheck the case alternatives first.
396 -- The case patterns tend to give good type info to use
397 -- when typechecking the scrutinee. For example
400 -- will report that map is applied to too few arguments
402 -- Not only that, but it's better to check the matches on their
403 -- own, so that we get the expected results for scoped type variables.
405 -- (p::a, q::b) -> (q,p)
406 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
407 -- claimed by the pattern signatures. But if we typechecked the
408 -- match with x in scope and x's type as the expected type, we'd be hosed.
410 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
412 tcAddErrCtxt (caseScrutCtxt scrut) (
413 tcMonoExpr scrut scrut_ty
414 ) `thenTc` \ (scrut',lie1) ->
416 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
418 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
419 = tcAddSrcLoc src_loc $
420 tcAddErrCtxt (predCtxt pred) (
421 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
423 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
424 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
425 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
429 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
430 = tcDoStmts do_or_lc stmts src_loc res_ty
434 tcMonoExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list
435 = unifyListTy res_ty `thenTc` \ elt_ty ->
436 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
437 returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies)
440 = tcAddErrCtxt (listCtxt expr) $
441 tcMonoExpr expr elt_ty
443 tcMonoExpr (ExplicitTuple exprs boxed) res_ty
445 then unifyTupleTy (length exprs) res_ty
446 else unifyUnboxedTupleTy (length exprs) res_ty
447 ) `thenTc` \ arg_tys ->
448 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
449 (exprs `zip` arg_tys) -- we know they're of equal length.
450 `thenTc` \ (exprs', lies) ->
451 returnTc (ExplicitTuple exprs' boxed, plusLIEs lies)
453 tcMonoExpr (RecordCon con_name rbinds) res_ty
454 = tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
456 (_, record_ty) = splitFunTys con_tau
458 -- Con is syntactically constrained to be a data constructor
459 ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) )
460 unifyTauTy res_ty record_ty `thenTc_`
462 -- Check that the record bindings match the constructor
463 tcLookupDataCon con_name `thenTc` \ (data_con, _, _) ->
465 bad_fields = badFields rbinds data_con
467 if not (null bad_fields) then
468 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
469 failTc -- Fail now, because tcRecordBinds will crash on a bad field
472 -- Typecheck the record bindings
473 tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
475 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
478 -- The main complication with RecordUpd is that we need to explicitly
479 -- handle the *non-updated* fields. Consider:
481 -- data T a b = MkT1 { fa :: a, fb :: b }
482 -- | MkT2 { fa :: a, fc :: Int -> Int }
483 -- | MkT3 { fd :: a }
485 -- upd :: T a b -> c -> T a c
486 -- upd t x = t { fb = x}
488 -- The type signature on upd is correct (i.e. the result should not be (T a b))
489 -- because upd should be equivalent to:
491 -- upd t x = case t of
492 -- MkT1 p q -> MkT1 p x
493 -- MkT2 a b -> MkT2 p b
494 -- MkT3 d -> error ...
496 -- So we need to give a completely fresh type to the result record,
497 -- and then constrain it by the fields that are *not* updated ("p" above).
499 -- Note that because MkT3 doesn't contain all the fields being updated,
500 -- its RHS is simply an error, so it doesn't impose any type constraints
502 -- All this is done in STEP 4 below.
504 tcMonoExpr (RecordUpd record_expr rbinds) res_ty
505 = tcAddErrCtxt recordUpdCtxt $
508 -- Check that the field names are really field names
509 ASSERT( not (null rbinds) )
511 field_names = [field_name | (field_name, _, _) <- rbinds]
513 mapNF_Tc tcLookupValueMaybe field_names `thenNF_Tc` \ maybe_sel_ids ->
515 bad_guys = [field_name | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
518 Just sel_id -> not (isRecordSelector sel_id)
521 mapNF_Tc (addErrTc . notSelector) bad_guys `thenTc_`
522 if not (null bad_guys) then
527 -- Figure out the tycon and data cons from the first field name
529 (Just sel_id : _) = maybe_sel_ids
530 (_, tau) = splitForAllTys (idType sel_id)
531 Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector
532 (tycon, _, data_cons) = splitAlgTyConApp data_ty
533 (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
535 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
538 -- Check that at least one constructor has all the named fields
539 -- i.e. has an empty set of bad fields returned by badFields
540 checkTc (any (null . badFields rbinds) data_cons)
541 (badFieldsUpd rbinds) `thenTc_`
544 -- Typecheck the update bindings.
545 -- (Do this after checking for bad fields in case there's a field that
546 -- doesn't match the constructor.)
548 result_record_ty = mkTyConApp tycon result_inst_tys
550 unifyTauTy res_ty result_record_ty `thenTc_`
551 tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) ->
554 -- Use the un-updated fields to find a vector of booleans saying
555 -- which type arguments must be the same in updatee and result.
557 -- WARNING: this code assumes that all data_cons in a common tycon
558 -- have FieldLabels abstracted over the same tyvars.
560 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
561 con_field_lbls_s = map dataConFieldLabels data_cons
563 -- A constructor is only relevant to this process if
564 -- it contains all the fields that are being updated
565 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
566 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
568 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
569 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
571 mk_inst_ty (tyvar, result_inst_ty)
572 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
573 | otherwise = newTyVarTy boxedTypeKind -- Fresh type
575 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
578 -- Typecheck the expression to be updated
580 record_ty = mkTyConApp tycon inst_tys
582 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
585 -- Figure out the LIE we need. We have to generate some
586 -- dictionaries for the data type context, since we are going to
587 -- do some construction.
589 -- What dictionaries do we need? For the moment we assume that all
590 -- data constructors have the same context, and grab it from the first
591 -- constructor. If they have varying contexts then we'd have to
592 -- union the ones that could participate in the update.
594 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
595 inst_env = zipVarEnv tyvars result_inst_tys
596 theta' = substTopTheta inst_env theta
598 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) ->
601 returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds',
602 con_lie `plusLIE` record_lie `plusLIE` rbinds_lie)
604 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
605 = unifyListTy res_ty `thenTc` \ elt_ty ->
606 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
608 tcLookupValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id ->
609 newMethod (ArithSeqOrigin seq)
610 sel_id [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) ->
612 returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'),
615 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
616 = tcAddErrCtxt (arithSeqCtxt in_expr) $
617 unifyListTy res_ty `thenTc` \ elt_ty ->
618 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
619 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
620 tcLookupValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id ->
621 newMethod (ArithSeqOrigin seq)
622 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) ->
624 returnTc (ArithSeqOut (HsVar enum_from_then_id)
625 (FromThen expr1' expr2'),
626 lie1 `plusLIE` lie2 `plusLIE` lie3)
628 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
629 = tcAddErrCtxt (arithSeqCtxt in_expr) $
630 unifyListTy res_ty `thenTc` \ elt_ty ->
631 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
632 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
633 tcLookupValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id ->
634 newMethod (ArithSeqOrigin seq)
635 sel_id [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) ->
637 returnTc (ArithSeqOut (HsVar enum_from_to_id)
638 (FromTo expr1' expr2'),
639 lie1 `plusLIE` lie2 `plusLIE` lie3)
641 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
642 = tcAddErrCtxt (arithSeqCtxt in_expr) $
643 unifyListTy res_ty `thenTc` \ elt_ty ->
644 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
645 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
646 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
647 tcLookupValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id ->
648 newMethod (ArithSeqOrigin seq)
649 sel_id [elt_ty] `thenNF_Tc` \ (lie4, eft_id) ->
651 returnTc (ArithSeqOut (HsVar eft_id)
652 (FromThenTo expr1' expr2' expr3'),
653 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4)
656 %************************************************************************
658 \subsection{Expressions type signatures}
660 %************************************************************************
663 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
664 = tcSetErrCtxt (exprSigCtxt in_expr) $
665 tcHsType poly_ty `thenTc` \ sig_tc_ty ->
667 if not (isForAllTy sig_tc_ty) then
669 unifyTauTy sig_tc_ty res_ty `thenTc_`
670 tcMonoExpr expr sig_tc_ty
672 else -- Signature is polymorphic
673 tcPolyExpr expr sig_tc_ty `thenTc` \ (_, _, expr, expr_ty, lie) ->
675 -- Now match the signature type with res_ty.
676 -- We must not do this earlier, because res_ty might well
677 -- mention variables free in the environment, and we'd get
678 -- bogus complaints about not being able to for-all the
680 unifyTauTy res_ty expr_ty `thenTc_`
682 -- If everything is ok, return the stuff unchanged, except for
683 -- the effect of any substutions etc. We simply discard the
684 -- result of the tcSimplifyAndCheck (inside tcPolyExpr), except for any default
685 -- resolution it may have done, which is recorded in the
690 Typecheck expression which in most cases will be an Id.
693 tcExpr_id :: RenamedHsExpr
699 HsVar name -> tcId name `thenNF_Tc` \ stuff ->
701 other -> newTyVarTy_OpenKind `thenNF_Tc` \ id_ty ->
702 tcMonoExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) ->
703 returnTc (id_expr', lie_id, id_ty)
706 %************************************************************************
708 \subsection{@tcApp@ typchecks an application}
710 %************************************************************************
714 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
715 -> TcType -- Expected result type of application
716 -> TcM s (TcExpr, [TcExpr], -- Translated fun and args
719 tcApp fun args res_ty
720 = -- First type-check the function
721 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
723 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
724 split_fun_ty fun_ty (length args)
725 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
727 -- Unify with expected result before type-checking the args
728 -- This is when we might detect a too-few args situation
729 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) (
730 unifyTauTy res_ty actual_result_ty
733 -- Now typecheck the args
734 mapAndUnzipTc (tcArg fun)
735 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
737 -- Check that the result type doesn't have any nested for-alls.
738 -- For example, a "build" on its own is no good; it must be applied to something.
739 checkTc (isTauTy actual_result_ty)
740 (lurkingRank2Err fun fun_ty) `thenTc_`
742 returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s)
745 -- If an error happens we try to figure out whether the
746 -- function has been given too many or too few arguments,
748 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
749 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
750 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
752 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
753 (env2, act_ty'') = tidyOpenType env1 act_ty'
754 (exp_args, _) = splitFunTys exp_ty''
755 (act_args, _) = splitFunTys act_ty''
757 message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args
758 | length exp_args > length act_args = wrongArgsCtxt "too many" fun args
759 | otherwise = appCtxt fun args
761 returnNF_Tc (env2, message)
764 split_fun_ty :: TcType -- The type of the function
765 -> Int -- Number of arguments
766 -> TcM s ([TcType], -- Function argument types
767 TcType) -- Function result types
769 split_fun_ty fun_ty 0
770 = returnTc ([], fun_ty)
772 split_fun_ty fun_ty n
773 = -- Expect the function to have type A->B
774 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
775 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
776 returnTc (arg_ty:arg_tys, final_res_ty)
780 tcArg :: RenamedHsExpr -- The function (for error messages)
781 -> (RenamedHsExpr, TcType, Int) -- Actual argument and expected arg type
782 -> TcM s (TcExpr, LIE) -- Resulting argument and LIE
784 tcArg the_fun (arg, expected_arg_ty, arg_no)
785 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
786 tcExpr arg expected_arg_ty
790 %************************************************************************
792 \subsection{@tcId@ typchecks an identifier occurrence}
794 %************************************************************************
797 tcId :: Name -> NF_TcM s (TcExpr, LIE, TcType)
800 = -- Look up the Id and instantiate its type
801 tcLookupValueMaybe name `thenNF_Tc` \ maybe_local ->
804 Just tc_id -> instantiate_it tc_id (idType tc_id)
806 Nothing -> tcLookupValue name `thenNF_Tc` \ id ->
807 tcInstId id `thenNF_Tc` \ (tyvars, theta, tau) ->
808 instantiate_it2 id tyvars theta tau
811 -- The instantiate_it loop runs round instantiating the Id.
812 -- It has to be a loop because we are now prepared to entertain
814 -- f:: forall a. Eq a => forall b. Baz b => tau
815 -- We want to instantiate this to
816 -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
817 instantiate_it tc_id_occ ty
818 = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) ->
819 tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) ->
820 instantiate_it2 tc_id_occ tyvars theta tau
822 instantiate_it2 tc_id_occ tyvars theta tau
823 = if null theta then -- Is it overloaded?
824 returnNF_Tc (mkHsTyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau)
826 -- Yes, it's overloaded
827 newMethodWithGivenTy (OccurrenceOf tc_id_occ)
828 tc_id_occ arg_tys theta tau `thenNF_Tc` \ inst ->
829 instantiate_it (instToId inst) tau `thenNF_Tc` \ (expr, lie2, final_tau) ->
830 returnNF_Tc (expr, unitLIE inst `plusLIE` lie2, final_tau)
833 arg_tys = mkTyVarTys tyvars
836 %************************************************************************
838 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
840 %************************************************************************
843 tcDoStmts do_or_lc stmts src_loc res_ty
844 = -- get the Monad and MonadZero classes
845 -- create type consisting of a fresh monad tyvar
846 ASSERT( not (null stmts) )
847 tcAddSrcLoc src_loc $
849 newTyVarTy (mkArrowKind boxedTypeKind boxedTypeKind) `thenNF_Tc` \ m ->
850 newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty ->
851 unifyTauTy res_ty (mkAppTy m elt_ty) `thenTc_`
853 tcStmts do_or_lc (mkAppTy m) stmts elt_ty `thenTc` \ (stmts', stmts_lie) ->
855 -- Build the then and zero methods in case we need them
856 -- It's important that "then" and "return" appear just once in the final LIE,
857 -- not only for typechecker efficiency, but also because otherwise during
858 -- simplification we end up with silly stuff like
859 -- then = case d of (t,r) -> t
861 -- where the second "then" sees that it already exists in the "available" stuff.
863 tcLookupValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id ->
864 tcLookupValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id ->
865 tcLookupValueByKey zeroClassOpKey `thenNF_Tc` \ zero_sel_id ->
866 newMethod DoOrigin return_sel_id [m] `thenNF_Tc` \ (return_lie, return_id) ->
867 newMethod DoOrigin then_sel_id [m] `thenNF_Tc` \ (then_lie, then_id) ->
868 newMethod DoOrigin zero_sel_id [m] `thenNF_Tc` \ (zero_lie, zero_id) ->
870 monad_lie = then_lie `plusLIE` return_lie `plusLIE` perhaps_zero_lie
871 perhaps_zero_lie | all failure_free stmts' = emptyLIE
872 | otherwise = zero_lie
874 failure_free (BindStmt pat _ _) = failureFreePat pat
875 failure_free (GuardStmt _ _) = False
876 failure_free other_stmt = True
878 returnTc (HsDoOut do_or_lc stmts' return_id then_id zero_id res_ty src_loc,
879 stmts_lie `plusLIE` monad_lie)
883 %************************************************************************
885 \subsection{Record bindings}
887 %************************************************************************
889 Game plan for record bindings
890 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
893 1. look up "field", to find its selector Id, which must have type
894 forall a1..an. T a1 .. an -> tau
895 where tau is the type of the field.
897 2. Instantiate this type
899 3. Unify the (T a1 .. an) part with the "expected result type", which
900 is passed in. This checks that all the field labels come from the
903 4. Type check the value using tcArg, passing tau as the expected
906 This extends OK when the field types are universally quantified.
908 Actually, to save excessive creation of fresh type variables,
913 :: TcType -- Expected type of whole record
914 -> RenamedRecordBinds
915 -> TcM s (TcRecordBinds, LIE)
917 tcRecordBinds expected_record_ty rbinds
918 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
919 returnTc (rbinds', plusLIEs lies)
921 do_bind (field_label, rhs, pun_flag)
922 = tcLookupValue field_label `thenNF_Tc` \ sel_id ->
923 ASSERT( isRecordSelector sel_id )
924 -- This lookup and assertion will surely succeed, because
925 -- we check that the fields are indeed record selectors
926 -- before calling tcRecordBinds
928 tcInstId sel_id `thenNF_Tc` \ (_, _, tau) ->
930 -- Record selectors all have type
931 -- forall a1..an. T a1 .. an -> tau
932 ASSERT( maybeToBool (splitFunTy_maybe tau) )
934 -- Selector must have type RecordType -> FieldType
935 Just (record_ty, field_ty) = splitFunTy_maybe tau
937 unifyTauTy expected_record_ty record_ty `thenTc_`
938 tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie, _, _, _) ->
939 returnTc ((sel_id, rhs', pun_flag), lie)
941 badFields rbinds data_con
942 = [field_name | (field_name, _, _) <- rbinds,
943 not (field_name `elem` field_names)
946 field_names = map fieldLabelName (dataConFieldLabels data_con)
949 %************************************************************************
951 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
953 %************************************************************************
956 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM s ([TcExpr], LIE)
958 tcMonoExprs [] [] = returnTc ([], emptyLIE)
959 tcMonoExprs (expr:exprs) (ty:tys)
960 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
961 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
962 returnTc (expr':exprs', lie1 `plusLIE` lie2)
966 % =================================================
973 pp_nest_hang :: String -> SDoc -> SDoc
974 pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff)
977 Boring and alphabetical:
980 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
983 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
986 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
989 = hang (ptext SLIT("In an expression with a type signature:"))
993 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
996 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
999 = hang (ptext SLIT("In the right section:")) 4 (ppr expr)
1001 sectionLAppCtxt expr
1002 = hang (ptext SLIT("In the left section:")) 4 (ppr expr)
1004 funAppCtxt fun arg arg_no
1005 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1006 quotes (ppr fun) <> text ", namely"])
1007 4 (quotes (ppr arg))
1009 wrongArgsCtxt too_many_or_few fun args
1010 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1011 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1012 <+> ptext SLIT("arguments in the call"))
1013 4 (parens (ppr the_app))
1015 the_app = foldl HsApp fun args -- Used in error messages
1018 = ptext SLIT("In the application") <+> (ppr the_app)
1020 the_app = foldl HsApp fun args -- Used in error messages
1022 lurkingRank2Err fun fun_ty
1023 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1024 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1025 ptext SLIT("so that the result type has for-alls in it")])
1027 rank2ArgCtxt arg expected_arg_ty
1028 = ptext SLIT("In a polymorphic function argument:") <+> ppr arg
1031 = hang (ptext SLIT("No constructor has all these fields:"))
1032 4 (pprQuotedList fields)
1034 fields = [field | (field, _, _) <- rbinds]
1036 recordUpdCtxt = ptext SLIT("In a record update construct")
1039 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]