2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcMonoExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsMatchContext(..), HsDoContext(..), mkMonoBind
14 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
15 import TcHsSyn ( TcExpr, TcRecordBinds, simpleHsLitTy )
18 import TcUnify ( tcSubExp, tcGen, (<$>),
19 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
21 import BasicTypes ( RecFlag(..), isMarkedStrict )
22 import Inst ( InstOrigin(..),
23 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
24 newOverloadedLit, newMethod, newIPDict,
25 newDicts, newMethodWithGivenTy,
28 import TcBinds ( tcBindsAndThen )
29 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
30 tcLookupTyCon, tcLookupDataCon, tcLookupId
32 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
33 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
34 import TcPat ( badFieldCon )
35 import TcSimplify ( tcSimplifyIPs )
36 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
37 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
38 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
39 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
40 isSigmaTy, mkFunTy, mkAppTy, mkTyConTy,
41 mkTyConApp, mkClassPred, tcFunArgTy,
42 tyVarsOfTypes, isLinearPred,
43 liftedTypeKind, openTypeKind, mkArrowKind,
44 tcSplitSigmaTy, tcTyConAppTyCon,
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
48 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
49 import DataCon ( dataConFieldLabels, dataConSig,
53 import TyCon ( TyCon, tyConTyVars, isAlgTyCon, tyConDataCons )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( emptyVarSet, elemVarSet )
56 import TysWiredIn ( boolTy, mkListTy, mkPArrTy, listTyCon, parrTyCon )
57 import PrelNames ( cCallableClassName,
59 enumFromName, enumFromThenName,
60 enumFromToName, enumFromThenToName,
61 enumFromToPName, enumFromThenToPName,
62 thenMName, failMName, returnMName, ioTyConName
65 import ListSetOps ( minusList )
68 import HscTypes ( TyThing(..) )
72 %************************************************************************
74 \subsection{Main wrappers}
76 %************************************************************************
79 tcExpr :: RenamedHsExpr -- Expession to type check
80 -> TcSigmaType -- Expected type (could be a polytpye)
81 -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
83 tcExpr expr expected_ty
84 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenNF_Tc_`
85 tc_expr' expr expected_ty
87 tc_expr' expr expected_ty
88 | not (isSigmaTy expected_ty) -- Monomorphic case
89 = tcMonoExpr expr expected_ty
92 = tcGen expected_ty emptyVarSet (
94 ) `thenTc` \ (gen_fn, expr', lie) ->
95 returnTc (gen_fn <$> expr', lie)
99 %************************************************************************
101 \subsection{The TAUT rules for variables}
103 %************************************************************************
106 tcMonoExpr :: RenamedHsExpr -- Expession to type check
107 -> TcRhoType -- Expected type (could be a type variable)
108 -- Definitely no foralls at the top
112 tcMonoExpr (HsVar name) res_ty
113 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
114 tcSubExp res_ty id_ty `thenTc` \ (co_fn, lie2) ->
115 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
117 tcMonoExpr (HsIPVar ip) res_ty
118 = -- Implicit parameters must have a *tau-type* not a
119 -- type scheme. We enforce this by creating a fresh
120 -- type variable as its type. (Because res_ty may not
122 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
123 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
124 tcSubExp res_ty ip_ty `thenTc` \ (co_fn, lie) ->
125 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
129 %************************************************************************
131 \subsection{Expressions type signatures}
133 %************************************************************************
136 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
137 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
138 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
140 -- Must instantiate the outer for-alls of sig_tc_ty
141 -- else we risk instantiating a ? res_ty to a forall-type
142 -- which breaks the invariant that tcMonoExpr only returns phi-types
143 tcAddErrCtxt (exprSigCtxt in_expr) $
144 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
145 tcSubExp res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
147 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
151 %************************************************************************
153 \subsection{Other expression forms}
155 %************************************************************************
158 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
159 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
160 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
162 tcMonoExpr (NegApp expr neg_name) res_ty
163 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
165 tcMonoExpr (HsLam match) res_ty
166 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
167 returnTc (HsLam match', lie)
169 tcMonoExpr (HsApp e1 e2) res_ty
170 = tcApp e1 [e2] res_ty
173 Note that the operators in sections are expected to be binary, and
174 a type error will occur if they aren't.
177 -- Left sections, equivalent to
184 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
185 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
186 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
187 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
188 tcAddErrCtxt (exprCtxt in_expr) $
189 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
190 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
192 -- Right sections, equivalent to \ x -> x op expr, or
195 tcMonoExpr in_expr@(SectionR op arg2) res_ty
196 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
197 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
198 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
199 tcAddErrCtxt (exprCtxt in_expr) $
200 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
201 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
203 -- equivalent to (op e1) e2:
205 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
206 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
207 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
208 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
209 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
210 tcAddErrCtxt (exprCtxt in_expr) $
211 tcSubExp res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
212 returnTc (OpApp arg1' op' fix arg2',
213 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
216 The interesting thing about @ccall@ is that it is just a template
217 which we instantiate by filling in details about the types of its
218 argument and result (ie minimal typechecking is performed). So, the
219 basic story is that we allocate a load of type variables (to hold the
220 arg/result types); unify them with the args/result; and store them for
224 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
226 = getDOptsTc `thenNF_Tc` \ dflags ->
228 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
229 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
230 text "Either compile with -fvia-C, or, better, rewrite your code",
231 text "to use the foreign function interface. _casm_s are deprecated",
232 text "and support for them may one day disappear."])
235 -- Get the callable and returnable classes.
236 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
237 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
238 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
240 new_arg_dict (arg, arg_ty)
241 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
242 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
243 returnNF_Tc arg_dicts -- Actually a singleton bag
245 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
249 let tv_idxs | null args = []
250 | otherwise = [1..length args]
252 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
253 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
255 -- The argument types can be unlifted or lifted; the result
256 -- type must, however, be lifted since it's an argument to the IO
258 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
260 io_result_ty = mkTyConApp ioTyCon [result_ty]
262 unifyTauTy res_ty io_result_ty `thenTc_`
264 -- Construct the extra insts, which encode the
265 -- constraints on the argument and result types.
266 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
267 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
268 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
269 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
273 tcMonoExpr (HsSCC lbl expr) res_ty
274 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
275 returnTc (HsSCC lbl expr', lie)
277 tcMonoExpr (HsLet binds expr) res_ty
280 binds -- Bindings to check
281 tc_expr `thenTc` \ (expr', lie) ->
282 returnTc (expr', lie)
284 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
285 returnTc (expr', lie)
286 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
288 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
289 = tcAddSrcLoc src_loc $
290 tcAddErrCtxt (caseCtxt in_expr) $
292 -- Typecheck the case alternatives first.
293 -- The case patterns tend to give good type info to use
294 -- when typechecking the scrutinee. For example
297 -- will report that map is applied to too few arguments
299 -- Not only that, but it's better to check the matches on their
300 -- own, so that we get the expected results for scoped type variables.
302 -- (p::a, q::b) -> (q,p)
303 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
304 -- claimed by the pattern signatures. But if we typechecked the
305 -- match with x in scope and x's type as the expected type, we'd be hosed.
307 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
309 tcAddErrCtxt (caseScrutCtxt scrut) (
310 tcMonoExpr scrut scrut_ty
311 ) `thenTc` \ (scrut',lie1) ->
313 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
315 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
316 = tcAddSrcLoc src_loc $
317 tcAddErrCtxt (predCtxt pred) (
318 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
320 zapToType res_ty `thenTc` \ res_ty' ->
321 -- C.f. the call to zapToType in TcMatches.tcMatches
323 tcMonoExpr b1 res_ty' `thenTc` \ (b1',lie2) ->
324 tcMonoExpr b2 res_ty' `thenTc` \ (b2',lie3) ->
325 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
329 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
330 = tcDoStmts do_or_lc stmts src_loc res_ty
334 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
335 = unifyListTy res_ty `thenTc` \ elt_ty ->
336 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
337 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
340 = tcAddErrCtxt (listCtxt expr) $
341 tcMonoExpr expr elt_ty
343 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
344 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
345 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
346 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
349 = tcAddErrCtxt (parrCtxt expr) $
350 tcMonoExpr expr elt_ty
352 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
353 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
354 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
355 (exprs `zip` arg_tys) -- we know they're of equal length.
356 `thenTc` \ (exprs', lies) ->
357 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
359 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
360 = tcAddErrCtxt (recordConCtxt expr) $
361 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
363 (_, record_ty) = tcSplitFunTys con_tau
364 (tycon, ty_args) = tcSplitTyConApp record_ty
366 ASSERT( isAlgTyCon tycon )
367 unifyTauTy res_ty record_ty `thenTc_`
369 -- Check that the record bindings match the constructor
370 -- con_name is syntactically constrained to be a data constructor
371 tcLookupDataCon con_name `thenTc` \ data_con ->
373 bad_fields = badFields rbinds data_con
375 if not (null bad_fields) then
376 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
377 failTc -- Fail now, because tcRecordBinds will crash on a bad field
380 -- Typecheck the record bindings
381 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
384 (missing_s_fields, missing_fields) = missingFields rbinds data_con
386 checkTcM (null missing_s_fields)
387 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
388 returnNF_Tc ()) `thenNF_Tc_`
389 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
390 checkTcM (not (warn && not (null missing_fields)))
391 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
392 returnNF_Tc ()) `thenNF_Tc_`
394 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
396 -- The main complication with RecordUpd is that we need to explicitly
397 -- handle the *non-updated* fields. Consider:
399 -- data T a b = MkT1 { fa :: a, fb :: b }
400 -- | MkT2 { fa :: a, fc :: Int -> Int }
401 -- | MkT3 { fd :: a }
403 -- upd :: T a b -> c -> T a c
404 -- upd t x = t { fb = x}
406 -- The type signature on upd is correct (i.e. the result should not be (T a b))
407 -- because upd should be equivalent to:
409 -- upd t x = case t of
410 -- MkT1 p q -> MkT1 p x
411 -- MkT2 a b -> MkT2 p b
412 -- MkT3 d -> error ...
414 -- So we need to give a completely fresh type to the result record,
415 -- and then constrain it by the fields that are *not* updated ("p" above).
417 -- Note that because MkT3 doesn't contain all the fields being updated,
418 -- its RHS is simply an error, so it doesn't impose any type constraints
420 -- All this is done in STEP 4 below.
422 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
423 = tcAddErrCtxt (recordUpdCtxt expr) $
426 -- Check that the field names are really field names
427 ASSERT( not (null rbinds) )
429 field_names = [field_name | (field_name, _, _) <- rbinds]
431 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
433 bad_guys = [ addErrTc (notSelector field_name)
434 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
436 Just (AnId sel_id) -> not (isRecordSelector sel_id)
440 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
443 -- Figure out the tycon and data cons from the first field name
445 -- It's OK to use the non-tc splitters here (for a selector)
446 (Just (AnId sel_id) : _) = maybe_sel_ids
447 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
448 -- when the data type has a context
449 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
450 tycon = tcTyConAppTyCon data_ty
451 data_cons = tyConDataCons tycon
452 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
454 tcInstTyVars VanillaTv con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
457 -- Check that at least one constructor has all the named fields
458 -- i.e. has an empty set of bad fields returned by badFields
459 checkTc (any (null . badFields rbinds) data_cons)
460 (badFieldsUpd rbinds) `thenTc_`
463 -- Typecheck the update bindings.
464 -- (Do this after checking for bad fields in case there's a field that
465 -- doesn't match the constructor.)
467 result_record_ty = mkTyConApp tycon result_inst_tys
469 unifyTauTy res_ty result_record_ty `thenTc_`
470 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
473 -- Use the un-updated fields to find a vector of booleans saying
474 -- which type arguments must be the same in updatee and result.
476 -- WARNING: this code assumes that all data_cons in a common tycon
477 -- have FieldLabels abstracted over the same tyvars.
479 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
480 con_field_lbls_s = map dataConFieldLabels data_cons
482 -- A constructor is only relevant to this process if
483 -- it contains all the fields that are being updated
484 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
485 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
487 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
488 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
490 mk_inst_ty (tyvar, result_inst_ty)
491 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
492 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
494 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
497 -- Typecheck the expression to be updated
499 record_ty = mkTyConApp tycon inst_tys
501 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
504 -- Figure out the LIE we need. We have to generate some
505 -- dictionaries for the data type context, since we are going to
506 -- do some construction.
508 -- What dictionaries do we need? For the moment we assume that all
509 -- data constructors have the same context, and grab it from the first
510 -- constructor. If they have varying contexts then we'd have to
511 -- union the ones that could participate in the update.
513 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
514 inst_env = mkTopTyVarSubst tyvars result_inst_tys
515 theta' = substTheta inst_env theta
517 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
520 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
521 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
523 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
524 = unifyListTy res_ty `thenTc` \ elt_ty ->
525 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
527 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
528 newMethod (ArithSeqOrigin seq)
529 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
531 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
532 lie1 `plusLIE` unitLIE enum_from)
534 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
535 = tcAddErrCtxt (arithSeqCtxt in_expr) $
536 unifyListTy res_ty `thenTc` \ elt_ty ->
537 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
538 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
539 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
540 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
542 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
543 (FromThen expr1' expr2'),
544 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
546 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
547 = tcAddErrCtxt (arithSeqCtxt in_expr) $
548 unifyListTy res_ty `thenTc` \ elt_ty ->
549 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
550 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
551 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
552 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
554 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
555 (FromTo expr1' expr2'),
556 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
558 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
559 = tcAddErrCtxt (arithSeqCtxt in_expr) $
560 unifyListTy res_ty `thenTc` \ elt_ty ->
561 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
562 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
563 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
564 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
565 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
567 returnTc (ArithSeqOut (HsVar (instToId eft))
568 (FromThenTo expr1' expr2' expr3'),
569 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
571 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
572 = tcAddErrCtxt (parrSeqCtxt in_expr) $
573 unifyPArrTy res_ty `thenTc` \ elt_ty ->
574 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
575 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
576 tcLookupGlobalId enumFromToPName `thenNF_Tc` \ sel_id ->
577 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
579 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
580 (FromTo expr1' expr2'),
581 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
583 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
584 = tcAddErrCtxt (parrSeqCtxt in_expr) $
585 unifyPArrTy res_ty `thenTc` \ elt_ty ->
586 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
587 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
588 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
589 tcLookupGlobalId enumFromThenToPName `thenNF_Tc` \ sel_id ->
590 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
592 returnTc (PArrSeqOut (HsVar (instToId eft))
593 (FromThenTo expr1' expr2' expr3'),
594 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
596 tcMonoExpr (PArrSeqIn _) _
597 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
598 -- the parser shouldn't have generated it and the renamer shouldn't have
602 %************************************************************************
604 \subsection{Implicit Parameter bindings}
606 %************************************************************************
609 tcMonoExpr (HsWith expr binds) res_ty
610 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
611 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
613 -- If the binding binds ?x = E, we must now
614 -- discharge any ?x constraints in expr_lie
615 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
617 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
619 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
622 = newTyVarTy openTypeKind `thenTc` \ ty ->
623 tcGetSrcLoc `thenTc` \ loc ->
624 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
625 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
626 returnTc (ip_inst, (ip', expr'), lie)
629 %************************************************************************
631 \subsection{@tcApp@ typchecks an application}
633 %************************************************************************
637 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
638 -> TcType -- Expected result type of application
639 -> TcM (TcExpr, LIE) -- Translated fun and args
641 tcApp (HsApp e1 e2) args res_ty
642 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
644 tcApp fun args res_ty
645 = -- First type-check the function
646 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
648 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
649 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenNF_Tc_`
650 split_fun_ty fun_ty (length args)
651 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
653 -- Now typecheck the args
654 mapAndUnzipTc (tcArg fun)
655 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
657 -- Unify with expected result after type-checking the args
658 -- so that the info from args percolates to actual_result_ty.
659 -- This is when we might detect a too-few args situation.
660 -- (One can think of cases when the opposite order would give
661 -- a better error message.)
662 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
663 (tcSubExp res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
665 returnTc (co_fn <$> foldl HsApp fun' args',
666 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
669 -- If an error happens we try to figure out whether the
670 -- function has been given too many or too few arguments,
672 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
673 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
674 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
676 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
677 (env2, act_ty'') = tidyOpenType env1 act_ty'
678 (exp_args, _) = tcSplitFunTys exp_ty''
679 (act_args, _) = tcSplitFunTys act_ty''
681 len_act_args = length act_args
682 len_exp_args = length exp_args
684 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
685 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
686 | otherwise = appCtxt fun args
688 returnNF_Tc (env2, message)
691 split_fun_ty :: TcType -- The type of the function
692 -> Int -- Number of arguments
693 -> TcM ([TcType], -- Function argument types
694 TcType) -- Function result types
696 split_fun_ty fun_ty 0
697 = returnTc ([], fun_ty)
699 split_fun_ty fun_ty n
700 = -- Expect the function to have type A->B
701 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
702 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
703 returnTc (arg_ty:arg_tys, final_res_ty)
707 tcArg :: RenamedHsExpr -- The function (for error messages)
708 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
709 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
711 tcArg the_fun (arg, expected_arg_ty, arg_no)
712 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
713 tcExpr arg expected_arg_ty
717 %************************************************************************
719 \subsection{@tcId@ typchecks an identifier occurrence}
721 %************************************************************************
723 tcId instantiates an occurrence of an Id.
724 The instantiate_it loop runs round instantiating the Id.
725 It has to be a loop because we are now prepared to entertain
727 f:: forall a. Eq a => forall b. Baz b => tau
728 We want to instantiate this to
729 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
731 The -fno-method-sharing flag controls what happens so far as the LIE
732 is concerned. The default case is that for an overloaded function we
733 generate a "method" Id, and add the Method Inst to the LIE. So you get
736 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
737 If you specify -fno-method-sharing, the dictionary application
738 isn't shared, so we get
740 f = /\a (d:Num a) (x:a) -> (+) a d x x
741 This gets a bit less sharing, but
742 a) it's better for RULEs involving overloaded functions
743 b) perhaps fewer separated lambdas
746 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
747 tcId name -- Look up the Id and instantiate its type
748 = tcLookupId name `thenNF_Tc` \ id ->
749 loop (OccurrenceOf id) (HsVar id) emptyLIE (idType id)
751 loop orig (HsVar fun_id) lie fun_ty
752 | want_method_inst fun_ty
753 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
754 newMethodWithGivenTy orig fun_id
755 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
756 loop orig (HsVar (instToId meth))
757 (unitLIE meth `plusLIE` lie) tau
759 loop orig fun lie fun_ty
761 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
762 loop orig (inst_fn fun) (inst_lie `plusLIE` lie) tau
765 = returnNF_Tc (fun, lie, fun_ty)
767 want_method_inst fun_ty
768 | opt_NoMethodSharing = False
769 | otherwise = case tcSplitSigmaTy fun_ty of
770 (_,[],_) -> False -- Not overloaded
771 (_,theta,_) -> not (any isLinearPred theta)
772 -- This is a slight hack.
773 -- If f :: (%x :: T) => Int -> Int
774 -- Then if we have two separate calls, (f 3, f 4), we cannot
775 -- make a method constraint that then gets shared, thus:
776 -- let m = f %x in (m 3, m 4)
777 -- because that loses the linearity of the constraint.
778 -- The simplest thing to do is never to construct a method constraint
779 -- in the first place that has a linear implicit parameter in it.
782 Typecheck expression which in most cases will be an Id.
783 The expression can return a higher-ranked type, such as
784 (forall a. a->a) -> Int
785 so we must create a HoleTyVarTy to pass in as the expected tyvar.
788 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
789 tcExpr_id (HsVar name) = tcId name
790 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
791 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
792 readHoleResult id_ty `thenTc` \ id_ty' ->
793 returnTc (expr', lie_id, id_ty')
797 %************************************************************************
799 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
801 %************************************************************************
804 -- I don't like this lumping together of do expression and list/array
805 -- comprehensions; creating the monad instances is entirely pointless in the
806 -- latter case; I'll leave the list case as it is for the moment, but handle
807 -- arrays extra (would be better to handle arrays and lists together, though)
810 tcDoStmts PArrComp stmts src_loc res_ty
812 ASSERT( not (null stmts) )
813 tcAddSrcLoc src_loc $
815 unifyPArrTy res_ty `thenTc` \elt_ty ->
816 let tc_ty = mkTyConTy parrTyCon
817 m_ty = (mkPArrTy, elt_ty)
819 tcStmts (DoCtxt PArrComp) m_ty stmts `thenTc` \(stmts', stmts_lie) ->
820 returnTc (HsDoOut PArrComp stmts'
821 undefined undefined undefined -- don't touch!
825 tcDoStmts do_or_lc stmts src_loc res_ty
826 = -- get the Monad and MonadZero classes
827 -- create type consisting of a fresh monad tyvar
828 ASSERT( not (null stmts) )
829 tcAddSrcLoc src_loc $
831 -- If it's a comprehension we're dealing with,
832 -- force it to be a list comprehension.
833 -- (as of Haskell 98, monad comprehensions are no more.)
834 -- Similarily, array comprehensions must involve parallel arrays types
837 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
838 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
840 PArrComp -> panic "TcExpr.tcDoStmts: How did we get here?!?"
842 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
843 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
844 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
845 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
846 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
848 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
850 -- Build the then and zero methods in case we need them
851 -- It's important that "then" and "return" appear just once in the final LIE,
852 -- not only for typechecker efficiency, but also because otherwise during
853 -- simplification we end up with silly stuff like
854 -- then = case d of (t,r) -> t
856 -- where the second "then" sees that it already exists in the "available" stuff.
858 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
859 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
860 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
861 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
862 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
863 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
865 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
867 returnTc (HsDoOut do_or_lc stmts'
868 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
870 stmts_lie `plusLIE` monad_lie)
874 %************************************************************************
876 \subsection{Record bindings}
878 %************************************************************************
880 Game plan for record bindings
881 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
882 1. Find the TyCon for the bindings, from the first field label.
884 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
886 For each binding field = value
888 3. Instantiate the field type (from the field label) using the type
891 4 Type check the value using tcArg, passing the field type as
892 the expected argument type.
894 This extends OK when the field types are universally quantified.
899 :: TyCon -- Type constructor for the record
900 -> [TcType] -- Args of this type constructor
901 -> RenamedRecordBinds
902 -> TcM (TcRecordBinds, LIE)
904 tcRecordBinds tycon ty_args rbinds
905 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
906 returnTc (rbinds', plusLIEs lies)
908 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
910 do_bind (field_lbl_name, rhs, pun_flag)
911 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
913 field_lbl = recordSelectorFieldLabel sel_id
914 field_ty = substTy tenv (fieldLabelType field_lbl)
916 ASSERT( isRecordSelector sel_id )
917 -- This lookup and assertion will surely succeed, because
918 -- we check that the fields are indeed record selectors
919 -- before calling tcRecordBinds
920 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
921 -- The caller of tcRecordBinds has already checked
922 -- that all the fields come from the same type
924 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
926 returnTc ((sel_id, rhs', pun_flag), lie)
928 badFields rbinds data_con
929 = [field_name | (field_name, _, _) <- rbinds,
930 not (field_name `elem` field_names)
933 field_names = map fieldLabelName (dataConFieldLabels data_con)
935 missingFields rbinds data_con
936 | null field_labels = ([], []) -- Not declared as a record;
937 -- But C{} is still valid
939 = (missing_strict_fields, other_missing_fields)
941 missing_strict_fields
942 = [ fl | (fl, str) <- field_info,
944 not (fieldLabelName fl `elem` field_names_used)
947 = [ fl | (fl, str) <- field_info,
948 not (isMarkedStrict str),
949 not (fieldLabelName fl `elem` field_names_used)
952 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
953 field_labels = dataConFieldLabels data_con
955 field_info = zipEqual "missingFields"
957 (dropList ex_theta (dataConStrictMarks data_con))
958 -- The 'drop' is because dataConStrictMarks
959 -- includes the existential dictionaries
960 (_, _, _, ex_theta, _, _) = dataConSig data_con
963 %************************************************************************
965 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
967 %************************************************************************
970 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
972 tcMonoExprs [] [] = returnTc ([], emptyLIE)
973 tcMonoExprs (expr:exprs) (ty:tys)
974 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
975 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
976 returnTc (expr':exprs', lie1 `plusLIE` lie2)
980 %************************************************************************
982 \subsection{Literals}
984 %************************************************************************
989 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
990 tcLit (HsLitLit s _) res_ty
991 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
992 newDicts (LitLitOrigin (_UNPK_ s))
993 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
994 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
997 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
998 returnTc (HsLit lit, emptyLIE)
1002 %************************************************************************
1004 \subsection{Errors and contexts}
1006 %************************************************************************
1010 Boring and alphabetical:
1013 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1016 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1019 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1022 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1025 = hang (ptext SLIT("When checking the type signature of the expression:"))
1029 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1032 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1035 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1038 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1040 funAppCtxt fun arg arg_no
1041 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1042 quotes (ppr fun) <> text ", namely"])
1043 4 (quotes (ppr arg))
1045 wrongArgsCtxt too_many_or_few fun args
1046 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1047 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1048 <+> ptext SLIT("arguments in the call"))
1049 4 (parens (ppr the_app))
1051 the_app = foldl HsApp fun args -- Used in error messages
1054 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1056 the_app = foldl HsApp fun args -- Used in error messages
1058 lurkingRank2Err fun fun_ty
1059 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1060 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1061 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1064 = hang (ptext SLIT("No constructor has all these fields:"))
1065 4 (pprQuotedList fields)
1067 fields = [field | (field, _, _) <- rbinds]
1069 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1070 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1073 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1075 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1076 missingStrictFieldCon con field
1077 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1078 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1080 missingFieldCon :: Name -> FieldLabel -> SDoc
1081 missingFieldCon con field
1082 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1083 ptext SLIT("is not initialised")]