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(..),
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds, simpleHsLitTy, mkHsDictApp, mkHsTyApp )
19 import TcUnify ( tcSubExp, tcGen, (<$>),
20 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
22 import BasicTypes ( RecFlag(..), isMarkedStrict )
23 import Inst ( InstOrigin(..),
24 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
25 newOverloadedLit, newMethodFromName, newIPDict,
26 newDicts, newMethodWithGivenTy,
27 instToId, tcInstCall, tcInstDataCon
29 import TcBinds ( tcBindsAndThen )
30 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
31 tcLookupTyCon, tcLookupDataCon, tcLookupId
33 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
34 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
35 import TcPat ( badFieldCon )
36 import TcSimplify ( tcSimplifyIPs )
37 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
38 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
39 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
40 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
41 isSigmaTy, mkFunTy, mkAppTy, mkTyConTy, mkFunTys,
42 mkTyConApp, mkClassPred, tcFunArgTy,
43 tyVarsOfTypes, isLinearPred,
44 liftedTypeKind, openTypeKind, mkArrowKind,
45 tcSplitSigmaTy, tcTyConAppTyCon,
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
49 import Id ( idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
50 import DataCon ( dataConFieldLabels, dataConSig,
54 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
55 import Subst ( mkTopTyVarSubst, substTheta, substTy )
56 import VarSet ( emptyVarSet, elemVarSet )
57 import TysWiredIn ( boolTy, mkListTy, mkPArrTy, listTyCon, parrTyCon )
58 import PrelNames ( cCallableClassName,
60 enumFromName, enumFromThenName,
61 enumFromToName, enumFromThenToName,
62 enumFromToPName, enumFromThenToPName,
63 thenMName, bindMName, failMName, returnMName, ioTyConName
66 import ListSetOps ( minusList )
69 import HscTypes ( TyThing(..) )
73 %************************************************************************
75 \subsection{Main wrappers}
77 %************************************************************************
80 tcExpr :: RenamedHsExpr -- Expession to type check
81 -> TcSigmaType -- Expected type (could be a polytpye)
82 -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
84 tcExpr expr expected_ty
85 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenNF_Tc_`
86 tc_expr' expr expected_ty
88 tc_expr' expr expected_ty
89 | not (isSigmaTy expected_ty) -- Monomorphic case
90 = tcMonoExpr expr expected_ty
93 = tcGen expected_ty emptyVarSet (
95 ) `thenTc` \ (gen_fn, expr', lie) ->
96 returnTc (gen_fn <$> expr', lie)
100 %************************************************************************
102 \subsection{The TAUT rules for variables}
104 %************************************************************************
107 tcMonoExpr :: RenamedHsExpr -- Expession to type check
108 -> TcRhoType -- Expected type (could be a type variable)
109 -- Definitely no foralls at the top
113 tcMonoExpr (HsVar name) res_ty
114 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
115 tcSubExp res_ty id_ty `thenTc` \ (co_fn, lie2) ->
116 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
118 tcMonoExpr (HsIPVar ip) res_ty
119 = -- Implicit parameters must have a *tau-type* not a
120 -- type scheme. We enforce this by creating a fresh
121 -- type variable as its type. (Because res_ty may not
123 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
124 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
125 tcSubExp res_ty ip_ty `thenTc` \ (co_fn, lie) ->
126 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
130 %************************************************************************
132 \subsection{Expressions type signatures}
134 %************************************************************************
137 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
138 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
139 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
141 -- Must instantiate the outer for-alls of sig_tc_ty
142 -- else we risk instantiating a ? res_ty to a forall-type
143 -- which breaks the invariant that tcMonoExpr only returns phi-types
144 tcAddErrCtxt (exprSigCtxt in_expr) $
145 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
146 tcSubExp res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
148 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
152 %************************************************************************
154 \subsection{Other expression forms}
156 %************************************************************************
159 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
160 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
161 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
163 tcMonoExpr (NegApp expr neg_name) res_ty
164 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
166 tcMonoExpr (HsLam match) res_ty
167 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
168 returnTc (HsLam match', lie)
170 tcMonoExpr (HsApp e1 e2) res_ty
171 = tcApp e1 [e2] res_ty
174 Note that the operators in sections are expected to be binary, and
175 a type error will occur if they aren't.
178 -- Left sections, equivalent to
185 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
186 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
187 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
188 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
189 tcAddErrCtxt (exprCtxt in_expr) $
190 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
191 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
193 -- Right sections, equivalent to \ x -> x op expr, or
196 tcMonoExpr in_expr@(SectionR op arg2) res_ty
197 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
198 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
199 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
200 tcAddErrCtxt (exprCtxt in_expr) $
201 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
202 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
204 -- equivalent to (op e1) e2:
206 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
207 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
208 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
209 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
210 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
211 tcAddErrCtxt (exprCtxt in_expr) $
212 tcSubExp res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
213 returnTc (OpApp arg1' op' fix arg2',
214 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
217 The interesting thing about @ccall@ is that it is just a template
218 which we instantiate by filling in details about the types of its
219 argument and result (ie minimal typechecking is performed). So, the
220 basic story is that we allocate a load of type variables (to hold the
221 arg/result types); unify them with the args/result; and store them for
225 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
227 = getDOptsTc `thenNF_Tc` \ dflags ->
229 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
230 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
231 text "Either compile with -fvia-C, or, better, rewrite your code",
232 text "to use the foreign function interface. _casm_s are deprecated",
233 text "and support for them may one day disappear."])
236 -- Get the callable and returnable classes.
237 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
238 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
239 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
241 new_arg_dict (arg, arg_ty)
242 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
243 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
244 returnNF_Tc arg_dicts -- Actually a singleton bag
246 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
250 let tv_idxs | null args = []
251 | otherwise = [1..length args]
253 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
254 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
256 -- The argument types can be unlifted or lifted; the result
257 -- type must, however, be lifted since it's an argument to the IO
259 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
261 io_result_ty = mkTyConApp ioTyCon [result_ty]
263 unifyTauTy res_ty io_result_ty `thenTc_`
265 -- Construct the extra insts, which encode the
266 -- constraints on the argument and result types.
267 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
268 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
269 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
270 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
274 tcMonoExpr (HsSCC lbl expr) res_ty
275 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
276 returnTc (HsSCC lbl expr', lie)
278 tcMonoExpr (HsLet binds expr) res_ty
281 binds -- Bindings to check
282 tc_expr `thenTc` \ (expr', lie) ->
283 returnTc (expr', lie)
285 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
286 returnTc (expr', lie)
287 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
289 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
290 = tcAddSrcLoc src_loc $
291 tcAddErrCtxt (caseCtxt in_expr) $
293 -- Typecheck the case alternatives first.
294 -- The case patterns tend to give good type info to use
295 -- when typechecking the scrutinee. For example
298 -- will report that map is applied to too few arguments
300 -- Not only that, but it's better to check the matches on their
301 -- own, so that we get the expected results for scoped type variables.
303 -- (p::a, q::b) -> (q,p)
304 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
305 -- claimed by the pattern signatures. But if we typechecked the
306 -- match with x in scope and x's type as the expected type, we'd be hosed.
308 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
310 tcAddErrCtxt (caseScrutCtxt scrut) (
311 tcMonoExpr scrut scrut_ty
312 ) `thenTc` \ (scrut',lie1) ->
314 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
316 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
317 = tcAddSrcLoc src_loc $
318 tcAddErrCtxt (predCtxt pred) (
319 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
321 zapToType res_ty `thenTc` \ res_ty' ->
322 -- C.f. the call to zapToType in TcMatches.tcMatches
324 tcMonoExpr b1 res_ty' `thenTc` \ (b1',lie2) ->
325 tcMonoExpr b2 res_ty' `thenTc` \ (b2',lie3) ->
326 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
330 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
331 = tcDoStmts do_or_lc stmts src_loc res_ty
335 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
336 = unifyListTy res_ty `thenTc` \ elt_ty ->
337 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
338 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
341 = tcAddErrCtxt (listCtxt expr) $
342 tcMonoExpr expr elt_ty
344 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
345 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
346 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
347 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
350 = tcAddErrCtxt (parrCtxt expr) $
351 tcMonoExpr expr elt_ty
353 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
354 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
355 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
356 (exprs `zip` arg_tys) -- we know they're of equal length.
357 `thenTc` \ (exprs', lies) ->
358 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
360 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
361 = tcAddErrCtxt (recordConCtxt expr) $
362 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
364 (_, record_ty) = tcSplitFunTys con_tau
365 (tycon, ty_args) = tcSplitTyConApp record_ty
367 ASSERT( isAlgTyCon tycon )
368 unifyTauTy res_ty record_ty `thenTc_`
370 -- Check that the record bindings match the constructor
371 -- con_name is syntactically constrained to be a data constructor
372 tcLookupDataCon con_name `thenTc` \ data_con ->
374 bad_fields = badFields rbinds data_con
376 if notNull bad_fields then
377 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
378 failTc -- Fail now, because tcRecordBinds will crash on a bad field
381 -- Typecheck the record bindings
382 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
385 (missing_s_fields, missing_fields) = missingFields rbinds data_con
387 checkTcM (null missing_s_fields)
388 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
389 returnNF_Tc ()) `thenNF_Tc_`
390 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
391 checkTcM (not (warn && notNull missing_fields))
392 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
393 returnNF_Tc ()) `thenNF_Tc_`
395 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
397 -- The main complication with RecordUpd is that we need to explicitly
398 -- handle the *non-updated* fields. Consider:
400 -- data T a b = MkT1 { fa :: a, fb :: b }
401 -- | MkT2 { fa :: a, fc :: Int -> Int }
402 -- | MkT3 { fd :: a }
404 -- upd :: T a b -> c -> T a c
405 -- upd t x = t { fb = x}
407 -- The type signature on upd is correct (i.e. the result should not be (T a b))
408 -- because upd should be equivalent to:
410 -- upd t x = case t of
411 -- MkT1 p q -> MkT1 p x
412 -- MkT2 a b -> MkT2 p b
413 -- MkT3 d -> error ...
415 -- So we need to give a completely fresh type to the result record,
416 -- and then constrain it by the fields that are *not* updated ("p" above).
418 -- Note that because MkT3 doesn't contain all the fields being updated,
419 -- its RHS is simply an error, so it doesn't impose any type constraints
421 -- All this is done in STEP 4 below.
423 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
424 = tcAddErrCtxt (recordUpdCtxt expr) $
427 -- Check that the field names are really field names
428 ASSERT( notNull rbinds )
430 field_names = [field_name | (field_name, _, _) <- rbinds]
432 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
434 bad_guys = [ addErrTc (notSelector field_name)
435 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
437 Just (AnId sel_id) -> not (isRecordSelector sel_id)
441 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
444 -- Figure out the tycon and data cons from the first field name
446 -- It's OK to use the non-tc splitters here (for a selector)
447 (Just (AnId sel_id) : _) = maybe_sel_ids
449 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
450 -- when the data type has a context
451 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
452 tycon = tcTyConAppTyCon data_ty
453 data_cons = tyConDataCons tycon
454 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
456 tcInstTyVars VanillaTv tycon_tyvars `thenNF_Tc` \ (_, result_inst_tys, inst_env) ->
459 -- Check that at least one constructor has all the named fields
460 -- i.e. has an empty set of bad fields returned by badFields
461 checkTc (any (null . badFields rbinds) data_cons)
462 (badFieldsUpd rbinds) `thenTc_`
465 -- Typecheck the update bindings.
466 -- (Do this after checking for bad fields in case there's a field that
467 -- doesn't match the constructor.)
469 result_record_ty = mkTyConApp tycon result_inst_tys
471 unifyTauTy res_ty result_record_ty `thenTc_`
472 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
475 -- Use the un-updated fields to find a vector of booleans saying
476 -- which type arguments must be the same in updatee and result.
478 -- WARNING: this code assumes that all data_cons in a common tycon
479 -- have FieldLabels abstracted over the same tyvars.
481 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
482 con_field_lbls_s = map dataConFieldLabels data_cons
484 -- A constructor is only relevant to this process if
485 -- it contains all the fields that are being updated
486 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
487 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
489 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
490 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
492 mk_inst_ty (tyvar, result_inst_ty)
493 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
494 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
496 mapNF_Tc mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
499 -- Typecheck the expression to be updated
501 record_ty = mkTyConApp tycon inst_tys
503 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
506 -- Figure out the LIE we need. We have to generate some
507 -- dictionaries for the data type context, since we are going to
508 -- do pattern matching over the data cons.
510 -- What dictionaries do we need?
511 -- We just take the context of the type constructor
513 theta' = substTheta inst_env (tyConTheta tycon)
515 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
518 returnTc (RecordUpdOut record_expr' record_ty result_record_ty rbinds',
519 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
521 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
522 = unifyListTy res_ty `thenTc` \ elt_ty ->
523 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
525 newMethodFromName (ArithSeqOrigin seq)
526 elt_ty enumFromName `thenNF_Tc` \ enum_from ->
528 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
529 lie1 `plusLIE` unitLIE enum_from)
531 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
532 = tcAddErrCtxt (arithSeqCtxt in_expr) $
533 unifyListTy res_ty `thenTc` \ elt_ty ->
534 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
535 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
536 newMethodFromName (ArithSeqOrigin seq)
537 elt_ty enumFromThenName `thenNF_Tc` \ enum_from_then ->
539 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
540 (FromThen expr1' expr2'),
541 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
543 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
544 = tcAddErrCtxt (arithSeqCtxt in_expr) $
545 unifyListTy res_ty `thenTc` \ elt_ty ->
546 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
547 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
548 newMethodFromName (ArithSeqOrigin seq)
549 elt_ty enumFromToName `thenNF_Tc` \ enum_from_to ->
551 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
552 (FromTo expr1' expr2'),
553 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
555 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
556 = tcAddErrCtxt (arithSeqCtxt in_expr) $
557 unifyListTy res_ty `thenTc` \ elt_ty ->
558 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
559 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
560 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
561 newMethodFromName (ArithSeqOrigin seq)
562 elt_ty enumFromThenToName `thenNF_Tc` \ eft ->
564 returnTc (ArithSeqOut (HsVar (instToId eft))
565 (FromThenTo expr1' expr2' expr3'),
566 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
568 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
569 = tcAddErrCtxt (parrSeqCtxt in_expr) $
570 unifyPArrTy res_ty `thenTc` \ elt_ty ->
571 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
572 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
573 newMethodFromName (PArrSeqOrigin seq)
574 elt_ty enumFromToPName `thenNF_Tc` \ enum_from_to ->
576 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
577 (FromTo expr1' expr2'),
578 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
580 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
581 = tcAddErrCtxt (parrSeqCtxt in_expr) $
582 unifyPArrTy res_ty `thenTc` \ elt_ty ->
583 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
584 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
585 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
586 newMethodFromName (PArrSeqOrigin seq)
587 elt_ty enumFromThenToPName `thenNF_Tc` \ eft ->
589 returnTc (PArrSeqOut (HsVar (instToId eft))
590 (FromThenTo expr1' expr2' expr3'),
591 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
593 tcMonoExpr (PArrSeqIn _) _
594 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
595 -- the parser shouldn't have generated it and the renamer shouldn't have
599 %************************************************************************
601 \subsection{Implicit Parameter bindings}
603 %************************************************************************
606 tcMonoExpr (HsWith expr binds is_with) res_ty
607 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
608 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
610 -- If the binding binds ?x = E, we must now
611 -- discharge any ?x constraints in expr_lie
612 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
614 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
616 returnTc (HsWith expr'' binds' is_with, expr_lie' `plusLIE` plusLIEs bind_lies)
619 = newTyVarTy openTypeKind `thenTc` \ ty ->
620 tcGetSrcLoc `thenTc` \ loc ->
621 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
622 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
623 returnTc (ip_inst, (ip', expr'), lie)
626 %************************************************************************
628 \subsection{@tcApp@ typchecks an application}
630 %************************************************************************
634 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
635 -> TcType -- Expected result type of application
636 -> TcM (TcExpr, LIE) -- Translated fun and args
638 tcApp (HsApp e1 e2) args res_ty
639 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
641 tcApp fun args res_ty
642 = -- First type-check the function
643 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
645 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
646 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenNF_Tc_`
647 split_fun_ty fun_ty (length args)
648 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
650 -- Now typecheck the args
651 mapAndUnzipTc (tcArg fun)
652 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
654 -- Unify with expected result after type-checking the args
655 -- so that the info from args percolates to actual_result_ty.
656 -- This is when we might detect a too-few args situation.
657 -- (One can think of cases when the opposite order would give
658 -- a better error message.)
659 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
660 (tcSubExp res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
662 returnTc (co_fn <$> foldl HsApp fun' args',
663 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
666 -- If an error happens we try to figure out whether the
667 -- function has been given too many or too few arguments,
669 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
670 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
671 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
673 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
674 (env2, act_ty'') = tidyOpenType env1 act_ty'
675 (exp_args, _) = tcSplitFunTys exp_ty''
676 (act_args, _) = tcSplitFunTys act_ty''
678 len_act_args = length act_args
679 len_exp_args = length exp_args
681 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
682 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
683 | otherwise = appCtxt fun args
685 returnNF_Tc (env2, message)
688 split_fun_ty :: TcType -- The type of the function
689 -> Int -- Number of arguments
690 -> TcM ([TcType], -- Function argument types
691 TcType) -- Function result types
693 split_fun_ty fun_ty 0
694 = returnTc ([], fun_ty)
696 split_fun_ty fun_ty n
697 = -- Expect the function to have type A->B
698 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
699 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
700 returnTc (arg_ty:arg_tys, final_res_ty)
704 tcArg :: RenamedHsExpr -- The function (for error messages)
705 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
706 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
708 tcArg the_fun (arg, expected_arg_ty, arg_no)
709 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
710 tcExpr arg expected_arg_ty
714 %************************************************************************
716 \subsection{@tcId@ typchecks an identifier occurrence}
718 %************************************************************************
720 tcId instantiates an occurrence of an Id.
721 The instantiate_it loop runs round instantiating the Id.
722 It has to be a loop because we are now prepared to entertain
724 f:: forall a. Eq a => forall b. Baz b => tau
725 We want to instantiate this to
726 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
728 The -fno-method-sharing flag controls what happens so far as the LIE
729 is concerned. The default case is that for an overloaded function we
730 generate a "method" Id, and add the Method Inst to the LIE. So you get
733 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
734 If you specify -fno-method-sharing, the dictionary application
735 isn't shared, so we get
737 f = /\a (d:Num a) (x:a) -> (+) a d x x
738 This gets a bit less sharing, but
739 a) it's better for RULEs involving overloaded functions
740 b) perhaps fewer separated lambdas
743 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
744 tcId name -- Look up the Id and instantiate its type
745 = tcLookupId name `thenNF_Tc` \ id ->
746 case isDataConWrapId_maybe id of
747 Nothing -> loop (HsVar id) emptyLIE (idType id)
748 Just data_con -> inst_data_con id data_con
750 orig = OccurrenceOf name
752 loop (HsVar fun_id) lie fun_ty
753 | want_method_inst fun_ty
754 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
755 newMethodWithGivenTy orig fun_id
756 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
757 loop (HsVar (instToId meth))
758 (unitLIE meth `plusLIE` lie) tau
762 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
763 loop (inst_fn fun) (inst_lie `plusLIE` lie) tau
766 = returnNF_Tc (fun, lie, fun_ty)
768 want_method_inst fun_ty
769 | opt_NoMethodSharing = False
770 | otherwise = case tcSplitSigmaTy fun_ty of
771 (_,[],_) -> False -- Not overloaded
772 (_,theta,_) -> not (any isLinearPred theta)
773 -- This is a slight hack.
774 -- If f :: (%x :: T) => Int -> Int
775 -- Then if we have two separate calls, (f 3, f 4), we cannot
776 -- make a method constraint that then gets shared, thus:
777 -- let m = f %x in (m 3, m 4)
778 -- because that loses the linearity of the constraint.
779 -- The simplest thing to do is never to construct a method constraint
780 -- in the first place that has a linear implicit parameter in it.
782 -- We treat data constructors differently, because we have to generate
783 -- constraints for their silly theta, which no longer appears in
784 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
785 inst_data_con id data_con
786 = tcInstDataCon orig data_con `thenNF_Tc` \ (ty_args, ex_dicts, arg_tys, result_ty, stupid_lie, ex_lie, _) ->
787 returnNF_Tc (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) ex_dicts,
788 stupid_lie `plusLIE` ex_lie,
789 mkFunTys arg_tys result_ty)
792 Typecheck expression which in most cases will be an Id.
793 The expression can return a higher-ranked type, such as
794 (forall a. a->a) -> Int
795 so we must create a HoleTyVarTy to pass in as the expected tyvar.
798 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
799 tcExpr_id (HsVar name) = tcId name
800 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
801 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
802 readHoleResult id_ty `thenTc` \ id_ty' ->
803 returnTc (expr', lie_id, id_ty')
807 %************************************************************************
809 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
811 %************************************************************************
814 -- I don't like this lumping together of do expression and list/array
815 -- comprehensions; creating the monad instances is entirely pointless in the
816 -- latter case; I'll leave the list case as it is for the moment, but handle
817 -- arrays extra (would be better to handle arrays and lists together, though)
820 tcDoStmts PArrComp stmts src_loc res_ty
822 ASSERT( notNull stmts )
823 tcAddSrcLoc src_loc $
825 unifyPArrTy res_ty `thenTc` \elt_ty ->
826 let tc_ty = mkTyConTy parrTyCon
827 m_ty = (mkPArrTy, elt_ty)
829 tcStmts (DoCtxt PArrComp) m_ty stmts `thenTc` \(stmts', stmts_lie) ->
830 returnTc (HsDoOut PArrComp stmts'
831 undefined -- don't touch!
835 tcDoStmts do_or_lc stmts src_loc res_ty
836 = -- get the Monad and MonadZero classes
837 -- create type consisting of a fresh monad tyvar
838 ASSERT( notNull stmts )
839 tcAddSrcLoc src_loc $
841 -- If it's a comprehension we're dealing with,
842 -- force it to be a list comprehension.
843 -- (as of Haskell 98, monad comprehensions are no more.)
844 -- Similarily, array comprehensions must involve parallel arrays types
847 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
848 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
850 PArrComp -> panic "TcExpr.tcDoStmts: How did we get here?!?"
852 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
853 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
854 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
855 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
856 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
858 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
860 -- Build the then and zero methods in case we need them
861 -- It's important that "then" and "return" appear just once in the final LIE,
862 -- not only for typechecker efficiency, but also because otherwise during
863 -- simplification we end up with silly stuff like
864 -- then = case d of (t,r) -> t
866 -- where the second "then" sees that it already exists in the "available" stuff.
868 mapNF_Tc (newMethodFromName DoOrigin tc_ty)
869 [returnMName, failMName, bindMName, thenMName] `thenNF_Tc` \ insts ->
871 returnTc (HsDoOut do_or_lc stmts'
874 stmts_lie `plusLIE` mkLIE insts)
878 %************************************************************************
880 \subsection{Record bindings}
882 %************************************************************************
884 Game plan for record bindings
885 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
886 1. Find the TyCon for the bindings, from the first field label.
888 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
890 For each binding field = value
892 3. Instantiate the field type (from the field label) using the type
895 4 Type check the value using tcArg, passing the field type as
896 the expected argument type.
898 This extends OK when the field types are universally quantified.
903 :: TyCon -- Type constructor for the record
904 -> [TcType] -- Args of this type constructor
905 -> RenamedRecordBinds
906 -> TcM (TcRecordBinds, LIE)
908 tcRecordBinds tycon ty_args rbinds
909 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
910 returnTc (rbinds', plusLIEs lies)
912 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
914 do_bind (field_lbl_name, rhs, pun_flag)
915 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
917 field_lbl = recordSelectorFieldLabel sel_id
918 field_ty = substTy tenv (fieldLabelType field_lbl)
920 ASSERT( isRecordSelector sel_id )
921 -- This lookup and assertion will surely succeed, because
922 -- we check that the fields are indeed record selectors
923 -- before calling tcRecordBinds
924 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
925 -- The caller of tcRecordBinds has already checked
926 -- that all the fields come from the same type
928 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
930 returnTc ((sel_id, rhs', pun_flag), lie)
932 badFields rbinds data_con
933 = [field_name | (field_name, _, _) <- rbinds,
934 not (field_name `elem` field_names)
937 field_names = map fieldLabelName (dataConFieldLabels data_con)
939 missingFields rbinds data_con
940 | null field_labels = ([], []) -- Not declared as a record;
941 -- But C{} is still valid
943 = (missing_strict_fields, other_missing_fields)
945 missing_strict_fields
946 = [ fl | (fl, str) <- field_info,
948 not (fieldLabelName fl `elem` field_names_used)
951 = [ fl | (fl, str) <- field_info,
952 not (isMarkedStrict str),
953 not (fieldLabelName fl `elem` field_names_used)
956 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
957 field_labels = dataConFieldLabels data_con
959 field_info = zipEqual "missingFields"
961 (dropList ex_theta (dataConStrictMarks data_con))
962 -- The 'drop' is because dataConStrictMarks
963 -- includes the existential dictionaries
964 (_, _, _, ex_theta, _, _) = dataConSig data_con
967 %************************************************************************
969 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
971 %************************************************************************
974 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
976 tcMonoExprs [] [] = returnTc ([], emptyLIE)
977 tcMonoExprs (expr:exprs) (ty:tys)
978 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
979 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
980 returnTc (expr':exprs', lie1 `plusLIE` lie2)
984 %************************************************************************
986 \subsection{Literals}
988 %************************************************************************
993 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
994 tcLit (HsLitLit s _) res_ty
995 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
996 newDicts (LitLitOrigin (_UNPK_ s))
997 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
998 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
1001 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
1002 returnTc (HsLit lit, emptyLIE)
1006 %************************************************************************
1008 \subsection{Errors and contexts}
1010 %************************************************************************
1014 Boring and alphabetical:
1017 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1020 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1023 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1026 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1029 = hang (ptext SLIT("When checking the type signature of the expression:"))
1033 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1036 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1039 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1042 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1044 funAppCtxt fun arg arg_no
1045 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1046 quotes (ppr fun) <> text ", namely"])
1047 4 (quotes (ppr arg))
1049 wrongArgsCtxt too_many_or_few fun args
1050 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1051 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1052 <+> ptext SLIT("arguments in the call"))
1053 4 (parens (ppr the_app))
1055 the_app = foldl HsApp fun args -- Used in error messages
1058 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1060 the_app = foldl HsApp fun args -- Used in error messages
1062 lurkingRank2Err fun fun_ty
1063 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1064 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1065 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1068 = hang (ptext SLIT("No constructor has all these fields:"))
1069 4 (pprQuotedList fields)
1071 fields = [field | (field, _, _) <- rbinds]
1073 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1074 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1077 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1079 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1080 missingStrictFieldCon con field
1081 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1082 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1084 missingFieldCon :: Name -> FieldLabel -> SDoc
1085 missingFieldCon con field
1086 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1087 ptext SLIT("is not initialised")]