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, 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 )
58 import PrelNames ( cCallableClassName,
60 enumFromName, enumFromThenName,
61 enumFromToName, enumFromThenToName,
62 enumFromToPName, enumFromThenToPName,
65 import ListSetOps ( minusList )
67 import HscTypes ( TyThing(..) )
74 %************************************************************************
76 \subsection{Main wrappers}
78 %************************************************************************
81 tcExpr :: RenamedHsExpr -- Expession to type check
82 -> TcSigmaType -- Expected type (could be a polytpye)
83 -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
85 tcExpr expr expected_ty
86 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenNF_Tc_`
87 tc_expr' expr expected_ty
89 tc_expr' expr expected_ty
90 | not (isSigmaTy expected_ty) -- Monomorphic case
91 = tcMonoExpr expr expected_ty
94 = tcGen expected_ty emptyVarSet (
96 ) `thenTc` \ (gen_fn, expr', lie) ->
97 returnTc (gen_fn <$> expr', lie)
101 %************************************************************************
103 \subsection{The TAUT rules for variables}
105 %************************************************************************
108 tcMonoExpr :: RenamedHsExpr -- Expession to type check
109 -> TcRhoType -- Expected type (could be a type variable)
110 -- Definitely no foralls at the top
114 tcMonoExpr (HsVar name) res_ty
115 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
116 tcSubExp res_ty id_ty `thenTc` \ (co_fn, lie2) ->
117 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
119 tcMonoExpr (HsIPVar ip) res_ty
120 = -- Implicit parameters must have a *tau-type* not a
121 -- type scheme. We enforce this by creating a fresh
122 -- type variable as its type. (Because res_ty may not
124 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
125 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
126 tcSubExp res_ty ip_ty `thenTc` \ (co_fn, lie) ->
127 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
131 %************************************************************************
133 \subsection{Expressions type signatures}
135 %************************************************************************
138 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
139 = tcAddErrCtxt (exprSigCtxt in_expr) $
140 tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
141 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
143 -- Must instantiate the outer for-alls of sig_tc_ty
144 -- else we risk instantiating a ? res_ty to a forall-type
145 -- which breaks the invariant that tcMonoExpr only returns phi-types
146 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
147 tcSubExp res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
149 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
151 tcMonoExpr (HsType ty) res_ty
152 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
153 -- This is the syntax for type applications that I was planning
154 -- but there are difficulties (e.g. what order for type args)
155 -- so it's not enabled yet.
156 -- Can't eliminate it altogether from the parser, because the
157 -- same parser parses *patterns*.
161 %************************************************************************
163 \subsection{Other expression forms}
165 %************************************************************************
168 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
169 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
170 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
172 tcMonoExpr (NegApp expr neg_name) res_ty
173 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
175 tcMonoExpr (HsLam match) res_ty
176 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
177 returnTc (HsLam match', lie)
179 tcMonoExpr (HsApp e1 e2) res_ty
180 = tcApp e1 [e2] res_ty
183 Note that the operators in sections are expected to be binary, and
184 a type error will occur if they aren't.
187 -- Left sections, equivalent to
194 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
195 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
196 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
197 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
198 tcAddErrCtxt (exprCtxt in_expr) $
199 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
200 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
202 -- Right sections, equivalent to \ x -> x op expr, or
205 tcMonoExpr in_expr@(SectionR op 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 (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
209 tcAddErrCtxt (exprCtxt in_expr) $
210 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
211 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
213 -- equivalent to (op e1) e2:
215 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
216 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
217 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
218 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
219 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
220 tcAddErrCtxt (exprCtxt in_expr) $
221 tcSubExp res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
222 returnTc (OpApp arg1' op' fix arg2',
223 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
226 The interesting thing about @ccall@ is that it is just a template
227 which we instantiate by filling in details about the types of its
228 argument and result (ie minimal typechecking is performed). So, the
229 basic story is that we allocate a load of type variables (to hold the
230 arg/result types); unify them with the args/result; and store them for
234 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
236 = getDOptsTc `thenNF_Tc` \ dflags ->
238 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
239 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
240 text "Either compile with -fvia-C, or, better, rewrite your code",
241 text "to use the foreign function interface. _casm_s are deprecated",
242 text "and support for them may one day disappear."])
245 -- Get the callable and returnable classes.
246 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
247 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
248 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
250 new_arg_dict (arg, arg_ty)
251 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
252 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
253 returnNF_Tc arg_dicts -- Actually a singleton bag
255 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
259 let tv_idxs | null args = []
260 | otherwise = [1..length args]
262 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
263 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
265 -- The argument types can be unlifted or lifted; the result
266 -- type must, however, be lifted since it's an argument to the IO
268 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
270 io_result_ty = mkTyConApp ioTyCon [result_ty]
272 unifyTauTy res_ty io_result_ty `thenTc_`
274 -- Construct the extra insts, which encode the
275 -- constraints on the argument and result types.
276 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
277 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
278 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
279 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
283 tcMonoExpr (HsSCC lbl expr) res_ty
284 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
285 returnTc (HsSCC lbl expr', lie)
287 tcMonoExpr (HsLet binds expr) res_ty
290 binds -- Bindings to check
291 tc_expr `thenTc` \ (expr', lie) ->
292 returnTc (expr', lie)
294 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
295 returnTc (expr', lie)
296 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
298 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
299 = tcAddSrcLoc src_loc $
300 tcAddErrCtxt (caseCtxt in_expr) $
302 -- Typecheck the case alternatives first.
303 -- The case patterns tend to give good type info to use
304 -- when typechecking the scrutinee. For example
307 -- will report that map is applied to too few arguments
309 -- Not only that, but it's better to check the matches on their
310 -- own, so that we get the expected results for scoped type variables.
312 -- (p::a, q::b) -> (q,p)
313 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
314 -- claimed by the pattern signatures. But if we typechecked the
315 -- match with x in scope and x's type as the expected type, we'd be hosed.
317 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
319 tcAddErrCtxt (caseScrutCtxt scrut) (
320 tcMonoExpr scrut scrut_ty
321 ) `thenTc` \ (scrut',lie1) ->
323 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
325 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
326 = tcAddSrcLoc src_loc $
327 tcAddErrCtxt (predCtxt pred) (
328 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
330 zapToType res_ty `thenTc` \ res_ty' ->
331 -- C.f. the call to zapToType in TcMatches.tcMatches
333 tcMonoExpr b1 res_ty' `thenTc` \ (b1',lie2) ->
334 tcMonoExpr b2 res_ty' `thenTc` \ (b2',lie3) ->
335 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
339 tcMonoExpr expr@(HsDo do_or_lc stmts method_names _ src_loc) res_ty
340 = tcAddSrcLoc src_loc (tcDoStmts do_or_lc stmts method_names src_loc res_ty)
344 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
345 = unifyListTy res_ty `thenTc` \ elt_ty ->
346 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
347 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
350 = tcAddErrCtxt (listCtxt expr) $
351 tcMonoExpr expr elt_ty
353 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
354 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
355 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
356 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
359 = tcAddErrCtxt (parrCtxt expr) $
360 tcMonoExpr expr elt_ty
362 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
363 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
364 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
365 (exprs `zip` arg_tys) -- we know they're of equal length.
366 `thenTc` \ (exprs', lies) ->
367 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
369 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
370 = tcAddErrCtxt (recordConCtxt expr) $
371 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
373 (_, record_ty) = tcSplitFunTys con_tau
374 (tycon, ty_args) = tcSplitTyConApp record_ty
376 ASSERT( isAlgTyCon tycon )
377 unifyTauTy res_ty record_ty `thenTc_`
379 -- Check that the record bindings match the constructor
380 -- con_name is syntactically constrained to be a data constructor
381 tcLookupDataCon con_name `thenTc` \ data_con ->
383 bad_fields = badFields rbinds data_con
385 if notNull bad_fields then
386 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
387 failTc -- Fail now, because tcRecordBinds will crash on a bad field
390 -- Typecheck the record bindings
391 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
394 (missing_s_fields, missing_fields) = missingFields rbinds data_con
396 checkTcM (null missing_s_fields)
397 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
398 returnNF_Tc ()) `thenNF_Tc_`
399 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
400 checkTcM (not (warn && notNull missing_fields))
401 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
402 returnNF_Tc ()) `thenNF_Tc_`
404 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
406 -- The main complication with RecordUpd is that we need to explicitly
407 -- handle the *non-updated* fields. Consider:
409 -- data T a b = MkT1 { fa :: a, fb :: b }
410 -- | MkT2 { fa :: a, fc :: Int -> Int }
411 -- | MkT3 { fd :: a }
413 -- upd :: T a b -> c -> T a c
414 -- upd t x = t { fb = x}
416 -- The type signature on upd is correct (i.e. the result should not be (T a b))
417 -- because upd should be equivalent to:
419 -- upd t x = case t of
420 -- MkT1 p q -> MkT1 p x
421 -- MkT2 a b -> MkT2 p b
422 -- MkT3 d -> error ...
424 -- So we need to give a completely fresh type to the result record,
425 -- and then constrain it by the fields that are *not* updated ("p" above).
427 -- Note that because MkT3 doesn't contain all the fields being updated,
428 -- its RHS is simply an error, so it doesn't impose any type constraints
430 -- All this is done in STEP 4 below.
432 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
433 = tcAddErrCtxt (recordUpdCtxt expr) $
436 -- Check that the field names are really field names
437 ASSERT( notNull rbinds )
439 field_names = [field_name | (field_name, _, _) <- rbinds]
441 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
443 bad_guys = [ addErrTc (notSelector field_name)
444 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
446 Just (AnId sel_id) -> not (isRecordSelector sel_id)
450 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
453 -- Figure out the tycon and data cons from the first field name
455 -- It's OK to use the non-tc splitters here (for a selector)
456 (Just (AnId sel_id) : _) = maybe_sel_ids
458 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
459 -- when the data type has a context
460 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
461 tycon = tcTyConAppTyCon data_ty
462 data_cons = tyConDataCons tycon
463 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
465 tcInstTyVars VanillaTv tycon_tyvars `thenNF_Tc` \ (_, result_inst_tys, inst_env) ->
468 -- Check that at least one constructor has all the named fields
469 -- i.e. has an empty set of bad fields returned by badFields
470 checkTc (any (null . badFields rbinds) data_cons)
471 (badFieldsUpd rbinds) `thenTc_`
474 -- Typecheck the update bindings.
475 -- (Do this after checking for bad fields in case there's a field that
476 -- doesn't match the constructor.)
478 result_record_ty = mkTyConApp tycon result_inst_tys
480 unifyTauTy res_ty result_record_ty `thenTc_`
481 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
484 -- Use the un-updated fields to find a vector of booleans saying
485 -- which type arguments must be the same in updatee and result.
487 -- WARNING: this code assumes that all data_cons in a common tycon
488 -- have FieldLabels abstracted over the same tyvars.
490 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
491 con_field_lbls_s = map dataConFieldLabels data_cons
493 -- A constructor is only relevant to this process if
494 -- it contains all the fields that are being updated
495 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
496 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
498 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
499 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
501 mk_inst_ty (tyvar, result_inst_ty)
502 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
503 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
505 mapNF_Tc mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
508 -- Typecheck the expression to be updated
510 record_ty = mkTyConApp tycon inst_tys
512 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
515 -- Figure out the LIE we need. We have to generate some
516 -- dictionaries for the data type context, since we are going to
517 -- do pattern matching over the data cons.
519 -- What dictionaries do we need?
520 -- We just take the context of the type constructor
522 theta' = substTheta inst_env (tyConTheta tycon)
524 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
527 returnTc (RecordUpdOut record_expr' record_ty result_record_ty rbinds',
528 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
530 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
531 = unifyListTy res_ty `thenTc` \ elt_ty ->
532 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
534 newMethodFromName (ArithSeqOrigin seq)
535 elt_ty enumFromName `thenNF_Tc` \ enum_from ->
537 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
538 lie1 `plusLIE` unitLIE enum_from)
540 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
541 = tcAddErrCtxt (arithSeqCtxt in_expr) $
542 unifyListTy res_ty `thenTc` \ elt_ty ->
543 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
544 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
545 newMethodFromName (ArithSeqOrigin seq)
546 elt_ty enumFromThenName `thenNF_Tc` \ enum_from_then ->
548 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
549 (FromThen expr1' expr2'),
550 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
552 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
553 = tcAddErrCtxt (arithSeqCtxt in_expr) $
554 unifyListTy res_ty `thenTc` \ elt_ty ->
555 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
556 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
557 newMethodFromName (ArithSeqOrigin seq)
558 elt_ty enumFromToName `thenNF_Tc` \ enum_from_to ->
560 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
561 (FromTo expr1' expr2'),
562 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
564 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
565 = tcAddErrCtxt (arithSeqCtxt in_expr) $
566 unifyListTy res_ty `thenTc` \ elt_ty ->
567 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
568 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
569 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
570 newMethodFromName (ArithSeqOrigin seq)
571 elt_ty enumFromThenToName `thenNF_Tc` \ eft ->
573 returnTc (ArithSeqOut (HsVar (instToId eft))
574 (FromThenTo expr1' expr2' expr3'),
575 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
577 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
578 = tcAddErrCtxt (parrSeqCtxt in_expr) $
579 unifyPArrTy res_ty `thenTc` \ elt_ty ->
580 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
581 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
582 newMethodFromName (PArrSeqOrigin seq)
583 elt_ty enumFromToPName `thenNF_Tc` \ enum_from_to ->
585 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
586 (FromTo expr1' expr2'),
587 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
589 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
590 = tcAddErrCtxt (parrSeqCtxt in_expr) $
591 unifyPArrTy res_ty `thenTc` \ elt_ty ->
592 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
593 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
594 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
595 newMethodFromName (PArrSeqOrigin seq)
596 elt_ty enumFromThenToPName `thenNF_Tc` \ eft ->
598 returnTc (PArrSeqOut (HsVar (instToId eft))
599 (FromThenTo expr1' expr2' expr3'),
600 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
602 tcMonoExpr (PArrSeqIn _) _
603 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
604 -- the parser shouldn't have generated it and the renamer shouldn't have
608 %************************************************************************
610 \subsection{Implicit Parameter bindings}
612 %************************************************************************
615 tcMonoExpr (HsWith expr binds is_with) res_ty
616 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
617 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
619 -- If the binding binds ?x = E, we must now
620 -- discharge any ?x constraints in expr_lie
621 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
623 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
625 returnTc (HsWith expr'' binds' is_with, expr_lie' `plusLIE` plusLIEs bind_lies)
628 = newTyVarTy openTypeKind `thenTc` \ ty ->
629 tcGetSrcLoc `thenTc` \ loc ->
630 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
631 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
632 returnTc (ip_inst, (ip', expr'), lie)
635 %************************************************************************
637 \subsection{@tcApp@ typchecks an application}
639 %************************************************************************
643 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
644 -> TcType -- Expected result type of application
645 -> TcM (TcExpr, LIE) -- Translated fun and args
647 tcApp (HsApp e1 e2) args res_ty
648 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
650 tcApp fun args res_ty
651 = -- First type-check the function
652 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
654 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
655 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenNF_Tc_`
656 split_fun_ty fun_ty (length args)
657 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
659 -- Now typecheck the args
660 mapAndUnzipTc (tcArg fun)
661 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
663 -- Unify with expected result after type-checking the args
664 -- so that the info from args percolates to actual_result_ty.
665 -- This is when we might detect a too-few args situation.
666 -- (One can think of cases when the opposite order would give
667 -- a better error message.)
668 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
669 (tcSubExp res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
671 returnTc (co_fn <$> foldl HsApp fun' args',
672 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
675 -- If an error happens we try to figure out whether the
676 -- function has been given too many or too few arguments,
678 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
679 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
680 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
682 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
683 (env2, act_ty'') = tidyOpenType env1 act_ty'
684 (exp_args, _) = tcSplitFunTys exp_ty''
685 (act_args, _) = tcSplitFunTys act_ty''
687 len_act_args = length act_args
688 len_exp_args = length exp_args
690 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
691 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
692 | otherwise = appCtxt fun args
694 returnNF_Tc (env2, message)
697 split_fun_ty :: TcType -- The type of the function
698 -> Int -- Number of arguments
699 -> TcM ([TcType], -- Function argument types
700 TcType) -- Function result types
702 split_fun_ty fun_ty 0
703 = returnTc ([], fun_ty)
705 split_fun_ty fun_ty n
706 = -- Expect the function to have type A->B
707 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
708 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
709 returnTc (arg_ty:arg_tys, final_res_ty)
713 tcArg :: RenamedHsExpr -- The function (for error messages)
714 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
715 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
717 tcArg the_fun (arg, expected_arg_ty, arg_no)
718 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
719 tcExpr arg expected_arg_ty
723 %************************************************************************
725 \subsection{@tcId@ typchecks an identifier occurrence}
727 %************************************************************************
729 tcId instantiates an occurrence of an Id.
730 The instantiate_it loop runs round instantiating the Id.
731 It has to be a loop because we are now prepared to entertain
733 f:: forall a. Eq a => forall b. Baz b => tau
734 We want to instantiate this to
735 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
737 The -fno-method-sharing flag controls what happens so far as the LIE
738 is concerned. The default case is that for an overloaded function we
739 generate a "method" Id, and add the Method Inst to the LIE. So you get
742 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
743 If you specify -fno-method-sharing, the dictionary application
744 isn't shared, so we get
746 f = /\a (d:Num a) (x:a) -> (+) a d x x
747 This gets a bit less sharing, but
748 a) it's better for RULEs involving overloaded functions
749 b) perhaps fewer separated lambdas
752 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
753 tcId name -- Look up the Id and instantiate its type
754 = tcLookupId name `thenNF_Tc` \ id ->
755 case isDataConWrapId_maybe id of
756 Nothing -> loop (HsVar id) emptyLIE (idType id)
757 Just data_con -> inst_data_con id data_con
759 orig = OccurrenceOf name
761 loop (HsVar fun_id) lie fun_ty
762 | want_method_inst fun_ty
763 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
764 newMethodWithGivenTy orig fun_id
765 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
766 loop (HsVar (instToId meth))
767 (unitLIE meth `plusLIE` lie) tau
771 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
772 loop (inst_fn fun) (inst_lie `plusLIE` lie) tau
775 = returnNF_Tc (fun, lie, fun_ty)
777 want_method_inst fun_ty
778 | opt_NoMethodSharing = False
779 | otherwise = case tcSplitSigmaTy fun_ty of
780 (_,[],_) -> False -- Not overloaded
781 (_,theta,_) -> not (any isLinearPred theta)
782 -- This is a slight hack.
783 -- If f :: (%x :: T) => Int -> Int
784 -- Then if we have two separate calls, (f 3, f 4), we cannot
785 -- make a method constraint that then gets shared, thus:
786 -- let m = f %x in (m 3, m 4)
787 -- because that loses the linearity of the constraint.
788 -- The simplest thing to do is never to construct a method constraint
789 -- in the first place that has a linear implicit parameter in it.
791 -- We treat data constructors differently, because we have to generate
792 -- constraints for their silly theta, which no longer appears in
793 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
794 inst_data_con id data_con
795 = tcInstDataCon orig data_con `thenNF_Tc` \ (ty_args, ex_dicts, arg_tys, result_ty, stupid_lie, ex_lie, _) ->
796 returnNF_Tc (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) ex_dicts,
797 stupid_lie `plusLIE` ex_lie,
798 mkFunTys arg_tys result_ty)
801 Typecheck expression which in most cases will be an Id.
802 The expression can return a higher-ranked type, such as
803 (forall a. a->a) -> Int
804 so we must create a HoleTyVarTy to pass in as the expected tyvar.
807 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
808 tcExpr_id (HsVar name) = tcId name
809 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
810 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
811 readHoleResult id_ty `thenTc` \ id_ty' ->
812 returnTc (expr', lie_id, id_ty')
816 %************************************************************************
818 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
820 %************************************************************************
823 tcDoStmts PArrComp stmts method_names src_loc res_ty
824 = unifyPArrTy res_ty `thenTc` \elt_ty ->
825 tcStmts (DoCtxt PArrComp)
826 (mkPArrTy, elt_ty) stmts `thenTc` \(stmts', stmts_lie) ->
827 returnTc (HsDo PArrComp stmts'
832 tcDoStmts ListComp stmts method_names src_loc res_ty
833 = unifyListTy res_ty `thenTc` \ elt_ty ->
834 tcStmts (DoCtxt ListComp)
835 (mkListTy, elt_ty) stmts `thenTc` \ (stmts', stmts_lie) ->
836 returnTc (HsDo ListComp stmts'
841 tcDoStmts DoExpr stmts method_names src_loc res_ty
842 = newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ tc_ty ->
843 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
844 unifyTauTy res_ty (mkAppTy tc_ty elt_ty) `thenTc_`
846 tcStmts (DoCtxt DoExpr) (mkAppTy tc_ty, elt_ty) stmts `thenTc` \ (stmts', stmts_lie) ->
848 -- Build the then and zero methods in case we need them
849 -- It's important that "then" and "return" appear just once in the final LIE,
850 -- not only for typechecker efficiency, but also because otherwise during
851 -- simplification we end up with silly stuff like
852 -- then = case d of (t,r) -> t
854 -- where the second "then" sees that it already exists in the "available" stuff.
856 mapNF_Tc (newMethodFromName DoOrigin tc_ty) method_names `thenNF_Tc` \ insts ->
858 returnTc (HsDo DoExpr stmts'
861 stmts_lie `plusLIE` mkLIE insts)
865 %************************************************************************
867 \subsection{Record bindings}
869 %************************************************************************
871 Game plan for record bindings
872 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
873 1. Find the TyCon for the bindings, from the first field label.
875 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
877 For each binding field = value
879 3. Instantiate the field type (from the field label) using the type
882 4 Type check the value using tcArg, passing the field type as
883 the expected argument type.
885 This extends OK when the field types are universally quantified.
890 :: TyCon -- Type constructor for the record
891 -> [TcType] -- Args of this type constructor
892 -> RenamedRecordBinds
893 -> TcM (TcRecordBinds, LIE)
895 tcRecordBinds tycon ty_args rbinds
896 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
897 returnTc (rbinds', plusLIEs lies)
899 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
901 do_bind (field_lbl_name, rhs, pun_flag)
902 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
904 field_lbl = recordSelectorFieldLabel sel_id
905 field_ty = substTy tenv (fieldLabelType field_lbl)
907 ASSERT( isRecordSelector sel_id )
908 -- This lookup and assertion will surely succeed, because
909 -- we check that the fields are indeed record selectors
910 -- before calling tcRecordBinds
911 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
912 -- The caller of tcRecordBinds has already checked
913 -- that all the fields come from the same type
915 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
917 returnTc ((sel_id, rhs', pun_flag), lie)
919 badFields rbinds data_con
920 = [field_name | (field_name, _, _) <- rbinds,
921 not (field_name `elem` field_names)
924 field_names = map fieldLabelName (dataConFieldLabels data_con)
926 missingFields rbinds data_con
927 | null field_labels = ([], []) -- Not declared as a record;
928 -- But C{} is still valid
930 = (missing_strict_fields, other_missing_fields)
932 missing_strict_fields
933 = [ fl | (fl, str) <- field_info,
935 not (fieldLabelName fl `elem` field_names_used)
938 = [ fl | (fl, str) <- field_info,
939 not (isMarkedStrict str),
940 not (fieldLabelName fl `elem` field_names_used)
943 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
944 field_labels = dataConFieldLabels data_con
946 field_info = zipEqual "missingFields"
948 (dropList ex_theta (dataConStrictMarks data_con))
949 -- The 'drop' is because dataConStrictMarks
950 -- includes the existential dictionaries
951 (_, _, _, ex_theta, _, _) = dataConSig data_con
954 %************************************************************************
956 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
958 %************************************************************************
961 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
963 tcMonoExprs [] [] = returnTc ([], emptyLIE)
964 tcMonoExprs (expr:exprs) (ty:tys)
965 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
966 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
967 returnTc (expr':exprs', lie1 `plusLIE` lie2)
971 %************************************************************************
973 \subsection{Literals}
975 %************************************************************************
980 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
981 tcLit (HsLitLit s _) res_ty
982 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
983 newDicts (LitLitOrigin (unpackFS s))
984 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
985 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
988 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
989 returnTc (HsLit lit, emptyLIE)
993 %************************************************************************
995 \subsection{Errors and contexts}
997 %************************************************************************
1001 Boring and alphabetical:
1004 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1007 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1010 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1013 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1016 = hang (ptext SLIT("When checking the type signature of the expression:"))
1020 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1023 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1026 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1029 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1031 funAppCtxt fun arg arg_no
1032 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1033 quotes (ppr fun) <> text ", namely"])
1034 4 (quotes (ppr arg))
1036 wrongArgsCtxt too_many_or_few fun args
1037 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1038 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1039 <+> ptext SLIT("arguments in the call"))
1040 4 (parens (ppr the_app))
1042 the_app = foldl HsApp fun args -- Used in error messages
1045 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1047 the_app = foldl HsApp fun args -- Used in error messages
1049 lurkingRank2Err fun fun_ty
1050 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1051 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1052 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1055 = hang (ptext SLIT("No constructor has all these fields:"))
1056 4 (pprQuotedList fields)
1058 fields = [field | (field, _, _) <- rbinds]
1060 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1061 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1064 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1066 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1067 missingStrictFieldCon con field
1068 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1069 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1071 missingFieldCon :: Name -> FieldLabel -> SDoc
1072 missingFieldCon con field
1073 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1074 ptext SLIT("is not initialised")]