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(..), MonoBinds(..),
13 mkMonoBind, andMonoBindList
15 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
16 import TcHsSyn ( TcExpr, TcRecordBinds, TypecheckedMonoBinds,
17 simpleHsLitTy, mkHsDictApp, mkHsTyApp, mkHsLet )
20 import TcUnify ( tcSubExp, tcGen, (<$>),
21 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
23 import BasicTypes ( RecFlag(..), isMarkedStrict )
24 import Inst ( InstOrigin(..),
25 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
26 newOverloadedLit, newMethodFromName, newIPDict,
27 newDicts, newMethodWithGivenTy, tcSyntaxName,
28 instToId, tcInstCall, tcInstDataCon
30 import TcBinds ( tcBindsAndThen )
31 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
32 tcLookupTyCon, tcLookupDataCon, tcLookupId
34 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
35 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
36 import TcPat ( badFieldCon )
37 import TcSimplify ( tcSimplifyIPs )
38 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
39 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
40 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
41 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
42 isSigmaTy, mkFunTy, mkAppTy, mkFunTys,
43 mkTyConApp, mkClassPred, tcFunArgTy,
44 tyVarsOfTypes, isLinearPred,
45 liftedTypeKind, openTypeKind, mkArrowKind,
46 tcSplitSigmaTy, tcTyConAppTyCon,
49 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
50 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector,
51 isDataConWrapId_maybe, mkSysLocal )
52 import DataCon ( dataConFieldLabels, dataConSig,
56 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
57 import Subst ( mkTopTyVarSubst, substTheta, substTy )
58 import VarSet ( emptyVarSet, elemVarSet )
59 import TysWiredIn ( boolTy, mkListTy, mkPArrTy )
60 import PrelNames ( cCallableClassName, cReturnableClassName,
61 enumFromName, enumFromThenName,
62 enumFromToName, enumFromThenToName,
63 enumFromToPName, enumFromThenToPName,
64 ioTyConName, monadNames
66 import ListSetOps ( minusList )
68 import HscTypes ( TyThing(..) )
75 %************************************************************************
77 \subsection{Main wrappers}
79 %************************************************************************
82 tcExpr :: RenamedHsExpr -- Expession to type check
83 -> TcSigmaType -- Expected type (could be a polytpye)
84 -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
86 tcExpr expr expected_ty
87 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenNF_Tc_`
88 tc_expr' expr expected_ty
90 tc_expr' expr expected_ty
91 | not (isSigmaTy expected_ty) -- Monomorphic case
92 = tcMonoExpr expr expected_ty
95 = tcGen expected_ty emptyVarSet (
97 ) `thenTc` \ (gen_fn, expr', lie) ->
98 returnTc (gen_fn <$> expr', lie)
102 %************************************************************************
104 \subsection{The TAUT rules for variables}
106 %************************************************************************
109 tcMonoExpr :: RenamedHsExpr -- Expession to type check
110 -> TcRhoType -- Expected type (could be a type variable)
111 -- Definitely no foralls at the top
115 tcMonoExpr (HsVar name) res_ty
116 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
117 tcSubExp res_ty id_ty `thenTc` \ (co_fn, lie2) ->
118 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
120 tcMonoExpr (HsIPVar ip) res_ty
121 = -- Implicit parameters must have a *tau-type* not a
122 -- type scheme. We enforce this by creating a fresh
123 -- type variable as its type. (Because res_ty may not
125 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
126 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
127 tcSubExp res_ty ip_ty `thenTc` \ (co_fn, lie) ->
128 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
132 %************************************************************************
134 \subsection{Expressions type signatures}
136 %************************************************************************
139 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
140 = tcAddErrCtxt (exprSigCtxt in_expr) $
141 tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
142 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
144 -- Must instantiate the outer for-alls of sig_tc_ty
145 -- else we risk instantiating a ? res_ty to a forall-type
146 -- which breaks the invariant that tcMonoExpr only returns phi-types
147 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
148 tcSubExp res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
150 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
152 tcMonoExpr (HsType ty) res_ty
153 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
154 -- This is the syntax for type applications that I was planning
155 -- but there are difficulties (e.g. what order for type args)
156 -- so it's not enabled yet.
157 -- Can't eliminate it altogether from the parser, because the
158 -- same parser parses *patterns*.
162 %************************************************************************
164 \subsection{Other expression forms}
166 %************************************************************************
169 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
170 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
171 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
173 tcMonoExpr (NegApp expr neg_name) res_ty
174 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
175 -- ToDo: use tcSyntaxName
177 tcMonoExpr (HsLam match) res_ty
178 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
179 returnTc (HsLam match', lie)
181 tcMonoExpr (HsApp e1 e2) res_ty
182 = tcApp e1 [e2] res_ty
185 Note that the operators in sections are expected to be binary, and
186 a type error will occur if they aren't.
189 -- Left sections, equivalent to
196 tcMonoExpr in_expr@(SectionL arg1 op) 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 (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
200 tcAddErrCtxt (exprCtxt in_expr) $
201 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
202 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
204 -- Right sections, equivalent to \ x -> x op expr, or
207 tcMonoExpr in_expr@(SectionR op arg2) res_ty
208 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
209 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
210 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
211 tcAddErrCtxt (exprCtxt in_expr) $
212 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
213 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
215 -- equivalent to (op e1) e2:
217 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
218 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
219 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
220 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
221 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
222 tcAddErrCtxt (exprCtxt in_expr) $
223 tcSubExp res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
224 returnTc (OpApp arg1' op' fix arg2',
225 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
228 The interesting thing about @ccall@ is that it is just a template
229 which we instantiate by filling in details about the types of its
230 argument and result (ie minimal typechecking is performed). So, the
231 basic story is that we allocate a load of type variables (to hold the
232 arg/result types); unify them with the args/result; and store them for
236 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
238 = getDOptsTc `thenNF_Tc` \ dflags ->
240 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
241 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
242 text "Either compile with -fvia-C, or, better, rewrite your code",
243 text "to use the foreign function interface. _casm_s are deprecated",
244 text "and support for them may one day disappear."])
247 -- Get the callable and returnable classes.
248 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
249 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
250 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
252 new_arg_dict (arg, arg_ty)
253 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
254 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
255 returnNF_Tc arg_dicts -- Actually a singleton bag
257 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
261 let tv_idxs | null args = []
262 | otherwise = [1..length args]
264 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
265 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
267 -- The argument types can be unlifted or lifted; the result
268 -- type must, however, be lifted since it's an argument to the IO
270 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
272 io_result_ty = mkTyConApp ioTyCon [result_ty]
274 unifyTauTy res_ty io_result_ty `thenTc_`
276 -- Construct the extra insts, which encode the
277 -- constraints on the argument and result types.
278 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
279 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
280 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
281 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
285 tcMonoExpr (HsSCC lbl expr) res_ty
286 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
287 returnTc (HsSCC lbl expr', lie)
289 tcMonoExpr (HsLet binds expr) res_ty
292 binds -- Bindings to check
293 tc_expr `thenTc` \ (expr', lie) ->
294 returnTc (expr', lie)
296 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
297 returnTc (expr', lie)
298 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
300 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
301 = tcAddSrcLoc src_loc $
302 tcAddErrCtxt (caseCtxt in_expr) $
304 -- Typecheck the case alternatives first.
305 -- The case patterns tend to give good type info to use
306 -- when typechecking the scrutinee. For example
309 -- will report that map is applied to too few arguments
311 -- Not only that, but it's better to check the matches on their
312 -- own, so that we get the expected results for scoped type variables.
314 -- (p::a, q::b) -> (q,p)
315 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
316 -- claimed by the pattern signatures. But if we typechecked the
317 -- match with x in scope and x's type as the expected type, we'd be hosed.
319 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
321 tcAddErrCtxt (caseScrutCtxt scrut) (
322 tcMonoExpr scrut scrut_ty
323 ) `thenTc` \ (scrut',lie1) ->
325 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
327 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
328 = tcAddSrcLoc src_loc $
329 tcAddErrCtxt (predCtxt pred) (
330 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
332 zapToType res_ty `thenTc` \ res_ty' ->
333 -- C.f. the call to zapToType in TcMatches.tcMatches
335 tcMonoExpr b1 res_ty' `thenTc` \ (b1',lie2) ->
336 tcMonoExpr b2 res_ty' `thenTc` \ (b2',lie3) ->
337 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
341 tcMonoExpr expr@(HsDo do_or_lc stmts method_names _ src_loc) res_ty
342 = tcAddSrcLoc src_loc (tcDoStmts do_or_lc stmts method_names src_loc res_ty)
346 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
347 = unifyListTy res_ty `thenTc` \ elt_ty ->
348 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
349 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
352 = tcAddErrCtxt (listCtxt expr) $
353 tcMonoExpr expr elt_ty
355 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
356 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
357 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
358 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
361 = tcAddErrCtxt (parrCtxt expr) $
362 tcMonoExpr expr elt_ty
364 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
365 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
366 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
367 (exprs `zip` arg_tys) -- we know they're of equal length.
368 `thenTc` \ (exprs', lies) ->
369 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
371 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
372 = tcAddErrCtxt (recordConCtxt expr) $
373 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
375 (_, record_ty) = tcSplitFunTys con_tau
376 (tycon, ty_args) = tcSplitTyConApp record_ty
378 ASSERT( isAlgTyCon tycon )
379 unifyTauTy res_ty record_ty `thenTc_`
381 -- Check that the record bindings match the constructor
382 -- con_name is syntactically constrained to be a data constructor
383 tcLookupDataCon con_name `thenTc` \ data_con ->
385 bad_fields = badFields rbinds data_con
387 if notNull bad_fields then
388 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
389 failTc -- Fail now, because tcRecordBinds will crash on a bad field
392 -- Typecheck the record bindings
393 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
396 (missing_s_fields, missing_fields) = missingFields rbinds data_con
398 checkTcM (null missing_s_fields)
399 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
400 returnNF_Tc ()) `thenNF_Tc_`
401 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
402 checkTcM (not (warn && notNull missing_fields))
403 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
404 returnNF_Tc ()) `thenNF_Tc_`
406 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
408 -- The main complication with RecordUpd is that we need to explicitly
409 -- handle the *non-updated* fields. Consider:
411 -- data T a b = MkT1 { fa :: a, fb :: b }
412 -- | MkT2 { fa :: a, fc :: Int -> Int }
413 -- | MkT3 { fd :: a }
415 -- upd :: T a b -> c -> T a c
416 -- upd t x = t { fb = x}
418 -- The type signature on upd is correct (i.e. the result should not be (T a b))
419 -- because upd should be equivalent to:
421 -- upd t x = case t of
422 -- MkT1 p q -> MkT1 p x
423 -- MkT2 a b -> MkT2 p b
424 -- MkT3 d -> error ...
426 -- So we need to give a completely fresh type to the result record,
427 -- and then constrain it by the fields that are *not* updated ("p" above).
429 -- Note that because MkT3 doesn't contain all the fields being updated,
430 -- its RHS is simply an error, so it doesn't impose any type constraints
432 -- All this is done in STEP 4 below.
434 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
435 = tcAddErrCtxt (recordUpdCtxt expr) $
438 -- Check that the field names are really field names
439 ASSERT( notNull rbinds )
441 field_names = [field_name | (field_name, _, _) <- rbinds]
443 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
445 bad_guys = [ addErrTc (notSelector field_name)
446 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
448 Just (AnId sel_id) -> not (isRecordSelector sel_id)
452 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
455 -- Figure out the tycon and data cons from the first field name
457 -- It's OK to use the non-tc splitters here (for a selector)
458 (Just (AnId sel_id) : _) = maybe_sel_ids
460 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
461 -- when the data type has a context
462 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
463 tycon = tcTyConAppTyCon data_ty
464 data_cons = tyConDataCons tycon
465 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
467 tcInstTyVars VanillaTv tycon_tyvars `thenNF_Tc` \ (_, result_inst_tys, inst_env) ->
470 -- Check that at least one constructor has all the named fields
471 -- i.e. has an empty set of bad fields returned by badFields
472 checkTc (any (null . badFields rbinds) data_cons)
473 (badFieldsUpd rbinds) `thenTc_`
476 -- Typecheck the update bindings.
477 -- (Do this after checking for bad fields in case there's a field that
478 -- doesn't match the constructor.)
480 result_record_ty = mkTyConApp tycon result_inst_tys
482 unifyTauTy res_ty result_record_ty `thenTc_`
483 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
486 -- Use the un-updated fields to find a vector of booleans saying
487 -- which type arguments must be the same in updatee and result.
489 -- WARNING: this code assumes that all data_cons in a common tycon
490 -- have FieldLabels abstracted over the same tyvars.
492 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
493 con_field_lbls_s = map dataConFieldLabels data_cons
495 -- A constructor is only relevant to this process if
496 -- it contains all the fields that are being updated
497 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
498 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
500 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
501 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
503 mk_inst_ty (tyvar, result_inst_ty)
504 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
505 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
507 mapNF_Tc mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
510 -- Typecheck the expression to be updated
512 record_ty = mkTyConApp tycon inst_tys
514 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
517 -- Figure out the LIE we need. We have to generate some
518 -- dictionaries for the data type context, since we are going to
519 -- do pattern matching over the data cons.
521 -- What dictionaries do we need?
522 -- We just take the context of the type constructor
524 theta' = substTheta inst_env (tyConTheta tycon)
526 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
529 returnTc (RecordUpdOut record_expr' record_ty result_record_ty rbinds',
530 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
532 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
533 = unifyListTy res_ty `thenTc` \ elt_ty ->
534 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
536 newMethodFromName (ArithSeqOrigin seq)
537 elt_ty enumFromName `thenNF_Tc` \ enum_from ->
539 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
540 lie1 `plusLIE` unitLIE enum_from)
542 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
543 = tcAddErrCtxt (arithSeqCtxt in_expr) $
544 unifyListTy res_ty `thenTc` \ elt_ty ->
545 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
546 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
547 newMethodFromName (ArithSeqOrigin seq)
548 elt_ty enumFromThenName `thenNF_Tc` \ enum_from_then ->
550 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
551 (FromThen expr1' expr2'),
552 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
554 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
555 = tcAddErrCtxt (arithSeqCtxt in_expr) $
556 unifyListTy res_ty `thenTc` \ elt_ty ->
557 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
558 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
559 newMethodFromName (ArithSeqOrigin seq)
560 elt_ty enumFromToName `thenNF_Tc` \ enum_from_to ->
562 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
563 (FromTo expr1' expr2'),
564 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
566 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
567 = tcAddErrCtxt (arithSeqCtxt in_expr) $
568 unifyListTy res_ty `thenTc` \ elt_ty ->
569 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
570 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
571 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
572 newMethodFromName (ArithSeqOrigin seq)
573 elt_ty enumFromThenToName `thenNF_Tc` \ eft ->
575 returnTc (ArithSeqOut (HsVar (instToId eft))
576 (FromThenTo expr1' expr2' expr3'),
577 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
579 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
580 = tcAddErrCtxt (parrSeqCtxt in_expr) $
581 unifyPArrTy res_ty `thenTc` \ elt_ty ->
582 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
583 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
584 newMethodFromName (PArrSeqOrigin seq)
585 elt_ty enumFromToPName `thenNF_Tc` \ enum_from_to ->
587 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
588 (FromTo expr1' expr2'),
589 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
591 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
592 = tcAddErrCtxt (parrSeqCtxt in_expr) $
593 unifyPArrTy res_ty `thenTc` \ elt_ty ->
594 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
595 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
596 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
597 newMethodFromName (PArrSeqOrigin seq)
598 elt_ty enumFromThenToPName `thenNF_Tc` \ eft ->
600 returnTc (PArrSeqOut (HsVar (instToId eft))
601 (FromThenTo expr1' expr2' expr3'),
602 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
604 tcMonoExpr (PArrSeqIn _) _
605 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
606 -- the parser shouldn't have generated it and the renamer shouldn't have
610 %************************************************************************
612 \subsection{Implicit Parameter bindings}
614 %************************************************************************
617 tcMonoExpr (HsWith expr binds is_with) res_ty
618 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
619 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
621 -- If the binding binds ?x = E, we must now
622 -- discharge any ?x constraints in expr_lie
623 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
625 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
627 returnTc (HsWith expr'' binds' is_with, expr_lie' `plusLIE` plusLIEs bind_lies)
630 = newTyVarTy openTypeKind `thenTc` \ ty ->
631 tcGetSrcLoc `thenTc` \ loc ->
632 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
633 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
634 returnTc (ip_inst, (ip', expr'), lie)
637 %************************************************************************
639 \subsection{@tcApp@ typchecks an application}
641 %************************************************************************
645 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
646 -> TcType -- Expected result type of application
647 -> TcM (TcExpr, LIE) -- Translated fun and args
649 tcApp (HsApp e1 e2) args res_ty
650 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
652 tcApp fun args res_ty
653 = -- First type-check the function
654 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
656 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
657 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenNF_Tc_`
658 split_fun_ty fun_ty (length args)
659 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
661 -- Now typecheck the args
662 mapAndUnzipTc (tcArg fun)
663 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
665 -- Unify with expected result after type-checking the args
666 -- so that the info from args percolates to actual_result_ty.
667 -- This is when we might detect a too-few args situation.
668 -- (One can think of cases when the opposite order would give
669 -- a better error message.)
670 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
671 (tcSubExp res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
673 returnTc (co_fn <$> foldl HsApp fun' args',
674 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
677 -- If an error happens we try to figure out whether the
678 -- function has been given too many or too few arguments,
680 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
681 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
682 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
684 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
685 (env2, act_ty'') = tidyOpenType env1 act_ty'
686 (exp_args, _) = tcSplitFunTys exp_ty''
687 (act_args, _) = tcSplitFunTys act_ty''
689 len_act_args = length act_args
690 len_exp_args = length exp_args
692 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
693 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
694 | otherwise = appCtxt fun args
696 returnNF_Tc (env2, message)
699 split_fun_ty :: TcType -- The type of the function
700 -> Int -- Number of arguments
701 -> TcM ([TcType], -- Function argument types
702 TcType) -- Function result types
704 split_fun_ty fun_ty 0
705 = returnTc ([], fun_ty)
707 split_fun_ty fun_ty n
708 = -- Expect the function to have type A->B
709 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
710 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
711 returnTc (arg_ty:arg_tys, final_res_ty)
715 tcArg :: RenamedHsExpr -- The function (for error messages)
716 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
717 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
719 tcArg the_fun (arg, expected_arg_ty, arg_no)
720 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
721 tcExpr arg expected_arg_ty
725 %************************************************************************
727 \subsection{@tcId@ typchecks an identifier occurrence}
729 %************************************************************************
731 tcId instantiates an occurrence of an Id.
732 The instantiate_it loop runs round instantiating the Id.
733 It has to be a loop because we are now prepared to entertain
735 f:: forall a. Eq a => forall b. Baz b => tau
736 We want to instantiate this to
737 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
739 The -fno-method-sharing flag controls what happens so far as the LIE
740 is concerned. The default case is that for an overloaded function we
741 generate a "method" Id, and add the Method Inst to the LIE. So you get
744 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
745 If you specify -fno-method-sharing, the dictionary application
746 isn't shared, so we get
748 f = /\a (d:Num a) (x:a) -> (+) a d x x
749 This gets a bit less sharing, but
750 a) it's better for RULEs involving overloaded functions
751 b) perhaps fewer separated lambdas
754 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
755 tcId name -- Look up the Id and instantiate its type
756 = tcLookupId name `thenNF_Tc` \ id ->
757 case isDataConWrapId_maybe id of
758 Nothing -> loop (HsVar id) emptyLIE (idType id)
759 Just data_con -> inst_data_con id data_con
761 orig = OccurrenceOf name
763 loop (HsVar fun_id) lie fun_ty
764 | want_method_inst fun_ty
765 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
766 newMethodWithGivenTy orig fun_id
767 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
768 loop (HsVar (instToId meth))
769 (unitLIE meth `plusLIE` lie) tau
773 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
774 loop (inst_fn fun) (inst_lie `plusLIE` lie) tau
777 = returnNF_Tc (fun, lie, fun_ty)
779 want_method_inst fun_ty
780 | opt_NoMethodSharing = False
781 | otherwise = case tcSplitSigmaTy fun_ty of
782 (_,[],_) -> False -- Not overloaded
783 (_,theta,_) -> not (any isLinearPred theta)
784 -- This is a slight hack.
785 -- If f :: (%x :: T) => Int -> Int
786 -- Then if we have two separate calls, (f 3, f 4), we cannot
787 -- make a method constraint that then gets shared, thus:
788 -- let m = f %x in (m 3, m 4)
789 -- because that loses the linearity of the constraint.
790 -- The simplest thing to do is never to construct a method constraint
791 -- in the first place that has a linear implicit parameter in it.
793 -- We treat data constructors differently, because we have to generate
794 -- constraints for their silly theta, which no longer appears in
795 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
796 inst_data_con id data_con
797 = tcInstDataCon orig data_con `thenNF_Tc` \ (ty_args, ex_dicts, arg_tys, result_ty, stupid_lie, ex_lie, _) ->
798 returnNF_Tc (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) ex_dicts,
799 stupid_lie `plusLIE` ex_lie,
800 mkFunTys arg_tys result_ty)
803 Typecheck expression which in most cases will be an Id.
804 The expression can return a higher-ranked type, such as
805 (forall a. a->a) -> Int
806 so we must create a HoleTyVarTy to pass in as the expected tyvar.
809 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
810 tcExpr_id (HsVar name) = tcId name
811 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
812 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
813 readHoleResult id_ty `thenTc` \ id_ty' ->
814 returnTc (expr', lie_id, id_ty')
818 %************************************************************************
820 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
822 %************************************************************************
825 tcDoStmts PArrComp stmts method_names src_loc res_ty
826 = unifyPArrTy res_ty `thenTc` \elt_ty ->
827 tcStmts (DoCtxt PArrComp)
828 (mkPArrTy, elt_ty) stmts `thenTc` \(stmts', stmts_lie) ->
829 returnTc (HsDo PArrComp stmts'
834 tcDoStmts ListComp stmts method_names src_loc res_ty
835 = unifyListTy res_ty `thenTc` \ elt_ty ->
836 tcStmts (DoCtxt ListComp)
837 (mkListTy, elt_ty) stmts `thenTc` \ (stmts', stmts_lie) ->
838 returnTc (HsDo ListComp stmts'
843 tcDoStmts DoExpr stmts method_names src_loc res_ty
844 = newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
845 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
846 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
848 tcStmts (DoCtxt DoExpr) (mkAppTy m_ty, elt_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 mapNF_Tc (tc_syn_name m_ty)
859 (zipEqual "tcDoStmts" monadNames method_names) `thenNF_Tc` \ stuff ->
861 (binds, ids, lies) = unzip3 stuff
864 returnTc (mkHsLet (andMonoBindList binds) $
865 HsDo DoExpr stmts' ids
867 stmts_lie `plusLIE` plusLIEs lies)
870 tc_syn_name :: TcType -> (Name,Name) -> TcM (TypecheckedMonoBinds, Id, LIE)
871 tc_syn_name m_ty (std_nm, usr_nm)
872 = tcSyntaxName DoOrigin m_ty std_nm usr_nm `thenTc` \ (expr, lie, expr_ty) ->
874 HsVar v -> returnTc (EmptyMonoBinds, v, lie)
875 other -> tcGetUnique `thenTc` \ uniq ->
877 id = mkSysLocal FSLIT("syn") uniq expr_ty
879 returnTc (VarMonoBind id expr, id, lie)
882 %************************************************************************
884 \subsection{Record bindings}
886 %************************************************************************
888 Game plan for record bindings
889 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
890 1. Find the TyCon for the bindings, from the first field label.
892 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
894 For each binding field = value
896 3. Instantiate the field type (from the field label) using the type
899 4 Type check the value using tcArg, passing the field type as
900 the expected argument type.
902 This extends OK when the field types are universally quantified.
907 :: TyCon -- Type constructor for the record
908 -> [TcType] -- Args of this type constructor
909 -> RenamedRecordBinds
910 -> TcM (TcRecordBinds, LIE)
912 tcRecordBinds tycon ty_args rbinds
913 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
914 returnTc (rbinds', plusLIEs lies)
916 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
918 do_bind (field_lbl_name, rhs, pun_flag)
919 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
921 field_lbl = recordSelectorFieldLabel sel_id
922 field_ty = substTy tenv (fieldLabelType field_lbl)
924 ASSERT( isRecordSelector sel_id )
925 -- This lookup and assertion will surely succeed, because
926 -- we check that the fields are indeed record selectors
927 -- before calling tcRecordBinds
928 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
929 -- The caller of tcRecordBinds has already checked
930 -- that all the fields come from the same type
932 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
934 returnTc ((sel_id, rhs', pun_flag), lie)
936 badFields rbinds data_con
937 = [field_name | (field_name, _, _) <- rbinds,
938 not (field_name `elem` field_names)
941 field_names = map fieldLabelName (dataConFieldLabels data_con)
943 missingFields rbinds data_con
944 | null field_labels = ([], []) -- Not declared as a record;
945 -- But C{} is still valid
947 = (missing_strict_fields, other_missing_fields)
949 missing_strict_fields
950 = [ fl | (fl, str) <- field_info,
952 not (fieldLabelName fl `elem` field_names_used)
955 = [ fl | (fl, str) <- field_info,
956 not (isMarkedStrict str),
957 not (fieldLabelName fl `elem` field_names_used)
960 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
961 field_labels = dataConFieldLabels data_con
963 field_info = zipEqual "missingFields"
965 (dropList ex_theta (dataConStrictMarks data_con))
966 -- The 'drop' is because dataConStrictMarks
967 -- includes the existential dictionaries
968 (_, _, _, ex_theta, _, _) = dataConSig data_con
971 %************************************************************************
973 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
975 %************************************************************************
978 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
980 tcMonoExprs [] [] = returnTc ([], emptyLIE)
981 tcMonoExprs (expr:exprs) (ty:tys)
982 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
983 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
984 returnTc (expr':exprs', lie1 `plusLIE` lie2)
988 %************************************************************************
990 \subsection{Literals}
992 %************************************************************************
997 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
998 tcLit (HsLitLit s _) res_ty
999 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
1000 newDicts (LitLitOrigin (unpackFS s))
1001 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
1002 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
1005 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
1006 returnTc (HsLit lit, emptyLIE)
1010 %************************************************************************
1012 \subsection{Errors and contexts}
1014 %************************************************************************
1018 Boring and alphabetical:
1021 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1024 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1027 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1030 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1033 = hang (ptext SLIT("When checking the type signature of the expression:"))
1037 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1039 funAppCtxt fun arg arg_no
1040 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1041 quotes (ppr fun) <> text ", namely"])
1042 4 (quotes (ppr arg))
1045 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1048 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1051 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1053 wrongArgsCtxt too_many_or_few fun args
1054 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1055 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1056 <+> ptext SLIT("arguments in the call"))
1057 4 (parens (ppr the_app))
1059 the_app = foldl HsApp fun args -- Used in error messages
1062 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1064 the_app = foldl HsApp fun args -- Used in error messages
1066 lurkingRank2Err fun fun_ty
1067 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1068 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1069 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1072 = hang (ptext SLIT("No constructor has all these fields:"))
1073 4 (pprQuotedList fields)
1075 fields = [field | (field, _, _) <- rbinds]
1077 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1078 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1081 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1083 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1084 missingStrictFieldCon con field
1085 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1086 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1088 missingFieldCon :: Name -> FieldLabel -> SDoc
1089 missingFieldCon con field
1090 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1091 ptext SLIT("is not initialised")]