2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcMonoExpr, tcId ) where
9 #include "HsVersions.h"
11 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
12 HsMatchContext(..), HsDoContext(..), mkMonoBind
14 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
15 import TcHsSyn ( TcExpr, TcRecordBinds, simpleHsLitTy )
18 import TcUnify ( tcSubExp, tcGen, (<$>),
19 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
21 import BasicTypes ( RecFlag(..), isMarkedStrict )
22 import Inst ( InstOrigin(..),
23 LIE, mkLIE, emptyLIE, unitLIE, plusLIE, plusLIEs,
24 newOverloadedLit, newMethod, newIPDict,
25 newDicts, newMethodWithGivenTy,
28 import TcBinds ( tcBindsAndThen )
29 import TcEnv ( tcLookupClass, tcLookupGlobalId, tcLookupGlobal_maybe,
30 tcLookupTyCon, tcLookupDataCon, tcLookupId
32 import TcMatches ( tcMatchesCase, tcMatchLambda, tcStmts )
33 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
34 import TcPat ( badFieldCon )
35 import TcSimplify ( tcSimplifyIPs )
36 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
37 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
38 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
39 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
40 isSigmaTy, mkFunTy, mkAppTy, mkTyConTy,
41 mkTyConApp, mkClassPred, tcFunArgTy,
42 tyVarsOfTypes, isLinearPred,
43 liftedTypeKind, openTypeKind, mkArrowKind,
44 tcSplitSigmaTy, tcTyConAppTyCon,
47 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
48 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
49 import DataCon ( dataConFieldLabels, dataConSig,
53 import TyCon ( TyCon, tyConTyVars, isAlgTyCon, tyConDataCons )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( emptyVarSet, elemVarSet )
56 import TysWiredIn ( boolTy, mkListTy, mkPArrTy, listTyCon, parrTyCon )
57 import PrelNames ( cCallableClassName,
59 enumFromName, enumFromThenName,
60 enumFromToName, enumFromThenToName,
61 enumFromToPName, enumFromThenToPName,
62 thenMName, failMName, returnMName, ioTyConName
65 import ListSetOps ( minusList )
68 import HscTypes ( TyThing(..) )
72 %************************************************************************
74 \subsection{Main wrappers}
76 %************************************************************************
79 tcExpr :: RenamedHsExpr -- Expession to type check
80 -> TcSigmaType -- Expected type (could be a polytpye)
81 -> TcM (TcExpr, LIE) -- Generalised expr with expected type, and LIE
83 tcExpr expr expected_ty
84 | not (isSigmaTy expected_ty) -- Monomorphic case
85 = tcMonoExpr expr expected_ty
88 = tcGen expected_ty emptyVarSet (
90 ) `thenTc` \ (gen_fn, expr', lie) ->
91 returnTc (gen_fn <$> expr', lie)
95 %************************************************************************
97 \subsection{The TAUT rules for variables}
99 %************************************************************************
102 tcMonoExpr :: RenamedHsExpr -- Expession to type check
103 -> TcRhoType -- Expected type (could be a type variable)
104 -- Definitely no foralls at the top
108 tcMonoExpr (HsVar name) res_ty
109 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
110 tcSubExp res_ty id_ty `thenTc` \ (co_fn, lie2) ->
111 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
113 tcMonoExpr (HsIPVar ip) res_ty
114 = -- Implicit parameters must have a *tau-type* not a
115 -- type scheme. We enforce this by creating a fresh
116 -- type variable as its type. (Because res_ty may not
118 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
119 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
120 tcSubExp res_ty ip_ty `thenTc` \ (co_fn, lie) ->
121 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
125 %************************************************************************
127 \subsection{Expressions type signatures}
129 %************************************************************************
132 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
133 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
134 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
136 -- Must instantiate the outer for-alls of sig_tc_ty
137 -- else we risk instantiating a ? res_ty to a forall-type
138 -- which breaks the invariant that tcMonoExpr only returns phi-types
139 tcAddErrCtxt (exprSigCtxt in_expr) $
140 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
141 tcSubExp res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
143 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
147 %************************************************************************
149 \subsection{Other expression forms}
151 %************************************************************************
154 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
155 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
156 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
158 tcMonoExpr (NegApp expr neg_name) res_ty
159 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
161 tcMonoExpr (HsLam match) res_ty
162 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
163 returnTc (HsLam match', lie)
165 tcMonoExpr (HsApp e1 e2) res_ty
166 = tcApp e1 [e2] res_ty
169 Note that the operators in sections are expected to be binary, and
170 a type error will occur if they aren't.
173 -- Left sections, equivalent to
180 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
181 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
182 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
183 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
184 tcAddErrCtxt (exprCtxt in_expr) $
185 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
186 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
188 -- Right sections, equivalent to \ x -> x op expr, or
191 tcMonoExpr in_expr@(SectionR op arg2) res_ty
192 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
193 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
194 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
195 tcAddErrCtxt (exprCtxt in_expr) $
196 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
197 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
199 -- equivalent to (op e1) e2:
201 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
202 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
203 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
204 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
205 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
206 tcAddErrCtxt (exprCtxt in_expr) $
207 tcSubExp res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
208 returnTc (OpApp arg1' op' fix arg2',
209 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
212 The interesting thing about @ccall@ is that it is just a template
213 which we instantiate by filling in details about the types of its
214 argument and result (ie minimal typechecking is performed). So, the
215 basic story is that we allocate a load of type variables (to hold the
216 arg/result types); unify them with the args/result; and store them for
220 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
222 = getDOptsTc `thenNF_Tc` \ dflags ->
224 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
225 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
226 text "Either compile with -fvia-C, or, better, rewrite your code",
227 text "to use the foreign function interface. _casm_s are deprecated",
228 text "and support for them may one day disappear."])
231 -- Get the callable and returnable classes.
232 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
233 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
234 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
236 new_arg_dict (arg, arg_ty)
237 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
238 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
239 returnNF_Tc arg_dicts -- Actually a singleton bag
241 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
245 let tv_idxs | null args = []
246 | otherwise = [1..length args]
248 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
249 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
251 -- The argument types can be unlifted or lifted; the result
252 -- type must, however, be lifted since it's an argument to the IO
254 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
256 io_result_ty = mkTyConApp ioTyCon [result_ty]
258 unifyTauTy res_ty io_result_ty `thenTc_`
260 -- Construct the extra insts, which encode the
261 -- constraints on the argument and result types.
262 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
263 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
264 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
265 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
269 tcMonoExpr (HsSCC lbl expr) res_ty
270 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
271 returnTc (HsSCC lbl expr', lie)
273 tcMonoExpr (HsLet binds expr) res_ty
276 binds -- Bindings to check
277 tc_expr `thenTc` \ (expr', lie) ->
278 returnTc (expr', lie)
280 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
281 returnTc (expr', lie)
282 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
284 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
285 = tcAddSrcLoc src_loc $
286 tcAddErrCtxt (caseCtxt in_expr) $
288 -- Typecheck the case alternatives first.
289 -- The case patterns tend to give good type info to use
290 -- when typechecking the scrutinee. For example
293 -- will report that map is applied to too few arguments
295 -- Not only that, but it's better to check the matches on their
296 -- own, so that we get the expected results for scoped type variables.
298 -- (p::a, q::b) -> (q,p)
299 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
300 -- claimed by the pattern signatures. But if we typechecked the
301 -- match with x in scope and x's type as the expected type, we'd be hosed.
303 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
305 tcAddErrCtxt (caseScrutCtxt scrut) (
306 tcMonoExpr scrut scrut_ty
307 ) `thenTc` \ (scrut',lie1) ->
309 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
311 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
312 = tcAddSrcLoc src_loc $
313 tcAddErrCtxt (predCtxt pred) (
314 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
316 zapToType res_ty `thenTc` \ res_ty' ->
317 -- C.f. the call to zapToType in TcMatches.tcMatches
319 tcMonoExpr b1 res_ty' `thenTc` \ (b1',lie2) ->
320 tcMonoExpr b2 res_ty' `thenTc` \ (b2',lie3) ->
321 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
325 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
326 = tcDoStmts do_or_lc stmts src_loc res_ty
330 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
331 = unifyListTy res_ty `thenTc` \ elt_ty ->
332 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
333 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
336 = tcAddErrCtxt (listCtxt expr) $
337 tcMonoExpr expr elt_ty
339 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
340 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
341 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
342 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
345 = tcAddErrCtxt (parrCtxt expr) $
346 tcMonoExpr expr elt_ty
348 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
349 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
350 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
351 (exprs `zip` arg_tys) -- we know they're of equal length.
352 `thenTc` \ (exprs', lies) ->
353 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
355 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
356 = tcAddErrCtxt (recordConCtxt expr) $
357 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
359 (_, record_ty) = tcSplitFunTys con_tau
360 (tycon, ty_args) = tcSplitTyConApp record_ty
362 ASSERT( isAlgTyCon tycon )
363 unifyTauTy res_ty record_ty `thenTc_`
365 -- Check that the record bindings match the constructor
366 -- con_name is syntactically constrained to be a data constructor
367 tcLookupDataCon con_name `thenTc` \ data_con ->
369 bad_fields = badFields rbinds data_con
371 if not (null bad_fields) then
372 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
373 failTc -- Fail now, because tcRecordBinds will crash on a bad field
376 -- Typecheck the record bindings
377 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
380 (missing_s_fields, missing_fields) = missingFields rbinds data_con
382 checkTcM (null missing_s_fields)
383 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
384 returnNF_Tc ()) `thenNF_Tc_`
385 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
386 checkTcM (not (warn && not (null missing_fields)))
387 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
388 returnNF_Tc ()) `thenNF_Tc_`
390 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
392 -- The main complication with RecordUpd is that we need to explicitly
393 -- handle the *non-updated* fields. Consider:
395 -- data T a b = MkT1 { fa :: a, fb :: b }
396 -- | MkT2 { fa :: a, fc :: Int -> Int }
397 -- | MkT3 { fd :: a }
399 -- upd :: T a b -> c -> T a c
400 -- upd t x = t { fb = x}
402 -- The type signature on upd is correct (i.e. the result should not be (T a b))
403 -- because upd should be equivalent to:
405 -- upd t x = case t of
406 -- MkT1 p q -> MkT1 p x
407 -- MkT2 a b -> MkT2 p b
408 -- MkT3 d -> error ...
410 -- So we need to give a completely fresh type to the result record,
411 -- and then constrain it by the fields that are *not* updated ("p" above).
413 -- Note that because MkT3 doesn't contain all the fields being updated,
414 -- its RHS is simply an error, so it doesn't impose any type constraints
416 -- All this is done in STEP 4 below.
418 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
419 = tcAddErrCtxt (recordUpdCtxt expr) $
422 -- Check that the field names are really field names
423 ASSERT( not (null rbinds) )
425 field_names = [field_name | (field_name, _, _) <- rbinds]
427 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
429 bad_guys = [ addErrTc (notSelector field_name)
430 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
432 Just (AnId sel_id) -> not (isRecordSelector sel_id)
436 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
439 -- Figure out the tycon and data cons from the first field name
441 -- It's OK to use the non-tc splitters here (for a selector)
442 (Just (AnId sel_id) : _) = maybe_sel_ids
443 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
444 -- when the data type has a context
445 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
446 tycon = tcTyConAppTyCon data_ty
447 data_cons = tyConDataCons tycon
448 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
450 tcInstTyVars VanillaTv con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
453 -- Check that at least one constructor has all the named fields
454 -- i.e. has an empty set of bad fields returned by badFields
455 checkTc (any (null . badFields rbinds) data_cons)
456 (badFieldsUpd rbinds) `thenTc_`
459 -- Typecheck the update bindings.
460 -- (Do this after checking for bad fields in case there's a field that
461 -- doesn't match the constructor.)
463 result_record_ty = mkTyConApp tycon result_inst_tys
465 unifyTauTy res_ty result_record_ty `thenTc_`
466 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
469 -- Use the un-updated fields to find a vector of booleans saying
470 -- which type arguments must be the same in updatee and result.
472 -- WARNING: this code assumes that all data_cons in a common tycon
473 -- have FieldLabels abstracted over the same tyvars.
475 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
476 con_field_lbls_s = map dataConFieldLabels data_cons
478 -- A constructor is only relevant to this process if
479 -- it contains all the fields that are being updated
480 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
481 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
483 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
484 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
486 mk_inst_ty (tyvar, result_inst_ty)
487 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
488 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
490 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
493 -- Typecheck the expression to be updated
495 record_ty = mkTyConApp tycon inst_tys
497 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
500 -- Figure out the LIE we need. We have to generate some
501 -- dictionaries for the data type context, since we are going to
502 -- do some construction.
504 -- What dictionaries do we need? For the moment we assume that all
505 -- data constructors have the same context, and grab it from the first
506 -- constructor. If they have varying contexts then we'd have to
507 -- union the ones that could participate in the update.
509 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
510 inst_env = mkTopTyVarSubst tyvars result_inst_tys
511 theta' = substTheta inst_env theta
513 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
516 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
517 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
519 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
520 = unifyListTy res_ty `thenTc` \ elt_ty ->
521 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
523 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
524 newMethod (ArithSeqOrigin seq)
525 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
527 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
528 lie1 `plusLIE` unitLIE enum_from)
530 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
531 = tcAddErrCtxt (arithSeqCtxt in_expr) $
532 unifyListTy res_ty `thenTc` \ elt_ty ->
533 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
534 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
535 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
536 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
538 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
539 (FromThen expr1' expr2'),
540 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
542 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo 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 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
548 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
550 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
551 (FromTo expr1' expr2'),
552 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
554 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) 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 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
560 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
561 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
563 returnTc (ArithSeqOut (HsVar (instToId eft))
564 (FromThenTo expr1' expr2' expr3'),
565 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
567 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
568 = tcAddErrCtxt (parrSeqCtxt in_expr) $
569 unifyPArrTy res_ty `thenTc` \ elt_ty ->
570 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
571 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
572 tcLookupGlobalId enumFromToPName `thenNF_Tc` \ sel_id ->
573 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
575 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
576 (FromTo expr1' expr2'),
577 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
579 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) 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 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
585 tcLookupGlobalId enumFromThenToPName `thenNF_Tc` \ sel_id ->
586 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
588 returnTc (PArrSeqOut (HsVar (instToId eft))
589 (FromThenTo expr1' expr2' expr3'),
590 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
592 tcMonoExpr (PArrSeqIn _) _
593 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
594 -- the parser shouldn't have generated it and the renamer shouldn't have
598 %************************************************************************
600 \subsection{Implicit Parameter bindings}
602 %************************************************************************
605 tcMonoExpr (HsWith expr binds) res_ty
606 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
607 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
609 -- If the binding binds ?x = E, we must now
610 -- discharge any ?x constraints in expr_lie
611 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
613 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
615 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
618 = newTyVarTy openTypeKind `thenTc` \ ty ->
619 tcGetSrcLoc `thenTc` \ loc ->
620 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
621 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
622 returnTc (ip_inst, (ip', expr'), lie)
625 %************************************************************************
627 \subsection{@tcApp@ typchecks an application}
629 %************************************************************************
633 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
634 -> TcType -- Expected result type of application
635 -> TcM (TcExpr, LIE) -- Translated fun and args
637 tcApp (HsApp e1 e2) args res_ty
638 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
640 tcApp fun args res_ty
641 = -- First type-check the function
642 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
644 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
645 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenNF_Tc_`
646 split_fun_ty fun_ty (length args)
647 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
649 -- Now typecheck the args
650 mapAndUnzipTc (tcArg fun)
651 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
653 -- Unify with expected result after type-checking the args
654 -- so that the info from args percolates to actual_result_ty.
655 -- This is when we might detect a too-few args situation.
656 -- (One can think of cases when the opposite order would give
657 -- a better error message.)
658 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
659 (tcSubExp res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
661 returnTc (co_fn <$> foldl HsApp fun' args',
662 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
665 -- If an error happens we try to figure out whether the
666 -- function has been given too many or too few arguments,
668 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
669 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
670 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
672 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
673 (env2, act_ty'') = tidyOpenType env1 act_ty'
674 (exp_args, _) = tcSplitFunTys exp_ty''
675 (act_args, _) = tcSplitFunTys act_ty''
677 len_act_args = length act_args
678 len_exp_args = length exp_args
680 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
681 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
682 | otherwise = appCtxt fun args
684 returnNF_Tc (env2, message)
687 split_fun_ty :: TcType -- The type of the function
688 -> Int -- Number of arguments
689 -> TcM ([TcType], -- Function argument types
690 TcType) -- Function result types
692 split_fun_ty fun_ty 0
693 = returnTc ([], fun_ty)
695 split_fun_ty fun_ty n
696 = -- Expect the function to have type A->B
697 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
698 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
699 returnTc (arg_ty:arg_tys, final_res_ty)
703 tcArg :: RenamedHsExpr -- The function (for error messages)
704 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
705 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
707 tcArg the_fun (arg, expected_arg_ty, arg_no)
708 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
709 tcExpr arg expected_arg_ty
713 %************************************************************************
715 \subsection{@tcId@ typchecks an identifier occurrence}
717 %************************************************************************
719 tcId instantiates an occurrence of an Id.
720 The instantiate_it loop runs round instantiating the Id.
721 It has to be a loop because we are now prepared to entertain
723 f:: forall a. Eq a => forall b. Baz b => tau
724 We want to instantiate this to
725 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
727 The -fno-method-sharing flag controls what happens so far as the LIE
728 is concerned. The default case is that for an overloaded function we
729 generate a "method" Id, and add the Method Inst to the LIE. So you get
732 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
733 If you specify -fno-method-sharing, the dictionary application
734 isn't shared, so we get
736 f = /\a (d:Num a) (x:a) -> (+) a d x x
737 This gets a bit less sharing, but
738 a) it's better for RULEs involving overloaded functions
739 b) perhaps fewer separated lambdas
742 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
743 tcId name -- Look up the Id and instantiate its type
744 = tcLookupId name `thenNF_Tc` \ id ->
745 loop (OccurrenceOf id) (HsVar id) emptyLIE (idType id)
747 loop orig (HsVar fun_id) lie fun_ty
748 | want_method_inst fun_ty
749 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
750 newMethodWithGivenTy orig fun_id
751 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
752 loop orig (HsVar (instToId meth))
753 (unitLIE meth `plusLIE` lie) tau
755 loop orig fun lie fun_ty
757 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
758 loop orig (inst_fn fun) (inst_lie `plusLIE` lie) tau
761 = returnNF_Tc (fun, lie, fun_ty)
763 want_method_inst fun_ty
764 | opt_NoMethodSharing = False
765 | otherwise = case tcSplitSigmaTy fun_ty of
766 (_,[],_) -> False -- Not overloaded
767 (_,theta,_) -> not (any isLinearPred theta)
768 -- This is a slight hack.
769 -- If f :: (%x :: T) => Int -> Int
770 -- Then if we have two separate calls, (f 3, f 4), we cannot
771 -- make a method constraint that then gets shared, thus:
772 -- let m = f %x in (m 3, m 4)
773 -- because that loses the linearity of the constraint.
774 -- The simplest thing to do is never to construct a method constraint
775 -- in the first place that has a linear implicit parameter in it.
778 Typecheck expression which in most cases will be an Id.
779 The expression can return a higher-ranked type, such as
780 (forall a. a->a) -> Int
781 so we must create a HoleTyVarTy to pass in as the expected tyvar.
784 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
785 tcExpr_id (HsVar name) = tcId name
786 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
787 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
788 readHoleResult id_ty `thenTc` \ id_ty' ->
789 returnTc (expr', lie_id, id_ty')
793 %************************************************************************
795 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
797 %************************************************************************
800 -- I don't like this lumping together of do expression and list/array
801 -- comprehensions; creating the monad instances is entirely pointless in the
802 -- latter case; I'll leave the list case as it is for the moment, but handle
803 -- arrays extra (would be better to handle arrays and lists together, though)
806 tcDoStmts PArrComp stmts src_loc res_ty
808 ASSERT( not (null stmts) )
809 tcAddSrcLoc src_loc $
811 unifyPArrTy res_ty `thenTc` \elt_ty ->
812 let tc_ty = mkTyConTy parrTyCon
813 m_ty = (mkPArrTy, elt_ty)
815 tcStmts (DoCtxt PArrComp) m_ty stmts `thenTc` \(stmts', stmts_lie) ->
816 returnTc (HsDoOut PArrComp stmts'
817 undefined undefined undefined -- don't touch!
821 tcDoStmts do_or_lc stmts src_loc res_ty
822 = -- get the Monad and MonadZero classes
823 -- create type consisting of a fresh monad tyvar
824 ASSERT( not (null stmts) )
825 tcAddSrcLoc src_loc $
827 -- If it's a comprehension we're dealing with,
828 -- force it to be a list comprehension.
829 -- (as of Haskell 98, monad comprehensions are no more.)
830 -- Similarily, array comprehensions must involve parallel arrays types
833 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
834 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
836 PArrComp -> panic "TcExpr.tcDoStmts: How did we get here?!?"
838 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
839 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
840 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
841 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
842 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
844 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
846 -- Build the then and zero methods in case we need them
847 -- It's important that "then" and "return" appear just once in the final LIE,
848 -- not only for typechecker efficiency, but also because otherwise during
849 -- simplification we end up with silly stuff like
850 -- then = case d of (t,r) -> t
852 -- where the second "then" sees that it already exists in the "available" stuff.
854 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
855 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
856 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
857 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
858 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
859 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
861 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
863 returnTc (HsDoOut do_or_lc stmts'
864 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
866 stmts_lie `plusLIE` monad_lie)
870 %************************************************************************
872 \subsection{Record bindings}
874 %************************************************************************
876 Game plan for record bindings
877 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
878 1. Find the TyCon for the bindings, from the first field label.
880 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
882 For each binding field = value
884 3. Instantiate the field type (from the field label) using the type
887 4 Type check the value using tcArg, passing the field type as
888 the expected argument type.
890 This extends OK when the field types are universally quantified.
895 :: TyCon -- Type constructor for the record
896 -> [TcType] -- Args of this type constructor
897 -> RenamedRecordBinds
898 -> TcM (TcRecordBinds, LIE)
900 tcRecordBinds tycon ty_args rbinds
901 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
902 returnTc (rbinds', plusLIEs lies)
904 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
906 do_bind (field_lbl_name, rhs, pun_flag)
907 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
909 field_lbl = recordSelectorFieldLabel sel_id
910 field_ty = substTy tenv (fieldLabelType field_lbl)
912 ASSERT( isRecordSelector sel_id )
913 -- This lookup and assertion will surely succeed, because
914 -- we check that the fields are indeed record selectors
915 -- before calling tcRecordBinds
916 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
917 -- The caller of tcRecordBinds has already checked
918 -- that all the fields come from the same type
920 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
922 returnTc ((sel_id, rhs', pun_flag), lie)
924 badFields rbinds data_con
925 = [field_name | (field_name, _, _) <- rbinds,
926 not (field_name `elem` field_names)
929 field_names = map fieldLabelName (dataConFieldLabels data_con)
931 missingFields rbinds data_con
932 | null field_labels = ([], []) -- Not declared as a record;
933 -- But C{} is still valid
935 = (missing_strict_fields, other_missing_fields)
937 missing_strict_fields
938 = [ fl | (fl, str) <- field_info,
940 not (fieldLabelName fl `elem` field_names_used)
943 = [ fl | (fl, str) <- field_info,
944 not (isMarkedStrict str),
945 not (fieldLabelName fl `elem` field_names_used)
948 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
949 field_labels = dataConFieldLabels data_con
951 field_info = zipEqual "missingFields"
953 (dropList ex_theta (dataConStrictMarks data_con))
954 -- The 'drop' is because dataConStrictMarks
955 -- includes the existential dictionaries
956 (_, _, _, ex_theta, _, _) = dataConSig data_con
959 %************************************************************************
961 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
963 %************************************************************************
966 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
968 tcMonoExprs [] [] = returnTc ([], emptyLIE)
969 tcMonoExprs (expr:exprs) (ty:tys)
970 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
971 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
972 returnTc (expr':exprs', lie1 `plusLIE` lie2)
976 %************************************************************************
978 \subsection{Literals}
980 %************************************************************************
985 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
986 tcLit (HsLitLit s _) res_ty
987 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
988 newDicts (LitLitOrigin (_UNPK_ s))
989 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
990 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
993 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
994 returnTc (HsLit lit, emptyLIE)
998 %************************************************************************
1000 \subsection{Errors and contexts}
1002 %************************************************************************
1006 Boring and alphabetical:
1009 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1012 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1015 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1018 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1021 = hang (ptext SLIT("When checking the type signature of the expression:"))
1025 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1028 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1031 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1034 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1036 funAppCtxt fun arg arg_no
1037 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1038 quotes (ppr fun) <> text ", namely"])
1039 4 (quotes (ppr arg))
1041 wrongArgsCtxt too_many_or_few fun args
1042 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1043 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1044 <+> ptext SLIT("arguments in the call"))
1045 4 (parens (ppr the_app))
1047 the_app = foldl HsApp fun args -- Used in error messages
1050 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1052 the_app = foldl HsApp fun args -- Used in error messages
1054 lurkingRank2Err fun fun_ty
1055 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1056 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1057 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1060 = hang (ptext SLIT("No constructor has all these fields:"))
1061 4 (pprQuotedList fields)
1063 fields = [field | (field, _, _) <- rbinds]
1065 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1066 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1069 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1071 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1072 missingStrictFieldCon con field
1073 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1074 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1076 missingFieldCon :: Name -> FieldLabel -> SDoc
1077 missingFieldCon con field
1078 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1079 ptext SLIT("is not initialised")]