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 ( tcSub, 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,
37 newTyVarTy, newTyVarTys, zonkTcType )
38 import TcType ( TcType, TcSigmaType, TcPhiType,
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 ( 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 (tcMonoExpr expr) `thenTc` \ (gen_fn, expr', lie) ->
89 returnTc (gen_fn <$> expr', lie)
93 %************************************************************************
95 \subsection{The TAUT rules for variables}
97 %************************************************************************
100 tcMonoExpr :: RenamedHsExpr -- Expession to type check
101 -> TcPhiType -- Expected type (could be a type variable)
102 -- Definitely no foralls at the top
106 tcMonoExpr (HsVar name) res_ty
107 = tcId name `thenNF_Tc` \ (expr', lie1, id_ty) ->
108 tcSub res_ty id_ty `thenTc` \ (co_fn, lie2) ->
109 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
111 tcMonoExpr (HsIPVar ip) res_ty
112 = -- Implicit parameters must have a *tau-type* not a
113 -- type scheme. We enforce this by creating a fresh
114 -- type variable as its type. (Because res_ty may not
116 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
117 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
118 tcSub res_ty ip_ty `thenTc` \ (co_fn, lie) ->
119 returnNF_Tc (co_fn <$> HsIPVar ip', lie `plusLIE` unitLIE inst)
123 %************************************************************************
125 \subsection{Expressions type signatures}
127 %************************************************************************
130 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
131 = tcHsSigType ExprSigCtxt poly_ty `thenTc` \ sig_tc_ty ->
132 tcAddErrCtxt (exprSigCtxt in_expr) $
133 tcExpr expr sig_tc_ty `thenTc` \ (expr', lie1) ->
135 -- Must instantiate the outer for-alls of sig_tc_ty
136 -- else we risk instantiating a ? res_ty to a forall-type
137 -- which breaks the invariant that tcMonoExpr only returns phi-types
138 tcInstCall SignatureOrigin sig_tc_ty `thenNF_Tc` \ (inst_fn, lie2, inst_sig_ty) ->
139 tcSub res_ty inst_sig_ty `thenTc` \ (co_fn, lie3) ->
141 returnTc (co_fn <$> inst_fn expr', lie1 `plusLIE` lie2 `plusLIE` lie3)
145 %************************************************************************
147 \subsection{Other expression forms}
149 %************************************************************************
152 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
153 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
154 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty
156 tcMonoExpr (NegApp expr neg_name) res_ty
157 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
159 tcMonoExpr (HsLam match) res_ty
160 = tcMatchLambda match res_ty `thenTc` \ (match',lie) ->
161 returnTc (HsLam match', lie)
163 tcMonoExpr (HsApp e1 e2) res_ty
164 = tcApp e1 [e2] res_ty
167 Note that the operators in sections are expected to be binary, and
168 a type error will occur if they aren't.
171 -- Left sections, equivalent to
178 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
179 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
180 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
181 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2) ->
182 tcAddErrCtxt (exprCtxt in_expr) $
183 tcSub res_ty (mkFunTy arg2_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
184 returnTc (co_fn <$> SectionL arg1' op', lie1 `plusLIE` lie2 `plusLIE` lie3)
186 -- Right sections, equivalent to \ x -> x op expr, or
189 tcMonoExpr in_expr@(SectionR op arg2) res_ty
190 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
191 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
192 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2) ->
193 tcAddErrCtxt (exprCtxt in_expr) $
194 tcSub res_ty (mkFunTy arg1_ty op_res_ty) `thenTc` \ (co_fn, lie3) ->
195 returnTc (co_fn <$> SectionR op' arg2', lie1 `plusLIE` lie2 `plusLIE` lie3)
197 -- equivalent to (op e1) e2:
199 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
200 = tcExpr_id op `thenTc` \ (op', lie1, op_ty) ->
201 split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) ->
202 tcArg op (arg1, arg1_ty, 1) `thenTc` \ (arg1',lie2a) ->
203 tcArg op (arg2, arg2_ty, 2) `thenTc` \ (arg2',lie2b) ->
204 tcAddErrCtxt (exprCtxt in_expr) $
205 tcSub res_ty op_res_ty `thenTc` \ (co_fn, lie3) ->
206 returnTc (OpApp arg1' op' fix arg2',
207 lie1 `plusLIE` lie2a `plusLIE` lie2b `plusLIE` lie3)
210 The interesting thing about @ccall@ is that it is just a template
211 which we instantiate by filling in details about the types of its
212 argument and result (ie minimal typechecking is performed). So, the
213 basic story is that we allocate a load of type variables (to hold the
214 arg/result types); unify them with the args/result; and store them for
218 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
220 = getDOptsTc `thenNF_Tc` \ dflags ->
222 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
223 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
224 text "Either compile with -fvia-C, or, better, rewrite your code",
225 text "to use the foreign function interface. _casm_s are deprecated",
226 text "and support for them may one day disappear."])
229 -- Get the callable and returnable classes.
230 tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
231 tcLookupClass cReturnableClassName `thenNF_Tc` \ cReturnableClass ->
232 tcLookupTyCon ioTyConName `thenNF_Tc` \ ioTyCon ->
234 new_arg_dict (arg, arg_ty)
235 = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg))
236 [mkClassPred cCallableClass [arg_ty]] `thenNF_Tc` \ arg_dicts ->
237 returnNF_Tc arg_dicts -- Actually a singleton bag
239 result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -}
243 let tv_idxs | null args = []
244 | otherwise = [1..length args]
246 newTyVarTys (length tv_idxs) openTypeKind `thenNF_Tc` \ arg_tys ->
247 tcMonoExprs args arg_tys `thenTc` \ (args', args_lie) ->
249 -- The argument types can be unlifted or lifted; the result
250 -- type must, however, be lifted since it's an argument to the IO
252 newTyVarTy liftedTypeKind `thenNF_Tc` \ result_ty ->
254 io_result_ty = mkTyConApp ioTyCon [result_ty]
256 unifyTauTy res_ty io_result_ty `thenTc_`
258 -- Construct the extra insts, which encode the
259 -- constraints on the argument and result types.
260 mapNF_Tc new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenNF_Tc` \ ccarg_dicts_s ->
261 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenNF_Tc` \ ccres_dict ->
262 returnTc (HsCCall lbl args' may_gc is_casm io_result_ty,
263 mkLIE (ccres_dict ++ concat ccarg_dicts_s) `plusLIE` args_lie)
267 tcMonoExpr (HsSCC lbl expr) res_ty
268 = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
269 returnTc (HsSCC lbl expr', lie)
271 tcMonoExpr (HsLet binds expr) res_ty
274 binds -- Bindings to check
275 tc_expr `thenTc` \ (expr', lie) ->
276 returnTc (expr', lie)
278 tc_expr = tcMonoExpr expr res_ty `thenTc` \ (expr', lie) ->
279 returnTc (expr', lie)
280 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
282 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
283 = tcAddSrcLoc src_loc $
284 tcAddErrCtxt (caseCtxt in_expr) $
286 -- Typecheck the case alternatives first.
287 -- The case patterns tend to give good type info to use
288 -- when typechecking the scrutinee. For example
291 -- will report that map is applied to too few arguments
293 -- Not only that, but it's better to check the matches on their
294 -- own, so that we get the expected results for scoped type variables.
296 -- (p::a, q::b) -> (q,p)
297 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
298 -- claimed by the pattern signatures. But if we typechecked the
299 -- match with x in scope and x's type as the expected type, we'd be hosed.
301 tcMatchesCase matches res_ty `thenTc` \ (scrut_ty, matches', lie2) ->
303 tcAddErrCtxt (caseScrutCtxt scrut) (
304 tcMonoExpr scrut scrut_ty
305 ) `thenTc` \ (scrut',lie1) ->
307 returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2)
309 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
310 = tcAddSrcLoc src_loc $
311 tcAddErrCtxt (predCtxt pred) (
312 tcMonoExpr pred boolTy ) `thenTc` \ (pred',lie1) ->
314 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
315 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
316 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
320 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
321 = tcDoStmts do_or_lc stmts src_loc res_ty
325 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
326 = unifyListTy res_ty `thenTc` \ elt_ty ->
327 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
328 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
331 = tcAddErrCtxt (listCtxt expr) $
332 tcMonoExpr expr elt_ty
334 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
335 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
336 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
337 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
340 = tcAddErrCtxt (parrCtxt expr) $
341 tcMonoExpr expr elt_ty
343 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
344 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
345 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
346 (exprs `zip` arg_tys) -- we know they're of equal length.
347 `thenTc` \ (exprs', lies) ->
348 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
350 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
351 = tcAddErrCtxt (recordConCtxt expr) $
352 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
354 (_, record_ty) = tcSplitFunTys con_tau
355 (tycon, ty_args) = tcSplitTyConApp record_ty
357 ASSERT( isAlgTyCon tycon )
358 unifyTauTy res_ty record_ty `thenTc_`
360 -- Check that the record bindings match the constructor
361 -- con_name is syntactically constrained to be a data constructor
362 tcLookupDataCon con_name `thenTc` \ data_con ->
364 bad_fields = badFields rbinds data_con
366 if not (null bad_fields) then
367 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
368 failTc -- Fail now, because tcRecordBinds will crash on a bad field
371 -- Typecheck the record bindings
372 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
375 (missing_s_fields, missing_fields) = missingFields rbinds data_con
377 checkTcM (null missing_s_fields)
378 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
379 returnNF_Tc ()) `thenNF_Tc_`
380 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
381 checkTcM (not (warn && not (null missing_fields)))
382 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
383 returnNF_Tc ()) `thenNF_Tc_`
385 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
387 -- The main complication with RecordUpd is that we need to explicitly
388 -- handle the *non-updated* fields. Consider:
390 -- data T a b = MkT1 { fa :: a, fb :: b }
391 -- | MkT2 { fa :: a, fc :: Int -> Int }
392 -- | MkT3 { fd :: a }
394 -- upd :: T a b -> c -> T a c
395 -- upd t x = t { fb = x}
397 -- The type signature on upd is correct (i.e. the result should not be (T a b))
398 -- because upd should be equivalent to:
400 -- upd t x = case t of
401 -- MkT1 p q -> MkT1 p x
402 -- MkT2 a b -> MkT2 p b
403 -- MkT3 d -> error ...
405 -- So we need to give a completely fresh type to the result record,
406 -- and then constrain it by the fields that are *not* updated ("p" above).
408 -- Note that because MkT3 doesn't contain all the fields being updated,
409 -- its RHS is simply an error, so it doesn't impose any type constraints
411 -- All this is done in STEP 4 below.
413 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
414 = tcAddErrCtxt (recordUpdCtxt expr) $
417 -- Check that the field names are really field names
418 ASSERT( not (null rbinds) )
420 field_names = [field_name | (field_name, _, _) <- rbinds]
422 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
424 bad_guys = [ addErrTc (notSelector field_name)
425 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
427 Just (AnId sel_id) -> not (isRecordSelector sel_id)
431 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
434 -- Figure out the tycon and data cons from the first field name
436 -- It's OK to use the non-tc splitters here (for a selector)
437 (Just (AnId sel_id) : _) = maybe_sel_ids
438 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
439 -- when the data type has a context
440 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
441 tycon = tcTyConAppTyCon data_ty
442 data_cons = tyConDataCons tycon
443 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
445 tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
448 -- Check that at least one constructor has all the named fields
449 -- i.e. has an empty set of bad fields returned by badFields
450 checkTc (any (null . badFields rbinds) data_cons)
451 (badFieldsUpd rbinds) `thenTc_`
454 -- Typecheck the update bindings.
455 -- (Do this after checking for bad fields in case there's a field that
456 -- doesn't match the constructor.)
458 result_record_ty = mkTyConApp tycon result_inst_tys
460 unifyTauTy res_ty result_record_ty `thenTc_`
461 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
464 -- Use the un-updated fields to find a vector of booleans saying
465 -- which type arguments must be the same in updatee and result.
467 -- WARNING: this code assumes that all data_cons in a common tycon
468 -- have FieldLabels abstracted over the same tyvars.
470 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
471 con_field_lbls_s = map dataConFieldLabels data_cons
473 -- A constructor is only relevant to this process if
474 -- it contains all the fields that are being updated
475 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
476 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
478 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
479 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
481 mk_inst_ty (tyvar, result_inst_ty)
482 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
483 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
485 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
488 -- Typecheck the expression to be updated
490 record_ty = mkTyConApp tycon inst_tys
492 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
495 -- Figure out the LIE we need. We have to generate some
496 -- dictionaries for the data type context, since we are going to
497 -- do some construction.
499 -- What dictionaries do we need? For the moment we assume that all
500 -- data constructors have the same context, and grab it from the first
501 -- constructor. If they have varying contexts then we'd have to
502 -- union the ones that could participate in the update.
504 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
505 inst_env = mkTopTyVarSubst tyvars result_inst_tys
506 theta' = substTheta inst_env theta
508 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
511 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
512 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
514 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
515 = unifyListTy res_ty `thenTc` \ elt_ty ->
516 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
518 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
519 newMethod (ArithSeqOrigin seq)
520 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
522 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
523 lie1 `plusLIE` unitLIE enum_from)
525 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
526 = tcAddErrCtxt (arithSeqCtxt in_expr) $
527 unifyListTy res_ty `thenTc` \ elt_ty ->
528 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
529 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
530 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
531 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
533 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
534 (FromThen expr1' expr2'),
535 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
537 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
538 = tcAddErrCtxt (arithSeqCtxt in_expr) $
539 unifyListTy res_ty `thenTc` \ elt_ty ->
540 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
541 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
542 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
543 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
545 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
546 (FromTo expr1' expr2'),
547 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
549 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
550 = tcAddErrCtxt (arithSeqCtxt in_expr) $
551 unifyListTy res_ty `thenTc` \ elt_ty ->
552 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
553 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
554 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
555 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
556 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
558 returnTc (ArithSeqOut (HsVar (instToId eft))
559 (FromThenTo expr1' expr2' expr3'),
560 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
562 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
563 = tcAddErrCtxt (parrSeqCtxt in_expr) $
564 unifyPArrTy res_ty `thenTc` \ elt_ty ->
565 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
566 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
567 tcLookupGlobalId enumFromToPName `thenNF_Tc` \ sel_id ->
568 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
570 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
571 (FromTo expr1' expr2'),
572 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
574 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
575 = tcAddErrCtxt (parrSeqCtxt in_expr) $
576 unifyPArrTy res_ty `thenTc` \ elt_ty ->
577 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
578 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
579 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
580 tcLookupGlobalId enumFromThenToPName `thenNF_Tc` \ sel_id ->
581 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
583 returnTc (PArrSeqOut (HsVar (instToId eft))
584 (FromThenTo expr1' expr2' expr3'),
585 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
587 tcMonoExpr (PArrSeqIn _) _
588 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
589 -- the parser shouldn't have generated it and the renamer shouldn't have
593 %************************************************************************
595 \subsection{Implicit Parameter bindings}
597 %************************************************************************
600 tcMonoExpr (HsWith expr binds) res_ty
601 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
602 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
604 -- If the binding binds ?x = E, we must now
605 -- discharge any ?x constraints in expr_lie
606 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
608 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
610 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
613 = newTyVarTy openTypeKind `thenTc` \ ty ->
614 tcGetSrcLoc `thenTc` \ loc ->
615 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
616 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
617 returnTc (ip_inst, (ip', expr'), lie)
620 %************************************************************************
622 \subsection{@tcApp@ typchecks an application}
624 %************************************************************************
628 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
629 -> TcType -- Expected result type of application
630 -> TcM (TcExpr, LIE) -- Translated fun and args
632 tcApp (HsApp e1 e2) args res_ty
633 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
635 tcApp fun args res_ty
636 = -- First type-check the function
637 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
639 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
640 split_fun_ty fun_ty (length args)
641 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
643 -- Now typecheck the args
644 mapAndUnzipTc (tcArg fun)
645 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
647 -- Unify with expected result after type-checking the args
648 -- so that the info from args percolates to actual_result_ty.
649 -- This is when we might detect a too-few args situation.
650 -- (One can think of cases when the opposite order would give
651 -- a better error message.)
652 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
653 (tcSub res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
655 returnTc (co_fn <$> foldl HsApp fun' args',
656 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
659 -- If an error happens we try to figure out whether the
660 -- function has been given too many or too few arguments,
662 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
663 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
664 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
666 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
667 (env2, act_ty'') = tidyOpenType env1 act_ty'
668 (exp_args, _) = tcSplitFunTys exp_ty''
669 (act_args, _) = tcSplitFunTys act_ty''
671 len_act_args = length act_args
672 len_exp_args = length exp_args
674 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
675 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
676 | otherwise = appCtxt fun args
678 returnNF_Tc (env2, message)
681 split_fun_ty :: TcType -- The type of the function
682 -> Int -- Number of arguments
683 -> TcM ([TcType], -- Function argument types
684 TcType) -- Function result types
686 split_fun_ty fun_ty 0
687 = returnTc ([], fun_ty)
689 split_fun_ty fun_ty n
690 = -- Expect the function to have type A->B
691 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
692 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
693 returnTc (arg_ty:arg_tys, final_res_ty)
697 tcArg :: RenamedHsExpr -- The function (for error messages)
698 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
699 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
701 tcArg the_fun (arg, expected_arg_ty, arg_no)
702 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
703 tcExpr arg expected_arg_ty
707 %************************************************************************
709 \subsection{@tcId@ typchecks an identifier occurrence}
711 %************************************************************************
713 tcId instantiates an occurrence of an Id.
714 The instantiate_it loop runs round instantiating the Id.
715 It has to be a loop because we are now prepared to entertain
717 f:: forall a. Eq a => forall b. Baz b => tau
718 We want to instantiate this to
719 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
721 The -fno-method-sharing flag controls what happens so far as the LIE
722 is concerned. The default case is that for an overloaded function we
723 generate a "method" Id, and add the Method Inst to the LIE. So you get
726 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
727 If you specify -fno-method-sharing, the dictionary application
728 isn't shared, so we get
730 f = /\a (d:Num a) (x:a) -> (+) a d x x
731 This gets a bit less sharing, but
732 a) it's better for RULEs involving overloaded functions
733 b) perhaps fewer separated lambdas
736 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
737 tcId name -- Look up the Id and instantiate its type
738 = tcLookupId name `thenNF_Tc` \ id ->
739 loop (OccurrenceOf id) (HsVar id) emptyLIE (idType id)
741 loop orig (HsVar fun_id) lie fun_ty
742 | want_method_inst fun_ty
743 = tcInstType fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
744 newMethodWithGivenTy orig fun_id
745 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
746 loop orig (HsVar (instToId meth))
747 (unitLIE meth `plusLIE` lie) tau
749 loop orig fun lie fun_ty
751 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
752 loop orig (inst_fn fun) (inst_lie `plusLIE` lie) tau
755 = returnNF_Tc (fun, lie, fun_ty)
757 want_method_inst fun_ty
758 | opt_NoMethodSharing = False
759 | otherwise = case tcSplitSigmaTy fun_ty of
760 (_,[],_) -> False -- Not overloaded
761 (_,theta,_) -> not (any isLinearPred theta)
762 -- This is a slight hack.
763 -- If f :: (%x :: T) => Int -> Int
764 -- Then if we have two separate calls, (f 3, f 4), we cannot
765 -- make a method constraint that then gets shared, thus:
766 -- let m = f %x in (m 3, m 4)
767 -- because that loses the linearity of the constraint.
768 -- The simplest thing to do is never to construct a method constraint
769 -- in the first place that has a linear implicit parameter in it.
772 Typecheck expression which in most cases will be an Id.
773 The expression can return a higher-ranked type, such as
774 (forall a. a->a) -> Int
775 so we must create a HoleTyVarTy to pass in as the expected tyvar.
778 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
779 tcExpr_id (HsVar name) = tcId name
780 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
781 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
782 returnTc (expr', lie_id, id_ty)
786 %************************************************************************
788 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
790 %************************************************************************
793 -- I don't like this lumping together of do expression and list/array
794 -- comprehensions; creating the monad instances is entirely pointless in the
795 -- latter case; I'll leave the list case as it is for the moment, but handle
796 -- arrays extra (would be better to handle arrays and lists together, though)
799 tcDoStmts PArrComp stmts src_loc res_ty
801 ASSERT( not (null stmts) )
802 tcAddSrcLoc src_loc $
804 unifyPArrTy res_ty `thenTc` \elt_ty ->
805 let tc_ty = mkTyConTy parrTyCon
806 m_ty = (mkPArrTy, elt_ty)
808 tcStmts (DoCtxt PArrComp) m_ty stmts `thenTc` \(stmts', stmts_lie) ->
809 returnTc (HsDoOut PArrComp stmts'
810 undefined undefined undefined -- don't touch!
814 tcDoStmts do_or_lc stmts src_loc res_ty
815 = -- get the Monad and MonadZero classes
816 -- create type consisting of a fresh monad tyvar
817 ASSERT( not (null stmts) )
818 tcAddSrcLoc src_loc $
820 -- If it's a comprehension we're dealing with,
821 -- force it to be a list comprehension.
822 -- (as of Haskell 98, monad comprehensions are no more.)
823 -- Similarily, array comprehensions must involve parallel arrays types
826 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
827 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
829 PArrComp -> panic "TcExpr.tcDoStmts: How did we get here?!?"
831 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
832 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
833 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
834 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
835 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
837 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
839 -- Build the then and zero methods in case we need them
840 -- It's important that "then" and "return" appear just once in the final LIE,
841 -- not only for typechecker efficiency, but also because otherwise during
842 -- simplification we end up with silly stuff like
843 -- then = case d of (t,r) -> t
845 -- where the second "then" sees that it already exists in the "available" stuff.
847 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
848 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
849 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
850 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
851 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
852 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
854 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
856 returnTc (HsDoOut do_or_lc stmts'
857 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
859 stmts_lie `plusLIE` monad_lie)
863 %************************************************************************
865 \subsection{Record bindings}
867 %************************************************************************
869 Game plan for record bindings
870 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
871 1. Find the TyCon for the bindings, from the first field label.
873 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
875 For each binding field = value
877 3. Instantiate the field type (from the field label) using the type
880 4 Type check the value using tcArg, passing the field type as
881 the expected argument type.
883 This extends OK when the field types are universally quantified.
888 :: TyCon -- Type constructor for the record
889 -> [TcType] -- Args of this type constructor
890 -> RenamedRecordBinds
891 -> TcM (TcRecordBinds, LIE)
893 tcRecordBinds tycon ty_args rbinds
894 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
895 returnTc (rbinds', plusLIEs lies)
897 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
899 do_bind (field_lbl_name, rhs, pun_flag)
900 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
902 field_lbl = recordSelectorFieldLabel sel_id
903 field_ty = substTy tenv (fieldLabelType field_lbl)
905 ASSERT( isRecordSelector sel_id )
906 -- This lookup and assertion will surely succeed, because
907 -- we check that the fields are indeed record selectors
908 -- before calling tcRecordBinds
909 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
910 -- The caller of tcRecordBinds has already checked
911 -- that all the fields come from the same type
913 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
915 returnTc ((sel_id, rhs', pun_flag), lie)
917 badFields rbinds data_con
918 = [field_name | (field_name, _, _) <- rbinds,
919 not (field_name `elem` field_names)
922 field_names = map fieldLabelName (dataConFieldLabels data_con)
924 missingFields rbinds data_con
925 | null field_labels = ([], []) -- Not declared as a record;
926 -- But C{} is still valid
928 = (missing_strict_fields, other_missing_fields)
930 missing_strict_fields
931 = [ fl | (fl, str) <- field_info,
933 not (fieldLabelName fl `elem` field_names_used)
936 = [ fl | (fl, str) <- field_info,
937 not (isMarkedStrict str),
938 not (fieldLabelName fl `elem` field_names_used)
941 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
942 field_labels = dataConFieldLabels data_con
944 field_info = zipEqual "missingFields"
946 (dropList ex_theta (dataConStrictMarks data_con))
947 -- The 'drop' is because dataConStrictMarks
948 -- includes the existential dictionaries
949 (_, _, _, ex_theta, _, _) = dataConSig data_con
952 %************************************************************************
954 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
956 %************************************************************************
959 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
961 tcMonoExprs [] [] = returnTc ([], emptyLIE)
962 tcMonoExprs (expr:exprs) (ty:tys)
963 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
964 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
965 returnTc (expr':exprs', lie1 `plusLIE` lie2)
969 %************************************************************************
971 \subsection{Literals}
973 %************************************************************************
978 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
979 tcLit (HsLitLit s _) res_ty
980 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
981 newDicts (LitLitOrigin (_UNPK_ s))
982 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
983 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
986 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
987 returnTc (HsLit lit, emptyLIE)
991 %************************************************************************
993 \subsection{Errors and contexts}
995 %************************************************************************
999 Boring and alphabetical:
1002 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1005 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1008 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1011 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1014 = hang (ptext SLIT("In an expression with a type signature:"))
1018 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1021 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1024 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1027 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1029 funAppCtxt fun arg arg_no
1030 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1031 quotes (ppr fun) <> text ", namely"])
1032 4 (quotes (ppr arg))
1034 wrongArgsCtxt too_many_or_few fun args
1035 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1036 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1037 <+> ptext SLIT("arguments in the call"))
1038 4 (parens (ppr the_app))
1040 the_app = foldl HsApp fun args -- Used in error messages
1043 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1045 the_app = foldl HsApp fun args -- Used in error messages
1047 lurkingRank2Err fun fun_ty
1048 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1049 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1050 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1053 = hang (ptext SLIT("No constructor has all these fields:"))
1054 4 (pprQuotedList fields)
1056 fields = [field | (field, _, _) <- rbinds]
1058 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1059 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1062 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1064 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1065 missingStrictFieldCon con field
1066 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1067 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1069 missingFieldCon :: Name -> FieldLabel -> SDoc
1070 missingFieldCon con field
1071 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1072 ptext SLIT("is not initialised")]