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, 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 -> TcPhiType -- 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 tcSub res_ty id_ty `thenTc` \ (co_fn, lie2) ->
111 returnTc (co_fn <$> expr', lie1 `plusLIE` lie2)
113 tcMonoExpr (HsIPVar ip) res_ty
114 = -- Implicit parameters must have a *tau-type* not a
115 -- type scheme. We enforce this by creating a fresh
116 -- type variable as its type. (Because res_ty may not
118 newTyVarTy openTypeKind `thenNF_Tc` \ ip_ty ->
119 newIPDict (IPOcc ip) ip ip_ty `thenNF_Tc` \ (ip', inst) ->
120 tcSub res_ty ip_ty `thenTc` \ (co_fn, lie) ->
121 returnNF_Tc (co_fn <$> 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 tcSub 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 tcSub 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 tcSub 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 tcSub 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 tcMonoExpr b1 res_ty `thenTc` \ (b1',lie2) ->
317 tcMonoExpr b2 res_ty `thenTc` \ (b2',lie3) ->
318 returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3))
322 tcMonoExpr expr@(HsDo do_or_lc stmts src_loc) res_ty
323 = tcDoStmts do_or_lc stmts src_loc res_ty
327 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
328 = unifyListTy res_ty `thenTc` \ elt_ty ->
329 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
330 returnTc (ExplicitList elt_ty exprs', plusLIEs lies)
333 = tcAddErrCtxt (listCtxt expr) $
334 tcMonoExpr expr elt_ty
336 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
337 = unifyPArrTy res_ty `thenTc` \ elt_ty ->
338 mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) ->
339 returnTc (ExplicitPArr elt_ty exprs', plusLIEs lies)
342 = tcAddErrCtxt (parrCtxt expr) $
343 tcMonoExpr expr elt_ty
345 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
346 = unifyTupleTy boxity (length exprs) res_ty `thenTc` \ arg_tys ->
347 mapAndUnzipTc (\ (expr, arg_ty) -> tcMonoExpr expr arg_ty)
348 (exprs `zip` arg_tys) -- we know they're of equal length.
349 `thenTc` \ (exprs', lies) ->
350 returnTc (ExplicitTuple exprs' boxity, plusLIEs lies)
352 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
353 = tcAddErrCtxt (recordConCtxt expr) $
354 tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) ->
356 (_, record_ty) = tcSplitFunTys con_tau
357 (tycon, ty_args) = tcSplitTyConApp record_ty
359 ASSERT( isAlgTyCon tycon )
360 unifyTauTy res_ty record_ty `thenTc_`
362 -- Check that the record bindings match the constructor
363 -- con_name is syntactically constrained to be a data constructor
364 tcLookupDataCon con_name `thenTc` \ data_con ->
366 bad_fields = badFields rbinds data_con
368 if not (null bad_fields) then
369 mapNF_Tc (addErrTc . badFieldCon con_name) bad_fields `thenNF_Tc_`
370 failTc -- Fail now, because tcRecordBinds will crash on a bad field
373 -- Typecheck the record bindings
374 tcRecordBinds tycon ty_args rbinds `thenTc` \ (rbinds', rbinds_lie) ->
377 (missing_s_fields, missing_fields) = missingFields rbinds data_con
379 checkTcM (null missing_s_fields)
380 (mapNF_Tc (addErrTc . missingStrictFieldCon con_name) missing_s_fields `thenNF_Tc_`
381 returnNF_Tc ()) `thenNF_Tc_`
382 doptsTc Opt_WarnMissingFields `thenNF_Tc` \ warn ->
383 checkTcM (not (warn && not (null missing_fields)))
384 (mapNF_Tc ((warnTc True) . missingFieldCon con_name) missing_fields `thenNF_Tc_`
385 returnNF_Tc ()) `thenNF_Tc_`
387 returnTc (RecordConOut data_con con_expr rbinds', con_lie `plusLIE` rbinds_lie)
389 -- The main complication with RecordUpd is that we need to explicitly
390 -- handle the *non-updated* fields. Consider:
392 -- data T a b = MkT1 { fa :: a, fb :: b }
393 -- | MkT2 { fa :: a, fc :: Int -> Int }
394 -- | MkT3 { fd :: a }
396 -- upd :: T a b -> c -> T a c
397 -- upd t x = t { fb = x}
399 -- The type signature on upd is correct (i.e. the result should not be (T a b))
400 -- because upd should be equivalent to:
402 -- upd t x = case t of
403 -- MkT1 p q -> MkT1 p x
404 -- MkT2 a b -> MkT2 p b
405 -- MkT3 d -> error ...
407 -- So we need to give a completely fresh type to the result record,
408 -- and then constrain it by the fields that are *not* updated ("p" above).
410 -- Note that because MkT3 doesn't contain all the fields being updated,
411 -- its RHS is simply an error, so it doesn't impose any type constraints
413 -- All this is done in STEP 4 below.
415 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
416 = tcAddErrCtxt (recordUpdCtxt expr) $
419 -- Check that the field names are really field names
420 ASSERT( not (null rbinds) )
422 field_names = [field_name | (field_name, _, _) <- rbinds]
424 mapNF_Tc tcLookupGlobal_maybe field_names `thenNF_Tc` \ maybe_sel_ids ->
426 bad_guys = [ addErrTc (notSelector field_name)
427 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
429 Just (AnId sel_id) -> not (isRecordSelector sel_id)
433 checkTcM (null bad_guys) (listNF_Tc bad_guys `thenNF_Tc_` failTc) `thenTc_`
436 -- Figure out the tycon and data cons from the first field name
438 -- It's OK to use the non-tc splitters here (for a selector)
439 (Just (AnId sel_id) : _) = maybe_sel_ids
440 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
441 -- when the data type has a context
442 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
443 tycon = tcTyConAppTyCon data_ty
444 data_cons = tyConDataCons tycon
445 (con_tyvars, _, _, _, _, _) = dataConSig (head data_cons)
447 tcInstTyVars VanillaTv con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) ->
450 -- Check that at least one constructor has all the named fields
451 -- i.e. has an empty set of bad fields returned by badFields
452 checkTc (any (null . badFields rbinds) data_cons)
453 (badFieldsUpd rbinds) `thenTc_`
456 -- Typecheck the update bindings.
457 -- (Do this after checking for bad fields in case there's a field that
458 -- doesn't match the constructor.)
460 result_record_ty = mkTyConApp tycon result_inst_tys
462 unifyTauTy res_ty result_record_ty `thenTc_`
463 tcRecordBinds tycon result_inst_tys rbinds `thenTc` \ (rbinds', rbinds_lie) ->
466 -- Use the un-updated fields to find a vector of booleans saying
467 -- which type arguments must be the same in updatee and result.
469 -- WARNING: this code assumes that all data_cons in a common tycon
470 -- have FieldLabels abstracted over the same tyvars.
472 upd_field_lbls = [recordSelectorFieldLabel sel_id | (sel_id, _, _) <- rbinds']
473 con_field_lbls_s = map dataConFieldLabels data_cons
475 -- A constructor is only relevant to this process if
476 -- it contains all the fields that are being updated
477 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
478 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
480 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
481 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
483 mk_inst_ty (tyvar, result_inst_ty)
484 | tyvar `elemVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type
485 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
487 mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys ->
490 -- Typecheck the expression to be updated
492 record_ty = mkTyConApp tycon inst_tys
494 tcMonoExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) ->
497 -- Figure out the LIE we need. We have to generate some
498 -- dictionaries for the data type context, since we are going to
499 -- do some construction.
501 -- What dictionaries do we need? For the moment we assume that all
502 -- data constructors have the same context, and grab it from the first
503 -- constructor. If they have varying contexts then we'd have to
504 -- union the ones that could participate in the update.
506 (tyvars, theta, _, _, _, _) = dataConSig (head data_cons)
507 inst_env = mkTopTyVarSubst tyvars result_inst_tys
508 theta' = substTheta inst_env theta
510 newDicts RecordUpdOrigin theta' `thenNF_Tc` \ dicts ->
513 returnTc (RecordUpdOut record_expr' record_ty result_record_ty (map instToId dicts) rbinds',
514 mkLIE dicts `plusLIE` record_lie `plusLIE` rbinds_lie)
516 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
517 = unifyListTy res_ty `thenTc` \ elt_ty ->
518 tcMonoExpr expr elt_ty `thenTc` \ (expr', lie1) ->
520 tcLookupGlobalId enumFromName `thenNF_Tc` \ sel_id ->
521 newMethod (ArithSeqOrigin seq)
522 sel_id [elt_ty] `thenNF_Tc` \ enum_from ->
524 returnTc (ArithSeqOut (HsVar (instToId enum_from)) (From expr'),
525 lie1 `plusLIE` unitLIE enum_from)
527 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
528 = tcAddErrCtxt (arithSeqCtxt in_expr) $
529 unifyListTy res_ty `thenTc` \ elt_ty ->
530 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
531 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
532 tcLookupGlobalId enumFromThenName `thenNF_Tc` \ sel_id ->
533 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_then ->
535 returnTc (ArithSeqOut (HsVar (instToId enum_from_then))
536 (FromThen expr1' expr2'),
537 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_then)
539 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
540 = tcAddErrCtxt (arithSeqCtxt in_expr) $
541 unifyListTy res_ty `thenTc` \ elt_ty ->
542 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
543 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
544 tcLookupGlobalId enumFromToName `thenNF_Tc` \ sel_id ->
545 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
547 returnTc (ArithSeqOut (HsVar (instToId enum_from_to))
548 (FromTo expr1' expr2'),
549 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
551 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
552 = tcAddErrCtxt (arithSeqCtxt in_expr) $
553 unifyListTy res_ty `thenTc` \ elt_ty ->
554 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
555 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
556 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
557 tcLookupGlobalId enumFromThenToName `thenNF_Tc` \ sel_id ->
558 newMethod (ArithSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
560 returnTc (ArithSeqOut (HsVar (instToId eft))
561 (FromThenTo expr1' expr2' expr3'),
562 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
564 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
565 = tcAddErrCtxt (parrSeqCtxt in_expr) $
566 unifyPArrTy res_ty `thenTc` \ elt_ty ->
567 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
568 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
569 tcLookupGlobalId enumFromToPName `thenNF_Tc` \ sel_id ->
570 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ enum_from_to ->
572 returnTc (PArrSeqOut (HsVar (instToId enum_from_to))
573 (FromTo expr1' expr2'),
574 lie1 `plusLIE` lie2 `plusLIE` unitLIE enum_from_to)
576 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
577 = tcAddErrCtxt (parrSeqCtxt in_expr) $
578 unifyPArrTy res_ty `thenTc` \ elt_ty ->
579 tcMonoExpr expr1 elt_ty `thenTc` \ (expr1',lie1) ->
580 tcMonoExpr expr2 elt_ty `thenTc` \ (expr2',lie2) ->
581 tcMonoExpr expr3 elt_ty `thenTc` \ (expr3',lie3) ->
582 tcLookupGlobalId enumFromThenToPName `thenNF_Tc` \ sel_id ->
583 newMethod (PArrSeqOrigin seq) sel_id [elt_ty] `thenNF_Tc` \ eft ->
585 returnTc (PArrSeqOut (HsVar (instToId eft))
586 (FromThenTo expr1' expr2' expr3'),
587 lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` unitLIE eft)
589 tcMonoExpr (PArrSeqIn _) _
590 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
591 -- the parser shouldn't have generated it and the renamer shouldn't have
595 %************************************************************************
597 \subsection{Implicit Parameter bindings}
599 %************************************************************************
602 tcMonoExpr (HsWith expr binds) res_ty
603 = tcMonoExpr expr res_ty `thenTc` \ (expr', expr_lie) ->
604 mapAndUnzip3Tc tcIPBind binds `thenTc` \ (avail_ips, binds', bind_lies) ->
606 -- If the binding binds ?x = E, we must now
607 -- discharge any ?x constraints in expr_lie
608 tcSimplifyIPs avail_ips expr_lie `thenTc` \ (expr_lie', dict_binds) ->
610 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
612 returnTc (HsWith expr'' binds', expr_lie' `plusLIE` plusLIEs bind_lies)
615 = newTyVarTy openTypeKind `thenTc` \ ty ->
616 tcGetSrcLoc `thenTc` \ loc ->
617 newIPDict (IPBind ip) ip ty `thenNF_Tc` \ (ip', ip_inst) ->
618 tcMonoExpr expr ty `thenTc` \ (expr', lie) ->
619 returnTc (ip_inst, (ip', expr'), lie)
622 %************************************************************************
624 \subsection{@tcApp@ typchecks an application}
626 %************************************************************************
630 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
631 -> TcType -- Expected result type of application
632 -> TcM (TcExpr, LIE) -- Translated fun and args
634 tcApp (HsApp e1 e2) args res_ty
635 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
637 tcApp fun args res_ty
638 = -- First type-check the function
639 tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) ->
641 tcAddErrCtxt (wrongArgsCtxt "too many" fun args) (
642 split_fun_ty fun_ty (length args)
643 ) `thenTc` \ (expected_arg_tys, actual_result_ty) ->
645 -- Now typecheck the args
646 mapAndUnzipTc (tcArg fun)
647 (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) ->
649 -- Unify with expected result after type-checking the args
650 -- so that the info from args percolates to actual_result_ty.
651 -- This is when we might detect a too-few args situation.
652 -- (One can think of cases when the opposite order would give
653 -- a better error message.)
654 tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
655 (tcSub res_ty actual_result_ty) `thenTc` \ (co_fn, lie_res) ->
657 returnTc (co_fn <$> foldl HsApp fun' args',
658 lie_res `plusLIE` lie_fun `plusLIE` plusLIEs lie_args_s)
661 -- If an error happens we try to figure out whether the
662 -- function has been given too many or too few arguments,
664 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
665 = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' ->
666 zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' ->
668 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
669 (env2, act_ty'') = tidyOpenType env1 act_ty'
670 (exp_args, _) = tcSplitFunTys exp_ty''
671 (act_args, _) = tcSplitFunTys act_ty''
673 len_act_args = length act_args
674 len_exp_args = length exp_args
676 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
677 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
678 | otherwise = appCtxt fun args
680 returnNF_Tc (env2, message)
683 split_fun_ty :: TcType -- The type of the function
684 -> Int -- Number of arguments
685 -> TcM ([TcType], -- Function argument types
686 TcType) -- Function result types
688 split_fun_ty fun_ty 0
689 = returnTc ([], fun_ty)
691 split_fun_ty fun_ty n
692 = -- Expect the function to have type A->B
693 unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) ->
694 split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) ->
695 returnTc (arg_ty:arg_tys, final_res_ty)
699 tcArg :: RenamedHsExpr -- The function (for error messages)
700 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
701 -> TcM (TcExpr, LIE) -- Resulting argument and LIE
703 tcArg the_fun (arg, expected_arg_ty, arg_no)
704 = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $
705 tcExpr arg expected_arg_ty
709 %************************************************************************
711 \subsection{@tcId@ typchecks an identifier occurrence}
713 %************************************************************************
715 tcId instantiates an occurrence of an Id.
716 The instantiate_it loop runs round instantiating the Id.
717 It has to be a loop because we are now prepared to entertain
719 f:: forall a. Eq a => forall b. Baz b => tau
720 We want to instantiate this to
721 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
723 The -fno-method-sharing flag controls what happens so far as the LIE
724 is concerned. The default case is that for an overloaded function we
725 generate a "method" Id, and add the Method Inst to the LIE. So you get
728 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
729 If you specify -fno-method-sharing, the dictionary application
730 isn't shared, so we get
732 f = /\a (d:Num a) (x:a) -> (+) a d x x
733 This gets a bit less sharing, but
734 a) it's better for RULEs involving overloaded functions
735 b) perhaps fewer separated lambdas
738 tcId :: Name -> NF_TcM (TcExpr, LIE, TcType)
739 tcId name -- Look up the Id and instantiate its type
740 = tcLookupId name `thenNF_Tc` \ id ->
741 loop (OccurrenceOf id) (HsVar id) emptyLIE (idType id)
743 loop orig (HsVar fun_id) lie fun_ty
744 | want_method_inst fun_ty
745 = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) ->
746 newMethodWithGivenTy orig fun_id
747 (mkTyVarTys tyvars) theta tau `thenNF_Tc` \ meth ->
748 loop orig (HsVar (instToId meth))
749 (unitLIE meth `plusLIE` lie) tau
751 loop orig fun lie fun_ty
753 = tcInstCall orig fun_ty `thenNF_Tc` \ (inst_fn, inst_lie, tau) ->
754 loop orig (inst_fn fun) (inst_lie `plusLIE` lie) tau
757 = returnNF_Tc (fun, lie, fun_ty)
759 want_method_inst fun_ty
760 | opt_NoMethodSharing = False
761 | otherwise = case tcSplitSigmaTy fun_ty of
762 (_,[],_) -> False -- Not overloaded
763 (_,theta,_) -> not (any isLinearPred theta)
764 -- This is a slight hack.
765 -- If f :: (%x :: T) => Int -> Int
766 -- Then if we have two separate calls, (f 3, f 4), we cannot
767 -- make a method constraint that then gets shared, thus:
768 -- let m = f %x in (m 3, m 4)
769 -- because that loses the linearity of the constraint.
770 -- The simplest thing to do is never to construct a method constraint
771 -- in the first place that has a linear implicit parameter in it.
774 Typecheck expression which in most cases will be an Id.
775 The expression can return a higher-ranked type, such as
776 (forall a. a->a) -> Int
777 so we must create a HoleTyVarTy to pass in as the expected tyvar.
780 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, LIE, TcType)
781 tcExpr_id (HsVar name) = tcId name
782 tcExpr_id expr = newHoleTyVarTy `thenNF_Tc` \ id_ty ->
783 tcMonoExpr expr id_ty `thenTc` \ (expr', lie_id) ->
784 returnTc (expr', lie_id, id_ty)
788 %************************************************************************
790 \subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
792 %************************************************************************
795 -- I don't like this lumping together of do expression and list/array
796 -- comprehensions; creating the monad instances is entirely pointless in the
797 -- latter case; I'll leave the list case as it is for the moment, but handle
798 -- arrays extra (would be better to handle arrays and lists together, though)
801 tcDoStmts PArrComp stmts src_loc res_ty
803 ASSERT( not (null stmts) )
804 tcAddSrcLoc src_loc $
806 unifyPArrTy res_ty `thenTc` \elt_ty ->
807 let tc_ty = mkTyConTy parrTyCon
808 m_ty = (mkPArrTy, elt_ty)
810 tcStmts (DoCtxt PArrComp) m_ty stmts `thenTc` \(stmts', stmts_lie) ->
811 returnTc (HsDoOut PArrComp stmts'
812 undefined undefined undefined -- don't touch!
816 tcDoStmts do_or_lc stmts src_loc res_ty
817 = -- get the Monad and MonadZero classes
818 -- create type consisting of a fresh monad tyvar
819 ASSERT( not (null stmts) )
820 tcAddSrcLoc src_loc $
822 -- If it's a comprehension we're dealing with,
823 -- force it to be a list comprehension.
824 -- (as of Haskell 98, monad comprehensions are no more.)
825 -- Similarily, array comprehensions must involve parallel arrays types
828 ListComp -> unifyListTy res_ty `thenTc` \ elt_ty ->
829 returnNF_Tc (mkTyConTy listTyCon, (mkListTy, elt_ty))
831 PArrComp -> panic "TcExpr.tcDoStmts: How did we get here?!?"
833 _ -> newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenNF_Tc` \ m_ty ->
834 newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
835 unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenTc_`
836 returnNF_Tc (m_ty, (mkAppTy m_ty, elt_ty))
837 ) `thenNF_Tc` \ (tc_ty, m_ty) ->
839 tcStmts (DoCtxt do_or_lc) m_ty stmts `thenTc` \ (stmts', stmts_lie) ->
841 -- Build the then and zero methods in case we need them
842 -- It's important that "then" and "return" appear just once in the final LIE,
843 -- not only for typechecker efficiency, but also because otherwise during
844 -- simplification we end up with silly stuff like
845 -- then = case d of (t,r) -> t
847 -- where the second "then" sees that it already exists in the "available" stuff.
849 tcLookupGlobalId returnMName `thenNF_Tc` \ return_sel_id ->
850 tcLookupGlobalId thenMName `thenNF_Tc` \ then_sel_id ->
851 tcLookupGlobalId failMName `thenNF_Tc` \ fail_sel_id ->
852 newMethod DoOrigin return_sel_id [tc_ty] `thenNF_Tc` \ return_inst ->
853 newMethod DoOrigin then_sel_id [tc_ty] `thenNF_Tc` \ then_inst ->
854 newMethod DoOrigin fail_sel_id [tc_ty] `thenNF_Tc` \ fail_inst ->
856 monad_lie = mkLIE [return_inst, then_inst, fail_inst]
858 returnTc (HsDoOut do_or_lc stmts'
859 (instToId return_inst) (instToId then_inst) (instToId fail_inst)
861 stmts_lie `plusLIE` monad_lie)
865 %************************************************************************
867 \subsection{Record bindings}
869 %************************************************************************
871 Game plan for record bindings
872 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
873 1. Find the TyCon for the bindings, from the first field label.
875 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
877 For each binding field = value
879 3. Instantiate the field type (from the field label) using the type
882 4 Type check the value using tcArg, passing the field type as
883 the expected argument type.
885 This extends OK when the field types are universally quantified.
890 :: TyCon -- Type constructor for the record
891 -> [TcType] -- Args of this type constructor
892 -> RenamedRecordBinds
893 -> TcM (TcRecordBinds, LIE)
895 tcRecordBinds tycon ty_args rbinds
896 = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) ->
897 returnTc (rbinds', plusLIEs lies)
899 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
901 do_bind (field_lbl_name, rhs, pun_flag)
902 = tcLookupGlobalId field_lbl_name `thenNF_Tc` \ sel_id ->
904 field_lbl = recordSelectorFieldLabel sel_id
905 field_ty = substTy tenv (fieldLabelType field_lbl)
907 ASSERT( isRecordSelector sel_id )
908 -- This lookup and assertion will surely succeed, because
909 -- we check that the fields are indeed record selectors
910 -- before calling tcRecordBinds
911 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
912 -- The caller of tcRecordBinds has already checked
913 -- that all the fields come from the same type
915 tcExpr rhs field_ty `thenTc` \ (rhs', lie) ->
917 returnTc ((sel_id, rhs', pun_flag), lie)
919 badFields rbinds data_con
920 = [field_name | (field_name, _, _) <- rbinds,
921 not (field_name `elem` field_names)
924 field_names = map fieldLabelName (dataConFieldLabels data_con)
926 missingFields rbinds data_con
927 | null field_labels = ([], []) -- Not declared as a record;
928 -- But C{} is still valid
930 = (missing_strict_fields, other_missing_fields)
932 missing_strict_fields
933 = [ fl | (fl, str) <- field_info,
935 not (fieldLabelName fl `elem` field_names_used)
938 = [ fl | (fl, str) <- field_info,
939 not (isMarkedStrict str),
940 not (fieldLabelName fl `elem` field_names_used)
943 field_names_used = [ field_name | (field_name, _, _) <- rbinds ]
944 field_labels = dataConFieldLabels data_con
946 field_info = zipEqual "missingFields"
948 (dropList ex_theta (dataConStrictMarks data_con))
949 -- The 'drop' is because dataConStrictMarks
950 -- includes the existential dictionaries
951 (_, _, _, ex_theta, _, _) = dataConSig data_con
954 %************************************************************************
956 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
958 %************************************************************************
961 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM ([TcExpr], LIE)
963 tcMonoExprs [] [] = returnTc ([], emptyLIE)
964 tcMonoExprs (expr:exprs) (ty:tys)
965 = tcMonoExpr expr ty `thenTc` \ (expr', lie1) ->
966 tcMonoExprs exprs tys `thenTc` \ (exprs', lie2) ->
967 returnTc (expr':exprs', lie1 `plusLIE` lie2)
971 %************************************************************************
973 \subsection{Literals}
975 %************************************************************************
980 tcLit :: HsLit -> TcType -> TcM (TcExpr, LIE)
981 tcLit (HsLitLit s _) res_ty
982 = tcLookupClass cCallableClassName `thenNF_Tc` \ cCallableClass ->
983 newDicts (LitLitOrigin (_UNPK_ s))
984 [mkClassPred cCallableClass [res_ty]] `thenNF_Tc` \ dicts ->
985 returnTc (HsLit (HsLitLit s res_ty), mkLIE dicts)
988 = unifyTauTy res_ty (simpleHsLitTy lit) `thenTc_`
989 returnTc (HsLit lit, emptyLIE)
993 %************************************************************************
995 \subsection{Errors and contexts}
997 %************************************************************************
1001 Boring and alphabetical:
1004 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1007 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1010 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1013 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1016 = hang (ptext SLIT("When checking the type signature of the expression:"))
1020 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1023 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1026 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1029 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1031 funAppCtxt fun arg arg_no
1032 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1033 quotes (ppr fun) <> text ", namely"])
1034 4 (quotes (ppr arg))
1036 wrongArgsCtxt too_many_or_few fun args
1037 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1038 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1039 <+> ptext SLIT("arguments in the call"))
1040 4 (parens (ppr the_app))
1042 the_app = foldl HsApp fun args -- Used in error messages
1045 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1047 the_app = foldl HsApp fun args -- Used in error messages
1049 lurkingRank2Err fun fun_ty
1050 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1051 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1052 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1055 = hang (ptext SLIT("No constructor has all these fields:"))
1056 4 (pprQuotedList fields)
1058 fields = [field | (field, _, _) <- rbinds]
1060 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1061 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1064 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1066 missingStrictFieldCon :: Name -> FieldLabel -> SDoc
1067 missingStrictFieldCon con field
1068 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
1069 ptext SLIT("does not have the required strict field"), quotes (ppr field)]
1071 missingFieldCon :: Name -> FieldLabel -> SDoc
1072 missingFieldCon con field
1073 = hsep [ptext SLIT("Field") <+> quotes (ppr field),
1074 ptext SLIT("is not initialised")]