2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcCheckSigma, tcCheckRho, tcInferRho, tcMonoExpr ) where
9 #include "HsVersions.h"
11 #ifdef GHCI /* Only if bootstrapped */
12 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
14 import TcType ( isTauTy )
15 import TcEnv ( checkWellStaged )
16 import qualified DsMeta
19 import HsSyn ( HsExpr(..), LHsExpr, HsLit(..), ArithSeqInfo(..), recBindFields,
20 HsMatchContext(..), HsRecordBinds, mkHsApp, nlHsVar,
22 import TcHsSyn ( hsLitType, mkHsDictApp, mkHsTyApp, (<$>) )
24 import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedTo, tcSubExp, tcGen,
25 unifyFunTy, zapToListTy, zapToPArrTy, zapToTupleTy )
26 import BasicTypes ( isMarkedStrict )
27 import Inst ( InstOrigin(..),
28 newOverloadedLit, newMethodFromName, newIPDict,
29 newDicts, newMethodWithGivenTy,
30 instToId, tcInstCall, tcInstDataCon
32 import TcBinds ( tcBindsAndThen )
33 import TcEnv ( tcLookup, tcLookupId, checkProcLevel,
34 tcLookupDataCon, tcLookupGlobalId
36 import TcArrows ( tcProc )
37 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig, TcMatchCtxt(..) )
38 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
39 import TcPat ( badFieldCon )
40 import TcMType ( tcInstTyVars, tcInstType, newTyVarTy, zonkTcType )
41 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
42 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
43 isSigmaTy, mkFunTy, mkFunTys,
44 mkTyConApp, tyVarsOfTypes, isLinearPred,
45 liftedTypeKind, openTypeKind,
46 tcSplitSigmaTy, tidyOpenType
48 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
49 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
50 import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks, dataConWrapId )
52 import TyCon ( TyCon, tyConTyVars, tyConTheta, tyConDataCons )
53 import Subst ( mkTopTyVarSubst, substTheta, substTy )
54 import VarSet ( emptyVarSet, elemVarSet )
55 import TysWiredIn ( boolTy )
56 import PrelNames ( enumFromName, enumFromThenName,
57 enumFromToName, enumFromThenToName,
58 enumFromToPName, enumFromThenToPName
60 import ListSetOps ( minusList )
62 import HscTypes ( TyThing(..) )
63 import SrcLoc ( Located(..), unLoc, getLoc )
69 import TyCon ( isAlgTyCon )
73 %************************************************************************
75 \subsection{Main wrappers}
77 %************************************************************************
80 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
81 tcCheckSigma :: LHsExpr Name -- Expession to type check
82 -> TcSigmaType -- Expected type (could be a polytpye)
83 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
85 tcCheckSigma expr expected_ty
86 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
87 tc_expr' expr expected_ty
89 tc_expr' expr sigma_ty
91 = tcGen sigma_ty emptyVarSet (
92 \ rho_ty -> tcCheckRho expr rho_ty
93 ) `thenM` \ (gen_fn, expr') ->
94 returnM (L (getLoc expr') (gen_fn <$> unLoc expr'))
96 tc_expr' expr rho_ty -- Monomorphic case
97 = tcCheckRho expr rho_ty
100 Typecheck expression which in most cases will be an Id.
101 The expression can return a higher-ranked type, such as
102 (forall a. a->a) -> Int
103 so we must create a hole to pass in as the expected tyvar.
106 tcCheckRho :: LHsExpr Name -> TcRhoType -> TcM (LHsExpr TcId)
107 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
109 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
110 tcInferRho (L loc (HsVar name)) = addSrcSpan loc $
111 do { (e,ty) <- tcId name; return (L loc e, ty)}
112 tcInferRho expr = newHole `thenM` \ hole ->
113 tcMonoExpr expr (Infer hole) `thenM` \ expr' ->
114 readMutVar hole `thenM` \ rho_ty ->
115 returnM (expr', rho_ty)
120 %************************************************************************
122 \subsection{The TAUT rules for variables}TcExpr
124 %************************************************************************
127 tcMonoExpr :: LHsExpr Name -- Expession to type check
128 -> Expected TcRhoType -- Expected type (could be a type variable)
129 -- Definitely no foralls at the top
131 -> TcM (LHsExpr TcId)
133 tcMonoExpr (L loc expr) res_ty
134 = addSrcSpan loc (do { expr' <- tc_expr expr res_ty
135 ; return (L loc expr') })
137 tc_expr :: HsExpr Name -> Expected TcRhoType -> TcM (HsExpr TcId)
138 tc_expr (HsVar name) res_ty
139 = tcId name `thenM` \ (expr', id_ty) ->
140 tcSubExp res_ty id_ty `thenM` \ co_fn ->
141 returnM (co_fn <$> expr')
143 tc_expr (HsIPVar ip) res_ty
144 = -- Implicit parameters must have a *tau-type* not a
145 -- type scheme. We enforce this by creating a fresh
146 -- type variable as its type. (Because res_ty may not
148 newTyVarTy openTypeKind `thenM` \ ip_ty ->
149 newIPDict (IPOccOrigin ip) ip ip_ty `thenM` \ (ip', inst) ->
150 extendLIE inst `thenM_`
151 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
152 returnM (co_fn <$> HsIPVar ip')
156 %************************************************************************
158 \subsection{Expressions type signatures}
160 %************************************************************************
163 tc_expr in_expr@(ExprWithTySig expr poly_ty) res_ty
164 = addErrCtxt (exprSigCtxt in_expr) $
165 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
166 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
167 returnM (co_fn <$> unLoc expr')
170 tc_expr (HsType ty) res_ty
171 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
172 -- This is the syntax for type applications that I was planning
173 -- but there are difficulties (e.g. what order for type args)
174 -- so it's not enabled yet.
175 -- Can't eliminate it altogether from the parser, because the
176 -- same parser parses *patterns*.
180 %************************************************************************
182 \subsection{Other expression forms}
184 %************************************************************************
187 tc_expr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
188 returnM (HsPar expr')
189 tc_expr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
190 returnM (HsSCC lbl expr')
191 tc_expr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
192 returnM (HsCoreAnn lbl expr')
194 tc_expr (HsLit lit) res_ty = tcLit lit res_ty
196 tc_expr (HsOverLit lit) res_ty
197 = zapExpectedType res_ty `thenM` \ res_ty' ->
198 newOverloadedLit (LiteralOrigin lit) lit res_ty' `thenM` \ lit_expr ->
199 returnM (unLoc lit_expr) -- ToDo: nasty unLoc
201 tc_expr (NegApp expr neg_name) res_ty
202 = tc_expr (HsApp (nlHsVar neg_name) expr) res_ty
203 -- ToDo: use tcSyntaxName
205 tc_expr (HsLam match) res_ty
206 = tcMatchLambda match res_ty `thenM` \ match' ->
207 returnM (HsLam match')
209 tc_expr (HsApp e1 e2) res_ty
210 = tcApp e1 [e2] res_ty
213 Note that the operators in sections are expected to be binary, and
214 a type error will occur if they aren't.
217 -- Left sections, equivalent to
224 tc_expr in_expr@(SectionL arg1 op) res_ty
225 = tcInferRho op `thenM` \ (op', op_ty) ->
226 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
227 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
228 addErrCtxt (exprCtxt in_expr) $
229 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
230 returnM (co_fn <$> SectionL arg1' op')
232 -- Right sections, equivalent to \ x -> x op expr, or
235 tc_expr in_expr@(SectionR op arg2) res_ty
236 = tcInferRho op `thenM` \ (op', op_ty) ->
237 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
238 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
239 addErrCtxt (exprCtxt in_expr) $
240 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
241 returnM (co_fn <$> SectionR op' arg2')
243 -- equivalent to (op e1) e2:
245 tc_expr in_expr@(OpApp arg1 op fix arg2) res_ty
246 = tcInferRho op `thenM` \ (op', op_ty) ->
247 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
248 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
249 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
250 addErrCtxt (exprCtxt in_expr) $
251 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
252 returnM (OpApp arg1' op' fix arg2')
256 tc_expr (HsLet binds (L loc expr)) res_ty
259 binds -- Bindings to check
260 (tc_expr expr res_ty)
262 glue bind expr = HsLet [bind] (L loc expr)
264 tc_expr in_expr@(HsCase scrut matches) res_ty
265 = addErrCtxt (caseCtxt in_expr) $
267 -- Typecheck the case alternatives first.
268 -- The case patterns tend to give good type info to use
269 -- when typechecking the scrutinee. For example
272 -- will report that map is applied to too few arguments
274 tcMatchesCase match_ctxt matches res_ty `thenM` \ (scrut_ty, matches') ->
276 addErrCtxt (caseScrutCtxt scrut) (
277 tcCheckRho scrut scrut_ty
278 ) `thenM` \ scrut' ->
280 returnM (HsCase scrut' matches')
282 match_ctxt = MC { mc_what = CaseAlt,
283 mc_body = tcMonoExpr }
285 tc_expr (HsIf pred b1 b2) res_ty
286 = addErrCtxt (predCtxt pred) (
287 tcCheckRho pred boolTy ) `thenM` \ pred' ->
289 zapExpectedType res_ty `thenM` \ res_ty' ->
290 -- C.f. the call to zapToType in TcMatches.tcMatches
292 tcCheckRho b1 res_ty' `thenM` \ b1' ->
293 tcCheckRho b2 res_ty' `thenM` \ b2' ->
294 returnM (HsIf pred' b1' b2')
296 tc_expr (HsDo do_or_lc stmts method_names _) res_ty
297 = zapExpectedType res_ty `thenM` \ res_ty' ->
298 -- All comprehensions yield a monotype
299 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
300 returnM (HsDo do_or_lc stmts' methods' res_ty')
302 tc_expr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
303 = zapToListTy res_ty `thenM` \ elt_ty ->
304 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
305 returnM (ExplicitList elt_ty exprs')
308 = addErrCtxt (listCtxt expr) $
309 tcCheckRho expr elt_ty
311 tc_expr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
312 = zapToPArrTy res_ty `thenM` \ elt_ty ->
313 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
314 returnM (ExplicitPArr elt_ty exprs')
317 = addErrCtxt (parrCtxt expr) $
318 tcCheckRho expr elt_ty
320 tc_expr (ExplicitTuple exprs boxity) res_ty
321 = zapToTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
322 tcCheckRhos exprs arg_tys `thenM` \ exprs' ->
323 returnM (ExplicitTuple exprs' boxity)
325 tc_expr (HsProc pat cmd) res_ty
326 = tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
327 returnM (HsProc pat' cmd')
330 %************************************************************************
332 Record construction and update
334 %************************************************************************
337 tc_expr expr@(RecordCon con@(L _ con_name) rbinds) res_ty
338 = addErrCtxt (recordConCtxt expr) $
339 addLocM tcId con `thenM` \ (con_expr, con_tau) ->
341 (_, record_ty) = tcSplitFunTys con_tau
342 (tycon, ty_args) = tcSplitTyConApp record_ty
344 ASSERT( isAlgTyCon tycon )
345 zapExpectedTo res_ty record_ty `thenM_`
347 -- Check that the record bindings match the constructor
348 -- con_name is syntactically constrained to be a data constructor
349 tcLookupDataCon con_name `thenM` \ data_con ->
351 bad_fields = badFields rbinds data_con
353 if notNull bad_fields then
354 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
355 failM -- Fail now, because tcRecordBinds will crash on a bad field
358 -- Typecheck the record bindings
359 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
361 -- Check for missing fields
362 checkMissingFields data_con rbinds `thenM_`
364 getSrcSpanM `thenM` \ loc ->
365 returnM (RecordConOut data_con (L loc con_expr) rbinds')
367 -- The main complication with RecordUpd is that we need to explicitly
368 -- handle the *non-updated* fields. Consider:
370 -- data T a b = MkT1 { fa :: a, fb :: b }
371 -- | MkT2 { fa :: a, fc :: Int -> Int }
372 -- | MkT3 { fd :: a }
374 -- upd :: T a b -> c -> T a c
375 -- upd t x = t { fb = x}
377 -- The type signature on upd is correct (i.e. the result should not be (T a b))
378 -- because upd should be equivalent to:
380 -- upd t x = case t of
381 -- MkT1 p q -> MkT1 p x
382 -- MkT2 a b -> MkT2 p b
383 -- MkT3 d -> error ...
385 -- So we need to give a completely fresh type to the result record,
386 -- and then constrain it by the fields that are *not* updated ("p" above).
388 -- Note that because MkT3 doesn't contain all the fields being updated,
389 -- its RHS is simply an error, so it doesn't impose any type constraints
391 -- All this is done in STEP 4 below.
393 tc_expr expr@(RecordUpd record_expr rbinds) res_ty
394 = addErrCtxt (recordUpdCtxt expr) $
397 -- Check that the field names are really field names
398 ASSERT( notNull rbinds )
400 field_names = map fst rbinds
402 mappM (tcLookupGlobalId.unLoc) field_names `thenM` \ sel_ids ->
403 -- The renamer has already checked that they
406 bad_guys = [ addSrcSpan loc $ addErrTc (notSelector field_name)
407 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
408 not (isRecordSelector sel_id) -- Excludes class ops
411 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
414 -- Figure out the tycon and data cons from the first field name
416 -- It's OK to use the non-tc splitters here (for a selector)
418 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
419 tycon = fieldLabelTyCon field_lbl -- it's not a field label
420 data_cons = tyConDataCons tycon
421 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
423 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
426 -- Check that at least one constructor has all the named fields
427 -- i.e. has an empty set of bad fields returned by badFields
428 checkTc (any (null . badFields rbinds) data_cons)
429 (badFieldsUpd rbinds) `thenM_`
432 -- Typecheck the update bindings.
433 -- (Do this after checking for bad fields in case there's a field that
434 -- doesn't match the constructor.)
436 result_record_ty = mkTyConApp tycon result_inst_tys
438 zapExpectedTo res_ty result_record_ty `thenM_`
439 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
442 -- Use the un-updated fields to find a vector of booleans saying
443 -- which type arguments must be the same in updatee and result.
445 -- WARNING: this code assumes that all data_cons in a common tycon
446 -- have FieldLabels abstracted over the same tyvars.
448 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
449 con_field_lbls_s = map dataConFieldLabels data_cons
451 -- A constructor is only relevant to this process if
452 -- it contains all the fields that are being updated
453 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
454 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
456 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
457 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
459 mk_inst_ty (tyvar, result_inst_ty)
460 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
461 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
463 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
466 -- Typecheck the expression to be updated
468 record_ty = mkTyConApp tycon inst_tys
470 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
473 -- Figure out the LIE we need. We have to generate some
474 -- dictionaries for the data type context, since we are going to
475 -- do pattern matching over the data cons.
477 -- What dictionaries do we need?
478 -- We just take the context of the type constructor
480 theta' = substTheta inst_env (tyConTheta tycon)
482 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
483 extendLIEs dicts `thenM_`
486 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
490 %************************************************************************
492 Arithmetic sequences e.g. [a,b..]
493 and their parallel-array counterparts e.g. [: a,b.. :]
496 %************************************************************************
499 tc_expr (ArithSeqIn seq@(From expr)) res_ty
500 = zapToListTy res_ty `thenM` \ elt_ty ->
501 tcCheckRho expr elt_ty `thenM` \ expr' ->
503 newMethodFromName (ArithSeqOrigin seq)
504 elt_ty enumFromName `thenM` \ enum_from ->
506 returnM (ArithSeqOut (nlHsVar enum_from) (From expr'))
508 tc_expr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
509 = addErrCtxt (arithSeqCtxt in_expr) $
510 zapToListTy res_ty `thenM` \ elt_ty ->
511 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
512 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
513 newMethodFromName (ArithSeqOrigin seq)
514 elt_ty enumFromThenName `thenM` \ enum_from_then ->
516 returnM (ArithSeqOut (nlHsVar enum_from_then) (FromThen expr1' expr2'))
519 tc_expr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
520 = addErrCtxt (arithSeqCtxt in_expr) $
521 zapToListTy res_ty `thenM` \ elt_ty ->
522 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
523 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
524 newMethodFromName (ArithSeqOrigin seq)
525 elt_ty enumFromToName `thenM` \ enum_from_to ->
527 returnM (ArithSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
529 tc_expr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
530 = addErrCtxt (arithSeqCtxt in_expr) $
531 zapToListTy res_ty `thenM` \ elt_ty ->
532 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
533 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
534 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
535 newMethodFromName (ArithSeqOrigin seq)
536 elt_ty enumFromThenToName `thenM` \ eft ->
538 returnM (ArithSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
540 tc_expr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
541 = addErrCtxt (parrSeqCtxt in_expr) $
542 zapToPArrTy res_ty `thenM` \ elt_ty ->
543 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
544 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
545 newMethodFromName (PArrSeqOrigin seq)
546 elt_ty enumFromToPName `thenM` \ enum_from_to ->
548 returnM (PArrSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
550 tc_expr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
551 = addErrCtxt (parrSeqCtxt in_expr) $
552 zapToPArrTy res_ty `thenM` \ elt_ty ->
553 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
554 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
555 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
556 newMethodFromName (PArrSeqOrigin seq)
557 elt_ty enumFromThenToPName `thenM` \ eft ->
559 returnM (PArrSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
561 tc_expr (PArrSeqIn _) _
562 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
563 -- the parser shouldn't have generated it and the renamer shouldn't have
568 %************************************************************************
572 %************************************************************************
575 #ifdef GHCI /* Only if bootstrapped */
576 -- Rename excludes these cases otherwise
578 tc_expr (HsSplice n expr) res_ty = tcSpliceExpr n expr res_ty
579 tc_expr (HsBracket brack) res_ty = do
580 e <- tcBracket brack res_ty
586 %************************************************************************
590 %************************************************************************
593 tc_expr other _ = pprPanic "tcMonoExpr" (ppr other)
597 %************************************************************************
599 \subsection{@tcApp@ typchecks an application}
601 %************************************************************************
605 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
606 -> Expected TcRhoType -- Expected result type of application
607 -> TcM (HsExpr TcId) -- Translated fun and args
609 tcApp (L _ (HsApp e1 e2)) args res_ty
610 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
612 tcApp fun args res_ty
613 = -- First type-check the function
614 tcInferRho fun `thenM` \ (fun', fun_ty) ->
616 addErrCtxt (wrongArgsCtxt "too many" fun args) (
617 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
618 split_fun_ty fun_ty (length args)
619 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
621 -- Unify with expected result before (was: after) type-checking the args
622 -- so that the info from res_ty (was: args) percolates to args (was actual_result_ty).
623 -- This is when we might detect a too-few args situation.
624 -- (One can think of cases when the opposite order would give
625 -- a better error message.)
626 -- [March 2003: I'm experimenting with putting this first. Here's an
627 -- example where it actually makes a real difference
628 -- class C t a b | t a -> b
629 -- instance C Char a Bool
631 -- data P t a = forall b. (C t a b) => MkP b
632 -- data Q t = MkQ (forall a. P t a)
635 -- f1 = MkQ (MkP True)
636 -- f2 = MkQ (MkP True :: forall a. P Char a)
638 -- With the change, f1 will type-check, because the 'Char' info from
639 -- the signature is propagated into MkQ's argument. With the check
640 -- in the other order, the extra signature in f2 is reqd.]
642 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
643 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
645 -- Now typecheck the args
647 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
649 returnM (co_fn <$> unLoc (foldl mkHsApp fun' args'))
652 -- If an error happens we try to figure out whether the
653 -- function has been given too many or too few arguments,
655 -- The ~(Check...) is because in the Infer case the tcSubExp
656 -- definitely won't fail, so we can be certain we're in the Check branch
657 checkArgsCtxt fun args ~(Check expected_res_ty) actual_res_ty tidy_env
658 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
659 zonkTcType actual_res_ty `thenM` \ act_ty' ->
661 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
662 (env2, act_ty'') = tidyOpenType env1 act_ty'
663 (exp_args, _) = tcSplitFunTys exp_ty''
664 (act_args, _) = tcSplitFunTys act_ty''
666 len_act_args = length act_args
667 len_exp_args = length exp_args
669 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
670 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
671 | otherwise = appCtxt fun args
673 returnM (env2, message)
676 split_fun_ty :: TcRhoType -- The type of the function
677 -> Int -- Number of arguments
678 -> TcM ([TcType], -- Function argument types
679 TcType) -- Function result types
681 split_fun_ty fun_ty 0
682 = returnM ([], fun_ty)
684 split_fun_ty fun_ty n
685 = -- Expect the function to have type A->B
686 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
687 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
688 returnM (arg_ty:arg_tys, final_res_ty)
692 tcArg :: LHsExpr Name -- The function (for error messages)
693 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
694 -> TcM (LHsExpr TcId) -- Resulting argument
696 tcArg the_fun (arg, expected_arg_ty, arg_no)
697 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
698 tcCheckSigma arg expected_arg_ty
702 %************************************************************************
704 \subsection{@tcId@ typchecks an identifier occurrence}
706 %************************************************************************
708 tcId instantiates an occurrence of an Id.
709 The instantiate_it loop runs round instantiating the Id.
710 It has to be a loop because we are now prepared to entertain
712 f:: forall a. Eq a => forall b. Baz b => tau
713 We want to instantiate this to
714 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
716 The -fno-method-sharing flag controls what happens so far as the LIE
717 is concerned. The default case is that for an overloaded function we
718 generate a "method" Id, and add the Method Inst to the LIE. So you get
721 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
722 If you specify -fno-method-sharing, the dictionary application
723 isn't shared, so we get
725 f = /\a (d:Num a) (x:a) -> (+) a d x x
726 This gets a bit less sharing, but
727 a) it's better for RULEs involving overloaded functions
728 b) perhaps fewer separated lambdas
731 tcId :: Name -> TcM (HsExpr TcId, TcRhoType)
732 tcId name -- Look up the Id and instantiate its type
733 = -- First check whether it's a DataCon
734 -- Reason: we must not forget to chuck in the
735 -- constraints from their "silly context"
736 tcLookup name `thenM` \ thing ->
738 AGlobal (ADataCon data_con) -> inst_data_con data_con
739 ; AGlobal (AnId id) -> loop (HsVar id) (idType id)
740 -- A global cannot possibly be ill-staged
741 -- nor does it need the 'lifting' treatment
743 ; ATcId id th_level proc_level -> tc_local_id id th_level proc_level
744 ; other -> pprPanic "tcId" (ppr name $$ ppr thing)
749 tc_local_id id th_bind_lvl proc_lvl -- Non-TH case
750 = checkProcLevel id proc_lvl `thenM_`
751 loop (HsVar id) (idType id)
753 #else /* GHCI and TH is on */
754 tc_local_id id th_bind_lvl proc_lvl -- TH case
755 = checkProcLevel id proc_lvl `thenM_`
757 -- Check for cross-stage lifting
758 getStage `thenM` \ use_stage ->
760 Brack use_lvl ps_var lie_var
761 | use_lvl > th_bind_lvl
762 -> -- E.g. \x -> [| h x |]
763 -- We must behave as if the reference to x was
766 -- We use 'x' itself as the splice proxy, used by
767 -- the desugarer to stitch it all back together.
768 -- If 'x' occurs many times we may get many identical
769 -- bindings of the same splice proxy, but that doesn't
770 -- matter, although it's a mite untidy.
774 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
775 -- If x is polymorphic, its occurrence sites might
776 -- have different instantiations, so we can't use plain
777 -- 'x' as the splice proxy name. I don't know how to
778 -- solve this, and it's probably unimportant, so I'm
779 -- just going to flag an error for now
782 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
783 -- Put the 'lift' constraint into the right LIE
785 -- Update the pending splices
786 readMutVar ps_var `thenM` \ ps ->
787 writeMutVar ps_var ((name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps) `thenM_`
789 returnM (HsVar id, id_ty))
792 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
793 loop (HsVar id) (idType id)
796 loop (HsVar fun_id) fun_ty
797 | want_method_inst fun_ty
798 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
799 newMethodWithGivenTy orig fun_id
800 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
801 loop (HsVar meth_id) tau
805 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
806 loop (inst_fn <$> fun) tau
809 = returnM (fun, fun_ty)
811 -- Hack Alert (want_method_inst)!
812 -- If f :: (%x :: T) => Int -> Int
813 -- Then if we have two separate calls, (f 3, f 4), we cannot
814 -- make a method constraint that then gets shared, thus:
815 -- let m = f %x in (m 3, m 4)
816 -- because that loses the linearity of the constraint.
817 -- The simplest thing to do is never to construct a method constraint
818 -- in the first place that has a linear implicit parameter in it.
819 want_method_inst fun_ty
820 | opt_NoMethodSharing = False
821 | otherwise = case tcSplitSigmaTy fun_ty of
822 (_,[],_) -> False -- Not overloaded
823 (_,theta,_) -> not (any isLinearPred theta)
826 -- We treat data constructors differently, because we have to generate
827 -- constraints for their silly theta, which no longer appears in
828 -- the type of dataConWrapId (see note on "stupid context" in DataCon.lhs
829 -- It's dual to TcPat.tcConstructor
830 inst_data_con data_con
831 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
832 extendLIEs ex_dicts `thenM_`
833 getSrcSpanM `thenM` \ loc ->
834 returnM (unLoc (mkHsDictApp (mkHsTyApp (L loc (HsVar (dataConWrapId data_con))) ty_args)
835 (map instToId ex_dicts)),
836 mkFunTys arg_tys result_ty)
837 -- ToDo: nasty loc/unloc stuff here
839 orig = OccurrenceOf name
842 %************************************************************************
844 \subsection{Record bindings}
846 %************************************************************************
848 Game plan for record bindings
849 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
850 1. Find the TyCon for the bindings, from the first field label.
852 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
854 For each binding field = value
856 3. Instantiate the field type (from the field label) using the type
859 4 Type check the value using tcArg, passing the field type as
860 the expected argument type.
862 This extends OK when the field types are universally quantified.
867 :: TyCon -- Type constructor for the record
868 -> [TcType] -- Args of this type constructor
869 -> HsRecordBinds Name
870 -> TcM (HsRecordBinds TcId)
872 tcRecordBinds tycon ty_args rbinds
873 = mappM do_bind rbinds
875 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
877 do_bind (L loc field_lbl_name, rhs)
878 = addErrCtxt (fieldCtxt field_lbl_name) $
879 tcLookupId field_lbl_name `thenM` \ sel_id ->
881 field_lbl = recordSelectorFieldLabel sel_id
882 field_ty = substTy tenv (fieldLabelType field_lbl)
884 ASSERT( isRecordSelector sel_id )
885 -- This lookup and assertion will surely succeed, because
886 -- we check that the fields are indeed record selectors
887 -- before calling tcRecordBinds
888 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
889 -- The caller of tcRecordBinds has already checked
890 -- that all the fields come from the same type
892 tcCheckSigma rhs field_ty `thenM` \ rhs' ->
894 returnM (L loc sel_id, rhs')
896 badFields rbinds data_con
897 = filter (not . (`elem` field_names)) (recBindFields rbinds)
899 field_names = map fieldLabelName (dataConFieldLabels data_con)
901 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
902 checkMissingFields data_con rbinds
903 | null field_labels -- Not declared as a record;
904 -- But C{} is still valid if no strict fields
905 = if any isMarkedStrict field_strs then
906 -- Illegal if any arg is strict
907 addErrTc (missingStrictFields data_con [])
911 | otherwise -- A record
912 = checkM (null missing_s_fields)
913 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
915 doptM Opt_WarnMissingFields `thenM` \ warn ->
916 checkM (not (warn && notNull missing_ns_fields))
917 (warnTc True (missingFields data_con missing_ns_fields))
921 = [ fl | (fl, str) <- field_info,
923 not (fieldLabelName fl `elem` field_names_used)
926 = [ fl | (fl, str) <- field_info,
927 not (isMarkedStrict str),
928 not (fieldLabelName fl `elem` field_names_used)
931 field_names_used = recBindFields rbinds
932 field_labels = dataConFieldLabels data_con
934 field_info = zipEqual "missingFields"
938 field_strs = dataConStrictMarks data_con
941 %************************************************************************
943 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
945 %************************************************************************
948 tcCheckRhos :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
950 tcCheckRhos [] [] = returnM []
951 tcCheckRhos (expr:exprs) (ty:tys)
952 = tcCheckRho expr ty `thenM` \ expr' ->
953 tcCheckRhos exprs tys `thenM` \ exprs' ->
954 returnM (expr':exprs')
958 %************************************************************************
960 \subsection{Literals}
962 %************************************************************************
967 tcLit :: HsLit -> Expected TcRhoType -> TcM (HsExpr TcId)
969 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
974 %************************************************************************
976 \subsection{Errors and contexts}
978 %************************************************************************
980 Boring and alphabetical:
983 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
986 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
989 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
992 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
995 = hang (ptext SLIT("In the type signature of the expression:"))
999 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1001 fieldCtxt field_name
1002 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1004 funAppCtxt fun arg arg_no
1005 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1006 quotes (ppr fun) <> text ", namely"])
1007 4 (quotes (ppr arg))
1010 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1013 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1016 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1019 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1021 the_app = foldl mkHsApp fun args -- Used in error messages
1024 = hang (ptext SLIT("No constructor has all these fields:"))
1025 4 (pprQuotedList (recBindFields rbinds))
1027 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1028 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1031 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1033 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1034 missingStrictFields con fields
1037 rest | null fields = empty -- Happens for non-record constructors
1038 -- with strict fields
1039 | otherwise = colon <+> pprWithCommas ppr fields
1041 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1042 ptext SLIT("does not have the required strict field(s)")
1044 missingFields :: DataCon -> [FieldLabel] -> SDoc
1045 missingFields con fields
1046 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1047 <+> pprWithCommas ppr fields
1049 wrongArgsCtxt too_many_or_few fun args
1050 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1051 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1052 <+> ptext SLIT("arguments in the call"))
1053 4 (parens (ppr the_app))
1055 the_app = foldl mkHsApp fun args -- Used in error messages
1058 polySpliceErr :: Id -> SDoc
1060 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)