2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcCheckSigma, tcCheckRho, tcInferRho,
8 tcMonoExpr, tcExpr, tcSyntaxOp
11 #include "HsVersions.h"
13 #ifdef GHCI /* Only if bootstrapped */
14 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
15 import HsSyn ( nlHsVar )
17 import Name ( isExternalName )
18 import TcType ( isTauTy )
19 import TcEnv ( checkWellStaged )
20 import HsSyn ( nlHsApp )
21 import qualified DsMeta
24 import HsSyn ( HsExpr(..), LHsExpr, HsLit(..), ArithSeqInfo(..), recBindFields,
25 HsMatchContext(..), HsRecordBinds, mkHsApp )
26 import TcHsSyn ( hsLitType, (<$>) )
28 import TcUnify ( Expected(..), tcInfer, zapExpectedType, zapExpectedTo,
29 tcSubExp, tcGen, tcSub,
30 unifyFunTys, zapToListTy, zapToTyConApp )
31 import BasicTypes ( isMarkedStrict )
32 import Inst ( tcOverloadedLit, newMethodFromName, newIPDict,
33 newDicts, newMethodWithGivenTy, tcInstStupidTheta, tcInstCall )
34 import TcBinds ( tcBindsAndThen )
35 import TcEnv ( tcLookup, tcLookupId,
36 tcLookupDataCon, tcLookupGlobalId
38 import TcArrows ( tcProc )
39 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig, TcMatchCtxt(..) )
40 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
41 import TcPat ( badFieldCon, refineTyVars )
42 import TcMType ( tcInstTyVars, tcInstType, newTyFlexiVarTy, zonkTcType )
43 import TcType ( Type, TcTyVar, TcType, TcSigmaType, TcRhoType,
44 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
45 isSigmaTy, mkFunTy, mkTyConApp, tyVarsOfTypes, isLinearPred,
46 tcSplitSigmaTy, tidyOpenType
48 import Kind ( openTypeKind, liftedTypeKind, argTypeKind )
50 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
51 import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks,
54 import TyCon ( TyCon, FieldLabel, tyConTyVars, tyConStupidTheta,
55 tyConDataCons, tyConFields )
56 import Type ( zipTopTvSubst, substTheta, substTy )
57 import Var ( tyVarKind )
58 import VarSet ( emptyVarSet, elemVarSet )
59 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
60 import PrelNames ( enumFromName, enumFromThenName,
61 enumFromToName, enumFromThenToName,
62 enumFromToPName, enumFromThenToPName, negateName
64 import ListSetOps ( minusList )
66 import StaticFlags ( opt_NoMethodSharing )
67 import HscTypes ( TyThing(..) )
68 import SrcLoc ( Located(..), unLoc, getLoc )
74 import TyCon ( isAlgTyCon )
78 %************************************************************************
80 \subsection{Main wrappers}
82 %************************************************************************
85 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
86 tcCheckSigma :: LHsExpr Name -- Expession to type check
87 -> TcSigmaType -- Expected type (could be a polytpye)
88 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
90 tcCheckSigma expr expected_ty
91 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
92 tc_expr' expr expected_ty
94 tc_expr' expr sigma_ty
96 = tcGen sigma_ty emptyVarSet (
97 \ rho_ty -> tcCheckRho expr rho_ty
98 ) `thenM` \ (gen_fn, expr') ->
99 returnM (L (getLoc expr') (gen_fn <$> unLoc expr'))
101 tc_expr' expr rho_ty -- Monomorphic case
102 = tcCheckRho expr rho_ty
105 Typecheck expression which in most cases will be an Id.
106 The expression can return a higher-ranked type, such as
107 (forall a. a->a) -> Int
108 so we must create a hole to pass in as the expected tyvar.
111 tcCheckRho :: LHsExpr Name -> TcRhoType -> TcM (LHsExpr TcId)
112 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
114 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
115 tcInferRho (L loc (HsVar name)) = setSrcSpan loc $ do
116 { (e,_,ty) <- tcId (OccurrenceOf name) name
117 ; return (L loc e, ty) }
118 tcInferRho expr = tcInfer (tcMonoExpr expr)
120 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
121 -- Typecheck a syntax operator, checking that it has the specified type
122 -- The operator is always a variable at this stage (i.e. renamer output)
123 tcSyntaxOp orig (HsVar op) ty = do { (expr', _, id_ty) <- tcId orig op
124 ; co_fn <- tcSub ty id_ty
125 ; returnM (co_fn <$> expr') }
126 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
131 %************************************************************************
133 \subsection{The TAUT rules for variables}TcExpr
135 %************************************************************************
138 tcMonoExpr :: LHsExpr Name -- Expession to type check
139 -> Expected TcRhoType -- Expected type (could be a type variable)
140 -- Definitely no foralls at the top
142 -> TcM (LHsExpr TcId)
144 tcMonoExpr (L loc expr) res_ty
145 = setSrcSpan loc (do { expr' <- tcExpr expr res_ty
146 ; return (L loc expr') })
148 tcExpr :: HsExpr Name -> Expected TcRhoType -> TcM (HsExpr TcId)
149 tcExpr (HsVar name) res_ty
150 = do { (expr', _, id_ty) <- tcId (OccurrenceOf name) name
151 ; co_fn <- tcSubExp res_ty id_ty
152 ; returnM (co_fn <$> expr') }
154 tcExpr (HsIPVar ip) res_ty
155 = -- Implicit parameters must have a *tau-type* not a
156 -- type scheme. We enforce this by creating a fresh
157 -- type variable as its type. (Because res_ty may not
159 newTyFlexiVarTy argTypeKind `thenM` \ ip_ty ->
160 -- argTypeKind: it can't be an unboxed tuple
161 newIPDict (IPOccOrigin ip) ip ip_ty `thenM` \ (ip', inst) ->
162 extendLIE inst `thenM_`
163 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
164 returnM (co_fn <$> HsIPVar ip')
168 %************************************************************************
170 \subsection{Expressions type signatures}
172 %************************************************************************
175 tcExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
176 = addErrCtxt (exprCtxt in_expr) $
177 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
178 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
179 returnM (co_fn <$> ExprWithTySigOut expr' poly_ty)
181 tcExpr (HsType ty) res_ty
182 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
183 -- This is the syntax for type applications that I was planning
184 -- but there are difficulties (e.g. what order for type args)
185 -- so it's not enabled yet.
186 -- Can't eliminate it altogether from the parser, because the
187 -- same parser parses *patterns*.
191 %************************************************************************
193 \subsection{Other expression forms}
195 %************************************************************************
198 tcExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
199 returnM (HsPar expr')
200 tcExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
201 returnM (HsSCC lbl expr')
202 tcExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
203 returnM (HsCoreAnn lbl expr')
205 tcExpr (HsLit lit) res_ty = tcLit lit res_ty
207 tcExpr (HsOverLit lit) res_ty
208 = zapExpectedType res_ty liftedTypeKind `thenM` \ res_ty' ->
209 -- Overloaded literals must have liftedTypeKind, because
210 -- we're instantiating an overloaded function here,
211 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
212 tcOverloadedLit (LiteralOrigin lit) lit res_ty' `thenM` \ lit' ->
213 returnM (HsOverLit lit')
215 tcExpr (NegApp expr neg_expr) res_ty
216 = do { res_ty' <- zapExpectedType res_ty liftedTypeKind
217 ; neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
218 (mkFunTy res_ty' res_ty')
219 ; expr' <- tcCheckRho expr res_ty'
220 ; return (NegApp expr' neg_expr') }
222 tcExpr (HsLam match) res_ty
223 = tcMatchLambda match res_ty `thenM` \ match' ->
224 returnM (HsLam match')
226 tcExpr (HsApp e1 e2) res_ty
227 = tcApp e1 [e2] res_ty
230 Note that the operators in sections are expected to be binary, and
231 a type error will occur if they aren't.
234 -- Left sections, equivalent to
241 tcExpr in_expr@(SectionL arg1 op) res_ty
242 = tcInferRho op `thenM` \ (op', op_ty) ->
243 unifyFunTys 2 op_ty {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
244 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
245 addErrCtxt (exprCtxt in_expr) $
246 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
247 returnM (co_fn <$> SectionL arg1' op')
249 -- Right sections, equivalent to \ x -> x op expr, or
252 tcExpr in_expr@(SectionR op arg2) res_ty
253 = tcInferRho op `thenM` \ (op', op_ty) ->
254 unifyFunTys 2 op_ty {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
255 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
256 addErrCtxt (exprCtxt in_expr) $
257 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
258 returnM (co_fn <$> SectionR op' arg2')
260 -- equivalent to (op e1) e2:
262 tcExpr in_expr@(OpApp arg1 op fix arg2) res_ty
263 = tcInferRho op `thenM` \ (op', op_ty) ->
264 unifyFunTys 2 op_ty {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
265 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
266 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
267 addErrCtxt (exprCtxt in_expr) $
268 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
269 returnM (OpApp arg1' op' fix arg2')
273 tcExpr (HsLet binds (L loc expr)) res_ty
276 binds -- Bindings to check
277 (setSrcSpan loc $ tcExpr expr res_ty)
279 glue bind expr = HsLet [bind] (L loc expr)
281 tcExpr in_expr@(HsCase scrut matches) exp_ty
282 = -- We used to typecheck the case alternatives first.
283 -- The case patterns tend to give good type info to use
284 -- when typechecking the scrutinee. For example
287 -- will report that map is applied to too few arguments
289 -- But now, in the GADT world, we need to typecheck the scrutinee
290 -- first, to get type info that may be refined in the case alternatives
291 addErrCtxt (caseScrutCtxt scrut)
292 (tcInferRho scrut) `thenM` \ (scrut', scrut_ty) ->
294 addErrCtxt (caseCtxt in_expr) $
295 tcMatchesCase match_ctxt scrut_ty matches exp_ty `thenM` \ matches' ->
296 returnM (HsCase scrut' matches')
298 match_ctxt = MC { mc_what = CaseAlt,
299 mc_body = tcMonoExpr }
301 tcExpr (HsIf pred b1 b2) res_ty
302 = addErrCtxt (predCtxt pred)
303 (tcCheckRho pred boolTy) `thenM` \ pred' ->
305 zapExpectedType res_ty openTypeKind `thenM` \ res_ty' ->
306 -- C.f. the call to zapToType in TcMatches.tcMatches
308 tcCheckRho b1 res_ty' `thenM` \ b1' ->
309 tcCheckRho b2 res_ty' `thenM` \ b2' ->
310 returnM (HsIf pred' b1' b2')
312 tcExpr (HsDo do_or_lc stmts body _) res_ty
313 = tcDoStmts do_or_lc stmts body res_ty
315 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
316 = zapToListTy res_ty `thenM` \ elt_ty ->
317 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
318 returnM (ExplicitList elt_ty exprs')
321 = addErrCtxt (listCtxt expr) $
322 tcCheckRho expr elt_ty
324 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
325 = do { [elt_ty] <- zapToTyConApp parrTyCon res_ty
326 ; exprs' <- mappM (tc_elt elt_ty) exprs
327 ; return (ExplicitPArr elt_ty exprs') }
330 = addErrCtxt (parrCtxt expr) (tcCheckRho expr elt_ty)
332 tcExpr (ExplicitTuple exprs boxity) res_ty
333 = do { arg_tys <- zapToTyConApp (tupleTyCon boxity (length exprs)) res_ty
334 ; exprs' <- tcCheckRhos exprs arg_tys
335 ; return (ExplicitTuple exprs' boxity) }
337 tcExpr (HsProc pat cmd) res_ty
338 = tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
339 returnM (HsProc pat' cmd')
341 tcExpr e@(HsArrApp _ _ _ _ _) _
342 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
343 ptext SLIT("was found where an expression was expected")])
345 tcExpr e@(HsArrForm _ _ _) _
346 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
347 ptext SLIT("was found where an expression was expected")])
350 %************************************************************************
352 Record construction and update
354 %************************************************************************
357 tcExpr expr@(RecordCon con@(L loc con_name) _ rbinds) res_ty
358 = addErrCtxt (recordConCtxt expr) $
359 addLocM (tcId (OccurrenceOf con_name)) con `thenM` \ (con_expr, _, con_tau) ->
361 (_, record_ty) = tcSplitFunTys con_tau
362 (tycon, ty_args) = tcSplitTyConApp record_ty
364 ASSERT( isAlgTyCon tycon )
365 zapExpectedTo res_ty record_ty `thenM_`
367 -- Check that the record bindings match the constructor
368 -- con_name is syntactically constrained to be a data constructor
369 tcLookupDataCon con_name `thenM` \ data_con ->
371 bad_fields = badFields rbinds data_con
373 if notNull bad_fields then
374 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
375 failM -- Fail now, because tcRecordBinds will crash on a bad field
378 -- Typecheck the record bindings
379 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
381 -- Check for missing fields
382 checkMissingFields data_con rbinds `thenM_`
384 returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds')
386 -- The main complication with RecordUpd is that we need to explicitly
387 -- handle the *non-updated* fields. Consider:
389 -- data T a b = MkT1 { fa :: a, fb :: b }
390 -- | MkT2 { fa :: a, fc :: Int -> Int }
391 -- | MkT3 { fd :: a }
393 -- upd :: T a b -> c -> T a c
394 -- upd t x = t { fb = x}
396 -- The type signature on upd is correct (i.e. the result should not be (T a b))
397 -- because upd should be equivalent to:
399 -- upd t x = case t of
400 -- MkT1 p q -> MkT1 p x
401 -- MkT2 a b -> MkT2 p b
402 -- MkT3 d -> error ...
404 -- So we need to give a completely fresh type to the result record,
405 -- and then constrain it by the fields that are *not* updated ("p" above).
407 -- Note that because MkT3 doesn't contain all the fields being updated,
408 -- its RHS is simply an error, so it doesn't impose any type constraints
410 -- All this is done in STEP 4 below.
412 tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
413 = addErrCtxt (recordUpdCtxt expr) $
416 -- Check that the field names are really field names
417 ASSERT( notNull rbinds )
419 field_names = map fst rbinds
421 mappM (tcLookupGlobalId.unLoc) field_names `thenM` \ sel_ids ->
422 -- The renamer has already checked that they
425 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
426 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
427 not (isRecordSelector sel_id) -- Excludes class ops
430 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
433 -- Figure out the tycon and data cons from the first field name
435 -- It's OK to use the non-tc splitters here (for a selector)
437 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
438 data_cons = tyConDataCons tycon -- it's not a field label
439 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
441 tcInstTyVars tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
444 -- Check that at least one constructor has all the named fields
445 -- i.e. has an empty set of bad fields returned by badFields
446 checkTc (any (null . badFields rbinds) data_cons)
447 (badFieldsUpd rbinds) `thenM_`
450 -- Typecheck the update bindings.
451 -- (Do this after checking for bad fields in case there's a field that
452 -- doesn't match the constructor.)
454 result_record_ty = mkTyConApp tycon result_inst_tys
456 zapExpectedTo res_ty result_record_ty `thenM_`
457 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
460 -- Use the un-updated fields to find a vector of booleans saying
461 -- which type arguments must be the same in updatee and result.
463 -- WARNING: this code assumes that all data_cons in a common tycon
464 -- have FieldLabels abstracted over the same tyvars.
466 upd_field_lbls = recBindFields rbinds
467 con_field_lbls_s = map dataConFieldLabels data_cons
469 -- A constructor is only relevant to this process if
470 -- it contains all the fields that are being updated
471 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
472 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
474 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
475 common_tyvars = tyVarsOfTypes [ty | (fld,ty,_) <- tyConFields tycon,
476 fld `elem` non_upd_field_lbls]
477 is_common_tv tv = tv `elemVarSet` common_tyvars
479 mk_inst_ty tv result_inst_ty
480 | is_common_tv tv = returnM result_inst_ty -- Same as result type
481 | otherwise = newTyFlexiVarTy (tyVarKind tv) -- Fresh type, of correct kind
483 zipWithM mk_inst_ty tycon_tyvars result_inst_tys `thenM` \ inst_tys ->
486 -- Typecheck the expression to be updated
488 record_ty = mkTyConApp tycon inst_tys
490 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
493 -- Figure out the LIE we need. We have to generate some
494 -- dictionaries for the data type context, since we are going to
495 -- do pattern matching over the data cons.
497 -- What dictionaries do we need?
498 -- We just take the context of the type constructor
500 theta' = substTheta inst_env (tyConStupidTheta tycon)
502 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
503 extendLIEs dicts `thenM_`
506 returnM (RecordUpd record_expr' rbinds' record_ty result_record_ty)
510 %************************************************************************
512 Arithmetic sequences e.g. [a,b..]
513 and their parallel-array counterparts e.g. [: a,b.. :]
516 %************************************************************************
519 tcExpr (ArithSeq _ seq@(From expr)) res_ty
520 = zapToListTy res_ty `thenM` \ elt_ty ->
521 tcCheckRho expr elt_ty `thenM` \ expr' ->
523 newMethodFromName (ArithSeqOrigin seq)
524 elt_ty enumFromName `thenM` \ enum_from ->
526 returnM (ArithSeq (HsVar enum_from) (From expr'))
528 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
529 = addErrCtxt (arithSeqCtxt in_expr) $
530 zapToListTy res_ty `thenM` \ elt_ty ->
531 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
532 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
533 newMethodFromName (ArithSeqOrigin seq)
534 elt_ty enumFromThenName `thenM` \ enum_from_then ->
536 returnM (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2'))
539 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
540 = addErrCtxt (arithSeqCtxt in_expr) $
541 zapToListTy res_ty `thenM` \ elt_ty ->
542 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
543 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
544 newMethodFromName (ArithSeqOrigin seq)
545 elt_ty enumFromToName `thenM` \ enum_from_to ->
547 returnM (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2'))
549 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
550 = addErrCtxt (arithSeqCtxt in_expr) $
551 zapToListTy res_ty `thenM` \ elt_ty ->
552 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
553 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
554 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
555 newMethodFromName (ArithSeqOrigin seq)
556 elt_ty enumFromThenToName `thenM` \ eft ->
558 returnM (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3'))
560 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
561 = addErrCtxt (parrSeqCtxt in_expr) $
562 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
563 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
564 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
565 newMethodFromName (PArrSeqOrigin seq)
566 elt_ty enumFromToPName `thenM` \ enum_from_to ->
568 returnM (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2'))
570 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
571 = addErrCtxt (parrSeqCtxt in_expr) $
572 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
573 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
574 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
575 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
576 newMethodFromName (PArrSeqOrigin seq)
577 elt_ty enumFromThenToPName `thenM` \ eft ->
579 returnM (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3'))
581 tcExpr (PArrSeq _ _) _
582 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
583 -- the parser shouldn't have generated it and the renamer shouldn't have
588 %************************************************************************
592 %************************************************************************
595 #ifdef GHCI /* Only if bootstrapped */
596 -- Rename excludes these cases otherwise
597 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
598 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
604 %************************************************************************
608 %************************************************************************
611 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
615 %************************************************************************
617 \subsection{@tcApp@ typchecks an application}
619 %************************************************************************
623 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
624 -> Expected TcRhoType -- Expected result type of application
625 -> TcM (HsExpr TcId) -- Translated fun and args
627 tcApp (L _ (HsApp e1 e2)) args res_ty
628 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
630 tcApp fun args res_ty
631 = do { (fun', fun_tvs, fun_tau) <- tcFun fun -- Type-check the function
633 -- Extract its argument types
634 ; (expected_arg_tys, actual_res_ty)
635 <- addErrCtxt (wrongArgsCtxt "too many" fun args) $ do
636 { traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_tau))
637 ; unifyFunTys (length args) fun_tau }
641 Check _ -> do -- Connect to result type first
642 -- See Note [Push result type in]
643 { co_fn <- tcResult fun args res_ty actual_res_ty
644 ; the_app' <- tcArgs fun fun' args expected_arg_tys
645 ; traceTc (text "tcApp: check" <+> vcat [ppr fun <+> ppr args,
646 ppr the_app', ppr actual_res_ty])
647 ; returnM (co_fn <$> the_app') }
649 Infer _ -> do -- Type check args first, then
650 -- refine result type, then do tcResult
651 { the_app' <- tcArgs fun fun' args expected_arg_tys
652 ; subst <- refineTyVars fun_tvs
653 ; let actual_res_ty' = substTy subst actual_res_ty
654 ; co_fn <- tcResult fun args res_ty actual_res_ty'
655 ; traceTc (text "tcApp: infer" <+> vcat [ppr fun <+> ppr args, ppr the_app',
656 ppr actual_res_ty, ppr actual_res_ty'])
657 ; returnM (co_fn <$> the_app') }
660 -- Note [Push result type in]
662 -- Unify with expected result before (was: after) type-checking the args
663 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
664 -- This is when we might detect a too-few args situation.
665 -- (One can think of cases when the opposite order would give
666 -- a better error message.)
667 -- [March 2003: I'm experimenting with putting this first. Here's an
668 -- example where it actually makes a real difference
669 -- class C t a b | t a -> b
670 -- instance C Char a Bool
672 -- data P t a = forall b. (C t a b) => MkP b
673 -- data Q t = MkQ (forall a. P t a)
676 -- f1 = MkQ (MkP True)
677 -- f2 = MkQ (MkP True :: forall a. P Char a)
679 -- With the change, f1 will type-check, because the 'Char' info from
680 -- the signature is propagated into MkQ's argument. With the check
681 -- in the other order, the extra signature in f2 is reqd.]
684 tcFun :: LHsExpr Name -> TcM (LHsExpr TcId, [TcTyVar], TcRhoType)
685 -- Instantiate the function, returning the type variables used
686 -- If the function isn't simple, infer its type, and return no
688 tcFun (L loc (HsVar f)) = setSrcSpan loc $ do
689 { (fun', tvs, fun_tau) <- tcId (OccurrenceOf f) f
690 ; return (L loc fun', tvs, fun_tau) }
691 tcFun fun = do { (fun', fun_tau) <- tcInfer (tcMonoExpr fun)
692 ; return (fun', [], fun_tau) }
695 tcArgs :: LHsExpr Name -- The function (for error messages)
696 -> LHsExpr TcId -- The function (to build into result)
697 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
698 -> TcM (HsExpr TcId) -- Resulting application
700 tcArgs fun fun' args expected_arg_tys
701 = do { args' <- mappM (tcArg fun) (zip3 args expected_arg_tys [1..])
702 ; return (unLoc (foldl mkHsApp fun' args')) }
704 tcArg :: LHsExpr Name -- The function (for error messages)
705 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
706 -> TcM (LHsExpr TcId) -- Resulting argument
707 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
708 (tcCheckSigma arg ty)
711 tcResult fun args res_ty actual_res_ty
712 = addErrCtxtM (checkArgsCtxt fun args res_ty actual_res_ty)
713 (tcSubExp res_ty actual_res_ty)
716 -- If an error happens we try to figure out whether the
717 -- function has been given too many or too few arguments,
719 -- The ~(Check...) is because in the Infer case the tcSubExp
720 -- definitely won't fail, so we can be certain we're in the Check branch
721 checkArgsCtxt fun args (Infer _) actual_res_ty tidy_env
722 = return (tidy_env, ptext SLIT("Urk infer"))
724 checkArgsCtxt fun args (Check expected_res_ty) actual_res_ty tidy_env
725 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
726 zonkTcType actual_res_ty `thenM` \ act_ty' ->
728 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
729 (env2, act_ty'') = tidyOpenType env1 act_ty'
730 (exp_args, _) = tcSplitFunTys exp_ty''
731 (act_args, _) = tcSplitFunTys act_ty''
733 len_act_args = length act_args
734 len_exp_args = length exp_args
736 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
737 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
738 | otherwise = appCtxt fun args
740 returnM (env2, message)
744 %************************************************************************
746 \subsection{@tcId@ typchecks an identifier occurrence}
748 %************************************************************************
750 tcId instantiates an occurrence of an Id.
751 The instantiate_it loop runs round instantiating the Id.
752 It has to be a loop because we are now prepared to entertain
754 f:: forall a. Eq a => forall b. Baz b => tau
755 We want to instantiate this to
756 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
758 The -fno-method-sharing flag controls what happens so far as the LIE
759 is concerned. The default case is that for an overloaded function we
760 generate a "method" Id, and add the Method Inst to the LIE. So you get
763 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
764 If you specify -fno-method-sharing, the dictionary application
765 isn't shared, so we get
767 f = /\a (d:Num a) (x:a) -> (+) a d x x
768 This gets a bit less sharing, but
769 a) it's better for RULEs involving overloaded functions
770 b) perhaps fewer separated lambdas
773 tcId :: InstOrigin -> Name -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
774 -- Return the type variables at which the function
775 -- is instantiated, as well as the translated variable and its type
777 tcId orig id_name -- Look up the Id and instantiate its type
778 = tcLookup id_name `thenM` \ thing ->
780 AGlobal (ADataCon con) -- Similar, but instantiate the stupid theta too
781 -> do { (expr, tvs, tau) <- instantiate (dataConWrapId con)
782 ; tcInstStupidTheta con (mkTyVarTys tvs)
783 -- Remember to chuck in the constraints from the "silly context"
784 ; return (expr, tvs, tau) }
786 ; AGlobal (AnId id) -> instantiate id
787 -- A global cannot possibly be ill-staged
788 -- nor does it need the 'lifting' treatment
790 ; ATcId id th_level -> tc_local_id id th_level
792 ; other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
797 tc_local_id id th_bind_lvl -- Non-TH case
800 #else /* GHCI and TH is on */
801 tc_local_id id th_bind_lvl -- TH case
802 = -- Check for cross-stage lifting
803 getStage `thenM` \ use_stage ->
805 Brack use_lvl ps_var lie_var
806 | use_lvl > th_bind_lvl
807 -> if isExternalName id_name then
808 -- Top-level identifiers in this module,
809 -- (which have External Names)
810 -- are just like the imported case:
811 -- no need for the 'lifting' treatment
812 -- E.g. this is fine:
815 -- But we do need to put f into the keep-alive
816 -- set, because after desugaring the code will
817 -- only mention f's *name*, not f itself.
818 keepAliveTc id_name `thenM_`
821 else -- Nested identifiers, such as 'x' in
822 -- E.g. \x -> [| h x |]
823 -- We must behave as if the reference to x was
825 -- We use 'x' itself as the splice proxy, used by
826 -- the desugarer to stitch it all back together.
827 -- If 'x' occurs many times we may get many identical
828 -- bindings of the same splice proxy, but that doesn't
829 -- matter, although it's a mite untidy.
833 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
834 -- If x is polymorphic, its occurrence sites might
835 -- have different instantiations, so we can't use plain
836 -- 'x' as the splice proxy name. I don't know how to
837 -- solve this, and it's probably unimportant, so I'm
838 -- just going to flag an error for now
841 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
842 -- Put the 'lift' constraint into the right LIE
844 -- Update the pending splices
845 readMutVar ps_var `thenM` \ ps ->
846 writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps) `thenM_`
848 returnM (HsVar id, [], id_ty))
851 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
855 instantiate :: TcId -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
856 instantiate fun_id = loop (HsVar fun_id) [] (idType fun_id)
858 loop (HsVar fun_id) tvs fun_ty
859 | want_method_inst fun_ty
860 = tcInstType fun_ty `thenM` \ (tyvars, theta, tau) ->
861 newMethodWithGivenTy orig fun_id
862 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
863 loop (HsVar meth_id) (tvs ++ tyvars) tau
867 = tcInstCall orig fun_ty `thenM` \ (inst_fn, new_tvs, tau) ->
868 loop (inst_fn <$> fun) (tvs ++ new_tvs) tau
871 = returnM (fun, tvs, fun_ty)
873 -- Hack Alert (want_method_inst)!
874 -- If f :: (%x :: T) => Int -> Int
875 -- Then if we have two separate calls, (f 3, f 4), we cannot
876 -- make a method constraint that then gets shared, thus:
877 -- let m = f %x in (m 3, m 4)
878 -- because that loses the linearity of the constraint.
879 -- The simplest thing to do is never to construct a method constraint
880 -- in the first place that has a linear implicit parameter in it.
881 want_method_inst fun_ty
882 | opt_NoMethodSharing = False
883 | otherwise = case tcSplitSigmaTy fun_ty of
884 (_,[],_) -> False -- Not overloaded
885 (_,theta,_) -> not (any isLinearPred theta)
888 %************************************************************************
890 \subsection{Record bindings}
892 %************************************************************************
894 Game plan for record bindings
895 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
896 1. Find the TyCon for the bindings, from the first field label.
898 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
900 For each binding field = value
902 3. Instantiate the field type (from the field label) using the type
905 4 Type check the value using tcArg, passing the field type as
906 the expected argument type.
908 This extends OK when the field types are universally quantified.
913 :: TyCon -- Type constructor for the record
914 -> [TcType] -- Args of this type constructor
915 -> HsRecordBinds Name
916 -> TcM (HsRecordBinds TcId)
918 tcRecordBinds tycon ty_args rbinds
919 = mappM do_bind rbinds
921 tenv = zipTopTvSubst (tyConTyVars tycon) ty_args
923 do_bind (L loc field_lbl, rhs)
924 = addErrCtxt (fieldCtxt field_lbl) $
926 field_ty = tyConFieldType tycon field_lbl
927 field_ty' = substTy tenv field_ty
929 tcCheckSigma rhs field_ty' `thenM` \ rhs' ->
930 tcLookupId field_lbl `thenM` \ sel_id ->
931 ASSERT( isRecordSelector sel_id )
932 returnM (L loc sel_id, rhs')
934 tyConFieldType :: TyCon -> FieldLabel -> Type
935 tyConFieldType tycon field_lbl
936 = case [ty | (f,ty,_) <- tyConFields tycon, f == field_lbl] of
937 (ty:other) -> ASSERT( null other) ty
938 -- This lookup and assertion will surely succeed, because
939 -- we check that the fields are indeed record selectors
940 -- before calling tcRecordBinds
942 badFields rbinds data_con
943 = filter (not . (`elem` field_names)) (recBindFields rbinds)
945 field_names = dataConFieldLabels data_con
947 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
948 checkMissingFields data_con rbinds
949 | null field_labels -- Not declared as a record;
950 -- But C{} is still valid if no strict fields
951 = if any isMarkedStrict field_strs then
952 -- Illegal if any arg is strict
953 addErrTc (missingStrictFields data_con [])
957 | otherwise -- A record
958 = checkM (null missing_s_fields)
959 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
961 doptM Opt_WarnMissingFields `thenM` \ warn ->
962 checkM (not (warn && notNull missing_ns_fields))
963 (warnTc True (missingFields data_con missing_ns_fields))
967 = [ fl | (fl, str) <- field_info,
969 not (fl `elem` field_names_used)
972 = [ fl | (fl, str) <- field_info,
973 not (isMarkedStrict str),
974 not (fl `elem` field_names_used)
977 field_names_used = recBindFields rbinds
978 field_labels = dataConFieldLabels data_con
980 field_info = zipEqual "missingFields"
984 field_strs = dataConStrictMarks data_con
987 %************************************************************************
989 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
991 %************************************************************************
994 tcCheckRhos :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
996 tcCheckRhos [] [] = returnM []
997 tcCheckRhos (expr:exprs) (ty:tys)
998 = tcCheckRho expr ty `thenM` \ expr' ->
999 tcCheckRhos exprs tys `thenM` \ exprs' ->
1000 returnM (expr':exprs')
1004 %************************************************************************
1006 \subsection{Literals}
1008 %************************************************************************
1010 Overloaded literals.
1013 tcLit :: HsLit -> Expected TcRhoType -> TcM (HsExpr TcId)
1015 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
1020 %************************************************************************
1022 \subsection{Errors and contexts}
1024 %************************************************************************
1026 Boring and alphabetical:
1029 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1032 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1035 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1038 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1041 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1043 fieldCtxt field_name
1044 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1046 funAppCtxt fun arg arg_no
1047 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1048 quotes (ppr fun) <> text ", namely"])
1049 4 (quotes (ppr arg))
1052 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1055 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1058 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1061 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1063 the_app = foldl mkHsApp fun args -- Used in error messages
1066 = hang (ptext SLIT("No constructor has all these fields:"))
1067 4 (pprQuotedList (recBindFields rbinds))
1069 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1070 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1073 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1075 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1076 missingStrictFields con fields
1079 rest | null fields = empty -- Happens for non-record constructors
1080 -- with strict fields
1081 | otherwise = colon <+> pprWithCommas ppr fields
1083 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1084 ptext SLIT("does not have the required strict field(s)")
1086 missingFields :: DataCon -> [FieldLabel] -> SDoc
1087 missingFields con fields
1088 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1089 <+> pprWithCommas ppr fields
1091 wrongArgsCtxt too_many_or_few fun args
1092 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1093 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1094 <+> ptext SLIT("arguments in the call"))
1095 4 (parens (ppr the_app))
1097 the_app = foldl mkHsApp fun args -- Used in error messages
1100 polySpliceErr :: Id -> SDoc
1102 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)