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 Name ( isExternalName )
15 import TcType ( isTauTy )
16 import TcEnv ( checkWellStaged )
17 import HsSyn ( nlHsApp )
18 import qualified DsMeta
21 import HsSyn ( HsExpr(..), LHsExpr, HsLit(..), ArithSeqInfo(..), recBindFields,
22 HsMatchContext(..), HsRecordBinds, mkHsApp, nlHsVar )
23 import TcHsSyn ( hsLitType, (<$>) )
25 import TcUnify ( Expected(..), tcInfer, zapExpectedType, zapExpectedTo, tcSubExp, tcGen,
26 unifyFunTys, zapToListTy, zapToTyConApp )
27 import BasicTypes ( isMarkedStrict )
28 import Inst ( newOverloadedLit, newMethodFromName, newIPDict,
29 newDicts, newMethodWithGivenTy, tcInstStupidTheta, tcInstCall )
30 import TcBinds ( tcBindsAndThen )
31 import TcEnv ( tcLookup, tcLookupId, checkProcLevel,
32 tcLookupDataCon, tcLookupGlobalId
34 import TcArrows ( tcProc )
35 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig, TcMatchCtxt(..) )
36 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
37 import TcPat ( badFieldCon, refineTyVars )
38 import TcMType ( tcInstTyVars, tcInstType, newTyFlexiVarTy, zonkTcType )
39 import TcType ( Type, TcTyVar, TcType, TcSigmaType, TcRhoType,
40 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
41 isSigmaTy, mkFunTy, mkTyConApp, tyVarsOfTypes, isLinearPred,
42 tcSplitSigmaTy, tidyOpenType
44 import Kind ( openTypeKind, liftedTypeKind, argTypeKind )
46 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
47 import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks, dataConWrapId )
49 import TyCon ( TyCon, FieldLabel, tyConTyVars, tyConStupidTheta,
50 tyConDataCons, tyConFields )
51 import Type ( zipTopTvSubst, substTheta, substTy )
52 import Var ( tyVarKind )
53 import VarSet ( emptyVarSet, elemVarSet )
54 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
55 import PrelNames ( enumFromName, enumFromThenName,
56 enumFromToName, enumFromThenToName,
57 enumFromToPName, enumFromThenToPName
59 import ListSetOps ( minusList )
61 import StaticFlags ( opt_NoMethodSharing )
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)) = setSrcSpan loc $ do
111 { (e,_,ty) <- tcId name; return (L loc e, ty)}
112 tcInferRho expr = tcInfer (tcMonoExpr expr)
117 %************************************************************************
119 \subsection{The TAUT rules for variables}TcExpr
121 %************************************************************************
124 tcMonoExpr :: LHsExpr Name -- Expession to type check
125 -> Expected TcRhoType -- Expected type (could be a type variable)
126 -- Definitely no foralls at the top
128 -> TcM (LHsExpr TcId)
130 tcMonoExpr (L loc expr) res_ty
131 = setSrcSpan loc (do { expr' <- tc_expr expr res_ty
132 ; return (L loc expr') })
134 tc_expr :: HsExpr Name -> Expected TcRhoType -> TcM (HsExpr TcId)
135 tc_expr (HsVar name) res_ty
136 = do { (expr', _, id_ty) <- tcId name
137 ; co_fn <- tcSubExp res_ty id_ty
138 ; returnM (co_fn <$> expr') }
140 tc_expr (HsIPVar ip) res_ty
141 = -- Implicit parameters must have a *tau-type* not a
142 -- type scheme. We enforce this by creating a fresh
143 -- type variable as its type. (Because res_ty may not
145 newTyFlexiVarTy argTypeKind `thenM` \ ip_ty ->
146 -- argTypeKind: it can't be an unboxed tuple
147 newIPDict (IPOccOrigin ip) ip ip_ty `thenM` \ (ip', inst) ->
148 extendLIE inst `thenM_`
149 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
150 returnM (co_fn <$> HsIPVar ip')
154 %************************************************************************
156 \subsection{Expressions type signatures}
158 %************************************************************************
161 tc_expr in_expr@(ExprWithTySig expr poly_ty) res_ty
162 = addErrCtxt (exprCtxt in_expr) $
163 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
164 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
165 returnM (co_fn <$> ExprWithTySigOut expr' poly_ty)
167 tc_expr (HsType ty) res_ty
168 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
169 -- This is the syntax for type applications that I was planning
170 -- but there are difficulties (e.g. what order for type args)
171 -- so it's not enabled yet.
172 -- Can't eliminate it altogether from the parser, because the
173 -- same parser parses *patterns*.
177 %************************************************************************
179 \subsection{Other expression forms}
181 %************************************************************************
184 tc_expr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
185 returnM (HsPar expr')
186 tc_expr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
187 returnM (HsSCC lbl expr')
188 tc_expr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
189 returnM (HsCoreAnn lbl expr')
191 tc_expr (HsLit lit) res_ty = tcLit lit res_ty
193 tc_expr (HsOverLit lit) res_ty
194 = zapExpectedType res_ty liftedTypeKind `thenM` \ res_ty' ->
195 -- Overloaded literals must have liftedTypeKind, because
196 -- we're instantiating an overloaded function here,
197 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
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 unifyFunTys 2 op_ty {- 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 unifyFunTys 2 op_ty {- 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 unifyFunTys 2 op_ty {- 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 (setSrcSpan loc $ tc_expr expr res_ty)
262 glue bind expr = HsLet [bind] (L loc expr)
264 tc_expr in_expr@(HsCase scrut matches) exp_ty
265 = -- We used to typecheck the case alternatives first.
266 -- The case patterns tend to give good type info to use
267 -- when typechecking the scrutinee. For example
270 -- will report that map is applied to too few arguments
272 -- But now, in the GADT world, we need to typecheck the scrutinee
273 -- first, to get type info that may be refined in the case alternatives
274 addErrCtxt (caseScrutCtxt scrut)
275 (tcInferRho scrut) `thenM` \ (scrut', scrut_ty) ->
277 addErrCtxt (caseCtxt in_expr) $
278 tcMatchesCase match_ctxt scrut_ty matches exp_ty `thenM` \ matches' ->
279 returnM (HsCase scrut' matches')
281 match_ctxt = MC { mc_what = CaseAlt,
282 mc_body = tcMonoExpr }
284 tc_expr (HsIf pred b1 b2) res_ty
285 = addErrCtxt (predCtxt pred) (
286 tcCheckRho pred boolTy ) `thenM` \ pred' ->
288 zapExpectedType res_ty openTypeKind `thenM` \ res_ty' ->
289 -- C.f. the call to zapToType in TcMatches.tcMatches
291 tcCheckRho b1 res_ty' `thenM` \ b1' ->
292 tcCheckRho b2 res_ty' `thenM` \ b2' ->
293 returnM (HsIf pred' b1' b2')
295 tc_expr (HsDo do_or_lc stmts method_names _) res_ty
296 = zapExpectedType res_ty liftedTypeKind `thenM` \ res_ty' ->
297 -- All comprehensions yield a monotype of kind *
298 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
299 returnM (HsDo do_or_lc stmts' methods' res_ty')
301 tc_expr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
302 = zapToListTy res_ty `thenM` \ elt_ty ->
303 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
304 returnM (ExplicitList elt_ty exprs')
307 = addErrCtxt (listCtxt expr) $
308 tcCheckRho expr elt_ty
310 tc_expr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
311 = do { [elt_ty] <- zapToTyConApp parrTyCon res_ty
312 ; exprs' <- mappM (tc_elt elt_ty) exprs
313 ; return (ExplicitPArr elt_ty exprs') }
316 = addErrCtxt (parrCtxt expr) (tcCheckRho expr elt_ty)
318 tc_expr (ExplicitTuple exprs boxity) res_ty
319 = do { arg_tys <- zapToTyConApp (tupleTyCon boxity (length exprs)) res_ty
320 ; exprs' <- tcCheckRhos exprs arg_tys
321 ; return (ExplicitTuple exprs' boxity) }
323 tc_expr (HsProc pat cmd) res_ty
324 = tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
325 returnM (HsProc pat' cmd')
327 tc_expr e@(HsArrApp _ _ _ _ _) _
328 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
329 ptext SLIT("was found where an expression was expected")])
331 tc_expr e@(HsArrForm _ _ _) _
332 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
333 ptext SLIT("was found where an expression was expected")])
336 %************************************************************************
338 Record construction and update
340 %************************************************************************
343 tc_expr expr@(RecordCon con@(L loc con_name) rbinds) res_ty
344 = addErrCtxt (recordConCtxt expr) $
345 addLocM tcId con `thenM` \ (con_expr, _, con_tau) ->
347 (_, record_ty) = tcSplitFunTys con_tau
348 (tycon, ty_args) = tcSplitTyConApp record_ty
350 ASSERT( isAlgTyCon tycon )
351 zapExpectedTo res_ty record_ty `thenM_`
353 -- Check that the record bindings match the constructor
354 -- con_name is syntactically constrained to be a data constructor
355 tcLookupDataCon con_name `thenM` \ data_con ->
357 bad_fields = badFields rbinds data_con
359 if notNull bad_fields then
360 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
361 failM -- Fail now, because tcRecordBinds will crash on a bad field
364 -- Typecheck the record bindings
365 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
367 -- Check for missing fields
368 checkMissingFields data_con rbinds `thenM_`
370 returnM (RecordConOut data_con (L loc con_expr) rbinds')
372 -- The main complication with RecordUpd is that we need to explicitly
373 -- handle the *non-updated* fields. Consider:
375 -- data T a b = MkT1 { fa :: a, fb :: b }
376 -- | MkT2 { fa :: a, fc :: Int -> Int }
377 -- | MkT3 { fd :: a }
379 -- upd :: T a b -> c -> T a c
380 -- upd t x = t { fb = x}
382 -- The type signature on upd is correct (i.e. the result should not be (T a b))
383 -- because upd should be equivalent to:
385 -- upd t x = case t of
386 -- MkT1 p q -> MkT1 p x
387 -- MkT2 a b -> MkT2 p b
388 -- MkT3 d -> error ...
390 -- So we need to give a completely fresh type to the result record,
391 -- and then constrain it by the fields that are *not* updated ("p" above).
393 -- Note that because MkT3 doesn't contain all the fields being updated,
394 -- its RHS is simply an error, so it doesn't impose any type constraints
396 -- All this is done in STEP 4 below.
398 tc_expr expr@(RecordUpd record_expr rbinds) res_ty
399 = addErrCtxt (recordUpdCtxt expr) $
402 -- Check that the field names are really field names
403 ASSERT( notNull rbinds )
405 field_names = map fst rbinds
407 mappM (tcLookupGlobalId.unLoc) field_names `thenM` \ sel_ids ->
408 -- The renamer has already checked that they
411 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
412 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
413 not (isRecordSelector sel_id) -- Excludes class ops
416 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
419 -- Figure out the tycon and data cons from the first field name
421 -- It's OK to use the non-tc splitters here (for a selector)
423 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
424 data_cons = tyConDataCons tycon -- it's not a field label
425 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
427 tcInstTyVars tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
430 -- Check that at least one constructor has all the named fields
431 -- i.e. has an empty set of bad fields returned by badFields
432 checkTc (any (null . badFields rbinds) data_cons)
433 (badFieldsUpd rbinds) `thenM_`
436 -- Typecheck the update bindings.
437 -- (Do this after checking for bad fields in case there's a field that
438 -- doesn't match the constructor.)
440 result_record_ty = mkTyConApp tycon result_inst_tys
442 zapExpectedTo res_ty result_record_ty `thenM_`
443 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
446 -- Use the un-updated fields to find a vector of booleans saying
447 -- which type arguments must be the same in updatee and result.
449 -- WARNING: this code assumes that all data_cons in a common tycon
450 -- have FieldLabels abstracted over the same tyvars.
452 upd_field_lbls = recBindFields rbinds
453 con_field_lbls_s = map dataConFieldLabels data_cons
455 -- A constructor is only relevant to this process if
456 -- it contains all the fields that are being updated
457 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
458 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
460 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
461 common_tyvars = tyVarsOfTypes [ty | (fld,ty,_) <- tyConFields tycon,
462 fld `elem` non_upd_field_lbls]
463 is_common_tv tv = tv `elemVarSet` common_tyvars
465 mk_inst_ty tv result_inst_ty
466 | is_common_tv tv = returnM result_inst_ty -- Same as result type
467 | otherwise = newTyFlexiVarTy (tyVarKind tv) -- Fresh type, of correct kind
469 zipWithM mk_inst_ty tycon_tyvars result_inst_tys `thenM` \ inst_tys ->
472 -- Typecheck the expression to be updated
474 record_ty = mkTyConApp tycon inst_tys
476 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
479 -- Figure out the LIE we need. We have to generate some
480 -- dictionaries for the data type context, since we are going to
481 -- do pattern matching over the data cons.
483 -- What dictionaries do we need?
484 -- We just take the context of the type constructor
486 theta' = substTheta inst_env (tyConStupidTheta tycon)
488 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
489 extendLIEs dicts `thenM_`
492 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
496 %************************************************************************
498 Arithmetic sequences e.g. [a,b..]
499 and their parallel-array counterparts e.g. [: a,b.. :]
502 %************************************************************************
505 tc_expr (ArithSeqIn seq@(From expr)) res_ty
506 = zapToListTy res_ty `thenM` \ elt_ty ->
507 tcCheckRho expr elt_ty `thenM` \ expr' ->
509 newMethodFromName (ArithSeqOrigin seq)
510 elt_ty enumFromName `thenM` \ enum_from ->
512 returnM (ArithSeqOut (nlHsVar enum_from) (From expr'))
514 tc_expr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
515 = addErrCtxt (arithSeqCtxt in_expr) $
516 zapToListTy res_ty `thenM` \ elt_ty ->
517 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
518 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
519 newMethodFromName (ArithSeqOrigin seq)
520 elt_ty enumFromThenName `thenM` \ enum_from_then ->
522 returnM (ArithSeqOut (nlHsVar enum_from_then) (FromThen expr1' expr2'))
525 tc_expr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
526 = addErrCtxt (arithSeqCtxt in_expr) $
527 zapToListTy res_ty `thenM` \ elt_ty ->
528 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
529 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
530 newMethodFromName (ArithSeqOrigin seq)
531 elt_ty enumFromToName `thenM` \ enum_from_to ->
533 returnM (ArithSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
535 tc_expr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
536 = addErrCtxt (arithSeqCtxt in_expr) $
537 zapToListTy res_ty `thenM` \ elt_ty ->
538 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
539 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
540 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
541 newMethodFromName (ArithSeqOrigin seq)
542 elt_ty enumFromThenToName `thenM` \ eft ->
544 returnM (ArithSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
546 tc_expr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
547 = addErrCtxt (parrSeqCtxt in_expr) $
548 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
549 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
550 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
551 newMethodFromName (PArrSeqOrigin seq)
552 elt_ty enumFromToPName `thenM` \ enum_from_to ->
554 returnM (PArrSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
556 tc_expr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
557 = addErrCtxt (parrSeqCtxt in_expr) $
558 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
559 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
560 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
561 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
562 newMethodFromName (PArrSeqOrigin seq)
563 elt_ty enumFromThenToPName `thenM` \ eft ->
565 returnM (PArrSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
567 tc_expr (PArrSeqIn _) _
568 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
569 -- the parser shouldn't have generated it and the renamer shouldn't have
574 %************************************************************************
578 %************************************************************************
581 #ifdef GHCI /* Only if bootstrapped */
582 -- Rename excludes these cases otherwise
583 tc_expr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
584 tc_expr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
590 %************************************************************************
594 %************************************************************************
597 tc_expr other _ = pprPanic "tcMonoExpr" (ppr other)
601 %************************************************************************
603 \subsection{@tcApp@ typchecks an application}
605 %************************************************************************
609 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
610 -> Expected TcRhoType -- Expected result type of application
611 -> TcM (HsExpr TcId) -- Translated fun and args
613 tcApp (L _ (HsApp e1 e2)) args res_ty
614 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
616 tcApp fun args res_ty
617 = do { (fun', fun_tvs, fun_tau) <- tcFun fun -- Type-check the function
619 -- Extract its argument types
620 ; (expected_arg_tys, actual_res_ty)
621 <- addErrCtxt (wrongArgsCtxt "too many" fun args) $ do
622 { traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_tau))
623 ; unifyFunTys (length args) fun_tau }
627 Check _ -> do -- Connect to result type first
628 -- See Note [Push result type in]
629 { co_fn <- tcResult fun args res_ty actual_res_ty
630 ; the_app' <- tcArgs fun fun' args expected_arg_tys
631 ; traceTc (text "tcApp: check" <+> vcat [ppr fun <+> ppr args,
632 ppr the_app', ppr actual_res_ty])
633 ; returnM (co_fn <$> the_app') }
635 Infer _ -> do -- Type check args first, then
636 -- refine result type, then do tcResult
637 { the_app' <- tcArgs fun fun' args expected_arg_tys
638 ; subst <- refineTyVars fun_tvs
639 ; let actual_res_ty' = substTy subst actual_res_ty
640 ; co_fn <- tcResult fun args res_ty actual_res_ty'
641 ; traceTc (text "tcApp: infer" <+> vcat [ppr fun <+> ppr args, ppr the_app',
642 ppr actual_res_ty, ppr actual_res_ty'])
643 ; returnM (co_fn <$> the_app') }
646 -- Note [Push result type in]
648 -- Unify with expected result before (was: after) type-checking the args
649 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
650 -- This is when we might detect a too-few args situation.
651 -- (One can think of cases when the opposite order would give
652 -- a better error message.)
653 -- [March 2003: I'm experimenting with putting this first. Here's an
654 -- example where it actually makes a real difference
655 -- class C t a b | t a -> b
656 -- instance C Char a Bool
658 -- data P t a = forall b. (C t a b) => MkP b
659 -- data Q t = MkQ (forall a. P t a)
662 -- f1 = MkQ (MkP True)
663 -- f2 = MkQ (MkP True :: forall a. P Char a)
665 -- With the change, f1 will type-check, because the 'Char' info from
666 -- the signature is propagated into MkQ's argument. With the check
667 -- in the other order, the extra signature in f2 is reqd.]
670 tcFun :: LHsExpr Name -> TcM (LHsExpr TcId, [TcTyVar], TcRhoType)
671 -- Instantiate the function, returning the type variables used
672 -- If the function isn't simple, infer its type, and return no
674 tcFun (L loc (HsVar f)) = setSrcSpan loc $ do
675 { (fun', tvs, fun_tau) <- tcId f
676 ; return (L loc fun', tvs, fun_tau) }
677 tcFun fun = do { (fun', fun_tau) <- tcInfer (tcMonoExpr fun)
678 ; return (fun', [], fun_tau) }
681 tcArgs :: LHsExpr Name -- The function (for error messages)
682 -> LHsExpr TcId -- The function (to build into result)
683 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
684 -> TcM (HsExpr TcId) -- Resulting application
686 tcArgs fun fun' args expected_arg_tys
687 = do { args' <- mappM (tcArg fun) (zip3 args expected_arg_tys [1..])
688 ; return (unLoc (foldl mkHsApp fun' args')) }
690 tcArg :: LHsExpr Name -- The function (for error messages)
691 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
692 -> TcM (LHsExpr TcId) -- Resulting argument
693 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
694 (tcCheckSigma arg ty)
697 tcResult fun args res_ty actual_res_ty
698 = addErrCtxtM (checkArgsCtxt fun args res_ty actual_res_ty)
699 (tcSubExp res_ty actual_res_ty)
702 -- If an error happens we try to figure out whether the
703 -- function has been given too many or too few arguments,
705 -- The ~(Check...) is because in the Infer case the tcSubExp
706 -- definitely won't fail, so we can be certain we're in the Check branch
707 checkArgsCtxt fun args (Infer _) actual_res_ty tidy_env
708 = return (tidy_env, ptext SLIT("Urk infer"))
710 checkArgsCtxt fun args (Check expected_res_ty) actual_res_ty tidy_env
711 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
712 zonkTcType actual_res_ty `thenM` \ act_ty' ->
714 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
715 (env2, act_ty'') = tidyOpenType env1 act_ty'
716 (exp_args, _) = tcSplitFunTys exp_ty''
717 (act_args, _) = tcSplitFunTys act_ty''
719 len_act_args = length act_args
720 len_exp_args = length exp_args
722 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
723 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
724 | otherwise = appCtxt fun args
726 returnM (env2, message)
730 %************************************************************************
732 \subsection{@tcId@ typchecks an identifier occurrence}
734 %************************************************************************
736 tcId instantiates an occurrence of an Id.
737 The instantiate_it loop runs round instantiating the Id.
738 It has to be a loop because we are now prepared to entertain
740 f:: forall a. Eq a => forall b. Baz b => tau
741 We want to instantiate this to
742 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
744 The -fno-method-sharing flag controls what happens so far as the LIE
745 is concerned. The default case is that for an overloaded function we
746 generate a "method" Id, and add the Method Inst to the LIE. So you get
749 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
750 If you specify -fno-method-sharing, the dictionary application
751 isn't shared, so we get
753 f = /\a (d:Num a) (x:a) -> (+) a d x x
754 This gets a bit less sharing, but
755 a) it's better for RULEs involving overloaded functions
756 b) perhaps fewer separated lambdas
759 tcId :: Name -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
760 -- Return the type variables at which the function
761 -- is instantiated, as well as the translated variable and its type
763 tcId id_name -- Look up the Id and instantiate its type
764 = tcLookup id_name `thenM` \ thing ->
766 AGlobal (ADataCon con) -- Similar, but instantiate the stupid theta too
767 -> do { (expr, tvs, tau) <- instantiate (dataConWrapId con)
768 ; tcInstStupidTheta con (mkTyVarTys tvs)
769 -- Remember to chuck in the constraints from the "silly context"
770 ; return (expr, tvs, tau) }
772 ; AGlobal (AnId id) -> instantiate id
773 -- A global cannot possibly be ill-staged
774 -- nor does it need the 'lifting' treatment
776 ; ATcId id th_level proc_level
777 -> do { checkProcLevel id proc_level
778 ; tc_local_id id th_level }
781 ; other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
786 tc_local_id id th_bind_lvl -- Non-TH case
789 #else /* GHCI and TH is on */
790 tc_local_id id th_bind_lvl -- TH case
791 = -- Check for cross-stage lifting
792 getStage `thenM` \ use_stage ->
794 Brack use_lvl ps_var lie_var
795 | use_lvl > th_bind_lvl
796 -> if isExternalName id_name then
797 -- Top-level identifiers in this module,
798 -- (which have External Names)
799 -- are just like the imported case:
800 -- no need for the 'lifting' treatment
801 -- E.g. this is fine:
804 -- But we do need to put f into the keep-alive
805 -- set, because after desugaring the code will
806 -- only mention f's *name*, not f itself.
807 keepAliveTc id_name `thenM_`
810 else -- Nested identifiers, such as 'x' in
811 -- E.g. \x -> [| h x |]
812 -- We must behave as if the reference to x was
814 -- We use 'x' itself as the splice proxy, used by
815 -- the desugarer to stitch it all back together.
816 -- If 'x' occurs many times we may get many identical
817 -- bindings of the same splice proxy, but that doesn't
818 -- matter, although it's a mite untidy.
822 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
823 -- If x is polymorphic, its occurrence sites might
824 -- have different instantiations, so we can't use plain
825 -- 'x' as the splice proxy name. I don't know how to
826 -- solve this, and it's probably unimportant, so I'm
827 -- just going to flag an error for now
830 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
831 -- Put the 'lift' constraint into the right LIE
833 -- Update the pending splices
834 readMutVar ps_var `thenM` \ ps ->
835 writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps) `thenM_`
837 returnM (HsVar id, [], id_ty))
840 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
844 instantiate :: TcId -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
845 instantiate fun_id = loop (HsVar fun_id) [] (idType fun_id)
847 loop (HsVar fun_id) tvs fun_ty
848 | want_method_inst fun_ty
849 = tcInstType fun_ty `thenM` \ (tyvars, theta, tau) ->
850 newMethodWithGivenTy orig fun_id
851 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
852 loop (HsVar meth_id) (tvs ++ tyvars) tau
856 = tcInstCall orig fun_ty `thenM` \ (inst_fn, new_tvs, tau) ->
857 loop (inst_fn <$> fun) (tvs ++ new_tvs) tau
860 = returnM (fun, tvs, fun_ty)
862 -- Hack Alert (want_method_inst)!
863 -- If f :: (%x :: T) => Int -> Int
864 -- Then if we have two separate calls, (f 3, f 4), we cannot
865 -- make a method constraint that then gets shared, thus:
866 -- let m = f %x in (m 3, m 4)
867 -- because that loses the linearity of the constraint.
868 -- The simplest thing to do is never to construct a method constraint
869 -- in the first place that has a linear implicit parameter in it.
870 want_method_inst fun_ty
871 | opt_NoMethodSharing = False
872 | otherwise = case tcSplitSigmaTy fun_ty of
873 (_,[],_) -> False -- Not overloaded
874 (_,theta,_) -> not (any isLinearPred theta)
876 orig = OccurrenceOf id_name
879 %************************************************************************
881 \subsection{Record bindings}
883 %************************************************************************
885 Game plan for record bindings
886 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
887 1. Find the TyCon for the bindings, from the first field label.
889 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
891 For each binding field = value
893 3. Instantiate the field type (from the field label) using the type
896 4 Type check the value using tcArg, passing the field type as
897 the expected argument type.
899 This extends OK when the field types are universally quantified.
904 :: TyCon -- Type constructor for the record
905 -> [TcType] -- Args of this type constructor
906 -> HsRecordBinds Name
907 -> TcM (HsRecordBinds TcId)
909 tcRecordBinds tycon ty_args rbinds
910 = mappM do_bind rbinds
912 tenv = zipTopTvSubst (tyConTyVars tycon) ty_args
914 do_bind (L loc field_lbl, rhs)
915 = addErrCtxt (fieldCtxt field_lbl) $
917 field_ty = tyConFieldType tycon field_lbl
918 field_ty' = substTy tenv field_ty
920 tcCheckSigma rhs field_ty' `thenM` \ rhs' ->
921 tcLookupId field_lbl `thenM` \ sel_id ->
922 ASSERT( isRecordSelector sel_id )
923 returnM (L loc sel_id, rhs')
925 tyConFieldType :: TyCon -> FieldLabel -> Type
926 tyConFieldType tycon field_lbl
927 = case [ty | (f,ty,_) <- tyConFields tycon, f == field_lbl] of
928 (ty:other) -> ASSERT( null other) ty
929 -- This lookup and assertion will surely succeed, because
930 -- we check that the fields are indeed record selectors
931 -- before calling tcRecordBinds
933 badFields rbinds data_con
934 = filter (not . (`elem` field_names)) (recBindFields rbinds)
936 field_names = dataConFieldLabels data_con
938 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
939 checkMissingFields data_con rbinds
940 | null field_labels -- Not declared as a record;
941 -- But C{} is still valid if no strict fields
942 = if any isMarkedStrict field_strs then
943 -- Illegal if any arg is strict
944 addErrTc (missingStrictFields data_con [])
948 | otherwise -- A record
949 = checkM (null missing_s_fields)
950 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
952 doptM Opt_WarnMissingFields `thenM` \ warn ->
953 checkM (not (warn && notNull missing_ns_fields))
954 (warnTc True (missingFields data_con missing_ns_fields))
958 = [ fl | (fl, str) <- field_info,
960 not (fl `elem` field_names_used)
963 = [ fl | (fl, str) <- field_info,
964 not (isMarkedStrict str),
965 not (fl `elem` field_names_used)
968 field_names_used = recBindFields rbinds
969 field_labels = dataConFieldLabels data_con
971 field_info = zipEqual "missingFields"
975 field_strs = dataConStrictMarks data_con
978 %************************************************************************
980 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
982 %************************************************************************
985 tcCheckRhos :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
987 tcCheckRhos [] [] = returnM []
988 tcCheckRhos (expr:exprs) (ty:tys)
989 = tcCheckRho expr ty `thenM` \ expr' ->
990 tcCheckRhos exprs tys `thenM` \ exprs' ->
991 returnM (expr':exprs')
995 %************************************************************************
997 \subsection{Literals}
999 %************************************************************************
1001 Overloaded literals.
1004 tcLit :: HsLit -> Expected TcRhoType -> TcM (HsExpr TcId)
1006 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
1011 %************************************************************************
1013 \subsection{Errors and contexts}
1015 %************************************************************************
1017 Boring and alphabetical:
1020 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1023 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1026 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1029 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1032 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1034 fieldCtxt field_name
1035 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1037 funAppCtxt fun arg arg_no
1038 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1039 quotes (ppr fun) <> text ", namely"])
1040 4 (quotes (ppr arg))
1043 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1046 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1049 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1052 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1054 the_app = foldl mkHsApp fun args -- Used in error messages
1057 = hang (ptext SLIT("No constructor has all these fields:"))
1058 4 (pprQuotedList (recBindFields 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 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1067 missingStrictFields con fields
1070 rest | null fields = empty -- Happens for non-record constructors
1071 -- with strict fields
1072 | otherwise = colon <+> pprWithCommas ppr fields
1074 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1075 ptext SLIT("does not have the required strict field(s)")
1077 missingFields :: DataCon -> [FieldLabel] -> SDoc
1078 missingFields con fields
1079 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1080 <+> pprWithCommas ppr fields
1082 wrongArgsCtxt too_many_or_few fun args
1083 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1084 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1085 <+> ptext SLIT("arguments in the call"))
1086 4 (parens (ppr the_app))
1088 the_app = foldl mkHsApp fun args -- Used in error messages
1091 polySpliceErr :: Id -> SDoc
1093 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)