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 HsSyn ( nlHsApp )
17 import qualified DsMeta
20 import HsSyn ( HsExpr(..), LHsExpr, HsLit(..), ArithSeqInfo(..), recBindFields,
21 HsMatchContext(..), HsRecordBinds, mkHsApp, nlHsVar )
22 import TcHsSyn ( hsLitType, (<$>) )
24 import TcUnify ( Expected(..), tcInfer, zapExpectedType, zapExpectedTo, tcSubExp, tcGen,
25 unifyFunTys, zapToListTy, zapToTyConApp )
26 import BasicTypes ( isMarkedStrict )
27 import Inst ( InstOrigin(..),
28 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 )
38 import TcMType ( tcInstTyVars, tcInstType, newTyFlexiVarTy, zonkTcType, readMetaTyVar )
39 import TcType ( Type, TcTyVar, TcType, TcSigmaType, TcRhoType, MetaDetails(..),
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, mkTopTvSubst, substTheta, substTy )
52 import VarSet ( emptyVarSet, elemVarSet )
53 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
54 import PrelNames ( enumFromName, enumFromThenName,
55 enumFromToName, enumFromThenToName,
56 enumFromToPName, enumFromThenToPName
58 import ListSetOps ( minusList )
60 import HscTypes ( TyThing(..) )
61 import SrcLoc ( Located(..), unLoc, getLoc )
63 import Maybes ( catMaybes )
68 import TyCon ( isAlgTyCon )
72 %************************************************************************
74 \subsection{Main wrappers}
76 %************************************************************************
79 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
80 tcCheckSigma :: LHsExpr Name -- Expession to type check
81 -> TcSigmaType -- Expected type (could be a polytpye)
82 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
84 tcCheckSigma expr expected_ty
85 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
86 tc_expr' expr expected_ty
88 tc_expr' expr sigma_ty
90 = tcGen sigma_ty emptyVarSet (
91 \ rho_ty -> tcCheckRho expr rho_ty
92 ) `thenM` \ (gen_fn, expr') ->
93 returnM (L (getLoc expr') (gen_fn <$> unLoc expr'))
95 tc_expr' expr rho_ty -- Monomorphic case
96 = tcCheckRho expr rho_ty
99 Typecheck expression which in most cases will be an Id.
100 The expression can return a higher-ranked type, such as
101 (forall a. a->a) -> Int
102 so we must create a hole to pass in as the expected tyvar.
105 tcCheckRho :: LHsExpr Name -> TcRhoType -> TcM (LHsExpr TcId)
106 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
108 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
109 tcInferRho (L loc (HsVar name)) = setSrcSpan loc $ do
110 { (e,_,ty) <- tcId name; return (L loc e, ty)}
111 tcInferRho expr = tcInfer (tcMonoExpr expr)
116 %************************************************************************
118 \subsection{The TAUT rules for variables}TcExpr
120 %************************************************************************
123 tcMonoExpr :: LHsExpr Name -- Expession to type check
124 -> Expected TcRhoType -- Expected type (could be a type variable)
125 -- Definitely no foralls at the top
127 -> TcM (LHsExpr TcId)
129 tcMonoExpr (L loc expr) res_ty
130 = setSrcSpan loc (do { expr' <- tc_expr expr res_ty
131 ; return (L loc expr') })
133 tc_expr :: HsExpr Name -> Expected TcRhoType -> TcM (HsExpr TcId)
134 tc_expr (HsVar name) res_ty
135 = do { (expr', _, id_ty) <- tcId name
136 ; co_fn <- tcSubExp res_ty id_ty
137 ; returnM (co_fn <$> expr') }
139 tc_expr (HsIPVar ip) res_ty
140 = -- Implicit parameters must have a *tau-type* not a
141 -- type scheme. We enforce this by creating a fresh
142 -- type variable as its type. (Because res_ty may not
144 newTyFlexiVarTy argTypeKind `thenM` \ ip_ty ->
145 -- argTypeKind: it can't be an unboxed tuple
146 newIPDict (IPOccOrigin ip) ip ip_ty `thenM` \ (ip', inst) ->
147 extendLIE inst `thenM_`
148 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
149 returnM (co_fn <$> HsIPVar ip')
153 %************************************************************************
155 \subsection{Expressions type signatures}
157 %************************************************************************
160 tc_expr in_expr@(ExprWithTySig expr poly_ty) res_ty
161 = addErrCtxt (exprCtxt in_expr) $
162 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
163 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
164 returnM (co_fn <$> ExprWithTySigOut expr' poly_ty)
166 tc_expr (HsType ty) res_ty
167 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
168 -- This is the syntax for type applications that I was planning
169 -- but there are difficulties (e.g. what order for type args)
170 -- so it's not enabled yet.
171 -- Can't eliminate it altogether from the parser, because the
172 -- same parser parses *patterns*.
176 %************************************************************************
178 \subsection{Other expression forms}
180 %************************************************************************
183 tc_expr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
184 returnM (HsPar expr')
185 tc_expr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
186 returnM (HsSCC lbl expr')
187 tc_expr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
188 returnM (HsCoreAnn lbl expr')
190 tc_expr (HsLit lit) res_ty = tcLit lit res_ty
192 tc_expr (HsOverLit lit) res_ty
193 = zapExpectedType res_ty liftedTypeKind `thenM` \ res_ty' ->
194 newOverloadedLit (LiteralOrigin lit) lit res_ty' `thenM` \ lit_expr ->
195 returnM (unLoc lit_expr) -- ToDo: nasty unLoc
197 tc_expr (NegApp expr neg_name) res_ty
198 = tc_expr (HsApp (nlHsVar neg_name) expr) res_ty
199 -- ToDo: use tcSyntaxName
201 tc_expr (HsLam match) res_ty
202 = tcMatchLambda match res_ty `thenM` \ match' ->
203 returnM (HsLam match')
205 tc_expr (HsApp e1 e2) res_ty
206 = tcApp e1 [e2] res_ty
209 Note that the operators in sections are expected to be binary, and
210 a type error will occur if they aren't.
213 -- Left sections, equivalent to
220 tc_expr in_expr@(SectionL arg1 op) res_ty
221 = tcInferRho op `thenM` \ (op', op_ty) ->
222 unifyFunTys 2 op_ty {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
223 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
224 addErrCtxt (exprCtxt in_expr) $
225 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
226 returnM (co_fn <$> SectionL arg1' op')
228 -- Right sections, equivalent to \ x -> x op expr, or
231 tc_expr in_expr@(SectionR op arg2) res_ty
232 = tcInferRho op `thenM` \ (op', op_ty) ->
233 unifyFunTys 2 op_ty {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
234 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
235 addErrCtxt (exprCtxt in_expr) $
236 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
237 returnM (co_fn <$> SectionR op' arg2')
239 -- equivalent to (op e1) e2:
241 tc_expr in_expr@(OpApp arg1 op fix arg2) 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 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
246 addErrCtxt (exprCtxt in_expr) $
247 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
248 returnM (OpApp arg1' op' fix arg2')
252 tc_expr (HsLet binds (L loc expr)) res_ty
255 binds -- Bindings to check
256 (setSrcSpan loc $ tc_expr expr res_ty)
258 glue bind expr = HsLet [bind] (L loc expr)
260 tc_expr in_expr@(HsCase scrut matches) exp_ty
261 = -- We used to typecheck the case alternatives first.
262 -- The case patterns tend to give good type info to use
263 -- when typechecking the scrutinee. For example
266 -- will report that map is applied to too few arguments
268 -- But now, in the GADT world, we need to typecheck the scrutinee
269 -- first, to get type info that may be refined in the case alternatives
270 addErrCtxt (caseScrutCtxt scrut)
271 (tcInferRho scrut) `thenM` \ (scrut', scrut_ty) ->
273 addErrCtxt (caseCtxt in_expr) $
274 tcMatchesCase match_ctxt scrut_ty matches exp_ty `thenM` \ matches' ->
275 returnM (HsCase scrut' matches')
277 match_ctxt = MC { mc_what = CaseAlt,
278 mc_body = tcMonoExpr }
280 tc_expr (HsIf pred b1 b2) res_ty
281 = addErrCtxt (predCtxt pred) (
282 tcCheckRho pred boolTy ) `thenM` \ pred' ->
284 zapExpectedType res_ty openTypeKind `thenM` \ res_ty' ->
285 -- C.f. the call to zapToType in TcMatches.tcMatches
287 tcCheckRho b1 res_ty' `thenM` \ b1' ->
288 tcCheckRho b2 res_ty' `thenM` \ b2' ->
289 returnM (HsIf pred' b1' b2')
291 tc_expr (HsDo do_or_lc stmts method_names _) res_ty
292 = zapExpectedType res_ty liftedTypeKind `thenM` \ res_ty' ->
293 -- All comprehensions yield a monotype of kind *
294 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
295 returnM (HsDo do_or_lc stmts' methods' res_ty')
297 tc_expr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
298 = zapToListTy res_ty `thenM` \ elt_ty ->
299 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
300 returnM (ExplicitList elt_ty exprs')
303 = addErrCtxt (listCtxt expr) $
304 tcCheckRho expr elt_ty
306 tc_expr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
307 = do { [elt_ty] <- zapToTyConApp parrTyCon res_ty
308 ; exprs' <- mappM (tc_elt elt_ty) exprs
309 ; return (ExplicitPArr elt_ty exprs') }
312 = addErrCtxt (parrCtxt expr) (tcCheckRho expr elt_ty)
314 tc_expr (ExplicitTuple exprs boxity) res_ty
315 = do { arg_tys <- zapToTyConApp (tupleTyCon boxity (length exprs)) res_ty
316 ; exprs' <- tcCheckRhos exprs arg_tys
317 ; return (ExplicitTuple exprs' boxity) }
319 tc_expr (HsProc pat cmd) res_ty
320 = tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
321 returnM (HsProc pat' cmd')
323 tc_expr e@(HsArrApp _ _ _ _ _) _
324 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
325 ptext SLIT("was found where an expression was expected")])
327 tc_expr e@(HsArrForm _ _ _) _
328 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
329 ptext SLIT("was found where an expression was expected")])
332 %************************************************************************
334 Record construction and update
336 %************************************************************************
339 tc_expr expr@(RecordCon con@(L loc con_name) rbinds) res_ty
340 = addErrCtxt (recordConCtxt expr) $
341 addLocM tcId con `thenM` \ (con_expr, _, con_tau) ->
343 (_, record_ty) = tcSplitFunTys con_tau
344 (tycon, ty_args) = tcSplitTyConApp record_ty
346 ASSERT( isAlgTyCon tycon )
347 zapExpectedTo res_ty record_ty `thenM_`
349 -- Check that the record bindings match the constructor
350 -- con_name is syntactically constrained to be a data constructor
351 tcLookupDataCon con_name `thenM` \ data_con ->
353 bad_fields = badFields rbinds data_con
355 if notNull bad_fields then
356 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
357 failM -- Fail now, because tcRecordBinds will crash on a bad field
360 -- Typecheck the record bindings
361 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
363 -- Check for missing fields
364 checkMissingFields data_con rbinds `thenM_`
366 returnM (RecordConOut data_con (L loc con_expr) rbinds')
368 -- The main complication with RecordUpd is that we need to explicitly
369 -- handle the *non-updated* fields. Consider:
371 -- data T a b = MkT1 { fa :: a, fb :: b }
372 -- | MkT2 { fa :: a, fc :: Int -> Int }
373 -- | MkT3 { fd :: a }
375 -- upd :: T a b -> c -> T a c
376 -- upd t x = t { fb = x}
378 -- The type signature on upd is correct (i.e. the result should not be (T a b))
379 -- because upd should be equivalent to:
381 -- upd t x = case t of
382 -- MkT1 p q -> MkT1 p x
383 -- MkT2 a b -> MkT2 p b
384 -- MkT3 d -> error ...
386 -- So we need to give a completely fresh type to the result record,
387 -- and then constrain it by the fields that are *not* updated ("p" above).
389 -- Note that because MkT3 doesn't contain all the fields being updated,
390 -- its RHS is simply an error, so it doesn't impose any type constraints
392 -- All this is done in STEP 4 below.
394 tc_expr expr@(RecordUpd record_expr rbinds) res_ty
395 = addErrCtxt (recordUpdCtxt expr) $
398 -- Check that the field names are really field names
399 ASSERT( notNull rbinds )
401 field_names = map fst rbinds
403 mappM (tcLookupGlobalId.unLoc) field_names `thenM` \ sel_ids ->
404 -- The renamer has already checked that they
407 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
408 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
409 not (isRecordSelector sel_id) -- Excludes class ops
412 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
415 -- Figure out the tycon and data cons from the first field name
417 -- It's OK to use the non-tc splitters here (for a selector)
419 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
420 data_cons = tyConDataCons tycon -- it's not a field label
421 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
423 tcInstTyVars 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 = 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 [ty | (fld,ty,_) <- tyConFields tycon,
458 fld `elem` non_upd_field_lbls]
460 mk_inst_ty tyvar result_inst_ty
461 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
463 | otherwise = newTyFlexiVarTy liftedTypeKind -- Fresh type
465 zipWithM mk_inst_ty tycon_tyvars result_inst_tys `thenM` \ inst_tys ->
468 -- Typecheck the expression to be updated
470 record_ty = mkTyConApp tycon inst_tys
472 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
475 -- Figure out the LIE we need. We have to generate some
476 -- dictionaries for the data type context, since we are going to
477 -- do pattern matching over the data cons.
479 -- What dictionaries do we need?
480 -- We just take the context of the type constructor
482 theta' = substTheta inst_env (tyConStupidTheta tycon)
484 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
485 extendLIEs dicts `thenM_`
488 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
492 %************************************************************************
494 Arithmetic sequences e.g. [a,b..]
495 and their parallel-array counterparts e.g. [: a,b.. :]
498 %************************************************************************
501 tc_expr (ArithSeqIn seq@(From expr)) res_ty
502 = zapToListTy res_ty `thenM` \ elt_ty ->
503 tcCheckRho expr elt_ty `thenM` \ expr' ->
505 newMethodFromName (ArithSeqOrigin seq)
506 elt_ty enumFromName `thenM` \ enum_from ->
508 returnM (ArithSeqOut (nlHsVar enum_from) (From expr'))
510 tc_expr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
511 = addErrCtxt (arithSeqCtxt in_expr) $
512 zapToListTy res_ty `thenM` \ elt_ty ->
513 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
514 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
515 newMethodFromName (ArithSeqOrigin seq)
516 elt_ty enumFromThenName `thenM` \ enum_from_then ->
518 returnM (ArithSeqOut (nlHsVar enum_from_then) (FromThen expr1' expr2'))
521 tc_expr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
522 = addErrCtxt (arithSeqCtxt in_expr) $
523 zapToListTy res_ty `thenM` \ elt_ty ->
524 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
525 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
526 newMethodFromName (ArithSeqOrigin seq)
527 elt_ty enumFromToName `thenM` \ enum_from_to ->
529 returnM (ArithSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
531 tc_expr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
532 = addErrCtxt (arithSeqCtxt in_expr) $
533 zapToListTy res_ty `thenM` \ elt_ty ->
534 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
535 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
536 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
537 newMethodFromName (ArithSeqOrigin seq)
538 elt_ty enumFromThenToName `thenM` \ eft ->
540 returnM (ArithSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
542 tc_expr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
543 = addErrCtxt (parrSeqCtxt in_expr) $
544 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
545 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
546 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
547 newMethodFromName (PArrSeqOrigin seq)
548 elt_ty enumFromToPName `thenM` \ enum_from_to ->
550 returnM (PArrSeqOut (nlHsVar enum_from_to) (FromTo expr1' expr2'))
552 tc_expr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
553 = addErrCtxt (parrSeqCtxt in_expr) $
554 zapToTyConApp parrTyCon res_ty `thenM` \ [elt_ty] ->
555 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
556 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
557 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
558 newMethodFromName (PArrSeqOrigin seq)
559 elt_ty enumFromThenToPName `thenM` \ eft ->
561 returnM (PArrSeqOut (nlHsVar eft) (FromThenTo expr1' expr2' expr3'))
563 tc_expr (PArrSeqIn _) _
564 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
565 -- the parser shouldn't have generated it and the renamer shouldn't have
570 %************************************************************************
574 %************************************************************************
577 #ifdef GHCI /* Only if bootstrapped */
578 -- Rename excludes these cases otherwise
579 tc_expr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
580 tc_expr (HsBracket brack) res_ty = do { 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 = do { (fun', fun_tvs, fun_tau) <- tcFun fun -- Type-check the function
615 -- Extract its argument types
616 ; (expected_arg_tys, actual_res_ty)
617 <- addErrCtxt (wrongArgsCtxt "too many" fun args) $ do
618 { traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_tau))
619 ; unifyFunTys (length args) fun_tau }
623 Check _ -> do -- Connect to result type first
624 -- See Note [Push result type in]
625 { co_fn <- tcResult fun args res_ty actual_res_ty
626 ; the_app' <- tcArgs fun fun' args expected_arg_tys
627 ; traceTc (text "tcApp: check" <+> vcat [ppr fun <+> ppr args,
628 ppr the_app', ppr actual_res_ty])
629 ; returnM (co_fn <$> the_app') }
631 Infer _ -> do -- Type check args first, then
632 -- refine result type, then do tcResult
633 { the_app' <- tcArgs fun fun' args expected_arg_tys
634 ; actual_res_ty' <- refineResultTy fun_tvs actual_res_ty
635 ; co_fn <- tcResult fun args res_ty actual_res_ty'
636 ; traceTc (text "tcApp: infer" <+> vcat [ppr fun <+> ppr args, ppr the_app',
637 ppr actual_res_ty, ppr actual_res_ty'])
638 ; returnM (co_fn <$> the_app') }
641 -- Note [Push result type in]
643 -- Unify with expected result before (was: after) type-checking the args
644 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
645 -- This is when we might detect a too-few args situation.
646 -- (One can think of cases when the opposite order would give
647 -- a better error message.)
648 -- [March 2003: I'm experimenting with putting this first. Here's an
649 -- example where it actually makes a real difference
650 -- class C t a b | t a -> b
651 -- instance C Char a Bool
653 -- data P t a = forall b. (C t a b) => MkP b
654 -- data Q t = MkQ (forall a. P t a)
657 -- f1 = MkQ (MkP True)
658 -- f2 = MkQ (MkP True :: forall a. P Char a)
660 -- With the change, f1 will type-check, because the 'Char' info from
661 -- the signature is propagated into MkQ's argument. With the check
662 -- in the other order, the extra signature in f2 is reqd.]
665 tcFun :: LHsExpr Name -> TcM (LHsExpr TcId, [TcTyVar], TcRhoType)
666 -- Instantiate the function, returning the type variables used
667 -- If the function isn't simple, infer its type, and return no
669 tcFun (L loc (HsVar f)) = setSrcSpan loc $ do
670 { (fun', tvs, fun_tau) <- tcId f
671 ; return (L loc fun', tvs, fun_tau) }
672 tcFun fun = do { (fun', fun_tau) <- tcInfer (tcMonoExpr fun)
673 ; return (fun', [], fun_tau) }
676 tcArgs :: LHsExpr Name -- The function (for error messages)
677 -> LHsExpr TcId -- The function (to build into result)
678 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
679 -> TcM (HsExpr TcId) -- Resulting application
681 tcArgs fun fun' args expected_arg_tys
682 = do { args' <- mappM (tcArg fun) (zip3 args expected_arg_tys [1..])
683 ; return (unLoc (foldl mkHsApp fun' args')) }
685 tcArg :: LHsExpr Name -- The function (for error messages)
686 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
687 -> TcM (LHsExpr TcId) -- Resulting argument
688 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
689 (tcCheckSigma arg ty)
692 tcResult fun args res_ty actual_res_ty
693 = addErrCtxtM (checkArgsCtxt fun args res_ty actual_res_ty)
694 (tcSubExp res_ty actual_res_ty)
697 -- If an error happens we try to figure out whether the
698 -- function has been given too many or too few arguments,
700 -- The ~(Check...) is because in the Infer case the tcSubExp
701 -- definitely won't fail, so we can be certain we're in the Check branch
702 checkArgsCtxt fun args (Infer _) actual_res_ty tidy_env
703 = return (tidy_env, ptext SLIT("Urk infer"))
705 checkArgsCtxt fun args (Check expected_res_ty) actual_res_ty tidy_env
706 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
707 zonkTcType actual_res_ty `thenM` \ act_ty' ->
709 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
710 (env2, act_ty'') = tidyOpenType env1 act_ty'
711 (exp_args, _) = tcSplitFunTys exp_ty''
712 (act_args, _) = tcSplitFunTys act_ty''
714 len_act_args = length act_args
715 len_exp_args = length exp_args
717 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
718 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
719 | otherwise = appCtxt fun args
721 returnM (env2, message)
724 refineResultTy :: [TcTyVar] -- Newly instantiated meta-tyvars of the function
725 -> TcType -- Result type, instantiated with those tyvars
726 -> TcM TcType -- Refined result type
727 -- De-wobblify the result type, by taking account what we learned
728 -- from type-checking the arguments. Just one level of de-wobblification
729 -- though. What a hack!
730 refineResultTy tvs res_ty
731 = do { mb_prs <- mapM mk_pr tvs
732 ; let subst = mkTopTvSubst (catMaybes mb_prs)
733 ; return (substTy subst res_ty) }
735 mk_pr tv = do { details <- readMetaTyVar tv
737 Indirect ty -> return (Just (tv,ty))
738 other -> return Nothing
743 %************************************************************************
745 \subsection{@tcId@ typchecks an identifier occurrence}
747 %************************************************************************
749 tcId instantiates an occurrence of an Id.
750 The instantiate_it loop runs round instantiating the Id.
751 It has to be a loop because we are now prepared to entertain
753 f:: forall a. Eq a => forall b. Baz b => tau
754 We want to instantiate this to
755 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
757 The -fno-method-sharing flag controls what happens so far as the LIE
758 is concerned. The default case is that for an overloaded function we
759 generate a "method" Id, and add the Method Inst to the LIE. So you get
762 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
763 If you specify -fno-method-sharing, the dictionary application
764 isn't shared, so we get
766 f = /\a (d:Num a) (x:a) -> (+) a d x x
767 This gets a bit less sharing, but
768 a) it's better for RULEs involving overloaded functions
769 b) perhaps fewer separated lambdas
772 tcId :: Name -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
773 -- Return the type variables at which the function
774 -- is instantiated, as well as the translated variable and its type
776 tcId name -- Look up the Id and instantiate its type
777 = tcLookup name `thenM` \ thing ->
779 AGlobal (AnId id) -> instantiate id
780 -- A global cannot possibly be ill-staged
781 -- nor does it need the 'lifting' treatment
783 ; AGlobal (ADataCon con) -- Similar, but instantiate the stupid theta too
784 -> do { (expr, tvs, tau) <- instantiate (dataConWrapId con)
785 ; tcInstStupidTheta con (mkTyVarTys tvs)
786 -- Remember to chuck in the constraints from the "silly context"
787 ; return (expr, tvs, tau) }
789 ; ATcId id th_level proc_level
790 -> do { checkProcLevel id proc_level
791 ; tc_local_id id th_level }
793 ; other -> pprPanic "tcId" (ppr name $$ ppr thing)
798 tc_local_id id th_bind_lvl -- Non-TH case
801 #else /* GHCI and TH is on */
802 tc_local_id id th_bind_lvl -- TH case
803 = -- Check for cross-stage lifting
804 getStage `thenM` \ use_stage ->
806 Brack use_lvl ps_var lie_var
807 | use_lvl > th_bind_lvl
808 -> -- E.g. \x -> [| h x |]
809 -- We must behave as if the reference to x was
811 -- We use 'x' itself as the splice proxy, used by
812 -- the desugarer to stitch it all back together.
813 -- If 'x' occurs many times we may get many identical
814 -- bindings of the same splice proxy, but that doesn't
815 -- matter, although it's a mite untidy.
819 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
820 -- If x is polymorphic, its occurrence sites might
821 -- have different instantiations, so we can't use plain
822 -- 'x' as the splice proxy name. I don't know how to
823 -- solve this, and it's probably unimportant, so I'm
824 -- just going to flag an error for now
827 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
828 -- Put the 'lift' constraint into the right LIE
830 -- Update the pending splices
831 readMutVar ps_var `thenM` \ ps ->
832 writeMutVar ps_var ((name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps) `thenM_`
834 returnM (HsVar id, [], id_ty))
837 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
841 instantiate :: TcId -> TcM (HsExpr TcId, [TcTyVar], TcRhoType)
842 instantiate fun_id = loop (HsVar fun_id) [] (idType fun_id)
844 loop (HsVar fun_id) tvs fun_ty
845 | want_method_inst fun_ty
846 = tcInstType fun_ty `thenM` \ (tyvars, theta, tau) ->
847 newMethodWithGivenTy orig fun_id
848 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
849 loop (HsVar meth_id) (tvs ++ tyvars) tau
853 = tcInstCall orig fun_ty `thenM` \ (inst_fn, new_tvs, tau) ->
854 loop (inst_fn <$> fun) (tvs ++ new_tvs) tau
857 = returnM (fun, tvs, fun_ty)
859 -- Hack Alert (want_method_inst)!
860 -- If f :: (%x :: T) => Int -> Int
861 -- Then if we have two separate calls, (f 3, f 4), we cannot
862 -- make a method constraint that then gets shared, thus:
863 -- let m = f %x in (m 3, m 4)
864 -- because that loses the linearity of the constraint.
865 -- The simplest thing to do is never to construct a method constraint
866 -- in the first place that has a linear implicit parameter in it.
867 want_method_inst fun_ty
868 | opt_NoMethodSharing = False
869 | otherwise = case tcSplitSigmaTy fun_ty of
870 (_,[],_) -> False -- Not overloaded
871 (_,theta,_) -> not (any isLinearPred theta)
873 orig = OccurrenceOf name
876 %************************************************************************
878 \subsection{Record bindings}
880 %************************************************************************
882 Game plan for record bindings
883 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
884 1. Find the TyCon for the bindings, from the first field label.
886 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
888 For each binding field = value
890 3. Instantiate the field type (from the field label) using the type
893 4 Type check the value using tcArg, passing the field type as
894 the expected argument type.
896 This extends OK when the field types are universally quantified.
901 :: TyCon -- Type constructor for the record
902 -> [TcType] -- Args of this type constructor
903 -> HsRecordBinds Name
904 -> TcM (HsRecordBinds TcId)
906 tcRecordBinds tycon ty_args rbinds
907 = mappM do_bind rbinds
909 tenv = zipTopTvSubst (tyConTyVars tycon) ty_args
911 do_bind (L loc field_lbl, rhs)
912 = addErrCtxt (fieldCtxt field_lbl) $
914 field_ty = tyConFieldType tycon field_lbl
915 field_ty' = substTy tenv field_ty
917 tcCheckSigma rhs field_ty' `thenM` \ rhs' ->
918 tcLookupId field_lbl `thenM` \ sel_id ->
919 ASSERT( isRecordSelector sel_id )
920 returnM (L loc sel_id, rhs')
922 tyConFieldType :: TyCon -> FieldLabel -> Type
923 tyConFieldType tycon field_lbl
924 = case [ty | (f,ty,_) <- tyConFields tycon, f == field_lbl] of
925 (ty:other) -> ASSERT( null other) ty
926 -- This lookup and assertion will surely succeed, because
927 -- we check that the fields are indeed record selectors
928 -- before calling tcRecordBinds
930 badFields rbinds data_con
931 = filter (not . (`elem` field_names)) (recBindFields rbinds)
933 field_names = dataConFieldLabels data_con
935 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
936 checkMissingFields data_con rbinds
937 | null field_labels -- Not declared as a record;
938 -- But C{} is still valid if no strict fields
939 = if any isMarkedStrict field_strs then
940 -- Illegal if any arg is strict
941 addErrTc (missingStrictFields data_con [])
945 | otherwise -- A record
946 = checkM (null missing_s_fields)
947 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
949 doptM Opt_WarnMissingFields `thenM` \ warn ->
950 checkM (not (warn && notNull missing_ns_fields))
951 (warnTc True (missingFields data_con missing_ns_fields))
955 = [ fl | (fl, str) <- field_info,
957 not (fl `elem` field_names_used)
960 = [ fl | (fl, str) <- field_info,
961 not (isMarkedStrict str),
962 not (fl `elem` field_names_used)
965 field_names_used = recBindFields rbinds
966 field_labels = dataConFieldLabels data_con
968 field_info = zipEqual "missingFields"
972 field_strs = dataConStrictMarks data_con
975 %************************************************************************
977 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
979 %************************************************************************
982 tcCheckRhos :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
984 tcCheckRhos [] [] = returnM []
985 tcCheckRhos (expr:exprs) (ty:tys)
986 = tcCheckRho expr ty `thenM` \ expr' ->
987 tcCheckRhos exprs tys `thenM` \ exprs' ->
988 returnM (expr':exprs')
992 %************************************************************************
994 \subsection{Literals}
996 %************************************************************************
1001 tcLit :: HsLit -> Expected TcRhoType -> TcM (HsExpr TcId)
1003 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
1008 %************************************************************************
1010 \subsection{Errors and contexts}
1012 %************************************************************************
1014 Boring and alphabetical:
1017 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1020 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1023 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1026 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1029 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1031 fieldCtxt field_name
1032 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1034 funAppCtxt fun arg arg_no
1035 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1036 quotes (ppr fun) <> text ", namely"])
1037 4 (quotes (ppr arg))
1040 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1043 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1046 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1049 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1051 the_app = foldl mkHsApp fun args -- Used in error messages
1054 = hang (ptext SLIT("No constructor has all these fields:"))
1055 4 (pprQuotedList (recBindFields rbinds))
1057 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1058 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1061 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1063 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1064 missingStrictFields con fields
1067 rest | null fields = empty -- Happens for non-record constructors
1068 -- with strict fields
1069 | otherwise = colon <+> pprWithCommas ppr fields
1071 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1072 ptext SLIT("does not have the required strict field(s)")
1074 missingFields :: DataCon -> [FieldLabel] -> SDoc
1075 missingFields con fields
1076 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1077 <+> pprWithCommas ppr fields
1079 wrongArgsCtxt too_many_or_few fun args
1080 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1081 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1082 <+> ptext SLIT("arguments in the call"))
1083 4 (parens (ppr the_app))
1085 the_app = foldl mkHsApp fun args -- Used in error messages
1088 polySpliceErr :: Id -> SDoc
1090 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)