2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
8 module TcExpr ( tcPolyExpr, tcPolyExprNC,
9 tcMonoExpr, tcInferRho, tcSyntaxOp ) where
11 #include "HsVersions.h"
13 #ifdef GHCI /* Only if bootstrapped */
14 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
15 import qualified DsMeta
53 %************************************************************************
55 \subsection{Main wrappers}
57 %************************************************************************
60 tcPolyExpr, tcPolyExprNC
61 :: LHsExpr Name -- Expession to type check
62 -> BoxySigmaType -- Expected type (could be a polytpye)
63 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
65 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
66 -- to add context information.
67 -- The NC version does not do so, usually because the caller wants
70 tcPolyExpr expr res_ty
71 = addErrCtxt (exprCtxt (unLoc expr)) $
72 tcPolyExprNC expr res_ty
74 tcPolyExprNC expr res_ty
76 = do { (gen_fn, expr') <- tcGen res_ty emptyVarSet (\_ -> tcPolyExprNC expr)
77 -- Note the recursive call to tcPolyExpr, because the
78 -- type may have multiple layers of for-alls
79 -- E.g. forall a. Eq a => forall b. Ord b => ....
80 ; return (mkLHsWrap gen_fn expr') }
83 = tcMonoExpr expr res_ty
86 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
87 tcPolyExprs [] [] = returnM []
88 tcPolyExprs (expr:exprs) (ty:tys)
89 = do { expr' <- tcPolyExpr expr ty
90 ; exprs' <- tcPolyExprs exprs tys
91 ; returnM (expr':exprs') }
92 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
95 tcMonoExpr :: LHsExpr Name -- Expression to type check
96 -> BoxyRhoType -- Expected type (could be a type variable)
97 -- Definitely no foralls at the top
98 -- Can contain boxes, which will be filled in
101 tcMonoExpr (L loc expr) res_ty
102 = ASSERT( not (isSigmaTy res_ty) )
104 do { expr' <- tcExpr expr res_ty
105 ; return (L loc expr') }
108 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
109 tcInferRho expr = tcInfer (tcMonoExpr expr)
114 %************************************************************************
116 tcExpr: the main expression typechecker
118 %************************************************************************
121 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
122 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
124 tcExpr (HsLit lit) res_ty = do { boxyUnify (hsLitType lit) res_ty
125 ; return (HsLit lit) }
127 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
128 ; return (HsPar expr') }
130 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
131 ; returnM (HsSCC lbl expr') }
132 tcExpr (HsTickPragma info expr) res_ty
133 = do { expr' <- tcMonoExpr expr res_ty
134 ; returnM (HsTickPragma info expr') }
136 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
137 = do { expr' <- tcMonoExpr expr res_ty
138 ; return (HsCoreAnn lbl expr') }
140 tcExpr (HsOverLit lit) res_ty
141 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
142 ; return (HsOverLit lit') }
144 tcExpr (NegApp expr neg_expr) res_ty
145 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
146 (mkFunTy res_ty res_ty)
147 ; expr' <- tcMonoExpr expr res_ty
148 ; return (NegApp expr' neg_expr') }
150 tcExpr (HsIPVar ip) res_ty
151 = do { -- Implicit parameters must have a *tau-type* not a
152 -- type scheme. We enforce this by creating a fresh
153 -- type variable as its type. (Because res_ty may not
155 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
156 ; co_fn <- tcSubExp ip_ty res_ty
157 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
159 ; return (mkHsWrap co_fn (HsIPVar ip')) }
161 tcExpr (HsApp e1 e2) res_ty
164 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
165 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
166 go lfun@(L loc fun) args
167 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
168 tcApp fun (length args) (tcArgs lfun args) res_ty
169 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
171 tcExpr (HsLam match) res_ty
172 = do { (co_fn, match') <- tcMatchLambda match res_ty
173 ; return (mkHsWrap co_fn (HsLam match')) }
175 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
176 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
178 -- Remember to extend the lexical type-variable environment
179 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
180 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
181 tcPolyExprNC expr res_ty)
183 ; co_fn <- tcSubExp sig_tc_ty res_ty
184 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
186 tcExpr (HsType ty) res_ty
187 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
188 -- This is the syntax for type applications that I was planning
189 -- but there are difficulties (e.g. what order for type args)
190 -- so it's not enabled yet.
191 -- Can't eliminate it altogether from the parser, because the
192 -- same parser parses *patterns*.
196 %************************************************************************
198 Infix operators and sections
200 %************************************************************************
203 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
204 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
205 ; return (OpApp arg1' (L loc op') fix arg2') }
207 -- Left sections, equivalent to
214 -- We treat it as similar to the latter, so we don't
215 -- actually require the function to take two arguments
216 -- at all. For example, (x `not`) means (not x);
217 -- you get postfix operators! Not really Haskell 98
218 -- I suppose, but it's less work and kind of useful.
220 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
221 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
222 ; return (SectionL arg1' (L loc op')) }
224 -- Right sections, equivalent to \ x -> x `op` expr, or
227 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
228 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
229 tcApp op 2 (tc_args arg1_ty') res_ty'
230 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
232 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
233 <+> ptext SLIT("takes one argument")
234 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
235 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
236 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
237 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
238 ; return (qtys', arg2') }
239 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
243 tcExpr (HsLet binds expr) res_ty
244 = do { (binds', expr') <- tcLocalBinds binds $
245 tcMonoExpr expr res_ty
246 ; return (HsLet binds' expr') }
248 tcExpr (HsCase scrut matches) exp_ty
249 = do { -- We used to typecheck the case alternatives first.
250 -- The case patterns tend to give good type info to use
251 -- when typechecking the scrutinee. For example
254 -- will report that map is applied to too few arguments
256 -- But now, in the GADT world, we need to typecheck the scrutinee
257 -- first, to get type info that may be refined in the case alternatives
258 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
261 ; traceTc (text "HsCase" <+> ppr scrut_ty)
262 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
263 ; return (HsCase scrut' matches') }
265 match_ctxt = MC { mc_what = CaseAlt,
268 tcExpr (HsIf pred b1 b2) res_ty
269 = do { pred' <- addErrCtxt (predCtxt pred) $
270 tcMonoExpr pred boolTy
271 ; b1' <- tcMonoExpr b1 res_ty
272 ; b2' <- tcMonoExpr b2 res_ty
273 ; return (HsIf pred' b1' b2') }
275 tcExpr (HsDo do_or_lc stmts body _) res_ty
276 = tcDoStmts do_or_lc stmts body res_ty
278 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
279 = do { elt_ty <- boxySplitListTy res_ty
280 ; exprs' <- mappM (tc_elt elt_ty) exprs
281 ; return (ExplicitList elt_ty exprs') }
283 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
285 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
286 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
287 ; exprs' <- mappM (tc_elt elt_ty) exprs
288 ; ifM (null exprs) (zapToMonotype elt_ty)
289 -- If there are no expressions in the comprehension
290 -- we must still fill in the box
291 -- (Not needed for [] and () becuase they happen
292 -- to parse as data constructors.)
293 ; return (ExplicitPArr elt_ty exprs') }
295 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
297 tcExpr (ExplicitTuple exprs boxity) res_ty
298 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length exprs)) res_ty
299 ; exprs' <- tcPolyExprs exprs arg_tys
300 ; return (ExplicitTuple exprs' boxity) }
302 tcExpr (HsProc pat cmd) res_ty
303 = do { (pat', cmd') <- tcProc pat cmd res_ty
304 ; return (HsProc pat' cmd') }
306 tcExpr e@(HsArrApp _ _ _ _ _) _
307 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
308 ptext SLIT("was found where an expression was expected")])
310 tcExpr e@(HsArrForm _ _ _) _
311 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
312 ptext SLIT("was found where an expression was expected")])
315 %************************************************************************
317 Record construction and update
319 %************************************************************************
322 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
323 = do { data_con <- tcLookupDataCon con_name
325 -- Check for missing fields
326 ; checkMissingFields data_con rbinds
328 ; let arity = dataConSourceArity data_con
329 check_fields qtvs qtys arg_tys
330 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
331 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
332 ; qtys' <- mapM refineBoxToTau qtys
333 ; return (qtys', rbinds') }
334 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
335 -- filled, which is the invariant expected by tcIdApp
336 -- How could this not be the case? Consider a record construction
337 -- that does not mention all the fields.
339 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
341 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
343 -- The main complication with RecordUpd is that we need to explicitly
344 -- handle the *non-updated* fields. Consider:
346 -- data T a b = MkT1 { fa :: a, fb :: b }
347 -- | MkT2 { fa :: a, fc :: Int -> Int }
348 -- | MkT3 { fd :: a }
350 -- upd :: T a b -> c -> T a c
351 -- upd t x = t { fb = x}
353 -- The type signature on upd is correct (i.e. the result should not be (T a b))
354 -- because upd should be equivalent to:
356 -- upd t x = case t of
357 -- MkT1 p q -> MkT1 p x
358 -- MkT2 a b -> MkT2 p b
359 -- MkT3 d -> error ...
361 -- So we need to give a completely fresh type to the result record,
362 -- and then constrain it by the fields that are *not* updated ("p" above).
364 -- Note that because MkT3 doesn't contain all the fields being updated,
365 -- its RHS is simply an error, so it doesn't impose any type constraints
367 -- All this is done in STEP 4 below.
371 -- For record update we require that every constructor involved in the
372 -- update (i.e. that has all the specified fields) is "vanilla". I
373 -- don't know how to do the update otherwise.
376 tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
378 -- Check that the field names are really field names
379 ASSERT( notNull rbinds )
381 field_names = map fst rbinds
383 mappM (tcLookupField . unLoc) field_names `thenM` \ sel_ids ->
384 -- The renamer has already checked that they
387 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
388 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
389 not (isRecordSelector sel_id) -- Excludes class ops
392 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
395 -- Figure out the tycon and data cons from the first field name
397 -- It's OK to use the non-tc splitters here (for a selector)
398 upd_field_lbls = recBindFields rbinds
400 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
401 data_cons = tyConDataCons tycon -- it's not a field label
402 relevant_cons = filter is_relevant data_cons
403 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
407 -- Check that at least one constructor has all the named fields
408 -- i.e. has an empty set of bad fields returned by badFields
409 checkTc (not (null relevant_cons))
410 (badFieldsUpd rbinds) `thenM_`
412 -- Check that all relevant data cons are vanilla. Doing record updates on
413 -- GADTs and/or existentials is more than my tiny brain can cope with today
414 checkTc (all isVanillaDataCon relevant_cons)
415 (nonVanillaUpd tycon) `thenM_`
418 -- Use the un-updated fields to find a vector of booleans saying
419 -- which type arguments must be the same in updatee and result.
421 -- WARNING: this code assumes that all data_cons in a common tycon
422 -- have FieldLabels abstracted over the same tyvars.
424 -- A constructor is only relevant to this process if
425 -- it contains *all* the fields that are being updated
426 con1 = head relevant_cons -- A representative constructor
427 con1_tyvars = dataConUnivTyVars con1
428 con1_flds = dataConFieldLabels con1
429 con1_arg_tys = dataConOrigArgTys con1
430 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
431 , not (fld `elem` upd_field_lbls) ]
433 is_common_tv tv = tv `elemVarSet` common_tyvars
435 mk_inst_ty tv result_inst_ty
436 | is_common_tv tv = returnM result_inst_ty -- Same as result type
437 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
439 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
440 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
443 -- Typecheck the update bindings.
444 -- (Do this after checking for bad fields in case there's a field that
445 -- doesn't match the constructor.)
447 result_record_ty = mkTyConApp tycon result_inst_tys
448 con1_arg_tys' = map (substTy inst_env) con1_arg_tys
450 tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
451 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
454 -- Typecheck the expression to be updated
456 record_ty = ASSERT( length inst_tys == tyConArity tycon )
457 mkTyConApp tycon inst_tys
458 -- This is one place where the isVanilla check is important
459 -- So that inst_tys matches the tycon
461 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
464 -- Figure out the LIE we need. We have to generate some
465 -- dictionaries for the data type context, since we are going to
466 -- do pattern matching over the data cons.
468 -- What dictionaries do we need? The tyConStupidTheta tells us.
470 theta' = substTheta inst_env (tyConStupidTheta tycon)
472 instStupidTheta RecordUpdOrigin theta' `thenM_`
475 returnM (mkHsWrap co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
479 %************************************************************************
481 Arithmetic sequences e.g. [a,b..]
482 and their parallel-array counterparts e.g. [: a,b.. :]
485 %************************************************************************
488 tcExpr (ArithSeq _ seq@(From expr)) res_ty
489 = do { elt_ty <- boxySplitListTy res_ty
490 ; expr' <- tcPolyExpr expr elt_ty
491 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
493 ; return (ArithSeq (HsVar enum_from) (From expr')) }
495 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
496 = do { elt_ty <- boxySplitListTy res_ty
497 ; expr1' <- tcPolyExpr expr1 elt_ty
498 ; expr2' <- tcPolyExpr expr2 elt_ty
499 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
500 elt_ty enumFromThenName
501 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
504 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
505 = do { elt_ty <- boxySplitListTy res_ty
506 ; expr1' <- tcPolyExpr expr1 elt_ty
507 ; expr2' <- tcPolyExpr expr2 elt_ty
508 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
509 elt_ty enumFromToName
510 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
512 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
513 = do { elt_ty <- boxySplitListTy res_ty
514 ; expr1' <- tcPolyExpr expr1 elt_ty
515 ; expr2' <- tcPolyExpr expr2 elt_ty
516 ; expr3' <- tcPolyExpr expr3 elt_ty
517 ; eft <- newMethodFromName (ArithSeqOrigin seq)
518 elt_ty enumFromThenToName
519 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
521 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
522 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
523 ; expr1' <- tcPolyExpr expr1 elt_ty
524 ; expr2' <- tcPolyExpr expr2 elt_ty
525 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
526 elt_ty enumFromToPName
527 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
529 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
530 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
531 ; expr1' <- tcPolyExpr expr1 elt_ty
532 ; expr2' <- tcPolyExpr expr2 elt_ty
533 ; expr3' <- tcPolyExpr expr3 elt_ty
534 ; eft <- newMethodFromName (PArrSeqOrigin seq)
535 elt_ty enumFromThenToPName
536 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
538 tcExpr (PArrSeq _ _) _
539 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
540 -- the parser shouldn't have generated it and the renamer shouldn't have
545 %************************************************************************
549 %************************************************************************
552 #ifdef GHCI /* Only if bootstrapped */
553 -- Rename excludes these cases otherwise
554 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
555 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
561 %************************************************************************
565 %************************************************************************
568 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
572 %************************************************************************
576 %************************************************************************
579 ---------------------------
580 tcApp :: HsExpr Name -- Function
581 -> Arity -- Number of args reqd
582 -> ArgChecker results
583 -> BoxyRhoType -- Result type
584 -> TcM (HsExpr TcId, results)
586 -- (tcFun fun n_args arg_checker res_ty)
587 -- The argument type checker, arg_checker, will be passed exactly n_args types
589 tcApp (HsVar fun_name) n_args arg_checker res_ty
590 = tcIdApp fun_name n_args arg_checker res_ty
592 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
593 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
594 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
595 ; arg_tys' <- mapM readFilledBox arg_boxes
596 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
597 ; return (fun', args') }
599 ---------------------------
600 tcIdApp :: Name -- Function
601 -> Arity -- Number of args reqd
602 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
603 -> BoxyRhoType -- Result type
604 -> TcM (HsExpr TcId, results)
606 -- Call (f e1 ... en) :: res_ty
607 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
608 -- (where k <= n; fres has the rest)
609 -- NB: if k < n then the function doesn't have enough args, and
610 -- presumably fres is a type variable that we are going to
611 -- instantiate with a function type
613 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
615 tcIdApp fun_name n_args arg_checker res_ty
616 = do { let orig = OccurrenceOf fun_name
617 ; (fun, fun_ty) <- lookupFun orig fun_name
619 -- Split up the function type
620 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
621 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
623 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
624 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
625 res_qtvs = exactTyVarsOfType fun_res_ty
626 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
627 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
628 k = length fun_arg_tys -- k <= n_args
629 n_missing_args = n_args - k -- Always >= 0
631 -- Match the result type of the function with the
632 -- result type of the context, to get an inital substitution
633 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
634 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
635 res_ty' = mkFunTys extra_arg_tys' res_ty
636 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
638 -- Typecheck the arguments!
639 -- Doing so will fill arg_qtvs and extra_arg_tys'
640 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
642 -- Strip boxes from the qtvs that have been filled in by the arg checking
643 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
645 -- Result subsumption
646 -- This fills in res_qtvs
647 ; let res_subst = zipOpenTvSubst qtvs qtys''
648 fun_res_ty'' = substTy res_subst fun_res_ty
649 res_ty'' = mkFunTys extra_arg_tys'' res_ty
650 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
652 -- And pack up the results
653 -- By applying the coercion just to the *function* we can make
654 -- tcFun work nicely for OpApp and Sections too
655 ; fun' <- instFun orig fun res_subst tv_theta_prs
656 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
657 ; return (mkHsWrap co_fn' fun', args') }
660 Note [Silly type synonyms in smart-app]
661 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
662 When we call sripBoxyType, all of the boxes should be filled
663 in. But we need to be careful about type synonyms:
667 In the call (f x) we'll typecheck x, expecting it to have type
668 (T box). Usually that would fill in the box, but in this case not;
669 because 'a' is discarded by the silly type synonym T. So we must
670 use exactTyVarsOfType to figure out which type variables are free
671 in the argument type.
674 -- tcId is a specialisation of tcIdApp when there are no arguments
675 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
680 -> BoxyRhoType -- Result type
682 tcId orig fun_name res_ty
683 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
684 ; (fun, fun_ty) <- lookupFun orig fun_name
686 -- Split up the function type
687 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
688 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
689 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
690 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
692 -- Do the subsumption check wrt the result type
693 ; let res_subst = zipTopTvSubst qtvs qtv_tys
694 fun_tau' = substTy res_subst fun_tau
696 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
698 -- And pack up the results
699 ; fun' <- instFun orig fun res_subst tv_theta_prs
700 ; return (mkHsWrap co_fn fun') }
702 -- Note [Push result type in]
704 -- Unify with expected result before (was: after) type-checking the args
705 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
706 -- This is when we might detect a too-few args situation.
707 -- (One can think of cases when the opposite order would give
708 -- a better error message.)
709 -- [March 2003: I'm experimenting with putting this first. Here's an
710 -- example where it actually makes a real difference
711 -- class C t a b | t a -> b
712 -- instance C Char a Bool
714 -- data P t a = forall b. (C t a b) => MkP b
715 -- data Q t = MkQ (forall a. P t a)
718 -- f1 = MkQ (MkP True)
719 -- f2 = MkQ (MkP True :: forall a. P Char a)
721 -- With the change, f1 will type-check, because the 'Char' info from
722 -- the signature is propagated into MkQ's argument. With the check
723 -- in the other order, the extra signature in f2 is reqd.]
725 ---------------------------
726 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
727 -- Typecheck a syntax operator, checking that it has the specified type
728 -- The operator is always a variable at this stage (i.e. renamer output)
729 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
730 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
732 ---------------------------
733 instFun :: InstOrigin
735 -> TvSubst -- The instantiating substitution
736 -> [([TyVar], ThetaType)] -- Stuff to instantiate
739 instFun orig fun subst []
740 = return fun -- Common short cut
742 instFun orig fun subst tv_theta_prs
743 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
745 -- Make two ad-hoc checks
746 ; doStupidChecks fun ty_theta_prs'
748 -- Now do normal instantiation
749 ; go True fun ty_theta_prs' }
751 subst_pr (tvs, theta)
752 = (substTyVars subst tvs, substTheta subst theta)
754 go _ fun [] = return fun
756 go True (HsVar fun_id) ((tys,theta) : prs)
757 | want_method_inst theta
758 = do { meth_id <- newMethodWithGivenTy orig fun_id tys
759 ; go False (HsVar meth_id) prs }
760 -- Go round with 'False' to prevent further use
761 -- of newMethod: see Note [Multiple instantiation]
763 go _ fun ((tys, theta) : prs)
764 = do { co_fn <- instCall orig tys theta
765 ; go False (HsWrap co_fn fun) prs }
767 -- See Note [No method sharing]
768 want_method_inst theta = not (null theta) -- Overloaded
769 && not opt_NoMethodSharing
772 Note [Multiple instantiation]
773 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
774 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
775 For example, consider
776 f :: forall a. Eq a => forall b. Ord b => a -> b
777 At a call to f, at say [Int, Bool], it's tempting to translate the call to
781 f_m1 :: forall b. Ord b => Int -> b
785 f_m2 = f_m1 Bool dOrdBool
787 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
788 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
790 But it's entirely possible that f_m2 will continue to float out, because it
791 mentions no type variables. Result, f_m1 isn't in scope.
793 Here's a concrete example that does this (test tc200):
796 f :: Eq b => b -> a -> Int
797 baz :: Eq a => Int -> a -> Int
802 Current solution: only do the "method sharing" thing for the first type/dict
803 application, not for the iterated ones. A horribly subtle point.
805 Note [No method sharing]
806 ~~~~~~~~~~~~~~~~~~~~~~~~
807 The -fno-method-sharing flag controls what happens so far as the LIE
808 is concerned. The default case is that for an overloaded function we
809 generate a "method" Id, and add the Method Inst to the LIE. So you get
812 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
813 If you specify -fno-method-sharing, the dictionary application
814 isn't shared, so we get
816 f = /\a (d:Num a) (x:a) -> (+) a d x x
817 This gets a bit less sharing, but
818 a) it's better for RULEs involving overloaded functions
819 b) perhaps fewer separated lambdas
823 tcArgs implements a left-to-right order, which goes beyond what is described in the
824 impredicative type inference paper. In particular, it allows
826 where runST :: (forall s. ST s a) -> a
827 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
828 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
829 before checking foo. The left-to-right order really helps here.
832 tcArgs :: LHsExpr Name -- The function (for error messages)
833 -> [LHsExpr Name] -- Actual args
834 -> ArgChecker [LHsExpr TcId]
836 type ArgChecker results
837 = [TyVar] -> [TcSigmaType] -- Current instantiation
838 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
839 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
841 tcArgs fun args qtvs qtys arg_tys
842 = go 1 qtys args arg_tys
844 go n qtys [] [] = return (qtys, [])
845 go n qtys (arg:args) (arg_ty:arg_tys)
846 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
847 ; qtys' <- mapM refineBox qtys -- Exploit new info
848 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
849 ; return (qtys'', arg':args') }
851 tcArg :: LHsExpr Name -- The function
852 -> Int -- and arg number (for error messages)
854 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
856 -> TcM (LHsExpr TcId) -- Resulting argument
857 tcArg fun arg_no arg qtvs qtys ty
858 = addErrCtxt (funAppCtxt fun arg arg_no) $
859 tcPolyExprNC arg (substTyWith qtvs qtys ty)
865 Nasty check to ensure that tagToEnum# is applied to a type that is an
866 enumeration TyCon. Unification may refine the type later, but this
867 check won't see that, alas. It's crude but it works.
869 Here's are two cases that should fail
871 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
874 g = tagToEnum# 0 -- Int is not an enumeration
878 doStupidChecks :: HsExpr TcId
879 -> [([TcType], ThetaType)]
881 -- Check two tiresome and ad-hoc cases
882 -- (a) the "stupid theta" for a data con; add the constraints
883 -- from the "stupid theta" of a data constructor (sigh)
884 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
886 doStupidChecks (HsVar fun_id) ((tys,_):_)
887 | Just con <- isDataConId_maybe fun_id -- (a)
888 = addDataConStupidTheta con tys
890 | fun_id `hasKey` tagToEnumKey -- (b)
891 = do { tys' <- zonkTcTypes tys
892 ; checkTc (ok tys') (tagToEnumError tys')
896 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
897 Just (tc,_) -> isEnumerationTyCon tc
900 doStupidChecks fun tv_theta_prs
901 = return () -- The common case
905 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
906 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
907 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
909 at_type | null tys = empty -- Probably never happens
910 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
913 %************************************************************************
915 \subsection{@tcId@ typchecks an identifier occurrence}
917 %************************************************************************
920 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
921 lookupFun orig id_name
922 = do { thing <- tcLookup id_name
924 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
926 wrap_id = dataConWrapId con
929 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
930 | otherwise -> return (HsVar id, idType id)
931 -- A global cannot possibly be ill-staged
932 -- nor does it need the 'lifting' treatment
934 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
935 -> do { thLocalId orig id ty lvl
937 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
938 Just co -> return (mkHsWrap co (HsVar id), ty) }
940 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
943 #ifndef GHCI /* GHCI and TH is off */
944 --------------------------------------
945 -- thLocalId : Check for cross-stage lifting
946 thLocalId orig id id_ty th_bind_lvl
949 #else /* GHCI and TH is on */
950 thLocalId orig id id_ty th_bind_lvl
951 = do { use_stage <- getStage -- TH case
953 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
954 -> thBrackId orig id ps_var lie_var
955 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
959 --------------------------------------
960 thBrackId orig id ps_var lie_var
961 | isExternalName id_name
962 = -- Top-level identifiers in this module,
963 -- (which have External Names)
964 -- are just like the imported case:
965 -- no need for the 'lifting' treatment
966 -- E.g. this is fine:
969 -- But we do need to put f into the keep-alive
970 -- set, because after desugaring the code will
971 -- only mention f's *name*, not f itself.
972 do { keepAliveTc id_name; return id }
975 = -- Nested identifiers, such as 'x' in
976 -- E.g. \x -> [| h x |]
977 -- We must behave as if the reference to x was
979 -- We use 'x' itself as the splice proxy, used by
980 -- the desugarer to stitch it all back together.
981 -- If 'x' occurs many times we may get many identical
982 -- bindings of the same splice proxy, but that doesn't
983 -- matter, although it's a mite untidy.
984 do { let id_ty = idType id
985 ; checkTc (isTauTy id_ty) (polySpliceErr id)
986 -- If x is polymorphic, its occurrence sites might
987 -- have different instantiations, so we can't use plain
988 -- 'x' as the splice proxy name. I don't know how to
989 -- solve this, and it's probably unimportant, so I'm
990 -- just going to flag an error for now
992 ; id_ty' <- zapToMonotype id_ty
993 -- The id_ty might have an OpenTypeKind, but we
994 -- can't instantiate the Lift class at that kind,
995 -- so we zap it to a LiftedTypeKind monotype
996 -- C.f. the call in TcPat.newLitInst
998 ; setLIEVar lie_var $ do
999 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1000 -- Put the 'lift' constraint into the right LIE
1002 -- Update the pending splices
1003 ; ps <- readMutVar ps_var
1004 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1013 %************************************************************************
1015 \subsection{Record bindings}
1017 %************************************************************************
1019 Game plan for record bindings
1020 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1021 1. Find the TyCon for the bindings, from the first field label.
1023 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1025 For each binding field = value
1027 3. Instantiate the field type (from the field label) using the type
1030 4 Type check the value using tcArg, passing the field type as
1031 the expected argument type.
1033 This extends OK when the field types are universally quantified.
1039 -> [TcType] -- Expected type for each field
1040 -> HsRecordBinds Name
1041 -> TcM (HsRecordBinds TcId)
1043 tcRecordBinds data_con arg_tys rbinds
1044 = do { mb_binds <- mappM do_bind rbinds
1045 ; return (catMaybes mb_binds) }
1047 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1048 do_bind (L loc field_lbl, rhs)
1049 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1050 = addErrCtxt (fieldCtxt field_lbl) $
1051 do { rhs' <- tcPolyExprNC rhs field_ty
1052 ; sel_id <- tcLookupField field_lbl
1053 ; ASSERT( isRecordSelector sel_id )
1054 return (Just (L loc sel_id, rhs')) }
1056 = do { addErrTc (badFieldCon data_con field_lbl)
1059 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1060 checkMissingFields data_con rbinds
1061 | null field_labels -- Not declared as a record;
1062 -- But C{} is still valid if no strict fields
1063 = if any isMarkedStrict field_strs then
1064 -- Illegal if any arg is strict
1065 addErrTc (missingStrictFields data_con [])
1069 | otherwise -- A record
1070 = checkM (null missing_s_fields)
1071 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1073 doptM Opt_WarnMissingFields `thenM` \ warn ->
1074 checkM (not (warn && notNull missing_ns_fields))
1075 (warnTc True (missingFields data_con missing_ns_fields))
1079 = [ fl | (fl, str) <- field_info,
1081 not (fl `elem` field_names_used)
1084 = [ fl | (fl, str) <- field_info,
1085 not (isMarkedStrict str),
1086 not (fl `elem` field_names_used)
1089 field_names_used = recBindFields rbinds
1090 field_labels = dataConFieldLabels data_con
1092 field_info = zipEqual "missingFields"
1096 field_strs = dataConStrictMarks data_con
1099 %************************************************************************
1101 \subsection{Errors and contexts}
1103 %************************************************************************
1105 Boring and alphabetical:
1108 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1111 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1113 fieldCtxt field_name
1114 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1116 funAppCtxt fun arg arg_no
1117 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1118 quotes (ppr fun) <> text ", namely"])
1119 4 (quotes (ppr arg))
1122 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1125 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
1126 <+> ptext SLIT("is not (yet) supported"),
1127 ptext SLIT("Use pattern-matching instead")]
1129 = hang (ptext SLIT("No constructor has all these fields:"))
1130 4 (pprQuotedList (recBindFields rbinds))
1132 naughtyRecordSel sel_id
1133 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1134 ptext SLIT("as a function due to escaped type variables") $$
1135 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1138 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1140 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1141 missingStrictFields con fields
1144 rest | null fields = empty -- Happens for non-record constructors
1145 -- with strict fields
1146 | otherwise = colon <+> pprWithCommas ppr fields
1148 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1149 ptext SLIT("does not have the required strict field(s)")
1151 missingFields :: DataCon -> [FieldLabel] -> SDoc
1152 missingFields con fields
1153 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1154 <+> pprWithCommas ppr fields
1157 = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1160 polySpliceErr :: Id -> SDoc
1162 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)