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') }
133 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
134 = do { expr' <- tcMonoExpr expr res_ty
135 ; return (HsCoreAnn lbl expr') }
137 tcExpr (HsOverLit lit) res_ty
138 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
139 ; return (HsOverLit lit') }
141 tcExpr (NegApp expr neg_expr) res_ty
142 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
143 (mkFunTy res_ty res_ty)
144 ; expr' <- tcMonoExpr expr res_ty
145 ; return (NegApp expr' neg_expr') }
147 tcExpr (HsIPVar ip) res_ty
148 = do { -- Implicit parameters must have a *tau-type* not a
149 -- type scheme. We enforce this by creating a fresh
150 -- type variable as its type. (Because res_ty may not
152 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
153 ; co_fn <- tcSubExp ip_ty res_ty
154 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
156 ; return (mkHsWrap co_fn (HsIPVar ip')) }
158 tcExpr (HsApp e1 e2) res_ty
161 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
162 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
163 go lfun@(L loc fun) args
164 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
165 tcApp fun (length args) (tcArgs lfun args) res_ty
166 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
168 tcExpr (HsLam match) res_ty
169 = do { (co_fn, match') <- tcMatchLambda match res_ty
170 ; return (mkHsWrap co_fn (HsLam match')) }
172 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
173 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
175 -- Remember to extend the lexical type-variable environment
176 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
177 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
178 tcPolyExprNC expr res_ty)
180 ; co_fn <- tcSubExp sig_tc_ty res_ty
181 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
183 tcExpr (HsType ty) res_ty
184 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
185 -- This is the syntax for type applications that I was planning
186 -- but there are difficulties (e.g. what order for type args)
187 -- so it's not enabled yet.
188 -- Can't eliminate it altogether from the parser, because the
189 -- same parser parses *patterns*.
193 %************************************************************************
195 Infix operators and sections
197 %************************************************************************
200 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
201 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
202 ; return (OpApp arg1' (L loc op') fix arg2') }
204 -- Left sections, equivalent to
211 -- We treat it as similar to the latter, so we don't
212 -- actually require the function to take two arguments
213 -- at all. For example, (x `not`) means (not x);
214 -- you get postfix operators! Not really Haskell 98
215 -- I suppose, but it's less work and kind of useful.
217 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
218 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
219 ; return (SectionL arg1' (L loc op')) }
221 -- Right sections, equivalent to \ x -> x `op` expr, or
224 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
225 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
226 tcApp op 2 (tc_args arg1_ty') res_ty'
227 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
229 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
230 <+> ptext SLIT("takes one argument")
231 tc_args arg1_ty' [arg1_ty, arg2_ty]
232 = do { boxyUnify arg1_ty' arg1_ty
233 ; tcArg lop (arg2, arg2_ty, 2) }
234 tc_args arg1_ty' other = panic "tcExpr SectionR"
238 tcExpr (HsLet binds expr) res_ty
239 = do { (binds', expr') <- tcLocalBinds binds $
240 tcMonoExpr expr res_ty
241 ; return (HsLet binds' expr') }
243 tcExpr (HsCase scrut matches) exp_ty
244 = do { -- We used to typecheck the case alternatives first.
245 -- The case patterns tend to give good type info to use
246 -- when typechecking the scrutinee. For example
249 -- will report that map is applied to too few arguments
251 -- But now, in the GADT world, we need to typecheck the scrutinee
252 -- first, to get type info that may be refined in the case alternatives
253 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
256 ; traceTc (text "HsCase" <+> ppr scrut_ty)
257 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
258 ; return (HsCase scrut' matches') }
260 match_ctxt = MC { mc_what = CaseAlt,
263 tcExpr (HsIf pred b1 b2) res_ty
264 = do { pred' <- addErrCtxt (predCtxt pred) $
265 tcMonoExpr pred boolTy
266 ; b1' <- tcMonoExpr b1 res_ty
267 ; b2' <- tcMonoExpr b2 res_ty
268 ; return (HsIf pred' b1' b2') }
270 tcExpr (HsDo do_or_lc stmts body _) res_ty
271 = tcDoStmts do_or_lc stmts body res_ty
273 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
274 = do { elt_ty <- boxySplitListTy res_ty
275 ; exprs' <- mappM (tc_elt elt_ty) exprs
276 ; return (ExplicitList elt_ty exprs') }
278 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
280 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
281 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
282 ; exprs' <- mappM (tc_elt elt_ty) exprs
283 ; ifM (null exprs) (zapToMonotype elt_ty)
284 -- If there are no expressions in the comprehension
285 -- we must still fill in the box
286 -- (Not needed for [] and () becuase they happen
287 -- to parse as data constructors.)
288 ; return (ExplicitPArr elt_ty exprs') }
290 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
292 tcExpr (ExplicitTuple exprs boxity) res_ty
293 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length exprs)) res_ty
294 ; exprs' <- tcPolyExprs exprs arg_tys
295 ; return (ExplicitTuple exprs' boxity) }
297 tcExpr (HsProc pat cmd) res_ty
298 = do { (pat', cmd') <- tcProc pat cmd res_ty
299 ; return (HsProc pat' cmd') }
301 tcExpr e@(HsArrApp _ _ _ _ _) _
302 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
303 ptext SLIT("was found where an expression was expected")])
305 tcExpr e@(HsArrForm _ _ _) _
306 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
307 ptext SLIT("was found where an expression was expected")])
310 %************************************************************************
312 Record construction and update
314 %************************************************************************
317 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
318 = do { data_con <- tcLookupDataCon con_name
320 -- Check for missing fields
321 ; checkMissingFields data_con rbinds
323 ; let arity = dataConSourceArity data_con
325 = do { rbinds' <- tcRecordBinds data_con arg_tys rbinds
328 -- The unBox ensures that all the boxes in arg_tys are indeed
329 -- filled, which is the invariant expected by tcIdApp
331 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
333 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
335 -- The main complication with RecordUpd is that we need to explicitly
336 -- handle the *non-updated* fields. Consider:
338 -- data T a b = MkT1 { fa :: a, fb :: b }
339 -- | MkT2 { fa :: a, fc :: Int -> Int }
340 -- | MkT3 { fd :: a }
342 -- upd :: T a b -> c -> T a c
343 -- upd t x = t { fb = x}
345 -- The type signature on upd is correct (i.e. the result should not be (T a b))
346 -- because upd should be equivalent to:
348 -- upd t x = case t of
349 -- MkT1 p q -> MkT1 p x
350 -- MkT2 a b -> MkT2 p b
351 -- MkT3 d -> error ...
353 -- So we need to give a completely fresh type to the result record,
354 -- and then constrain it by the fields that are *not* updated ("p" above).
356 -- Note that because MkT3 doesn't contain all the fields being updated,
357 -- its RHS is simply an error, so it doesn't impose any type constraints
359 -- All this is done in STEP 4 below.
363 -- For record update we require that every constructor involved in the
364 -- update (i.e. that has all the specified fields) is "vanilla". I
365 -- don't know how to do the update otherwise.
368 tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
370 -- Check that the field names are really field names
371 ASSERT( notNull rbinds )
373 field_names = map fst rbinds
375 mappM (tcLookupField . unLoc) field_names `thenM` \ sel_ids ->
376 -- The renamer has already checked that they
379 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
380 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
381 not (isRecordSelector sel_id) -- Excludes class ops
384 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
387 -- Figure out the tycon and data cons from the first field name
389 -- It's OK to use the non-tc splitters here (for a selector)
390 upd_field_lbls = recBindFields rbinds
392 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
393 data_cons = tyConDataCons tycon -- it's not a field label
394 relevant_cons = filter is_relevant data_cons
395 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
399 -- Check that at least one constructor has all the named fields
400 -- i.e. has an empty set of bad fields returned by badFields
401 checkTc (not (null relevant_cons))
402 (badFieldsUpd rbinds) `thenM_`
404 -- Check that all relevant data cons are vanilla. Doing record updates on
405 -- GADTs and/or existentials is more than my tiny brain can cope with today
406 checkTc (all isVanillaDataCon relevant_cons)
407 (nonVanillaUpd tycon) `thenM_`
410 -- Use the un-updated fields to find a vector of booleans saying
411 -- which type arguments must be the same in updatee and result.
413 -- WARNING: this code assumes that all data_cons in a common tycon
414 -- have FieldLabels abstracted over the same tyvars.
416 -- A constructor is only relevant to this process if
417 -- it contains *all* the fields that are being updated
418 con1 = head relevant_cons -- A representative constructor
419 con1_tyvars = dataConUnivTyVars con1
420 con1_flds = dataConFieldLabels con1
421 con1_arg_tys = dataConOrigArgTys con1
422 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
423 , not (fld `elem` upd_field_lbls) ]
425 is_common_tv tv = tv `elemVarSet` common_tyvars
427 mk_inst_ty tv result_inst_ty
428 | is_common_tv tv = returnM result_inst_ty -- Same as result type
429 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
431 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
432 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
435 -- Typecheck the update bindings.
436 -- (Do this after checking for bad fields in case there's a field that
437 -- doesn't match the constructor.)
439 result_record_ty = mkTyConApp tycon result_inst_tys
440 con1_arg_tys' = map (substTy inst_env) con1_arg_tys
442 tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
443 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
446 -- Typecheck the expression to be updated
448 record_ty = ASSERT( length inst_tys == tyConArity tycon )
449 mkTyConApp tycon inst_tys
450 -- This is one place where the isVanilla check is important
451 -- So that inst_tys matches the tycon
453 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
456 -- Figure out the LIE we need. We have to generate some
457 -- dictionaries for the data type context, since we are going to
458 -- do pattern matching over the data cons.
460 -- What dictionaries do we need? The tyConStupidTheta tells us.
462 theta' = substTheta inst_env (tyConStupidTheta tycon)
464 instStupidTheta RecordUpdOrigin theta' `thenM_`
467 returnM (mkHsWrap co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
471 %************************************************************************
473 Arithmetic sequences e.g. [a,b..]
474 and their parallel-array counterparts e.g. [: a,b.. :]
477 %************************************************************************
480 tcExpr (ArithSeq _ seq@(From expr)) res_ty
481 = do { elt_ty <- boxySplitListTy res_ty
482 ; expr' <- tcPolyExpr expr elt_ty
483 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
485 ; return (ArithSeq (HsVar enum_from) (From expr')) }
487 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
488 = do { elt_ty <- boxySplitListTy res_ty
489 ; expr1' <- tcPolyExpr expr1 elt_ty
490 ; expr2' <- tcPolyExpr expr2 elt_ty
491 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
492 elt_ty enumFromThenName
493 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
496 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
497 = do { elt_ty <- boxySplitListTy res_ty
498 ; expr1' <- tcPolyExpr expr1 elt_ty
499 ; expr2' <- tcPolyExpr expr2 elt_ty
500 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
501 elt_ty enumFromToName
502 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
504 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
505 = do { elt_ty <- boxySplitListTy res_ty
506 ; expr1' <- tcPolyExpr expr1 elt_ty
507 ; expr2' <- tcPolyExpr expr2 elt_ty
508 ; expr3' <- tcPolyExpr expr3 elt_ty
509 ; eft <- newMethodFromName (ArithSeqOrigin seq)
510 elt_ty enumFromThenToName
511 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
513 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
514 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
515 ; expr1' <- tcPolyExpr expr1 elt_ty
516 ; expr2' <- tcPolyExpr expr2 elt_ty
517 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
518 elt_ty enumFromToPName
519 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
521 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
522 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
523 ; expr1' <- tcPolyExpr expr1 elt_ty
524 ; expr2' <- tcPolyExpr expr2 elt_ty
525 ; expr3' <- tcPolyExpr expr3 elt_ty
526 ; eft <- newMethodFromName (PArrSeqOrigin seq)
527 elt_ty enumFromThenToPName
528 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
530 tcExpr (PArrSeq _ _) _
531 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
532 -- the parser shouldn't have generated it and the renamer shouldn't have
537 %************************************************************************
541 %************************************************************************
544 #ifdef GHCI /* Only if bootstrapped */
545 -- Rename excludes these cases otherwise
546 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
547 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
553 %************************************************************************
557 %************************************************************************
560 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
564 %************************************************************************
568 %************************************************************************
571 ---------------------------
572 tcApp :: HsExpr Name -- Function
573 -> Arity -- Number of args reqd
574 -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
575 -> BoxyRhoType -- Result type
576 -> TcM (HsExpr TcId, arg_results)
578 -- (tcFun fun n_args arg_checker res_ty)
579 -- The argument type checker, arg_checker, will be passed exactly n_args types
581 tcApp (HsVar fun_name) n_args arg_checker res_ty
582 = tcIdApp fun_name n_args arg_checker res_ty
584 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
585 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
586 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
587 ; arg_tys' <- mapM readFilledBox arg_boxes
588 ; args' <- arg_checker arg_tys'
589 ; return (fun', args') }
591 ---------------------------
592 tcIdApp :: Name -- Function
593 -> Arity -- Number of args reqd
594 -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
595 -- The arg-checker guarantees to fill all boxes in the arg types
596 -> BoxyRhoType -- Result type
597 -> TcM (HsExpr TcId, arg_results)
599 -- Call (f e1 ... en) :: res_ty
600 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
601 -- (where k <= n; fres has the rest)
602 -- NB: if k < n then the function doesn't have enough args, and
603 -- presumably fres is a type variable that we are going to
604 -- instantiate with a function type
606 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
608 tcIdApp fun_name n_args arg_checker res_ty
609 = do { let orig = OccurrenceOf fun_name
610 ; (fun, fun_ty) <- lookupFun orig fun_name
612 -- Split up the function type
613 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
614 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
616 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
617 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
618 res_qtvs = exactTyVarsOfType fun_res_ty
619 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
620 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
621 k = length fun_arg_tys -- k <= n_args
622 n_missing_args = n_args - k -- Always >= 0
624 -- Match the result type of the function with the
625 -- result type of the context, to get an inital substitution
626 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
627 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
628 res_ty' = mkFunTys extra_arg_tys' res_ty
629 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
630 ; let arg_subst = zipOpenTvSubst qtvs qtys'
631 fun_arg_tys' = substTys arg_subst fun_arg_tys
633 -- Typecheck the arguments!
634 -- Doing so will fill arg_qtvs and extra_arg_tys'
635 ; args' <- arg_checker (fun_arg_tys' ++ extra_arg_tys')
637 -- Strip boxes from the qtvs that have been filled in by the arg checking
638 -- AND any variables that are mentioned in neither arg nor result
639 -- the latter are mentioned only in constraints; stripBoxyType will
640 -- fill them with a monotype
641 ; let strip qtv qty' | qtv `elemVarSet` arg_qtvs = stripBoxyType qty'
642 | otherwise = return qty'
643 ; qtys'' <- zipWithM strip qtvs qtys'
644 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
646 -- Result subsumption
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 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 = (map (substTyVar 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
822 tcArgs :: LHsExpr Name -- The function (for error messages)
823 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
824 -> TcM [LHsExpr TcId] -- Resulting args
826 tcArgs fun args expected_arg_tys
827 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
829 tcArg :: LHsExpr Name -- The function (for error messages)
830 -> (LHsExpr Name, BoxySigmaType, Int) -- Actual argument and expected arg type
831 -> TcM (LHsExpr TcId) -- Resulting argument
832 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no) $
839 Nasty check to ensure that tagToEnum# is applied to a type that is an
840 enumeration TyCon. Unification may refine the type later, but this
841 check won't see that, alas. It's crude but it works.
843 Here's are two cases that should fail
845 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
848 g = tagToEnum# 0 -- Int is not an enumeration
852 doStupidChecks :: HsExpr TcId
853 -> [([TcType], ThetaType)]
855 -- Check two tiresome and ad-hoc cases
856 -- (a) the "stupid theta" for a data con; add the constraints
857 -- from the "stupid theta" of a data constructor (sigh)
858 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
860 doStupidChecks (HsVar fun_id) ((tys,_):_)
861 | Just con <- isDataConId_maybe fun_id -- (a)
862 = addDataConStupidTheta con tys
864 | fun_id `hasKey` tagToEnumKey -- (b)
865 = do { tys' <- zonkTcTypes tys
866 ; checkTc (ok tys') (tagToEnumError tys')
870 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
871 Just (tc,_) -> isEnumerationTyCon tc
874 doStupidChecks fun tv_theta_prs
875 = return () -- The common case
879 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
880 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
881 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
883 at_type | null tys = empty -- Probably never happens
884 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
887 %************************************************************************
889 \subsection{@tcId@ typchecks an identifier occurrence}
891 %************************************************************************
894 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
895 lookupFun orig id_name
896 = do { thing <- tcLookup id_name
898 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
900 wrap_id = dataConWrapId con
903 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
904 | otherwise -> return (HsVar id, idType id)
905 -- A global cannot possibly be ill-staged
906 -- nor does it need the 'lifting' treatment
908 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
909 -> do { thLocalId orig id ty lvl
911 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
912 Just co -> return (mkHsWrap co (HsVar id), ty) }
914 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
917 #ifndef GHCI /* GHCI and TH is off */
918 --------------------------------------
919 -- thLocalId : Check for cross-stage lifting
920 thLocalId orig id id_ty th_bind_lvl
923 #else /* GHCI and TH is on */
924 thLocalId orig id id_ty th_bind_lvl
925 = do { use_stage <- getStage -- TH case
927 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
928 -> thBrackId orig id ps_var lie_var
929 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
933 --------------------------------------
934 thBrackId orig id ps_var lie_var
935 | isExternalName id_name
936 = -- Top-level identifiers in this module,
937 -- (which have External Names)
938 -- are just like the imported case:
939 -- no need for the 'lifting' treatment
940 -- E.g. this is fine:
943 -- But we do need to put f into the keep-alive
944 -- set, because after desugaring the code will
945 -- only mention f's *name*, not f itself.
946 do { keepAliveTc id_name; return id }
949 = -- Nested identifiers, such as 'x' in
950 -- E.g. \x -> [| h x |]
951 -- We must behave as if the reference to x was
953 -- We use 'x' itself as the splice proxy, used by
954 -- the desugarer to stitch it all back together.
955 -- If 'x' occurs many times we may get many identical
956 -- bindings of the same splice proxy, but that doesn't
957 -- matter, although it's a mite untidy.
958 do { let id_ty = idType id
959 ; checkTc (isTauTy id_ty) (polySpliceErr id)
960 -- If x is polymorphic, its occurrence sites might
961 -- have different instantiations, so we can't use plain
962 -- 'x' as the splice proxy name. I don't know how to
963 -- solve this, and it's probably unimportant, so I'm
964 -- just going to flag an error for now
966 ; id_ty' <- zapToMonotype id_ty
967 -- The id_ty might have an OpenTypeKind, but we
968 -- can't instantiate the Lift class at that kind,
969 -- so we zap it to a LiftedTypeKind monotype
970 -- C.f. the call in TcPat.newLitInst
972 ; setLIEVar lie_var $ do
973 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
974 -- Put the 'lift' constraint into the right LIE
976 -- Update the pending splices
977 ; ps <- readMutVar ps_var
978 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
987 %************************************************************************
989 \subsection{Record bindings}
991 %************************************************************************
993 Game plan for record bindings
994 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
995 1. Find the TyCon for the bindings, from the first field label.
997 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
999 For each binding field = value
1001 3. Instantiate the field type (from the field label) using the type
1004 4 Type check the value using tcArg, passing the field type as
1005 the expected argument type.
1007 This extends OK when the field types are universally quantified.
1013 -> [TcType] -- Expected type for each field
1014 -> HsRecordBinds Name
1015 -> TcM (HsRecordBinds TcId)
1017 tcRecordBinds data_con arg_tys rbinds
1018 = do { mb_binds <- mappM do_bind rbinds
1019 ; return (catMaybes mb_binds) }
1021 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1022 do_bind (L loc field_lbl, rhs)
1023 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1024 = addErrCtxt (fieldCtxt field_lbl) $
1025 do { rhs' <- tcPolyExprNC rhs field_ty
1026 ; sel_id <- tcLookupField field_lbl
1027 ; ASSERT( isRecordSelector sel_id )
1028 return (Just (L loc sel_id, rhs')) }
1030 = do { addErrTc (badFieldCon data_con field_lbl)
1033 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1034 checkMissingFields data_con rbinds
1035 | null field_labels -- Not declared as a record;
1036 -- But C{} is still valid if no strict fields
1037 = if any isMarkedStrict field_strs then
1038 -- Illegal if any arg is strict
1039 addErrTc (missingStrictFields data_con [])
1043 | otherwise -- A record
1044 = checkM (null missing_s_fields)
1045 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1047 doptM Opt_WarnMissingFields `thenM` \ warn ->
1048 checkM (not (warn && notNull missing_ns_fields))
1049 (warnTc True (missingFields data_con missing_ns_fields))
1053 = [ fl | (fl, str) <- field_info,
1055 not (fl `elem` field_names_used)
1058 = [ fl | (fl, str) <- field_info,
1059 not (isMarkedStrict str),
1060 not (fl `elem` field_names_used)
1063 field_names_used = recBindFields rbinds
1064 field_labels = dataConFieldLabels data_con
1066 field_info = zipEqual "missingFields"
1070 field_strs = dataConStrictMarks data_con
1073 %************************************************************************
1075 \subsection{Errors and contexts}
1077 %************************************************************************
1079 Boring and alphabetical:
1082 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1085 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1087 fieldCtxt field_name
1088 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1090 funAppCtxt fun arg arg_no
1091 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1092 quotes (ppr fun) <> text ", namely"])
1093 4 (quotes (ppr arg))
1096 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1099 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
1100 <+> ptext SLIT("is not (yet) supported"),
1101 ptext SLIT("Use pattern-matching instead")]
1103 = hang (ptext SLIT("No constructor has all these fields:"))
1104 4 (pprQuotedList (recBindFields rbinds))
1106 naughtyRecordSel sel_id
1107 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1108 ptext SLIT("as a function due to escaped type variables") $$
1109 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1112 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1114 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1115 missingStrictFields con fields
1118 rest | null fields = empty -- Happens for non-record constructors
1119 -- with strict fields
1120 | otherwise = colon <+> pprWithCommas ppr fields
1122 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1123 ptext SLIT("does not have the required strict field(s)")
1125 missingFields :: DataCon -> [FieldLabel] -> SDoc
1126 missingFields con fields
1127 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1128 <+> pprWithCommas ppr fields
1131 = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1134 polySpliceErr :: Id -> SDoc
1136 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)