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' qtvs qtys [arg1_ty, arg2_ty]
232 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
233 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
234 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
235 ; return (qtys', arg2') }
236 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
240 tcExpr (HsLet binds expr) res_ty
241 = do { (binds', expr') <- tcLocalBinds binds $
242 tcMonoExpr expr res_ty
243 ; return (HsLet binds' expr') }
245 tcExpr (HsCase scrut matches) exp_ty
246 = do { -- We used to typecheck the case alternatives first.
247 -- The case patterns tend to give good type info to use
248 -- when typechecking the scrutinee. For example
251 -- will report that map is applied to too few arguments
253 -- But now, in the GADT world, we need to typecheck the scrutinee
254 -- first, to get type info that may be refined in the case alternatives
255 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
258 ; traceTc (text "HsCase" <+> ppr scrut_ty)
259 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
260 ; return (HsCase scrut' matches') }
262 match_ctxt = MC { mc_what = CaseAlt,
265 tcExpr (HsIf pred b1 b2) res_ty
266 = do { pred' <- addErrCtxt (predCtxt pred) $
267 tcMonoExpr pred boolTy
268 ; b1' <- tcMonoExpr b1 res_ty
269 ; b2' <- tcMonoExpr b2 res_ty
270 ; return (HsIf pred' b1' b2') }
272 tcExpr (HsDo do_or_lc stmts body _) res_ty
273 = tcDoStmts do_or_lc stmts body res_ty
275 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
276 = do { elt_ty <- boxySplitListTy res_ty
277 ; exprs' <- mappM (tc_elt elt_ty) exprs
278 ; return (ExplicitList elt_ty exprs') }
280 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
282 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
283 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
284 ; exprs' <- mappM (tc_elt elt_ty) exprs
285 ; ifM (null exprs) (zapToMonotype elt_ty)
286 -- If there are no expressions in the comprehension
287 -- we must still fill in the box
288 -- (Not needed for [] and () becuase they happen
289 -- to parse as data constructors.)
290 ; return (ExplicitPArr elt_ty exprs') }
292 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
294 tcExpr (ExplicitTuple exprs boxity) res_ty
295 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length exprs)) res_ty
296 ; exprs' <- tcPolyExprs exprs arg_tys
297 ; return (ExplicitTuple exprs' boxity) }
299 tcExpr (HsProc pat cmd) res_ty
300 = do { (pat', cmd') <- tcProc pat cmd res_ty
301 ; return (HsProc pat' cmd') }
303 tcExpr e@(HsArrApp _ _ _ _ _) _
304 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
305 ptext SLIT("was found where an expression was expected")])
307 tcExpr e@(HsArrForm _ _ _) _
308 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
309 ptext SLIT("was found where an expression was expected")])
312 %************************************************************************
314 Record construction and update
316 %************************************************************************
319 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
320 = do { data_con <- tcLookupDataCon con_name
322 -- Check for missing fields
323 ; checkMissingFields data_con rbinds
325 ; let arity = dataConSourceArity data_con
326 check_fields qtvs qtys arg_tys
327 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
328 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
329 ; qtys' <- mapM refineBoxToTau qtys
330 ; return (qtys', rbinds') }
331 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
332 -- filled, which is the invariant expected by tcIdApp
333 -- How could this not be the case? Consider a record construction
334 -- that does not mention all the fields.
336 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
338 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
340 -- The main complication with RecordUpd is that we need to explicitly
341 -- handle the *non-updated* fields. Consider:
343 -- data T a b = MkT1 { fa :: a, fb :: b }
344 -- | MkT2 { fa :: a, fc :: Int -> Int }
345 -- | MkT3 { fd :: a }
347 -- upd :: T a b -> c -> T a c
348 -- upd t x = t { fb = x}
350 -- The type signature on upd is correct (i.e. the result should not be (T a b))
351 -- because upd should be equivalent to:
353 -- upd t x = case t of
354 -- MkT1 p q -> MkT1 p x
355 -- MkT2 a b -> MkT2 p b
356 -- MkT3 d -> error ...
358 -- So we need to give a completely fresh type to the result record,
359 -- and then constrain it by the fields that are *not* updated ("p" above).
361 -- Note that because MkT3 doesn't contain all the fields being updated,
362 -- its RHS is simply an error, so it doesn't impose any type constraints
364 -- All this is done in STEP 4 below.
368 -- For record update we require that every constructor involved in the
369 -- update (i.e. that has all the specified fields) is "vanilla". I
370 -- don't know how to do the update otherwise.
373 tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
375 -- Check that the field names are really field names
376 ASSERT( notNull rbinds )
378 field_names = map fst rbinds
380 mappM (tcLookupField . unLoc) field_names `thenM` \ sel_ids ->
381 -- The renamer has already checked that they
384 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
385 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
386 not (isRecordSelector sel_id) -- Excludes class ops
389 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
392 -- Figure out the tycon and data cons from the first field name
394 -- It's OK to use the non-tc splitters here (for a selector)
395 upd_field_lbls = recBindFields rbinds
397 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
398 data_cons = tyConDataCons tycon -- it's not a field label
399 relevant_cons = filter is_relevant data_cons
400 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
404 -- Check that at least one constructor has all the named fields
405 -- i.e. has an empty set of bad fields returned by badFields
406 checkTc (not (null relevant_cons))
407 (badFieldsUpd rbinds) `thenM_`
409 -- Check that all relevant data cons are vanilla. Doing record updates on
410 -- GADTs and/or existentials is more than my tiny brain can cope with today
411 checkTc (all isVanillaDataCon relevant_cons)
412 (nonVanillaUpd tycon) `thenM_`
415 -- Use the un-updated fields to find a vector of booleans saying
416 -- which type arguments must be the same in updatee and result.
418 -- WARNING: this code assumes that all data_cons in a common tycon
419 -- have FieldLabels abstracted over the same tyvars.
421 -- A constructor is only relevant to this process if
422 -- it contains *all* the fields that are being updated
423 con1 = head relevant_cons -- A representative constructor
424 con1_tyvars = dataConUnivTyVars con1
425 con1_flds = dataConFieldLabels con1
426 con1_arg_tys = dataConOrigArgTys con1
427 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
428 , not (fld `elem` upd_field_lbls) ]
430 is_common_tv tv = tv `elemVarSet` common_tyvars
432 mk_inst_ty tv result_inst_ty
433 | is_common_tv tv = returnM result_inst_ty -- Same as result type
434 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
436 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
437 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
440 -- Typecheck the update bindings.
441 -- (Do this after checking for bad fields in case there's a field that
442 -- doesn't match the constructor.)
444 result_record_ty = mkTyConApp tycon result_inst_tys
445 con1_arg_tys' = map (substTy inst_env) con1_arg_tys
447 tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
448 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
451 -- Typecheck the expression to be updated
453 record_ty = ASSERT( length inst_tys == tyConArity tycon )
454 mkTyConApp tycon inst_tys
455 -- This is one place where the isVanilla check is important
456 -- So that inst_tys matches the tycon
458 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
461 -- Figure out the LIE we need. We have to generate some
462 -- dictionaries for the data type context, since we are going to
463 -- do pattern matching over the data cons.
465 -- What dictionaries do we need? The tyConStupidTheta tells us.
467 theta' = substTheta inst_env (tyConStupidTheta tycon)
469 instStupidTheta RecordUpdOrigin theta' `thenM_`
472 returnM (mkHsWrap co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
476 %************************************************************************
478 Arithmetic sequences e.g. [a,b..]
479 and their parallel-array counterparts e.g. [: a,b.. :]
482 %************************************************************************
485 tcExpr (ArithSeq _ seq@(From expr)) res_ty
486 = do { elt_ty <- boxySplitListTy res_ty
487 ; expr' <- tcPolyExpr expr elt_ty
488 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
490 ; return (ArithSeq (HsVar enum_from) (From expr')) }
492 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
493 = do { elt_ty <- boxySplitListTy res_ty
494 ; expr1' <- tcPolyExpr expr1 elt_ty
495 ; expr2' <- tcPolyExpr expr2 elt_ty
496 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
497 elt_ty enumFromThenName
498 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
501 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
502 = do { elt_ty <- boxySplitListTy res_ty
503 ; expr1' <- tcPolyExpr expr1 elt_ty
504 ; expr2' <- tcPolyExpr expr2 elt_ty
505 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
506 elt_ty enumFromToName
507 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
509 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
510 = do { elt_ty <- boxySplitListTy res_ty
511 ; expr1' <- tcPolyExpr expr1 elt_ty
512 ; expr2' <- tcPolyExpr expr2 elt_ty
513 ; expr3' <- tcPolyExpr expr3 elt_ty
514 ; eft <- newMethodFromName (ArithSeqOrigin seq)
515 elt_ty enumFromThenToName
516 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
518 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
519 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
520 ; expr1' <- tcPolyExpr expr1 elt_ty
521 ; expr2' <- tcPolyExpr expr2 elt_ty
522 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
523 elt_ty enumFromToPName
524 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
526 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
527 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
528 ; expr1' <- tcPolyExpr expr1 elt_ty
529 ; expr2' <- tcPolyExpr expr2 elt_ty
530 ; expr3' <- tcPolyExpr expr3 elt_ty
531 ; eft <- newMethodFromName (PArrSeqOrigin seq)
532 elt_ty enumFromThenToPName
533 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
535 tcExpr (PArrSeq _ _) _
536 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
537 -- the parser shouldn't have generated it and the renamer shouldn't have
542 %************************************************************************
546 %************************************************************************
549 #ifdef GHCI /* Only if bootstrapped */
550 -- Rename excludes these cases otherwise
551 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
552 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
558 %************************************************************************
562 %************************************************************************
565 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
569 %************************************************************************
573 %************************************************************************
576 ---------------------------
577 tcApp :: HsExpr Name -- Function
578 -> Arity -- Number of args reqd
579 -> ArgChecker results
580 -> BoxyRhoType -- Result type
581 -> TcM (HsExpr TcId, results)
583 -- (tcFun fun n_args arg_checker res_ty)
584 -- The argument type checker, arg_checker, will be passed exactly n_args types
586 tcApp (HsVar fun_name) n_args arg_checker res_ty
587 = tcIdApp fun_name n_args arg_checker res_ty
589 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
590 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
591 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
592 ; arg_tys' <- mapM readFilledBox arg_boxes
593 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
594 ; return (fun', args') }
596 ---------------------------
597 tcIdApp :: Name -- Function
598 -> Arity -- Number of args reqd
599 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
600 -> BoxyRhoType -- Result type
601 -> TcM (HsExpr TcId, results)
603 -- Call (f e1 ... en) :: res_ty
604 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
605 -- (where k <= n; fres has the rest)
606 -- NB: if k < n then the function doesn't have enough args, and
607 -- presumably fres is a type variable that we are going to
608 -- instantiate with a function type
610 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
612 tcIdApp fun_name n_args arg_checker res_ty
613 = do { let orig = OccurrenceOf fun_name
614 ; (fun, fun_ty) <- lookupFun orig fun_name
616 -- Split up the function type
617 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
618 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
620 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
621 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
622 res_qtvs = exactTyVarsOfType fun_res_ty
623 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
624 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
625 k = length fun_arg_tys -- k <= n_args
626 n_missing_args = n_args - k -- Always >= 0
628 -- Match the result type of the function with the
629 -- result type of the context, to get an inital substitution
630 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
631 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
632 res_ty' = mkFunTys extra_arg_tys' res_ty
633 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
635 -- Typecheck the arguments!
636 -- Doing so will fill arg_qtvs and extra_arg_tys'
637 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
639 -- Strip boxes from the qtvs that have been filled in by the arg checking
640 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
642 -- Result subsumption
643 -- This fills in res_qtvs
644 ; let res_subst = zipOpenTvSubst qtvs qtys''
645 fun_res_ty'' = substTy res_subst fun_res_ty
646 res_ty'' = mkFunTys extra_arg_tys'' res_ty
647 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
649 -- And pack up the results
650 -- By applying the coercion just to the *function* we can make
651 -- tcFun work nicely for OpApp and Sections too
652 ; fun' <- instFun orig fun res_subst tv_theta_prs
653 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
654 ; return (mkHsWrap co_fn' fun', args') }
657 Note [Silly type synonyms in smart-app]
658 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
659 When we call sripBoxyType, all of the boxes should be filled
660 in. But we need to be careful about type synonyms:
664 In the call (f x) we'll typecheck x, expecting it to have type
665 (T box). Usually that would fill in the box, but in this case not;
666 because 'a' is discarded by the silly type synonym T. So we must
667 use exactTyVarsOfType to figure out which type variables are free
668 in the argument type.
671 -- tcId is a specialisation of tcIdApp when there are no arguments
672 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
677 -> BoxyRhoType -- Result type
679 tcId orig fun_name res_ty
680 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
681 ; (fun, fun_ty) <- lookupFun orig fun_name
683 -- Split up the function type
684 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
685 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
686 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
687 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
689 -- Do the subsumption check wrt the result type
690 ; let res_subst = zipTopTvSubst qtvs qtv_tys
691 fun_tau' = substTy res_subst fun_tau
693 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
695 -- And pack up the results
696 ; fun' <- instFun orig fun res_subst tv_theta_prs
697 ; return (mkHsWrap co_fn fun') }
699 -- Note [Push result type in]
701 -- Unify with expected result before (was: after) type-checking the args
702 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
703 -- This is when we might detect a too-few args situation.
704 -- (One can think of cases when the opposite order would give
705 -- a better error message.)
706 -- [March 2003: I'm experimenting with putting this first. Here's an
707 -- example where it actually makes a real difference
708 -- class C t a b | t a -> b
709 -- instance C Char a Bool
711 -- data P t a = forall b. (C t a b) => MkP b
712 -- data Q t = MkQ (forall a. P t a)
715 -- f1 = MkQ (MkP True)
716 -- f2 = MkQ (MkP True :: forall a. P Char a)
718 -- With the change, f1 will type-check, because the 'Char' info from
719 -- the signature is propagated into MkQ's argument. With the check
720 -- in the other order, the extra signature in f2 is reqd.]
722 ---------------------------
723 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
724 -- Typecheck a syntax operator, checking that it has the specified type
725 -- The operator is always a variable at this stage (i.e. renamer output)
726 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
727 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
729 ---------------------------
730 instFun :: InstOrigin
732 -> TvSubst -- The instantiating substitution
733 -> [([TyVar], ThetaType)] -- Stuff to instantiate
736 instFun orig fun subst []
737 = return fun -- Common short cut
739 instFun orig fun subst tv_theta_prs
740 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
742 -- Make two ad-hoc checks
743 ; doStupidChecks fun ty_theta_prs'
745 -- Now do normal instantiation
746 ; go True fun ty_theta_prs' }
748 subst_pr (tvs, theta)
749 = (map (substTyVar subst) tvs, substTheta subst theta)
751 go _ fun [] = return fun
753 go True (HsVar fun_id) ((tys,theta) : prs)
754 | want_method_inst theta
755 = do { meth_id <- newMethodWithGivenTy orig fun_id tys
756 ; go False (HsVar meth_id) prs }
757 -- Go round with 'False' to prevent further use
758 -- of newMethod: see Note [Multiple instantiation]
760 go _ fun ((tys, theta) : prs)
761 = do { co_fn <- instCall orig tys theta
762 ; go False (HsWrap co_fn fun) prs }
764 -- See Note [No method sharing]
765 want_method_inst theta = not (null theta) -- Overloaded
766 && not opt_NoMethodSharing
769 Note [Multiple instantiation]
770 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
771 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
772 For example, consider
773 f :: forall a. Eq a => forall b. Ord b => a -> b
774 At a call to f, at say [Int, Bool], it's tempting to translate the call to
778 f_m1 :: forall b. Ord b => Int -> b
782 f_m2 = f_m1 Bool dOrdBool
784 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
785 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
787 But it's entirely possible that f_m2 will continue to float out, because it
788 mentions no type variables. Result, f_m1 isn't in scope.
790 Here's a concrete example that does this (test tc200):
793 f :: Eq b => b -> a -> Int
794 baz :: Eq a => Int -> a -> Int
799 Current solution: only do the "method sharing" thing for the first type/dict
800 application, not for the iterated ones. A horribly subtle point.
802 Note [No method sharing]
803 ~~~~~~~~~~~~~~~~~~~~~~~~
804 The -fno-method-sharing flag controls what happens so far as the LIE
805 is concerned. The default case is that for an overloaded function we
806 generate a "method" Id, and add the Method Inst to the LIE. So you get
809 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
810 If you specify -fno-method-sharing, the dictionary application
811 isn't shared, so we get
813 f = /\a (d:Num a) (x:a) -> (+) a d x x
814 This gets a bit less sharing, but
815 a) it's better for RULEs involving overloaded functions
816 b) perhaps fewer separated lambdas
820 tcArgs implements a left-to-right order, which goes beyond what is described in the
821 impredicative type inference paper. In particular, it allows
823 where runST :: (forall s. ST s a) -> a
824 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
825 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
826 before checking foo. The left-to-right order really helps here.
829 tcArgs :: LHsExpr Name -- The function (for error messages)
830 -> [LHsExpr Name] -- Actual args
831 -> ArgChecker [LHsExpr TcId]
833 type ArgChecker results
834 = [TyVar] -> [TcSigmaType] -- Current instantiation
835 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
836 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
838 tcArgs fun args qtvs qtys arg_tys
839 = go 1 qtys args arg_tys
841 go n qtys [] [] = return (qtys, [])
842 go n qtys (arg:args) (arg_ty:arg_tys)
843 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
844 ; qtys' <- mapM refineBox qtys -- Exploit new info
845 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
846 ; return (qtys'', arg':args') }
848 tcArg :: LHsExpr Name -- The function
849 -> Int -- and arg number (for error messages)
851 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
853 -> TcM (LHsExpr TcId) -- Resulting argument
854 tcArg fun arg_no arg qtvs qtys ty
855 = addErrCtxt (funAppCtxt fun arg arg_no) $
856 tcPolyExprNC arg (substTyWith qtvs qtys ty)
862 Nasty check to ensure that tagToEnum# is applied to a type that is an
863 enumeration TyCon. Unification may refine the type later, but this
864 check won't see that, alas. It's crude but it works.
866 Here's are two cases that should fail
868 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
871 g = tagToEnum# 0 -- Int is not an enumeration
875 doStupidChecks :: HsExpr TcId
876 -> [([TcType], ThetaType)]
878 -- Check two tiresome and ad-hoc cases
879 -- (a) the "stupid theta" for a data con; add the constraints
880 -- from the "stupid theta" of a data constructor (sigh)
881 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
883 doStupidChecks (HsVar fun_id) ((tys,_):_)
884 | Just con <- isDataConId_maybe fun_id -- (a)
885 = addDataConStupidTheta con tys
887 | fun_id `hasKey` tagToEnumKey -- (b)
888 = do { tys' <- zonkTcTypes tys
889 ; checkTc (ok tys') (tagToEnumError tys')
893 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
894 Just (tc,_) -> isEnumerationTyCon tc
897 doStupidChecks fun tv_theta_prs
898 = return () -- The common case
902 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
903 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
904 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
906 at_type | null tys = empty -- Probably never happens
907 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
910 %************************************************************************
912 \subsection{@tcId@ typchecks an identifier occurrence}
914 %************************************************************************
917 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
918 lookupFun orig id_name
919 = do { thing <- tcLookup id_name
921 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
923 wrap_id = dataConWrapId con
926 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
927 | otherwise -> return (HsVar id, idType id)
928 -- A global cannot possibly be ill-staged
929 -- nor does it need the 'lifting' treatment
931 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
932 -> do { thLocalId orig id ty lvl
934 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
935 Just co -> return (mkHsWrap co (HsVar id), ty) }
937 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
940 #ifndef GHCI /* GHCI and TH is off */
941 --------------------------------------
942 -- thLocalId : Check for cross-stage lifting
943 thLocalId orig id id_ty th_bind_lvl
946 #else /* GHCI and TH is on */
947 thLocalId orig id id_ty th_bind_lvl
948 = do { use_stage <- getStage -- TH case
950 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
951 -> thBrackId orig id ps_var lie_var
952 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
956 --------------------------------------
957 thBrackId orig id ps_var lie_var
958 | isExternalName id_name
959 = -- Top-level identifiers in this module,
960 -- (which have External Names)
961 -- are just like the imported case:
962 -- no need for the 'lifting' treatment
963 -- E.g. this is fine:
966 -- But we do need to put f into the keep-alive
967 -- set, because after desugaring the code will
968 -- only mention f's *name*, not f itself.
969 do { keepAliveTc id_name; return id }
972 = -- Nested identifiers, such as 'x' in
973 -- E.g. \x -> [| h x |]
974 -- We must behave as if the reference to x was
976 -- We use 'x' itself as the splice proxy, used by
977 -- the desugarer to stitch it all back together.
978 -- If 'x' occurs many times we may get many identical
979 -- bindings of the same splice proxy, but that doesn't
980 -- matter, although it's a mite untidy.
981 do { let id_ty = idType id
982 ; checkTc (isTauTy id_ty) (polySpliceErr id)
983 -- If x is polymorphic, its occurrence sites might
984 -- have different instantiations, so we can't use plain
985 -- 'x' as the splice proxy name. I don't know how to
986 -- solve this, and it's probably unimportant, so I'm
987 -- just going to flag an error for now
989 ; id_ty' <- zapToMonotype id_ty
990 -- The id_ty might have an OpenTypeKind, but we
991 -- can't instantiate the Lift class at that kind,
992 -- so we zap it to a LiftedTypeKind monotype
993 -- C.f. the call in TcPat.newLitInst
995 ; setLIEVar lie_var $ do
996 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
997 -- Put the 'lift' constraint into the right LIE
999 -- Update the pending splices
1000 ; ps <- readMutVar ps_var
1001 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1010 %************************************************************************
1012 \subsection{Record bindings}
1014 %************************************************************************
1016 Game plan for record bindings
1017 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1018 1. Find the TyCon for the bindings, from the first field label.
1020 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1022 For each binding field = value
1024 3. Instantiate the field type (from the field label) using the type
1027 4 Type check the value using tcArg, passing the field type as
1028 the expected argument type.
1030 This extends OK when the field types are universally quantified.
1036 -> [TcType] -- Expected type for each field
1037 -> HsRecordBinds Name
1038 -> TcM (HsRecordBinds TcId)
1040 tcRecordBinds data_con arg_tys rbinds
1041 = do { mb_binds <- mappM do_bind rbinds
1042 ; return (catMaybes mb_binds) }
1044 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1045 do_bind (L loc field_lbl, rhs)
1046 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1047 = addErrCtxt (fieldCtxt field_lbl) $
1048 do { rhs' <- tcPolyExprNC rhs field_ty
1049 ; sel_id <- tcLookupField field_lbl
1050 ; ASSERT( isRecordSelector sel_id )
1051 return (Just (L loc sel_id, rhs')) }
1053 = do { addErrTc (badFieldCon data_con field_lbl)
1056 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1057 checkMissingFields data_con rbinds
1058 | null field_labels -- Not declared as a record;
1059 -- But C{} is still valid if no strict fields
1060 = if any isMarkedStrict field_strs then
1061 -- Illegal if any arg is strict
1062 addErrTc (missingStrictFields data_con [])
1066 | otherwise -- A record
1067 = checkM (null missing_s_fields)
1068 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1070 doptM Opt_WarnMissingFields `thenM` \ warn ->
1071 checkM (not (warn && notNull missing_ns_fields))
1072 (warnTc True (missingFields data_con missing_ns_fields))
1076 = [ fl | (fl, str) <- field_info,
1078 not (fl `elem` field_names_used)
1081 = [ fl | (fl, str) <- field_info,
1082 not (isMarkedStrict str),
1083 not (fl `elem` field_names_used)
1086 field_names_used = recBindFields rbinds
1087 field_labels = dataConFieldLabels data_con
1089 field_info = zipEqual "missingFields"
1093 field_strs = dataConStrictMarks data_con
1096 %************************************************************************
1098 \subsection{Errors and contexts}
1100 %************************************************************************
1102 Boring and alphabetical:
1105 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1108 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1110 fieldCtxt field_name
1111 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1113 funAppCtxt fun arg arg_no
1114 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1115 quotes (ppr fun) <> text ", namely"])
1116 4 (quotes (ppr arg))
1119 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1122 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
1123 <+> ptext SLIT("is not (yet) supported"),
1124 ptext SLIT("Use pattern-matching instead")]
1126 = hang (ptext SLIT("No constructor has all these fields:"))
1127 4 (pprQuotedList (recBindFields rbinds))
1129 naughtyRecordSel sel_id
1130 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1131 ptext SLIT("as a function due to escaped type variables") $$
1132 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1135 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1137 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1138 missingStrictFields con fields
1141 rest | null fields = empty -- Happens for non-record constructors
1142 -- with strict fields
1143 | otherwise = colon <+> pprWithCommas ppr fields
1145 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1146 ptext SLIT("does not have the required strict field(s)")
1148 missingFields :: DataCon -> [FieldLabel] -> SDoc
1149 missingFields con fields
1150 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1151 <+> pprWithCommas ppr fields
1154 = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1157 polySpliceErr :: Id -> SDoc
1159 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)