2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
15 module TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC, tcInferRho, tcInferRhoNC, tcSyntaxOp, addExprErrCtxt ) where
17 #include "HsVersions.h"
19 #ifdef GHCI /* Only if bootstrapped */
20 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
21 import qualified DsMeta
38 import TcIface ( checkWiredInTyCon )
61 import Data.List( partition )
65 %************************************************************************
67 \subsection{Main wrappers}
69 %************************************************************************
72 tcPolyExpr, tcPolyExprNC
73 :: LHsExpr Name -- Expession to type check
74 -> BoxySigmaType -- Expected type (could be a polytpye)
75 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
77 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
78 -- to add context information.
79 -- The NC version does not do so, usually because the caller wants
82 tcPolyExpr expr res_ty
83 = addExprErrCtxt expr $
84 (do {traceTc (text "tcPolyExpr") ; tcPolyExprNC expr res_ty })
86 tcPolyExprNC expr res_ty
88 = do { traceTc (text "tcPolyExprNC" <+> ppr res_ty)
89 ; (gen_fn, expr') <- tcGen res_ty emptyVarSet Nothing $ \ _ res_ty ->
90 tcPolyExprNC expr res_ty
91 -- Note the recursive call to tcPolyExpr, because the
92 -- type may have multiple layers of for-alls
93 -- E.g. forall a. Eq a => forall b. Ord b => ....
94 ; return (mkLHsWrap gen_fn expr') }
97 = tcMonoExprNC expr res_ty
100 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
101 tcPolyExprs [] [] = return []
102 tcPolyExprs (expr:exprs) (ty:tys)
103 = do { expr' <- tcPolyExpr expr ty
104 ; exprs' <- tcPolyExprs exprs tys
105 ; return (expr':exprs') }
106 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
109 tcMonoExpr, tcMonoExprNC
110 :: LHsExpr Name -- Expression to type check
111 -> BoxyRhoType -- Expected type (could be a type variable)
112 -- Definitely no foralls at the top
113 -- Can contain boxes, which will be filled in
114 -> TcM (LHsExpr TcId)
116 tcMonoExpr expr res_ty
117 = addErrCtxt (exprCtxt expr) $
118 tcMonoExprNC expr res_ty
120 tcMonoExprNC (L loc expr) res_ty
121 = ASSERT( not (isSigmaTy res_ty) )
123 do { expr' <- tcExpr expr res_ty
124 ; return (L loc expr') }
127 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
128 tcInferRho expr = tcInfer (tcMonoExpr expr)
129 tcInferRhoNC expr = tcInfer (tcMonoExprNC expr)
133 %************************************************************************
135 tcExpr: the main expression typechecker
137 %************************************************************************
140 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
141 tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
142 = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
144 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
146 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
147 ; coi <- boxyUnify lit_ty res_ty
148 ; return $ mkHsWrapCoI coi (HsLit lit)
151 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
152 ; return (HsPar expr') }
154 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
155 ; return (HsSCC lbl expr') }
156 tcExpr (HsTickPragma info expr) res_ty
157 = do { expr' <- tcMonoExpr expr res_ty
158 ; return (HsTickPragma info expr') }
160 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
161 = do { expr' <- tcMonoExpr expr res_ty
162 ; return (HsCoreAnn lbl expr') }
164 tcExpr (HsOverLit lit) res_ty
165 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
166 ; return (HsOverLit lit') }
168 tcExpr (NegApp expr neg_expr) res_ty
169 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
170 (mkFunTy res_ty res_ty)
171 ; expr' <- tcMonoExpr expr res_ty
172 ; return (NegApp expr' neg_expr') }
174 tcExpr (HsIPVar ip) res_ty
175 = do { let origin = IPOccOrigin ip
176 -- Implicit parameters must have a *tau-type* not a
177 -- type scheme. We enforce this by creating a fresh
178 -- type variable as its type. (Because res_ty may not
180 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
181 ; co_fn <- tcSubExp origin ip_ty res_ty
182 ; (ip', inst) <- newIPDict origin ip ip_ty
184 ; return (mkHsWrap co_fn (HsIPVar ip')) }
186 tcExpr (HsApp e1 e2) res_ty
189 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
190 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
191 go lfun@(L loc fun) args
192 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
193 tcApp fun (length args) (tcArgs lfun args) res_ty
194 ; traceTc (text "tcExpr args': " <+> ppr args')
195 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
197 tcExpr (HsLam match) res_ty
198 = do { (co_fn, match') <- tcMatchLambda match res_ty
199 ; return (mkHsWrap co_fn (HsLam match')) }
201 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
202 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
204 -- Remember to extend the lexical type-variable environment
205 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (Just ExprSigCtxt) $ \ skol_tvs res_ty ->
206 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
207 -- See Note [More instantiated than scoped] in TcBinds
208 tcMonoExprNC expr res_ty
210 ; co_fn <- tcSubExp ExprSigOrigin sig_tc_ty res_ty
211 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
213 tcExpr (HsType ty) res_ty
214 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
215 -- This is the syntax for type applications that I was planning
216 -- but there are difficulties (e.g. what order for type args)
217 -- so it's not enabled yet.
218 -- Can't eliminate it altogether from the parser, because the
219 -- same parser parses *patterns*.
223 %************************************************************************
225 Infix operators and sections
227 %************************************************************************
230 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
231 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
232 ; return (OpApp arg1' (L loc op') fix arg2') }
234 -- Left sections, equivalent to
238 -- or, if PostfixOperators is enabled, just
241 -- With PostfixOperators we don't
242 -- actually require the function to take two arguments
243 -- at all. For example, (x `not`) means (not x);
244 -- you get postfix operators! Not Haskell 98,
245 -- but it's less work and kind of useful.
247 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
248 = do dflags <- getDOpts
249 if dopt Opt_PostfixOperators dflags
250 then do (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
251 return (SectionL arg1' (L loc op'))
252 else do (co_fn, (op', arg1'))
253 <- subFunTys doc 1 res_ty Nothing
254 $ \ [arg2_ty'] res_ty' ->
255 tcApp op 2 (tc_args arg2_ty') res_ty'
256 return (mkHsWrap co_fn (SectionL arg1' (L loc op')))
258 doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
259 <+> ptext (sLit "takes one argument")
260 tc_args arg2_ty' qtvs qtys [arg1_ty, arg2_ty]
261 = do { boxyUnify arg2_ty' (substTyWith qtvs qtys arg2_ty)
262 ; arg1' <- tcArg lop 2 arg1 qtvs qtys arg1_ty
263 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
264 ; return (qtys', arg1') }
265 tc_args _ _ _ _ = panic "tcExpr SectionL"
267 -- Right sections, equivalent to \ x -> x `op` expr, or
270 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
271 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty Nothing $ \ [arg1_ty'] res_ty' ->
272 tcApp op 2 (tc_args arg1_ty') res_ty'
273 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
275 doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
276 <+> ptext (sLit "takes one argument")
277 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
278 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
279 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
280 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
281 ; return (qtys', arg2') }
282 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
286 tcExpr (HsLet binds expr) res_ty
287 = do { (binds', expr') <- tcLocalBinds binds $
288 tcMonoExpr expr res_ty
289 ; return (HsLet binds' expr') }
291 tcExpr (HsCase scrut matches) exp_ty
292 = do { -- We used to typecheck the case alternatives first.
293 -- The case patterns tend to give good type info to use
294 -- when typechecking the scrutinee. For example
297 -- will report that map is applied to too few arguments
299 -- But now, in the GADT world, we need to typecheck the scrutinee
300 -- first, to get type info that may be refined in the case alternatives
301 (scrut', scrut_ty) <- tcInferRho scrut
303 ; traceTc (text "HsCase" <+> ppr scrut_ty)
304 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
305 ; return (HsCase scrut' matches') }
307 match_ctxt = MC { mc_what = CaseAlt,
310 tcExpr (HsIf pred b1 b2) res_ty
311 = do { pred' <- tcMonoExpr pred boolTy
312 ; b1' <- tcMonoExpr b1 res_ty
313 ; b2' <- tcMonoExpr b2 res_ty
314 ; return (HsIf pred' b1' b2') }
316 tcExpr (HsDo do_or_lc stmts body _) res_ty
317 = tcDoStmts do_or_lc stmts body res_ty
319 tcExpr in_expr@(ExplicitList _ exprs) res_ty
320 = do { (elt_ty, coi) <- boxySplitListTy res_ty
321 ; exprs' <- mapM (tc_elt elt_ty) exprs
322 ; when (null exprs) (zapToMonotype elt_ty >> return ())
323 -- If there are no expressions in the comprehension
324 -- we must still fill in the box
326 -- The GHC front end never generates an empty ExplicitList
327 -- (instead it generates the [] data constructor) but
328 -- Template Haskell might. We could fix the bit of
329 -- TH that generates ExplicitList, but it seems less
330 -- fragile to just handle the case here.
331 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
333 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
335 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
336 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
337 ; exprs' <- mapM (tc_elt elt_ty) exprs
338 ; when (null exprs) (zapToMonotype elt_ty >> return ())
339 -- If there are no expressions in the comprehension
340 -- we must still fill in the box
341 -- (Not needed for [] and () becuase they happen
342 -- to parse as data constructors.)
343 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
345 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
347 -- For tuples, take care to preserve rigidity
348 -- E.g. case (x,y) of ....
349 -- The scrutinee should have a rigid type if x,y do
350 -- The general scheme is the same as in tcIdApp
351 tcExpr (ExplicitTuple exprs boxity) res_ty
352 = do { let kind = case boxity of { Boxed -> liftedTypeKind
353 ; Unboxed -> argTypeKind }
354 ; tvs <- newBoxyTyVars [kind | e <- exprs]
355 ; let tup_tc = tupleTyCon boxity (length exprs)
356 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
357 ; checkWiredInTyCon tup_tc -- Ensure instances are available
358 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
359 ; exprs' <- tcPolyExprs exprs arg_tys
360 ; arg_tys' <- mapM refineBox arg_tys
361 ; co_fn <- tcSubExp TupleOrigin (mkTyConApp tup_tc arg_tys') res_ty
362 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
364 tcExpr (HsProc pat cmd) res_ty
365 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
366 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
368 tcExpr e@(HsArrApp _ _ _ _ _) _
369 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
370 ptext (sLit "was found where an expression was expected")])
372 tcExpr e@(HsArrForm _ _ _) _
373 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
374 ptext (sLit "was found where an expression was expected")])
377 %************************************************************************
379 Record construction and update
381 %************************************************************************
384 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
385 = do { data_con <- tcLookupDataCon con_name
387 -- Check for missing fields
388 ; checkMissingFields data_con rbinds
390 ; let arity = dataConSourceArity data_con
391 check_fields qtvs qtys arg_tys
392 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
393 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
394 ; qtys' <- mapM refineBoxToTau qtys
395 ; return (qtys', rbinds') }
396 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
397 -- filled, which is the invariant expected by tcIdApp
398 -- How could this not be the case? Consider a record construction
399 -- that does not mention all the fields.
401 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
403 ; return (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
406 Note [Type of a record update]
407 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
408 The main complication with RecordUpd is that we need to explicitly
409 handle the *non-updated* fields. Consider:
411 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
412 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
415 upd :: T a b c -> (b',c) -> T a b' c
416 upd t x = t { fb = x}
418 The result type should be (T a b' c)
419 not (T a b c), because 'b' *is not* mentioned in a non-updated field
420 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
421 NB that it's not good enough to look at just one constructor; we must
422 look at them all; cf Trac #3219
424 After all, upd should be equivalent to:
430 So we need to give a completely fresh type to the result record,
431 and then constrain it by the fields that are *not* updated ("p" above).
432 We call these the "fixed" type variables, and compute them in getFixedTyVars.
434 Note that because MkT3 doesn't contain all the fields being updated,
435 its RHS is simply an error, so it doesn't impose any type constraints.
436 Hence the use of 'relevant_cont'.
438 Note [Implict type sharing]
439 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
440 We also take into account any "implicit" non-update fields. For example
441 data T a b where { MkT { f::a } :: T a a; ... }
442 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
447 upd :: T a b -> a -> T a b
448 upd (t::T a b) (x::a)
449 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
450 We can't give it the more general type
451 upd :: T a b -> c -> T c b
453 Note [Criteria for update]
454 ~~~~~~~~~~~~~~~~~~~~~~~~~~
455 We want to allow update for existentials etc, provided the updated
456 field isn't part of the existential. For example, this should be ok.
457 data T a where { MkT { f1::a, f2::b->b } :: T a }
461 The criterion we use is this:
463 The types of the updated fields
464 mention only the universally-quantified type variables
465 of the data constructor
467 NB: this is not (quite) the same as being a "naughty" record selector
468 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
469 in the case of GADTs. Consider
470 data T a where { MkT :: { f :: a } :: T [a] }
471 Then f is not "naughty" because it has a well-typed record selector.
472 But we don't allow updates for 'f'. (One could consider trying to
473 allow this, but it makes my head hurt. Badly. And no one has asked
476 In principle one could go further, and allow
478 g t = t { f2 = \x -> x }
479 because the expression is polymorphic...but that seems a bridge too far.
481 Note [Data family example]
482 ~~~~~~~~~~~~~~~~~~~~~~~~~~
483 data instance T (a,b) = MkT { x::a, y::b }
485 data :TP a b = MkT { a::a, y::b }
486 coTP a b :: T (a,b) ~ :TP a b
488 Suppose r :: T (t1,t2), e :: t3
489 Then r { x=e } :: T (t3,t1)
492 MkT x y -> MkT e y |> co2
493 where co1 :: T (t1,t2) ~ :TP t1 t2
494 co2 :: :TP t3 t2 ~ T (t3,t2)
495 The wrapping with co2 is done by the constructor wrapper for MkT
499 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
501 * cons are the data constructors to be updated
503 * in_inst_tys, out_inst_tys have same length, and instantiate the
504 *representation* tycon of the data cons. In Note [Data
505 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
508 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
509 = ASSERT( notNull upd_fld_names )
512 -- Check that the field names are really field names
513 ; sel_ids <- mapM tcLookupField upd_fld_names
514 -- The renamer has already checked that
515 -- selectors are all in scope
516 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
517 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
518 not (isRecordSelector sel_id), -- Excludes class ops
519 let L loc fld_name = hsRecFieldId fld ]
520 ; unless (null bad_guys) (sequence bad_guys >> failM)
523 -- Figure out the tycon and data cons from the first field name
524 ; let -- It's OK to use the non-tc splitters here (for a selector)
526 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
527 data_cons = tyConDataCons tycon -- it's not a field label
528 -- NB: for a data type family, the tycon is the instance tycon
530 relevant_cons = filter is_relevant data_cons
531 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
532 -- A constructor is only relevant to this process if
533 -- it contains *all* the fields that are being updated
534 -- Other ones will cause a runtime error if they occur
536 -- Take apart a representative constructor
537 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
538 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
539 con1_flds = dataConFieldLabels con1
540 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
543 -- Check that at least one constructor has all the named fields
544 -- i.e. has an empty set of bad fields returned by badFields
545 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
547 -- STEP 3 Note [Criteria for update]
548 -- Check that each updated field is polymorphic; that is, its type
549 -- mentions only the universally-quantified variables of the data con
550 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
551 (upd_flds1_w_tys, fixed_flds1_w_tys) = partition is_updated flds1_w_tys
552 is_updated (fld,ty) = fld `elem` upd_fld_names
554 bad_upd_flds = filter bad_fld upd_flds1_w_tys
555 con1_tv_set = mkVarSet con1_tvs
556 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
557 not (tyVarsOfType ty `subVarSet` con1_tv_set)
558 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
560 -- STEP 4 Note [Type of a record update]
561 -- Figure out types for the scrutinee and result
562 -- Both are of form (T a b c), with fresh type variables, but with
563 -- common variables where the scrutinee and result must have the same type
564 -- These are variables that appear in *any* arg of *any* of the
565 -- relevant constructors *except* in the updated fields
567 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
568 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
569 mk_inst_ty tv result_inst_ty
570 | is_fixed_tv tv = return result_inst_ty -- Same as result type
571 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
573 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
574 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
576 ; let result_ty = substTy result_inst_env con1_res_ty
577 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
578 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
579 scrut_ty = substTy scrut_subst con1_res_ty
582 -- Typecheck the thing to be updated, and the bindings
583 ; record_expr' <- tcMonoExpr record_expr scrut_ty
584 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
586 ; let origin = RecordUpdOrigin
587 ; co_fn <- tcSubExp origin result_ty res_ty
589 -- STEP 6: Deal with the stupid theta
590 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
591 ; instStupidTheta origin theta'
593 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
594 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
595 = WpCast $ mkTyConApp co_con scrut_inst_tys
600 ; return (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
601 relevant_cons scrut_inst_tys result_inst_tys)) }
603 upd_fld_names = hsRecFields rbinds
605 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
606 -- These tyvars must not change across the updates
607 getFixedTyVars tvs1 cons
608 = mkVarSet [tv1 | con <- cons
609 , let (tvs, theta, arg_tys, _) = dataConSig con
610 flds = dataConFieldLabels con
611 fixed_tvs = exactTyVarsOfTypes fixed_tys
612 -- fixed_tys: See Note [Type of a record update]
613 `unionVarSet` tyVarsOfTheta theta
614 -- Universally-quantified tyvars that
615 -- appear in any of the *implicit*
616 -- arguments to the constructor are fixed
617 -- See Note [Implict type sharing]
619 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
620 , not (fld `elem` upd_fld_names)]
621 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
622 , tv `elemVarSet` fixed_tvs ]
625 %************************************************************************
627 Arithmetic sequences e.g. [a,b..]
628 and their parallel-array counterparts e.g. [: a,b.. :]
631 %************************************************************************
634 tcExpr (ArithSeq _ seq@(From expr)) res_ty
635 = do { (elt_ty, coi) <- boxySplitListTy res_ty
636 ; expr' <- tcPolyExpr expr elt_ty
637 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
639 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
641 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
642 = do { (elt_ty, coi) <- boxySplitListTy res_ty
643 ; expr1' <- tcPolyExpr expr1 elt_ty
644 ; expr2' <- tcPolyExpr expr2 elt_ty
645 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
646 elt_ty enumFromThenName
647 ; return $ mkHsWrapCoI coi
648 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
650 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
651 = do { (elt_ty, coi) <- boxySplitListTy res_ty
652 ; expr1' <- tcPolyExpr expr1 elt_ty
653 ; expr2' <- tcPolyExpr expr2 elt_ty
654 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
655 elt_ty enumFromToName
656 ; return $ mkHsWrapCoI coi
657 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
659 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
660 = do { (elt_ty, coi) <- boxySplitListTy res_ty
661 ; expr1' <- tcPolyExpr expr1 elt_ty
662 ; expr2' <- tcPolyExpr expr2 elt_ty
663 ; expr3' <- tcPolyExpr expr3 elt_ty
664 ; eft <- newMethodFromName (ArithSeqOrigin seq)
665 elt_ty enumFromThenToName
666 ; return $ mkHsWrapCoI coi
667 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
669 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
670 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
671 ; expr1' <- tcPolyExpr expr1 elt_ty
672 ; expr2' <- tcPolyExpr expr2 elt_ty
673 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
674 elt_ty enumFromToPName
675 ; return $ mkHsWrapCoI coi
676 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
678 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
679 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
680 ; expr1' <- tcPolyExpr expr1 elt_ty
681 ; expr2' <- tcPolyExpr expr2 elt_ty
682 ; expr3' <- tcPolyExpr expr3 elt_ty
683 ; eft <- newMethodFromName (PArrSeqOrigin seq)
684 elt_ty enumFromThenToPName
685 ; return $ mkHsWrapCoI coi
686 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
688 tcExpr (PArrSeq _ _) _
689 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
690 -- the parser shouldn't have generated it and the renamer shouldn't have
695 %************************************************************************
699 %************************************************************************
702 #ifdef GHCI /* Only if bootstrapped */
703 -- Rename excludes these cases otherwise
704 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
705 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
707 tcExpr e@(HsQuasiQuoteE _) res_ty =
708 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
713 %************************************************************************
717 %************************************************************************
720 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
724 %************************************************************************
728 %************************************************************************
731 ---------------------------
732 tcApp :: HsExpr Name -- Function
733 -> Arity -- Number of args reqd
734 -> ArgChecker results
735 -> BoxyRhoType -- Result type
736 -> TcM (HsExpr TcId, results)
738 -- (tcFun fun n_args arg_checker res_ty)
739 -- The argument type checker, arg_checker, will be passed exactly n_args types
741 tcApp (HsVar fun_name) n_args arg_checker res_ty
742 = tcIdApp fun_name n_args arg_checker res_ty
744 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
745 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
746 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
747 ; arg_tys' <- mapM readFilledBox arg_boxes
748 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
749 ; return (fun', args') }
751 ---------------------------
752 tcIdApp :: Name -- Function
753 -> Arity -- Number of args reqd
754 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
755 -> BoxyRhoType -- Result type
756 -> TcM (HsExpr TcId, results)
758 -- Call (f e1 ... en) :: res_ty
759 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
760 -- (where k <= n; fres has the rest)
761 -- NB: if k < n then the function doesn't have enough args, and
762 -- presumably fres is a type variable that we are going to
763 -- instantiate with a function type
765 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
767 tcIdApp fun_name n_args arg_checker res_ty
768 = do { let orig = OccurrenceOf fun_name
769 ; (fun, fun_ty) <- lookupFun orig fun_name
771 -- Split up the function type
772 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
773 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
775 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
776 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
777 res_qtvs = exactTyVarsOfType fun_res_ty
778 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
779 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
780 k = length fun_arg_tys -- k <= n_args
781 n_missing_args = n_args - k -- Always >= 0
783 -- Match the result type of the function with the
784 -- result type of the context, to get an inital substitution
785 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
786 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
787 res_ty' = mkFunTys extra_arg_tys' res_ty
788 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
790 -- Typecheck the arguments!
791 -- Doing so will fill arg_qtvs and extra_arg_tys'
792 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
794 -- Strip boxes from the qtvs that have been filled in by the arg checking
795 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
797 -- Result subsumption
798 -- This fills in res_qtvs
799 ; let res_subst = zipOpenTvSubst qtvs qtys''
800 fun_res_ty'' = substTy res_subst fun_res_ty
801 res_ty'' = mkFunTys extra_arg_tys'' res_ty
802 ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
804 -- And pack up the results
805 -- By applying the coercion just to the *function* we can make
806 -- tcFun work nicely for OpApp and Sections too
807 ; fun' <- instFun orig fun res_subst tv_theta_prs
808 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
809 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
810 ; return (mkHsWrap co_fn' fun', args') }
813 Note [Silly type synonyms in smart-app]
814 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
815 When we call sripBoxyType, all of the boxes should be filled
816 in. But we need to be careful about type synonyms:
820 In the call (f x) we'll typecheck x, expecting it to have type
821 (T box). Usually that would fill in the box, but in this case not;
822 because 'a' is discarded by the silly type synonym T. So we must
823 use exactTyVarsOfType to figure out which type variables are free
824 in the argument type.
827 -- tcId is a specialisation of tcIdApp when there are no arguments
828 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
833 -> BoxyRhoType -- Result type
835 tcId orig fun_name res_ty
836 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
837 ; (fun, fun_ty) <- lookupFun orig fun_name
839 -- Split up the function type
840 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
841 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
842 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
843 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
845 -- Do the subsumption check wrt the result type
846 ; let res_subst = zipTopTvSubst qtvs qtv_tys
847 fun_tau' = substTy res_subst fun_tau
849 ; co_fn <- tcSubExp orig fun_tau' res_ty
851 -- And pack up the results
852 ; fun' <- instFun orig fun res_subst tv_theta_prs
853 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
854 ; return (mkHsWrap co_fn fun') }
856 -- Note [Push result type in]
858 -- Unify with expected result before (was: after) type-checking the args
859 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
860 -- This is when we might detect a too-few args situation.
861 -- (One can think of cases when the opposite order would give
862 -- a better error message.)
863 -- [March 2003: I'm experimenting with putting this first. Here's an
864 -- example where it actually makes a real difference
865 -- class C t a b | t a -> b
866 -- instance C Char a Bool
868 -- data P t a = forall b. (C t a b) => MkP b
869 -- data Q t = MkQ (forall a. P t a)
872 -- f1 = MkQ (MkP True)
873 -- f2 = MkQ (MkP True :: forall a. P Char a)
875 -- With the change, f1 will type-check, because the 'Char' info from
876 -- the signature is propagated into MkQ's argument. With the check
877 -- in the other order, the extra signature in f2 is reqd.]
879 ---------------------------
880 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
881 -- Typecheck a syntax operator, checking that it has the specified type
882 -- The operator is always a variable at this stage (i.e. renamer output)
883 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
884 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
886 ---------------------------
887 instFun :: InstOrigin
889 -> TvSubst -- The instantiating substitution
890 -> [([TyVar], ThetaType)] -- Stuff to instantiate
893 instFun orig fun subst []
894 = return fun -- Common short cut
896 instFun orig fun subst tv_theta_prs
897 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
898 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
899 -- Make two ad-hoc checks
900 ; doStupidChecks fun ty_theta_prs'
902 -- Now do normal instantiation
903 ; method_sharing <- doptM Opt_MethodSharing
904 ; result <- go method_sharing True fun ty_theta_prs'
905 ; traceTc (text "instFun result" <+> ppr result)
909 subst_pr (tvs, theta)
910 = (substTyVars subst tvs, substTheta subst theta)
912 go _ _ fun [] = do {traceTc (text "go _ _ fun [] returns" <+> ppr fun) ; return fun }
914 go method_sharing True (HsVar fun_id) ((tys,theta) : prs)
915 | want_method_inst method_sharing theta
916 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
917 ; meth_id <- newMethodWithGivenTy orig fun_id tys
918 ; go method_sharing False (HsVar meth_id) prs }
919 -- Go round with 'False' to prevent further use
920 -- of newMethod: see Note [Multiple instantiation]
922 go method_sharing _ fun ((tys, theta) : prs)
923 = do { co_fn <- instCall orig tys theta
924 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
925 ; go method_sharing False (HsWrap co_fn fun) prs }
927 -- See Note [No method sharing]
928 want_method_inst method_sharing theta = not (null theta) -- Overloaded
932 Note [Multiple instantiation]
933 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
934 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
935 For example, consider
936 f :: forall a. Eq a => forall b. Ord b => a -> b
937 At a call to f, at say [Int, Bool], it's tempting to translate the call to
941 f_m1 :: forall b. Ord b => Int -> b
945 f_m2 = f_m1 Bool dOrdBool
947 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
948 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
950 But it's entirely possible that f_m2 will continue to float out, because it
951 mentions no type variables. Result, f_m1 isn't in scope.
953 Here's a concrete example that does this (test tc200):
956 f :: Eq b => b -> a -> Int
957 baz :: Eq a => Int -> a -> Int
962 Current solution: only do the "method sharing" thing for the first type/dict
963 application, not for the iterated ones. A horribly subtle point.
965 Note [No method sharing]
966 ~~~~~~~~~~~~~~~~~~~~~~~~
967 The -fno-method-sharing flag controls what happens so far as the LIE
968 is concerned. The default case is that for an overloaded function we
969 generate a "method" Id, and add the Method Inst to the LIE. So you get
972 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
973 If you specify -fno-method-sharing, the dictionary application
974 isn't shared, so we get
976 f = /\a (d:Num a) (x:a) -> (+) a d x x
977 This gets a bit less sharing, but
978 a) it's better for RULEs involving overloaded functions
979 b) perhaps fewer separated lambdas
983 tcArgs implements a left-to-right order, which goes beyond what is described in the
984 impredicative type inference paper. In particular, it allows
986 where runST :: (forall s. ST s a) -> a
987 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
988 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
989 before checking foo. The left-to-right order really helps here.
992 tcArgs :: LHsExpr Name -- The function (for error messages)
993 -> [LHsExpr Name] -- Actual args
994 -> ArgChecker [LHsExpr TcId]
996 type ArgChecker results
997 = [TyVar] -> [TcSigmaType] -- Current instantiation
998 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
999 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
1001 tcArgs fun args qtvs qtys arg_tys
1002 = go 1 qtys args arg_tys
1004 go n qtys [] [] = return (qtys, [])
1005 go n qtys (arg:args) (arg_ty:arg_tys)
1006 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
1007 ; qtys' <- mapM refineBox qtys -- Exploit new info
1008 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
1009 ; return (qtys'', arg':args') }
1010 go n qtys args arg_tys = panic "tcArgs"
1012 tcArg :: LHsExpr Name -- The function
1013 -> Int -- and arg number (for error messages)
1015 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
1017 -> TcM (LHsExpr TcId) -- Resulting argument
1018 tcArg fun arg_no arg qtvs qtys ty
1019 = addErrCtxt (funAppCtxt fun arg arg_no) $
1020 tcPolyExprNC arg (substTyWith qtvs qtys ty)
1026 Nasty check to ensure that tagToEnum# is applied to a type that is an
1027 enumeration TyCon. Unification may refine the type later, but this
1028 check won't see that, alas. It's crude but it works.
1030 Here's are two cases that should fail
1032 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1035 g = tagToEnum# 0 -- Int is not an enumeration
1039 doStupidChecks :: HsExpr TcId
1040 -> [([TcType], ThetaType)]
1042 -- Check two tiresome and ad-hoc cases
1043 -- (a) the "stupid theta" for a data con; add the constraints
1044 -- from the "stupid theta" of a data constructor (sigh)
1045 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
1047 doStupidChecks (HsVar fun_id) ((tys,_):_)
1048 | Just con <- isDataConId_maybe fun_id -- (a)
1049 = addDataConStupidTheta con tys
1051 | fun_id `hasKey` tagToEnumKey -- (b)
1052 = do { tys' <- zonkTcTypes tys
1053 ; checkTc (ok tys') (tagToEnumError tys')
1057 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
1058 Just (tc,_) -> isEnumerationTyCon tc
1061 doStupidChecks fun tv_theta_prs
1062 = return () -- The common case
1066 = hang (ptext (sLit "Bad call to tagToEnum#") <+> at_type)
1067 2 (vcat [ptext (sLit "Specify the type by giving a type signature"),
1068 ptext (sLit "e.g. (tagToEnum# x) :: Bool")])
1070 at_type | null tys = empty -- Probably never happens
1071 | otherwise = ptext (sLit "at type") <+> ppr (head tys)
1074 %************************************************************************
1076 \subsection{@tcId@ typechecks an identifier occurrence}
1078 %************************************************************************
1081 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
1082 lookupFun orig id_name
1083 = do { thing <- tcLookup id_name
1085 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
1087 wrap_id = dataConWrapId con
1090 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1091 | otherwise -> return (HsVar id, idType id)
1092 -- A global cannot possibly be ill-staged
1093 -- nor does it need the 'lifting' treatment
1095 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
1096 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1097 -- Note [Local record selectors]
1099 -> do { thLocalId orig id ty lvl
1101 Unrefineable -> return (HsVar id, ty)
1102 Rigid co -> return (mkHsWrap co (HsVar id), ty)
1103 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
1104 WobblyInvisible -> failWithTc (ppr id_name <+> ptext (sLit " not in scope because it has a wobbly type (solution: add a type annotation)"))
1107 other -> failWithTc (ppr other <+> ptext (sLit "used where a value identifer was expected"))
1110 #ifndef GHCI /* GHCI and TH is off */
1111 --------------------------------------
1112 -- thLocalId : Check for cross-stage lifting
1113 thLocalId orig id id_ty th_bind_lvl
1116 #else /* GHCI and TH is on */
1117 thLocalId orig id id_ty th_bind_lvl
1118 = do { use_stage <- getStage -- TH case
1120 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
1121 -> thBrackId orig id ps_var lie_var
1122 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1126 --------------------------------------
1127 thBrackId orig id ps_var lie_var
1129 = -- Top-level identifiers in this module,
1130 -- (which have External Names)
1131 -- are just like the imported case:
1132 -- no need for the 'lifting' treatment
1133 -- E.g. this is fine:
1136 -- But we do need to put f into the keep-alive
1137 -- set, because after desugaring the code will
1138 -- only mention f's *name*, not f itself.
1139 do { keepAliveTc id; return id }
1142 = -- Nested identifiers, such as 'x' in
1143 -- E.g. \x -> [| h x |]
1144 -- We must behave as if the reference to x was
1146 -- We use 'x' itself as the splice proxy, used by
1147 -- the desugarer to stitch it all back together.
1148 -- If 'x' occurs many times we may get many identical
1149 -- bindings of the same splice proxy, but that doesn't
1150 -- matter, although it's a mite untidy.
1151 do { let id_ty = idType id
1152 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1153 -- If x is polymorphic, its occurrence sites might
1154 -- have different instantiations, so we can't use plain
1155 -- 'x' as the splice proxy name. I don't know how to
1156 -- solve this, and it's probably unimportant, so I'm
1157 -- just going to flag an error for now
1159 ; id_ty' <- zapToMonotype id_ty
1160 -- The id_ty might have an OpenTypeKind, but we
1161 -- can't instantiate the Lift class at that kind,
1162 -- so we zap it to a LiftedTypeKind monotype
1163 -- C.f. the call in TcPat.newLitInst
1165 ; lift <- if isStringTy id_ty' then
1166 tcLookupId DsMeta.liftStringName
1167 -- See Note [Lifting strings]
1169 setLIEVar lie_var $ do -- Put the 'lift' constraint into the right LIE
1170 newMethodFromName orig id_ty' DsMeta.liftName
1172 -- Update the pending splices
1173 ; ps <- readMutVar ps_var
1174 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1180 Note [Lifting strings]
1181 ~~~~~~~~~~~~~~~~~~~~~~
1182 If we see $(... [| s |] ...) where s::String, we don't want to
1183 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1184 So this conditional short-circuits the lifting mechanism to generate
1185 (liftString "xy") in that case. I didn't want to use overlapping instances
1186 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1187 errors in a polymorphic situation.
1189 If this check fails (which isn't impossible) we get another chance; see
1190 Note [Converting strings] in Convert.lhs
1192 Local record selectors
1193 ~~~~~~~~~~~~~~~~~~~~~~
1194 Record selectors for TyCons in this module are ordinary local bindings,
1195 which show up as ATcIds rather than AGlobals. So we need to check for
1196 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1199 %************************************************************************
1201 \subsection{Record bindings}
1203 %************************************************************************
1205 Game plan for record bindings
1206 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1207 1. Find the TyCon for the bindings, from the first field label.
1209 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1211 For each binding field = value
1213 3. Instantiate the field type (from the field label) using the type
1216 4 Type check the value using tcArg, passing the field type as
1217 the expected argument type.
1219 This extends OK when the field types are universally quantified.
1225 -> [TcType] -- Expected type for each field
1226 -> HsRecordBinds Name
1227 -> TcM (HsRecordBinds TcId)
1229 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1230 = do { mb_binds <- mapM do_bind rbinds
1231 ; return (HsRecFields (catMaybes mb_binds) dd) }
1233 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1234 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1235 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1236 = addErrCtxt (fieldCtxt field_lbl) $
1237 do { rhs' <- tcPolyExprNC rhs field_ty
1238 ; let field_id = mkUserLocal (nameOccName field_lbl)
1239 (nameUnique field_lbl)
1241 -- Yuk: the field_id has the *unique* of the selector Id
1242 -- (so we can find it easily)
1243 -- but is a LocalId with the appropriate type of the RHS
1244 -- (so the desugarer knows the type of local binder to make)
1245 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1247 = do { addErrTc (badFieldCon data_con field_lbl)
1250 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1251 checkMissingFields data_con rbinds
1252 | null field_labels -- Not declared as a record;
1253 -- But C{} is still valid if no strict fields
1254 = if any isMarkedStrict field_strs then
1255 -- Illegal if any arg is strict
1256 addErrTc (missingStrictFields data_con [])
1260 | otherwise = do -- A record
1261 unless (null missing_s_fields)
1262 (addErrTc (missingStrictFields data_con missing_s_fields))
1264 warn <- doptM Opt_WarnMissingFields
1265 unless (not (warn && notNull missing_ns_fields))
1266 (warnTc True (missingFields data_con missing_ns_fields))
1270 = [ fl | (fl, str) <- field_info,
1272 not (fl `elem` field_names_used)
1275 = [ fl | (fl, str) <- field_info,
1276 not (isMarkedStrict str),
1277 not (fl `elem` field_names_used)
1280 field_names_used = hsRecFields rbinds
1281 field_labels = dataConFieldLabels data_con
1283 field_info = zipEqual "missingFields"
1287 field_strs = dataConStrictMarks data_con
1290 %************************************************************************
1292 \subsection{Errors and contexts}
1294 %************************************************************************
1296 Boring and alphabetical:
1298 addExprErrCtxt :: OutputableBndr id => LHsExpr id -> TcM a -> TcM a
1299 addExprErrCtxt expr = addErrCtxt (exprCtxt (unLoc expr))
1302 = hang (ptext (sLit "In the expression:")) 4 (ppr expr)
1304 fieldCtxt field_name
1305 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1307 funAppCtxt fun arg arg_no
1308 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1309 quotes (ppr fun) <> text ", namely"])
1310 4 (quotes (ppr arg))
1313 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1314 <> plural prs <> colon)
1315 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1318 = hang (ptext (sLit "No constructor has all these fields:"))
1319 4 (pprQuotedList (hsRecFields rbinds))
1321 naughtyRecordSel sel_id
1322 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1323 ptext (sLit "as a function due to escaped type variables") $$
1324 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1327 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1329 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1330 missingStrictFields con fields
1333 rest | null fields = empty -- Happens for non-record constructors
1334 -- with strict fields
1335 | otherwise = colon <+> pprWithCommas ppr fields
1337 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1338 ptext (sLit "does not have the required strict field(s)")
1340 missingFields :: DataCon -> [FieldLabel] -> SDoc
1341 missingFields con fields
1342 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1343 <+> pprWithCommas ppr fields
1345 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1348 polySpliceErr :: Id -> SDoc
1350 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)