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 }
460 The criterion we use is this:
462 The types of the updated fields
463 mention only the universally-quantified type variables
464 of the data constructor
466 In principle one could go further, and allow
468 g t = t { f2 = \x -> x }
469 because the expression is polymorphic...but that seems a bridge too far.
471 Note [Data family example]
472 ~~~~~~~~~~~~~~~~~~~~~~~~~~
473 data instance T (a,b) = MkT { x::a, y::b }
475 data :TP a b = MkT { a::a, y::b }
476 coTP a b :: T (a,b) ~ :TP a b
478 Suppose r :: T (t1,t2), e :: t3
479 Then r { x=e } :: T (t3,t1)
482 MkT x y -> MkT e y |> co2
483 where co1 :: T (t1,t2) ~ :TP t1 t2
484 co2 :: :TP t3 t2 ~ T (t3,t2)
485 The wrapping with co2 is done by the constructor wrapper for MkT
489 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
491 * cons are the data constructors to be updated
493 * in_inst_tys, out_inst_tys have same length, and instantiate the
494 *representation* tycon of the data cons. In Note [Data
495 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
498 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
499 = ASSERT( notNull upd_fld_names )
502 -- Check that the field names are really field names
503 ; sel_ids <- mapM tcLookupField upd_fld_names
504 -- The renamer has already checked that
505 -- selectors are all in scope
506 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
507 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
508 not (isRecordSelector sel_id), -- Excludes class ops
509 let L loc fld_name = hsRecFieldId fld ]
510 ; unless (null bad_guys) (sequence bad_guys >> failM)
513 -- Figure out the tycon and data cons from the first field name
514 ; let -- It's OK to use the non-tc splitters here (for a selector)
516 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
517 data_cons = tyConDataCons tycon -- it's not a field label
518 -- NB: for a data type family, the tycon is the instance tycon
520 relevant_cons = filter is_relevant data_cons
521 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
522 -- A constructor is only relevant to this process if
523 -- it contains *all* the fields that are being updated
524 -- Other ones will cause a runtime error if they occur
526 -- Take apart a representative constructor
527 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
528 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
529 con1_flds = dataConFieldLabels con1
530 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
533 -- Check that at least one constructor has all the named fields
534 -- i.e. has an empty set of bad fields returned by badFields
535 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
537 -- STEP 3 Note [Criteria for update]
538 -- Check that each updated field is polymorphic; that is, its type
539 -- mentions only the universally-quantified variables of the data con
540 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
541 (upd_flds1_w_tys, fixed_flds1_w_tys) = partition is_updated flds1_w_tys
542 is_updated (fld,ty) = fld `elem` upd_fld_names
544 bad_upd_flds = filter bad_fld upd_flds1_w_tys
545 con1_tv_set = mkVarSet con1_tvs
546 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
547 not (tyVarsOfType ty `subVarSet` con1_tv_set)
548 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
550 -- STEP 4 Note [Type of a record update]
551 -- Figure out types for the scrutinee and result
552 -- Both are of form (T a b c), with fresh type variables, but with
553 -- common variables where the scrutinee and result must have the same type
554 -- These are variables that appear in *any* arg of *any* of the
555 -- relevant constructors *except* in the updated fields
557 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
558 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
559 mk_inst_ty tv result_inst_ty
560 | is_fixed_tv tv = return result_inst_ty -- Same as result type
561 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
563 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
564 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
566 ; let result_ty = substTy result_inst_env con1_res_ty
567 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
568 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
569 scrut_ty = substTy scrut_subst con1_res_ty
572 -- Typecheck the thing to be updated, and the bindings
573 ; record_expr' <- tcMonoExpr record_expr scrut_ty
574 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
576 ; let origin = RecordUpdOrigin
577 ; co_fn <- tcSubExp origin result_ty res_ty
579 -- STEP 6: Deal with the stupid theta
580 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
581 ; instStupidTheta origin theta'
583 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
584 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
585 = WpCast $ mkTyConApp co_con scrut_inst_tys
590 ; return (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
591 relevant_cons scrut_inst_tys result_inst_tys)) }
593 upd_fld_names = hsRecFields rbinds
595 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
596 -- These tyvars must not change across the updates
597 getFixedTyVars tvs1 cons
598 = mkVarSet [tv1 | con <- cons
599 , let (tvs, theta, arg_tys, _) = dataConSig con
600 flds = dataConFieldLabels con
601 fixed_tvs = exactTyVarsOfTypes fixed_tys
602 -- fixed_tys: See Note [Type of a record update]
603 `unionVarSet` tyVarsOfTheta theta
604 -- Universally-quantified tyvars that
605 -- appear in any of the *implicit*
606 -- arguments to the constructor are fixed
607 -- See Note [Implict type sharing]
609 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
610 , not (fld `elem` upd_fld_names)]
611 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
612 , tv `elemVarSet` fixed_tvs ]
615 %************************************************************************
617 Arithmetic sequences e.g. [a,b..]
618 and their parallel-array counterparts e.g. [: a,b.. :]
621 %************************************************************************
624 tcExpr (ArithSeq _ seq@(From expr)) res_ty
625 = do { (elt_ty, coi) <- boxySplitListTy res_ty
626 ; expr' <- tcPolyExpr expr elt_ty
627 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
629 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
631 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
632 = do { (elt_ty, coi) <- boxySplitListTy res_ty
633 ; expr1' <- tcPolyExpr expr1 elt_ty
634 ; expr2' <- tcPolyExpr expr2 elt_ty
635 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
636 elt_ty enumFromThenName
637 ; return $ mkHsWrapCoI coi
638 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
640 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
641 = do { (elt_ty, coi) <- boxySplitListTy res_ty
642 ; expr1' <- tcPolyExpr expr1 elt_ty
643 ; expr2' <- tcPolyExpr expr2 elt_ty
644 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
645 elt_ty enumFromToName
646 ; return $ mkHsWrapCoI coi
647 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
649 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
650 = do { (elt_ty, coi) <- boxySplitListTy res_ty
651 ; expr1' <- tcPolyExpr expr1 elt_ty
652 ; expr2' <- tcPolyExpr expr2 elt_ty
653 ; expr3' <- tcPolyExpr expr3 elt_ty
654 ; eft <- newMethodFromName (ArithSeqOrigin seq)
655 elt_ty enumFromThenToName
656 ; return $ mkHsWrapCoI coi
657 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
659 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
660 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
661 ; expr1' <- tcPolyExpr expr1 elt_ty
662 ; expr2' <- tcPolyExpr expr2 elt_ty
663 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
664 elt_ty enumFromToPName
665 ; return $ mkHsWrapCoI coi
666 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
668 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
669 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
670 ; expr1' <- tcPolyExpr expr1 elt_ty
671 ; expr2' <- tcPolyExpr expr2 elt_ty
672 ; expr3' <- tcPolyExpr expr3 elt_ty
673 ; eft <- newMethodFromName (PArrSeqOrigin seq)
674 elt_ty enumFromThenToPName
675 ; return $ mkHsWrapCoI coi
676 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
678 tcExpr (PArrSeq _ _) _
679 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
680 -- the parser shouldn't have generated it and the renamer shouldn't have
685 %************************************************************************
689 %************************************************************************
692 #ifdef GHCI /* Only if bootstrapped */
693 -- Rename excludes these cases otherwise
694 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
695 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
697 tcExpr e@(HsQuasiQuoteE _) res_ty =
698 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
703 %************************************************************************
707 %************************************************************************
710 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
714 %************************************************************************
718 %************************************************************************
721 ---------------------------
722 tcApp :: HsExpr Name -- Function
723 -> Arity -- Number of args reqd
724 -> ArgChecker results
725 -> BoxyRhoType -- Result type
726 -> TcM (HsExpr TcId, results)
728 -- (tcFun fun n_args arg_checker res_ty)
729 -- The argument type checker, arg_checker, will be passed exactly n_args types
731 tcApp (HsVar fun_name) n_args arg_checker res_ty
732 = tcIdApp fun_name n_args arg_checker res_ty
734 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
735 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
736 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
737 ; arg_tys' <- mapM readFilledBox arg_boxes
738 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
739 ; return (fun', args') }
741 ---------------------------
742 tcIdApp :: Name -- Function
743 -> Arity -- Number of args reqd
744 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
745 -> BoxyRhoType -- Result type
746 -> TcM (HsExpr TcId, results)
748 -- Call (f e1 ... en) :: res_ty
749 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
750 -- (where k <= n; fres has the rest)
751 -- NB: if k < n then the function doesn't have enough args, and
752 -- presumably fres is a type variable that we are going to
753 -- instantiate with a function type
755 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
757 tcIdApp fun_name n_args arg_checker res_ty
758 = do { let orig = OccurrenceOf fun_name
759 ; (fun, fun_ty) <- lookupFun orig fun_name
761 -- Split up the function type
762 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
763 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
765 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
766 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
767 res_qtvs = exactTyVarsOfType fun_res_ty
768 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
769 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
770 k = length fun_arg_tys -- k <= n_args
771 n_missing_args = n_args - k -- Always >= 0
773 -- Match the result type of the function with the
774 -- result type of the context, to get an inital substitution
775 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
776 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
777 res_ty' = mkFunTys extra_arg_tys' res_ty
778 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
780 -- Typecheck the arguments!
781 -- Doing so will fill arg_qtvs and extra_arg_tys'
782 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
784 -- Strip boxes from the qtvs that have been filled in by the arg checking
785 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
787 -- Result subsumption
788 -- This fills in res_qtvs
789 ; let res_subst = zipOpenTvSubst qtvs qtys''
790 fun_res_ty'' = substTy res_subst fun_res_ty
791 res_ty'' = mkFunTys extra_arg_tys'' res_ty
792 ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
794 -- And pack up the results
795 -- By applying the coercion just to the *function* we can make
796 -- tcFun work nicely for OpApp and Sections too
797 ; fun' <- instFun orig fun res_subst tv_theta_prs
798 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
799 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
800 ; return (mkHsWrap co_fn' fun', args') }
803 Note [Silly type synonyms in smart-app]
804 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
805 When we call sripBoxyType, all of the boxes should be filled
806 in. But we need to be careful about type synonyms:
810 In the call (f x) we'll typecheck x, expecting it to have type
811 (T box). Usually that would fill in the box, but in this case not;
812 because 'a' is discarded by the silly type synonym T. So we must
813 use exactTyVarsOfType to figure out which type variables are free
814 in the argument type.
817 -- tcId is a specialisation of tcIdApp when there are no arguments
818 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
823 -> BoxyRhoType -- Result type
825 tcId orig fun_name res_ty
826 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
827 ; (fun, fun_ty) <- lookupFun orig fun_name
829 -- Split up the function type
830 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
831 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
832 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
833 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
835 -- Do the subsumption check wrt the result type
836 ; let res_subst = zipTopTvSubst qtvs qtv_tys
837 fun_tau' = substTy res_subst fun_tau
839 ; co_fn <- tcSubExp orig fun_tau' res_ty
841 -- And pack up the results
842 ; fun' <- instFun orig fun res_subst tv_theta_prs
843 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
844 ; return (mkHsWrap co_fn fun') }
846 -- Note [Push result type in]
848 -- Unify with expected result before (was: after) type-checking the args
849 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
850 -- This is when we might detect a too-few args situation.
851 -- (One can think of cases when the opposite order would give
852 -- a better error message.)
853 -- [March 2003: I'm experimenting with putting this first. Here's an
854 -- example where it actually makes a real difference
855 -- class C t a b | t a -> b
856 -- instance C Char a Bool
858 -- data P t a = forall b. (C t a b) => MkP b
859 -- data Q t = MkQ (forall a. P t a)
862 -- f1 = MkQ (MkP True)
863 -- f2 = MkQ (MkP True :: forall a. P Char a)
865 -- With the change, f1 will type-check, because the 'Char' info from
866 -- the signature is propagated into MkQ's argument. With the check
867 -- in the other order, the extra signature in f2 is reqd.]
869 ---------------------------
870 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
871 -- Typecheck a syntax operator, checking that it has the specified type
872 -- The operator is always a variable at this stage (i.e. renamer output)
873 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
874 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
876 ---------------------------
877 instFun :: InstOrigin
879 -> TvSubst -- The instantiating substitution
880 -> [([TyVar], ThetaType)] -- Stuff to instantiate
883 instFun orig fun subst []
884 = return fun -- Common short cut
886 instFun orig fun subst tv_theta_prs
887 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
888 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
889 -- Make two ad-hoc checks
890 ; doStupidChecks fun ty_theta_prs'
892 -- Now do normal instantiation
893 ; method_sharing <- doptM Opt_MethodSharing
894 ; result <- go method_sharing True fun ty_theta_prs'
895 ; traceTc (text "instFun result" <+> ppr result)
899 subst_pr (tvs, theta)
900 = (substTyVars subst tvs, substTheta subst theta)
902 go _ _ fun [] = do {traceTc (text "go _ _ fun [] returns" <+> ppr fun) ; return fun }
904 go method_sharing True (HsVar fun_id) ((tys,theta) : prs)
905 | want_method_inst method_sharing theta
906 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
907 ; meth_id <- newMethodWithGivenTy orig fun_id tys
908 ; go method_sharing False (HsVar meth_id) prs }
909 -- Go round with 'False' to prevent further use
910 -- of newMethod: see Note [Multiple instantiation]
912 go method_sharing _ fun ((tys, theta) : prs)
913 = do { co_fn <- instCall orig tys theta
914 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
915 ; go method_sharing False (HsWrap co_fn fun) prs }
917 -- See Note [No method sharing]
918 want_method_inst method_sharing theta = not (null theta) -- Overloaded
922 Note [Multiple instantiation]
923 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
924 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
925 For example, consider
926 f :: forall a. Eq a => forall b. Ord b => a -> b
927 At a call to f, at say [Int, Bool], it's tempting to translate the call to
931 f_m1 :: forall b. Ord b => Int -> b
935 f_m2 = f_m1 Bool dOrdBool
937 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
938 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
940 But it's entirely possible that f_m2 will continue to float out, because it
941 mentions no type variables. Result, f_m1 isn't in scope.
943 Here's a concrete example that does this (test tc200):
946 f :: Eq b => b -> a -> Int
947 baz :: Eq a => Int -> a -> Int
952 Current solution: only do the "method sharing" thing for the first type/dict
953 application, not for the iterated ones. A horribly subtle point.
955 Note [No method sharing]
956 ~~~~~~~~~~~~~~~~~~~~~~~~
957 The -fno-method-sharing flag controls what happens so far as the LIE
958 is concerned. The default case is that for an overloaded function we
959 generate a "method" Id, and add the Method Inst to the LIE. So you get
962 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
963 If you specify -fno-method-sharing, the dictionary application
964 isn't shared, so we get
966 f = /\a (d:Num a) (x:a) -> (+) a d x x
967 This gets a bit less sharing, but
968 a) it's better for RULEs involving overloaded functions
969 b) perhaps fewer separated lambdas
973 tcArgs implements a left-to-right order, which goes beyond what is described in the
974 impredicative type inference paper. In particular, it allows
976 where runST :: (forall s. ST s a) -> a
977 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
978 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
979 before checking foo. The left-to-right order really helps here.
982 tcArgs :: LHsExpr Name -- The function (for error messages)
983 -> [LHsExpr Name] -- Actual args
984 -> ArgChecker [LHsExpr TcId]
986 type ArgChecker results
987 = [TyVar] -> [TcSigmaType] -- Current instantiation
988 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
989 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
991 tcArgs fun args qtvs qtys arg_tys
992 = go 1 qtys args arg_tys
994 go n qtys [] [] = return (qtys, [])
995 go n qtys (arg:args) (arg_ty:arg_tys)
996 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
997 ; qtys' <- mapM refineBox qtys -- Exploit new info
998 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
999 ; return (qtys'', arg':args') }
1000 go n qtys args arg_tys = panic "tcArgs"
1002 tcArg :: LHsExpr Name -- The function
1003 -> Int -- and arg number (for error messages)
1005 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
1007 -> TcM (LHsExpr TcId) -- Resulting argument
1008 tcArg fun arg_no arg qtvs qtys ty
1009 = addErrCtxt (funAppCtxt fun arg arg_no) $
1010 tcPolyExprNC arg (substTyWith qtvs qtys ty)
1016 Nasty check to ensure that tagToEnum# is applied to a type that is an
1017 enumeration TyCon. Unification may refine the type later, but this
1018 check won't see that, alas. It's crude but it works.
1020 Here's are two cases that should fail
1022 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1025 g = tagToEnum# 0 -- Int is not an enumeration
1029 doStupidChecks :: HsExpr TcId
1030 -> [([TcType], ThetaType)]
1032 -- Check two tiresome and ad-hoc cases
1033 -- (a) the "stupid theta" for a data con; add the constraints
1034 -- from the "stupid theta" of a data constructor (sigh)
1035 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
1037 doStupidChecks (HsVar fun_id) ((tys,_):_)
1038 | Just con <- isDataConId_maybe fun_id -- (a)
1039 = addDataConStupidTheta con tys
1041 | fun_id `hasKey` tagToEnumKey -- (b)
1042 = do { tys' <- zonkTcTypes tys
1043 ; checkTc (ok tys') (tagToEnumError tys')
1047 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
1048 Just (tc,_) -> isEnumerationTyCon tc
1051 doStupidChecks fun tv_theta_prs
1052 = return () -- The common case
1056 = hang (ptext (sLit "Bad call to tagToEnum#") <+> at_type)
1057 2 (vcat [ptext (sLit "Specify the type by giving a type signature"),
1058 ptext (sLit "e.g. (tagToEnum# x) :: Bool")])
1060 at_type | null tys = empty -- Probably never happens
1061 | otherwise = ptext (sLit "at type") <+> ppr (head tys)
1064 %************************************************************************
1066 \subsection{@tcId@ typechecks an identifier occurrence}
1068 %************************************************************************
1071 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
1072 lookupFun orig id_name
1073 = do { thing <- tcLookup id_name
1075 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
1077 wrap_id = dataConWrapId con
1080 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1081 | otherwise -> return (HsVar id, idType id)
1082 -- A global cannot possibly be ill-staged
1083 -- nor does it need the 'lifting' treatment
1085 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
1086 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1087 -- Note [Local record selectors]
1089 -> do { thLocalId orig id ty lvl
1091 Unrefineable -> return (HsVar id, ty)
1092 Rigid co -> return (mkHsWrap co (HsVar id), ty)
1093 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
1094 WobblyInvisible -> failWithTc (ppr id_name <+> ptext (sLit " not in scope because it has a wobbly type (solution: add a type annotation)"))
1097 other -> failWithTc (ppr other <+> ptext (sLit "used where a value identifer was expected"))
1100 #ifndef GHCI /* GHCI and TH is off */
1101 --------------------------------------
1102 -- thLocalId : Check for cross-stage lifting
1103 thLocalId orig id id_ty th_bind_lvl
1106 #else /* GHCI and TH is on */
1107 thLocalId orig id id_ty th_bind_lvl
1108 = do { use_stage <- getStage -- TH case
1110 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
1111 -> thBrackId orig id ps_var lie_var
1112 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1116 --------------------------------------
1117 thBrackId orig id ps_var lie_var
1119 = -- Top-level identifiers in this module,
1120 -- (which have External Names)
1121 -- are just like the imported case:
1122 -- no need for the 'lifting' treatment
1123 -- E.g. this is fine:
1126 -- But we do need to put f into the keep-alive
1127 -- set, because after desugaring the code will
1128 -- only mention f's *name*, not f itself.
1129 do { keepAliveTc id; return id }
1132 = -- Nested identifiers, such as 'x' in
1133 -- E.g. \x -> [| h x |]
1134 -- We must behave as if the reference to x was
1136 -- We use 'x' itself as the splice proxy, used by
1137 -- the desugarer to stitch it all back together.
1138 -- If 'x' occurs many times we may get many identical
1139 -- bindings of the same splice proxy, but that doesn't
1140 -- matter, although it's a mite untidy.
1141 do { let id_ty = idType id
1142 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1143 -- If x is polymorphic, its occurrence sites might
1144 -- have different instantiations, so we can't use plain
1145 -- 'x' as the splice proxy name. I don't know how to
1146 -- solve this, and it's probably unimportant, so I'm
1147 -- just going to flag an error for now
1149 ; id_ty' <- zapToMonotype id_ty
1150 -- The id_ty might have an OpenTypeKind, but we
1151 -- can't instantiate the Lift class at that kind,
1152 -- so we zap it to a LiftedTypeKind monotype
1153 -- C.f. the call in TcPat.newLitInst
1155 ; lift <- if isStringTy id_ty' then
1156 tcLookupId DsMeta.liftStringName
1157 -- See Note [Lifting strings]
1159 setLIEVar lie_var $ do -- Put the 'lift' constraint into the right LIE
1160 newMethodFromName orig id_ty' DsMeta.liftName
1162 -- Update the pending splices
1163 ; ps <- readMutVar ps_var
1164 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1170 Note [Lifting strings]
1171 ~~~~~~~~~~~~~~~~~~~~~~
1172 If we see $(... [| s |] ...) where s::String, we don't want to
1173 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1174 So this conditional short-circuits the lifting mechanism to generate
1175 (liftString "xy") in that case. I didn't want to use overlapping instances
1176 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1177 errors in a polymorphic situation.
1179 If this check fails (which isn't impossible) we get another chance; see
1180 Note [Converting strings] in Convert.lhs
1182 Local record selectors
1183 ~~~~~~~~~~~~~~~~~~~~~~
1184 Record selectors for TyCons in this module are ordinary local bindings,
1185 which show up as ATcIds rather than AGlobals. So we need to check for
1186 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1189 %************************************************************************
1191 \subsection{Record bindings}
1193 %************************************************************************
1195 Game plan for record bindings
1196 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1197 1. Find the TyCon for the bindings, from the first field label.
1199 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1201 For each binding field = value
1203 3. Instantiate the field type (from the field label) using the type
1206 4 Type check the value using tcArg, passing the field type as
1207 the expected argument type.
1209 This extends OK when the field types are universally quantified.
1215 -> [TcType] -- Expected type for each field
1216 -> HsRecordBinds Name
1217 -> TcM (HsRecordBinds TcId)
1219 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1220 = do { mb_binds <- mapM do_bind rbinds
1221 ; return (HsRecFields (catMaybes mb_binds) dd) }
1223 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1224 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1225 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1226 = addErrCtxt (fieldCtxt field_lbl) $
1227 do { rhs' <- tcPolyExprNC rhs field_ty
1228 ; let field_id = mkUserLocal (nameOccName field_lbl)
1229 (nameUnique field_lbl)
1231 -- Yuk: the field_id has the *unique* of the selector Id
1232 -- (so we can find it easily)
1233 -- but is a LocalId with the appropriate type of the RHS
1234 -- (so the desugarer knows the type of local binder to make)
1235 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1237 = do { addErrTc (badFieldCon data_con field_lbl)
1240 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1241 checkMissingFields data_con rbinds
1242 | null field_labels -- Not declared as a record;
1243 -- But C{} is still valid if no strict fields
1244 = if any isMarkedStrict field_strs then
1245 -- Illegal if any arg is strict
1246 addErrTc (missingStrictFields data_con [])
1250 | otherwise = do -- A record
1251 unless (null missing_s_fields)
1252 (addErrTc (missingStrictFields data_con missing_s_fields))
1254 warn <- doptM Opt_WarnMissingFields
1255 unless (not (warn && notNull missing_ns_fields))
1256 (warnTc True (missingFields data_con missing_ns_fields))
1260 = [ fl | (fl, str) <- field_info,
1262 not (fl `elem` field_names_used)
1265 = [ fl | (fl, str) <- field_info,
1266 not (isMarkedStrict str),
1267 not (fl `elem` field_names_used)
1270 field_names_used = hsRecFields rbinds
1271 field_labels = dataConFieldLabels data_con
1273 field_info = zipEqual "missingFields"
1277 field_strs = dataConStrictMarks data_con
1280 %************************************************************************
1282 \subsection{Errors and contexts}
1284 %************************************************************************
1286 Boring and alphabetical:
1288 addExprErrCtxt :: OutputableBndr id => LHsExpr id -> TcM a -> TcM a
1289 addExprErrCtxt expr = addErrCtxt (exprCtxt (unLoc expr))
1292 = hang (ptext (sLit "In the expression:")) 4 (ppr expr)
1294 fieldCtxt field_name
1295 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1297 funAppCtxt fun arg arg_no
1298 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1299 quotes (ppr fun) <> text ", namely"])
1300 4 (quotes (ppr arg))
1303 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1304 <> plural prs <> colon)
1305 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1308 = hang (ptext (sLit "No constructor has all these fields:"))
1309 4 (pprQuotedList (hsRecFields rbinds))
1311 naughtyRecordSel sel_id
1312 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1313 ptext (sLit "as a function due to escaped type variables") $$
1314 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1317 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1319 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1320 missingStrictFields con fields
1323 rest | null fields = empty -- Happens for non-record constructors
1324 -- with strict fields
1325 | otherwise = colon <+> pprWithCommas ppr fields
1327 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1328 ptext (sLit "does not have the required strict field(s)")
1330 missingFields :: DataCon -> [FieldLabel] -> SDoc
1331 missingFields con fields
1332 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1333 <+> pprWithCommas ppr fields
1335 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1338 polySpliceErr :: Id -> SDoc
1340 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)