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 = MkT1 { fa :: a, fb :: b }
412 | MkT2 { fa :: a, fc :: Int -> Int }
415 upd :: T a b -> c -> T a c
416 upd t x = t { fb = x}
418 The type signature on upd is correct (i.e. the result should not be (T a b))
419 because upd should be equivalent to:
426 So we need to give a completely fresh type to the result record,
427 and then constrain it by the fields that are *not* updated ("p" above).
429 Note that because MkT3 doesn't contain all the fields being updated,
430 its RHS is simply an error, so it doesn't impose any type constraints
432 Note [Implict type sharing]
433 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
434 We also take into account any "implicit" non-update fields. For example
435 data T a b where { MkT { f::a } :: T a a; ... }
436 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
441 upd :: T a b -> a -> T a b
442 upd (t::T a b) (x::a)
443 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
444 We can't give it the more general type
445 upd :: T a b -> c -> T c b
447 Note [Criteria for update]
448 ~~~~~~~~~~~~~~~~~~~~~~~~~~
449 We want to allow update for existentials etc, provided the updated
450 field isn't part of the existential. For example, this should be ok.
451 data T a where { MkT { f1::a, f2::b->b } :: T a }
454 The criterion we use is this:
456 The types of the updated fields
457 mention only the universally-quantified type variables
458 of the data constructor
460 In principle one could go further, and allow
462 g t = t { f2 = \x -> x }
463 because the expression is polymorphic...but that seems a bridge too far.
465 Note [Data family example]
466 ~~~~~~~~~~~~~~~~~~~~~~~~~~
467 data instance T (a,b) = MkT { x::a, y::b }
469 data :TP a b = MkT { a::a, y::b }
470 coTP a b :: T (a,b) ~ :TP a b
472 Suppose r :: T (t1,t2), e :: t3
473 Then r { x=e } :: T (t3,t1)
476 MkT x y -> MkT e y |> co2
477 where co1 :: T (t1,t2) ~ :TP t1 t2
478 co2 :: :TP t3 t2 ~ T (t3,t2)
479 The wrapping with co2 is done by the constructor wrapper for MkT
483 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
485 * cons are the data constructors to be updated
487 * in_inst_tys, out_inst_tys have same length, and instantiate the
488 *representation* tycon of the data cons. In Note [Data
489 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
492 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
495 -- Check that the field names are really field names
496 let upd_fld_names = hsRecFields rbinds
497 ; MASSERT( notNull upd_fld_names )
498 ; sel_ids <- mapM tcLookupField upd_fld_names
499 -- The renamer has already checked that
500 -- selectors are all in scope
501 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
502 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
503 not (isRecordSelector sel_id), -- Excludes class ops
504 let L loc fld_name = hsRecFieldId fld ]
505 ; unless (null bad_guys) (sequence bad_guys >> failM)
508 -- Figure out the tycon and data cons from the first field name
509 ; let -- It's OK to use the non-tc splitters here (for a selector)
511 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
512 data_cons = tyConDataCons tycon -- it's not a field label
513 -- NB: for a data type family, the tycon is the instance tycon
515 relevant_cons = filter is_relevant data_cons
516 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
517 -- A constructor is only relevant to this process if
518 -- it contains *all* the fields that are being updated
519 -- Other ones will cause a runtime error if they occur
521 -- Take apart a representative constructor
522 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
523 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
524 con1_flds = dataConFieldLabels con1
525 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
528 -- Check that at least one constructor has all the named fields
529 -- i.e. has an empty set of bad fields returned by badFields
530 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
532 -- STEP 3 Note [Criteria for update]
533 -- Check that each updated field is polymorphic; that is, its type
534 -- mentions only the universally-quantified variables of the data con
535 ; let flds_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
536 (upd_flds_w_tys, fixed_flds_w_tys) = partition is_updated flds_w_tys
537 is_updated (fld,ty) = fld `elem` upd_fld_names
539 bad_upd_flds = filter bad_fld upd_flds_w_tys
540 con1_tv_set = mkVarSet con1_tvs
541 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
542 not (tyVarsOfType ty `subVarSet` con1_tv_set)
543 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
545 -- STEP 4 Note [Type of a record update]
546 -- Figure out types for the scrutinee and result
547 -- Both are of form (T a b c), with fresh type variables, but with
548 -- common variables where the scrutinee and result must have the same type
549 -- These are variables that appear anywhere *except* in the updated fields
550 ; let common_tvs = exactTyVarsOfTypes (map snd fixed_flds_w_tys)
551 `unionVarSet` constrainedTyVars con1_tvs relevant_cons
552 is_common_tv tv = tv `elemVarSet` common_tvs
554 mk_inst_ty tv result_inst_ty
555 | is_common_tv tv = return result_inst_ty -- Same as result type
556 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
558 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
559 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
561 ; let result_ty = substTy result_inst_env con1_res_ty
562 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
563 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
564 scrut_ty = substTy scrut_subst con1_res_ty
567 -- Typecheck the thing to be updated, and the bindings
568 ; record_expr' <- tcMonoExpr record_expr scrut_ty
569 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
571 ; let origin = RecordUpdOrigin
572 ; co_fn <- tcSubExp origin result_ty res_ty
574 -- STEP 6: Deal with the stupid theta
575 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
576 ; instStupidTheta origin theta'
578 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
579 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
580 = WpCast $ mkTyConApp co_con scrut_inst_tys
585 ; return (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
586 relevant_cons scrut_inst_tys result_inst_tys)) }
588 constrainedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
589 -- Universally-quantified tyvars that appear in any of the
590 -- *implicit* arguments to the constructor
591 -- These tyvars must not change across the updates
592 -- See Note [Implict type sharing]
593 constrainedTyVars tvs1 cons
594 = mkVarSet [tv1 | con <- cons
595 , let (tvs, theta, _, _) = dataConSig con
596 bad_tvs = tyVarsOfTheta theta
597 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
598 , tv `elemVarSet` bad_tvs ]
601 %************************************************************************
603 Arithmetic sequences e.g. [a,b..]
604 and their parallel-array counterparts e.g. [: a,b.. :]
607 %************************************************************************
610 tcExpr (ArithSeq _ seq@(From expr)) res_ty
611 = do { (elt_ty, coi) <- boxySplitListTy res_ty
612 ; expr' <- tcPolyExpr expr elt_ty
613 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
615 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
617 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
618 = do { (elt_ty, coi) <- boxySplitListTy res_ty
619 ; expr1' <- tcPolyExpr expr1 elt_ty
620 ; expr2' <- tcPolyExpr expr2 elt_ty
621 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
622 elt_ty enumFromThenName
623 ; return $ mkHsWrapCoI coi
624 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
626 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
627 = do { (elt_ty, coi) <- boxySplitListTy res_ty
628 ; expr1' <- tcPolyExpr expr1 elt_ty
629 ; expr2' <- tcPolyExpr expr2 elt_ty
630 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
631 elt_ty enumFromToName
632 ; return $ mkHsWrapCoI coi
633 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
635 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
636 = do { (elt_ty, coi) <- boxySplitListTy res_ty
637 ; expr1' <- tcPolyExpr expr1 elt_ty
638 ; expr2' <- tcPolyExpr expr2 elt_ty
639 ; expr3' <- tcPolyExpr expr3 elt_ty
640 ; eft <- newMethodFromName (ArithSeqOrigin seq)
641 elt_ty enumFromThenToName
642 ; return $ mkHsWrapCoI coi
643 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
645 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
646 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
647 ; expr1' <- tcPolyExpr expr1 elt_ty
648 ; expr2' <- tcPolyExpr expr2 elt_ty
649 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
650 elt_ty enumFromToPName
651 ; return $ mkHsWrapCoI coi
652 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
654 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
655 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
656 ; expr1' <- tcPolyExpr expr1 elt_ty
657 ; expr2' <- tcPolyExpr expr2 elt_ty
658 ; expr3' <- tcPolyExpr expr3 elt_ty
659 ; eft <- newMethodFromName (PArrSeqOrigin seq)
660 elt_ty enumFromThenToPName
661 ; return $ mkHsWrapCoI coi
662 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
664 tcExpr (PArrSeq _ _) _
665 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
666 -- the parser shouldn't have generated it and the renamer shouldn't have
671 %************************************************************************
675 %************************************************************************
678 #ifdef GHCI /* Only if bootstrapped */
679 -- Rename excludes these cases otherwise
680 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
681 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
683 tcExpr e@(HsQuasiQuoteE _) res_ty =
684 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
689 %************************************************************************
693 %************************************************************************
696 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
700 %************************************************************************
704 %************************************************************************
707 ---------------------------
708 tcApp :: HsExpr Name -- Function
709 -> Arity -- Number of args reqd
710 -> ArgChecker results
711 -> BoxyRhoType -- Result type
712 -> TcM (HsExpr TcId, results)
714 -- (tcFun fun n_args arg_checker res_ty)
715 -- The argument type checker, arg_checker, will be passed exactly n_args types
717 tcApp (HsVar fun_name) n_args arg_checker res_ty
718 = tcIdApp fun_name n_args arg_checker res_ty
720 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
721 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
722 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
723 ; arg_tys' <- mapM readFilledBox arg_boxes
724 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
725 ; return (fun', args') }
727 ---------------------------
728 tcIdApp :: Name -- Function
729 -> Arity -- Number of args reqd
730 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
731 -> BoxyRhoType -- Result type
732 -> TcM (HsExpr TcId, results)
734 -- Call (f e1 ... en) :: res_ty
735 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
736 -- (where k <= n; fres has the rest)
737 -- NB: if k < n then the function doesn't have enough args, and
738 -- presumably fres is a type variable that we are going to
739 -- instantiate with a function type
741 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
743 tcIdApp fun_name n_args arg_checker res_ty
744 = do { let orig = OccurrenceOf fun_name
745 ; (fun, fun_ty) <- lookupFun orig fun_name
747 -- Split up the function type
748 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
749 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
751 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
752 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
753 res_qtvs = exactTyVarsOfType fun_res_ty
754 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
755 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
756 k = length fun_arg_tys -- k <= n_args
757 n_missing_args = n_args - k -- Always >= 0
759 -- Match the result type of the function with the
760 -- result type of the context, to get an inital substitution
761 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
762 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
763 res_ty' = mkFunTys extra_arg_tys' res_ty
764 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
766 -- Typecheck the arguments!
767 -- Doing so will fill arg_qtvs and extra_arg_tys'
768 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
770 -- Strip boxes from the qtvs that have been filled in by the arg checking
771 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
773 -- Result subsumption
774 -- This fills in res_qtvs
775 ; let res_subst = zipOpenTvSubst qtvs qtys''
776 fun_res_ty'' = substTy res_subst fun_res_ty
777 res_ty'' = mkFunTys extra_arg_tys'' res_ty
778 ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
780 -- And pack up the results
781 -- By applying the coercion just to the *function* we can make
782 -- tcFun work nicely for OpApp and Sections too
783 ; fun' <- instFun orig fun res_subst tv_theta_prs
784 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
785 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
786 ; return (mkHsWrap co_fn' fun', args') }
789 Note [Silly type synonyms in smart-app]
790 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
791 When we call sripBoxyType, all of the boxes should be filled
792 in. But we need to be careful about type synonyms:
796 In the call (f x) we'll typecheck x, expecting it to have type
797 (T box). Usually that would fill in the box, but in this case not;
798 because 'a' is discarded by the silly type synonym T. So we must
799 use exactTyVarsOfType to figure out which type variables are free
800 in the argument type.
803 -- tcId is a specialisation of tcIdApp when there are no arguments
804 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
809 -> BoxyRhoType -- Result type
811 tcId orig fun_name res_ty
812 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
813 ; (fun, fun_ty) <- lookupFun orig fun_name
815 -- Split up the function type
816 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
817 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
818 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
819 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
821 -- Do the subsumption check wrt the result type
822 ; let res_subst = zipTopTvSubst qtvs qtv_tys
823 fun_tau' = substTy res_subst fun_tau
825 ; co_fn <- tcSubExp orig fun_tau' res_ty
827 -- And pack up the results
828 ; fun' <- instFun orig fun res_subst tv_theta_prs
829 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
830 ; return (mkHsWrap co_fn fun') }
832 -- Note [Push result type in]
834 -- Unify with expected result before (was: after) type-checking the args
835 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
836 -- This is when we might detect a too-few args situation.
837 -- (One can think of cases when the opposite order would give
838 -- a better error message.)
839 -- [March 2003: I'm experimenting with putting this first. Here's an
840 -- example where it actually makes a real difference
841 -- class C t a b | t a -> b
842 -- instance C Char a Bool
844 -- data P t a = forall b. (C t a b) => MkP b
845 -- data Q t = MkQ (forall a. P t a)
848 -- f1 = MkQ (MkP True)
849 -- f2 = MkQ (MkP True :: forall a. P Char a)
851 -- With the change, f1 will type-check, because the 'Char' info from
852 -- the signature is propagated into MkQ's argument. With the check
853 -- in the other order, the extra signature in f2 is reqd.]
855 ---------------------------
856 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
857 -- Typecheck a syntax operator, checking that it has the specified type
858 -- The operator is always a variable at this stage (i.e. renamer output)
859 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
860 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
862 ---------------------------
863 instFun :: InstOrigin
865 -> TvSubst -- The instantiating substitution
866 -> [([TyVar], ThetaType)] -- Stuff to instantiate
869 instFun orig fun subst []
870 = return fun -- Common short cut
872 instFun orig fun subst tv_theta_prs
873 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
874 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
875 -- Make two ad-hoc checks
876 ; doStupidChecks fun ty_theta_prs'
878 -- Now do normal instantiation
879 ; method_sharing <- doptM Opt_MethodSharing
880 ; result <- go method_sharing True fun ty_theta_prs'
881 ; traceTc (text "instFun result" <+> ppr result)
885 subst_pr (tvs, theta)
886 = (substTyVars subst tvs, substTheta subst theta)
888 go _ _ fun [] = do {traceTc (text "go _ _ fun [] returns" <+> ppr fun) ; return fun }
890 go method_sharing True (HsVar fun_id) ((tys,theta) : prs)
891 | want_method_inst method_sharing theta
892 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
893 ; meth_id <- newMethodWithGivenTy orig fun_id tys
894 ; go method_sharing False (HsVar meth_id) prs }
895 -- Go round with 'False' to prevent further use
896 -- of newMethod: see Note [Multiple instantiation]
898 go method_sharing _ fun ((tys, theta) : prs)
899 = do { co_fn <- instCall orig tys theta
900 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
901 ; go method_sharing False (HsWrap co_fn fun) prs }
903 -- See Note [No method sharing]
904 want_method_inst method_sharing theta = not (null theta) -- Overloaded
908 Note [Multiple instantiation]
909 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
910 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
911 For example, consider
912 f :: forall a. Eq a => forall b. Ord b => a -> b
913 At a call to f, at say [Int, Bool], it's tempting to translate the call to
917 f_m1 :: forall b. Ord b => Int -> b
921 f_m2 = f_m1 Bool dOrdBool
923 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
924 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
926 But it's entirely possible that f_m2 will continue to float out, because it
927 mentions no type variables. Result, f_m1 isn't in scope.
929 Here's a concrete example that does this (test tc200):
932 f :: Eq b => b -> a -> Int
933 baz :: Eq a => Int -> a -> Int
938 Current solution: only do the "method sharing" thing for the first type/dict
939 application, not for the iterated ones. A horribly subtle point.
941 Note [No method sharing]
942 ~~~~~~~~~~~~~~~~~~~~~~~~
943 The -fno-method-sharing flag controls what happens so far as the LIE
944 is concerned. The default case is that for an overloaded function we
945 generate a "method" Id, and add the Method Inst to the LIE. So you get
948 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
949 If you specify -fno-method-sharing, the dictionary application
950 isn't shared, so we get
952 f = /\a (d:Num a) (x:a) -> (+) a d x x
953 This gets a bit less sharing, but
954 a) it's better for RULEs involving overloaded functions
955 b) perhaps fewer separated lambdas
959 tcArgs implements a left-to-right order, which goes beyond what is described in the
960 impredicative type inference paper. In particular, it allows
962 where runST :: (forall s. ST s a) -> a
963 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
964 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
965 before checking foo. The left-to-right order really helps here.
968 tcArgs :: LHsExpr Name -- The function (for error messages)
969 -> [LHsExpr Name] -- Actual args
970 -> ArgChecker [LHsExpr TcId]
972 type ArgChecker results
973 = [TyVar] -> [TcSigmaType] -- Current instantiation
974 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
975 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
977 tcArgs fun args qtvs qtys arg_tys
978 = go 1 qtys args arg_tys
980 go n qtys [] [] = return (qtys, [])
981 go n qtys (arg:args) (arg_ty:arg_tys)
982 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
983 ; qtys' <- mapM refineBox qtys -- Exploit new info
984 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
985 ; return (qtys'', arg':args') }
986 go n qtys args arg_tys = panic "tcArgs"
988 tcArg :: LHsExpr Name -- The function
989 -> Int -- and arg number (for error messages)
991 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
993 -> TcM (LHsExpr TcId) -- Resulting argument
994 tcArg fun arg_no arg qtvs qtys ty
995 = addErrCtxt (funAppCtxt fun arg arg_no) $
996 tcPolyExprNC arg (substTyWith qtvs qtys ty)
1002 Nasty check to ensure that tagToEnum# is applied to a type that is an
1003 enumeration TyCon. Unification may refine the type later, but this
1004 check won't see that, alas. It's crude but it works.
1006 Here's are two cases that should fail
1008 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1011 g = tagToEnum# 0 -- Int is not an enumeration
1015 doStupidChecks :: HsExpr TcId
1016 -> [([TcType], ThetaType)]
1018 -- Check two tiresome and ad-hoc cases
1019 -- (a) the "stupid theta" for a data con; add the constraints
1020 -- from the "stupid theta" of a data constructor (sigh)
1021 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
1023 doStupidChecks (HsVar fun_id) ((tys,_):_)
1024 | Just con <- isDataConId_maybe fun_id -- (a)
1025 = addDataConStupidTheta con tys
1027 | fun_id `hasKey` tagToEnumKey -- (b)
1028 = do { tys' <- zonkTcTypes tys
1029 ; checkTc (ok tys') (tagToEnumError tys')
1033 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
1034 Just (tc,_) -> isEnumerationTyCon tc
1037 doStupidChecks fun tv_theta_prs
1038 = return () -- The common case
1042 = hang (ptext (sLit "Bad call to tagToEnum#") <+> at_type)
1043 2 (vcat [ptext (sLit "Specify the type by giving a type signature"),
1044 ptext (sLit "e.g. (tagToEnum# x) :: Bool")])
1046 at_type | null tys = empty -- Probably never happens
1047 | otherwise = ptext (sLit "at type") <+> ppr (head tys)
1050 %************************************************************************
1052 \subsection{@tcId@ typechecks an identifier occurrence}
1054 %************************************************************************
1057 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
1058 lookupFun orig id_name
1059 = do { thing <- tcLookup id_name
1061 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
1063 wrap_id = dataConWrapId con
1066 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1067 | otherwise -> return (HsVar id, idType id)
1068 -- A global cannot possibly be ill-staged
1069 -- nor does it need the 'lifting' treatment
1071 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
1072 -> do { thLocalId orig id ty lvl
1074 Unrefineable -> return (HsVar id, ty)
1075 Rigid co -> return (mkHsWrap co (HsVar id), ty)
1076 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
1077 WobblyInvisible -> failWithTc (ppr id_name <+> ptext (sLit " not in scope because it has a wobbly type (solution: add a type annotation)"))
1080 other -> failWithTc (ppr other <+> ptext (sLit "used where a value identifer was expected"))
1083 #ifndef GHCI /* GHCI and TH is off */
1084 --------------------------------------
1085 -- thLocalId : Check for cross-stage lifting
1086 thLocalId orig id id_ty th_bind_lvl
1089 #else /* GHCI and TH is on */
1090 thLocalId orig id id_ty th_bind_lvl
1091 = do { use_stage <- getStage -- TH case
1093 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
1094 -> thBrackId orig id ps_var lie_var
1095 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1099 --------------------------------------
1100 thBrackId orig id ps_var lie_var
1102 = -- Top-level identifiers in this module,
1103 -- (which have External Names)
1104 -- are just like the imported case:
1105 -- no need for the 'lifting' treatment
1106 -- E.g. this is fine:
1109 -- But we do need to put f into the keep-alive
1110 -- set, because after desugaring the code will
1111 -- only mention f's *name*, not f itself.
1112 do { keepAliveTc id; return id }
1115 = -- Nested identifiers, such as 'x' in
1116 -- E.g. \x -> [| h x |]
1117 -- We must behave as if the reference to x was
1119 -- We use 'x' itself as the splice proxy, used by
1120 -- the desugarer to stitch it all back together.
1121 -- If 'x' occurs many times we may get many identical
1122 -- bindings of the same splice proxy, but that doesn't
1123 -- matter, although it's a mite untidy.
1124 do { let id_ty = idType id
1125 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1126 -- If x is polymorphic, its occurrence sites might
1127 -- have different instantiations, so we can't use plain
1128 -- 'x' as the splice proxy name. I don't know how to
1129 -- solve this, and it's probably unimportant, so I'm
1130 -- just going to flag an error for now
1132 ; id_ty' <- zapToMonotype id_ty
1133 -- The id_ty might have an OpenTypeKind, but we
1134 -- can't instantiate the Lift class at that kind,
1135 -- so we zap it to a LiftedTypeKind monotype
1136 -- C.f. the call in TcPat.newLitInst
1138 ; setLIEVar lie_var $ do
1139 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1140 -- Put the 'lift' constraint into the right LIE
1142 -- Update the pending splices
1143 ; ps <- readMutVar ps_var
1144 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1151 %************************************************************************
1153 \subsection{Record bindings}
1155 %************************************************************************
1157 Game plan for record bindings
1158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1159 1. Find the TyCon for the bindings, from the first field label.
1161 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1163 For each binding field = value
1165 3. Instantiate the field type (from the field label) using the type
1168 4 Type check the value using tcArg, passing the field type as
1169 the expected argument type.
1171 This extends OK when the field types are universally quantified.
1177 -> [TcType] -- Expected type for each field
1178 -> HsRecordBinds Name
1179 -> TcM (HsRecordBinds TcId)
1181 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1182 = do { mb_binds <- mapM do_bind rbinds
1183 ; return (HsRecFields (catMaybes mb_binds) dd) }
1185 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1186 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1187 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1188 = addErrCtxt (fieldCtxt field_lbl) $
1189 do { rhs' <- tcPolyExprNC rhs field_ty
1190 ; let field_id = mkUserLocal (nameOccName field_lbl)
1191 (nameUnique field_lbl)
1193 -- Yuk: the field_id has the *unique* of the selector Id
1194 -- (so we can find it easily)
1195 -- but is a LocalId with the appropriate type of the RHS
1196 -- (so the desugarer knows the type of local binder to make)
1197 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1199 = do { addErrTc (badFieldCon data_con field_lbl)
1202 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1203 checkMissingFields data_con rbinds
1204 | null field_labels -- Not declared as a record;
1205 -- But C{} is still valid if no strict fields
1206 = if any isMarkedStrict field_strs then
1207 -- Illegal if any arg is strict
1208 addErrTc (missingStrictFields data_con [])
1212 | otherwise = do -- A record
1213 unless (null missing_s_fields)
1214 (addErrTc (missingStrictFields data_con missing_s_fields))
1216 warn <- doptM Opt_WarnMissingFields
1217 unless (not (warn && notNull missing_ns_fields))
1218 (warnTc True (missingFields data_con missing_ns_fields))
1222 = [ fl | (fl, str) <- field_info,
1224 not (fl `elem` field_names_used)
1227 = [ fl | (fl, str) <- field_info,
1228 not (isMarkedStrict str),
1229 not (fl `elem` field_names_used)
1232 field_names_used = hsRecFields rbinds
1233 field_labels = dataConFieldLabels data_con
1235 field_info = zipEqual "missingFields"
1239 field_strs = dataConStrictMarks data_con
1242 %************************************************************************
1244 \subsection{Errors and contexts}
1246 %************************************************************************
1248 Boring and alphabetical:
1250 addExprErrCtxt :: OutputableBndr id => LHsExpr id -> TcM a -> TcM a
1251 addExprErrCtxt expr = addErrCtxt (exprCtxt (unLoc expr))
1254 = hang (ptext (sLit "In the expression:")) 4 (ppr expr)
1256 fieldCtxt field_name
1257 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1259 funAppCtxt fun arg arg_no
1260 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1261 quotes (ppr fun) <> text ", namely"])
1262 4 (quotes (ppr arg))
1265 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1266 <> plural prs <> colon)
1267 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1270 = hang (ptext (sLit "No constructor has all these fields:"))
1271 4 (pprQuotedList (hsRecFields rbinds))
1273 naughtyRecordSel sel_id
1274 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1275 ptext (sLit "as a function due to escaped type variables") $$
1276 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1279 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1281 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1282 missingStrictFields con fields
1285 rest | null fields = empty -- Happens for non-record constructors
1286 -- with strict fields
1287 | otherwise = colon <+> pprWithCommas ppr fields
1289 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1290 ptext (sLit "does not have the required strict field(s)")
1292 missingFields :: DataCon -> [FieldLabel] -> SDoc
1293 missingFields con fields
1294 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1295 <+> pprWithCommas ppr fields
1297 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1300 polySpliceErr :: Id -> SDoc
1302 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)