2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
8 -- The above warning supression flag is a temporary kludge.
9 -- While working on this module you are encouraged to remove it and fix
10 -- any warnings in the module. See
11 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
14 module TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC,
15 tcInferRho, tcInferRhoNC,
16 tcSyntaxOp, tcCheckId,
17 addExprErrCtxt ) where
19 #include "HsVersions.h"
21 #ifdef GHCI /* Only if bootstrapped */
22 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
23 import qualified DsMeta
49 import TysPrim( intPrimTy )
50 import PrimOp( tagToEnumKey )
63 %************************************************************************
65 \subsection{Main wrappers}
67 %************************************************************************
70 tcPolyExpr, tcPolyExprNC
71 :: LHsExpr Name -- Expression to type check
72 -> TcSigmaType -- Expected type (could be a polytpye)
73 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
75 -- tcPolyExpr is a convenient place (frequent but not too frequent)
76 -- place to add context information.
77 -- The NC version does not do so, usually because the caller wants
80 tcPolyExpr expr res_ty
81 = addExprErrCtxt expr $
82 do { traceTc "tcPolyExpr" (ppr res_ty); tcPolyExprNC expr res_ty }
84 tcPolyExprNC expr res_ty
85 = do { traceTc "tcPolyExprNC" (ppr res_ty)
86 ; (gen_fn, expr') <- tcGen GenSigCtxt res_ty $ \ _ rho ->
88 ; return (mkLHsWrap gen_fn expr') }
91 tcMonoExpr, tcMonoExprNC
92 :: LHsExpr Name -- Expression to type check
93 -> TcRhoType -- Expected type (could be a type variable)
94 -- Definitely no foralls at the top
97 tcMonoExpr expr res_ty
98 = addErrCtxt (exprCtxt expr) $
99 tcMonoExprNC expr res_ty
101 tcMonoExprNC (L loc expr) res_ty
102 = ASSERT( not (isSigmaTy res_ty) )
104 do { expr' <- tcExpr expr res_ty
105 ; return (L loc expr') }
108 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
109 -- Infer a *rho*-type. This is, in effect, a special case
110 -- for ids and partial applications, so that if
111 -- f :: Int -> (forall a. a -> a) -> Int
113 -- f 3 :: (forall a. a -> a) -> Int
114 -- And that in turn is useful
115 -- (a) for the function part of any application (see tcApp)
116 -- (b) for the special rule for '$'
117 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
119 tcInferRhoNC (L loc expr)
121 do { (expr', rho) <- tcInfExpr expr
122 ; return (L loc expr', rho) }
124 tcInfExpr :: HsExpr Name -> TcM (HsExpr TcId, TcRhoType)
125 tcInfExpr (HsVar f) = tcInferId f
126 tcInfExpr (HsPar e) = do { (e', ty) <- tcInferRhoNC e
127 ; return (HsPar e', ty) }
128 tcInfExpr (HsApp e1 e2) = tcInferApp e1 [e2]
129 tcInfExpr e = tcInfer (tcExpr e)
133 %************************************************************************
135 tcExpr: the main expression typechecker
137 %************************************************************************
140 tcExpr :: HsExpr Name -> TcRhoType -> 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 = tcCheckId name res_ty
146 tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty
148 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
149 ; tcWrapResult (HsLit lit) lit_ty res_ty }
151 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
152 ; return (HsPar expr') }
154 tcExpr (HsSCC lbl expr) res_ty
155 = do { expr' <- tcMonoExpr expr res_ty
156 ; return (HsSCC lbl expr') }
158 tcExpr (HsTickPragma info expr) res_ty
159 = do { expr' <- tcMonoExpr expr res_ty
160 ; return (HsTickPragma info expr') }
162 tcExpr (HsCoreAnn lbl expr) res_ty
163 = do { expr' <- tcMonoExpr expr res_ty
164 ; return (HsCoreAnn lbl expr') }
166 tcExpr (HsOverLit lit) res_ty
167 = do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty
168 ; return (HsOverLit lit') }
170 tcExpr (NegApp expr neg_expr) res_ty
171 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
172 (mkFunTy res_ty res_ty)
173 ; expr' <- tcMonoExpr expr res_ty
174 ; return (NegApp expr' neg_expr') }
176 tcExpr (HsIPVar ip) res_ty
177 = do { let origin = IPOccOrigin ip
178 -- Implicit parameters must have a *tau-type* not a
179 -- type scheme. We enforce this by creating a fresh
180 -- type variable as its type. (Because res_ty may not
182 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
183 ; ip_var <- emitWanted origin (mkIPPred ip ip_ty)
184 ; tcWrapResult (HsIPVar (IPName ip_var)) ip_ty res_ty }
186 tcExpr (HsLam match) res_ty
187 = do { (co_fn, match') <- tcMatchLambda match res_ty
188 ; return (mkHsWrap co_fn (HsLam match')) }
190 tcExpr (ExprWithTySig expr sig_ty) res_ty
191 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
193 -- Remember to extend the lexical type-variable environment
195 <- tcGen ExprSigCtxt sig_tc_ty $ \ skol_tvs res_ty ->
196 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
197 -- See Note [More instantiated than scoped] in TcBinds
198 tcMonoExprNC expr res_ty
200 ; let inner_expr = ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty
202 ; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin sig_tc_ty
203 ; tcWrapResult (mkHsWrap inst_wrap inner_expr) rho res_ty }
206 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
207 -- This is the syntax for type applications that I was planning
208 -- but there are difficulties (e.g. what order for type args)
209 -- so it's not enabled yet.
210 -- Can't eliminate it altogether from the parser, because the
211 -- same parser parses *patterns*.
215 %************************************************************************
217 Infix operators and sections
219 %************************************************************************
223 Left sections, like (4 *), are equivalent to
225 or, if PostfixOperators is enabled, just
227 With PostfixOperators we don't actually require the function to take
228 two arguments at all. For example, (x `not`) means (not x); you get
229 postfix operators! Not Haskell 98, but it's less work and kind of
232 Note [Typing rule for ($)]
233 ~~~~~~~~~~~~~~~~~~~~~~~~~~
237 runST :: (forall s. ST s a) -> a
238 that I have finally given in and written a special type-checking
239 rule just for saturated appliations of ($).
240 * Infer the type of the first argument
241 * Decompose it; should be of form (arg2_ty -> res_ty),
242 where arg2_ty might be a polytype
243 * Use arg2_ty to typecheck arg2
245 Note [Typing rule for seq]
246 ~~~~~~~~~~~~~~~~~~~~~~~~~~
249 which suggests this type for seq:
250 seq :: forall (a:*) (b:??). a -> b -> b,
251 with (b:??) meaning that be can be instantiated with an unboxed tuple.
252 But that's ill-kinded! Function arguments can't be unboxed tuples.
253 And indeed, you could not expect to do this with a partially-applied
254 'seq'; it's only going to work when it's fully applied. so it turns
256 case x of _ -> (# p,q #)
258 For a while I slid by by giving 'seq' an ill-kinded type, but then
259 the simplifier eta-reduced an application of seq and Lint blew up
260 with a kind error. It seems more uniform to treat 'seq' as it it
261 was a language construct.
263 See Note [seqId magic] in MkId, and
267 tcExpr (OpApp arg1 op fix arg2) res_ty
268 | (L loc (HsVar op_name)) <- op
269 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
270 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
271 ; let arg2_ty = res_ty
272 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
273 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
274 ; op_id <- tcLookupId op_name
275 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar op_id))
276 ; return $ OpApp arg1' op' fix arg2' }
278 | (L loc (HsVar op_name)) <- op
279 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
280 = do { traceTc "Application rule" (ppr op)
281 ; (arg1', arg1_ty) <- tcInferRho arg1
282 ; let doc = ptext (sLit "The first argument of ($) takes")
283 ; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty
284 -- arg2_ty maybe polymorphic; that's the point
285 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
286 ; co_res <- unifyType op_res_ty res_ty
287 ; op_id <- tcLookupId op_name
288 ; let op' = L loc (HsWrap (mkWpTyApps [arg2_ty, op_res_ty]) (HsVar op_id))
289 ; return $ mkHsWrapCoI co_res $
290 OpApp (mkLHsWrapCoI co_arg1 arg1') op' fix arg2' }
293 = do { traceTc "Non Application rule" (ppr op)
294 ; (op', op_ty) <- tcInferFun op
295 ; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTys op 2 op_ty
296 ; co_res <- unifyType op_res_ty res_ty
297 ; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys
298 ; return $ mkHsWrapCoI co_res $
299 OpApp arg1' (mkLHsWrapCoI co_fn op') fix arg2' }
301 -- Right sections, equivalent to \ x -> x `op` expr, or
304 tcExpr (SectionR op arg2) res_ty
305 = do { (op', op_ty) <- tcInferFun op
306 ; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTys op 2 op_ty
307 ; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty
308 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
309 ; return $ mkHsWrapCoI co_res $
310 SectionR (mkLHsWrapCoI co_fn op') arg2' }
312 tcExpr (SectionL arg1 op) res_ty
313 = do { (op', op_ty) <- tcInferFun op
314 ; dflags <- getDOpts -- Note [Left sections]
315 ; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1
318 ; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTys op n_reqd_args op_ty
319 ; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty
320 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
321 ; return $ mkHsWrapCoI co_res $
322 SectionL arg1' (mkLHsWrapCoI co_fn op') }
324 tcExpr (ExplicitTuple tup_args boxity) res_ty
325 | all tupArgPresent tup_args
326 = do { let tup_tc = tupleTyCon boxity (length tup_args)
327 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
328 ; tup_args1 <- tcTupArgs tup_args arg_tys
329 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
332 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
333 do { let kind = case boxity of { Boxed -> liftedTypeKind
334 ; Unboxed -> argTypeKind }
335 arity = length tup_args
336 tup_tc = tupleTyCon boxity arity
338 ; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind
340 = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
341 (mkTyConApp tup_tc arg_tys)
343 ; coi <- unifyType actual_res_ty res_ty
345 -- Handle tuple sections where
346 ; tup_args1 <- tcTupArgs tup_args arg_tys
348 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
350 tcExpr (ExplicitList _ exprs) res_ty
351 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
352 ; exprs' <- mapM (tc_elt elt_ty) exprs
353 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
355 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
357 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
358 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
359 ; exprs' <- mapM (tc_elt elt_ty) exprs
360 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
362 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
365 %************************************************************************
369 %************************************************************************
372 tcExpr (HsLet binds expr) res_ty
373 = do { (binds', expr') <- tcLocalBinds binds $
374 tcMonoExpr expr res_ty
375 ; return (HsLet binds' expr') }
377 tcExpr (HsCase scrut matches) exp_ty
378 = do { -- We used to typecheck the case alternatives first.
379 -- The case patterns tend to give good type info to use
380 -- when typechecking the scrutinee. For example
383 -- will report that map is applied to too few arguments
385 -- But now, in the GADT world, we need to typecheck the scrutinee
386 -- first, to get type info that may be refined in the case alternatives
387 (scrut', scrut_ty) <- tcInferRho scrut
389 ; traceTc "HsCase" (ppr scrut_ty)
390 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
391 ; return (HsCase scrut' matches') }
393 match_ctxt = MC { mc_what = CaseAlt,
396 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
397 = do { pred' <- tcMonoExpr pred boolTy
398 ; b1' <- tcMonoExpr b1 res_ty
399 ; b2' <- tcMonoExpr b2 res_ty
400 ; return (HsIf Nothing pred' b1' b2') }
402 tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Note [Rebindable syntax for if]
403 = do { pred_ty <- newFlexiTyVarTy openTypeKind
404 ; b1_ty <- newFlexiTyVarTy openTypeKind
405 ; b2_ty <- newFlexiTyVarTy openTypeKind
406 ; let if_ty = mkFunTys [pred_ty, b1_ty, b2_ty] res_ty
407 ; fun' <- tcSyntaxOp IfOrigin fun if_ty
408 ; pred' <- tcMonoExpr pred pred_ty
409 ; b1' <- tcMonoExpr b1 b1_ty
410 ; b2' <- tcMonoExpr b2 b2_ty
411 -- Fundamentally we are just typing (ifThenElse e1 e2 e3)
412 -- so maybe we should use the code for function applications
413 -- (which would allow ifThenElse to be higher rank).
414 -- But it's a little awkward, so I'm leaving it alone for now
415 -- and it maintains uniformity with other rebindable syntax
416 ; return (HsIf (Just fun') pred' b1' b2') }
418 tcExpr (HsDo do_or_lc stmts body _) res_ty
419 = tcDoStmts do_or_lc stmts body res_ty
421 tcExpr (HsProc pat cmd) res_ty
422 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
423 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
425 tcExpr e@(HsArrApp _ _ _ _ _) _
426 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
427 ptext (sLit "was found where an expression was expected")])
429 tcExpr e@(HsArrForm _ _ _) _
430 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
431 ptext (sLit "was found where an expression was expected")])
434 Note [Rebindable syntax for if]
435 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
436 The rebindable syntax for 'if' uses the most flexible possible type
438 ifThenElse :: p -> b1 -> b2 -> res
439 to support expressions like this:
441 ifThenElse :: Maybe a -> (a -> b) -> b -> b
442 ifThenElse (Just a) f _ = f a ifThenElse Nothing _ e = e
450 %************************************************************************
452 Record construction and update
454 %************************************************************************
457 tcExpr (RecordCon (L loc con_name) _ rbinds) res_ty
458 = do { data_con <- tcLookupDataCon con_name
460 -- Check for missing fields
461 ; checkMissingFields data_con rbinds
463 ; (con_expr, con_tau) <- tcInferId con_name
464 ; let arity = dataConSourceArity data_con
465 (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
466 con_id = dataConWrapId data_con
468 ; co_res <- unifyType actual_res_ty res_ty
469 ; rbinds' <- tcRecordBinds data_con arg_tys rbinds
470 ; return $ mkHsWrapCoI co_res $
471 RecordCon (L loc con_id) con_expr rbinds' }
474 Note [Type of a record update]
475 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
476 The main complication with RecordUpd is that we need to explicitly
477 handle the *non-updated* fields. Consider:
479 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
480 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
483 upd :: T a b c -> (b',c) -> T a b' c
484 upd t x = t { fb = x}
486 The result type should be (T a b' c)
487 not (T a b c), because 'b' *is not* mentioned in a non-updated field
488 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
489 NB that it's not good enough to look at just one constructor; we must
490 look at them all; cf Trac #3219
492 After all, upd should be equivalent to:
498 So we need to give a completely fresh type to the result record,
499 and then constrain it by the fields that are *not* updated ("p" above).
500 We call these the "fixed" type variables, and compute them in getFixedTyVars.
502 Note that because MkT3 doesn't contain all the fields being updated,
503 its RHS is simply an error, so it doesn't impose any type constraints.
504 Hence the use of 'relevant_cont'.
506 Note [Implict type sharing]
507 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
508 We also take into account any "implicit" non-update fields. For example
509 data T a b where { MkT { f::a } :: T a a; ... }
510 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
515 upd :: T a b -> a -> T a b
516 upd (t::T a b) (x::a)
517 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
518 We can't give it the more general type
519 upd :: T a b -> c -> T c b
521 Note [Criteria for update]
522 ~~~~~~~~~~~~~~~~~~~~~~~~~~
523 We want to allow update for existentials etc, provided the updated
524 field isn't part of the existential. For example, this should be ok.
525 data T a where { MkT { f1::a, f2::b->b } :: T a }
529 The criterion we use is this:
531 The types of the updated fields
532 mention only the universally-quantified type variables
533 of the data constructor
535 NB: this is not (quite) the same as being a "naughty" record selector
536 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
537 in the case of GADTs. Consider
538 data T a where { MkT :: { f :: a } :: T [a] }
539 Then f is not "naughty" because it has a well-typed record selector.
540 But we don't allow updates for 'f'. (One could consider trying to
541 allow this, but it makes my head hurt. Badly. And no one has asked
544 In principle one could go further, and allow
546 g t = t { f2 = \x -> x }
547 because the expression is polymorphic...but that seems a bridge too far.
549 Note [Data family example]
550 ~~~~~~~~~~~~~~~~~~~~~~~~~~
551 data instance T (a,b) = MkT { x::a, y::b }
553 data :TP a b = MkT { a::a, y::b }
554 coTP a b :: T (a,b) ~ :TP a b
556 Suppose r :: T (t1,t2), e :: t3
557 Then r { x=e } :: T (t3,t1)
560 MkT x y -> MkT e y |> co2
561 where co1 :: T (t1,t2) ~ :TP t1 t2
562 co2 :: :TP t3 t2 ~ T (t3,t2)
563 The wrapping with co2 is done by the constructor wrapper for MkT
567 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
569 * cons are the data constructors to be updated
571 * in_inst_tys, out_inst_tys have same length, and instantiate the
572 *representation* tycon of the data cons. In Note [Data
573 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
576 tcExpr (RecordUpd record_expr rbinds _ _ _) res_ty
577 = ASSERT( notNull upd_fld_names )
580 -- Check that the field names are really field names
581 ; sel_ids <- mapM tcLookupField upd_fld_names
582 -- The renamer has already checked that
583 -- selectors are all in scope
584 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
585 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
586 not (isRecordSelector sel_id), -- Excludes class ops
587 let L loc fld_name = hsRecFieldId fld ]
588 ; unless (null bad_guys) (sequence bad_guys >> failM)
591 -- Figure out the tycon and data cons from the first field name
592 ; let -- It's OK to use the non-tc splitters here (for a selector)
594 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
595 data_cons = tyConDataCons tycon -- it's not a field label
596 -- NB: for a data type family, the tycon is the instance tycon
598 relevant_cons = filter is_relevant data_cons
599 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
600 -- A constructor is only relevant to this process if
601 -- it contains *all* the fields that are being updated
602 -- Other ones will cause a runtime error if they occur
604 -- Take apart a representative constructor
605 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
606 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
607 con1_flds = dataConFieldLabels con1
608 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
611 -- Check that at least one constructor has all the named fields
612 -- i.e. has an empty set of bad fields returned by badFields
613 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
615 -- STEP 3 Note [Criteria for update]
616 -- Check that each updated field is polymorphic; that is, its type
617 -- mentions only the universally-quantified variables of the data con
618 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
619 upd_flds1_w_tys = filter is_updated flds1_w_tys
620 is_updated (fld,_) = fld `elem` upd_fld_names
622 bad_upd_flds = filter bad_fld upd_flds1_w_tys
623 con1_tv_set = mkVarSet con1_tvs
624 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
625 not (tyVarsOfType ty `subVarSet` con1_tv_set)
626 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
628 -- STEP 4 Note [Type of a record update]
629 -- Figure out types for the scrutinee and result
630 -- Both are of form (T a b c), with fresh type variables, but with
631 -- common variables where the scrutinee and result must have the same type
632 -- These are variables that appear in *any* arg of *any* of the
633 -- relevant constructors *except* in the updated fields
635 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
636 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
637 mk_inst_ty tv result_inst_ty
638 | is_fixed_tv tv = return result_inst_ty -- Same as result type
639 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
641 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
642 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
644 ; let rec_res_ty = substTy result_inst_env con1_res_ty
645 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
646 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
647 scrut_ty = substTy scrut_subst con1_res_ty
649 ; co_res <- unifyType rec_res_ty res_ty
652 -- Typecheck the thing to be updated, and the bindings
653 ; record_expr' <- tcMonoExpr record_expr scrut_ty
654 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
656 -- STEP 6: Deal with the stupid theta
657 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
658 ; instStupidTheta RecordUpdOrigin theta'
660 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
661 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
662 = WpCast $ mkTyConApp co_con scrut_inst_tys
666 ; return $ mkHsWrapCoI co_res $
667 RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
668 relevant_cons scrut_inst_tys result_inst_tys }
670 upd_fld_names = hsRecFields rbinds
672 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
673 -- These tyvars must not change across the updates
674 getFixedTyVars tvs1 cons
675 = mkVarSet [tv1 | con <- cons
676 , let (tvs, theta, arg_tys, _) = dataConSig con
677 flds = dataConFieldLabels con
678 fixed_tvs = exactTyVarsOfTypes fixed_tys
679 -- fixed_tys: See Note [Type of a record update]
680 `unionVarSet` tyVarsOfTheta theta
681 -- Universally-quantified tyvars that
682 -- appear in any of the *implicit*
683 -- arguments to the constructor are fixed
684 -- See Note [Implict type sharing]
686 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
687 , not (fld `elem` upd_fld_names)]
688 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
689 , tv `elemVarSet` fixed_tvs ]
692 %************************************************************************
694 Arithmetic sequences e.g. [a,b..]
695 and their parallel-array counterparts e.g. [: a,b.. :]
698 %************************************************************************
701 tcExpr (ArithSeq _ seq@(From expr)) res_ty
702 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
703 ; expr' <- tcPolyExpr expr elt_ty
704 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
706 ; return $ mkHsWrapCoI coi (ArithSeq enum_from (From expr')) }
708 tcExpr (ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
709 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
710 ; expr1' <- tcPolyExpr expr1 elt_ty
711 ; expr2' <- tcPolyExpr expr2 elt_ty
712 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
713 enumFromThenName elt_ty
714 ; return $ mkHsWrapCoI coi
715 (ArithSeq enum_from_then (FromThen expr1' expr2')) }
717 tcExpr (ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
718 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
719 ; expr1' <- tcPolyExpr expr1 elt_ty
720 ; expr2' <- tcPolyExpr expr2 elt_ty
721 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
722 enumFromToName elt_ty
723 ; return $ mkHsWrapCoI coi
724 (ArithSeq enum_from_to (FromTo expr1' expr2')) }
726 tcExpr (ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
727 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
728 ; expr1' <- tcPolyExpr expr1 elt_ty
729 ; expr2' <- tcPolyExpr expr2 elt_ty
730 ; expr3' <- tcPolyExpr expr3 elt_ty
731 ; eft <- newMethodFromName (ArithSeqOrigin seq)
732 enumFromThenToName elt_ty
733 ; return $ mkHsWrapCoI coi
734 (ArithSeq eft (FromThenTo expr1' expr2' expr3')) }
736 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
737 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
738 ; expr1' <- tcPolyExpr expr1 elt_ty
739 ; expr2' <- tcPolyExpr expr2 elt_ty
740 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
741 (enumFromToPName basePackageId) elt_ty -- !!!FIXME: chak
742 ; return $ mkHsWrapCoI coi
743 (PArrSeq enum_from_to (FromTo expr1' expr2')) }
745 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
746 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
747 ; expr1' <- tcPolyExpr expr1 elt_ty
748 ; expr2' <- tcPolyExpr expr2 elt_ty
749 ; expr3' <- tcPolyExpr expr3 elt_ty
750 ; eft <- newMethodFromName (PArrSeqOrigin seq)
751 (enumFromThenToPName basePackageId) elt_ty -- !!!FIXME: chak
752 ; return $ mkHsWrapCoI coi
753 (PArrSeq eft (FromThenTo expr1' expr2' expr3')) }
755 tcExpr (PArrSeq _ _) _
756 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
757 -- the parser shouldn't have generated it and the renamer shouldn't have
762 %************************************************************************
766 %************************************************************************
769 #ifdef GHCI /* Only if bootstrapped */
770 -- Rename excludes these cases otherwise
771 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
772 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
774 tcExpr e@(HsQuasiQuoteE _) _ =
775 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
780 %************************************************************************
784 %************************************************************************
787 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
791 %************************************************************************
795 %************************************************************************
798 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
799 -> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args
801 tcApp (L _ (HsPar e)) args res_ty
802 = tcApp e args res_ty
804 tcApp (L _ (HsApp e1 e2)) args res_ty
805 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
807 tcApp (L loc (HsVar fun)) args res_ty
808 | fun `hasKey` tagToEnumKey
810 = tcTagToEnum loc fun arg res_ty
812 tcApp fun args res_ty
813 = do { -- Type-check the function
814 ; (fun1, fun_tau) <- tcInferFun fun
816 -- Extract its argument types
817 ; (co_fun, expected_arg_tys, actual_res_ty)
818 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
820 -- Typecheck the result, thereby propagating
821 -- info (if any) from result into the argument types
822 -- Both actual_res_ty and res_ty are deeply skolemised
823 ; co_res <- addErrCtxt (funResCtxt fun) $
824 unifyType actual_res_ty res_ty
826 -- Typecheck the arguments
827 ; args1 <- tcArgs fun args expected_arg_tys
829 -- Assemble the result
830 ; let fun2 = mkLHsWrapCoI co_fun fun1
831 app = mkLHsWrapCoI co_res (foldl mkHsApp fun2 args1)
833 ; return (unLoc app) }
836 mk_app_msg :: LHsExpr Name -> SDoc
837 mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun)
838 , ptext (sLit "is applied to")]
841 tcInferApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
842 -> TcM (HsExpr TcId, TcRhoType) -- Translated fun and args
844 tcInferApp (L _ (HsPar e)) args = tcInferApp e args
845 tcInferApp (L _ (HsApp e1 e2)) args = tcInferApp e1 (e2:args)
847 = -- Very like the tcApp version, except that there is
848 -- no expected result type passed in
849 do { (fun1, fun_tau) <- tcInferFun fun
850 ; (co_fun, expected_arg_tys, actual_res_ty)
851 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
852 ; args1 <- tcArgs fun args expected_arg_tys
853 ; let fun2 = mkLHsWrapCoI co_fun fun1
854 app = foldl mkHsApp fun2 args1
855 ; return (unLoc app, actual_res_ty) }
858 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
859 -- Infer and instantiate the type of a function
860 tcInferFun (L loc (HsVar name))
861 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
862 -- Don't wrap a context around a plain Id
863 ; return (L loc fun, ty) }
866 = do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun)
868 -- Zonk the function type carefully, to expose any polymorphism
869 -- E.g. (( \(x::forall a. a->a). blah ) e)
870 -- We can see the rank-2 type of the lambda in time to genrealise e
871 ; fun_ty' <- zonkTcTypeCarefully fun_ty
873 ; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty'
874 ; return (mkLHsWrap wrap fun, rho) }
877 tcArgs :: LHsExpr Name -- The function (for error messages)
878 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
879 -> TcM [LHsExpr TcId] -- Resulting args
881 tcArgs fun args expected_arg_tys
882 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
885 tcArg :: LHsExpr Name -- The function (for error messages)
886 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
887 -> TcM (LHsExpr TcId) -- Resulting argument
888 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
889 (tcPolyExprNC arg ty)
892 tcTupArgs :: [HsTupArg Name] -> [TcSigmaType] -> TcM [HsTupArg TcId]
894 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
896 go (Missing {}, arg_ty) = return (Missing arg_ty)
897 go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
898 ; return (Present expr') }
901 unifyOpFunTys :: LHsExpr Name -> Arity -> TcRhoType
902 -> TcM (CoercionI, [TcSigmaType], TcRhoType)
903 -- A wrapper for matchExpectedFunTys
904 unifyOpFunTys op arity ty = matchExpectedFunTys herald arity ty
906 herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes")
908 ---------------------------
909 tcSyntaxOp :: CtOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
910 -- Typecheck a syntax operator, checking that it has the specified type
911 -- The operator is always a variable at this stage (i.e. renamer output)
912 -- This version assumes res_ty is a monotype
913 tcSyntaxOp orig (HsVar op) res_ty = do { (expr, rho) <- tcInferIdWithOrig orig op
914 ; tcWrapResult expr rho res_ty }
915 tcSyntaxOp _ other _ = pprPanic "tcSyntaxOp" (ppr other)
919 Note [Push result type in]
920 ~~~~~~~~~~~~~~~~~~~~~~~~~~
921 Unify with expected result before type-checking the args so that the
922 info from res_ty percolates to args. This is when we might detect a
923 too-few args situation. (One can think of cases when the opposite
924 order would give a better error message.)
925 experimenting with putting this first.
927 Here's an example where it actually makes a real difference
929 class C t a b | t a -> b
930 instance C Char a Bool
932 data P t a = forall b. (C t a b) => MkP b
933 data Q t = MkQ (forall a. P t a)
937 f2 = MkQ (MkP True :: forall a. P Char a)
939 With the change, f1 will type-check, because the 'Char' info from
940 the signature is propagated into MkQ's argument. With the check
941 in the other order, the extra signature in f2 is reqd.
944 %************************************************************************
948 %************************************************************************
951 tcCheckId :: Name -> TcRhoType -> TcM (HsExpr TcId)
952 tcCheckId name res_ty = do { (expr, rho) <- tcInferId name
953 ; tcWrapResult expr rho res_ty }
955 ------------------------
956 tcInferId :: Name -> TcM (HsExpr TcId, TcRhoType)
957 -- Infer type, and deeply instantiate
958 tcInferId n = tcInferIdWithOrig (OccurrenceOf n) n
960 ------------------------
961 tcInferIdWithOrig :: CtOrigin -> Name -> TcM (HsExpr TcId, TcRhoType)
962 -- Look up an occurrence of an Id, and instantiate it (deeply)
964 tcInferIdWithOrig orig id_name
965 = do { id <- lookup_id
966 ; (id_expr, id_rho) <- instantiateOuter orig id
967 ; (wrap, rho) <- deeplyInstantiate orig id_rho
968 ; return (mkHsWrap wrap id_expr, rho) }
970 lookup_id :: TcM TcId
972 = do { thing <- tcLookup id_name
974 ATcId { tct_id = id, tct_level = lvl }
975 -> do { check_naughty id -- Note [Local record selectors]
976 ; checkThLocalId id lvl
980 -> do { check_naughty id; return id }
981 -- A global cannot possibly be ill-staged
982 -- nor does it need the 'lifting' treatment
983 -- hence no checkTh stuff here
985 AGlobal (ADataCon con) -> return (dataConWrapId con)
987 other -> failWithTc (bad_lookup other) }
989 bad_lookup thing = ppr thing <+> ptext (sLit "used where a value identifer was expected")
992 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel id)
993 | otherwise = return ()
995 ------------------------
996 instantiateOuter :: CtOrigin -> TcId -> TcM (HsExpr TcId, TcSigmaType)
997 -- Do just the first level of instantiation of an Id
998 -- a) Deal with method sharing
999 -- b) Deal with stupid checks
1000 -- Only look at the *outer level* of quantification
1001 -- See Note [Multiple instantiation]
1003 instantiateOuter orig id
1004 | null tvs && null theta
1005 = return (HsVar id, tau)
1008 = do { (_, tys, subst) <- tcInstTyVars tvs
1009 ; doStupidChecks id tys
1010 ; let theta' = substTheta subst theta
1011 ; traceTc "Instantiating" (ppr id <+> text "with" <+> (ppr tys $$ ppr theta'))
1012 ; wrap <- instCall orig tys theta'
1013 ; return (mkHsWrap wrap (HsVar id), substTy subst tau) }
1015 (tvs, theta, tau) = tcSplitSigmaTy (idType id)
1018 Note [Multiple instantiation]
1019 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1020 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
1021 For example, consider
1022 f :: forall a. Eq a => forall b. Ord b => a -> b
1023 At a call to f, at say [Int, Bool], it's tempting to translate the call to
1027 f_m1 :: forall b. Ord b => Int -> b
1031 f_m2 = f_m1 Bool dOrdBool
1033 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
1034 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
1036 But it's entirely possible that f_m2 will continue to float out, because it
1037 mentions no type variables. Result, f_m1 isn't in scope.
1039 Here's a concrete example that does this (test tc200):
1042 f :: Eq b => b -> a -> Int
1043 baz :: Eq a => Int -> a -> Int
1045 instance C Int where
1048 Current solution: only do the "method sharing" thing for the first type/dict
1049 application, not for the iterated ones. A horribly subtle point.
1051 Note [No method sharing]
1052 ~~~~~~~~~~~~~~~~~~~~~~~~
1053 The -fno-method-sharing flag controls what happens so far as the LIE
1054 is concerned. The default case is that for an overloaded function we
1055 generate a "method" Id, and add the Method Inst to the LIE. So you get
1057 f :: Num a => a -> a
1058 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
1059 If you specify -fno-method-sharing, the dictionary application
1060 isn't shared, so we get
1061 f :: Num a => a -> a
1062 f = /\a (d:Num a) (x:a) -> (+) a d x x
1063 This gets a bit less sharing, but
1064 a) it's better for RULEs involving overloaded functions
1065 b) perhaps fewer separated lambdas
1068 doStupidChecks :: TcId
1071 -- Check two tiresome and ad-hoc cases
1072 -- (a) the "stupid theta" for a data con; add the constraints
1073 -- from the "stupid theta" of a data constructor (sigh)
1075 doStupidChecks fun_id tys
1076 | Just con <- isDataConId_maybe fun_id -- (a)
1077 = addDataConStupidTheta con tys
1079 | fun_id `hasKey` tagToEnumKey -- (b)
1080 = failWithTc (ptext (sLit "tagToEnum# must appear applied to one argument"))
1083 = return () -- The common case
1088 Nasty check to ensure that tagToEnum# is applied to a type that is an
1089 enumeration TyCon. Unification may refine the type later, but this
1090 check won't see that, alas. It's crude, because it relies on our
1091 knowing *now* that the type is ok, which in turn relies on the
1092 eager-unification part of the type checker pushing enough information
1093 here. In theory the Right Thing to do is to have a new form of
1094 constraint but I definitely cannot face that! And it works ok as-is.
1096 Here's are two cases that should fail
1098 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1101 g = tagToEnum# 0 -- Int is not an enumeration
1103 When data type families are involved it's a bit more complicated.
1105 data instance F [Int] = A | B | C
1106 Then we want to generate something like
1107 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1108 Usually that coercion is hidden inside the wrappers for
1109 constructors of F [Int] but here we have to do it explicitly.
1111 It's all grotesquely complicated.
1114 tcTagToEnum :: SrcSpan -> Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
1115 -- tagToEnum# :: forall a. Int# -> a
1116 -- See Note [tagToEnum#] Urgh!
1117 tcTagToEnum loc fun_name arg res_ty
1118 = do { fun <- tcLookupId fun_name
1119 ; ty' <- zonkTcType res_ty
1121 -- Check that the type is algebraic
1122 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1123 Just (tc, tc_args) = mb_tc_app
1124 ; checkTc (isJust mb_tc_app)
1125 (tagToEnumError ty' doc1)
1127 -- Look through any type family
1128 ; (coi, rep_tc, rep_args) <- get_rep_ty ty' tc tc_args
1130 ; checkTc (isEnumerationTyCon rep_tc)
1131 (tagToEnumError ty' doc2)
1133 ; arg' <- tcMonoExpr arg intPrimTy
1134 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar fun))
1135 rep_ty = mkTyConApp rep_tc rep_args
1137 ; return (mkHsWrapCoI coi $ HsApp fun' arg') }
1139 doc1 = vcat [ ptext (sLit "Specify the type by giving a type signature")
1140 , ptext (sLit "e.g. (tagToEnum# x) :: Bool") ]
1141 doc2 = ptext (sLit "Result type must be an enumeration type")
1142 doc3 = ptext (sLit "No family instance for this type")
1144 get_rep_ty :: TcType -> TyCon -> [TcType]
1145 -> TcM (CoercionI, TyCon, [TcType])
1146 -- Converts a family type (eg F [a]) to its rep type (eg FList a)
1147 -- and returns a coercion between the two
1148 get_rep_ty ty tc tc_args
1149 | not (isFamilyTyCon tc)
1150 = return (IdCo ty, tc, tc_args)
1152 = do { mb_fam <- tcLookupFamInst tc tc_args
1154 Nothing -> failWithTc (tagToEnumError ty doc3)
1155 Just (rep_tc, rep_args)
1156 -> return ( ACo (mkSymCoercion (mkTyConApp co_tc rep_args))
1157 , rep_tc, rep_args )
1159 co_tc = expectJust "tcTagToEnum" $
1160 tyConFamilyCoercion_maybe rep_tc }
1162 tagToEnumError :: TcType -> SDoc -> SDoc
1163 tagToEnumError ty what
1164 = hang (ptext (sLit "Bad call to tagToEnum#")
1165 <+> ptext (sLit "at type") <+> ppr ty)
1170 %************************************************************************
1172 Template Haskell checks
1174 %************************************************************************
1177 checkThLocalId :: Id -> ThLevel -> TcM ()
1178 #ifndef GHCI /* GHCI and TH is off */
1179 --------------------------------------
1180 -- Check for cross-stage lifting
1181 checkThLocalId _id _bind_lvl
1184 #else /* GHCI and TH is on */
1185 checkThLocalId id bind_lvl
1186 = do { use_stage <- getStage -- TH case
1187 ; let use_lvl = thLevel use_stage
1188 ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
1189 ; traceTc "thLocalId" (ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
1190 ; when (use_lvl > bind_lvl) $
1191 checkCrossStageLifting id bind_lvl use_stage }
1193 --------------------------------------
1194 checkCrossStageLifting :: Id -> ThLevel -> ThStage -> TcM ()
1195 -- We are inside brackets, and (use_lvl > bind_lvl)
1196 -- Now we must check whether there's a cross-stage lift to do
1197 -- Examples \x -> [| x |]
1200 checkCrossStageLifting _ _ Comp = return ()
1201 checkCrossStageLifting _ _ Splice = return ()
1203 checkCrossStageLifting id _ (Brack _ ps_var lie_var)
1205 = -- Top-level identifiers in this module,
1206 -- (which have External Names)
1207 -- are just like the imported case:
1208 -- no need for the 'lifting' treatment
1209 -- E.g. this is fine:
1212 -- But we do need to put f into the keep-alive
1213 -- set, because after desugaring the code will
1214 -- only mention f's *name*, not f itself.
1217 | otherwise -- bind_lvl = outerLevel presumably,
1218 -- but the Id is not bound at top level
1219 = -- Nested identifiers, such as 'x' in
1220 -- E.g. \x -> [| h x |]
1221 -- We must behave as if the reference to x was
1223 -- We use 'x' itself as the splice proxy, used by
1224 -- the desugarer to stitch it all back together.
1225 -- If 'x' occurs many times we may get many identical
1226 -- bindings of the same splice proxy, but that doesn't
1227 -- matter, although it's a mite untidy.
1228 do { let id_ty = idType id
1229 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1230 -- If x is polymorphic, its occurrence sites might
1231 -- have different instantiations, so we can't use plain
1232 -- 'x' as the splice proxy name. I don't know how to
1233 -- solve this, and it's probably unimportant, so I'm
1234 -- just going to flag an error for now
1236 ; lift <- if isStringTy id_ty then
1237 do { sid <- tcLookupId DsMeta.liftStringName
1238 -- See Note [Lifting strings]
1239 ; return (HsVar sid) }
1241 setConstraintVar lie_var $ do
1242 -- Put the 'lift' constraint into the right LIE
1243 newMethodFromName (OccurrenceOf (idName id))
1244 DsMeta.liftName id_ty
1246 -- Update the pending splices
1247 ; ps <- readMutVar ps_var
1248 ; writeMutVar ps_var ((idName id, nlHsApp (noLoc lift) (nlHsVar id)) : ps)
1254 Note [Lifting strings]
1255 ~~~~~~~~~~~~~~~~~~~~~~
1256 If we see $(... [| s |] ...) where s::String, we don't want to
1257 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1258 So this conditional short-circuits the lifting mechanism to generate
1259 (liftString "xy") in that case. I didn't want to use overlapping instances
1260 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1261 errors in a polymorphic situation.
1263 If this check fails (which isn't impossible) we get another chance; see
1264 Note [Converting strings] in Convert.lhs
1266 Local record selectors
1267 ~~~~~~~~~~~~~~~~~~~~~~
1268 Record selectors for TyCons in this module are ordinary local bindings,
1269 which show up as ATcIds rather than AGlobals. So we need to check for
1270 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1273 %************************************************************************
1275 \subsection{Record bindings}
1277 %************************************************************************
1279 Game plan for record bindings
1280 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1281 1. Find the TyCon for the bindings, from the first field label.
1283 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1285 For each binding field = value
1287 3. Instantiate the field type (from the field label) using the type
1290 4 Type check the value using tcArg, passing the field type as
1291 the expected argument type.
1293 This extends OK when the field types are universally quantified.
1299 -> [TcType] -- Expected type for each field
1300 -> HsRecordBinds Name
1301 -> TcM (HsRecordBinds TcId)
1303 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1304 = do { mb_binds <- mapM do_bind rbinds
1305 ; return (HsRecFields (catMaybes mb_binds) dd) }
1307 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1308 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1309 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1310 = addErrCtxt (fieldCtxt field_lbl) $
1311 do { rhs' <- tcPolyExprNC rhs field_ty
1312 ; let field_id = mkUserLocal (nameOccName field_lbl)
1313 (nameUnique field_lbl)
1315 -- Yuk: the field_id has the *unique* of the selector Id
1316 -- (so we can find it easily)
1317 -- but is a LocalId with the appropriate type of the RHS
1318 -- (so the desugarer knows the type of local binder to make)
1319 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1321 = do { addErrTc (badFieldCon data_con field_lbl)
1324 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1325 checkMissingFields data_con rbinds
1326 | null field_labels -- Not declared as a record;
1327 -- But C{} is still valid if no strict fields
1328 = if any isBanged field_strs then
1329 -- Illegal if any arg is strict
1330 addErrTc (missingStrictFields data_con [])
1334 | otherwise = do -- A record
1335 unless (null missing_s_fields)
1336 (addErrTc (missingStrictFields data_con missing_s_fields))
1338 warn <- doptM Opt_WarnMissingFields
1339 unless (not (warn && notNull missing_ns_fields))
1340 (warnTc True (missingFields data_con missing_ns_fields))
1344 = [ fl | (fl, str) <- field_info,
1346 not (fl `elem` field_names_used)
1349 = [ fl | (fl, str) <- field_info,
1351 not (fl `elem` field_names_used)
1354 field_names_used = hsRecFields rbinds
1355 field_labels = dataConFieldLabels data_con
1357 field_info = zipEqual "missingFields"
1361 field_strs = dataConStrictMarks data_con
1364 %************************************************************************
1366 \subsection{Errors and contexts}
1368 %************************************************************************
1370 Boring and alphabetical:
1372 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
1373 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
1375 exprCtxt :: LHsExpr Name -> SDoc
1377 = hang (ptext (sLit "In the expression:")) 2 (ppr expr)
1379 fieldCtxt :: Name -> SDoc
1380 fieldCtxt field_name
1381 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1383 funAppCtxt :: LHsExpr Name -> LHsExpr Name -> Int -> SDoc
1384 funAppCtxt fun arg arg_no
1385 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1386 quotes (ppr fun) <> text ", namely"])
1387 2 (quotes (ppr arg))
1389 funResCtxt :: LHsExpr Name -> SDoc
1391 = ptext (sLit "In the return type of a call of") <+> quotes (ppr fun)
1393 badFieldTypes :: [(Name,TcType)] -> SDoc
1395 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1396 <> plural prs <> colon)
1397 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1399 badFieldsUpd :: HsRecFields Name a -> SDoc
1401 = hang (ptext (sLit "No constructor has all these fields:"))
1402 2 (pprQuotedList (hsRecFields rbinds))
1404 naughtyRecordSel :: TcId -> SDoc
1405 naughtyRecordSel sel_id
1406 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1407 ptext (sLit "as a function due to escaped type variables") $$
1408 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1410 notSelector :: Name -> SDoc
1412 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1414 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1415 missingStrictFields con fields
1418 rest | null fields = empty -- Happens for non-record constructors
1419 -- with strict fields
1420 | otherwise = colon <+> pprWithCommas ppr fields
1422 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1423 ptext (sLit "does not have the required strict field(s)")
1425 missingFields :: DataCon -> [FieldLabel] -> SDoc
1426 missingFields con fields
1427 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1428 <+> pprWithCommas ppr fields
1430 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1433 polySpliceErr :: Id -> SDoc
1435 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)