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
50 import TysPrim( intPrimTy )
51 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 %************************************************************************
141 updHetMetLevel :: ([TyVar] -> [TyVar]) -> TcM a -> TcM a
142 updHetMetLevel f comp =
144 (\oldenv -> let oldlev = (case oldenv of Env { env_lcl = e' } -> case e' of TcLclEnv { tcl_hetMetLevel = x } -> x)
145 in (oldenv { env_lcl = (env_lcl oldenv) { tcl_hetMetLevel = f oldlev } }))
149 addEscapes :: [TyVar] -> HsExpr Name -> HsExpr Name
151 addEscapes (t:ts) e = HsHetMetEsc (TyVarTy t) placeHolderType (noLoc (addEscapes ts e))
153 getIdLevel :: Name -> TcM [TyVar]
155 = do { thing <- tcLookup name
157 ATcId { tct_hetMetLevel = variable_hetMetLevel } -> return $ variable_hetMetLevel
161 tcExpr :: HsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
162 tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
163 = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
165 tcExpr (HsVar name) res_ty = tcCheckId name res_ty
167 tcExpr (HsHetMetBrak _ e) res_ty =
168 do { (coi, [inferred_name,elt_ty]) <- matchExpectedTyConApp hetMetCodeTypeTyCon res_ty
169 ; fresh_ec_name <- newFlexiTyVar liftedTypeKind
170 ; expr' <- updHetMetLevel (\old_lev -> (fresh_ec_name:old_lev))
171 $ tcPolyExpr e elt_ty
172 ; unifyType (TyVarTy fresh_ec_name) inferred_name
173 ; return $ mkHsWrapCoI coi (HsHetMetBrak (TyVarTy fresh_ec_name) expr') }
174 tcExpr (HsHetMetEsc _ _ e) res_ty =
175 do { cur_level <- getHetMetLevel
176 ; expr' <- updHetMetLevel (\old_lev -> tail old_lev)
177 $ tcExpr (unLoc e) (mkTyConApp hetMetCodeTypeTyCon [(TyVarTy $ head cur_level),res_ty])
178 ; ty' <- zonkTcType res_ty
179 ; return $ mkHsWrapCoI (ACo res_ty) (HsHetMetEsc (TyVarTy $ head cur_level) ty' (noLoc expr')) }
180 tcExpr (HsHetMetCSP _ e) res_ty =
181 do { cur_level <- getHetMetLevel
182 ; expr' <- updHetMetLevel (\old_lev -> tail old_lev)
183 $ tcExpr (unLoc e) res_ty
184 ; return $ mkHsWrapCoI (ACo res_ty) (HsHetMetCSP (TyVarTy $ head cur_level) (noLoc expr')) }
186 tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty
188 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
189 ; tcWrapResult (HsLit lit) lit_ty res_ty }
191 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
192 ; return (HsPar expr') }
194 tcExpr (HsSCC lbl expr) res_ty
195 = do { expr' <- tcMonoExpr expr res_ty
196 ; return (HsSCC lbl expr') }
198 tcExpr (HsTickPragma info expr) res_ty
199 = do { expr' <- tcMonoExpr expr res_ty
200 ; return (HsTickPragma info expr') }
202 tcExpr (HsCoreAnn lbl expr) res_ty
203 = do { expr' <- tcMonoExpr expr res_ty
204 ; return (HsCoreAnn lbl expr') }
206 tcExpr (HsOverLit lit) res_ty
207 = do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty
208 ; return (HsOverLit lit') }
210 tcExpr (NegApp expr neg_expr) res_ty
211 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
212 (mkFunTy res_ty res_ty)
213 ; expr' <- tcMonoExpr expr res_ty
214 ; return (NegApp expr' neg_expr') }
216 tcExpr (HsIPVar ip) res_ty
217 = do { let origin = IPOccOrigin ip
218 -- Implicit parameters must have a *tau-type* not a
219 -- type scheme. We enforce this by creating a fresh
220 -- type variable as its type. (Because res_ty may not
222 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
223 ; ip_var <- emitWanted origin (mkIPPred ip ip_ty)
224 ; tcWrapResult (HsIPVar (IPName ip_var)) ip_ty res_ty }
226 tcExpr (HsLam match) res_ty
227 = do { (co_fn, match') <- tcMatchLambda match res_ty
228 ; return (mkHsWrap co_fn (HsLam match')) }
230 tcExpr (ExprWithTySig expr sig_ty) res_ty
231 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
233 -- Remember to extend the lexical type-variable environment
235 <- tcGen ExprSigCtxt sig_tc_ty $ \ skol_tvs res_ty ->
236 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
237 -- See Note [More instantiated than scoped] in TcBinds
238 tcMonoExprNC expr res_ty
240 ; let inner_expr = ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty
242 ; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin sig_tc_ty
243 ; tcWrapResult (mkHsWrap inst_wrap inner_expr) rho res_ty }
246 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
247 -- This is the syntax for type applications that I was planning
248 -- but there are difficulties (e.g. what order for type args)
249 -- so it's not enabled yet.
250 -- Can't eliminate it altogether from the parser, because the
251 -- same parser parses *patterns*.
255 %************************************************************************
257 Infix operators and sections
259 %************************************************************************
263 Left sections, like (4 *), are equivalent to
265 or, if PostfixOperators is enabled, just
267 With PostfixOperators we don't actually require the function to take
268 two arguments at all. For example, (x `not`) means (not x); you get
269 postfix operators! Not Haskell 98, but it's less work and kind of
272 Note [Typing rule for ($)]
273 ~~~~~~~~~~~~~~~~~~~~~~~~~~
277 runST :: (forall s. ST s a) -> a
278 that I have finally given in and written a special type-checking
279 rule just for saturated appliations of ($).
280 * Infer the type of the first argument
281 * Decompose it; should be of form (arg2_ty -> res_ty),
282 where arg2_ty might be a polytype
283 * Use arg2_ty to typecheck arg2
285 Note [Typing rule for seq]
286 ~~~~~~~~~~~~~~~~~~~~~~~~~~
289 which suggests this type for seq:
290 seq :: forall (a:*) (b:??). a -> b -> b,
291 with (b:??) meaning that be can be instantiated with an unboxed tuple.
292 But that's ill-kinded! Function arguments can't be unboxed tuples.
293 And indeed, you could not expect to do this with a partially-applied
294 'seq'; it's only going to work when it's fully applied. so it turns
296 case x of _ -> (# p,q #)
298 For a while I slid by by giving 'seq' an ill-kinded type, but then
299 the simplifier eta-reduced an application of seq and Lint blew up
300 with a kind error. It seems more uniform to treat 'seq' as it it
301 was a language construct.
303 See Note [seqId magic] in MkId, and
307 tcExpr (OpApp arg1 op fix arg2) res_ty
308 | (L loc (HsVar op_name)) <- op
309 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
310 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
311 ; let arg2_ty = res_ty
312 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
313 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
314 ; op_id <- tcLookupId op_name
315 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar op_id))
316 ; return $ OpApp arg1' op' fix arg2' }
318 | (L loc (HsVar op_name)) <- op
319 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
320 = do { traceTc "Application rule" (ppr op)
321 ; (arg1', arg1_ty) <- tcInferRho arg1
322 ; let doc = ptext (sLit "The first argument of ($) takes")
323 ; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty
324 -- arg2_ty maybe polymorphic; that's the point
325 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
326 ; co_res <- unifyType op_res_ty res_ty
327 ; op_id <- tcLookupId op_name
328 ; let op' = L loc (HsWrap (mkWpTyApps [arg2_ty, op_res_ty]) (HsVar op_id))
329 ; return $ mkHsWrapCoI co_res $
330 OpApp (mkLHsWrapCoI co_arg1 arg1') op' fix arg2' }
333 = do { traceTc "Non Application rule" (ppr op)
334 ; (op', op_ty) <- tcInferFun op
335 ; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTys op 2 op_ty
336 ; co_res <- unifyType op_res_ty res_ty
337 ; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys
338 ; return $ mkHsWrapCoI co_res $
339 OpApp arg1' (mkLHsWrapCoI co_fn op') fix arg2' }
341 -- Right sections, equivalent to \ x -> x `op` expr, or
344 tcExpr (SectionR op arg2) res_ty
345 = do { (op', op_ty) <- tcInferFun op
346 ; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTys op 2 op_ty
347 ; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty
348 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
349 ; return $ mkHsWrapCoI co_res $
350 SectionR (mkLHsWrapCoI co_fn op') arg2' }
352 tcExpr (SectionL arg1 op) res_ty
353 = do { (op', op_ty) <- tcInferFun op
354 ; dflags <- getDOpts -- Note [Left sections]
355 ; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1
358 ; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTys op n_reqd_args op_ty
359 ; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty
360 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
361 ; return $ mkHsWrapCoI co_res $
362 SectionL arg1' (mkLHsWrapCoI co_fn op') }
364 tcExpr (ExplicitTuple tup_args boxity) res_ty
365 | all tupArgPresent tup_args
366 = do { let tup_tc = tupleTyCon boxity (length tup_args)
367 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
368 ; tup_args1 <- tcTupArgs tup_args arg_tys
369 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
372 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
373 do { let kind = case boxity of { Boxed -> liftedTypeKind
374 ; Unboxed -> argTypeKind }
375 arity = length tup_args
376 tup_tc = tupleTyCon boxity arity
378 ; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind
380 = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
381 (mkTyConApp tup_tc arg_tys)
383 ; coi <- unifyType actual_res_ty res_ty
385 -- Handle tuple sections where
386 ; tup_args1 <- tcTupArgs tup_args arg_tys
388 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
390 tcExpr (ExplicitList _ exprs) res_ty
391 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
392 ; exprs' <- mapM (tc_elt elt_ty) exprs
393 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
395 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
397 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
398 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
399 ; exprs' <- mapM (tc_elt elt_ty) exprs
400 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
402 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
405 %************************************************************************
409 %************************************************************************
412 tcExpr (HsLet binds expr) res_ty
413 = do { (binds', expr') <- tcLocalBinds binds $
414 tcMonoExpr expr res_ty
415 ; return (HsLet binds' expr') }
417 tcExpr (HsCase scrut matches) exp_ty
418 = do { -- We used to typecheck the case alternatives first.
419 -- The case patterns tend to give good type info to use
420 -- when typechecking the scrutinee. For example
423 -- will report that map is applied to too few arguments
425 -- But now, in the GADT world, we need to typecheck the scrutinee
426 -- first, to get type info that may be refined in the case alternatives
427 (scrut', scrut_ty) <- tcInferRho scrut
429 ; traceTc "HsCase" (ppr scrut_ty)
430 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
431 ; return (HsCase scrut' matches') }
433 match_ctxt = MC { mc_what = CaseAlt,
436 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
437 = do { pred' <- tcMonoExpr pred boolTy
438 ; b1' <- tcMonoExpr b1 res_ty
439 ; b2' <- tcMonoExpr b2 res_ty
440 ; return (HsIf Nothing pred' b1' b2') }
442 tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Note [Rebindable syntax for if]
443 = do { pred_ty <- newFlexiTyVarTy openTypeKind
444 ; b1_ty <- newFlexiTyVarTy openTypeKind
445 ; b2_ty <- newFlexiTyVarTy openTypeKind
446 ; let if_ty = mkFunTys [pred_ty, b1_ty, b2_ty] res_ty
447 ; fun' <- tcSyntaxOp IfOrigin fun if_ty
448 ; pred' <- tcMonoExpr pred pred_ty
449 ; b1' <- tcMonoExpr b1 b1_ty
450 ; b2' <- tcMonoExpr b2 b2_ty
451 -- Fundamentally we are just typing (ifThenElse e1 e2 e3)
452 -- so maybe we should use the code for function applications
453 -- (which would allow ifThenElse to be higher rank).
454 -- But it's a little awkward, so I'm leaving it alone for now
455 -- and it maintains uniformity with other rebindable syntax
456 ; return (HsIf (Just fun') pred' b1' b2') }
458 tcExpr (HsDo do_or_lc stmts body _) res_ty
459 = tcDoStmts do_or_lc stmts body res_ty
461 tcExpr (HsProc pat cmd) res_ty
462 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
463 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
465 tcExpr e@(HsArrApp _ _ _ _ _) _
466 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
467 ptext (sLit "was found where an expression was expected")])
469 tcExpr e@(HsArrForm _ _ _) _
470 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
471 ptext (sLit "was found where an expression was expected")])
474 Note [Rebindable syntax for if]
475 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
476 The rebindable syntax for 'if' uses the most flexible possible type
478 ifThenElse :: p -> b1 -> b2 -> res
479 to support expressions like this:
481 ifThenElse :: Maybe a -> (a -> b) -> b -> b
482 ifThenElse (Just a) f _ = f a ifThenElse Nothing _ e = e
490 %************************************************************************
492 Record construction and update
494 %************************************************************************
497 tcExpr (RecordCon (L loc con_name) _ rbinds) res_ty
498 = do { data_con <- tcLookupDataCon con_name
500 -- Check for missing fields
501 ; checkMissingFields data_con rbinds
503 ; (con_expr, con_tau) <- tcInferId con_name
504 ; let arity = dataConSourceArity data_con
505 (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
506 con_id = dataConWrapId data_con
508 ; co_res <- unifyType actual_res_ty res_ty
509 ; rbinds' <- tcRecordBinds data_con arg_tys rbinds
510 ; return $ mkHsWrapCoI co_res $
511 RecordCon (L loc con_id) con_expr rbinds' }
514 Note [Type of a record update]
515 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
516 The main complication with RecordUpd is that we need to explicitly
517 handle the *non-updated* fields. Consider:
519 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
520 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
523 upd :: T a b c -> (b',c) -> T a b' c
524 upd t x = t { fb = x}
526 The result type should be (T a b' c)
527 not (T a b c), because 'b' *is not* mentioned in a non-updated field
528 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
529 NB that it's not good enough to look at just one constructor; we must
530 look at them all; cf Trac #3219
532 After all, upd should be equivalent to:
538 So we need to give a completely fresh type to the result record,
539 and then constrain it by the fields that are *not* updated ("p" above).
540 We call these the "fixed" type variables, and compute them in getFixedTyVars.
542 Note that because MkT3 doesn't contain all the fields being updated,
543 its RHS is simply an error, so it doesn't impose any type constraints.
544 Hence the use of 'relevant_cont'.
546 Note [Implict type sharing]
547 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
548 We also take into account any "implicit" non-update fields. For example
549 data T a b where { MkT { f::a } :: T a a; ... }
550 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
555 upd :: T a b -> a -> T a b
556 upd (t::T a b) (x::a)
557 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
558 We can't give it the more general type
559 upd :: T a b -> c -> T c b
561 Note [Criteria for update]
562 ~~~~~~~~~~~~~~~~~~~~~~~~~~
563 We want to allow update for existentials etc, provided the updated
564 field isn't part of the existential. For example, this should be ok.
565 data T a where { MkT { f1::a, f2::b->b } :: T a }
569 The criterion we use is this:
571 The types of the updated fields
572 mention only the universally-quantified type variables
573 of the data constructor
575 NB: this is not (quite) the same as being a "naughty" record selector
576 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
577 in the case of GADTs. Consider
578 data T a where { MkT :: { f :: a } :: T [a] }
579 Then f is not "naughty" because it has a well-typed record selector.
580 But we don't allow updates for 'f'. (One could consider trying to
581 allow this, but it makes my head hurt. Badly. And no one has asked
584 In principle one could go further, and allow
586 g t = t { f2 = \x -> x }
587 because the expression is polymorphic...but that seems a bridge too far.
589 Note [Data family example]
590 ~~~~~~~~~~~~~~~~~~~~~~~~~~
591 data instance T (a,b) = MkT { x::a, y::b }
593 data :TP a b = MkT { a::a, y::b }
594 coTP a b :: T (a,b) ~ :TP a b
596 Suppose r :: T (t1,t2), e :: t3
597 Then r { x=e } :: T (t3,t1)
600 MkT x y -> MkT e y |> co2
601 where co1 :: T (t1,t2) ~ :TP t1 t2
602 co2 :: :TP t3 t2 ~ T (t3,t2)
603 The wrapping with co2 is done by the constructor wrapper for MkT
607 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
609 * cons are the data constructors to be updated
611 * in_inst_tys, out_inst_tys have same length, and instantiate the
612 *representation* tycon of the data cons. In Note [Data
613 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
616 tcExpr (RecordUpd record_expr rbinds _ _ _) res_ty
617 = ASSERT( notNull upd_fld_names )
620 -- Check that the field names are really field names
621 ; sel_ids <- mapM tcLookupField upd_fld_names
622 -- The renamer has already checked that
623 -- selectors are all in scope
624 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
625 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
626 not (isRecordSelector sel_id), -- Excludes class ops
627 let L loc fld_name = hsRecFieldId fld ]
628 ; unless (null bad_guys) (sequence bad_guys >> failM)
631 -- Figure out the tycon and data cons from the first field name
632 ; let -- It's OK to use the non-tc splitters here (for a selector)
634 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
635 data_cons = tyConDataCons tycon -- it's not a field label
636 -- NB: for a data type family, the tycon is the instance tycon
638 relevant_cons = filter is_relevant data_cons
639 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
640 -- A constructor is only relevant to this process if
641 -- it contains *all* the fields that are being updated
642 -- Other ones will cause a runtime error if they occur
644 -- Take apart a representative constructor
645 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
646 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
647 con1_flds = dataConFieldLabels con1
648 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
651 -- Check that at least one constructor has all the named fields
652 -- i.e. has an empty set of bad fields returned by badFields
653 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
655 -- STEP 3 Note [Criteria for update]
656 -- Check that each updated field is polymorphic; that is, its type
657 -- mentions only the universally-quantified variables of the data con
658 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
659 upd_flds1_w_tys = filter is_updated flds1_w_tys
660 is_updated (fld,_) = fld `elem` upd_fld_names
662 bad_upd_flds = filter bad_fld upd_flds1_w_tys
663 con1_tv_set = mkVarSet con1_tvs
664 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
665 not (tyVarsOfType ty `subVarSet` con1_tv_set)
666 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
668 -- STEP 4 Note [Type of a record update]
669 -- Figure out types for the scrutinee and result
670 -- Both are of form (T a b c), with fresh type variables, but with
671 -- common variables where the scrutinee and result must have the same type
672 -- These are variables that appear in *any* arg of *any* of the
673 -- relevant constructors *except* in the updated fields
675 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
676 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
677 mk_inst_ty tv result_inst_ty
678 | is_fixed_tv tv = return result_inst_ty -- Same as result type
679 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
681 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
682 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
684 ; let rec_res_ty = substTy result_inst_env con1_res_ty
685 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
686 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
687 scrut_ty = substTy scrut_subst con1_res_ty
689 ; co_res <- unifyType rec_res_ty res_ty
692 -- Typecheck the thing to be updated, and the bindings
693 ; record_expr' <- tcMonoExpr record_expr scrut_ty
694 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
696 -- STEP 6: Deal with the stupid theta
697 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
698 ; instStupidTheta RecordUpdOrigin theta'
700 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
701 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
702 = WpCast $ mkTyConApp co_con scrut_inst_tys
706 ; return $ mkHsWrapCoI co_res $
707 RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
708 relevant_cons scrut_inst_tys result_inst_tys }
710 upd_fld_names = hsRecFields rbinds
712 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
713 -- These tyvars must not change across the updates
714 getFixedTyVars tvs1 cons
715 = mkVarSet [tv1 | con <- cons
716 , let (tvs, theta, arg_tys, _) = dataConSig con
717 flds = dataConFieldLabels con
718 fixed_tvs = exactTyVarsOfTypes fixed_tys
719 -- fixed_tys: See Note [Type of a record update]
720 `unionVarSet` tyVarsOfTheta theta
721 -- Universally-quantified tyvars that
722 -- appear in any of the *implicit*
723 -- arguments to the constructor are fixed
724 -- See Note [Implict type sharing]
726 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
727 , not (fld `elem` upd_fld_names)]
728 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
729 , tv `elemVarSet` fixed_tvs ]
732 %************************************************************************
734 Arithmetic sequences e.g. [a,b..]
735 and their parallel-array counterparts e.g. [: a,b.. :]
738 %************************************************************************
741 tcExpr (ArithSeq _ seq@(From expr)) res_ty
742 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
743 ; expr' <- tcPolyExpr expr elt_ty
744 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
746 ; return $ mkHsWrapCoI coi (ArithSeq enum_from (From expr')) }
748 tcExpr (ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
749 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
750 ; expr1' <- tcPolyExpr expr1 elt_ty
751 ; expr2' <- tcPolyExpr expr2 elt_ty
752 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
753 enumFromThenName elt_ty
754 ; return $ mkHsWrapCoI coi
755 (ArithSeq enum_from_then (FromThen expr1' expr2')) }
757 tcExpr (ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
758 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
759 ; expr1' <- tcPolyExpr expr1 elt_ty
760 ; expr2' <- tcPolyExpr expr2 elt_ty
761 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
762 enumFromToName elt_ty
763 ; return $ mkHsWrapCoI coi
764 (ArithSeq enum_from_to (FromTo expr1' expr2')) }
766 tcExpr (ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
767 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
768 ; expr1' <- tcPolyExpr expr1 elt_ty
769 ; expr2' <- tcPolyExpr expr2 elt_ty
770 ; expr3' <- tcPolyExpr expr3 elt_ty
771 ; eft <- newMethodFromName (ArithSeqOrigin seq)
772 enumFromThenToName elt_ty
773 ; return $ mkHsWrapCoI coi
774 (ArithSeq eft (FromThenTo expr1' expr2' expr3')) }
776 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
777 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
778 ; expr1' <- tcPolyExpr expr1 elt_ty
779 ; expr2' <- tcPolyExpr expr2 elt_ty
780 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
781 enumFromToPName elt_ty
782 ; return $ mkHsWrapCoI coi
783 (PArrSeq enum_from_to (FromTo expr1' expr2')) }
785 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
786 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
787 ; expr1' <- tcPolyExpr expr1 elt_ty
788 ; expr2' <- tcPolyExpr expr2 elt_ty
789 ; expr3' <- tcPolyExpr expr3 elt_ty
790 ; eft <- newMethodFromName (PArrSeqOrigin seq)
791 enumFromThenToPName elt_ty
792 ; return $ mkHsWrapCoI coi
793 (PArrSeq eft (FromThenTo expr1' expr2' expr3')) }
795 tcExpr (PArrSeq _ _) _
796 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
797 -- the parser shouldn't have generated it and the renamer shouldn't have
802 %************************************************************************
806 %************************************************************************
809 #ifdef GHCI /* Only if bootstrapped */
810 -- Rename excludes these cases otherwise
811 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
812 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
814 tcExpr e@(HsQuasiQuoteE _) _ =
815 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
820 %************************************************************************
824 %************************************************************************
827 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
831 %************************************************************************
835 %************************************************************************
838 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
839 -> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args
841 tcApp (L _ (HsPar e)) args res_ty
842 = tcApp e args res_ty
844 tcApp (L _ (HsApp e1 e2)) args res_ty
845 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
847 tcApp (L loc (HsVar fun)) args res_ty
848 | fun `hasKey` tagToEnumKey
850 = tcTagToEnum loc fun arg res_ty
852 tcApp fun args res_ty
853 = do { -- Type-check the function
854 ; (fun1, fun_tau) <- tcInferFun fun
856 -- Extract its argument types
857 ; (co_fun, expected_arg_tys, actual_res_ty)
858 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
860 -- Typecheck the result, thereby propagating
861 -- info (if any) from result into the argument types
862 -- Both actual_res_ty and res_ty are deeply skolemised
863 ; co_res <- addErrCtxt (funResCtxt fun) $
864 unifyType actual_res_ty res_ty
866 -- Typecheck the arguments
867 ; args1 <- tcArgs fun args expected_arg_tys
869 -- Assemble the result
870 ; let fun2 = mkLHsWrapCoI co_fun fun1
871 app = mkLHsWrapCoI co_res (foldl mkHsApp fun2 args1)
873 ; return (unLoc app) }
876 mk_app_msg :: LHsExpr Name -> SDoc
877 mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun)
878 , ptext (sLit "is applied to")]
881 tcInferApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
882 -> TcM (HsExpr TcId, TcRhoType) -- Translated fun and args
884 tcInferApp (L _ (HsPar e)) args = tcInferApp e args
885 tcInferApp (L _ (HsApp e1 e2)) args = tcInferApp e1 (e2:args)
887 = -- Very like the tcApp version, except that there is
888 -- no expected result type passed in
889 do { (fun1, fun_tau) <- tcInferFun fun
890 ; (co_fun, expected_arg_tys, actual_res_ty)
891 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
892 ; args1 <- tcArgs fun args expected_arg_tys
893 ; let fun2 = mkLHsWrapCoI co_fun fun1
894 app = foldl mkHsApp fun2 args1
895 ; return (unLoc app, actual_res_ty) }
898 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
899 -- Infer and instantiate the type of a function
900 tcInferFun (L loc (HsVar name))
901 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
902 -- Don't wrap a context around a plain Id
903 ; return (L loc fun, ty) }
906 = do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun)
908 -- Zonk the function type carefully, to expose any polymorphism
909 -- E.g. (( \(x::forall a. a->a). blah ) e)
910 -- We can see the rank-2 type of the lambda in time to genrealise e
911 ; fun_ty' <- zonkTcTypeCarefully fun_ty
913 ; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty'
914 ; return (mkLHsWrap wrap fun, rho) }
917 tcArgs :: LHsExpr Name -- The function (for error messages)
918 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
919 -> TcM [LHsExpr TcId] -- Resulting args
921 tcArgs fun args expected_arg_tys
922 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
925 tcArg :: LHsExpr Name -- The function (for error messages)
926 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
927 -> TcM (LHsExpr TcId) -- Resulting argument
928 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
929 (tcPolyExprNC arg ty)
932 tcTupArgs :: [HsTupArg Name] -> [TcSigmaType] -> TcM [HsTupArg TcId]
934 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
936 go (Missing {}, arg_ty) = return (Missing arg_ty)
937 go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
938 ; return (Present expr') }
941 unifyOpFunTys :: LHsExpr Name -> Arity -> TcRhoType
942 -> TcM (CoercionI, [TcSigmaType], TcRhoType)
943 -- A wrapper for matchExpectedFunTys
944 unifyOpFunTys op arity ty = matchExpectedFunTys herald arity ty
946 herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes")
948 ---------------------------
949 tcSyntaxOp :: CtOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
950 -- Typecheck a syntax operator, checking that it has the specified type
951 -- The operator is always a variable at this stage (i.e. renamer output)
952 -- This version assumes res_ty is a monotype
953 tcSyntaxOp orig (HsVar op) res_ty = do { (expr, rho) <- tcInferIdWithOrig orig op
954 ; tcWrapResult expr rho res_ty }
955 tcSyntaxOp _ other _ = pprPanic "tcSyntaxOp" (ppr other)
959 Note [Push result type in]
960 ~~~~~~~~~~~~~~~~~~~~~~~~~~
961 Unify with expected result before type-checking the args so that the
962 info from res_ty percolates to args. This is when we might detect a
963 too-few args situation. (One can think of cases when the opposite
964 order would give a better error message.)
965 experimenting with putting this first.
967 Here's an example where it actually makes a real difference
969 class C t a b | t a -> b
970 instance C Char a Bool
972 data P t a = forall b. (C t a b) => MkP b
973 data Q t = MkQ (forall a. P t a)
977 f2 = MkQ (MkP True :: forall a. P Char a)
979 With the change, f1 will type-check, because the 'Char' info from
980 the signature is propagated into MkQ's argument. With the check
981 in the other order, the extra signature in f2 is reqd.
984 %************************************************************************
988 %************************************************************************
991 tcCheckId :: Name -> TcRhoType -> TcM (HsExpr TcId)
992 tcCheckId name res_ty = do { (expr, rho) <- tcInferId name
993 ; tcWrapResult expr rho res_ty }
995 ------------------------
996 tcInferId :: Name -> TcM (HsExpr TcId, TcRhoType)
997 -- Infer type, and deeply instantiate
998 tcInferId n = tcInferIdWithOrig (OccurrenceOf n) n
1000 ------------------------
1001 tcInferIdWithOrig :: CtOrigin -> Name -> TcM (HsExpr TcId, TcRhoType)
1002 -- Look up an occurrence of an Id, and instantiate it (deeply)
1004 tcInferIdWithOrig orig id_name =
1005 do { id_level <- getIdLevel id_name
1006 ; cur_level <- getHetMetLevel
1007 ; if (length id_level < length cur_level)
1008 then do { (lhexp, tcrho) <-
1009 tcInferRho (noLoc $ addEscapes (take ((length cur_level) - (length id_level)) cur_level) (HsVar id_name))
1010 ; return (unLoc lhexp, tcrho)
1012 else tcInferIdWithOrig' orig id_name
1015 tcInferIdWithOrig' orig id_name =
1016 do { id <- lookup_id
1017 ; (id_expr, id_rho) <- instantiateOuter orig id
1018 ; (wrap, rho) <- deeplyInstantiate orig id_rho
1019 ; return (mkHsWrap wrap id_expr, rho) }
1021 lookup_id :: TcM TcId
1023 = do { thing <- tcLookup id_name
1025 ATcId { tct_id = id, tct_level = lvl, tct_hetMetLevel = variable_hetMetLevel }
1026 -> do { check_naughty id -- Note [Local record selectors]
1027 ; checkThLocalId id lvl
1028 ; current_hetMetLevel <- getHetMetLevel
1030 (\(name1,name2) -> unifyType (TyVarTy name1) (TyVarTy name2))
1031 (zip variable_hetMetLevel current_hetMetLevel)
1035 -> do { check_naughty id
1037 -- A global cannot possibly be ill-staged in Template Haskell
1038 -- nor does it need the 'lifting' treatment
1039 -- hence no checkTh stuff here
1041 AGlobal (ADataCon con) -> return (dataConWrapId con)
1043 other -> failWithTc (bad_lookup other) }
1045 bad_lookup thing = ppr thing <+> ptext (sLit "used where a value identifer was expected")
1048 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel id)
1049 | otherwise = return ()
1051 ------------------------
1052 instantiateOuter :: CtOrigin -> TcId -> TcM (HsExpr TcId, TcSigmaType)
1053 -- Do just the first level of instantiation of an Id
1054 -- a) Deal with method sharing
1055 -- b) Deal with stupid checks
1056 -- Only look at the *outer level* of quantification
1057 -- See Note [Multiple instantiation]
1059 instantiateOuter orig id
1060 | null tvs && null theta
1061 = return (HsVar id, tau)
1064 = do { (_, tys, subst) <- tcInstTyVars tvs
1065 ; doStupidChecks id tys
1066 ; let theta' = substTheta subst theta
1067 ; traceTc "Instantiating" (ppr id <+> text "with" <+> (ppr tys $$ ppr theta'))
1068 ; wrap <- instCall orig tys theta'
1069 ; return (mkHsWrap wrap (HsVar id), substTy subst tau) }
1071 (tvs, theta, tau) = tcSplitSigmaTy (idType id)
1074 Note [Multiple instantiation]
1075 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1076 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
1077 For example, consider
1078 f :: forall a. Eq a => forall b. Ord b => a -> b
1079 At a call to f, at say [Int, Bool], it's tempting to translate the call to
1083 f_m1 :: forall b. Ord b => Int -> b
1087 f_m2 = f_m1 Bool dOrdBool
1089 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
1090 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
1092 But it's entirely possible that f_m2 will continue to float out, because it
1093 mentions no type variables. Result, f_m1 isn't in scope.
1095 Here's a concrete example that does this (test tc200):
1098 f :: Eq b => b -> a -> Int
1099 baz :: Eq a => Int -> a -> Int
1101 instance C Int where
1104 Current solution: only do the "method sharing" thing for the first type/dict
1105 application, not for the iterated ones. A horribly subtle point.
1107 Note [No method sharing]
1108 ~~~~~~~~~~~~~~~~~~~~~~~~
1109 The -fno-method-sharing flag controls what happens so far as the LIE
1110 is concerned. The default case is that for an overloaded function we
1111 generate a "method" Id, and add the Method Inst to the LIE. So you get
1113 f :: Num a => a -> a
1114 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
1115 If you specify -fno-method-sharing, the dictionary application
1116 isn't shared, so we get
1117 f :: Num a => a -> a
1118 f = /\a (d:Num a) (x:a) -> (+) a d x x
1119 This gets a bit less sharing, but
1120 a) it's better for RULEs involving overloaded functions
1121 b) perhaps fewer separated lambdas
1124 doStupidChecks :: TcId
1127 -- Check two tiresome and ad-hoc cases
1128 -- (a) the "stupid theta" for a data con; add the constraints
1129 -- from the "stupid theta" of a data constructor (sigh)
1131 doStupidChecks fun_id tys
1132 | Just con <- isDataConId_maybe fun_id -- (a)
1133 = addDataConStupidTheta con tys
1135 | fun_id `hasKey` tagToEnumKey -- (b)
1136 = failWithTc (ptext (sLit "tagToEnum# must appear applied to one argument"))
1139 = return () -- The common case
1144 Nasty check to ensure that tagToEnum# is applied to a type that is an
1145 enumeration TyCon. Unification may refine the type later, but this
1146 check won't see that, alas. It's crude, because it relies on our
1147 knowing *now* that the type is ok, which in turn relies on the
1148 eager-unification part of the type checker pushing enough information
1149 here. In theory the Right Thing to do is to have a new form of
1150 constraint but I definitely cannot face that! And it works ok as-is.
1152 Here's are two cases that should fail
1154 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1157 g = tagToEnum# 0 -- Int is not an enumeration
1159 When data type families are involved it's a bit more complicated.
1161 data instance F [Int] = A | B | C
1162 Then we want to generate something like
1163 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1164 Usually that coercion is hidden inside the wrappers for
1165 constructors of F [Int] but here we have to do it explicitly.
1167 It's all grotesquely complicated.
1170 tcTagToEnum :: SrcSpan -> Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
1171 -- tagToEnum# :: forall a. Int# -> a
1172 -- See Note [tagToEnum#] Urgh!
1173 tcTagToEnum loc fun_name arg res_ty
1174 = do { fun <- tcLookupId fun_name
1175 ; ty' <- zonkTcType res_ty
1177 -- Check that the type is algebraic
1178 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1179 Just (tc, tc_args) = mb_tc_app
1180 ; checkTc (isJust mb_tc_app)
1181 (tagToEnumError ty' doc1)
1183 -- Look through any type family
1184 ; (coi, rep_tc, rep_args) <- get_rep_ty ty' tc tc_args
1186 ; checkTc (isEnumerationTyCon rep_tc)
1187 (tagToEnumError ty' doc2)
1189 ; arg' <- tcMonoExpr arg intPrimTy
1190 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar fun))
1191 rep_ty = mkTyConApp rep_tc rep_args
1193 ; return (mkHsWrapCoI coi $ HsApp fun' arg') }
1195 doc1 = vcat [ ptext (sLit "Specify the type by giving a type signature")
1196 , ptext (sLit "e.g. (tagToEnum# x) :: Bool") ]
1197 doc2 = ptext (sLit "Result type must be an enumeration type")
1198 doc3 = ptext (sLit "No family instance for this type")
1200 get_rep_ty :: TcType -> TyCon -> [TcType]
1201 -> TcM (CoercionI, TyCon, [TcType])
1202 -- Converts a family type (eg F [a]) to its rep type (eg FList a)
1203 -- and returns a coercion between the two
1204 get_rep_ty ty tc tc_args
1205 | not (isFamilyTyCon tc)
1206 = return (IdCo ty, tc, tc_args)
1208 = do { mb_fam <- tcLookupFamInst tc tc_args
1210 Nothing -> failWithTc (tagToEnumError ty doc3)
1211 Just (rep_tc, rep_args)
1212 -> return ( ACo (mkSymCoercion (mkTyConApp co_tc rep_args))
1213 , rep_tc, rep_args )
1215 co_tc = expectJust "tcTagToEnum" $
1216 tyConFamilyCoercion_maybe rep_tc }
1218 tagToEnumError :: TcType -> SDoc -> SDoc
1219 tagToEnumError ty what
1220 = hang (ptext (sLit "Bad call to tagToEnum#")
1221 <+> ptext (sLit "at type") <+> ppr ty)
1226 %************************************************************************
1228 Template Haskell checks
1230 %************************************************************************
1233 checkThLocalId :: Id -> ThLevel -> TcM ()
1234 #ifndef GHCI /* GHCI and TH is off */
1235 --------------------------------------
1236 -- Check for cross-stage lifting
1237 checkThLocalId _id _bind_lvl
1240 #else /* GHCI and TH is on */
1241 checkThLocalId id bind_lvl
1242 = do { use_stage <- getStage -- TH case
1243 ; let use_lvl = thLevel use_stage
1244 ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
1245 ; traceTc "thLocalId" (ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
1246 ; when (use_lvl > bind_lvl) $
1247 checkCrossStageLifting id bind_lvl use_stage }
1249 --------------------------------------
1250 checkCrossStageLifting :: Id -> ThLevel -> ThStage -> TcM ()
1251 -- We are inside brackets, and (use_lvl > bind_lvl)
1252 -- Now we must check whether there's a cross-stage lift to do
1253 -- Examples \x -> [| x |]
1256 checkCrossStageLifting _ _ Comp = return ()
1257 checkCrossStageLifting _ _ Splice = return ()
1259 checkCrossStageLifting id _ (Brack _ ps_var lie_var)
1261 = -- Top-level identifiers in this module,
1262 -- (which have External Names)
1263 -- are just like the imported case:
1264 -- no need for the 'lifting' treatment
1265 -- E.g. this is fine:
1268 -- But we do need to put f into the keep-alive
1269 -- set, because after desugaring the code will
1270 -- only mention f's *name*, not f itself.
1273 | otherwise -- bind_lvl = outerLevel presumably,
1274 -- but the Id is not bound at top level
1275 = -- Nested identifiers, such as 'x' in
1276 -- E.g. \x -> [| h x |]
1277 -- We must behave as if the reference to x was
1279 -- We use 'x' itself as the splice proxy, used by
1280 -- the desugarer to stitch it all back together.
1281 -- If 'x' occurs many times we may get many identical
1282 -- bindings of the same splice proxy, but that doesn't
1283 -- matter, although it's a mite untidy.
1284 do { let id_ty = idType id
1285 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1286 -- If x is polymorphic, its occurrence sites might
1287 -- have different instantiations, so we can't use plain
1288 -- 'x' as the splice proxy name. I don't know how to
1289 -- solve this, and it's probably unimportant, so I'm
1290 -- just going to flag an error for now
1292 ; lift <- if isStringTy id_ty then
1293 do { sid <- tcLookupId DsMeta.liftStringName
1294 -- See Note [Lifting strings]
1295 ; return (HsVar sid) }
1297 setConstraintVar lie_var $ do
1298 -- Put the 'lift' constraint into the right LIE
1299 newMethodFromName (OccurrenceOf (idName id))
1300 DsMeta.liftName id_ty
1302 -- Update the pending splices
1303 ; ps <- readMutVar ps_var
1304 ; writeMutVar ps_var ((idName id, nlHsApp (noLoc lift) (nlHsVar id)) : ps)
1310 Note [Lifting strings]
1311 ~~~~~~~~~~~~~~~~~~~~~~
1312 If we see $(... [| s |] ...) where s::String, we don't want to
1313 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1314 So this conditional short-circuits the lifting mechanism to generate
1315 (liftString "xy") in that case. I didn't want to use overlapping instances
1316 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1317 errors in a polymorphic situation.
1319 If this check fails (which isn't impossible) we get another chance; see
1320 Note [Converting strings] in Convert.lhs
1322 Local record selectors
1323 ~~~~~~~~~~~~~~~~~~~~~~
1324 Record selectors for TyCons in this module are ordinary local bindings,
1325 which show up as ATcIds rather than AGlobals. So we need to check for
1326 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1329 %************************************************************************
1331 \subsection{Record bindings}
1333 %************************************************************************
1335 Game plan for record bindings
1336 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1337 1. Find the TyCon for the bindings, from the first field label.
1339 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1341 For each binding field = value
1343 3. Instantiate the field type (from the field label) using the type
1346 4 Type check the value using tcArg, passing the field type as
1347 the expected argument type.
1349 This extends OK when the field types are universally quantified.
1355 -> [TcType] -- Expected type for each field
1356 -> HsRecordBinds Name
1357 -> TcM (HsRecordBinds TcId)
1359 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1360 = do { mb_binds <- mapM do_bind rbinds
1361 ; return (HsRecFields (catMaybes mb_binds) dd) }
1363 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1364 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1365 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1366 = addErrCtxt (fieldCtxt field_lbl) $
1367 do { rhs' <- tcPolyExprNC rhs field_ty
1368 ; let field_id = mkUserLocal (nameOccName field_lbl)
1369 (nameUnique field_lbl)
1371 -- Yuk: the field_id has the *unique* of the selector Id
1372 -- (so we can find it easily)
1373 -- but is a LocalId with the appropriate type of the RHS
1374 -- (so the desugarer knows the type of local binder to make)
1375 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1377 = do { addErrTc (badFieldCon data_con field_lbl)
1380 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1381 checkMissingFields data_con rbinds
1382 | null field_labels -- Not declared as a record;
1383 -- But C{} is still valid if no strict fields
1384 = if any isBanged field_strs then
1385 -- Illegal if any arg is strict
1386 addErrTc (missingStrictFields data_con [])
1390 | otherwise = do -- A record
1391 unless (null missing_s_fields)
1392 (addErrTc (missingStrictFields data_con missing_s_fields))
1394 warn <- doptM Opt_WarnMissingFields
1395 unless (not (warn && notNull missing_ns_fields))
1396 (warnTc True (missingFields data_con missing_ns_fields))
1400 = [ fl | (fl, str) <- field_info,
1402 not (fl `elem` field_names_used)
1405 = [ fl | (fl, str) <- field_info,
1407 not (fl `elem` field_names_used)
1410 field_names_used = hsRecFields rbinds
1411 field_labels = dataConFieldLabels data_con
1413 field_info = zipEqual "missingFields"
1417 field_strs = dataConStrictMarks data_con
1420 %************************************************************************
1422 \subsection{Errors and contexts}
1424 %************************************************************************
1426 Boring and alphabetical:
1428 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
1429 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
1431 exprCtxt :: LHsExpr Name -> SDoc
1433 = hang (ptext (sLit "In the expression:")) 2 (ppr expr)
1435 fieldCtxt :: Name -> SDoc
1436 fieldCtxt field_name
1437 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1439 funAppCtxt :: LHsExpr Name -> LHsExpr Name -> Int -> SDoc
1440 funAppCtxt fun arg arg_no
1441 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1442 quotes (ppr fun) <> text ", namely"])
1443 2 (quotes (ppr arg))
1445 funResCtxt :: LHsExpr Name -> SDoc
1447 = ptext (sLit "In the return type of a call of") <+> quotes (ppr fun)
1449 badFieldTypes :: [(Name,TcType)] -> SDoc
1451 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1452 <> plural prs <> colon)
1453 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1455 badFieldsUpd :: HsRecFields Name a -> SDoc
1457 = hang (ptext (sLit "No constructor has all these fields:"))
1458 2 (pprQuotedList (hsRecFields rbinds))
1460 naughtyRecordSel :: TcId -> SDoc
1461 naughtyRecordSel sel_id
1462 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1463 ptext (sLit "as a function due to escaped type variables") $$
1464 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1466 notSelector :: Name -> SDoc
1468 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1470 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1471 missingStrictFields con fields
1474 rest | null fields = empty -- Happens for non-record constructors
1475 -- with strict fields
1476 | otherwise = colon <+> pprWithCommas ppr fields
1478 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1479 ptext (sLit "does not have the required strict field(s)")
1481 missingFields :: DataCon -> [FieldLabel] -> SDoc
1482 missingFields con fields
1483 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1484 <+> pprWithCommas ppr fields
1486 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1489 polySpliceErr :: Id -> SDoc
1491 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)