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 )
62 %************************************************************************
64 \subsection{Main wrappers}
66 %************************************************************************
69 tcPolyExpr, tcPolyExprNC
70 :: LHsExpr Name -- Expression to type check
71 -> TcSigmaType -- Expected type (could be a polytpye)
72 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
74 -- tcPolyExpr is a convenient place (frequent but not too frequent)
75 -- place to add context information.
76 -- The NC version does not do so, usually because the caller wants
79 tcPolyExpr expr res_ty
80 = addExprErrCtxt expr $
81 do { traceTc "tcPolyExpr" (ppr res_ty); tcPolyExprNC expr res_ty }
83 tcPolyExprNC expr res_ty
84 = do { traceTc "tcPolyExprNC" (ppr res_ty)
85 ; (gen_fn, expr') <- tcGen (GenSkol res_ty) res_ty $ \ _ rho ->
87 ; return (mkLHsWrap gen_fn expr') }
90 tcMonoExpr, tcMonoExprNC
91 :: LHsExpr Name -- Expression to type check
92 -> TcRhoType -- Expected type (could be a type variable)
93 -- Definitely no foralls at the top
96 tcMonoExpr expr res_ty
97 = addErrCtxt (exprCtxt expr) $
98 tcMonoExprNC expr res_ty
100 tcMonoExprNC (L loc expr) res_ty
101 = ASSERT( not (isSigmaTy res_ty) )
103 do { expr' <- tcExpr expr res_ty
104 ; return (L loc expr') }
107 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
108 -- Infer a *rho*-type. This is, in effect, a special case
109 -- for ids and partial applications, so that if
110 -- f :: Int -> (forall a. a -> a) -> Int
112 -- f 3 :: (forall a. a -> a) -> Int
113 -- And that in turn is useful
114 -- (a) for the function part of any application (see tcApp)
115 -- (b) for the special rule for '$'
116 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
118 tcInferRhoNC (L loc expr)
120 do { (expr', rho) <- tcInfExpr expr
121 ; return (L loc expr', rho) }
123 tcInfExpr :: HsExpr Name -> TcM (HsExpr TcId, TcRhoType)
124 tcInfExpr (HsVar f) = tcInferId f
125 tcInfExpr (HsPar e) = do { (e', ty) <- tcInferRhoNC e
126 ; return (HsPar e', ty) }
127 tcInfExpr (HsApp e1 e2) = tcInferApp e1 [e2]
128 tcInfExpr e = tcInfer (tcExpr e)
132 %************************************************************************
134 tcExpr: the main expression typechecker
136 %************************************************************************
139 tcExpr :: HsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
140 tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
141 = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
143 tcExpr (HsVar name) res_ty = tcCheckId name res_ty
145 tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty
147 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
148 ; tcWrapResult (HsLit lit) lit_ty res_ty }
150 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
151 ; return (HsPar expr') }
153 tcExpr (HsSCC lbl expr) res_ty
154 = do { expr' <- tcMonoExpr expr res_ty
155 ; return (HsSCC lbl expr') }
157 tcExpr (HsTickPragma info expr) res_ty
158 = do { expr' <- tcMonoExpr expr res_ty
159 ; return (HsTickPragma info expr') }
161 tcExpr (HsCoreAnn lbl expr) res_ty
162 = do { expr' <- tcMonoExpr expr res_ty
163 ; return (HsCoreAnn lbl expr') }
165 tcExpr (HsOverLit lit) res_ty
166 = do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty
167 ; return (HsOverLit lit') }
169 tcExpr (NegApp expr neg_expr) res_ty
170 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
171 (mkFunTy res_ty res_ty)
172 ; expr' <- tcMonoExpr expr res_ty
173 ; return (NegApp expr' neg_expr') }
175 tcExpr (HsIPVar ip) res_ty
176 = do { let origin = IPOccOrigin ip
177 -- Implicit parameters must have a *tau-type* not a
178 -- type scheme. We enforce this by creating a fresh
179 -- type variable as its type. (Because res_ty may not
181 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
182 ; ip_var <- emitWanted origin (mkIPPred ip ip_ty)
183 ; tcWrapResult (HsIPVar (IPName ip_var)) ip_ty res_ty }
185 tcExpr (HsLam match) res_ty
186 = do { (co_fn, match') <- tcMatchLambda match res_ty
187 ; return (mkHsWrap co_fn (HsLam match')) }
189 tcExpr (ExprWithTySig expr sig_ty) res_ty
190 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
192 -- Remember to extend the lexical type-variable environment
194 <- tcGen (SigSkol ExprSigCtxt) sig_tc_ty $ \ skol_tvs res_ty ->
195 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
196 -- See Note [More instantiated than scoped] in TcBinds
197 tcMonoExprNC expr res_ty
199 ; let inner_expr = ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty
201 ; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin sig_tc_ty
202 ; tcWrapResult (mkHsWrap inst_wrap inner_expr) rho res_ty }
205 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
206 -- This is the syntax for type applications that I was planning
207 -- but there are difficulties (e.g. what order for type args)
208 -- so it's not enabled yet.
209 -- Can't eliminate it altogether from the parser, because the
210 -- same parser parses *patterns*.
214 %************************************************************************
216 Infix operators and sections
218 %************************************************************************
222 Left sections, like (4 *), are equivalent to
224 or, if PostfixOperators is enabled, just
226 With PostfixOperators we don't actually require the function to take
227 two arguments at all. For example, (x `not`) means (not x); you get
228 postfix operators! Not Haskell 98, but it's less work and kind of
231 Note [Typing rule for ($)]
232 ~~~~~~~~~~~~~~~~~~~~~~~~~~
236 runST :: (forall s. ST s a) -> a
237 that I have finally given in and written a special type-checking
238 rule just for saturated appliations of ($).
239 * Infer the type of the first argument
240 * Decompose it; should be of form (arg2_ty -> res_ty),
241 where arg2_ty might be a polytype
242 * Use arg2_ty to typecheck arg2
244 Note [Typing rule for seq]
245 ~~~~~~~~~~~~~~~~~~~~~~~~~~
248 which suggests this type for seq:
249 seq :: forall (a:*) (b:??). a -> b -> b,
250 with (b:??) meaning that be can be instantiated with an unboxed tuple.
251 But that's ill-kinded! Function arguments can't be unboxed tuples.
252 And indeed, you could not expect to do this with a partially-applied
253 'seq'; it's only going to work when it's fully applied. so it turns
255 case x of _ -> (# p,q #)
257 For a while I slid by by giving 'seq' an ill-kinded type, but then
258 the simplifier eta-reduced an application of seq and Lint blew up
259 with a kind error. It seems more uniform to treat 'seq' as it it
260 was a language construct.
262 See Note [seqId magic] in MkId, and
266 tcExpr (OpApp arg1 op fix arg2) res_ty
267 | (L loc (HsVar op_name)) <- op
268 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
269 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
270 ; let arg2_ty = res_ty
271 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
272 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
273 ; op_id <- tcLookupId op_name
274 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar op_id))
275 ; return $ OpApp arg1' op' fix arg2' }
277 | (L loc (HsVar op_name)) <- op
278 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
279 = do { traceTc "Application rule" (ppr op)
280 ; (arg1', arg1_ty) <- tcInferRho arg1
281 ; let doc = ptext (sLit "The first argument of ($) takes")
282 ; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty
283 -- arg2_ty maybe polymorphic; that's the point
284 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
285 ; co_res <- unifyType op_res_ty res_ty
286 ; op_id <- tcLookupId op_name
287 ; let op' = L loc (HsWrap (mkWpTyApps [arg2_ty, op_res_ty]) (HsVar op_id))
288 ; return $ mkHsWrapCoI co_res $
289 OpApp (mkLHsWrapCoI co_arg1 arg1') op' fix arg2' }
292 = do { traceTc "Non Application rule" (ppr op)
293 ; (op', op_ty) <- tcInferFun op
294 ; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTys op 2 op_ty
295 ; co_res <- unifyType op_res_ty res_ty
296 ; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys
297 ; return $ mkHsWrapCoI co_res $
298 OpApp arg1' (mkLHsWrapCoI co_fn op') fix arg2' }
300 -- Right sections, equivalent to \ x -> x `op` expr, or
303 tcExpr (SectionR op arg2) res_ty
304 = do { (op', op_ty) <- tcInferFun op
305 ; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTys op 2 op_ty
306 ; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty
307 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
308 ; return $ mkHsWrapCoI co_res $
309 SectionR (mkLHsWrapCoI co_fn op') arg2' }
311 tcExpr (SectionL arg1 op) res_ty
312 = do { (op', op_ty) <- tcInferFun op
313 ; dflags <- getDOpts -- Note [Left sections]
314 ; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1
317 ; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTys op n_reqd_args op_ty
318 ; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty
319 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
320 ; return $ mkHsWrapCoI co_res $
321 SectionL arg1' (mkLHsWrapCoI co_fn op') }
323 tcExpr (ExplicitTuple tup_args boxity) res_ty
324 | all tupArgPresent tup_args
325 = do { let tup_tc = tupleTyCon boxity (length tup_args)
326 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
327 ; tup_args1 <- tcTupArgs tup_args arg_tys
328 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
331 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
332 do { let kind = case boxity of { Boxed -> liftedTypeKind
333 ; Unboxed -> argTypeKind }
334 arity = length tup_args
335 tup_tc = tupleTyCon boxity arity
337 ; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind
339 = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
340 (mkTyConApp tup_tc arg_tys)
342 ; coi <- unifyType actual_res_ty res_ty
344 -- Handle tuple sections where
345 ; tup_args1 <- tcTupArgs tup_args arg_tys
347 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
349 tcExpr (ExplicitList _ exprs) res_ty
350 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
351 ; exprs' <- mapM (tc_elt elt_ty) exprs
352 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
354 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
356 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
357 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
358 ; exprs' <- mapM (tc_elt elt_ty) exprs
359 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
361 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
364 %************************************************************************
368 %************************************************************************
371 tcExpr (HsLet binds expr) res_ty
372 = do { (binds', expr') <- tcLocalBinds binds $
373 tcMonoExpr expr res_ty
374 ; return (HsLet binds' expr') }
376 tcExpr (HsCase scrut matches) exp_ty
377 = do { -- We used to typecheck the case alternatives first.
378 -- The case patterns tend to give good type info to use
379 -- when typechecking the scrutinee. For example
382 -- will report that map is applied to too few arguments
384 -- But now, in the GADT world, we need to typecheck the scrutinee
385 -- first, to get type info that may be refined in the case alternatives
386 (scrut', scrut_ty) <- tcInferRho scrut
388 ; traceTc "HsCase" (ppr scrut_ty)
389 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
390 ; return (HsCase scrut' matches') }
392 match_ctxt = MC { mc_what = CaseAlt,
395 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
396 = do { pred' <- tcMonoExpr pred boolTy
397 ; b1' <- tcMonoExpr b1 res_ty
398 ; b2' <- tcMonoExpr b2 res_ty
399 ; return (HsIf Nothing pred' b1' b2') }
401 tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Rebindable syntax
402 = do { pred_ty <- newFlexiTyVarTy openTypeKind
403 ; b_ty <- newFlexiTyVarTy openTypeKind
404 ; let if_ty = mkFunTys [pred_ty, b_ty, b_ty] res_ty
405 ; fun' <- tcSyntaxOp IfOrigin fun if_ty
406 ; pred' <- tcMonoExpr pred pred_ty
407 ; b1' <- tcMonoExpr b1 b_ty
408 ; b2' <- tcMonoExpr b2 b_ty
409 ; return (HsIf (Just fun') pred' b1' b2') }
411 tcExpr (HsDo do_or_lc stmts body _) res_ty
412 = tcDoStmts do_or_lc stmts body res_ty
414 tcExpr (HsProc pat cmd) res_ty
415 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
416 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
418 tcExpr e@(HsArrApp _ _ _ _ _) _
419 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
420 ptext (sLit "was found where an expression was expected")])
422 tcExpr e@(HsArrForm _ _ _) _
423 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
424 ptext (sLit "was found where an expression was expected")])
427 %************************************************************************
429 Record construction and update
431 %************************************************************************
434 tcExpr (RecordCon (L loc con_name) _ rbinds) res_ty
435 = do { data_con <- tcLookupDataCon con_name
437 -- Check for missing fields
438 ; checkMissingFields data_con rbinds
440 ; (con_expr, con_tau) <- tcInferId con_name
441 ; let arity = dataConSourceArity data_con
442 (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
443 con_id = dataConWrapId data_con
445 ; co_res <- unifyType actual_res_ty res_ty
446 ; rbinds' <- tcRecordBinds data_con arg_tys rbinds
447 ; return $ mkHsWrapCoI co_res $
448 RecordCon (L loc con_id) con_expr rbinds' }
451 Note [Type of a record update]
452 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
453 The main complication with RecordUpd is that we need to explicitly
454 handle the *non-updated* fields. Consider:
456 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
457 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
460 upd :: T a b c -> (b',c) -> T a b' c
461 upd t x = t { fb = x}
463 The result type should be (T a b' c)
464 not (T a b c), because 'b' *is not* mentioned in a non-updated field
465 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
466 NB that it's not good enough to look at just one constructor; we must
467 look at them all; cf Trac #3219
469 After all, upd should be equivalent to:
475 So we need to give a completely fresh type to the result record,
476 and then constrain it by the fields that are *not* updated ("p" above).
477 We call these the "fixed" type variables, and compute them in getFixedTyVars.
479 Note that because MkT3 doesn't contain all the fields being updated,
480 its RHS is simply an error, so it doesn't impose any type constraints.
481 Hence the use of 'relevant_cont'.
483 Note [Implict type sharing]
484 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
485 We also take into account any "implicit" non-update fields. For example
486 data T a b where { MkT { f::a } :: T a a; ... }
487 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
492 upd :: T a b -> a -> T a b
493 upd (t::T a b) (x::a)
494 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
495 We can't give it the more general type
496 upd :: T a b -> c -> T c b
498 Note [Criteria for update]
499 ~~~~~~~~~~~~~~~~~~~~~~~~~~
500 We want to allow update for existentials etc, provided the updated
501 field isn't part of the existential. For example, this should be ok.
502 data T a where { MkT { f1::a, f2::b->b } :: T a }
506 The criterion we use is this:
508 The types of the updated fields
509 mention only the universally-quantified type variables
510 of the data constructor
512 NB: this is not (quite) the same as being a "naughty" record selector
513 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
514 in the case of GADTs. Consider
515 data T a where { MkT :: { f :: a } :: T [a] }
516 Then f is not "naughty" because it has a well-typed record selector.
517 But we don't allow updates for 'f'. (One could consider trying to
518 allow this, but it makes my head hurt. Badly. And no one has asked
521 In principle one could go further, and allow
523 g t = t { f2 = \x -> x }
524 because the expression is polymorphic...but that seems a bridge too far.
526 Note [Data family example]
527 ~~~~~~~~~~~~~~~~~~~~~~~~~~
528 data instance T (a,b) = MkT { x::a, y::b }
530 data :TP a b = MkT { a::a, y::b }
531 coTP a b :: T (a,b) ~ :TP a b
533 Suppose r :: T (t1,t2), e :: t3
534 Then r { x=e } :: T (t3,t1)
537 MkT x y -> MkT e y |> co2
538 where co1 :: T (t1,t2) ~ :TP t1 t2
539 co2 :: :TP t3 t2 ~ T (t3,t2)
540 The wrapping with co2 is done by the constructor wrapper for MkT
544 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
546 * cons are the data constructors to be updated
548 * in_inst_tys, out_inst_tys have same length, and instantiate the
549 *representation* tycon of the data cons. In Note [Data
550 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
553 tcExpr (RecordUpd record_expr rbinds _ _ _) res_ty
554 = ASSERT( notNull upd_fld_names )
557 -- Check that the field names are really field names
558 ; sel_ids <- mapM tcLookupField upd_fld_names
559 -- The renamer has already checked that
560 -- selectors are all in scope
561 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
562 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
563 not (isRecordSelector sel_id), -- Excludes class ops
564 let L loc fld_name = hsRecFieldId fld ]
565 ; unless (null bad_guys) (sequence bad_guys >> failM)
568 -- Figure out the tycon and data cons from the first field name
569 ; let -- It's OK to use the non-tc splitters here (for a selector)
571 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
572 data_cons = tyConDataCons tycon -- it's not a field label
573 -- NB: for a data type family, the tycon is the instance tycon
575 relevant_cons = filter is_relevant data_cons
576 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
577 -- A constructor is only relevant to this process if
578 -- it contains *all* the fields that are being updated
579 -- Other ones will cause a runtime error if they occur
581 -- Take apart a representative constructor
582 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
583 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
584 con1_flds = dataConFieldLabels con1
585 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
588 -- Check that at least one constructor has all the named fields
589 -- i.e. has an empty set of bad fields returned by badFields
590 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
592 -- STEP 3 Note [Criteria for update]
593 -- Check that each updated field is polymorphic; that is, its type
594 -- mentions only the universally-quantified variables of the data con
595 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
596 upd_flds1_w_tys = filter is_updated flds1_w_tys
597 is_updated (fld,_) = fld `elem` upd_fld_names
599 bad_upd_flds = filter bad_fld upd_flds1_w_tys
600 con1_tv_set = mkVarSet con1_tvs
601 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
602 not (tyVarsOfType ty `subVarSet` con1_tv_set)
603 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
605 -- STEP 4 Note [Type of a record update]
606 -- Figure out types for the scrutinee and result
607 -- Both are of form (T a b c), with fresh type variables, but with
608 -- common variables where the scrutinee and result must have the same type
609 -- These are variables that appear in *any* arg of *any* of the
610 -- relevant constructors *except* in the updated fields
612 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
613 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
614 mk_inst_ty tv result_inst_ty
615 | is_fixed_tv tv = return result_inst_ty -- Same as result type
616 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
618 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
619 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
621 ; let rec_res_ty = substTy result_inst_env con1_res_ty
622 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
623 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
624 scrut_ty = substTy scrut_subst con1_res_ty
626 ; co_res <- unifyType rec_res_ty res_ty
629 -- Typecheck the thing to be updated, and the bindings
630 ; record_expr' <- tcMonoExpr record_expr scrut_ty
631 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
633 -- STEP 6: Deal with the stupid theta
634 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
635 ; instStupidTheta RecordUpdOrigin theta'
637 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
638 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
639 = WpCast $ mkTyConApp co_con scrut_inst_tys
643 ; return $ mkHsWrapCoI co_res $
644 RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
645 relevant_cons scrut_inst_tys result_inst_tys }
647 upd_fld_names = hsRecFields rbinds
649 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
650 -- These tyvars must not change across the updates
651 getFixedTyVars tvs1 cons
652 = mkVarSet [tv1 | con <- cons
653 , let (tvs, theta, arg_tys, _) = dataConSig con
654 flds = dataConFieldLabels con
655 fixed_tvs = exactTyVarsOfTypes fixed_tys
656 -- fixed_tys: See Note [Type of a record update]
657 `unionVarSet` tyVarsOfTheta theta
658 -- Universally-quantified tyvars that
659 -- appear in any of the *implicit*
660 -- arguments to the constructor are fixed
661 -- See Note [Implict type sharing]
663 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
664 , not (fld `elem` upd_fld_names)]
665 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
666 , tv `elemVarSet` fixed_tvs ]
669 %************************************************************************
671 Arithmetic sequences e.g. [a,b..]
672 and their parallel-array counterparts e.g. [: a,b.. :]
675 %************************************************************************
678 tcExpr (ArithSeq _ seq@(From expr)) res_ty
679 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
680 ; expr' <- tcPolyExpr expr elt_ty
681 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
683 ; return $ mkHsWrapCoI coi (ArithSeq enum_from (From expr')) }
685 tcExpr (ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
686 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
687 ; expr1' <- tcPolyExpr expr1 elt_ty
688 ; expr2' <- tcPolyExpr expr2 elt_ty
689 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
690 enumFromThenName elt_ty
691 ; return $ mkHsWrapCoI coi
692 (ArithSeq enum_from_then (FromThen expr1' expr2')) }
694 tcExpr (ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
695 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
696 ; expr1' <- tcPolyExpr expr1 elt_ty
697 ; expr2' <- tcPolyExpr expr2 elt_ty
698 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
699 enumFromToName elt_ty
700 ; return $ mkHsWrapCoI coi
701 (ArithSeq enum_from_to (FromTo expr1' expr2')) }
703 tcExpr (ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
704 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
705 ; expr1' <- tcPolyExpr expr1 elt_ty
706 ; expr2' <- tcPolyExpr expr2 elt_ty
707 ; expr3' <- tcPolyExpr expr3 elt_ty
708 ; eft <- newMethodFromName (ArithSeqOrigin seq)
709 enumFromThenToName elt_ty
710 ; return $ mkHsWrapCoI coi
711 (ArithSeq eft (FromThenTo expr1' expr2' expr3')) }
713 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
714 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
715 ; expr1' <- tcPolyExpr expr1 elt_ty
716 ; expr2' <- tcPolyExpr expr2 elt_ty
717 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
718 enumFromToPName elt_ty
719 ; return $ mkHsWrapCoI coi
720 (PArrSeq enum_from_to (FromTo expr1' expr2')) }
722 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
723 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
724 ; expr1' <- tcPolyExpr expr1 elt_ty
725 ; expr2' <- tcPolyExpr expr2 elt_ty
726 ; expr3' <- tcPolyExpr expr3 elt_ty
727 ; eft <- newMethodFromName (PArrSeqOrigin seq)
728 enumFromThenToPName elt_ty
729 ; return $ mkHsWrapCoI coi
730 (PArrSeq eft (FromThenTo expr1' expr2' expr3')) }
732 tcExpr (PArrSeq _ _) _
733 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
734 -- the parser shouldn't have generated it and the renamer shouldn't have
739 %************************************************************************
743 %************************************************************************
746 #ifdef GHCI /* Only if bootstrapped */
747 -- Rename excludes these cases otherwise
748 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
749 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
751 tcExpr e@(HsQuasiQuoteE _) _ =
752 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
757 %************************************************************************
761 %************************************************************************
764 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
768 %************************************************************************
772 %************************************************************************
775 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
776 -> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args
778 tcApp (L _ (HsPar e)) args res_ty
779 = tcApp e args res_ty
781 tcApp (L _ (HsApp e1 e2)) args res_ty
782 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
784 tcApp (L loc (HsVar fun)) args res_ty
785 | fun `hasKey` tagToEnumKey
787 = tcTagToEnum loc fun arg res_ty
789 tcApp fun args res_ty
790 = do { -- Type-check the function
791 ; (fun1, fun_tau) <- tcInferFun fun
793 -- Extract its argument types
794 ; (co_fun, expected_arg_tys, actual_res_ty)
795 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
797 -- Typecheck the result, thereby propagating
798 -- info (if any) from result into the argument types
799 -- Both actual_res_ty and res_ty are deeply skolemised
800 ; co_res <- unifyType actual_res_ty res_ty
802 -- Typecheck the arguments
803 ; args1 <- tcArgs fun args expected_arg_tys
805 -- Assemble the result
806 ; let fun2 = mkLHsWrapCoI co_fun fun1
807 app = mkLHsWrapCoI co_res (foldl mkHsApp fun2 args1)
809 ; return (unLoc app) }
812 mk_app_msg :: LHsExpr Name -> SDoc
813 mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun)
814 , ptext (sLit "is applied to")]
817 tcInferApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
818 -> TcM (HsExpr TcId, TcRhoType) -- Translated fun and args
820 tcInferApp (L _ (HsPar e)) args = tcInferApp e args
821 tcInferApp (L _ (HsApp e1 e2)) args = tcInferApp e1 (e2:args)
823 = -- Very like the tcApp version, except that there is
824 -- no expected result type passed in
825 do { (fun1, fun_tau) <- tcInferFun fun
826 ; (co_fun, expected_arg_tys, actual_res_ty)
827 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
828 ; args1 <- tcArgs fun args expected_arg_tys
829 ; let fun2 = mkLHsWrapCoI co_fun fun1
830 app = foldl mkHsApp fun2 args1
831 ; return (unLoc app, actual_res_ty) }
834 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
835 -- Infer and instantiate the type of a function
836 tcInferFun (L loc (HsVar name))
837 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
838 -- Don't wrap a context around a plain Id
839 ; return (L loc fun, ty) }
842 = do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun)
844 -- Zonk the function type carefully, to expose any polymorphism
845 -- E.g. (( \(x::forall a. a->a). blah ) e)
846 -- We can see the rank-2 type of the lambda in time to genrealise e
847 ; fun_ty' <- zonkTcTypeCarefully fun_ty
849 ; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty'
850 ; return (mkLHsWrap wrap fun, rho) }
853 tcArgs :: LHsExpr Name -- The function (for error messages)
854 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
855 -> TcM [LHsExpr TcId] -- Resulting args
857 tcArgs fun args expected_arg_tys
858 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
861 tcArg :: LHsExpr Name -- The function (for error messages)
862 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
863 -> TcM (LHsExpr TcId) -- Resulting argument
864 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
865 (tcPolyExprNC arg ty)
868 tcTupArgs :: [HsTupArg Name] -> [TcSigmaType] -> TcM [HsTupArg TcId]
870 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
872 go (Missing {}, arg_ty) = return (Missing arg_ty)
873 go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
874 ; return (Present expr') }
877 unifyOpFunTys :: LHsExpr Name -> Arity -> TcRhoType
878 -> TcM (CoercionI, [TcSigmaType], TcRhoType)
879 -- A wrapper for matchExpectedFunTys
880 unifyOpFunTys op arity ty = matchExpectedFunTys herald arity ty
882 herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes")
884 ---------------------------
885 tcSyntaxOp :: CtOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
886 -- Typecheck a syntax operator, checking that it has the specified type
887 -- The operator is always a variable at this stage (i.e. renamer output)
888 -- This version assumes res_ty is a monotype
889 tcSyntaxOp orig (HsVar op) res_ty = do { (expr, rho) <- tcInferIdWithOrig orig op
890 ; tcWrapResult expr rho res_ty }
891 tcSyntaxOp _ other _ = pprPanic "tcSyntaxOp" (ppr other)
895 Note [Push result type in]
896 ~~~~~~~~~~~~~~~~~~~~~~~~~~
897 Unify with expected result before type-checking the args so that the
898 info from res_ty percolates to args. This is when we might detect a
899 too-few args situation. (One can think of cases when the opposite
900 order would give a better error message.)
901 experimenting with putting this first.
903 Here's an example where it actually makes a real difference
905 class C t a b | t a -> b
906 instance C Char a Bool
908 data P t a = forall b. (C t a b) => MkP b
909 data Q t = MkQ (forall a. P t a)
913 f2 = MkQ (MkP True :: forall a. P Char a)
915 With the change, f1 will type-check, because the 'Char' info from
916 the signature is propagated into MkQ's argument. With the check
917 in the other order, the extra signature in f2 is reqd.
920 %************************************************************************
924 %************************************************************************
927 tcCheckId :: Name -> TcRhoType -> TcM (HsExpr TcId)
928 tcCheckId name res_ty = do { (expr, rho) <- tcInferId name
929 ; tcWrapResult expr rho res_ty }
931 ------------------------
932 tcInferId :: Name -> TcM (HsExpr TcId, TcRhoType)
933 -- Infer type, and deeply instantiate
934 tcInferId n = tcInferIdWithOrig (OccurrenceOf n) n
936 ------------------------
937 tcInferIdWithOrig :: CtOrigin -> Name -> TcM (HsExpr TcId, TcRhoType)
938 -- Look up an occurrence of an Id, and instantiate it (deeply)
940 tcInferIdWithOrig orig id_name
941 = do { id <- lookup_id
942 ; (id_expr, id_rho) <- instantiateOuter orig id
943 ; (wrap, rho) <- deeplyInstantiate orig id_rho
944 ; return (mkHsWrap wrap id_expr, rho) }
946 lookup_id :: TcM TcId
948 = do { thing <- tcLookup id_name
950 ATcId { tct_id = id, tct_level = lvl }
951 -> do { check_naughty id -- Note [Local record selectors]
952 ; checkThLocalId id lvl
956 -> do { check_naughty id; return id }
957 -- A global cannot possibly be ill-staged
958 -- nor does it need the 'lifting' treatment
959 -- hence no checkTh stuff here
961 AGlobal (ADataCon con) -> return (dataConWrapId con)
963 other -> failWithTc (bad_lookup other) }
965 bad_lookup thing = ppr thing <+> ptext (sLit "used where a value identifer was expected")
968 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel id)
969 | otherwise = return ()
971 ------------------------
972 instantiateOuter :: CtOrigin -> TcId -> TcM (HsExpr TcId, TcSigmaType)
973 -- Do just the first level of instantiation of an Id
974 -- a) Deal with method sharing
975 -- b) Deal with stupid checks
976 -- Only look at the *outer level* of quantification
977 -- See Note [Multiple instantiation]
979 instantiateOuter orig id
980 | null tvs && null theta
981 = return (HsVar id, tau)
984 = do { (_, tys, subst) <- tcInstTyVars tvs
985 ; doStupidChecks id tys
986 ; let theta' = substTheta subst theta
987 ; traceTc "Instantiating" (ppr id <+> text "with" <+> (ppr tys $$ ppr theta'))
988 ; wrap <- instCall orig tys theta'
989 ; return (mkHsWrap wrap (HsVar id), substTy subst tau) }
991 (tvs, theta, tau) = tcSplitSigmaTy (idType id)
994 Note [Multiple instantiation]
995 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
996 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
997 For example, consider
998 f :: forall a. Eq a => forall b. Ord b => a -> b
999 At a call to f, at say [Int, Bool], it's tempting to translate the call to
1003 f_m1 :: forall b. Ord b => Int -> b
1007 f_m2 = f_m1 Bool dOrdBool
1009 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
1010 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
1012 But it's entirely possible that f_m2 will continue to float out, because it
1013 mentions no type variables. Result, f_m1 isn't in scope.
1015 Here's a concrete example that does this (test tc200):
1018 f :: Eq b => b -> a -> Int
1019 baz :: Eq a => Int -> a -> Int
1021 instance C Int where
1024 Current solution: only do the "method sharing" thing for the first type/dict
1025 application, not for the iterated ones. A horribly subtle point.
1027 Note [No method sharing]
1028 ~~~~~~~~~~~~~~~~~~~~~~~~
1029 The -fno-method-sharing flag controls what happens so far as the LIE
1030 is concerned. The default case is that for an overloaded function we
1031 generate a "method" Id, and add the Method Inst to the LIE. So you get
1033 f :: Num a => a -> a
1034 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
1035 If you specify -fno-method-sharing, the dictionary application
1036 isn't shared, so we get
1037 f :: Num a => a -> a
1038 f = /\a (d:Num a) (x:a) -> (+) a d x x
1039 This gets a bit less sharing, but
1040 a) it's better for RULEs involving overloaded functions
1041 b) perhaps fewer separated lambdas
1044 doStupidChecks :: TcId
1047 -- Check two tiresome and ad-hoc cases
1048 -- (a) the "stupid theta" for a data con; add the constraints
1049 -- from the "stupid theta" of a data constructor (sigh)
1051 doStupidChecks fun_id tys
1052 | Just con <- isDataConId_maybe fun_id -- (a)
1053 = addDataConStupidTheta con tys
1055 | fun_id `hasKey` tagToEnumKey -- (b)
1056 = failWithTc (ptext (sLit "tagToEnum# must appear applied to one argument"))
1059 = return () -- The common case
1064 Nasty check to ensure that tagToEnum# is applied to a type that is an
1065 enumeration TyCon. Unification may refine the type later, but this
1066 check won't see that, alas. It's crude, because it relies on our
1067 knowing *now* that the type is ok, which in turn relies on the
1068 eager-unification part of the type checker pushing enough information
1069 here. In theory the Right Thing to do is to have a new form of
1070 constraint but I definitely cannot face that! And it works ok as-is.
1072 Here's are two cases that should fail
1074 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1077 g = tagToEnum# 0 -- Int is not an enumeration
1079 When data type families are involved it's a bit more complicated.
1081 data instance F [Int] = A | B | C
1082 Then we want to generate something like
1083 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1084 Usually that coercion is hidden inside the wrappers for
1085 constructors of F [Int] but here we have to do it explicitly.
1087 It's all grotesquely complicated.
1090 tcTagToEnum :: SrcSpan -> Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
1091 -- tagToEnum# :: forall a. Int# -> a
1092 -- See Note [tagToEnum#] Urgh!
1093 tcTagToEnum loc fun_name arg res_ty
1094 = do { fun <- tcLookupId fun_name
1095 ; ty' <- zonkTcType res_ty
1097 -- Check that the type is algebraic
1098 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1099 Just (tc, tc_args) = mb_tc_app
1100 ; checkTc (isJust mb_tc_app)
1101 (tagToEnumError ty' doc1)
1103 -- Look through any type family
1104 ; (coi, rep_tc, rep_args) <- get_rep_ty ty' tc tc_args
1106 ; checkTc (isEnumerationTyCon rep_tc)
1107 (tagToEnumError ty' doc2)
1109 ; arg' <- tcMonoExpr arg intPrimTy
1110 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar fun))
1111 rep_ty = mkTyConApp rep_tc rep_args
1113 ; return (mkHsWrapCoI coi $ HsApp fun' arg') }
1115 doc1 = vcat [ ptext (sLit "Specify the type by giving a type signature")
1116 , ptext (sLit "e.g. (tagToEnum# x) :: Bool") ]
1117 doc2 = ptext (sLit "Result type must be an enumeration type")
1118 doc3 = ptext (sLit "No family instance for this type")
1120 get_rep_ty :: TcType -> TyCon -> [TcType]
1121 -> TcM (CoercionI, TyCon, [TcType])
1122 -- Converts a family type (eg F [a]) to its rep type (eg FList a)
1123 -- and returns a coercion between the two
1124 get_rep_ty ty tc tc_args
1125 | not (isFamilyTyCon tc)
1126 = return (IdCo ty, tc, tc_args)
1128 = do { mb_fam <- tcLookupFamInst tc tc_args
1130 Nothing -> failWithTc (tagToEnumError ty doc3)
1131 Just (rep_tc, rep_args)
1132 -> return ( ACo (mkSymCoercion (mkTyConApp co_tc rep_args))
1133 , rep_tc, rep_args )
1135 co_tc = expectJust "tcTagToEnum" $
1136 tyConFamilyCoercion_maybe rep_tc }
1138 tagToEnumError :: TcType -> SDoc -> SDoc
1139 tagToEnumError ty what
1140 = hang (ptext (sLit "Bad call to tagToEnum#")
1141 <+> ptext (sLit "at type") <+> ppr ty)
1146 %************************************************************************
1148 Template Haskell checks
1150 %************************************************************************
1153 checkThLocalId :: Id -> ThLevel -> TcM ()
1154 #ifndef GHCI /* GHCI and TH is off */
1155 --------------------------------------
1156 -- Check for cross-stage lifting
1157 checkThLocalId _id _bind_lvl
1160 #else /* GHCI and TH is on */
1161 checkThLocalId id bind_lvl
1162 = do { use_stage <- getStage -- TH case
1163 ; let use_lvl = thLevel use_stage
1164 ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
1165 ; traceTc "thLocalId" (ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
1166 ; when (use_lvl > bind_lvl) $
1167 checkCrossStageLifting id bind_lvl use_stage }
1169 --------------------------------------
1170 checkCrossStageLifting :: Id -> ThLevel -> ThStage -> TcM ()
1171 -- We are inside brackets, and (use_lvl > bind_lvl)
1172 -- Now we must check whether there's a cross-stage lift to do
1173 -- Examples \x -> [| x |]
1176 checkCrossStageLifting _ _ Comp = return ()
1177 checkCrossStageLifting _ _ Splice = return ()
1179 checkCrossStageLifting id _ (Brack _ ps_var lie_var)
1181 = -- Top-level identifiers in this module,
1182 -- (which have External Names)
1183 -- are just like the imported case:
1184 -- no need for the 'lifting' treatment
1185 -- E.g. this is fine:
1188 -- But we do need to put f into the keep-alive
1189 -- set, because after desugaring the code will
1190 -- only mention f's *name*, not f itself.
1193 | otherwise -- bind_lvl = outerLevel presumably,
1194 -- but the Id is not bound at top level
1195 = -- Nested identifiers, such as 'x' in
1196 -- E.g. \x -> [| h x |]
1197 -- We must behave as if the reference to x was
1199 -- We use 'x' itself as the splice proxy, used by
1200 -- the desugarer to stitch it all back together.
1201 -- If 'x' occurs many times we may get many identical
1202 -- bindings of the same splice proxy, but that doesn't
1203 -- matter, although it's a mite untidy.
1204 do { let id_ty = idType id
1205 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1206 -- If x is polymorphic, its occurrence sites might
1207 -- have different instantiations, so we can't use plain
1208 -- 'x' as the splice proxy name. I don't know how to
1209 -- solve this, and it's probably unimportant, so I'm
1210 -- just going to flag an error for now
1212 ; lift <- if isStringTy id_ty then
1213 do { sid <- tcLookupId DsMeta.liftStringName
1214 -- See Note [Lifting strings]
1215 ; return (HsVar sid) }
1217 setConstraintVar lie_var $ do
1218 -- Put the 'lift' constraint into the right LIE
1219 newMethodFromName (OccurrenceOf (idName id))
1220 DsMeta.liftName id_ty
1222 -- Update the pending splices
1223 ; ps <- readMutVar ps_var
1224 ; writeMutVar ps_var ((idName id, nlHsApp (noLoc lift) (nlHsVar id)) : ps)
1230 Note [Lifting strings]
1231 ~~~~~~~~~~~~~~~~~~~~~~
1232 If we see $(... [| s |] ...) where s::String, we don't want to
1233 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1234 So this conditional short-circuits the lifting mechanism to generate
1235 (liftString "xy") in that case. I didn't want to use overlapping instances
1236 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1237 errors in a polymorphic situation.
1239 If this check fails (which isn't impossible) we get another chance; see
1240 Note [Converting strings] in Convert.lhs
1242 Local record selectors
1243 ~~~~~~~~~~~~~~~~~~~~~~
1244 Record selectors for TyCons in this module are ordinary local bindings,
1245 which show up as ATcIds rather than AGlobals. So we need to check for
1246 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1249 %************************************************************************
1251 \subsection{Record bindings}
1253 %************************************************************************
1255 Game plan for record bindings
1256 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1257 1. Find the TyCon for the bindings, from the first field label.
1259 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1261 For each binding field = value
1263 3. Instantiate the field type (from the field label) using the type
1266 4 Type check the value using tcArg, passing the field type as
1267 the expected argument type.
1269 This extends OK when the field types are universally quantified.
1275 -> [TcType] -- Expected type for each field
1276 -> HsRecordBinds Name
1277 -> TcM (HsRecordBinds TcId)
1279 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1280 = do { mb_binds <- mapM do_bind rbinds
1281 ; return (HsRecFields (catMaybes mb_binds) dd) }
1283 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1284 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1285 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1286 = addErrCtxt (fieldCtxt field_lbl) $
1287 do { rhs' <- tcPolyExprNC rhs field_ty
1288 ; let field_id = mkUserLocal (nameOccName field_lbl)
1289 (nameUnique field_lbl)
1291 -- Yuk: the field_id has the *unique* of the selector Id
1292 -- (so we can find it easily)
1293 -- but is a LocalId with the appropriate type of the RHS
1294 -- (so the desugarer knows the type of local binder to make)
1295 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1297 = do { addErrTc (badFieldCon data_con field_lbl)
1300 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1301 checkMissingFields data_con rbinds
1302 | null field_labels -- Not declared as a record;
1303 -- But C{} is still valid if no strict fields
1304 = if any isBanged field_strs then
1305 -- Illegal if any arg is strict
1306 addErrTc (missingStrictFields data_con [])
1310 | otherwise = do -- A record
1311 unless (null missing_s_fields)
1312 (addErrTc (missingStrictFields data_con missing_s_fields))
1314 warn <- doptM Opt_WarnMissingFields
1315 unless (not (warn && notNull missing_ns_fields))
1316 (warnTc True (missingFields data_con missing_ns_fields))
1320 = [ fl | (fl, str) <- field_info,
1322 not (fl `elem` field_names_used)
1325 = [ fl | (fl, str) <- field_info,
1327 not (fl `elem` field_names_used)
1330 field_names_used = hsRecFields rbinds
1331 field_labels = dataConFieldLabels data_con
1333 field_info = zipEqual "missingFields"
1337 field_strs = dataConStrictMarks data_con
1340 %************************************************************************
1342 \subsection{Errors and contexts}
1344 %************************************************************************
1346 Boring and alphabetical:
1348 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
1349 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
1351 exprCtxt :: LHsExpr Name -> SDoc
1353 = hang (ptext (sLit "In the expression:")) 2 (ppr expr)
1355 fieldCtxt :: Name -> SDoc
1356 fieldCtxt field_name
1357 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1359 funAppCtxt :: LHsExpr Name -> LHsExpr Name -> Int -> SDoc
1360 funAppCtxt fun arg arg_no
1361 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1362 quotes (ppr fun) <> text ", namely"])
1363 2 (quotes (ppr arg))
1365 badFieldTypes :: [(Name,TcType)] -> SDoc
1367 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1368 <> plural prs <> colon)
1369 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1371 badFieldsUpd :: HsRecFields Name a -> SDoc
1373 = hang (ptext (sLit "No constructor has all these fields:"))
1374 2 (pprQuotedList (hsRecFields rbinds))
1376 naughtyRecordSel :: TcId -> SDoc
1377 naughtyRecordSel sel_id
1378 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1379 ptext (sLit "as a function due to escaped type variables") $$
1380 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1382 notSelector :: Name -> SDoc
1384 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1386 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1387 missingStrictFields con fields
1390 rest | null fields = empty -- Happens for non-record constructors
1391 -- with strict fields
1392 | otherwise = colon <+> pprWithCommas ppr fields
1394 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1395 ptext (sLit "does not have the required strict field(s)")
1397 missingFields :: DataCon -> [FieldLabel] -> SDoc
1398 missingFields con fields
1399 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1400 <+> pprWithCommas ppr fields
1402 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1405 polySpliceErr :: Id -> SDoc
1407 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)