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 )
64 %************************************************************************
66 \subsection{Main wrappers}
68 %************************************************************************
71 tcPolyExpr, tcPolyExprNC
72 :: LHsExpr Name -- Expression to type check
73 -> TcSigmaType -- Expected type (could be a polytpye)
74 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
76 -- tcPolyExpr is a convenient place (frequent but not too frequent)
77 -- place to add context information.
78 -- The NC version does not do so, usually because the caller wants
81 tcPolyExpr expr res_ty
82 = addExprErrCtxt expr $
83 do { traceTc "tcPolyExpr" (ppr res_ty); tcPolyExprNC expr res_ty }
85 tcPolyExprNC expr res_ty
86 = do { traceTc "tcPolyExprNC" (ppr res_ty)
87 ; (gen_fn, expr') <- tcGen GenSigCtxt res_ty $ \ _ rho ->
89 ; return (mkLHsWrap gen_fn expr') }
92 tcMonoExpr, tcMonoExprNC
93 :: LHsExpr Name -- Expression to type check
94 -> TcRhoType -- Expected type (could be a type variable)
95 -- Definitely no foralls at the top
98 tcMonoExpr expr res_ty
99 = addErrCtxt (exprCtxt expr) $
100 tcMonoExprNC expr res_ty
102 tcMonoExprNC (L loc expr) res_ty
103 = ASSERT( not (isSigmaTy res_ty) )
105 do { expr' <- tcExpr expr res_ty
106 ; return (L loc expr') }
109 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
110 -- Infer a *rho*-type. This is, in effect, a special case
111 -- for ids and partial applications, so that if
112 -- f :: Int -> (forall a. a -> a) -> Int
114 -- f 3 :: (forall a. a -> a) -> Int
115 -- And that in turn is useful
116 -- (a) for the function part of any application (see tcApp)
117 -- (b) for the special rule for '$'
118 tcInferRho expr = addErrCtxt (exprCtxt expr) (tcInferRhoNC expr)
120 tcInferRhoNC (L loc expr)
122 do { (expr', rho) <- tcInfExpr expr
123 ; return (L loc expr', rho) }
125 tcInfExpr :: HsExpr Name -> TcM (HsExpr TcId, TcRhoType)
126 tcInfExpr (HsVar f) = tcInferId f
127 tcInfExpr (HsPar e) = do { (e', ty) <- tcInferRhoNC e
128 ; return (HsPar e', ty) }
129 tcInfExpr (HsApp e1 e2) = tcInferApp e1 [e2]
130 tcInfExpr e = tcInfer (tcExpr e)
134 %************************************************************************
136 tcExpr: the main expression typechecker
138 %************************************************************************
142 updHetMetLevel :: ([TyVar] -> [TyVar]) -> TcM a -> TcM a
143 updHetMetLevel f comp =
145 (\oldenv -> let oldlev = (case oldenv of Env { env_lcl = e' } -> case e' of TcLclEnv { tcl_hetMetLevel = x } -> x)
146 in (oldenv { env_lcl = (env_lcl oldenv) { tcl_hetMetLevel = f oldlev } }))
150 addEscapes :: [TyVar] -> HsExpr Name -> HsExpr Name
152 addEscapes (t:ts) e = HsHetMetEsc (TyVarTy t) placeHolderType (noLoc (addEscapes ts e))
154 getIdLevel :: Name -> TcM [TyVar]
156 = do { thing <- tcLookup name
158 ATcId { tct_hetMetLevel = variable_hetMetLevel } -> return $ variable_hetMetLevel
162 tcExpr :: HsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
163 tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
164 = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
166 tcExpr (HsVar name) res_ty = tcCheckId name res_ty
168 tcExpr (HsHetMetBrak _ e) res_ty =
169 do { (coi, [inferred_name,elt_ty]) <- matchExpectedTyConApp hetMetCodeTypeTyCon res_ty
170 ; fresh_ec_name <- newFlexiTyVar liftedTypeKind
171 ; expr' <- updHetMetLevel (\old_lev -> (fresh_ec_name:old_lev))
172 $ tcPolyExpr e elt_ty
173 ; unifyType (TyVarTy fresh_ec_name) inferred_name
174 ; return $ mkHsWrapCoI coi (HsHetMetBrak (TyVarTy fresh_ec_name) expr') }
175 tcExpr (HsHetMetEsc _ _ e) res_ty =
176 do { cur_level <- getHetMetLevel
177 ; expr' <- updHetMetLevel (\old_lev -> tail old_lev)
178 $ tcExpr (unLoc e) (mkTyConApp hetMetCodeTypeTyCon [(TyVarTy $ head cur_level),res_ty])
179 ; ty' <- zonkTcType res_ty
180 ; return $ mkHsWrapCoI (ACo res_ty) (HsHetMetEsc (TyVarTy $ head cur_level) ty' (noLoc expr')) }
181 tcExpr (HsHetMetCSP _ e) res_ty =
182 do { cur_level <- getHetMetLevel
183 ; expr' <- updHetMetLevel (\old_lev -> tail old_lev)
184 $ tcExpr (unLoc e) res_ty
185 ; return $ mkHsWrapCoI (ACo res_ty) (HsHetMetCSP (TyVarTy $ head cur_level) (noLoc expr')) }
187 tcExpr (HsApp e1 e2) res_ty = tcApp e1 [e2] res_ty
189 tcExpr (HsLit lit) res_ty =
190 getHetMetLevel >>= \lev ->
192 [] -> do { let lit_ty = hsLitType lit
193 ; tcWrapResult (HsLit lit) lit_ty res_ty }
194 (ec:rest) -> let n = case lit of
195 (HsChar c) -> hetmet_guest_char_literal_name
196 (HsString str) -> hetmet_guest_string_literal_name
197 (HsInteger i _) -> hetmet_guest_integer_literal_name
198 (HsInt i) -> hetmet_guest_integer_literal_name
199 _ -> error "literals of this sort are not allowed at depth >0"
200 in tcExpr (HsHetMetEsc (TyVarTy ec) placeHolderType $ noLoc $ HsApp (noLoc $ HsVar n) (noLoc $ HsLit lit)) res_ty
202 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
203 ; return (HsPar expr') }
205 tcExpr (HsSCC lbl expr) res_ty
206 = do { expr' <- tcMonoExpr expr res_ty
207 ; return (HsSCC lbl expr') }
209 tcExpr (HsTickPragma info expr) res_ty
210 = do { expr' <- tcMonoExpr expr res_ty
211 ; return (HsTickPragma info expr') }
213 tcExpr (HsCoreAnn lbl expr) res_ty
214 = do { expr' <- tcMonoExpr expr res_ty
215 ; return (HsCoreAnn lbl expr') }
217 tcExpr (HsOverLit lit) res_ty
218 = do { lit' <- newOverloadedLit (LiteralOrigin lit) lit res_ty
219 ; return (HsOverLit lit') }
221 tcExpr (NegApp expr neg_expr) res_ty
222 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
223 (mkFunTy res_ty res_ty)
224 ; expr' <- tcMonoExpr expr res_ty
225 ; return (NegApp expr' neg_expr') }
227 tcExpr (HsIPVar ip) res_ty
228 = do { let origin = IPOccOrigin ip
229 -- Implicit parameters must have a *tau-type* not a
230 -- type scheme. We enforce this by creating a fresh
231 -- type variable as its type. (Because res_ty may not
233 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
234 ; ip_var <- emitWanted origin (mkIPPred ip ip_ty)
235 ; tcWrapResult (HsIPVar (IPName ip_var)) ip_ty res_ty }
237 tcExpr (HsLam match) res_ty
238 = do { (co_fn, match') <- tcMatchLambda match res_ty
239 ; return (mkHsWrap co_fn (HsLam match')) }
241 tcExpr (ExprWithTySig expr sig_ty) res_ty
242 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
244 -- Remember to extend the lexical type-variable environment
246 <- tcGen ExprSigCtxt sig_tc_ty $ \ skol_tvs res_ty ->
247 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
248 -- See Note [More instantiated than scoped] in TcBinds
249 tcMonoExprNC expr res_ty
251 ; let inner_expr = ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty
253 ; (inst_wrap, rho) <- deeplyInstantiate ExprSigOrigin sig_tc_ty
254 ; tcWrapResult (mkHsWrap inst_wrap inner_expr) rho res_ty }
257 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
258 -- This is the syntax for type applications that I was planning
259 -- but there are difficulties (e.g. what order for type args)
260 -- so it's not enabled yet.
261 -- Can't eliminate it altogether from the parser, because the
262 -- same parser parses *patterns*.
266 %************************************************************************
268 Infix operators and sections
270 %************************************************************************
274 Left sections, like (4 *), are equivalent to
276 or, if PostfixOperators is enabled, just
278 With PostfixOperators we don't actually require the function to take
279 two arguments at all. For example, (x `not`) means (not x); you get
280 postfix operators! Not Haskell 98, but it's less work and kind of
283 Note [Typing rule for ($)]
284 ~~~~~~~~~~~~~~~~~~~~~~~~~~
288 runST :: (forall s. ST s a) -> a
289 that I have finally given in and written a special type-checking
290 rule just for saturated appliations of ($).
291 * Infer the type of the first argument
292 * Decompose it; should be of form (arg2_ty -> res_ty),
293 where arg2_ty might be a polytype
294 * Use arg2_ty to typecheck arg2
296 Note [Typing rule for seq]
297 ~~~~~~~~~~~~~~~~~~~~~~~~~~
300 which suggests this type for seq:
301 seq :: forall (a:*) (b:??). a -> b -> b,
302 with (b:??) meaning that be can be instantiated with an unboxed tuple.
303 But that's ill-kinded! Function arguments can't be unboxed tuples.
304 And indeed, you could not expect to do this with a partially-applied
305 'seq'; it's only going to work when it's fully applied. so it turns
307 case x of _ -> (# p,q #)
309 For a while I slid by by giving 'seq' an ill-kinded type, but then
310 the simplifier eta-reduced an application of seq and Lint blew up
311 with a kind error. It seems more uniform to treat 'seq' as it it
312 was a language construct.
314 See Note [seqId magic] in MkId, and
318 tcExpr (OpApp arg1 op fix arg2) res_ty
319 | (L loc (HsVar op_name)) <- op
320 , op_name `hasKey` seqIdKey -- Note [Typing rule for seq]
321 = do { arg1_ty <- newFlexiTyVarTy liftedTypeKind
322 ; let arg2_ty = res_ty
323 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
324 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
325 ; op_id <- tcLookupId op_name
326 ; let op' = L loc (HsWrap (mkWpTyApps [arg1_ty, arg2_ty]) (HsVar op_id))
327 ; return $ OpApp arg1' op' fix arg2' }
329 | (L loc (HsVar op_name)) <- op
330 , op_name `hasKey` dollarIdKey -- Note [Typing rule for ($)]
331 = do { traceTc "Application rule" (ppr op)
332 ; (arg1', arg1_ty) <- tcInferRho arg1
333 ; let doc = ptext (sLit "The first argument of ($) takes")
334 ; (co_arg1, [arg2_ty], op_res_ty) <- matchExpectedFunTys doc 1 arg1_ty
335 -- arg2_ty maybe polymorphic; that's the point
336 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
337 ; co_res <- unifyType op_res_ty res_ty
338 ; op_id <- tcLookupId op_name
339 ; let op' = L loc (HsWrap (mkWpTyApps [arg2_ty, op_res_ty]) (HsVar op_id))
340 ; return $ mkHsWrapCoI co_res $
341 OpApp (mkLHsWrapCoI co_arg1 arg1') op' fix arg2' }
344 = do { traceTc "Non Application rule" (ppr op)
345 ; (op', op_ty) <- tcInferFun op
346 ; (co_fn, arg_tys, op_res_ty) <- unifyOpFunTys op 2 op_ty
347 ; co_res <- unifyType op_res_ty res_ty
348 ; [arg1', arg2'] <- tcArgs op [arg1, arg2] arg_tys
349 ; return $ mkHsWrapCoI co_res $
350 OpApp arg1' (mkLHsWrapCoI co_fn op') fix arg2' }
352 -- Right sections, equivalent to \ x -> x `op` expr, or
355 tcExpr (SectionR op arg2) res_ty
356 = do { (op', op_ty) <- tcInferFun op
357 ; (co_fn, [arg1_ty, arg2_ty], op_res_ty) <- unifyOpFunTys op 2 op_ty
358 ; co_res <- unifyType (mkFunTy arg1_ty op_res_ty) res_ty
359 ; arg2' <- tcArg op (arg2, arg2_ty, 2)
360 ; return $ mkHsWrapCoI co_res $
361 SectionR (mkLHsWrapCoI co_fn op') arg2' }
363 tcExpr (SectionL arg1 op) res_ty
364 = do { (op', op_ty) <- tcInferFun op
365 ; dflags <- getDOpts -- Note [Left sections]
366 ; let n_reqd_args | xopt Opt_PostfixOperators dflags = 1
369 ; (co_fn, (arg1_ty:arg_tys), op_res_ty) <- unifyOpFunTys op n_reqd_args op_ty
370 ; co_res <- unifyType (mkFunTys arg_tys op_res_ty) res_ty
371 ; arg1' <- tcArg op (arg1, arg1_ty, 1)
372 ; return $ mkHsWrapCoI co_res $
373 SectionL arg1' (mkLHsWrapCoI co_fn op') }
375 tcExpr (ExplicitTuple tup_args boxity) res_ty
376 | all tupArgPresent tup_args
377 = do { let tup_tc = tupleTyCon boxity (length tup_args)
378 ; (coi, arg_tys) <- matchExpectedTyConApp tup_tc res_ty
379 ; tup_args1 <- tcTupArgs tup_args arg_tys
380 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
383 = -- The tup_args are a mixture of Present and Missing (for tuple sections)
384 do { let kind = case boxity of { Boxed -> liftedTypeKind
385 ; Unboxed -> argTypeKind }
386 arity = length tup_args
387 tup_tc = tupleTyCon boxity arity
389 ; arg_tys <- newFlexiTyVarTys (tyConArity tup_tc) kind
391 = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
392 (mkTyConApp tup_tc arg_tys)
394 ; coi <- unifyType actual_res_ty res_ty
396 -- Handle tuple sections where
397 ; tup_args1 <- tcTupArgs tup_args arg_tys
399 ; return $ mkHsWrapCoI coi (ExplicitTuple tup_args1 boxity) }
401 tcExpr (ExplicitList _ exprs) res_ty
402 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
403 ; exprs' <- mapM (tc_elt elt_ty) exprs
404 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
406 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
408 tcExpr (ExplicitPArr _ exprs) res_ty -- maybe empty
409 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
410 ; exprs' <- mapM (tc_elt elt_ty) exprs
411 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
413 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
416 %************************************************************************
420 %************************************************************************
423 tcExpr (HsLet binds expr) res_ty
424 = do { (binds', expr') <- tcLocalBinds binds $
425 tcMonoExpr expr res_ty
426 ; return (HsLet binds' expr') }
428 tcExpr (HsCase scrut matches) exp_ty
429 = do { -- We used to typecheck the case alternatives first.
430 -- The case patterns tend to give good type info to use
431 -- when typechecking the scrutinee. For example
434 -- will report that map is applied to too few arguments
436 -- But now, in the GADT world, we need to typecheck the scrutinee
437 -- first, to get type info that may be refined in the case alternatives
438 (scrut', scrut_ty) <- tcInferRho scrut
440 ; traceTc "HsCase" (ppr scrut_ty)
441 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
442 ; return (HsCase scrut' matches') }
444 match_ctxt = MC { mc_what = CaseAlt,
447 tcExpr (HsIf Nothing pred b1 b2) res_ty -- Ordinary 'if'
448 = do { pred' <- tcMonoExpr pred boolTy
449 ; b1' <- tcMonoExpr b1 res_ty
450 ; b2' <- tcMonoExpr b2 res_ty
451 ; return (HsIf Nothing pred' b1' b2') }
453 tcExpr (HsIf (Just fun) pred b1 b2) res_ty -- Note [Rebindable syntax for if]
454 = do { pred_ty <- newFlexiTyVarTy openTypeKind
455 ; b1_ty <- newFlexiTyVarTy openTypeKind
456 ; b2_ty <- newFlexiTyVarTy openTypeKind
457 ; let if_ty = mkFunTys [pred_ty, b1_ty, b2_ty] res_ty
458 ; fun' <- tcSyntaxOp IfOrigin fun if_ty
459 ; pred' <- tcMonoExpr pred pred_ty
460 ; b1' <- tcMonoExpr b1 b1_ty
461 ; b2' <- tcMonoExpr b2 b2_ty
462 -- Fundamentally we are just typing (ifThenElse e1 e2 e3)
463 -- so maybe we should use the code for function applications
464 -- (which would allow ifThenElse to be higher rank).
465 -- But it's a little awkward, so I'm leaving it alone for now
466 -- and it maintains uniformity with other rebindable syntax
467 ; return (HsIf (Just fun') pred' b1' b2') }
469 tcExpr (HsDo do_or_lc stmts body _) res_ty
470 = tcDoStmts do_or_lc stmts body res_ty
472 tcExpr (HsProc pat cmd) res_ty
473 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
474 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
476 tcExpr e@(HsArrApp _ _ _ _ _) _
477 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
478 ptext (sLit "was found where an expression was expected")])
480 tcExpr e@(HsArrForm _ _ _) _
481 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
482 ptext (sLit "was found where an expression was expected")])
485 Note [Rebindable syntax for if]
486 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
487 The rebindable syntax for 'if' uses the most flexible possible type
489 ifThenElse :: p -> b1 -> b2 -> res
490 to support expressions like this:
492 ifThenElse :: Maybe a -> (a -> b) -> b -> b
493 ifThenElse (Just a) f _ = f a ifThenElse Nothing _ e = e
501 %************************************************************************
503 Record construction and update
505 %************************************************************************
508 tcExpr (RecordCon (L loc con_name) _ rbinds) res_ty
509 = do { data_con <- tcLookupDataCon con_name
511 -- Check for missing fields
512 ; checkMissingFields data_con rbinds
514 ; (con_expr, con_tau) <- tcInferId con_name
515 ; let arity = dataConSourceArity data_con
516 (arg_tys, actual_res_ty) = tcSplitFunTysN con_tau arity
517 con_id = dataConWrapId data_con
519 ; co_res <- unifyType actual_res_ty res_ty
520 ; rbinds' <- tcRecordBinds data_con arg_tys rbinds
521 ; return $ mkHsWrapCoI co_res $
522 RecordCon (L loc con_id) con_expr rbinds' }
525 Note [Type of a record update]
526 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
527 The main complication with RecordUpd is that we need to explicitly
528 handle the *non-updated* fields. Consider:
530 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
531 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
534 upd :: T a b c -> (b',c) -> T a b' c
535 upd t x = t { fb = x}
537 The result type should be (T a b' c)
538 not (T a b c), because 'b' *is not* mentioned in a non-updated field
539 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
540 NB that it's not good enough to look at just one constructor; we must
541 look at them all; cf Trac #3219
543 After all, upd should be equivalent to:
549 So we need to give a completely fresh type to the result record,
550 and then constrain it by the fields that are *not* updated ("p" above).
551 We call these the "fixed" type variables, and compute them in getFixedTyVars.
553 Note that because MkT3 doesn't contain all the fields being updated,
554 its RHS is simply an error, so it doesn't impose any type constraints.
555 Hence the use of 'relevant_cont'.
557 Note [Implict type sharing]
558 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
559 We also take into account any "implicit" non-update fields. For example
560 data T a b where { MkT { f::a } :: T a a; ... }
561 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
566 upd :: T a b -> a -> T a b
567 upd (t::T a b) (x::a)
568 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
569 We can't give it the more general type
570 upd :: T a b -> c -> T c b
572 Note [Criteria for update]
573 ~~~~~~~~~~~~~~~~~~~~~~~~~~
574 We want to allow update for existentials etc, provided the updated
575 field isn't part of the existential. For example, this should be ok.
576 data T a where { MkT { f1::a, f2::b->b } :: T a }
580 The criterion we use is this:
582 The types of the updated fields
583 mention only the universally-quantified type variables
584 of the data constructor
586 NB: this is not (quite) the same as being a "naughty" record selector
587 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
588 in the case of GADTs. Consider
589 data T a where { MkT :: { f :: a } :: T [a] }
590 Then f is not "naughty" because it has a well-typed record selector.
591 But we don't allow updates for 'f'. (One could consider trying to
592 allow this, but it makes my head hurt. Badly. And no one has asked
595 In principle one could go further, and allow
597 g t = t { f2 = \x -> x }
598 because the expression is polymorphic...but that seems a bridge too far.
600 Note [Data family example]
601 ~~~~~~~~~~~~~~~~~~~~~~~~~~
602 data instance T (a,b) = MkT { x::a, y::b }
604 data :TP a b = MkT { a::a, y::b }
605 coTP a b :: T (a,b) ~ :TP a b
607 Suppose r :: T (t1,t2), e :: t3
608 Then r { x=e } :: T (t3,t1)
611 MkT x y -> MkT e y |> co2
612 where co1 :: T (t1,t2) ~ :TP t1 t2
613 co2 :: :TP t3 t2 ~ T (t3,t2)
614 The wrapping with co2 is done by the constructor wrapper for MkT
618 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
620 * cons are the data constructors to be updated
622 * in_inst_tys, out_inst_tys have same length, and instantiate the
623 *representation* tycon of the data cons. In Note [Data
624 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
627 tcExpr (RecordUpd record_expr rbinds _ _ _) res_ty
628 = ASSERT( notNull upd_fld_names )
631 -- Check that the field names are really field names
632 ; sel_ids <- mapM tcLookupField upd_fld_names
633 -- The renamer has already checked that
634 -- selectors are all in scope
635 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
636 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
637 not (isRecordSelector sel_id), -- Excludes class ops
638 let L loc fld_name = hsRecFieldId fld ]
639 ; unless (null bad_guys) (sequence bad_guys >> failM)
642 -- Figure out the tycon and data cons from the first field name
643 ; let -- It's OK to use the non-tc splitters here (for a selector)
645 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
646 data_cons = tyConDataCons tycon -- it's not a field label
647 -- NB: for a data type family, the tycon is the instance tycon
649 relevant_cons = filter is_relevant data_cons
650 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
651 -- A constructor is only relevant to this process if
652 -- it contains *all* the fields that are being updated
653 -- Other ones will cause a runtime error if they occur
655 -- Take apart a representative constructor
656 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
657 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
658 con1_flds = dataConFieldLabels con1
659 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
662 -- Check that at least one constructor has all the named fields
663 -- i.e. has an empty set of bad fields returned by badFields
664 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
666 -- STEP 3 Note [Criteria for update]
667 -- Check that each updated field is polymorphic; that is, its type
668 -- mentions only the universally-quantified variables of the data con
669 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
670 upd_flds1_w_tys = filter is_updated flds1_w_tys
671 is_updated (fld,_) = fld `elem` upd_fld_names
673 bad_upd_flds = filter bad_fld upd_flds1_w_tys
674 con1_tv_set = mkVarSet con1_tvs
675 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
676 not (tyVarsOfType ty `subVarSet` con1_tv_set)
677 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
679 -- STEP 4 Note [Type of a record update]
680 -- Figure out types for the scrutinee and result
681 -- Both are of form (T a b c), with fresh type variables, but with
682 -- common variables where the scrutinee and result must have the same type
683 -- These are variables that appear in *any* arg of *any* of the
684 -- relevant constructors *except* in the updated fields
686 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
687 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
688 mk_inst_ty tv result_inst_ty
689 | is_fixed_tv tv = return result_inst_ty -- Same as result type
690 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
692 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
693 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
695 ; let rec_res_ty = substTy result_inst_env con1_res_ty
696 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
697 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
698 scrut_ty = substTy scrut_subst con1_res_ty
700 ; co_res <- unifyType rec_res_ty res_ty
703 -- Typecheck the thing to be updated, and the bindings
704 ; record_expr' <- tcMonoExpr record_expr scrut_ty
705 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
707 -- STEP 6: Deal with the stupid theta
708 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
709 ; instStupidTheta RecordUpdOrigin theta'
711 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
712 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
713 = WpCast $ mkTyConApp co_con scrut_inst_tys
717 ; return $ mkHsWrapCoI co_res $
718 RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
719 relevant_cons scrut_inst_tys result_inst_tys }
721 upd_fld_names = hsRecFields rbinds
723 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
724 -- These tyvars must not change across the updates
725 getFixedTyVars tvs1 cons
726 = mkVarSet [tv1 | con <- cons
727 , let (tvs, theta, arg_tys, _) = dataConSig con
728 flds = dataConFieldLabels con
729 fixed_tvs = exactTyVarsOfTypes fixed_tys
730 -- fixed_tys: See Note [Type of a record update]
731 `unionVarSet` tyVarsOfTheta theta
732 -- Universally-quantified tyvars that
733 -- appear in any of the *implicit*
734 -- arguments to the constructor are fixed
735 -- See Note [Implict type sharing]
737 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
738 , not (fld `elem` upd_fld_names)]
739 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
740 , tv `elemVarSet` fixed_tvs ]
743 %************************************************************************
745 Arithmetic sequences e.g. [a,b..]
746 and their parallel-array counterparts e.g. [: a,b.. :]
749 %************************************************************************
752 tcExpr (ArithSeq _ seq@(From expr)) res_ty
753 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
754 ; expr' <- tcPolyExpr expr elt_ty
755 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
757 ; return $ mkHsWrapCoI coi (ArithSeq enum_from (From expr')) }
759 tcExpr (ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
760 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
761 ; expr1' <- tcPolyExpr expr1 elt_ty
762 ; expr2' <- tcPolyExpr expr2 elt_ty
763 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
764 enumFromThenName elt_ty
765 ; return $ mkHsWrapCoI coi
766 (ArithSeq enum_from_then (FromThen expr1' expr2')) }
768 tcExpr (ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
769 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
770 ; expr1' <- tcPolyExpr expr1 elt_ty
771 ; expr2' <- tcPolyExpr expr2 elt_ty
772 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
773 enumFromToName elt_ty
774 ; return $ mkHsWrapCoI coi
775 (ArithSeq enum_from_to (FromTo expr1' expr2')) }
777 tcExpr (ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
778 = do { (coi, elt_ty) <- matchExpectedListTy res_ty
779 ; expr1' <- tcPolyExpr expr1 elt_ty
780 ; expr2' <- tcPolyExpr expr2 elt_ty
781 ; expr3' <- tcPolyExpr expr3 elt_ty
782 ; eft <- newMethodFromName (ArithSeqOrigin seq)
783 enumFromThenToName elt_ty
784 ; return $ mkHsWrapCoI coi
785 (ArithSeq eft (FromThenTo expr1' expr2' expr3')) }
787 tcExpr (PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
788 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
789 ; expr1' <- tcPolyExpr expr1 elt_ty
790 ; expr2' <- tcPolyExpr expr2 elt_ty
791 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
792 (enumFromToPName basePackageId) elt_ty -- !!!FIXME: chak
793 ; return $ mkHsWrapCoI coi
794 (PArrSeq enum_from_to (FromTo expr1' expr2')) }
796 tcExpr (PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
797 = do { (coi, elt_ty) <- matchExpectedPArrTy res_ty
798 ; expr1' <- tcPolyExpr expr1 elt_ty
799 ; expr2' <- tcPolyExpr expr2 elt_ty
800 ; expr3' <- tcPolyExpr expr3 elt_ty
801 ; eft <- newMethodFromName (PArrSeqOrigin seq)
802 (enumFromThenToPName basePackageId) elt_ty -- !!!FIXME: chak
803 ; return $ mkHsWrapCoI coi
804 (PArrSeq eft (FromThenTo expr1' expr2' expr3')) }
806 tcExpr (PArrSeq _ _) _
807 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
808 -- the parser shouldn't have generated it and the renamer shouldn't have
813 %************************************************************************
817 %************************************************************************
820 #ifdef GHCI /* Only if bootstrapped */
821 -- Rename excludes these cases otherwise
822 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
823 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
825 tcExpr e@(HsQuasiQuoteE _) _ =
826 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
831 %************************************************************************
835 %************************************************************************
838 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
842 %************************************************************************
846 %************************************************************************
849 tcApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
850 -> TcRhoType -> TcM (HsExpr TcId) -- Translated fun and args
852 tcApp (L _ (HsPar e)) args res_ty
853 = tcApp e args res_ty
855 tcApp (L _ (HsApp e1 e2)) args res_ty
856 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
858 tcApp (L loc (HsVar fun)) args res_ty
859 | fun `hasKey` tagToEnumKey
861 = tcTagToEnum loc fun arg res_ty
863 tcApp fun args res_ty
864 = do { -- Type-check the function
865 ; (fun1, fun_tau) <- tcInferFun fun
867 -- Extract its argument types
868 ; (co_fun, expected_arg_tys, actual_res_ty)
869 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
871 -- Typecheck the result, thereby propagating
872 -- info (if any) from result into the argument types
873 -- Both actual_res_ty and res_ty are deeply skolemised
874 ; co_res <- addErrCtxt (funResCtxt fun) $
875 unifyType actual_res_ty res_ty
877 -- Typecheck the arguments
878 ; args1 <- tcArgs fun args expected_arg_tys
880 -- Assemble the result
881 ; let fun2 = mkLHsWrapCoI co_fun fun1
882 app = mkLHsWrapCoI co_res (foldl mkHsApp fun2 args1)
884 ; return (unLoc app) }
887 mk_app_msg :: LHsExpr Name -> SDoc
888 mk_app_msg fun = sep [ ptext (sLit "The function") <+> quotes (ppr fun)
889 , ptext (sLit "is applied to")]
892 tcInferApp :: LHsExpr Name -> [LHsExpr Name] -- Function and args
893 -> TcM (HsExpr TcId, TcRhoType) -- Translated fun and args
895 tcInferApp (L _ (HsPar e)) args = tcInferApp e args
896 tcInferApp (L _ (HsApp e1 e2)) args = tcInferApp e1 (e2:args)
898 = -- Very like the tcApp version, except that there is
899 -- no expected result type passed in
900 do { (fun1, fun_tau) <- tcInferFun fun
901 ; (co_fun, expected_arg_tys, actual_res_ty)
902 <- matchExpectedFunTys (mk_app_msg fun) (length args) fun_tau
903 ; args1 <- tcArgs fun args expected_arg_tys
904 ; let fun2 = mkLHsWrapCoI co_fun fun1
905 app = foldl mkHsApp fun2 args1
906 ; return (unLoc app, actual_res_ty) }
909 tcInferFun :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
910 -- Infer and instantiate the type of a function
911 tcInferFun (L loc (HsVar name))
912 = do { (fun, ty) <- setSrcSpan loc (tcInferId name)
913 -- Don't wrap a context around a plain Id
914 ; return (L loc fun, ty) }
917 = do { (fun, fun_ty) <- tcInfer (tcMonoExpr fun)
919 -- Zonk the function type carefully, to expose any polymorphism
920 -- E.g. (( \(x::forall a. a->a). blah ) e)
921 -- We can see the rank-2 type of the lambda in time to genrealise e
922 ; fun_ty' <- zonkTcTypeCarefully fun_ty
924 ; (wrap, rho) <- deeplyInstantiate AppOrigin fun_ty'
925 ; return (mkLHsWrap wrap fun, rho) }
928 tcArgs :: LHsExpr Name -- The function (for error messages)
929 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
930 -> TcM [LHsExpr TcId] -- Resulting args
932 tcArgs fun args expected_arg_tys
933 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
936 tcArg :: LHsExpr Name -- The function (for error messages)
937 -> (LHsExpr Name, TcSigmaType, Int) -- Actual argument and expected arg type
938 -> TcM (LHsExpr TcId) -- Resulting argument
939 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no)
940 (tcPolyExprNC arg ty)
943 tcTupArgs :: [HsTupArg Name] -> [TcSigmaType] -> TcM [HsTupArg TcId]
945 = ASSERT( equalLength args tys ) mapM go (args `zip` tys)
947 go (Missing {}, arg_ty) = return (Missing arg_ty)
948 go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
949 ; return (Present expr') }
952 unifyOpFunTys :: LHsExpr Name -> Arity -> TcRhoType
953 -> TcM (CoercionI, [TcSigmaType], TcRhoType)
954 -- A wrapper for matchExpectedFunTys
955 unifyOpFunTys op arity ty = matchExpectedFunTys herald arity ty
957 herald = ptext (sLit "The operator") <+> quotes (ppr op) <+> ptext (sLit "takes")
959 ---------------------------
960 tcSyntaxOp :: CtOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
961 -- Typecheck a syntax operator, checking that it has the specified type
962 -- The operator is always a variable at this stage (i.e. renamer output)
963 -- This version assumes res_ty is a monotype
964 tcSyntaxOp orig (HsVar op) res_ty = do { (expr, rho) <- tcInferIdWithOrig orig op
965 ; tcWrapResult expr rho res_ty }
966 tcSyntaxOp _ other _ = pprPanic "tcSyntaxOp" (ppr other)
970 Note [Push result type in]
971 ~~~~~~~~~~~~~~~~~~~~~~~~~~
972 Unify with expected result before type-checking the args so that the
973 info from res_ty percolates to args. This is when we might detect a
974 too-few args situation. (One can think of cases when the opposite
975 order would give a better error message.)
976 experimenting with putting this first.
978 Here's an example where it actually makes a real difference
980 class C t a b | t a -> b
981 instance C Char a Bool
983 data P t a = forall b. (C t a b) => MkP b
984 data Q t = MkQ (forall a. P t a)
988 f2 = MkQ (MkP True :: forall a. P Char a)
990 With the change, f1 will type-check, because the 'Char' info from
991 the signature is propagated into MkQ's argument. With the check
992 in the other order, the extra signature in f2 is reqd.
995 %************************************************************************
999 %************************************************************************
1002 tcCheckId :: Name -> TcRhoType -> TcM (HsExpr TcId)
1003 tcCheckId name res_ty = do { (expr, rho) <- tcInferId name
1004 ; tcWrapResult expr rho res_ty }
1006 ------------------------
1007 tcInferId :: Name -> TcM (HsExpr TcId, TcRhoType)
1008 -- Infer type, and deeply instantiate
1009 tcInferId n = tcInferIdWithOrig (OccurrenceOf n) n
1011 ------------------------
1012 tcInferIdWithOrig :: CtOrigin -> Name -> TcM (HsExpr TcId, TcRhoType)
1013 -- Look up an occurrence of an Id, and instantiate it (deeply)
1015 tcInferIdWithOrig orig id_name =
1016 do { id_level <- getIdLevel id_name
1017 ; cur_level <- getHetMetLevel
1018 ; if (length id_level < length cur_level)
1019 then do { (lhexp, tcrho) <-
1020 tcInferRho (noLoc $ addEscapes (take ((length cur_level) - (length id_level)) cur_level) (HsVar id_name))
1021 ; return (unLoc lhexp, tcrho)
1023 else tcInferIdWithOrig' orig id_name
1026 tcInferIdWithOrig' orig id_name =
1027 do { id <- lookup_id
1028 ; (id_expr, id_rho) <- instantiateOuter orig id
1029 ; (wrap, rho) <- deeplyInstantiate orig id_rho
1030 ; return (mkHsWrap wrap id_expr, rho) }
1032 lookup_id :: TcM TcId
1034 = do { thing <- tcLookup id_name
1036 ATcId { tct_id = id, tct_level = lvl, tct_hetMetLevel = variable_hetMetLevel }
1037 -> do { check_naughty id -- Note [Local record selectors]
1038 ; checkThLocalId id lvl
1039 ; current_hetMetLevel <- getHetMetLevel
1041 (\(name1,name2) -> unifyType (TyVarTy name1) (TyVarTy name2))
1042 (zip variable_hetMetLevel current_hetMetLevel)
1046 -> do { check_naughty id
1048 -- A global cannot possibly be ill-staged in Template Haskell
1049 -- nor does it need the 'lifting' treatment
1050 -- hence no checkTh stuff here
1052 AGlobal (ADataCon con) -> return (dataConWrapId con)
1054 other -> failWithTc (bad_lookup other) }
1056 bad_lookup thing = ppr thing <+> ptext (sLit "used where a value identifer was expected")
1059 | isNaughtyRecordSelector id = failWithTc (naughtyRecordSel id)
1060 | otherwise = return ()
1062 ------------------------
1063 instantiateOuter :: CtOrigin -> TcId -> TcM (HsExpr TcId, TcSigmaType)
1064 -- Do just the first level of instantiation of an Id
1065 -- a) Deal with method sharing
1066 -- b) Deal with stupid checks
1067 -- Only look at the *outer level* of quantification
1068 -- See Note [Multiple instantiation]
1070 instantiateOuter orig id
1071 | null tvs && null theta
1072 = return (HsVar id, tau)
1075 = do { (_, tys, subst) <- tcInstTyVars tvs
1076 ; doStupidChecks id tys
1077 ; let theta' = substTheta subst theta
1078 ; traceTc "Instantiating" (ppr id <+> text "with" <+> (ppr tys $$ ppr theta'))
1079 ; wrap <- instCall orig tys theta'
1080 ; return (mkHsWrap wrap (HsVar id), substTy subst tau) }
1082 (tvs, theta, tau) = tcSplitSigmaTy (idType id)
1085 Note [Multiple instantiation]
1086 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1087 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
1088 For example, consider
1089 f :: forall a. Eq a => forall b. Ord b => a -> b
1090 At a call to f, at say [Int, Bool], it's tempting to translate the call to
1094 f_m1 :: forall b. Ord b => Int -> b
1098 f_m2 = f_m1 Bool dOrdBool
1100 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
1101 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
1103 But it's entirely possible that f_m2 will continue to float out, because it
1104 mentions no type variables. Result, f_m1 isn't in scope.
1106 Here's a concrete example that does this (test tc200):
1109 f :: Eq b => b -> a -> Int
1110 baz :: Eq a => Int -> a -> Int
1112 instance C Int where
1115 Current solution: only do the "method sharing" thing for the first type/dict
1116 application, not for the iterated ones. A horribly subtle point.
1118 Note [No method sharing]
1119 ~~~~~~~~~~~~~~~~~~~~~~~~
1120 The -fno-method-sharing flag controls what happens so far as the LIE
1121 is concerned. The default case is that for an overloaded function we
1122 generate a "method" Id, and add the Method Inst to the LIE. So you get
1124 f :: Num a => a -> a
1125 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
1126 If you specify -fno-method-sharing, the dictionary application
1127 isn't shared, so we get
1128 f :: Num a => a -> a
1129 f = /\a (d:Num a) (x:a) -> (+) a d x x
1130 This gets a bit less sharing, but
1131 a) it's better for RULEs involving overloaded functions
1132 b) perhaps fewer separated lambdas
1135 doStupidChecks :: TcId
1138 -- Check two tiresome and ad-hoc cases
1139 -- (a) the "stupid theta" for a data con; add the constraints
1140 -- from the "stupid theta" of a data constructor (sigh)
1142 doStupidChecks fun_id tys
1143 | Just con <- isDataConId_maybe fun_id -- (a)
1144 = addDataConStupidTheta con tys
1146 | fun_id `hasKey` tagToEnumKey -- (b)
1147 = failWithTc (ptext (sLit "tagToEnum# must appear applied to one argument"))
1150 = return () -- The common case
1155 Nasty check to ensure that tagToEnum# is applied to a type that is an
1156 enumeration TyCon. Unification may refine the type later, but this
1157 check won't see that, alas. It's crude, because it relies on our
1158 knowing *now* that the type is ok, which in turn relies on the
1159 eager-unification part of the type checker pushing enough information
1160 here. In theory the Right Thing to do is to have a new form of
1161 constraint but I definitely cannot face that! And it works ok as-is.
1163 Here's are two cases that should fail
1165 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1168 g = tagToEnum# 0 -- Int is not an enumeration
1170 When data type families are involved it's a bit more complicated.
1172 data instance F [Int] = A | B | C
1173 Then we want to generate something like
1174 tagToEnum# R:FListInt 3# |> co :: R:FListInt ~ F [Int]
1175 Usually that coercion is hidden inside the wrappers for
1176 constructors of F [Int] but here we have to do it explicitly.
1178 It's all grotesquely complicated.
1181 tcTagToEnum :: SrcSpan -> Name -> LHsExpr Name -> TcRhoType -> TcM (HsExpr TcId)
1182 -- tagToEnum# :: forall a. Int# -> a
1183 -- See Note [tagToEnum#] Urgh!
1184 tcTagToEnum loc fun_name arg res_ty
1185 = do { fun <- tcLookupId fun_name
1186 ; ty' <- zonkTcType res_ty
1188 -- Check that the type is algebraic
1189 ; let mb_tc_app = tcSplitTyConApp_maybe ty'
1190 Just (tc, tc_args) = mb_tc_app
1191 ; checkTc (isJust mb_tc_app)
1192 (tagToEnumError ty' doc1)
1194 -- Look through any type family
1195 ; (coi, rep_tc, rep_args) <- get_rep_ty ty' tc tc_args
1197 ; checkTc (isEnumerationTyCon rep_tc)
1198 (tagToEnumError ty' doc2)
1200 ; arg' <- tcMonoExpr arg intPrimTy
1201 ; let fun' = L loc (HsWrap (WpTyApp rep_ty) (HsVar fun))
1202 rep_ty = mkTyConApp rep_tc rep_args
1204 ; return (mkHsWrapCoI coi $ HsApp fun' arg') }
1206 doc1 = vcat [ ptext (sLit "Specify the type by giving a type signature")
1207 , ptext (sLit "e.g. (tagToEnum# x) :: Bool") ]
1208 doc2 = ptext (sLit "Result type must be an enumeration type")
1209 doc3 = ptext (sLit "No family instance for this type")
1211 get_rep_ty :: TcType -> TyCon -> [TcType]
1212 -> TcM (CoercionI, TyCon, [TcType])
1213 -- Converts a family type (eg F [a]) to its rep type (eg FList a)
1214 -- and returns a coercion between the two
1215 get_rep_ty ty tc tc_args
1216 | not (isFamilyTyCon tc)
1217 = return (IdCo ty, tc, tc_args)
1219 = do { mb_fam <- tcLookupFamInst tc tc_args
1221 Nothing -> failWithTc (tagToEnumError ty doc3)
1222 Just (rep_tc, rep_args)
1223 -> return ( ACo (mkSymCoercion (mkTyConApp co_tc rep_args))
1224 , rep_tc, rep_args )
1226 co_tc = expectJust "tcTagToEnum" $
1227 tyConFamilyCoercion_maybe rep_tc }
1229 tagToEnumError :: TcType -> SDoc -> SDoc
1230 tagToEnumError ty what
1231 = hang (ptext (sLit "Bad call to tagToEnum#")
1232 <+> ptext (sLit "at type") <+> ppr ty)
1237 %************************************************************************
1239 Template Haskell checks
1241 %************************************************************************
1244 checkThLocalId :: Id -> ThLevel -> TcM ()
1245 #ifndef GHCI /* GHCI and TH is off */
1246 --------------------------------------
1247 -- Check for cross-stage lifting
1248 checkThLocalId _id _bind_lvl
1251 #else /* GHCI and TH is on */
1252 checkThLocalId id bind_lvl
1253 = do { use_stage <- getStage -- TH case
1254 ; let use_lvl = thLevel use_stage
1255 ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
1256 ; traceTc "thLocalId" (ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
1257 ; when (use_lvl > bind_lvl) $
1258 checkCrossStageLifting id bind_lvl use_stage }
1260 --------------------------------------
1261 checkCrossStageLifting :: Id -> ThLevel -> ThStage -> TcM ()
1262 -- We are inside brackets, and (use_lvl > bind_lvl)
1263 -- Now we must check whether there's a cross-stage lift to do
1264 -- Examples \x -> [| x |]
1267 checkCrossStageLifting _ _ Comp = return ()
1268 checkCrossStageLifting _ _ Splice = return ()
1270 checkCrossStageLifting id _ (Brack _ ps_var lie_var)
1272 = -- Top-level identifiers in this module,
1273 -- (which have External Names)
1274 -- are just like the imported case:
1275 -- no need for the 'lifting' treatment
1276 -- E.g. this is fine:
1279 -- But we do need to put f into the keep-alive
1280 -- set, because after desugaring the code will
1281 -- only mention f's *name*, not f itself.
1284 | otherwise -- bind_lvl = outerLevel presumably,
1285 -- but the Id is not bound at top level
1286 = -- Nested identifiers, such as 'x' in
1287 -- E.g. \x -> [| h x |]
1288 -- We must behave as if the reference to x was
1290 -- We use 'x' itself as the splice proxy, used by
1291 -- the desugarer to stitch it all back together.
1292 -- If 'x' occurs many times we may get many identical
1293 -- bindings of the same splice proxy, but that doesn't
1294 -- matter, although it's a mite untidy.
1295 do { let id_ty = idType id
1296 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1297 -- If x is polymorphic, its occurrence sites might
1298 -- have different instantiations, so we can't use plain
1299 -- 'x' as the splice proxy name. I don't know how to
1300 -- solve this, and it's probably unimportant, so I'm
1301 -- just going to flag an error for now
1303 ; lift <- if isStringTy id_ty then
1304 do { sid <- tcLookupId DsMeta.liftStringName
1305 -- See Note [Lifting strings]
1306 ; return (HsVar sid) }
1308 setConstraintVar lie_var $ do
1309 -- Put the 'lift' constraint into the right LIE
1310 newMethodFromName (OccurrenceOf (idName id))
1311 DsMeta.liftName id_ty
1313 -- Update the pending splices
1314 ; ps <- readMutVar ps_var
1315 ; writeMutVar ps_var ((idName id, nlHsApp (noLoc lift) (nlHsVar id)) : ps)
1321 Note [Lifting strings]
1322 ~~~~~~~~~~~~~~~~~~~~~~
1323 If we see $(... [| s |] ...) where s::String, we don't want to
1324 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1325 So this conditional short-circuits the lifting mechanism to generate
1326 (liftString "xy") in that case. I didn't want to use overlapping instances
1327 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1328 errors in a polymorphic situation.
1330 If this check fails (which isn't impossible) we get another chance; see
1331 Note [Converting strings] in Convert.lhs
1333 Local record selectors
1334 ~~~~~~~~~~~~~~~~~~~~~~
1335 Record selectors for TyCons in this module are ordinary local bindings,
1336 which show up as ATcIds rather than AGlobals. So we need to check for
1337 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1340 %************************************************************************
1342 \subsection{Record bindings}
1344 %************************************************************************
1346 Game plan for record bindings
1347 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1348 1. Find the TyCon for the bindings, from the first field label.
1350 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1352 For each binding field = value
1354 3. Instantiate the field type (from the field label) using the type
1357 4 Type check the value using tcArg, passing the field type as
1358 the expected argument type.
1360 This extends OK when the field types are universally quantified.
1366 -> [TcType] -- Expected type for each field
1367 -> HsRecordBinds Name
1368 -> TcM (HsRecordBinds TcId)
1370 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1371 = do { mb_binds <- mapM do_bind rbinds
1372 ; return (HsRecFields (catMaybes mb_binds) dd) }
1374 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1375 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1376 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1377 = addErrCtxt (fieldCtxt field_lbl) $
1378 do { rhs' <- tcPolyExprNC rhs field_ty
1379 ; let field_id = mkUserLocal (nameOccName field_lbl)
1380 (nameUnique field_lbl)
1382 -- Yuk: the field_id has the *unique* of the selector Id
1383 -- (so we can find it easily)
1384 -- but is a LocalId with the appropriate type of the RHS
1385 -- (so the desugarer knows the type of local binder to make)
1386 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1388 = do { addErrTc (badFieldCon data_con field_lbl)
1391 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1392 checkMissingFields data_con rbinds
1393 | null field_labels -- Not declared as a record;
1394 -- But C{} is still valid if no strict fields
1395 = if any isBanged field_strs then
1396 -- Illegal if any arg is strict
1397 addErrTc (missingStrictFields data_con [])
1401 | otherwise = do -- A record
1402 unless (null missing_s_fields)
1403 (addErrTc (missingStrictFields data_con missing_s_fields))
1405 warn <- doptM Opt_WarnMissingFields
1406 unless (not (warn && notNull missing_ns_fields))
1407 (warnTc True (missingFields data_con missing_ns_fields))
1411 = [ fl | (fl, str) <- field_info,
1413 not (fl `elem` field_names_used)
1416 = [ fl | (fl, str) <- field_info,
1418 not (fl `elem` field_names_used)
1421 field_names_used = hsRecFields rbinds
1422 field_labels = dataConFieldLabels data_con
1424 field_info = zipEqual "missingFields"
1428 field_strs = dataConStrictMarks data_con
1431 %************************************************************************
1433 \subsection{Errors and contexts}
1435 %************************************************************************
1437 Boring and alphabetical:
1439 addExprErrCtxt :: LHsExpr Name -> TcM a -> TcM a
1440 addExprErrCtxt expr = addErrCtxt (exprCtxt expr)
1442 exprCtxt :: LHsExpr Name -> SDoc
1444 = hang (ptext (sLit "In the expression:")) 2 (ppr expr)
1446 fieldCtxt :: Name -> SDoc
1447 fieldCtxt field_name
1448 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1450 funAppCtxt :: LHsExpr Name -> LHsExpr Name -> Int -> SDoc
1451 funAppCtxt fun arg arg_no
1452 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1453 quotes (ppr fun) <> text ", namely"])
1454 2 (quotes (ppr arg))
1456 funResCtxt :: LHsExpr Name -> SDoc
1458 = ptext (sLit "In the return type of a call of") <+> quotes (ppr fun)
1460 badFieldTypes :: [(Name,TcType)] -> SDoc
1462 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1463 <> plural prs <> colon)
1464 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1466 badFieldsUpd :: HsRecFields Name a -> SDoc
1468 = hang (ptext (sLit "No constructor has all these fields:"))
1469 2 (pprQuotedList (hsRecFields rbinds))
1471 naughtyRecordSel :: TcId -> SDoc
1472 naughtyRecordSel sel_id
1473 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1474 ptext (sLit "as a function due to escaped type variables") $$
1475 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1477 notSelector :: Name -> SDoc
1479 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1481 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1482 missingStrictFields con fields
1485 rest | null fields = empty -- Happens for non-record constructors
1486 -- with strict fields
1487 | otherwise = colon <+> pprWithCommas ppr fields
1489 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1490 ptext (sLit "does not have the required strict field(s)")
1492 missingFields :: DataCon -> [FieldLabel] -> SDoc
1493 missingFields con fields
1494 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1495 <+> pprWithCommas ppr fields
1497 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1500 polySpliceErr :: Id -> SDoc
1502 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)