2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
15 module TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC,
16 tcInferRho, tcInferRhoNC, tcSyntaxOp,
17 addExprErrCtxt ) where
19 #include "HsVersions.h"
21 #ifdef GHCI /* Only if bootstrapped */
22 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
23 import qualified DsMeta
40 import TcIface ( checkWiredInTyCon )
63 import Data.List( partition )
67 %************************************************************************
69 \subsection{Main wrappers}
71 %************************************************************************
74 tcPolyExpr, tcPolyExprNC
75 :: LHsExpr Name -- Expession to type check
76 -> BoxySigmaType -- Expected type (could be a polytpye)
77 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
79 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
80 -- to add context information.
81 -- The NC version does not do so, usually because the caller wants
84 tcPolyExpr expr res_ty
85 = addExprErrCtxt expr $
86 (do {traceTc (text "tcPolyExpr") ; tcPolyExprNC expr res_ty })
88 tcPolyExprNC expr res_ty
90 = do { traceTc (text "tcPolyExprNC" <+> ppr res_ty)
91 ; (gen_fn, expr') <- tcGen res_ty emptyVarSet Nothing $ \ _ res_ty ->
92 tcPolyExprNC expr res_ty
93 -- Note the recursive call to tcPolyExpr, because the
94 -- type may have multiple layers of for-alls
95 -- E.g. forall a. Eq a => forall b. Ord b => ....
96 ; return (mkLHsWrap gen_fn expr') }
99 = tcMonoExprNC expr res_ty
102 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
103 tcPolyExprs [] [] = return []
104 tcPolyExprs (expr:exprs) (ty:tys)
105 = do { expr' <- tcPolyExpr expr ty
106 ; exprs' <- tcPolyExprs exprs tys
107 ; return (expr':exprs') }
108 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
111 tcMonoExpr, tcMonoExprNC
112 :: LHsExpr Name -- Expression to type check
113 -> BoxyRhoType -- Expected type (could be a type variable)
114 -- Definitely no foralls at the top
115 -- Can contain boxes, which will be filled in
116 -> TcM (LHsExpr TcId)
118 tcMonoExpr expr res_ty
119 = addErrCtxt (exprCtxt expr) $
120 tcMonoExprNC expr res_ty
122 tcMonoExprNC (L loc expr) res_ty
123 = ASSERT( not (isSigmaTy res_ty) )
125 do { expr' <- tcExpr expr res_ty
126 ; return (L loc expr') }
129 tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
130 tcInferRho expr = tcInfer (tcMonoExpr expr)
131 tcInferRhoNC expr = tcInfer (tcMonoExprNC expr)
135 %************************************************************************
137 tcExpr: the main expression typechecker
139 %************************************************************************
142 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
143 tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
144 = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
146 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
148 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
149 ; coi <- boxyUnify lit_ty res_ty
150 ; return $ mkHsWrapCoI coi (HsLit lit)
153 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
154 ; return (HsPar expr') }
156 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
157 ; return (HsSCC lbl expr') }
158 tcExpr (HsTickPragma info expr) res_ty
159 = do { expr' <- tcMonoExpr expr res_ty
160 ; return (HsTickPragma info expr') }
162 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
163 = do { expr' <- tcMonoExpr expr res_ty
164 ; return (HsCoreAnn lbl expr') }
166 tcExpr (HsOverLit lit) res_ty
167 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
168 ; return (HsOverLit lit') }
170 tcExpr (NegApp expr neg_expr) res_ty
171 = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
172 (mkFunTy res_ty res_ty)
173 ; expr' <- tcMonoExpr expr res_ty
174 ; return (NegApp expr' neg_expr') }
176 tcExpr (HsIPVar ip) res_ty
177 = do { let origin = IPOccOrigin ip
178 -- Implicit parameters must have a *tau-type* not a
179 -- type scheme. We enforce this by creating a fresh
180 -- type variable as its type. (Because res_ty may not
182 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
183 ; co_fn <- tcSubExp origin ip_ty res_ty
184 ; (ip', inst) <- newIPDict origin ip ip_ty
186 ; return (mkHsWrap co_fn (HsIPVar ip')) }
188 tcExpr (HsApp e1 e2) res_ty
191 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
192 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
193 go lfun@(L loc fun) args
194 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
195 tcApp fun (length args) (tcArgs lfun args) res_ty
196 ; traceTc (text "tcExpr args': " <+> ppr args')
197 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
199 tcExpr (HsLam match) res_ty
200 = do { (co_fn, match') <- tcMatchLambda match res_ty
201 ; return (mkHsWrap co_fn (HsLam match')) }
203 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
204 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
206 -- Remember to extend the lexical type-variable environment
207 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (Just ExprSigCtxt) $ \ skol_tvs res_ty ->
208 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
209 -- See Note [More instantiated than scoped] in TcBinds
210 tcMonoExprNC expr res_ty
212 ; co_fn <- tcSubExp ExprSigOrigin sig_tc_ty res_ty
213 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
215 tcExpr (HsType ty) res_ty
216 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
217 -- This is the syntax for type applications that I was planning
218 -- but there are difficulties (e.g. what order for type args)
219 -- so it's not enabled yet.
220 -- Can't eliminate it altogether from the parser, because the
221 -- same parser parses *patterns*.
225 %************************************************************************
227 Infix operators and sections
229 %************************************************************************
232 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
233 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
234 ; return (OpApp arg1' (L loc op') fix arg2') }
236 -- Left sections, equivalent to
240 -- or, if PostfixOperators is enabled, just
243 -- With PostfixOperators we don't
244 -- actually require the function to take two arguments
245 -- at all. For example, (x `not`) means (not x);
246 -- you get postfix operators! Not Haskell 98,
247 -- but it's less work and kind of useful.
249 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
250 = do dflags <- getDOpts
251 if dopt Opt_PostfixOperators dflags
252 then do (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
253 return (SectionL arg1' (L loc op'))
254 else do (co_fn, (op', arg1'))
255 <- subFunTys doc 1 res_ty Nothing
256 $ \ [arg2_ty'] res_ty' ->
257 tcApp op 2 (tc_args arg2_ty') res_ty'
258 return (mkHsWrap co_fn (SectionL arg1' (L loc op')))
260 doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
261 <+> ptext (sLit "takes one argument")
262 tc_args arg2_ty' qtvs qtys [arg1_ty, arg2_ty]
263 = do { boxyUnify arg2_ty' (substTyWith qtvs qtys arg2_ty)
264 ; arg1' <- tcArg lop 1 arg1 qtvs qtys arg1_ty
265 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
266 ; return (qtys', arg1') }
267 tc_args _ _ _ _ = panic "tcExpr SectionL"
269 -- Right sections, equivalent to \ x -> x `op` expr, or
272 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
273 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty Nothing $ \ [arg1_ty'] res_ty' ->
274 tcApp op 2 (tc_args arg1_ty') res_ty'
275 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
277 doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
278 <+> ptext (sLit "takes one argument")
279 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
280 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
281 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
282 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
283 ; return (qtys', arg2') }
284 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
286 -- For tuples, take care to preserve rigidity
287 -- E.g. case (x,y) of ....
288 -- The scrutinee should have a rigid type if x,y do
289 -- The general scheme is the same as in tcIdApp
290 tcExpr in_expr@(ExplicitTuple tup_args boxity) res_ty
291 = do { let kind = case boxity of { Boxed -> liftedTypeKind
292 ; Unboxed -> argTypeKind }
293 arity = length tup_args
294 tup_tc = tupleTyCon boxity arity
295 mk_tup_res_ty arg_tys
296 = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
297 (mkTyConApp tup_tc arg_tys)
299 ; checkWiredInTyCon tup_tc -- Ensure instances are available
300 ; tvs <- newBoxyTyVars (replicate arity kind)
301 ; let arg_tys1 = map mkTyVarTy tvs
302 ; arg_tys2 <- preSubType tvs (mkVarSet tvs) (mk_tup_res_ty arg_tys1) res_ty
304 ; let go (Missing _, arg_ty) = return (Missing arg_ty)
305 go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
306 ; return (Present expr') }
307 ; tup_args' <- mapM go (tup_args `zip` arg_tys2)
309 ; arg_tys3 <- mapM refineBox arg_tys2
310 ; co_fn <- tcSubExp TupleOrigin (mk_tup_res_ty arg_tys3) res_ty
311 ; return (mkHsWrap co_fn (ExplicitTuple tup_args' boxity)) }
315 tcExpr (HsLet binds expr) res_ty
316 = do { (binds', expr') <- tcLocalBinds binds $
317 tcMonoExpr expr res_ty
318 ; return (HsLet binds' expr') }
320 tcExpr (HsCase scrut matches) exp_ty
321 = do { -- We used to typecheck the case alternatives first.
322 -- The case patterns tend to give good type info to use
323 -- when typechecking the scrutinee. For example
326 -- will report that map is applied to too few arguments
328 -- But now, in the GADT world, we need to typecheck the scrutinee
329 -- first, to get type info that may be refined in the case alternatives
330 (scrut', scrut_ty) <- tcInferRho scrut
332 ; traceTc (text "HsCase" <+> ppr scrut_ty)
333 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
334 ; return (HsCase scrut' matches') }
336 match_ctxt = MC { mc_what = CaseAlt,
339 tcExpr (HsIf pred b1 b2) res_ty
340 = do { pred' <- tcMonoExpr pred boolTy
341 ; b1' <- tcMonoExpr b1 res_ty
342 ; b2' <- tcMonoExpr b2 res_ty
343 ; return (HsIf pred' b1' b2') }
345 tcExpr (HsDo do_or_lc stmts body _) res_ty
346 = tcDoStmts do_or_lc stmts body res_ty
348 tcExpr in_expr@(ExplicitList _ exprs) res_ty
349 = do { (elt_ty, coi) <- boxySplitListTy res_ty
350 ; exprs' <- mapM (tc_elt elt_ty) exprs
351 ; when (null exprs) (zapToMonotype elt_ty >> return ())
352 -- If there are no expressions in the comprehension
353 -- we must still fill in the box
355 -- The GHC front end never generates an empty ExplicitList
356 -- (instead it generates the [] data constructor) but
357 -- Template Haskell might. We could fix the bit of
358 -- TH that generates ExplicitList, but it seems less
359 -- fragile to just handle the case here.
360 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
362 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
364 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
365 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
366 ; exprs' <- mapM (tc_elt elt_ty) exprs
367 ; when (null exprs) (zapToMonotype elt_ty >> return ())
368 -- If there are no expressions in the comprehension
369 -- we must still fill in the box
370 -- (Not needed for [] and () becuase they happen
371 -- to parse as data constructors.)
372 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
374 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
376 tcExpr (HsProc pat cmd) res_ty
377 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
378 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
380 tcExpr e@(HsArrApp _ _ _ _ _) _
381 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
382 ptext (sLit "was found where an expression was expected")])
384 tcExpr e@(HsArrForm _ _ _) _
385 = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
386 ptext (sLit "was found where an expression was expected")])
389 %************************************************************************
391 Record construction and update
393 %************************************************************************
396 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
397 = do { data_con <- tcLookupDataCon con_name
399 -- Check for missing fields
400 ; checkMissingFields data_con rbinds
402 ; let arity = dataConSourceArity data_con
403 check_fields qtvs qtys arg_tys
404 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
405 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
406 ; qtys' <- mapM refineBoxToTau qtys
407 ; return (qtys', rbinds') }
408 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
409 -- filled, which is the invariant expected by tcIdApp
410 -- How could this not be the case? Consider a record construction
411 -- that does not mention all the fields.
413 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
415 ; return (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
418 Note [Type of a record update]
419 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
420 The main complication with RecordUpd is that we need to explicitly
421 handle the *non-updated* fields. Consider:
423 data T a b c = MkT1 { fa :: a, fb :: (b,c) }
424 | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
427 upd :: T a b c -> (b',c) -> T a b' c
428 upd t x = t { fb = x}
430 The result type should be (T a b' c)
431 not (T a b c), because 'b' *is not* mentioned in a non-updated field
432 not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
433 NB that it's not good enough to look at just one constructor; we must
434 look at them all; cf Trac #3219
436 After all, upd should be equivalent to:
442 So we need to give a completely fresh type to the result record,
443 and then constrain it by the fields that are *not* updated ("p" above).
444 We call these the "fixed" type variables, and compute them in getFixedTyVars.
446 Note that because MkT3 doesn't contain all the fields being updated,
447 its RHS is simply an error, so it doesn't impose any type constraints.
448 Hence the use of 'relevant_cont'.
450 Note [Implict type sharing]
451 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
452 We also take into account any "implicit" non-update fields. For example
453 data T a b where { MkT { f::a } :: T a a; ... }
454 So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
459 upd :: T a b -> a -> T a b
460 upd (t::T a b) (x::a)
461 = case t of { MkT (co:a~b) (_:a) -> MkT co x }
462 We can't give it the more general type
463 upd :: T a b -> c -> T c b
465 Note [Criteria for update]
466 ~~~~~~~~~~~~~~~~~~~~~~~~~~
467 We want to allow update for existentials etc, provided the updated
468 field isn't part of the existential. For example, this should be ok.
469 data T a where { MkT { f1::a, f2::b->b } :: T a }
473 The criterion we use is this:
475 The types of the updated fields
476 mention only the universally-quantified type variables
477 of the data constructor
479 NB: this is not (quite) the same as being a "naughty" record selector
480 (See Note [Naughty record selectors]) in TcTyClsDecls), at least
481 in the case of GADTs. Consider
482 data T a where { MkT :: { f :: a } :: T [a] }
483 Then f is not "naughty" because it has a well-typed record selector.
484 But we don't allow updates for 'f'. (One could consider trying to
485 allow this, but it makes my head hurt. Badly. And no one has asked
488 In principle one could go further, and allow
490 g t = t { f2 = \x -> x }
491 because the expression is polymorphic...but that seems a bridge too far.
493 Note [Data family example]
494 ~~~~~~~~~~~~~~~~~~~~~~~~~~
495 data instance T (a,b) = MkT { x::a, y::b }
497 data :TP a b = MkT { a::a, y::b }
498 coTP a b :: T (a,b) ~ :TP a b
500 Suppose r :: T (t1,t2), e :: t3
501 Then r { x=e } :: T (t3,t1)
504 MkT x y -> MkT e y |> co2
505 where co1 :: T (t1,t2) ~ :TP t1 t2
506 co2 :: :TP t3 t2 ~ T (t3,t2)
507 The wrapping with co2 is done by the constructor wrapper for MkT
511 In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
513 * cons are the data constructors to be updated
515 * in_inst_tys, out_inst_tys have same length, and instantiate the
516 *representation* tycon of the data cons. In Note [Data
517 family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
520 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
521 = ASSERT( notNull upd_fld_names )
524 -- Check that the field names are really field names
525 ; sel_ids <- mapM tcLookupField upd_fld_names
526 -- The renamer has already checked that
527 -- selectors are all in scope
528 ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
529 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
530 not (isRecordSelector sel_id), -- Excludes class ops
531 let L loc fld_name = hsRecFieldId fld ]
532 ; unless (null bad_guys) (sequence bad_guys >> failM)
535 -- Figure out the tycon and data cons from the first field name
536 ; let -- It's OK to use the non-tc splitters here (for a selector)
538 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
539 data_cons = tyConDataCons tycon -- it's not a field label
540 -- NB: for a data type family, the tycon is the instance tycon
542 relevant_cons = filter is_relevant data_cons
543 is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
544 -- A constructor is only relevant to this process if
545 -- it contains *all* the fields that are being updated
546 -- Other ones will cause a runtime error if they occur
548 -- Take apart a representative constructor
549 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
550 (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
551 con1_flds = dataConFieldLabels con1
552 con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
555 -- Check that at least one constructor has all the named fields
556 -- i.e. has an empty set of bad fields returned by badFields
557 ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
559 -- STEP 3 Note [Criteria for update]
560 -- Check that each updated field is polymorphic; that is, its type
561 -- mentions only the universally-quantified variables of the data con
562 ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
563 (upd_flds1_w_tys, fixed_flds1_w_tys) = partition is_updated flds1_w_tys
564 is_updated (fld,ty) = fld `elem` upd_fld_names
566 bad_upd_flds = filter bad_fld upd_flds1_w_tys
567 con1_tv_set = mkVarSet con1_tvs
568 bad_fld (fld, ty) = fld `elem` upd_fld_names &&
569 not (tyVarsOfType ty `subVarSet` con1_tv_set)
570 ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
572 -- STEP 4 Note [Type of a record update]
573 -- Figure out types for the scrutinee and result
574 -- Both are of form (T a b c), with fresh type variables, but with
575 -- common variables where the scrutinee and result must have the same type
576 -- These are variables that appear in *any* arg of *any* of the
577 -- relevant constructors *except* in the updated fields
579 ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
580 is_fixed_tv tv = tv `elemVarSet` fixed_tvs
581 mk_inst_ty tv result_inst_ty
582 | is_fixed_tv tv = return result_inst_ty -- Same as result type
583 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
585 ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
586 ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
588 ; let result_ty = substTy result_inst_env con1_res_ty
589 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
590 scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
591 scrut_ty = substTy scrut_subst con1_res_ty
594 -- Typecheck the thing to be updated, and the bindings
595 ; record_expr' <- tcMonoExpr record_expr scrut_ty
596 ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
598 ; let origin = RecordUpdOrigin
599 ; co_fn <- tcSubExp origin result_ty res_ty
601 -- STEP 6: Deal with the stupid theta
602 ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
603 ; instStupidTheta origin theta'
605 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
606 ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
607 = WpCast $ mkTyConApp co_con scrut_inst_tys
612 ; return (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
613 relevant_cons scrut_inst_tys result_inst_tys)) }
615 upd_fld_names = hsRecFields rbinds
617 getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
618 -- These tyvars must not change across the updates
619 getFixedTyVars tvs1 cons
620 = mkVarSet [tv1 | con <- cons
621 , let (tvs, theta, arg_tys, _) = dataConSig con
622 flds = dataConFieldLabels con
623 fixed_tvs = exactTyVarsOfTypes fixed_tys
624 -- fixed_tys: See Note [Type of a record update]
625 `unionVarSet` tyVarsOfTheta theta
626 -- Universally-quantified tyvars that
627 -- appear in any of the *implicit*
628 -- arguments to the constructor are fixed
629 -- See Note [Implict type sharing]
631 fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
632 , not (fld `elem` upd_fld_names)]
633 , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
634 , tv `elemVarSet` fixed_tvs ]
637 %************************************************************************
639 Arithmetic sequences e.g. [a,b..]
640 and their parallel-array counterparts e.g. [: a,b.. :]
643 %************************************************************************
646 tcExpr (ArithSeq _ seq@(From expr)) res_ty
647 = do { (elt_ty, coi) <- boxySplitListTy res_ty
648 ; expr' <- tcPolyExpr expr elt_ty
649 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
651 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
653 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
654 = do { (elt_ty, coi) <- boxySplitListTy res_ty
655 ; expr1' <- tcPolyExpr expr1 elt_ty
656 ; expr2' <- tcPolyExpr expr2 elt_ty
657 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
658 elt_ty enumFromThenName
659 ; return $ mkHsWrapCoI coi
660 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
662 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
663 = do { (elt_ty, coi) <- boxySplitListTy res_ty
664 ; expr1' <- tcPolyExpr expr1 elt_ty
665 ; expr2' <- tcPolyExpr expr2 elt_ty
666 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
667 elt_ty enumFromToName
668 ; return $ mkHsWrapCoI coi
669 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
671 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
672 = do { (elt_ty, coi) <- boxySplitListTy res_ty
673 ; expr1' <- tcPolyExpr expr1 elt_ty
674 ; expr2' <- tcPolyExpr expr2 elt_ty
675 ; expr3' <- tcPolyExpr expr3 elt_ty
676 ; eft <- newMethodFromName (ArithSeqOrigin seq)
677 elt_ty enumFromThenToName
678 ; return $ mkHsWrapCoI coi
679 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
681 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
682 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
683 ; expr1' <- tcPolyExpr expr1 elt_ty
684 ; expr2' <- tcPolyExpr expr2 elt_ty
685 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
686 elt_ty enumFromToPName
687 ; return $ mkHsWrapCoI coi
688 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
690 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
691 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
692 ; expr1' <- tcPolyExpr expr1 elt_ty
693 ; expr2' <- tcPolyExpr expr2 elt_ty
694 ; expr3' <- tcPolyExpr expr3 elt_ty
695 ; eft <- newMethodFromName (PArrSeqOrigin seq)
696 elt_ty enumFromThenToPName
697 ; return $ mkHsWrapCoI coi
698 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
700 tcExpr (PArrSeq _ _) _
701 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
702 -- the parser shouldn't have generated it and the renamer shouldn't have
707 %************************************************************************
711 %************************************************************************
714 #ifdef GHCI /* Only if bootstrapped */
715 -- Rename excludes these cases otherwise
716 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
717 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
719 tcExpr e@(HsQuasiQuoteE _) res_ty =
720 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
725 %************************************************************************
729 %************************************************************************
732 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
736 %************************************************************************
740 %************************************************************************
743 ---------------------------
744 tcApp :: HsExpr Name -- Function
745 -> Arity -- Number of args reqd
746 -> ArgChecker results
747 -> BoxyRhoType -- Result type
748 -> TcM (HsExpr TcId, results)
750 -- (tcFun fun n_args arg_checker res_ty)
751 -- The argument type checker, arg_checker, will be passed exactly n_args types
753 tcApp (HsVar fun_name) n_args arg_checker res_ty
754 = tcIdApp fun_name n_args arg_checker res_ty
756 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
757 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
758 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
759 ; arg_tys' <- mapM readFilledBox arg_boxes
760 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
761 ; return (fun', args') }
763 ---------------------------
764 tcIdApp :: Name -- Function
765 -> Arity -- Number of args reqd
766 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
767 -> BoxyRhoType -- Result type
768 -> TcM (HsExpr TcId, results)
770 -- Call (f e1 ... en) :: res_ty
771 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
772 -- (where k <= n; fres has the rest)
773 -- NB: if k < n then the function doesn't have enough args, and
774 -- presumably fres is a type variable that we are going to
775 -- instantiate with a function type
777 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
779 tcIdApp fun_name n_args arg_checker res_ty
780 = do { let orig = OccurrenceOf fun_name
781 ; (fun, fun_ty) <- lookupFun orig fun_name
783 -- Split up the function type
784 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
785 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
787 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
788 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
789 res_qtvs = exactTyVarsOfType fun_res_ty
790 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
791 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
792 k = length fun_arg_tys -- k <= n_args
793 n_missing_args = n_args - k -- Always >= 0
795 -- Match the result type of the function with the
796 -- result type of the context, to get an inital substitution
797 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
798 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
799 res_ty' = mkFunTys extra_arg_tys' res_ty
800 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
802 -- Typecheck the arguments!
803 -- Doing so will fill arg_qtvs and extra_arg_tys'
804 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
806 -- Strip boxes from the qtvs that have been filled in by the arg checking
807 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
809 -- Result subsumption
810 -- This fills in res_qtvs
811 ; let res_subst = zipOpenTvSubst qtvs qtys''
812 fun_res_ty'' = substTy res_subst fun_res_ty
813 res_ty'' = mkFunTys extra_arg_tys'' res_ty
814 ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
816 -- And pack up the results
817 -- By applying the coercion just to the *function* we can make
818 -- tcFun work nicely for OpApp and Sections too
819 ; fun' <- instFun orig fun res_subst tv_theta_prs
820 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
821 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
822 ; return (mkHsWrap co_fn' fun', args') }
825 Note [Silly type synonyms in smart-app]
826 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
827 When we call sripBoxyType, all of the boxes should be filled
828 in. But we need to be careful about type synonyms:
832 In the call (f x) we'll typecheck x, expecting it to have type
833 (T box). Usually that would fill in the box, but in this case not;
834 because 'a' is discarded by the silly type synonym T. So we must
835 use exactTyVarsOfType to figure out which type variables are free
836 in the argument type.
839 -- tcId is a specialisation of tcIdApp when there are no arguments
840 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
845 -> BoxyRhoType -- Result type
847 tcId orig fun_name res_ty
848 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
849 ; (fun, fun_ty) <- lookupFun orig fun_name
851 -- Split up the function type
852 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
853 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
854 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
855 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
857 -- Do the subsumption check wrt the result type
858 ; let res_subst = zipTopTvSubst qtvs qtv_tys
859 fun_tau' = substTy res_subst fun_tau
861 ; co_fn <- tcSubExp orig fun_tau' res_ty
863 -- And pack up the results
864 ; fun' <- instFun orig fun res_subst tv_theta_prs
865 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
866 ; return (mkHsWrap co_fn fun') }
868 -- Note [Push result type in]
870 -- Unify with expected result before (was: after) type-checking the args
871 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
872 -- This is when we might detect a too-few args situation.
873 -- (One can think of cases when the opposite order would give
874 -- a better error message.)
875 -- [March 2003: I'm experimenting with putting this first. Here's an
876 -- example where it actually makes a real difference
877 -- class C t a b | t a -> b
878 -- instance C Char a Bool
880 -- data P t a = forall b. (C t a b) => MkP b
881 -- data Q t = MkQ (forall a. P t a)
884 -- f1 = MkQ (MkP True)
885 -- f2 = MkQ (MkP True :: forall a. P Char a)
887 -- With the change, f1 will type-check, because the 'Char' info from
888 -- the signature is propagated into MkQ's argument. With the check
889 -- in the other order, the extra signature in f2 is reqd.]
891 ---------------------------
892 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
893 -- Typecheck a syntax operator, checking that it has the specified type
894 -- The operator is always a variable at this stage (i.e. renamer output)
895 -- This version assumes ty is a monotype
896 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
897 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
899 ---------------------------
900 instFun :: InstOrigin
902 -> TvSubst -- The instantiating substitution
903 -> [([TyVar], ThetaType)] -- Stuff to instantiate
906 instFun orig fun subst []
907 = return fun -- Common short cut
909 instFun orig fun subst tv_theta_prs
910 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
911 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
912 -- Make two ad-hoc checks
913 ; doStupidChecks fun ty_theta_prs'
915 -- Now do normal instantiation
916 ; method_sharing <- doptM Opt_MethodSharing
917 ; result <- go method_sharing True fun ty_theta_prs'
918 ; traceTc (text "instFun result" <+> ppr result)
922 subst_pr (tvs, theta)
923 = (substTyVars subst tvs, substTheta subst theta)
925 go _ _ fun [] = do {traceTc (text "go _ _ fun [] returns" <+> ppr fun) ; return fun }
927 go method_sharing True (HsVar fun_id) ((tys,theta) : prs)
928 | want_method_inst method_sharing theta
929 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
930 ; meth_id <- newMethodWithGivenTy orig fun_id tys
931 ; go method_sharing False (HsVar meth_id) prs }
932 -- Go round with 'False' to prevent further use
933 -- of newMethod: see Note [Multiple instantiation]
935 go method_sharing _ fun ((tys, theta) : prs)
936 = do { co_fn <- instCall orig tys theta
937 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
938 ; go method_sharing False (HsWrap co_fn fun) prs }
940 -- See Note [No method sharing]
941 want_method_inst method_sharing theta = not (null theta) -- Overloaded
945 Note [Multiple instantiation]
946 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
947 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
948 For example, consider
949 f :: forall a. Eq a => forall b. Ord b => a -> b
950 At a call to f, at say [Int, Bool], it's tempting to translate the call to
954 f_m1 :: forall b. Ord b => Int -> b
958 f_m2 = f_m1 Bool dOrdBool
960 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
961 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
963 But it's entirely possible that f_m2 will continue to float out, because it
964 mentions no type variables. Result, f_m1 isn't in scope.
966 Here's a concrete example that does this (test tc200):
969 f :: Eq b => b -> a -> Int
970 baz :: Eq a => Int -> a -> Int
975 Current solution: only do the "method sharing" thing for the first type/dict
976 application, not for the iterated ones. A horribly subtle point.
978 Note [No method sharing]
979 ~~~~~~~~~~~~~~~~~~~~~~~~
980 The -fno-method-sharing flag controls what happens so far as the LIE
981 is concerned. The default case is that for an overloaded function we
982 generate a "method" Id, and add the Method Inst to the LIE. So you get
985 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
986 If you specify -fno-method-sharing, the dictionary application
987 isn't shared, so we get
989 f = /\a (d:Num a) (x:a) -> (+) a d x x
990 This gets a bit less sharing, but
991 a) it's better for RULEs involving overloaded functions
992 b) perhaps fewer separated lambdas
996 tcArgs implements a left-to-right order, which goes beyond what is described in the
997 impredicative type inference paper. In particular, it allows
999 where runST :: (forall s. ST s a) -> a
1000 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
1001 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
1002 before checking foo. The left-to-right order really helps here.
1005 tcArgs :: LHsExpr Name -- The function (for error messages)
1006 -> [LHsExpr Name] -- Actual args
1007 -> ArgChecker [LHsExpr TcId]
1009 type ArgChecker results
1010 = [TyVar] -> [TcSigmaType] -- Current instantiation
1011 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
1012 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
1014 tcArgs fun args qtvs qtys arg_tys
1015 = go 1 qtys args arg_tys
1017 go n qtys [] [] = return (qtys, [])
1018 go n qtys (arg:args) (arg_ty:arg_tys)
1019 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
1020 ; qtys' <- mapM refineBox qtys -- Exploit new info
1021 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
1022 ; return (qtys'', arg':args') }
1023 go n qtys args arg_tys = panic "tcArgs"
1025 tcArg :: LHsExpr Name -- The function
1026 -> Int -- and arg number (for error messages)
1028 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
1030 -> TcM (LHsExpr TcId) -- Resulting argument
1031 tcArg fun arg_no arg qtvs qtys ty
1032 = addErrCtxt (funAppCtxt fun arg arg_no) $
1033 tcPolyExprNC arg (substTyWith qtvs qtys ty)
1039 Nasty check to ensure that tagToEnum# is applied to a type that is an
1040 enumeration TyCon. Unification may refine the type later, but this
1041 check won't see that, alas. It's crude but it works.
1043 Here's are two cases that should fail
1045 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
1048 g = tagToEnum# 0 -- Int is not an enumeration
1052 doStupidChecks :: HsExpr TcId
1053 -> [([TcType], ThetaType)]
1055 -- Check two tiresome and ad-hoc cases
1056 -- (a) the "stupid theta" for a data con; add the constraints
1057 -- from the "stupid theta" of a data constructor (sigh)
1058 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
1060 doStupidChecks (HsVar fun_id) ((tys,_):_)
1061 | Just con <- isDataConId_maybe fun_id -- (a)
1062 = addDataConStupidTheta con tys
1064 | fun_id `hasKey` tagToEnumKey -- (b)
1065 = do { tys' <- zonkTcTypes tys
1066 ; checkTc (ok tys') (tagToEnumError tys')
1070 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
1071 Just (tc,_) -> isEnumerationTyCon tc
1074 doStupidChecks fun tv_theta_prs
1075 = return () -- The common case
1079 = hang (ptext (sLit "Bad call to tagToEnum#") <+> at_type)
1080 2 (vcat [ptext (sLit "Specify the type by giving a type signature"),
1081 ptext (sLit "e.g. (tagToEnum# x) :: Bool")])
1083 at_type | null tys = empty -- Probably never happens
1084 | otherwise = ptext (sLit "at type") <+> ppr (head tys)
1087 %************************************************************************
1089 \subsection{@tcId@ typechecks an identifier occurrence}
1091 %************************************************************************
1094 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
1095 lookupFun orig id_name
1096 = do { thing <- tcLookup id_name
1098 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
1100 wrap_id = dataConWrapId con
1103 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1104 | otherwise -> return (HsVar id, idType id)
1105 -- A global cannot possibly be ill-staged
1106 -- nor does it need the 'lifting' treatment
1108 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
1109 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
1110 -- Note [Local record selectors]
1112 -> do { thLocalId orig id ty lvl
1114 Unrefineable -> return (HsVar id, ty)
1115 Rigid co -> return (mkHsWrap co (HsVar id), ty)
1116 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
1117 WobblyInvisible -> failWithTc (ppr id_name <+> ptext (sLit " not in scope because it has a wobbly type (solution: add a type annotation)"))
1120 other -> failWithTc (ppr other <+> ptext (sLit "used where a value identifer was expected"))
1123 #ifndef GHCI /* GHCI and TH is off */
1124 --------------------------------------
1125 thLocalId :: InstOrigin -> Id -> TcType -> ThLevel -> TcM ()
1126 -- Check for cross-stage lifting
1127 thLocalId orig id id_ty bind_lvl
1130 #else /* GHCI and TH is on */
1131 thLocalId orig id id_ty bind_lvl
1132 = do { use_stage <- getStage -- TH case
1133 ; let use_lvl = thLevel use_stage
1134 ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
1135 ; traceTc (text "thLocalId" <+> ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
1136 ; when (use_lvl > bind_lvl) $
1137 checkCrossStageLifting orig id id_ty bind_lvl use_stage }
1139 --------------------------------------
1140 checkCrossStageLifting :: InstOrigin -> Id -> TcType -> ThLevel -> ThStage -> TcM ()
1141 -- We are inside brackets, and (use_lvl > bind_lvl)
1142 -- Now we must check whether there's a cross-stage lift to do
1143 -- Examples \x -> [| x |]
1146 checkCrossStageLifting _ _ _ _ Comp = return ()
1147 checkCrossStageLifting _ _ _ _ Splice = return ()
1149 checkCrossStageLifting orig id id_ty bind_lvl (Brack _ ps_var lie_var)
1151 = -- Top-level identifiers in this module,
1152 -- (which have External Names)
1153 -- are just like the imported case:
1154 -- no need for the 'lifting' treatment
1155 -- E.g. this is fine:
1158 -- But we do need to put f into the keep-alive
1159 -- set, because after desugaring the code will
1160 -- only mention f's *name*, not f itself.
1163 | otherwise -- bind_lvl = outerLevel presumably,
1164 -- but the Id is not bound at top level
1165 = -- Nested identifiers, such as 'x' in
1166 -- E.g. \x -> [| h x |]
1167 -- We must behave as if the reference to x was
1169 -- We use 'x' itself as the splice proxy, used by
1170 -- the desugarer to stitch it all back together.
1171 -- If 'x' occurs many times we may get many identical
1172 -- bindings of the same splice proxy, but that doesn't
1173 -- matter, although it's a mite untidy.
1174 do { checkTc (isTauTy id_ty) (polySpliceErr id)
1175 -- If x is polymorphic, its occurrence sites might
1176 -- have different instantiations, so we can't use plain
1177 -- 'x' as the splice proxy name. I don't know how to
1178 -- solve this, and it's probably unimportant, so I'm
1179 -- just going to flag an error for now
1181 ; id_ty' <- zapToMonotype id_ty
1182 -- The id_ty might have an OpenTypeKind, but we
1183 -- can't instantiate the Lift class at that kind,
1184 -- so we zap it to a LiftedTypeKind monotype
1185 -- C.f. the call in TcPat.newLitInst
1187 ; lift <- if isStringTy id_ty' then
1188 tcLookupId DsMeta.liftStringName
1189 -- See Note [Lifting strings]
1191 setLIEVar lie_var $ do -- Put the 'lift' constraint into the right LIE
1192 newMethodFromName orig id_ty' DsMeta.liftName
1194 -- Update the pending splices
1195 ; ps <- readMutVar ps_var
1196 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1202 Note [Lifting strings]
1203 ~~~~~~~~~~~~~~~~~~~~~~
1204 If we see $(... [| s |] ...) where s::String, we don't want to
1205 generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
1206 So this conditional short-circuits the lifting mechanism to generate
1207 (liftString "xy") in that case. I didn't want to use overlapping instances
1208 for the Lift class in TH.Syntax, because that can lead to overlapping-instance
1209 errors in a polymorphic situation.
1211 If this check fails (which isn't impossible) we get another chance; see
1212 Note [Converting strings] in Convert.lhs
1214 Local record selectors
1215 ~~~~~~~~~~~~~~~~~~~~~~
1216 Record selectors for TyCons in this module are ordinary local bindings,
1217 which show up as ATcIds rather than AGlobals. So we need to check for
1218 naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
1221 %************************************************************************
1223 \subsection{Record bindings}
1225 %************************************************************************
1227 Game plan for record bindings
1228 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1229 1. Find the TyCon for the bindings, from the first field label.
1231 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1233 For each binding field = value
1235 3. Instantiate the field type (from the field label) using the type
1238 4 Type check the value using tcArg, passing the field type as
1239 the expected argument type.
1241 This extends OK when the field types are universally quantified.
1247 -> [TcType] -- Expected type for each field
1248 -> HsRecordBinds Name
1249 -> TcM (HsRecordBinds TcId)
1251 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1252 = do { mb_binds <- mapM do_bind rbinds
1253 ; return (HsRecFields (catMaybes mb_binds) dd) }
1255 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1256 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1257 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1258 = addErrCtxt (fieldCtxt field_lbl) $
1259 do { rhs' <- tcPolyExprNC rhs field_ty
1260 ; let field_id = mkUserLocal (nameOccName field_lbl)
1261 (nameUnique field_lbl)
1263 -- Yuk: the field_id has the *unique* of the selector Id
1264 -- (so we can find it easily)
1265 -- but is a LocalId with the appropriate type of the RHS
1266 -- (so the desugarer knows the type of local binder to make)
1267 ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
1269 = do { addErrTc (badFieldCon data_con field_lbl)
1272 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1273 checkMissingFields data_con rbinds
1274 | null field_labels -- Not declared as a record;
1275 -- But C{} is still valid if no strict fields
1276 = if any isMarkedStrict field_strs then
1277 -- Illegal if any arg is strict
1278 addErrTc (missingStrictFields data_con [])
1282 | otherwise = do -- A record
1283 unless (null missing_s_fields)
1284 (addErrTc (missingStrictFields data_con missing_s_fields))
1286 warn <- doptM Opt_WarnMissingFields
1287 unless (not (warn && notNull missing_ns_fields))
1288 (warnTc True (missingFields data_con missing_ns_fields))
1292 = [ fl | (fl, str) <- field_info,
1294 not (fl `elem` field_names_used)
1297 = [ fl | (fl, str) <- field_info,
1298 not (isMarkedStrict str),
1299 not (fl `elem` field_names_used)
1302 field_names_used = hsRecFields rbinds
1303 field_labels = dataConFieldLabels data_con
1305 field_info = zipEqual "missingFields"
1309 field_strs = dataConStrictMarks data_con
1312 %************************************************************************
1314 \subsection{Errors and contexts}
1316 %************************************************************************
1318 Boring and alphabetical:
1320 addExprErrCtxt :: OutputableBndr id => LHsExpr id -> TcM a -> TcM a
1321 addExprErrCtxt expr = addErrCtxt (exprCtxt (unLoc expr))
1324 = hang (ptext (sLit "In the expression:")) 4 (ppr expr)
1326 fieldCtxt field_name
1327 = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
1329 funAppCtxt fun arg arg_no
1330 = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
1331 quotes (ppr fun) <> text ", namely"])
1332 4 (quotes (ppr arg))
1335 = hang (ptext (sLit "Record update for insufficiently polymorphic field")
1336 <> plural prs <> colon)
1337 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
1340 = hang (ptext (sLit "No constructor has all these fields:"))
1341 4 (pprQuotedList (hsRecFields rbinds))
1343 naughtyRecordSel sel_id
1344 = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
1345 ptext (sLit "as a function due to escaped type variables") $$
1346 ptext (sLit "Probable fix: use pattern-matching syntax instead")
1349 = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
1351 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1352 missingStrictFields con fields
1355 rest | null fields = empty -- Happens for non-record constructors
1356 -- with strict fields
1357 | otherwise = colon <+> pprWithCommas ppr fields
1359 header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
1360 ptext (sLit "does not have the required strict field(s)")
1362 missingFields :: DataCon -> [FieldLabel] -> SDoc
1363 missingFields con fields
1364 = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
1365 <+> pprWithCommas ppr fields
1367 -- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
1370 polySpliceErr :: Id -> SDoc
1372 = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)