import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
, ds_cls :: Class
, ds_tys :: [Type]
, ds_tc :: TyCon
+ , ds_tc_args :: [Type]
, ds_newtype :: Bool }
-- This spec implies a dfun declaration of the form
-- df :: forall tvs. theta => C tys
-- The tyvars bind all the variables in the theta
-- For family indexes, the tycon in
-- in ds_tys is the *family* tycon
- -- in ds_tc is the *representation* tycon
+ -- in ds_tc, ds_tc_args is the *representation* tycon
-- For non-family tycons, both are the same
-- ds_newtype = True <=> Newtype deriving
| otherwise = rm_dups (b:acc) bs
- rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
- = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
+ rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
+ = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs })
= -- Bring the right type variables into
spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
- , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc
+ , ds_cls = cls, ds_tys = inst_tys
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` all_constraints
, ds_newtype = False }
; return (if isJust mtheta then Right spec -- Specified context
else Left spec) } -- Infer context
-mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta
+mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
-- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
; loc <- getSrcSpanM
; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
- , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc
+ , ds_cls = cls, ds_tys = [mkTyConApp tycon []]
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
------------------------------------------------------------------
; loc <- getSrcSpanM
; let spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs
- , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon
+ , ds_cls = cls, ds_tys = inst_tys
+ , ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` all_preds
, ds_newtype = True }
; return (if isJust mtheta then Right spec
nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
-- For newtype T a b = MkT (S a a b), the TyCon machinery already
- -- eta-reduces the represenation type, so we know that
+ -- eta-reduces the representation type, so we know that
-- T a ~ S a a
-- That's convenient here, because we may have to apply
-- it to fewer than its original complement of arguments
-- eg not: newtype T ... deriving( ST )
-- because ST needs *2* type params
&& eta_ok -- Eta reduction works
- && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
- -- newtype A = MkA [A]
- -- Don't want
- -- instance Eq [A] => Eq A !!
- -- Here's a recursive newtype that's actually OK
- -- newtype S1 = S1 [T1 ()]
- -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
- -- It's currently rejected. Oh well.
- -- In fact we generate an instance decl that has method of form
- -- meth @ instTy = meth @ repTy
- -- (no coerce's). We'd need a coerce if we wanted to handle
- -- recursive newtypes too
+-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
-- Check that eta reduction is OK
eta_ok = nt_eta_arity <= length rep_tc_args
]
\end{code}
+Note [Recursive newtypes]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Newtype deriving works fine, even if the newtype is recursive.
+e.g. newtype S1 = S1 [T1 ()]
+ newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
+Remember, too, that type families are curretly (conservatively) given
+a recursive flag, so this also allows newtype deriving to work
+for type famillies.
+
+We used to exclude recursive types, because we had a rather simple
+minded way of generating the instance decl:
+ newtype A = MkA [A]
+ instance Eq [A] => Eq A -- Makes typechecker loop!
+But now we require a simple context, so it's ok.
+
%************************************************************************
%* *
| otherwise
= do { -- Extend the inst info from the explicit instance decls
-- with the current set of solutions, and simplify each RHS
- let inst_specs = zipWithEqual "add_solns" (mkInstance2 oflag)
+ let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
current_solns infer_specs
; new_solns <- checkNoErrs $
extendLocalInstEnv inst_specs $
; return (sortLe (<=) theta) } -- Canonicalise before returning the solution
------------------------------------------------------------------
-mkInstance1 :: OverlapFlag -> DerivSpec -> Instance
-mkInstance1 overlap_flag spec = mkInstance2 overlap_flag (ds_theta spec) spec
-
-mkInstance2 :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
-mkInstance2 overlap_flag theta
+mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
+mkInstance overlap_flag theta
(DS { ds_name = dfun_name
, ds_tvs = tyvars, ds_cls = clas, ds_tys = tys })
= mkLocalInstance dfun overlap_flag
genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
genInst oflag spec
| ds_newtype spec
- = return (InstInfo { iSpec = mkInstance1 oflag spec
- , iBinds = NewTypeDerived }, [])
+ = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec
+ , iBinds = NewTypeDerived co }, [])
| otherwise
= do { let loc = getSrcSpan (ds_name spec)
- inst = mkInstance1 oflag spec
+ inst = mkInstance oflag (ds_theta spec) spec
clas = ds_cls spec
- rep_tycon = ds_tc spec
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
iBinds = VanillaInst meth_binds [] },
aux_binds)
}
+ where
+ rep_tycon = ds_tc spec
+ rep_tc_args = ds_tc_args spec
+ co1 = case tyConFamilyCoercion_maybe rep_tycon of
+ Nothing -> IdCo
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co2 = case newTyConCo_maybe rep_tycon of
+ Nothing -> IdCo -- The newtype is transparent; no need for a cast
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co = co1 `mkTransCoI` co2
+
+-- Example: newtype instance N [a] = N1 (Tree a)
+-- deriving instance Eq b => Eq (N [(b,b)])
+-- From the instance, we get an implicit newtype R1:N a = N1 (Tree a)
+-- When dealing with the deriving clause
+-- co1 : N [(b,b)] ~ R1:N (b,b)
+-- co2 : R1:N (b,b) ~ Tree (b,b)
genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
genDerivBinds loc fix_env clas tycon
projects / ghc-hetmet.git / blobdiff