Commit d937e740 authored by chak@cse.unsw.edu.au.'s avatar chak@cse.unsw.edu.au.
Browse files

More on newtype deriving

Mon Sep 18 14:29:16 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * More on newtype deriving
  Sat Aug  5 21:22:29 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * More on newtype deriving
    Fri Jul  7 10:37:55 EDT 2006  simonpj@microsoft.com
parent ad4a18b1
......@@ -319,7 +319,7 @@ tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
-- axiom CoT a :: Tree [a] = T a
--
-- So all need is to generate a binding looking like
-- dfunFooT :: forall a. (Show (T a), Foo Int (Tree [a]) => Foo Int (T a)
-- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
-- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
-- case df `cast` (Foo Int (CoT a)) of
-- Foo _ op1 .. opn -> Foo ds op1 .. opn
......@@ -332,25 +332,37 @@ tcInstDecl2 (InstInfo { iSpec = ispec,
inst_ty = idType dfun_id
maybe_co_con = newTyConCo tycon
; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
; rep_dict <- newDict origin (head theta)
; if isSingleton theta then
return (unitBag (VarBind dfun_id $
case maybe_co_con of
Nothing -> rep_dict
Just co_con -> mkCoerce rep_dict $
mkAppCoercion (mkAppsCoercion tycon rep_tys)
(mkTyConApp co_con tvs)))
else do
let rep_dict_id = instToId rep_dict
coerced_dict = case maybe_co_con of
Nothing -> rep_dict_id
Just co_con -> mkCoerce rep_dict_id $
mkAppCoercion (mkAppsCoercion tycon rep_tys)
(mkTyConApp co_con tvs)
; return (unitBag (VarBind dfun_id
co_fn = CoTyLams tvs <.> CoLams [rep_dict_id] <.> ExprCoFn cast
; return (unitBag (VarBind dfun_id (HsCoerce co_fn (HsVar rep_dict_id))))
; dicts <- newDicts origin theta
; uniqs <- newUniqueSupply
; let (rep_dict_id:sc_dict_ids) = map instToId dicts
-- (Here, wee are relying on the order of dictionary
-- arguments built by NewTypeDerived in TcDeriv.)
wrap_fn = CoTyLams tvs <.> CoLams dict_ids
coerced_rep_dict = mkHsCoerce co_fn (HsVar rep_dict_id)
body | null sc_dicts = coerced_rep_dict
| otherwise = HsCase coerced_rep_dict $
MatchGroup [the_match] inst_head
the_match = mkSimpleMatch [the_pat] the_rhs
op_ids = zipWith (mkSysLocal FSLIT("op"))
(uniqsFromSupply uniqs) op_tys
the_pat = ConPatOut { pat_con = cls_data_con, pat_tvs = [],
pat_dicts = map (WildPat . idType) sc_dict_ids,
pat_binds = emptyDictBinds,
pat_args = PrefixCon (map VarPat op_ids),
pat_ty = <type of pattern> }
the_rhs = mkHsApps (dataConWrapId cls_data_con) types sc_dict_ids (map HsVar op_ids)
; return (unitBag (VarBind dfun_id (mkHsCoerce wrap_fn body))) }
where
co_fn :: ExprCoFn
co_fn | Just co_con <- newTyConCo tycon
= ExprCoFn (mkAppCoercion (mkAppsCoercion tycon rep_tys)
(mkTyConApp co_con tvs))
| otherwise
= idCoerecion
tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
avail_insts op_items (NewTypeDerived rep_tys)
......
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