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Introduce ForAllTyFlag, use it in matchUpSigWithDecl
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For now, this is simply a refactoring. We will make use of this more in a
subsequent commit in which we use `matchUpSigWithDecl` to determine the binders
of a promoted class declaration, in which case we will need to be able to tell
invisible binders from visible ones.
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RyanGlScott committed Jun 6, 2024
1 parent e0fda04 commit 1458610
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Showing 2 changed files with 46 additions and 12 deletions.
21 changes: 20 additions & 1 deletion singletons-th/src/Data/Singletons/TH/Single/Data.hs
Original file line number Diff line number Diff line change
Expand Up @@ -329,10 +329,29 @@ singDataSAK data_sak data_bndrs data_k = do
Map.fromList $ zip invis_data_sak_arg_nms invis_data_bndr_nms
(_, swizzled_sing_sak_tvbs) =
mapAccumL (swizzleTvb swizzle_env) Map.empty sing_sak_tvbs
swizzled_sing_sak_tvbs' =
map (fmap mk_data_sak_spec) swizzled_sing_sak_tvbs

-- (4) Finally, construct the kind of the singled data type.
pure $ DForallT (DForallInvis swizzled_sing_sak_tvbs)
pure $ DForallT (DForallInvis swizzled_sing_sak_tvbs')
$ DArrowT `DAppT` data_k `DAppT` DConT typeKindName
where
-- Convert a ForAllTyFlag value to a Specificity value, i.e., a binder
-- suitable for use in an invisible `forall`. We convert Required values
-- to SpecifiedSpec values because all of the binders in the `forall` are
-- invisible. For instance, we would single this data type:
--
-- type T :: forall k -> k -> Type
-- data T k (a :: k) where ...
--
-- Like so:
--
-- -- Note: the `k` is invisible, not visible
-- type ST :: forall k (a :: k). T k a -> Type
-- data ST z where ...
mk_data_sak_spec :: ForAllTyFlag -> Specificity
mk_data_sak_spec (Invisible spec) = spec
mk_data_sak_spec Required = SpecifiedSpec

{-
Note [singletons-th and record selectors]
Expand Down
37 changes: 26 additions & 11 deletions singletons-th/src/Data/Singletons/TH/Util.hs
Original file line number Diff line number Diff line change
Expand Up @@ -744,7 +744,7 @@ matchUpSigWithDecl ::
-- ^ The quantifiers in the declaration's standalone kind signature
-> [DTyVarBndrVis]
-- ^ The user-written binders in the declaration
-> q [DTyVarBndrSpec]
-> q [DTyVarBndr ForAllTyFlag]
matchUpSigWithDecl = go_fun_args Map.empty
where
go_fun_args ::
Expand All @@ -764,7 +764,7 @@ matchUpSigWithDecl = go_fun_args Map.empty
-- extended with @[a :-> x, b :-> y]@. This ensures that we will
-- produce @Maybe (x, y)@ instead of @Maybe (a, b)@ in
-- the kind for @z@.
-> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndrSpec]
-> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndr ForAllTyFlag]
go_fun_args _ DFANil [] =
pure []
-- This should not happen, per the function's precondition
Expand All @@ -790,12 +790,12 @@ matchUpSigWithDecl = go_fun_args Map.empty
let mb_match_subst = matchTy NoIgnore decl_bndr_kind anon' in
maybe decl_bndr_kind (`substType` decl_bndr_kind) mb_match_subst
sig_args' <- go_fun_args subst sig_args decl_bndrs
pure $ DKindedTV decl_bndr_name SpecifiedSpec anon'' : sig_args'
pure $ DKindedTV decl_bndr_name Required anon'' : sig_args'
-- This should not happen, per precondition (1).
go_fun_args _ _ [] =
fail "matchUpSigWithDecl.go_fun_args: Too few binders"

go_invis_tvbs :: DSubst -> [DTyVarBndrSpec] -> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndrSpec]
go_invis_tvbs :: DSubst -> [DTyVarBndrSpec] -> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndr ForAllTyFlag]
go_invis_tvbs subst [] sig_args decl_bndrs =
go_fun_args subst sig_args decl_bndrs
-- This should not happen, per precondition (2).
Expand All @@ -809,15 +809,15 @@ matchUpSigWithDecl = go_fun_args Map.empty
BndrReq -> do
let (subst', invis_tvb') = substTvb subst invis_tvb
sig_args' <- go_invis_tvbs subst' invis_tvbs sig_args decl_bndrss
pure $ invis_tvb' : sig_args'
pure $ fmap Invisible invis_tvb' : sig_args'
-- If the next decl_bndr is an invisible @-binder, then we must match it
-- against the invisible forall–bound variable in the kind.
BndrInvis -> do
let (subst', sig_tvb) = match_tvbs subst invis_tvb decl_bndr
sig_args' <- go_invis_tvbs subst' invis_tvbs sig_args decl_bndrs
pure (sig_tvb : sig_args')
pure (fmap Invisible sig_tvb : sig_args')

go_vis_tvbs :: DSubst -> [DTyVarBndrUnit] -> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndrSpec]
go_vis_tvbs :: DSubst -> [DTyVarBndrUnit] -> DFunArgs -> [DTyVarBndrVis] -> q [DTyVarBndr ForAllTyFlag]
go_vis_tvbs subst [] sig_args decl_bndrs =
go_fun_args subst sig_args decl_bndrs
-- This should not happen, per precondition (1).
Expand All @@ -830,7 +830,7 @@ matchUpSigWithDecl = go_fun_args Map.empty
BndrReq -> do
let (subst', sig_tvb) = match_tvbs subst vis_tvb decl_bndr
sig_args' <- go_vis_tvbs subst' vis_tvbs sig_args decl_bndrs
pure (sig_tvb : sig_args')
pure ((Required <$ sig_tvb) : sig_args')
-- We have a visible forall in the kind, but an invisible @-binder as
-- the next decl_bndr. This is ill kinded, so throw an error.
BndrInvis ->
Expand All @@ -847,12 +847,13 @@ matchUpSigWithDecl = go_fun_args Map.empty
--
-- 2. A 'DTyVarBndrSpec' that has the name of @decl_bndr@, but with the new
-- kind resulting from matching.
match_tvbs :: DSubst -> DTyVarBndr flag -> DTyVarBndrVis -> (DSubst, DTyVarBndrSpec)
match_tvbs :: DSubst -> DTyVarBndr flag -> DTyVarBndrVis -> (DSubst, DTyVarBndr flag)
match_tvbs subst sig_tvb decl_bndr =
let decl_bndr_name = extractTvbName decl_bndr
mb_decl_bndr_kind = extractTvbKind decl_bndr

sig_tvb_name = extractTvbName sig_tvb
sig_tvb_flag = extractTvbFlag sig_tvb
mb_sig_tvb_kind = substType subst <$> extractTvbKind sig_tvb

mb_kind :: Maybe DKind
Expand All @@ -867,8 +868,8 @@ matchUpSigWithDecl = go_fun_args Map.empty

subst' = Map.insert sig_tvb_name (DVarT decl_bndr_name) subst
sig_tvb' = case mb_kind of
Nothing -> DPlainTV decl_bndr_name SpecifiedSpec
Just kind -> DKindedTV decl_bndr_name SpecifiedSpec kind in
Nothing -> DPlainTV decl_bndr_name sig_tvb_flag
Just kind -> DKindedTV decl_bndr_name sig_tvb_flag kind in

(subst', sig_tvb')

Expand All @@ -885,3 +886,17 @@ swizzleTvb swizzle_env subst tvb =
case Map.lookup tvb_name swizzle_env of
Just user_name -> mapDTVName (const user_name) tvb1
Nothing -> tvb1

-- The visibility of a binder in a type-level declaration. This generalizes
-- 'Specificity' (which lacks an equivalent to 'Required') and 'BndrVis' (which
-- lacks an equivalent to @'Invisible' 'Inferred'@).
--
-- This is heavily inspired by a data type of the same name in GHC:
-- https://gitlab.haskell.org/ghc/ghc/-/blob/98597ad5fca81544d74f721fb508295fd2650232/compiler/GHC/Types/Var.hs#L458-465
data ForAllTyFlag
= Invisible !Specificity
-- ^ If the 'Specificity' value is 'SpecifiedSpec', then the binder is
-- permitted by request. If the 'Specificity' value is 'InferredSpec', then
-- the binder is prohibited from appearing in source Haskell.
| Required
-- ^ The binder is required to appear in source Haskell

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