singletons-2.6: src/Data/Singletons/Promote.hs
{- Data/Singletons/Promote.hs
(c) Richard Eisenberg 2013
rae@cs.brynmawr.edu
This file contains functions to promote term-level constructs to the
type level. It is an internal module to the singletons package.
-}
{-# LANGUAGE TemplateHaskell, MultiWayIf, LambdaCase, TupleSections #-}
module Data.Singletons.Promote where
import Language.Haskell.TH hiding ( Q, cxt )
import Language.Haskell.TH.Syntax ( Quasi(..) )
import Language.Haskell.TH.Desugar
import qualified Language.Haskell.TH.Desugar.OMap.Strict as OMap
import Language.Haskell.TH.Desugar.OMap.Strict (OMap)
import qualified Language.Haskell.TH.Desugar.OSet as OSet
import Language.Haskell.TH.Desugar.OSet (OSet)
import Data.Singletons.Names
import Data.Singletons.Promote.Monad
import Data.Singletons.Promote.Eq
import Data.Singletons.Promote.Defun
import Data.Singletons.Promote.Type
import Data.Singletons.Deriving.Ord
import Data.Singletons.Deriving.Bounded
import Data.Singletons.Deriving.Enum
import Data.Singletons.Deriving.Show
import Data.Singletons.Deriving.Util
import Data.Singletons.Partition
import Data.Singletons.Util
import Data.Singletons.Syntax
import Prelude hiding (exp)
import Control.Applicative (Alternative(..))
import Control.Arrow (second)
import Control.Monad
import Control.Monad.Trans.Maybe
import Control.Monad.Writer
import qualified Data.Map.Strict as Map
import Data.Map.Strict ( Map )
import Data.Maybe
import qualified GHC.LanguageExtensions.Type as LangExt
-- | Generate promoted definitions from a type that is already defined.
-- This is generally only useful with classes.
genPromotions :: DsMonad q => [Name] -> q [Dec]
genPromotions names = do
checkForRep names
infos <- mapM reifyWithLocals names
dinfos <- mapM dsInfo infos
ddecs <- promoteM_ [] $ mapM_ promoteInfo dinfos
return $ decsToTH ddecs
-- | Promote every declaration given to the type level, retaining the originals.
promote :: DsMonad q => q [Dec] -> q [Dec]
promote qdec = do
decls <- qdec
ddecls <- withLocalDeclarations decls $ dsDecs decls
promDecls <- promoteM_ decls $ promoteDecs ddecls
return $ decls ++ decsToTH promDecls
-- | Promote each declaration, discarding the originals. Note that a promoted
-- datatype uses the same definition as an original datatype, so this will
-- not work with datatypes. Classes, instances, and functions are all fine.
promoteOnly :: DsMonad q => q [Dec] -> q [Dec]
promoteOnly qdec = do
decls <- qdec
ddecls <- dsDecs decls
promDecls <- promoteM_ decls $ promoteDecs ddecls
return $ decsToTH promDecls
-- | Generate defunctionalization symbols for existing type families.
--
-- 'genDefunSymbols' has reasonable support for type families that use
-- dependent quantification. For instance, this:
--
-- @
-- type family MyProxy k (a :: k) :: Type where
-- MyProxy k (a :: k) = Proxy a
--
-- $('genDefunSymbols' [''MyProxy])
-- @
--
-- Will generate the following defunctionalization symbols:
--
-- @
-- data MyProxySym0 :: Type ~> k ~> Type
-- data MyProxySym1 (k :: Type) :: k ~> Type
-- @
--
-- Note that @MyProxySym0@ is a bit more general than it ought to be, since
-- there is no dependency between the first kind (@Type@) and the second kind
-- (@k@). But this would require the ability to write something like:
--
-- @
-- data MyProxySym0 :: forall (k :: Type) ~> k ~> Type
-- @
--
-- Which currently isn't possible. So for the time being, the kind of
-- @MyProxySym0@ will be slightly more general, which means that under rare
-- circumstances, you may have to provide extra type signatures if you write
-- code which exploits the dependency in @MyProxy@'s kind.
genDefunSymbols :: DsMonad q => [Name] -> q [Dec]
genDefunSymbols names = do
checkForRep names
infos <- mapM (dsInfo <=< reifyWithLocals) names
decs <- promoteMDecs [] $ concatMapM defunInfo infos
return $ decsToTH decs
-- | Produce instances for @(==)@ (type-level equality) from the given types
promoteEqInstances :: DsMonad q => [Name] -> q [Dec]
promoteEqInstances = concatMapM promoteEqInstance
-- | Produce instances for 'POrd' from the given types
promoteOrdInstances :: DsMonad q => [Name] -> q [Dec]
promoteOrdInstances = concatMapM promoteOrdInstance
-- | Produce an instance for 'POrd' from the given type
promoteOrdInstance :: DsMonad q => Name -> q [Dec]
promoteOrdInstance = promoteInstance mkOrdInstance "Ord"
-- | Produce instances for 'PBounded' from the given types
promoteBoundedInstances :: DsMonad q => [Name] -> q [Dec]
promoteBoundedInstances = concatMapM promoteBoundedInstance
-- | Produce an instance for 'PBounded' from the given type
promoteBoundedInstance :: DsMonad q => Name -> q [Dec]
promoteBoundedInstance = promoteInstance mkBoundedInstance "Bounded"
-- | Produce instances for 'PEnum' from the given types
promoteEnumInstances :: DsMonad q => [Name] -> q [Dec]
promoteEnumInstances = concatMapM promoteEnumInstance
-- | Produce an instance for 'PEnum' from the given type
promoteEnumInstance :: DsMonad q => Name -> q [Dec]
promoteEnumInstance = promoteInstance mkEnumInstance "Enum"
-- | Produce instances for 'PShow' from the given types
promoteShowInstances :: DsMonad q => [Name] -> q [Dec]
promoteShowInstances = concatMapM promoteShowInstance
-- | Produce an instance for 'PShow' from the given type
promoteShowInstance :: DsMonad q => Name -> q [Dec]
promoteShowInstance = promoteInstance (mkShowInstance ForPromotion) "Show"
-- | Produce an instance for @(==)@ (type-level equality) from the given type
promoteEqInstance :: DsMonad q => Name -> q [Dec]
promoteEqInstance name = do
(tvbs, cons) <- getDataD "I cannot make an instance of (==) for it." name
tvbs' <- mapM dsTvb tvbs
let data_ty = foldTypeTvbs (DConT name) tvbs'
cons' <- concatMapM (dsCon tvbs' data_ty) cons
kind <- promoteType (foldTypeTvbs (DConT name) tvbs')
inst_decs <- mkEqTypeInstance kind cons'
return $ decsToTH inst_decs
promoteInstance :: DsMonad q => DerivDesc q -> String -> Name -> q [Dec]
promoteInstance mk_inst class_name name = do
(tvbs, cons) <- getDataD ("I cannot make an instance of " ++ class_name
++ " for it.") name
tvbs' <- mapM dsTvb tvbs
let data_ty = foldTypeTvbs (DConT name) tvbs'
cons' <- concatMapM (dsCon tvbs' data_ty) cons
let data_decl = DataDecl name tvbs' cons'
raw_inst <- mk_inst Nothing data_ty data_decl
decs <- promoteM_ [] $ void $ promoteInstanceDec OMap.empty raw_inst
return $ decsToTH decs
promoteInfo :: DInfo -> PrM ()
promoteInfo (DTyConI dec _instances) = promoteDecs [dec]
promoteInfo (DPrimTyConI _name _numArgs _unlifted) =
fail "Promotion of primitive type constructors not supported"
promoteInfo (DVarI _name _ty _mdec) =
fail "Promotion of individual values not supported"
promoteInfo (DTyVarI _name _ty) =
fail "Promotion of individual type variables not supported"
promoteInfo (DPatSynI {}) =
fail "Promotion of pattern synonyms not supported"
-- Note [Promoting declarations in two stages]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- It is necessary to know the types of things when promoting. So,
-- we promote in two stages: first, we build a LetDecEnv, which allows
-- for easy lookup. Then, we go through the actual elements of the LetDecEnv,
-- performing the promotion.
--
-- Why do we need the types? For kind annotations on the type family. We also
-- need to have both the types and the actual function definition at the same
-- time, because the function definition tells us how many patterns are
-- matched. Note that an eta-contracted function needs to return a TyFun,
-- not a proper type-level function.
--
-- Consider this example:
--
-- foo :: Nat -> Bool -> Bool
-- foo Zero = id
-- foo _ = not
--
-- Here the first parameter to foo is non-uniform, because it is
-- inspected in a pattern and can be different in each defining
-- equation of foo. The second parameter to foo, specified in the type
-- signature as Bool, is a uniform parameter - it is not inspected and
-- each defining equation of foo uses it the same way. The foo
-- function will be promoted to a type familty Foo like this:
--
-- type family Foo (n :: Nat) :: Bool ~> Bool where
-- Foo Zero = Id
-- Foo a = Not
--
-- To generate type signature for Foo type family we must first learn
-- what is the actual number of patterns used in defining cequations
-- of foo. In this case there is only one so we declare Foo to take
-- one argument and have return type of Bool -> Bool.
-- Promote a list of top-level declarations.
promoteDecs :: [DDec] -> PrM ()
promoteDecs raw_decls = do
decls <- expand raw_decls -- expand type synonyms
checkForRepInDecls decls
PDecs { pd_let_decs = let_decs
, pd_class_decs = classes
, pd_instance_decs = insts
, pd_data_decs = datas
, pd_ty_syn_decs = ty_syns
, pd_open_type_family_decs = o_tyfams
, pd_closed_type_family_decs = c_tyfams
, pd_derived_eq_decs = derived_eq_decs } <- partitionDecs decls
defunTypeDecls ty_syns c_tyfams o_tyfams
-- promoteLetDecs returns LetBinds, which we don't need at top level
_ <- promoteLetDecs noPrefix let_decs
mapM_ promoteClassDec classes
let orig_meth_sigs = foldMap (lde_types . cd_lde) classes
mapM_ (promoteInstanceDec orig_meth_sigs) insts
mapM_ promoteDerivedEqDec derived_eq_decs
promoteDataDecs datas
promoteDataDecs :: [DataDecl] -> PrM ()
promoteDataDecs data_decs = do
rec_selectors <- concatMapM extract_rec_selectors data_decs
_ <- promoteLetDecs noPrefix rec_selectors
mapM_ promoteDataDec data_decs
where
extract_rec_selectors :: DataDecl -> PrM [DLetDec]
extract_rec_selectors (DataDecl data_name tvbs cons) =
let arg_ty = foldTypeTvbs (DConT data_name) tvbs
in
getRecordSelectors arg_ty cons
-- curious about ALetDecEnv? See the LetDecEnv module for an explanation.
promoteLetDecs :: (String, String) -- (alpha, symb) prefixes to use
-> [DLetDec] -> PrM ([LetBind], ALetDecEnv)
-- See Note [Promoting declarations in two stages]
promoteLetDecs prefixes decls = do
let_dec_env <- buildLetDecEnv decls
all_locals <- allLocals
let binds = [ (name, foldType (DConT sym) (map DVarT all_locals))
| (name, _) <- OMap.assocs $ lde_defns let_dec_env
, let proName = promoteValNameLhsPrefix prefixes name
sym = promoteTySym proName (length all_locals) ]
(decs, let_dec_env') <- letBind binds $ promoteLetDecEnv prefixes let_dec_env
emitDecs decs
return (binds, let_dec_env' { lde_proms = OMap.fromList binds })
-- Promotion of data types to kinds is automatic (see "Giving Haskell a
-- Promotion" paper for more details). Here we "plug into" the promotion
-- mechanism to add some extra stuff to the promotion:
--
-- * if data type derives Eq we generate a type family that implements the
-- equality test for the data type.
--
-- * for each data constructor with arity greater than 0 we generate type level
-- symbols for use with Apply type family. In this way promoted data
-- constructors and promoted functions can be used in a uniform way at the
-- type level in the same way they can be used uniformly at the type level.
--
-- * for each nullary data constructor we generate a type synonym
promoteDataDec :: DataDecl -> PrM ()
promoteDataDec (DataDecl _name _tvbs ctors) = do
ctorSyms <- buildDefunSymsDataD ctors
emitDecs ctorSyms
-- Note [CUSKification]
-- ~~~~~~~~~~~~~~~~~~~~
-- GHC #12928 means that sometimes, this TH code will produce a declaration
-- that has a kind signature even when we want kind inference to work. There
-- seems to be no way to avoid this, so we embrace it:
--
-- * If a class type variable has no explicit kind, we make no effort to
-- guess it and default to *. This is OK because before GHC 8.0, we were
-- limited by KProxy anyway.
--
-- * If a class type variable has an explicit kind, it is preserved.
--
-- This way, we always get proper CUSKs where we need them.
promoteClassDec :: UClassDecl
-> PrM AClassDecl
promoteClassDec decl@(ClassDecl { cd_name = cls_name
, cd_tvbs = tvbs'
, cd_fds = fundeps
, cd_lde = lde@LetDecEnv
{ lde_defns = defaults
, lde_types = meth_sigs
, lde_infix = infix_decls } }) = do
let
-- a workaround for GHC Trac #12928; see Note [CUSKification]
tvbs = map cuskify tvbs'
let pClsName = promoteClassName cls_name
forallBind cls_kvs_to_bind $ do
sig_decs <- mapM (uncurry promote_sig) (OMap.assocs meth_sigs)
let defaults_list = OMap.assocs defaults
defaults_names = map fst defaults_list
(default_decs, ann_rhss, prom_rhss)
<- mapAndUnzip3M (promoteMethod OMap.empty Nothing meth_sigs) defaults_list
let infix_decls' = catMaybes $ map (uncurry promoteInfixDecl)
$ OMap.assocs infix_decls
-- no need to do anything to the fundeps. They work as is!
emitDecs [DClassD [] pClsName tvbs fundeps
(sig_decs ++ default_decs ++ infix_decls')]
let defaults_list' = zip defaults_names ann_rhss
proms = zip defaults_names prom_rhss
cls_kvs_to_bind' = cls_kvs_to_bind <$ meth_sigs
return (decl { cd_lde = lde { lde_defns = OMap.fromList defaults_list'
, lde_proms = OMap.fromList proms
, lde_bound_kvs = cls_kvs_to_bind' } })
where
cls_kvb_names, cls_tvb_names, cls_kvs_to_bind :: OSet Name
cls_kvb_names = foldMap (foldMap fvDType . extractTvbKind) tvbs'
cls_tvb_names = OSet.fromList $ map extractTvbName tvbs'
cls_kvs_to_bind = cls_kvb_names `OSet.union` cls_tvb_names
promote_sig :: Name -> DType -> PrM DDec
promote_sig name ty = do
let proName = promoteValNameLhs name
(argKs, resK) <- promoteUnraveled ty
args <- mapM (const $ qNewName "arg") argKs
let tvbs = zipWith DKindedTV args argKs
emitDecsM $ defunReifyFixity proName tvbs (Just resK)
return $ DOpenTypeFamilyD (DTypeFamilyHead proName
tvbs
(DKindSig resK)
Nothing)
-- returns (unpromoted method name, ALetDecRHS) pairs
promoteInstanceDec :: OMap Name DType -> UInstDecl -> PrM AInstDecl
promoteInstanceDec orig_meth_sigs
decl@(InstDecl { id_name = cls_name
, id_arg_tys = inst_tys
, id_sigs = inst_sigs
, id_meths = meths }) = do
cls_tvb_names <- lookup_cls_tvb_names
inst_kis <- mapM promoteType inst_tys
let kvs_to_bind = foldMap fvDType inst_kis
forallBind kvs_to_bind $ do
let subst = Map.fromList $ zip cls_tvb_names inst_kis
(meths', ann_rhss, _) <- mapAndUnzip3M (promoteMethod inst_sigs (Just subst) orig_meth_sigs) meths
emitDecs [DInstanceD Nothing Nothing [] (foldType (DConT pClsName)
inst_kis) meths']
return (decl { id_meths = zip (map fst meths) ann_rhss })
where
pClsName = promoteClassName cls_name
lookup_cls_tvb_names :: PrM [Name]
lookup_cls_tvb_names = do
let mk_tvb_names = extract_tvb_names (dsReifyTypeNameInfo pClsName)
<|> extract_tvb_names (dsReifyTypeNameInfo cls_name)
-- See Note [Using dsReifyTypeNameInfo when promoting instances]
mb_tvb_names <- runMaybeT mk_tvb_names
case mb_tvb_names of
Just tvb_names -> pure tvb_names
Nothing -> fail $ "Cannot find class declaration annotation for " ++ show cls_name
extract_tvb_names :: PrM (Maybe DInfo) -> MaybeT PrM [Name]
extract_tvb_names reify_info = do
mb_info <- lift reify_info
case mb_info of
Just (DTyConI (DClassD _ _ tvbs _ _) _)
-> pure $ map extractTvbName tvbs
_ -> empty
{-
Note [Using dsReifyTypeNameInfo when promoting instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During the promotion of a class instance, it becomes necessary to reify the
original promoted class's info to learn various things. It's tempting to think
that just calling dsReify on the class name will be sufficient, but it's not.
Consider this class and its promotion:
class Eq a where
(==) :: a -> a -> Bool
class PEq a where
type (==) (x :: a) (y :: a) :: Bool
Notice how both of these classes have an identifier named (==), one at the
value level, and one at the type level. Now imagine what happens when you
attempt to promote this Template Haskell declaration:
[d| f :: Bool
f = () == () |]
When promoting ==, singletons will come up with its promoted equivalent (which also
happens to be ==). However, this promoted name is a raw Name, since it is created
with mkName. This becomes an issue when we call dsReify the raw "==" Name, as
Template Haskell has to arbitrarily choose between reifying the info for the
value-level (==) and the type-level (==), and in this case, it happens to pick the
value-level (==) info. We want the type-level (==) info, however, because we care
about the promoted version of (==).
Fortunately, there's a serviceable workaround. Instead of dsReify, we can use
dsReifyTypeNameInfo, which first calls lookupTypeName (to ensure we can find a Name
that's in the type namespace) and _then_ reifies it.
-}
promoteMethod :: OMap Name DType -- InstanceSigs for methods
-> Maybe (Map Name DKind)
-- ^ instantiations for class tyvars (Nothing for default decls)
-- See Note [Promoted class method kinds]
-> OMap Name DType -- method types
-> (Name, ULetDecRHS)
-> PrM (DDec, ALetDecRHS, DType)
-- returns (type instance, ALetDecRHS, promoted RHS)
promoteMethod inst_sigs_map m_subst orig_sigs_map (meth_name, meth_rhs) = do
(meth_arg_kis, meth_res_ki) <- lookup_meth_ty
meth_arg_tvs <- mapM (const $ qNewName "a") meth_arg_kis
let helperNameBase = case nameBase proName of
first:_ | not (isHsLetter first) -> "TFHelper"
alpha -> alpha
-- family_args are the type variables in a promoted class's
-- associated type family instance (or default implementation), e.g.,
--
-- class C k where
-- type T (a :: k) (b :: Bool)
-- type T a b = THelper1 a b -- family_args = [a, b]
--
-- instance C Bool where
-- type T a b = THelper2 a b -- family_args = [a, b]
--
-- We could annotate these variables with explicit kinds, but it's not
-- strictly necessary, as kind inference can figure them out just as well.
family_args = map DVarT meth_arg_tvs
helperName <- newUniqueName helperNameBase
let proHelperName = promoteValNameLhs helperName
((_, _, _, eqns), _defuns, ann_rhs)
<- promoteLetDecRHS (Just (meth_arg_kis, meth_res_ki)) OMap.empty OMap.empty
noPrefix helperName meth_rhs
let tvbs = zipWith DKindedTV meth_arg_tvs meth_arg_kis
emitDecs [DClosedTypeFamilyD (DTypeFamilyHead
proHelperName
tvbs
(DKindSig meth_res_ki)
Nothing)
eqns]
emitDecsM (defunctionalize proHelperName Nothing tvbs (Just meth_res_ki))
return ( DTySynInstD
(DTySynEqn Nothing
(foldType (DConT proName) family_args)
(foldApply (promoteValRhs helperName) (map DVarT meth_arg_tvs)))
, ann_rhs
, DConT (promoteTySym helperName 0) )
where
proName = promoteValNameLhs meth_name
lookup_meth_ty :: PrM ([DKind], DKind)
lookup_meth_ty =
case OMap.lookup meth_name inst_sigs_map of
Just ty ->
-- We have an InstanceSig. These are easy: no substitution for clas
-- variables is required at all!
promoteUnraveled ty
Nothing -> do
-- We don't have an InstanceSig, so we must compute the kind to use
-- ourselves (possibly substituting for class variables below).
(arg_kis, res_ki) <-
case OMap.lookup meth_name orig_sigs_map of
Nothing -> do
mb_info <- dsReifyTypeNameInfo proName
-- See Note [Using dsReifyTypeNameInfo when promoting instances]
case mb_info of
Just (DTyConI (DOpenTypeFamilyD (DTypeFamilyHead _ tvbs mb_res_ki _)) _)
-> let arg_kis = map (default_to_star . extractTvbKind) tvbs
res_ki = default_to_star (resultSigToMaybeKind mb_res_ki)
in return (arg_kis, res_ki)
_ -> fail $ "Cannot find type annotation for " ++ show proName
Just ty -> promoteUnraveled ty
let -- If we're dealing with an associated type family instance, substitute
-- in the kind of the instance for better kind information in the RHS
-- helper function. If we're dealing with a default family implementation
-- (m_subst = Nothing), there's no need for a substitution.
-- See Note [Promoted class method kinds]
do_subst = maybe id substKind m_subst
meth_arg_kis' = map do_subst arg_kis
meth_res_ki' = do_subst res_ki
pure (meth_arg_kis', meth_res_ki')
default_to_star Nothing = DConT typeKindName
default_to_star (Just k) = k
{-
Note [Promoted class method kinds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this example of a type class (and instance):
class C a where
m :: a -> Bool -> Bool
m _ x = x
instance C [a] where
m l _ = null l
The promoted version of these declarations would be:
class PC a where
type M (x :: a) (y :: Bool) (z :: Bool)
type M x y z = MHelper1 x y z
instance PC [a] where
type M x y z = MHelper2 x y z
type family MHelper1 (x :: a) (y :: Bool) (z :: Bool) where ...
type family MHelper2 (x :: [a]) (y :: Bool) (z :: Bool) where ...
Getting the kind signature for MHelper1 (the promoted default implementation of
M) is quite simple, as it corresponds exactly to the kind of M. We might even
choose to make that the kind of MHelper2, but then it would be overly general
(and more difficult to find in -ddump-splices output). For this reason, we
substitute in the kinds of the instance itself to determine the kinds of
promoted method implementations like MHelper2.
-}
promoteLetDecEnv :: (String, String) -> ULetDecEnv -> PrM ([DDec], ALetDecEnv)
promoteLetDecEnv prefixes (LetDecEnv { lde_defns = value_env
, lde_types = type_env
, lde_infix = fix_env }) = do
let infix_decls = catMaybes $ map (uncurry promoteInfixDecl)
$ OMap.assocs fix_env
-- promote all the declarations, producing annotated declarations
let (names, rhss) = unzip $ OMap.assocs value_env
(payloads, defun_decss, ann_rhss)
<- fmap unzip3 $ zipWithM (promoteLetDecRHS Nothing type_env fix_env prefixes) names rhss
emitDecs $ concat defun_decss
bound_kvs <- allBoundKindVars
let decs = map payload_to_dec payloads ++ infix_decls
-- build the ALetDecEnv
let let_dec_env' = LetDecEnv { lde_defns = OMap.fromList $ zip names ann_rhss
, lde_types = type_env
, lde_infix = fix_env
, lde_proms = OMap.empty -- filled in promoteLetDecs
, lde_bound_kvs = OMap.fromList $ map (, bound_kvs) names }
return (decs, let_dec_env')
where
payload_to_dec (name, tvbs, m_ki, eqns) = DClosedTypeFamilyD
(DTypeFamilyHead name tvbs sig Nothing)
eqns
where
sig = maybe DNoSig DKindSig m_ki
promoteInfixDecl :: Name -> Fixity -> Maybe DDec
promoteInfixDecl name fixity
| nameBase name == nameBase promoted_name
-- If a name and its promoted counterpart are the same (modulo module
-- prefixes), then there's no need to promote a fixity declaration for
-- that name, since the existing fixity declaration will cover both
-- the term- and type-level versions of that name. Names that fall into this
-- category include data constructor names and infix names.
= Nothing
| otherwise
= Just $ DLetDec $ DInfixD fixity promoted_name
where
promoted_name = promoteValNameLhs name
-- This function is used both to promote class method defaults and normal
-- let bindings. Thus, it can't quite do all the work locally and returns
-- an intermediate structure. Perhaps a better design is available.
promoteLetDecRHS :: Maybe ([DKind], DKind) -- the promoted type of the RHS (if known)
-- needed to fix #136
-> OMap Name DType -- local type env't
-> OMap Name Fixity -- local fixity env't
-> (String, String) -- let-binding prefixes
-> Name -- name of the thing being promoted
-> ULetDecRHS -- body of the thing
-> PrM ( (Name, [DTyVarBndr], Maybe DKind, [DTySynEqn]) -- "type family"
, [DDec] -- defunctionalization
, ALetDecRHS ) -- annotated RHS
promoteLetDecRHS m_rhs_ki type_env fix_env prefixes name (UValue exp) = do
(res_kind, num_arrows)
<- case m_rhs_ki of
Just (arg_kis, res_ki) -> return ( Just (ravelTyFun (arg_kis ++ [res_ki]))
, length arg_kis )
_ | Just ty <- OMap.lookup name type_env
-> do ki <- promoteType ty
return (Just ki, countArgs ty)
| otherwise
-> return (Nothing, 0)
case num_arrows of
0 -> do
all_locals <- allLocals
let lde_kvs_to_bind = foldMap fvDType res_kind
(exp', ann_exp) <- forallBind lde_kvs_to_bind $ promoteExp exp
let proName = promoteValNameLhsPrefix prefixes name
m_fixity = OMap.lookup name fix_env
tvbs = map DPlainTV all_locals
defuns <- defunctionalize proName m_fixity tvbs res_kind
return ( ( proName, tvbs, res_kind
, [DTySynEqn Nothing (foldType (DConT proName) $ map DVarT all_locals) exp'] )
, defuns
, AValue (foldType (DConT proName) (map DVarT all_locals))
num_arrows ann_exp )
_ -> do
names <- replicateM num_arrows (newUniqueName "a")
let pats = map DVarP names
newArgs = map DVarE names
promoteLetDecRHS m_rhs_ki type_env fix_env prefixes name
(UFunction [DClause pats (foldExp exp newArgs)])
promoteLetDecRHS m_rhs_ki type_env fix_env prefixes name (UFunction clauses) = do
numArgs <- count_args clauses
(m_argKs, m_resK, ty_num_args) <- case m_rhs_ki of
Just (arg_kis, res_ki) -> return (map Just arg_kis, Just res_ki, length arg_kis)
_ | Just ty <- OMap.lookup name type_env
-> do
-- promoteType turns arrows into TyFun. So, we unravel first to
-- avoid this behavior. Note the use of ravelTyFun in resultK
-- to make the return kind work out
(argKs, resultK) <- promoteUnraveled ty
-- invariant: countArgs ty == length argKs
return (map Just argKs, Just resultK, length argKs)
| otherwise
-> return (replicate numArgs Nothing, Nothing, numArgs)
let proName = promoteValNameLhsPrefix prefixes name
m_fixity = OMap.lookup name fix_env
all_locals <- allLocals
let local_tvbs = map DPlainTV all_locals
tyvarNames <- mapM (const $ qNewName "a") m_argKs
let args = zipWith inferMaybeKindTV tyvarNames m_argKs
all_args = local_tvbs ++ args
defun_decs <- defunctionalize proName m_fixity all_args m_resK
expClauses <- mapM (etaContractOrExpand ty_num_args numArgs) clauses
let lde_kvs_to_bind = foldMap (foldMap fvDType) m_argKs <> foldMap fvDType m_resK
(eqns, ann_clauses) <- forallBind lde_kvs_to_bind $
mapAndUnzipM (promoteClause proName) expClauses
prom_fun <- lookupVarE name
return ( (proName, all_args, m_resK, eqns)
, defun_decs
, AFunction prom_fun ty_num_args ann_clauses )
where
etaContractOrExpand :: Int -> Int -> DClause -> PrM DClause
etaContractOrExpand ty_num_args clause_num_args (DClause pats exp)
| n >= 0 = do -- Eta-expand
names <- replicateM n (newUniqueName "a")
let newPats = map DVarP names
newArgs = map DVarE names
return $ DClause (pats ++ newPats) (foldExp exp newArgs)
| otherwise = do -- Eta-contract
let (clausePats, lamPats) = splitAt ty_num_args pats
lamExp <- mkDLamEFromDPats lamPats exp
return $ DClause clausePats lamExp
where
n = ty_num_args - clause_num_args
count_args (DClause pats _ : _) = return $ length pats
count_args _ = fail $ "Impossible! A function without clauses."
promoteClause :: Name -> DClause -> PrM (DTySynEqn, ADClause)
promoteClause proName (DClause pats exp) = do
-- promoting the patterns creates variable bindings. These are passed
-- to the function promoted the RHS
((types, pats'), prom_pat_infos) <- evalForPair $ mapAndUnzipM promotePat pats
let PromDPatInfos { prom_dpat_vars = new_vars
, prom_dpat_sig_kvs = sig_kvs } = prom_pat_infos
(ty, ann_exp) <- forallBind sig_kvs $
lambdaBind new_vars $
promoteExp exp
all_locals <- allLocals -- these are bound *outside* of this clause
return ( DTySynEqn Nothing (foldType (DConT proName) $ map DVarT all_locals ++ types) ty
, ADClause new_vars pats' ann_exp )
promoteMatch :: Name -> DMatch -> PrM (DTySynEqn, ADMatch)
promoteMatch caseTFName (DMatch pat exp) = do
-- promoting the patterns creates variable bindings. These are passed
-- to the function promoted the RHS
((ty, pat'), prom_pat_infos) <- evalForPair $ promotePat pat
let PromDPatInfos { prom_dpat_vars = new_vars
, prom_dpat_sig_kvs = sig_kvs } = prom_pat_infos
(rhs, ann_exp) <- forallBind sig_kvs $
lambdaBind new_vars $
promoteExp exp
all_locals <- allLocals
return $ ( DTySynEqn Nothing
(foldType (DConT caseTFName) $ map DVarT all_locals ++ [ty])
rhs
, ADMatch new_vars pat' ann_exp)
-- promotes a term pattern into a type pattern, accumulating bound variable names
promotePat :: DPat -> QWithAux PromDPatInfos PrM (DType, ADPat)
promotePat (DLitP lit) = (, ADLitP lit) <$> promoteLitPat lit
promotePat (DVarP name) = do
-- term vars can be symbols... type vars can't!
tyName <- mkTyName name
tell $ PromDPatInfos [(name, tyName)] OSet.empty
return (DVarT tyName, ADVarP name)
promotePat (DConP name pats) = do
(types, pats') <- mapAndUnzipM promotePat pats
let name' = unboxed_tuple_to_tuple name
return (foldType (DConT name') types, ADConP name pats')
where
unboxed_tuple_to_tuple n
| Just deg <- unboxedTupleNameDegree_maybe n = tupleDataName deg
| otherwise = n
promotePat (DTildeP pat) = do
qReportWarning "Lazy pattern converted into regular pattern in promotion"
second ADTildeP <$> promotePat pat
promotePat (DBangP pat) = do
qReportWarning "Strict pattern converted into regular pattern in promotion"
second ADBangP <$> promotePat pat
promotePat (DSigP pat ty) = do
-- We must maintain the invariant that any promoted pattern signature must
-- not have any wildcards in the underlying pattern.
-- See Note [Singling pattern signatures].
wildless_pat <- removeWilds pat
(promoted, pat') <- promotePat wildless_pat
ki <- promoteType ty
tell $ PromDPatInfos [] (fvDType ki)
return (DSigT promoted ki, ADSigP promoted pat' ki)
promotePat DWildP = return (DWildCardT, ADWildP)
promoteExp :: DExp -> PrM (DType, ADExp)
promoteExp (DVarE name) = fmap (, ADVarE name) $ lookupVarE name
promoteExp (DConE name) = return $ (promoteValRhs name, ADConE name)
promoteExp (DLitE lit) = fmap (, ADLitE lit) $ promoteLitExp lit
promoteExp (DAppE exp1 exp2) = do
(exp1', ann_exp1) <- promoteExp exp1
(exp2', ann_exp2) <- promoteExp exp2
return (apply exp1' exp2', ADAppE ann_exp1 ann_exp2)
-- Until we get visible kind applications, this is the best we can do.
promoteExp (DAppTypeE exp _) = do
qReportWarning "Visible type applications are ignored by `singletons`."
promoteExp exp
promoteExp (DLamE names exp) = do
lambdaName <- newUniqueName "Lambda"
tyNames <- mapM mkTyName names
let var_proms = zip names tyNames
(rhs, ann_exp) <- lambdaBind var_proms $ promoteExp exp
tyFamLamTypes <- mapM (const $ qNewName "t") names
all_locals <- allLocals
let all_args = all_locals ++ tyFamLamTypes
tvbs = map DPlainTV all_args
emitDecs [DClosedTypeFamilyD (DTypeFamilyHead
lambdaName
tvbs
DNoSig
Nothing)
[DTySynEqn Nothing
(foldType (DConT lambdaName) $
map DVarT (all_locals ++ tyNames))
rhs]]
emitDecsM $ defunctionalize lambdaName Nothing tvbs Nothing
let promLambda = foldl apply (DConT (promoteTySym lambdaName 0))
(map DVarT all_locals)
return (promLambda, ADLamE tyNames promLambda names ann_exp)
promoteExp (DCaseE exp matches) = do
caseTFName <- newUniqueName "Case"
all_locals <- allLocals
let prom_case = foldType (DConT caseTFName) (map DVarT all_locals)
(exp', ann_exp) <- promoteExp exp
(eqns, ann_matches) <- mapAndUnzipM (promoteMatch caseTFName) matches
tyvarName <- qNewName "t"
let all_args = all_locals ++ [tyvarName]
tvbs = map DPlainTV all_args
emitDecs [DClosedTypeFamilyD (DTypeFamilyHead caseTFName tvbs DNoSig Nothing) eqns]
-- See Note [Annotate case return type] in Single
let applied_case = prom_case `DAppT` exp'
return ( applied_case
, ADCaseE ann_exp ann_matches applied_case )
promoteExp (DLetE decs exp) = do
unique <- qNewUnique
let letPrefixes = uniquePrefixes "Let" "<<<" unique
(binds, ann_env) <- promoteLetDecs letPrefixes decs
(exp', ann_exp) <- letBind binds $ promoteExp exp
return (exp', ADLetE ann_env ann_exp)
promoteExp (DSigE exp ty) = do
(exp', ann_exp) <- promoteExp exp
ty' <- promoteType ty
return (DSigT exp' ty', ADSigE exp' ann_exp ty')
promoteExp e@(DStaticE _) = fail ("Static expressions cannot be promoted: " ++ show e)
promoteLitExp :: Quasi q => Lit -> q DType
promoteLitExp (IntegerL n)
| n >= 0 = return $ (DConT tyFromIntegerName `DAppT` DLitT (NumTyLit n))
| otherwise = return $ (DConT tyNegateName `DAppT`
(DConT tyFromIntegerName `DAppT` DLitT (NumTyLit (-n))))
promoteLitExp (StringL str) = do
let prom_str_lit = DLitT (StrTyLit str)
os_enabled <- qIsExtEnabled LangExt.OverloadedStrings
pure $ if os_enabled
then DConT tyFromStringName `DAppT` prom_str_lit
else prom_str_lit
promoteLitExp lit =
fail ("Only string and natural number literals can be promoted: " ++ show lit)
promoteLitPat :: MonadFail m => Lit -> m DType
promoteLitPat (IntegerL n)
| n >= 0 = return $ (DLitT (NumTyLit n))
| otherwise =
fail $ "Negative literal patterns are not allowed,\n" ++
"because literal patterns are promoted to natural numbers."
promoteLitPat (StringL str) = return $ DLitT (StrTyLit str)
promoteLitPat lit =
fail ("Only string and natural number literals can be promoted: " ++ show lit)
-- See Note [DerivedDecl]
promoteDerivedEqDec :: DerivedEqDecl -> PrM ()
promoteDerivedEqDec (DerivedDecl { ded_type = ty
, ded_decl = DataDecl _ _ cons }) = do
kind <- promoteType ty
inst_decs <- mkEqTypeInstance kind cons
emitDecs inst_decs