-- | Utilities for constructing and destructing compound expressions.
--
--   For the Simple version of the AST.
module DDC.Core.Flow.Exp.Simple.Compounds
        ( module DDC.Type.Exp.Simple.Compounds

          -- * Lambdas
        , xLAMs
        , xLams
        , makeXLamFlags
        , takeXLAMs
        , takeXLams
        , takeXLamFlags

          -- * Applications
        , xApps
        , takeXApps
        , takeXApps1
        , takeXAppsAsList
        , takeXConApps
        , takeXPrimApps

          -- * Lets
        , xLets
        , splitXLets 
        , bindsOfLets
        , specBindsOfLets
        , valwitBindsOfLets

          -- * Patterns
        , bindsOfPat

          -- * Alternatives
        , takeCtorNameOfAlt

          -- * Witnesses
        , wApp
        , wApps
        , takeXWitness
        , takeWAppsAsList
        , takePrimWiConApps

          -- * Types
        , takeXType

          -- * Data Constructors
        , xUnit, C.dcUnit
        , C.takeNameOfDaCon
        , C.takeTypeOfDaCon)
where
import DDC.Core.Flow.Exp.Simple.Exp
import DDC.Type.Exp.Simple.Compounds
import qualified DDC.Core.Exp.Annot     as C


-- Lambdas ---------------------------------------------------------------------
-- | Make some nested type lambdas.
xLAMs :: [Bind n] -> Exp a n -> Exp a n
xLAMs bs x
        = foldr XLAM x bs


-- | Make some nested value or witness lambdas.
xLams :: [Bind n] -> Exp a n -> Exp a n
xLams bs x
        = foldr XLam x bs


-- | Split type lambdas from the front of an expression,
--   or `Nothing` if there aren't any.
takeXLAMs :: Exp a n -> Maybe ([Bind n], Exp a n)
takeXLAMs xx
 = let  go bs (XLAM b x) = go (b:bs) x
        go bs x            = (reverse bs, x)
   in   case go [] xx of
         ([], _)        -> Nothing
         (bs, body)     -> Just (bs, body)


-- | Split nested value or witness lambdas from the front of an expression,
--   or `Nothing` if there aren't any.
takeXLams :: Exp a n -> Maybe ([Bind n], Exp a n)
takeXLams xx
 = let  go bs (XLam b x) = go (b:bs) x
        go bs x          = (reverse bs, x)
   in   case go [] xx of
         ([], _)        -> Nothing
         (bs, body)     -> Just (bs, body)


-- | Make some nested lambda abstractions,
--   using a flag to indicate whether the lambda is a
--   level-1 (True), or level-0 (False) binder.
makeXLamFlags :: [(Bool, Bind n)] -> Exp a n -> Exp a n
makeXLamFlags fbs x
 = foldr (\(f, b) x'
           -> if f then XLAM b x'
                   else XLam b x')
                x fbs


-- | Split nested lambdas from the front of an expression, 
--   with a flag indicating whether the lambda was a level-1 (True), 
--   or level-0 (False) binder.
takeXLamFlags :: Exp a n -> Maybe ([(Bool, Bind n)], Exp a n)
takeXLamFlags xx
 = let  go bs (XLAM b x)  = go ((True,  b):bs) x
        go bs (XLam b x)  = go ((False, b):bs) x
        go bs x           = (reverse bs, x)
   in   case go [] xx of
         ([], _)        -> Nothing
         (bs, body)     -> Just (bs, body)


-- Applications ---------------------------------------------------------------
-- | Build sequence of value applications.
xApps   :: Exp a n -> [Exp a n] -> Exp a n
xApps t1 ts     = foldl XApp t1 ts


-- | Flatten an application into the function part and its arguments.
--
--   Returns `Nothing` if there is no outer application.
takeXApps :: Exp a n -> Maybe (Exp a n, [Exp a n])
takeXApps xx
 = case takeXAppsAsList xx of
        (x1 : xsArgs)   -> Just (x1, xsArgs)
        _               -> Nothing


-- | Flatten an application into the function part and its arguments.
--
--   This is like `takeXApps` above, except we know there is at least one argument.
takeXApps1 :: Exp a n -> Exp a n -> (Exp a n, [Exp a n])
takeXApps1 x1 x2
 = case takeXApps x1 of
        Nothing          -> (x1,  [x2])
        Just (x11, x12s) -> (x11, x12s ++ [x2])


-- | Flatten an application into the function parts and arguments, if any.
takeXAppsAsList  :: Exp a n -> [Exp a n]
takeXAppsAsList xx
 = case xx of
        XApp x1 x2      -> takeXAppsAsList x1 ++ [x2]
        _               -> [xx]


-- | Flatten an application of a primop into the variable
--   and its arguments.
--   
--   Returns `Nothing` if the expression isn't a primop application.
takeXPrimApps :: Exp a n -> Maybe (n, [Exp a n])
takeXPrimApps xx
 = case takeXAppsAsList xx of
        XVar (UPrim p _) : xs -> Just (p, xs)
        _                     -> Nothing

-- | Flatten an application of a data constructor into the constructor
--   and its arguments. 
--
--   Returns `Nothing` if the expression isn't a constructor application.
takeXConApps :: Exp a n -> Maybe (DaCon n (Type n), [Exp a n])
takeXConApps xx
 = case takeXAppsAsList xx of
        XCon dc : xs  -> Just (dc, xs)
        _             -> Nothing


-- Lets -----------------------------------------------------------------------
-- | Wrap some let-bindings around an expression.
xLets :: [Lets a n] -> Exp a n -> Exp a n
xLets lts x
 = foldr XLet x lts


-- | Split let-bindings from the front of an expression, if any.
splitXLets :: Exp a n -> ([Lets a n], Exp a n)
splitXLets xx
 = case xx of
        XLet lts x 
         -> let (lts', x')      = splitXLets x
            in  (lts : lts', x')

        _ -> ([], xx)


-- | Take the binds of a `Lets`.
--
--   The level-1 and level-0 binders are returned separately.
bindsOfLets :: Lets a n -> ([Bind n], [Bind n])
bindsOfLets ll
 = case ll of
        LLet b _          -> ([],  [b])
        LRec bxs          -> ([],  map fst bxs)
        LPrivate bs _ bbs -> (bs, bbs)


-- | Like `bindsOfLets` but only take the spec (level-1) binders.
specBindsOfLets :: Lets a n -> [Bind n]
specBindsOfLets ll
 = case ll of
        LLet _ _         -> []
        LRec _           -> []
        LPrivate bs _ _  -> bs


-- | Like `bindsOfLets` but only take the value and witness (level-0) binders.
valwitBindsOfLets :: Lets a n -> [Bind n]
valwitBindsOfLets ll
 = case ll of
        LLet b _        -> [b]
        LRec bxs        -> map fst bxs
        LPrivate _ _ bs -> bs


-- Alternatives ---------------------------------------------------------------
-- | Take the constructor name of an alternative, if there is one.
takeCtorNameOfAlt :: Alt a n -> Maybe n
takeCtorNameOfAlt aa
 = case aa of
        AAlt (PData dc _) _     -> C.takeNameOfDaCon dc
        _                       -> Nothing


-- Patterns -------------------------------------------------------------------
-- | Take the binds of a `Pat`.
bindsOfPat :: Pat n -> [Bind n]
bindsOfPat pp
 = case pp of
        PDefault          -> []
        PData _ bs        -> bs


-- Witnesses ------------------------------------------------------------------
-- | Construct a witness application
wApp :: Witness a n -> Witness a n -> Witness a n
wApp = WApp


-- | Construct a sequence of witness applications
wApps :: Witness a n -> [Witness a n] -> Witness a n
wApps = foldl wApp


-- | Take the witness from an `XWitness` argument, if any.
takeXWitness :: Exp a n -> Maybe (Witness a n)
takeXWitness xx
 = case xx of
        XWitness t -> Just t
        _          -> Nothing


-- | Flatten an application into the function parts and arguments, if any.
takeWAppsAsList :: Witness a n -> [Witness a n]
takeWAppsAsList ww
 = case ww of
        WApp w1 w2 -> takeWAppsAsList w1 ++ [w2]
        _          -> [ww]


-- | Flatten an application of a witness into the witness constructor
--   name and its arguments.
--
--   Returns nothing if there is no witness constructor in head position.
takePrimWiConApps :: Witness a n -> Maybe (n, [Witness a n])
takePrimWiConApps ww
 = case takeWAppsAsList ww of
        WCon wc : args | WiConBound (UPrim n _) _ <- wc
          -> Just (n, args)
        _ -> Nothing


-- Types ----------------------------------------------------------------------
-- | Take the type from an `XType` argument, if any.
takeXType :: Exp a n -> Maybe (Type n)
takeXType xx
 = case xx of
        XType t -> Just t
        _       -> Nothing


-- Units -----------------------------------------------------------------------
-- | Construct a value of unit type.
xUnit   :: Exp a n
xUnit = XCon C.dcUnit