module Core.Utils
    ( programRhss
    , programGlobals
    , isAtomic
    , freeVariables
    )
    where
----------------------------------------------------------------------------------
import Data.Functor.Foldable.TH     (makeBaseFunctor)
import Data.Functor.Foldable
import Data.Set                     (Set)
import Data.Set                     qualified as S
import Core.Syntax
import Control.Lens
import GHC.Exts                     (IsList(..))
----------------------------------------------------------------------------------

programGlobals :: Traversal' (Program b) b
programGlobals = programScDefs . each . _lhs . _1

programRhss :: Traversal' (Program b) (Expr b)
programRhss = programScDefs . each . _rhs

isAtomic :: Expr b -> Bool
isAtomic (Var _)  = True
isAtomic (Lit _)  = True
isAtomic _        = False

----------------------------------------------------------------------------------

freeVariables :: Expr b -> Set b
freeVariables = undefined

-- freeVariables :: Expr' -> Set Name
-- freeVariables = cata go
--     where
--         go :: ExprF Name (Set Name) -> Set Name
--         go (VarF k)         = S.singleton k
--         -- TODO: collect free vars in rhss of bs
--         go (LetF _ bs e)    = (e `S.union` esFree) `S.difference` ns
--             where
--                 es = bs ^.. each . _rhs :: [Expr']
--                 ns = S.fromList $ bs ^.. each . _lhs
--                 -- TODO: this feels a little wrong. maybe a different scheme is
--                 -- appropriate
--                 esFree = foldMap id $ freeVariables <$> es

--         go (CaseF e as)     = e `S.union` asFree
--             where
--                 -- asFree = foldMap id $ freeVariables <$> (fmap altToLam as)
--                 asFree = foldMap (freeVariables . altToLam) as
--                 -- we map alts to lambdas to avoid writing a 'freeVariablesAlt'
--                 altToLam (Alter _ ns e) = Lam ns e
--         go (LamF bs e)      = e `S.difference` (S.fromList bs)
--         go e                = foldMap id e