module Data.Array.Comfort.Construct.Private where

import qualified Data.Array.Comfort.Shape as Shape

import qualified Control.Monad.Trans.Writer as MW
import qualified Control.Monad.Trans.Class as MT


newtype T tag a i = Cons (MW.WriterT [a] (Shape.Construction tag) i)

instance Functor (T tag a) where
   fmap f (Cons w) = Cons (fmap f w)

instance Applicative (T tag a) where
   pure i = Cons (pure i)
   Cons f <*> Cons w = Cons (f<*>w)

element :: a -> T tag a (Shape.ConsIndex tag)
element a = Cons $ MW.tell [a] >> MT.lift Shape.consIndex

run :: T tag a ixs -> (ixs, (Shape.Constructed tag, [a]))
run (Cons mw) =
   case Shape.construct $ MW.runWriterT mw of
      (sh,(ixs,xs)) -> (ixs, (sh,xs))