{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleContexts #-}

module SavePos where

import Control.Applicative
import Control.Monad
import Generics.MultiRec
import Satisfy

class SavePos p where
  -- 
  type DataFam p :: * -> *
  
  -- | Signifies that the result of the parser is a member of the data type family and that its position information should be stored.
  savePos :: Ix (DataFam p) a => p a -> p a
  
  -- | A primitive for writing left-recursive grammars. @chainl p q@ recognises @p@, followed by zero or more @q@-@p@ combinations. @p@ is assumed to have already applied savePos on the resulting @a@. For any @q@-@p@ combination recognised in the input, 'savePos' is applied to the resulting @a@.
  chainl :: Ix (DataFam p) a => p a -> p (a -> a -> a) -> p a

-- | A polymorphic applicative parser.
type SatisfyA sym fam a = forall p. (Satisfy p, Alternative p, SavePos p, Input p ~ sym, DataFam p ~ fam) => p a

-- | A polymorphic monadic parser.
type SatisfyM sym fam a = forall p. (Satisfy p, Alternative p, MonadPlus p, SavePos p, Input p ~ sym, DataFam p ~ fam) => p a

-- chainr1 :: Alternative f => f a -> f (a -> a -> a) -> f a
-- chainr1 p op = scan where
--   scan = flip id <$> p <*> rest
--   rest = (flip <$> op <*> scan) <|> pure id