{-# LANGUAGE GADTs          #-}
{-# LANGUAGE KindSignatures #-}

module Signal.Core.Stream where

import Control.Monad.Operational.Higher

import Control.Applicative
import Control.Monad
import Prelude ((.), ($))

--------------------------------------------------------------------------------
-- * Streams
--------------------------------------------------------------------------------

-- | Imperative model of co-iterative streams
data Stream (instr :: (* -> *) -> * -> *) (a :: *)
  where
    Stream :: Program instr (Program instr a) -> Stream instr a
    
-- | `Shorthand` for streams which produce values of type `exp a`
type Str instr a = Stream instr (IExp instr a)

--------------------------------------------------------------------------------
-- **

-- | ...
repeat :: (e ~ IExp instr) => e a -> Str instr a
repeat = Stream . return . return

-- | ...
map :: (e ~ IExp instr) => (e a -> e b) -> Str instr a -> Str instr b
map f (Stream s) = Stream $ fmap (fmap f) s

--------------------------------------------------------------------------------
-- **

-- | Run stream to produce transition action
run :: Stream instr a -> Program instr a
run (Stream init) = join init

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