module test

import StdEnv

import Data.Functor
import Control.Applicative
import Control.Monad
import Control.Monad.State

import Text.Parsers.Simple.Core

:: In a b = (:.) infix 0 a b

:: Gram
	= Def (Gram -> In Gram Gram)
	| Def2 ((Gram,Gram) -> In (Gram, Gram) Gram)
	| Lit String
	| Int
	| (-.) infixr 2 Gram Gram
	| (|.) infix 1 Gram Gram
:: Gast
	= INT Int
	| LIT String
	| BIN Gast Gast

parseFromGram :: Gram -> Parser String Gast
parseFromGram (Def g)  = let (body :. gram) = g body in parseFromGram gram
parseFromGram  Int     = INT o toInt <$> pSatisfy (\s->toString (toInt s) == s)
parseFromGram (Lit i)  = LIT <$> pSatisfy ((==)i)
parseFromGram (a -. b) = BIN <$> parseFromGram a <*> parseFromGram b
parseFromGram (a |. b) = parseFromGram a <|> parseFromGram b

//Start = runParser (parseFromGram gram) [".","."]
Start = parse (parseFromGram gram) ["5"]
where
	gram =
		Def \lit =  Int
		         |. Lit "(" -. expr -. Lit ")"
		Def \fac =  lit -. Lit "*" -. fac
		         |. lit -. Lit "/" -. fac
		         |. lit :.
		Def \expr=  fac -. Lit "+" -. expr
		         |. fac -. Lit "-" -. expr
		         |. fac :.
		expr