module test

import StdEnv
import Data.Maybe
import Data.Functor
import Data.Tuple
import Data.List
import Control.Applicative
import Control.Monad

import Text.Parsers.Simple.ParserCombinators

operators :: [[Char]]
operators =
	[ ['+-']
	, ['*/']
	, ['^']
	]

preprocess :: [[Char]] [Char] -> [Char]
preprocess ops c = rep '(' maxb (foldr prep (rep ')' maxb []) c)
where
	maxb = length ops + 1

	rep :: Char Int [Char] -> [Char]
	rep c 0 r = r
	rep c i r = [c:rep c (i-1) r]

	prep '(' cs = rep '(' maxb cs
	prep ')' cs = rep ')' maxb cs
	prep c cs = maybe [c:cs] (\(_, s)->rep ')' s [c:rep '(' s cs])
		(find (isMember c o fst) (zip2 ops [maxb-1,maxb-2..0]))

:: Expr = BinOp Expr Char Expr | Lit Int | Var [Char]

parseExpr :: Parser Char Expr
parseExpr = flip pChainl1 (flip BinOp <$> pOneOf ['+^-/*'])
	(   Lit o toInt o toString <$> some pDigit
	<|> Var <$> some pAlpha
	<|> pToken '(' *> parseExpr <* pToken ')'
	)

//Start = parse parseExpr (preprocess ['a'])
//Start = preprocess operators ['a*1']
Start = runParser parseExpr (preprocess operators ['5+5*5'])