module test

import StdEnv

import Data.Functor
import Control.Applicative

import Text.Parsers.Simple.Core
import Text.Parsers.Simple.Chars

preprocess :: [Char] -> [Char]
preprocess c = ['((((':foldr prep ['))))'] c]
where
	prep '(' cs = ['(','(','(','(':cs]
	prep ')' cs = [')',')',')',')':cs]
	prep '^' cs = [')','^','(':cs]
	prep '*' cs = [')',')','*','(','(':cs]
	prep '/' cs = [')',')','/','(','(':cs]
	prep '+' cs = [')',')',')','+','(','(','(':cs]
	prep '-' cs = [')',')',')','-','(','(','(':cs]
	prep c cs   = [c:cs]

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

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

Start = parse parseExpr (preprocess ['a'])
//Start = parse parseExpr (preprocess ['a*b+c^d/e'])