import Text.Parsec
import qualified Text.Parsec.Token as P
import Text.Parsec.Language
import Control.Applicative hiding ((<|>))
import Control.Arrow

data T = N Double | T :* T | T :/ T | T :+ T | T :- T
       | B Bool | T :> T | T :< T | T :== T
       | If T T T
  deriving (Show)

a --> b = (a, b <$ rOp a)

-- Operators: from lowest to highest precedence
ops = [ [">" --> (:>), "<" --> (:<), "==" --> (:==)]
      , ["+" --> (:+), "-" --> (:-)]
      , ["*" --> (:*), "/" --> (:/)]
      ]

myL = P.makeTokenParser $ javaStyle {
		  P.reservedOpNames = map fst $ concat ops
		, P.reservedNames = ["if", "else", "true", "false"]
        }
rOp = P.reservedOp myL
rW = P.reserved myL
parens = P.parens myL
braces = P.braces myL
bool = B <$> ((True <$ rW "true") 
         <|> (False <$ rW "false"))
num = N <$> P.float myL
if_ = If <$> (rW "if" *> expr) 
         <*> (braces expr) 
         <*> (rW "else" *> braces expr)

infix_ x@(l:t) = do
  a <- math t
  f <- choice $ map snd l
  b <- math x
  return $ f a b

math' = parens $ math ops
math [] = try num <|> try bool <|> parens expr
math l@(_:t) = try math' <|> try (infix_ l) <|> math t

test1 = "1.3 + 1.0 * (2.1 + 3.1) + 1.5"

test2 = "if (2.0 + 2.0 * 1.5== 4.0) { \
        \  if(true == false) {        \ 
        \    true                     \
        \  } else {                   \ 
        \    2.1                      \
        \  }                          \ 
        \} else {                     \ 
        \  1.0                        \ 
        \}                            "

expr = try if_ <|> try bool <|> math ops

main = mapM (print . parse (expr <* eof) "") [test1, test2, "2.1 == 1.1"]