Haskell reverse polish notation

gistfile1.txt

consumeRPN []     st = last st
consumeRPN (x:xs) st
    | x == "+"  = consumeRPN xs (ll ++ [l1 + l2])
    | x == "-"  = consumeRPN xs (ll ++ [l1 - l2])
    | x == "*"  = consumeRPN xs (ll ++ [l1 * l2])
    | x == "/"  = consumeRPN xs (ll ++ [l1 / l2])
    | otherwise = consumeRPN xs (st ++ [read x])
    where
        l2 = last st
        l1 = last $ init st
        ll = init $ init st

solveRPN x =
    consumeRPN (words x) []
    
main = do
    line <- getLine
    putStrLn $ "The solution is: " ++ show (solveRPN line)
    main