area.hs

import System.Environment
import Data.List

-- takes first string element of given list of strings
first :: [String] -> String
first args
  | null args = error "You must provide a radius"
  | otherwise = head args

-- casts string to double
str2int :: String -> Double
str2int str = read str :: Double

-- TODO write the area function

main = do
  args <- getArgs
  print (area (str2int (first args)))