ExeMagic.hs

module ExeMagic where

    import qualified Data.ByteString.Lazy as L
    
    hasExeMagic :: L.ByteString -> Bool
    hasExeMagic content = L.take 2 content == exeMagic
        where exeMagic = L.pack [0x4D, 0x5A]

    isExeFile :: FilePath -> IO Bool
    isExeFile path = do
        content <- L.readFile path
        return (hasExeMagic content)

Main.hs

module Main (main) where
    import System.Environment (getArgs)
    import ExeMagic (isExeFile)

    main = do
        args <- getArgs
        case args of
            [inputFile] -> do
                result <- isExeFile inputFile
                print result
            _ -> print "You must pass 1 command line argument"