readIO parse error haskell, this close
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So i've been enjoying this challenging language, im currently working on an assingment for school 
now this is what it says 
i need to prompt the use for a list of numbers then display the avergae of the list , im so close of figuring it out. However i get this weird parse error "Exception: user error (Prelude.readIO: no parse)" 

here is my code Please ignore indentation on my textpad everything is indented correctly: 

      module Main (listM', diginums', getList, main) where 

      import System.IO     
      import Data.List

      diginums' = []
      listM' = [1, 2, 3]
      average' = (sum diginums') / (fromIntegral (length diginums'))
      getList :: IO [Double]
      getList = readLn

       main = do


       putStrLn "Please enter a few numbers" 
       diginums' <- getList
       putStrLn $ show average' 

Terminal Prompts : Enter a few #'s

I Enter : 123 

ERROR : Exception: user error (Prelude.readIO: no parse)

I know my functions are working correctly to calculate the avg now i think my problem is that when i take in the list of numbers from the user i dont correctly parse them to type double for my avg function. 

Thanks Everyone for looking ;) 