I am still in an imperative way of thinking. In this example here; how would I call "putStrLn" and then set the function with a value. Eg:

aa :: String -> IO ()
aa instr = do
putStrLn "abc"
putStrLn "abc"
return "123"

--- The error I am getting.

    Couldn't match expected type `()' against inferred type `[Char]'
    In the first argument of `return', namely `"123"'
    In the expression: return "123"
    In the expression:
    do putStrLn "abc"
       putStrLn "abc"
       return "123"