userinput.hs

module Main where

import           Control.Monad
import           System.Environment

main = do
  args <- getArgs
  if null args
    then mainCli
    else mainArgs args

mainArgs args = do
  let name = unwords args
  greet name

mainCli = do
  putStrLn "What's your name?"
  name <- getLine
  unless (null name) $ do
      greet name
      main

greet :: String -> IO ()
greet name = putStrLn $ "Hi " ++ name ++ "!"