Standard in and Standard out (STDIN/STDOUT) are very common methods of interacting with the user. Standard in is typically the keyboard and standard out is the terminal. Haskell makes this very easy to access. The getLine function gets a value from the user and putStrLn and putStr allow you to write to output. The ++ operator is used to concatenate strings.
In Haskell, you can access the command line arguments with getArgs. Check out this example.
Haskell is a purely functional programming language create in 1990. This Hello World example will help you get started with Haskell. Install Haskell for your system from the Haskell website. The program installed is called ghc which stands for the Glasgow Haskell Compiler. It can be run interactively or as a compiler.