I created my own version of getLine like this: getLine' :: IO String getLine' = do x <- getChar if x == '\n' then return [] else do xs <- getLine' return (x:xs) Basically I created a new file called test.hs and copied above code into it. I opened WinGHCi afresh and :load test.hs I can run getLine' in WinGHCi with no problem. But how does WinGHCi know about getChar and IO? I assumed I would have to import like this: import System.IO Is it because WinGHCi does this import for me? If I write this program and invoke using runghci: getLine' :: IO String getLine' = do x <- getChar if x == '\n' then return [] else do xs <- getLine' return (x:xs) main = do getLine' It also works without complaining. Is there a list of built-in libraries? Is that platform dependent?