You've seen such a prompt very often.
Your cursor is just after the prompt with 1 space. If you type
y the process will continue and if you type any other characters, not only
n, the process will stop. This is easy to implement in Ruby.
print "OK? [y/n] " if gets.chars.first == 'y' puts 'go go go' else puts 'nooo' end
It seems to be easy for Haskell beginners to implement it in Haskell like the following code.
main = do putStr "OK? [y/n] " s <- getLine case (head s) of 'y' -> putStrLn "Nice" otherwise -> putStrLn "omg"
But it doesn't work appropriately due to
stdout buffering. Haskell has
IO library that can control buffering. Add
hFlush stdout after importing the library.
import IO (hFlush, stdout) main = do putStr "OK? [y/n] " hFlush stdout s <- getLine case (head s) of 'y' -> putStrLn "Nice" otherwise -> putStrLn "omg"