On Fri, May 31, 2013 at 5:02 PM, Miro Karpis
Please, I'm trying to do some user user input validation, but it looks like my approach is not correct. Here is my code:
textInput :: IO () textInput | dataIn == "bye" = return () | otherwise = textInput where dataIn <- getLine
the idea is that when user inputs "bye" the program should end/return. Problem is that I'm getting 'parse error on input `<-'' error. How can I achieve it?
Another question I have is: how can I have more actions in guard, when the condition is valid. Something like (write on IO + return if dataIn == "bye):
textInput :: IO () textInput *| dataIn == "bye" = (puStrLn "quitting", return () ) -- * | otherwise = textInput where dataIn <- getLine
Millions of thanks for any kind of input..
Your initial attempt didn't work because the "foo <- bar" syntax is only available when using a "do block" A straightforward way to do this without "do block" syntax may look something like this: textInput :: IO () textInput = getLine >>= go where go dataIn | dataIn == "bye" = putStrLn "quitting" >> return () | otherwise = textInput Note that putStrLn actually returns IO (), which is the same thing as return (), so it is redundant. You can shorten it to this: textInput :: IO () textInput = getLine >>= go where go dataIn | dataIn == "bye" = putStrLn "quitting" | otherwise = textInput You could do this a bit more compactly by using an anonymous function: textInput :: IO () textInput = getLine >>= dataIn -> if dataIn == "bye" then putStrLn "quitting" else textInput With a do block, your example could go something like this. This is very similar to the above, only using do with "<-" instead of ">>=" and a function: textInput :: IO () textInput = do dataIn <- getLine if dataIn == "bye" then putStrLn "quitting" else textInput -bob