I'd rather use pattern matching in this case: check x assoc = case lookup x of Just found -> putStrLn ("found " ++ found) _ -> Not really shorter but I think it's cleaner this way. On Thu, Aug 1, 2013 at 5:00 PM, vold wrote:

I've defined a function similar to

check x assoc = let found = lookup x assoc in when (isJust found) $ putStrLn $ "found " ++ fromJust found

which I've used several times from within the IO monad. Is there a more compact way of doing this?

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

On Thu, Aug 1, 2013 at 6:00 PM, vold wrote:

I've defined a function similar to

check x assoc = let found = lookup x assoc in when (isJust found) $ putStrLn $ "found " ++ fromJust found

which I've used several times from within the IO monad. Is there a more compact way of doing this? Firstly, note that it is more idiomatic to move the IO code to other functions, which would allow check to be pure. Secondly, one can use the fact that Maybe is a Functor to rewrite check as follows: check x db = maybeToIO $ (putStrLn . ("found"++)) <$> x `lookup` db where maybeToIO = fromMaybe (return ()) The refactoring of maybeToIO isn't strictly necessary, but I found it clearer. HTH, Gesh