Question

How do I check a client?

case e of
    Just e -> let client = (e, sink)
    Nothing -> let client = false

case msg of
    _   | not client -> do nothing
        | msg -> do something
        | otherwise -> do print "i was born in..."

Probably not even close but hope its clear what I wanted to do.

Answer 1

I think you are looking for something like this:

m e sink = do
    case e of
        Nothing -> print "No Client"
        (Just c) -> do
            -- Client is in c

If it isn’t, we really need more code and description about what you are trying to do.

Otherwise, I have to tell you, it seems like you’re doing imperative stuff in Haskell. You should go back and read some tutorials, like Learn You A Haskell and Real World Haskell. Especially the latter contains a lot of Haskell application examples about actual Haskell programs.