Hey Haskellers, I had a design question:

I'm using Haskell for the first time for something other than a simple toy application.  I notice I'm coming up with a lot of IO based APIs that looks something like this:

type UserInfo = (String, String)  -- (name, password)

getMagicNumberFromHTTPServer :: UserInfo -> IO (Maybe Int)

getMagicNumberFromHTTPServer user = do

  let curlHTTPRequest = ... --Setup curl HTTP request

  httpRepsponse <- ... -- Make curl HTTP request

  return $ tryGetMagicNumberFromResponse httpResponse

I like this API, because it's easy to understand.  However, I find it hard to test.  In OO land, I'd create a mock CurlHTTPRequest object and pass that into the magic number logic and test for the correct usage of the curl library.  Is there a FP way of achieving the same goals?

I suppose given the example above I could break down the above into several smaller pure functions and test them.  I don't know if this strategy will hold-up when dealing with more complex monads.

Thanks for your time,

Dave