[Haskell-beginners] Testing IO based monads and functions
david.hinkes at gmail.com
Fri Jan 27 02:01:57 CET 2012
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,
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