On Tue, Jul 31, 2018 at 09:47:07AM +0200, Marc Busqué wrote:
Apologies, I clearly asked the question in a rushed way...
I'm working with [req](http://hackage.haskell.org/package/req) package. I need to parse a url from a string, but I don't know whether its schema will be `http` or `https`. However, `req` just provides me with two functions:
``` parseUrlHttp :: ByteString -> Maybe (Url Http, Option scheme) parseUrlHttps :: ByteString -> Maybe (Url Https, Option scheme) ```
This just sounds like bad API design from req. Why is the API not parseUrl :: ByteString -> Maybe (Either (Url Http) (Url Https), Option scheme)
What I think is a common case here (perhaps I'm wrong) is the need to choose between two or more `Maybe` values where at most one of them will be a `Just`.
If that invariant really does hold then the authors of those functions should encode the invariant in the type. Requiring clients to observe the invariant for themselves sounds like a bad idea. Tom