Abstract Handler

[jkarni]

@kosmikus suggested this a while back, but: is everyone okay with making Handler it's own abstract monad (rather than a type synonym)? This will make it easier to add more instances without breaking backwards compatibility.

Currently I'm thinking of making it a MonadResource (as part of the work on file uploads, I'd be using MonadResource anyhow, and it seems reasonable to allow handlers to also register cleanup actions). I've also thought about adding functions:

etagIs :: Etag -> Handler ()
lastModifiedAt :: DateTime -> Handler ()

With the functionality that if there is a If-Match/If-None-Match (or If-Modified-Since/If-Unmodified-Since) header in the request that doesn't/does match the mentioned Etag/DateTime, and appropriate throwError is thrown. (This seems like a nice API for servers, but I still haven't figured out how it would work for clients.)

[phadej]

I'm 👍, and let's make ClientM a newtype as well!

[jkarni]

ClientM already is!

[phadej]

Oh, I didn't even realised that. I'd say the Handler change should follow.

[kosmikus]

Unsurprisingly, I support this change. I still don't like the M in ClientM, but that's unrelated ...

[3noch]

Yes please!