warning about GHC 7.4 and happstack-state

[Jeremy Shaw]

Just a heads up!

happstack-state compiles and works with GHC 7.4. HOWEVER, it does not correctly read old checkpoint files.

The reason is because the names generated by the typeable instance are no longer fully qualified.

When compiling apps I get a warning:

  Warning: In the use of `mkTyCon'
(imported from Happstack.Data, but defined in Data.Typeable):
Deprecated: "either derive Typeable, or use mkTyCon3 instead"

I think that if we conditionally use mkTyCon3 when available that might provide backwards compatibility.

If someone wants to make a patch there is a bug:

http://code.google.com/p/happstack/issues/detail?id=164&thanks=164&ts=1328049703

On the other hand, maybe this is the kick in the pants you need to switch to acid-state. The migration guide for that is here:

http://code.google.com/p/happstack/wiki/HapstackStateToAcidState

- jeremy