Support for querying multiple databases via Idiom tracking

[schmitch]

currently It's possible to know that a query is only read only, transactionel or read/write.
however it's not possible to route the query to a different database once, because of type inference.

☝️ 23. November 2017 07:59

[mosyp]

@fwbrasil that's something I've been talking in #881 (comment).
I have been doing some research on this in https://github.com/mentegy/quill/blob/idiom-bound-quill/quill-core/src/main/scala/io/getquill/monad/IOMonad.scala#L56 and https://github.com/mentegy/quill/blob/idiom-bound-quill/quill-core/src/main/scala/io/getquill/idiom/Idiom.scala.

So the point is that Idiom will extends CoreDsl expect EncodingDsl, the latest will be still remained in contexts. All actions created within idiom will be IO monad and could be ran across several sources/contexts which support that idiom.
To track the idiom within IO I've enriched this with new type param trait IO[+T, -E <: Effect, I <: Idiom].

However I've not figured out yet how to do with type materialization, e.g. Run* -> context's bound type

[fwbrasil]

@mentegy the main challenge is the liftings and Quoted dependent type. I've tried something here but had a few problems. I'm not sure I understand your approach, could you give more details?