Very cool experiments there. Have you taken the time to understand JSONiq well enough to say whether that would be a good fit?
http://www.jsoniq.org/ On Sun, Jun 30, 2013 at 2:37 PM, Russell Branca <chewbra...@apache.org> wrote: > The discussion of alternative approaches to view engines is one that > bubbles up semi regularly, with the latest addition for a Lua native query > server described in COUCHDB-1842 by Alexander. Lua is a great language for > embedding into systems and provides powerful sandboxing facilities. > > I'm very intrigued by optimizing for the standard use case, where a user > wants to build a simple secondary index on their data, and then use a built > in reduce function. I think we can find a solution that allows a user to > define a doc level transformation in a DSL or query language or some other > approach that allows us to keep the view generation functionality within > the Erlang VM and avoid the overhead costs of using an external engine. > > I do think it makes sense to have an external engine for flexibility, and > allowing us to focus on the simple cases while providing a fallback for > more complex user defined functions. > > To experiment with different approaches, I built a Lisp interpreter on top > of Erlang with the premise of white listing the entire language, allowing > explicit control over what the user can and cannot do in view functions. > You can see it here: [Lispenport](https://github.com/chewbranca/lispenport). > It's by no means a full solution, but it has some interesting properties > such as really just being syntactic sugar on top of Erlang and all > constructs are direct Erlang terms, even lambdas are just Erlang funs. > > Now, while I would be intrigued by a Lisp DSL for user defined functions in > CouchDB, I didn't expect that to be well received by everyone, so I've > considered this just an experiment. If we were going to take this approach, > I would rather take Lisp Flavored Erlang (LFE, another project by Robert > Virding along with Luerl, and also erlog, a Prolog interpreter in Erlang), > and rip out all the pieces we would not want a user to access and use LFE > as a base starting point. LFE compiles down to intermediate Erlang bytecode > and is designed to follow Erlang functionality, making it a nice option for > building a view engine to execute in the Erlang VM. > > I've also toyed around with the idea of building a NIF around [JQ]( > http://stedolan.github.io/jq/) which is a great application for slicing and > dicing json data structures written in C. > > So my general proposal for discussion is that we build a minimal DSL of > some sort, providing fast and simple doc manipulations that executes > securely in the Erlang VM, and then we abstract out all functionality for a > "full" view engine, list functions, show functions, etc to a separate > engine that is easily swappable and not required for standard functionality. > > Thoughts? > > > -Russell
