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From Simon Metson <>
Subject Re: On Alternative View Engines
Date Mon, 01 Jul 2013 10:11:20 GMT
Would a DSL just define views or also be used to query them (manage start/end key, keys, limit,
reduce, group etc.)? What's the goal; something simpler than writing javascript? something
more familiar to SQL users? faster view builds? 

What about building something like

Worth noting that a DSL didn't come up in Alan's tour of customers. 

On Sunday, 30 June 2013 at 22:47, Robert Newson wrote:

> +1. A natively executed DSL has been on the wishlist for a while now.
> B.
> On 30 June 2013 22:37, Russell Branca < (>
> > 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](
> > 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](
> > 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 

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