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From Alexander Shorin <>
Subject Re: On Alternative View Engines
Date Mon, 01 Jul 2013 10:23:30 GMT
While DSL will be not yet another subset of SQL it's fine (: DSL
should focus on solving specific problem, but not try to adopt some
other solution for it. There are JSON Pointer[1] and JSON Patch[2]
specifications that may be used to play around. I think, this DSL have
to be JSON-driven as CouchDB is.

Anyway, it's very interesting, but also very hard task to create such
DSL that would be simple, effective,
not-allowing-to-shoot-yourself-in-leg and intuitive for the end user.


On Mon, Jul 1, 2013 at 2:11 PM, Simon Metson <> wrote:
> Hi,
> 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.
> Cheers
> Simon
> 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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