Re: Left field

James Fuller <jim@webcomposite.com> writes:
> I think you had some typos in some of the examples.

Quite possibly.

> We could use a variable to set expression language, like
>
>    $p:expression-language = "'com.marklogic:xquery:1.0-ml"

Maybe. It feels more like a declaration than a variable to me, but
setting it to a possibly structured string value like that makes
sense.

> The logic branching reminds me that boolean logic is just a
> constrained case of fuzzy logic ... there is some attraction to having
> a more rules based approach and I wonder if we could not achieve that
> here.

That’s an interesting idea.

> Lastly, your examples reinforce (for me) the need to delineate between
> pipes and variables.

I was trying to finesse my way around that issue, actually. The proposal
has, I think, only one kind of variable in the language: names for
binding contexts.

Binding contexts in turn are just hashes of names to values. The
values can be anything. One thing they can be is a pipe. If you use
the pipe in a context where some value is needed, then you’re going to
have to stop and wait and collect the values at that point. As long as
you don’t, the implementation is free to stream them any way it likes.

Take a linear pipe:

  a() -> b() -> c()

The implementation can run all three of these in parallel. It can even
run b() on a different node in the network, as long as it passes
everything that a() puts in its output binding context to b() and
everything b() outputs to c().

Making that work requires that the steps read from their ports ordinally
becaues the names will be wrong.

  a() -> [$source=ref("result") ]
      -> b()
      -> [$source=ref("result") ]
      -> c()

is probably still streamable as long as the implementation is clever
enough to recognize that all that’s going on is a little shuffling of
names in the binding context.

  a() -> [$source=ref("result") ]
      -> ( $source instanceof Object ) { something() -> [$source=ref("result")] }
      -> c()

Naively, irrespective of the expression language, whenever a binding
set feeds into a conditional or {{ }} block, the implementation has to
collect all of the outputs together and put them in the *expression*
context for the following expression. (Meaning, generally, that ports
have to be realized into sequences of objects.)

Less naively, if the implementation can do sufficient static analysis
of the expression to assure that some port value isn’t used, it can
just pass that through without stalling.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
Lead Engineer
MarkLogic Corporation
Phone: +1 512 761 6676
www.marklogic.com