Re: Composability

/ Jeni Tennison <jeni@jenitennison.com> was heard to say:
[...]
| I'm pretty sure the world won't end no matter what we do in XProc. I'm
| also pretty sure that once people start writing pipelines "in anger",
| a lot of them are going to bang up against this brick wall.

I hate having to make decisions based on what we think users will do
in the future. I'm not saying we can avoid it, I'm just saying...

| We have lots of built-in steps that accept XPath expressions as
| options, because it's so darned useful. It seems insane not to support
| users writing their own pipelines that similarly take XPath expression
| options, and not to support users writing wrappers around those
| built-in steps.

Nothing in the current design prevents users from writing pipelines
that take XPath expressions as options or writing wrappers around
built-in steps that take them.

What the current design does not enable are

1. XPath expressions passed as command-line options to a pipeline using
   prefixes different than the pipeline author provided in the
   pipeline.

2. XPath expressions loaded from external configuration files using
   prefixes different than the pipeline author provided in the
   pipeline.

I predict that, even if XProc is as wildly successful as XSLT, it will
be a fairly small minority of users who will encounter these problems.

Three things motivate me to attempt to solve this problem in V1:

1. If you encounter the problem, there's no straightforward workaround.

2. The real screw case is where you attempt to use a prefix that the
   pipeline author used, but with a different binding. In that case
   you don't get an error, you just get the wrong result. Languages
   shouldn't allow that sort of user error to go undetected.

3. I'm an engineer.

On the other hand, the longer it takes for us to get V1 out, and the
more complicated we make it, the less likely it is to be successful.
So there are pragmatic reasons to say, "not in V1".

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Use the memory of thy predecessor
http://nwalsh.com/            | fairly, and tenderly; for if thou dost
                              | not, it is a debt will sure be paid,
                              | when thou art gone.--Sir Francis Bacon