[parenscript-devel] Lexical scoping bug

Red Daly reddaly at gmail.com
Mon Apr 19 19:59:48 UTC 2010

On Mon, Apr 19, 2010 at 11:03 AM, Vladimir Sedach <vsedach at gmail.com> wrote:

> This work was removing the last of the old-style hacks from the
> compiler to clearly separate PS into three parts: the compiler itself,
> the special forms code, and the printer. This reduces code size and
> dependencies significantly, but the ultimate goal (which has mostly
> been achieved) is to provide an intermediary S-exp representation of
> JavaScript code that is directly and efficiently executable as Common
> Lisp code.

What is the motivation for using lists as the intermediate form rather than
CLOS objects?  I suppose that s-expressions makes it easy to use
tree-walking functions out of the box, but there seem to be disadvantages
when it comes to separating syntax from semantics, e.g. addressing the
'else' form of an if via (third if-statement) vs. (if-statement-else

I have not seen the intermediary form and I am sure you have good reasons,
but it is not the direction I would have gone.  Could you explain the choice
perhaps with some motivating examples, to enlighten us all?

> In the future I'll be moving the printer code to a separate project,
> which will also have a parser from JavaScript to this intermediary
> representation. That project will serve as a useful base for JS code
> transformation tools, and I am planning to write a JS->CL compiler on
> top.

Go, Vladimir, go!  That's an ambitious project but I would love to see it

Please not that there is a project with a viable javascript parser and
printer already.  See http://github.com/gonzojive/js-parser

I adapted the code from JWACS (Javascript With Advanced Continuations
Support) into a new project for parsing javascript.  The original JWACS
included a pretty printer and an obfuscating printer that would obfuscate
non-toplevel variables.  It also had a Javascript-like grammar with a few
extra syntax additions.

The syntax tree represents javascript with structures rather than lists for
everything, but you should be able to avoid writing the parser yourself, at
the very least.

> One user-visible change I made in the latest patches is to encourage
> use of CL equality predicates ('==' and '===' are still there but
> marked as deprecated).

> Vladimir

> 2010/4/19 John Pallister <john at synchromesh.com>:
> > +1, as they say...
> >
> > ++Thanks,
> >
> > John :^P
> >
> > On Mon, Apr 19, 2010 at 12:42 AM, Daniel Gackle <danielgackle at gmail.com>
> wrote:
> >> For those of us who are curious, could you talk a bit about the work you
> did
> >> on the compiler?
> >> Thanks Vladimir,
> >> Daniel
> >
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