Re: Nyacc question: [found] where are the actions bound?

[Matt Wette <matt.wette@gmail.com>]

On 3/14/20 4:59 AM, tomas@tuxteam.de wrote:
> On Sun, Mar 08, 2020 at 08:10:50AM -0700, Matt Wette wrote:
>>
>> On 3/8/20 3:14 AM, tomas@tuxteam.de wrote:
>>> Hi,
> [...]
>
>>> My question is: where is the stuff resolved which is mentioned
>>> in grammar actions?
> Hah. Managed to answer my own question by reading the source.
>
> For the benefits of others who might have a similar question
> (without knowing how to articulate it, like it happened to
> me), here's the answer:
>
> Yes, the actions are "resolved" wrt the (calling) module's
> top level environment. The magic happens here (that's wrt the
> all-fresh V1.01.2), around lines 47 ff, in module/nyacc/parse.scm:
>
>    (define (make-xct av)
>      (if (procedure? (vector-ref av 0))
>          av
>          (vector-map (lambda (ix f) (eval f (current-module)))
>        (vector-map (lambda (ix actn) (wrap-action actn)) av))))
>
> It's the (eval f (current-module)) which does the trick. The
> trick happens in make-lalr-parser.
>
> Background: I envisioned something like
>
>    (let ( ...some environment for the actions...)
>      ...make-lalr-parser...)
>
> and have make-lalr-parser pick up the bindings in the lexical
> environment.
>
> but had to realize that make-lalr-parser ignores the lexical
> environment. That's now clear to me, because (eval ... (current-module))
> looks at the caller's module's top-level bindings.
>
> One would have to call local-eval (from (ice-9 local-eval)) and
> explicitly pass (the-environment) (from the same module) to
> achieve what I had in mind.
>
> Not that I'm proposing that, mind you. I still barely know what
> I'm doing at this point. Probably there are very good reasons
> to resort to the (top-level) module bindings.
>
> I just wanted to understand, and I think I do now :-)
>
> As to your other proposal (writing out the pre-compiled parser
> with write-lalr-*), I think it's orthogonal to my issue. This
> might come in handy when the parser is heavy enough that it
> takes a significant time constructing it (which it is not in my
> little use case for now)
>
> Thanks & cheers
> -- tomás
I get it now.  What you expect makes much sense.
  I will think about that.

Matt