[racket] Lack of understanding of how module loading work with (for-syntax)

Jay,

Section 1.1.10 does not really answer my question:
I had no doubts in the first place about phase 0 and
phase1 being separated from each other.

I am not so sure about whether the phase 1 data
is shared between different "load chain" of a module.
That has to to with visits and instantiatiins I beleive.
I will keep reading, though would not mind if somebody
points me to the answer directly.

Regards,

Dmitry
On Sep 24, 2013 11:47 PM, "Jay McCarthy" <jay.mccarthy at gmail.com> wrote:

> The details of your answer are in Reference section 1.1.10
>
>
> http://docs.racket-lang.org/reference/eval-model.html#(part._module-eval-model)
>
> Basically, the runtime and compile time of every module is distinct
> and not shared between compiles of different modules. Racket
> guarantees that they are never shared, no matter how many modules are
> already (or not already) compiled when you start. You may think there
> is sharing, but there is not. Instead, when d runs it runs the syntax
> toplevel of b and c, despite having compiled them separately. (You
> could observe the difference if you changed your begin-for-syntax code
> into code that happens to run during the expansion of b and c.)
>
> The justification for this behavior is elaborated in Matthew Flatt's
> "Metaprogramming Time!" [1] and the paper "Composable and Compilable
> Macros" [2]
>
> Jay
>
> 1. http://www.infoq.com/presentations/racket
> 2. http://www.cs.utah.edu/plt/publications/macromod.pdf
>
> Jay
>
> On Tue, Sep 24, 2013 at 1:38 PM, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:
> > Hello,
> >
> > I have a problem that originates from the fact that I do not
> > really understand the innards of the mechanism of module loading.
> >
> > Basically, I want to share a hashtable stored in some module
> > between a number of other modules. Moreover, I want to do
> > that on the syntax level. In this example, I will do that
> > in parallel on run level and syntax level, showing problems
> > in the second case.
> >
> > ~~~~~ a.rkt:
> >
> > #lang racket
> > (provide h
> >          (for-syntax s-h))
> >
> > (define h (begin (printf "making h\n") (make-hash)))
> >
> > (define-for-syntax s-h  (begin (printf "making s-h\n") (make-hash)))
> >
> >
> > ~~~~~ b.rkt:
> >
> > #lang racket
> >
> > (require "a.rkt")
> > (hash-set! h 1 "x")
> > (begin-for-syntax
> >   (hash-set! s-h 1 "xx"))
> >
> >
> > ~~~~~ c.rkt:
> >
> > #lang racket
> > (require "a.rkt")
> > (hash-set! h 2 "y")
> > (begin-for-syntax
> >   (hash-set! s-h 2 "yy"))
> >
> > ~~~~~ d.rkt:
> >
> > #lang racket
> > (require "a.rkt")
> > (require "b.rkt")
> > (require "c.rkt")
> >
> > (define-syntax (print-s-h stx)
> >   (syntax-case stx ()
> >     ((_)
> >      (for (((key val) s-h))
> >        (printf "~a : ~a\n" key val))
> >      #'(void))))
> >
> > (for (((key val) h))
> >   (printf "~a : ~a\n" key val))
> >
> > (print-s-h)
> >
> >
> >
> > What I get:
> >
> > making s-h
> > making s-h
> > making s-h
> > making s-h
> > making s-h
> > making s-h
> > making s-h
> > 1 : xx
> > 2 : yy
> > making s-h
> > making s-h
> > making h
> > 1 : x
> > 2 : y
> >
> >
> > What I see: on the execution level everything works as I want.
> > (Is it guaranteed to work that way?)
> >
> > On the syntax level, the hash table is created eight times instead
> > of (as I would expect) one, but still only one of the instances
> > is in action, and is shared across modules. Is it guaranteed to
> > work that way? In my real (more complicated) code a similar
> > hash table is not shared, and in effect, the "top" procedure gets
> > a fresh and empty instance of it, therefore I am in trouble.
> > I am wondering what are Racket's rules for sharing module data on the
> > syntax level.
> >
> >
> > Regards,
> >
> > Dmitry
> > ____________________
> >  Racket Users list:
> >  http://lists.racket-lang.org/users
>
>
>
> --
> Jay McCarthy <jay at cs.byu.edu>
> Assistant Professor / Brigham Young University
> http://faculty.cs.byu.edu/~jay
>
> "The glory of God is Intelligence" - D&C 93
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
>
>
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