[plt-scheme] enclosing-module-name

From: support at taxupdate.com (support at taxupdate.com)
Date: Wed Apr 4 14:13:26 EDT 2007

On Thu, Apr 05, 2007 at 05:05:26AM +0800, Matthew Flatt wrote:
> It's possible that either `syntax-identifier-binding' or
> `syntax-source-module' will do what you want, but I'm not sure.

I tried both of these, and they don't seem to provide what's needed in
my situation.  Here's what I'd like to be able to do:

The application will interpret user files written in what I'll call
a "template language":

(template x "description of x"
    (image "image1.xpm"
	(text first "First Name")
	(fixed-2 wages "Wages")
	(fixed-2 agi "AGI" (+ wages 100))))
which gets transformed to (roughly):

(module x sandbox-language
    (register 'x 'first "")
    (register 'x 'wages 0)
    (register 'x 'agi (+ wages 100))      ; this field has a "formula"
    (reqister-image "image1.xpm")

(define *field-hash* (make-hash-table))
(define (register module var)
    (hash-table-put! *field-hash* (string->symbol (format "~a.~a" module var))))
The hash table gives me a simple namespace simulation which I can control


Here's the problem I'd like to solve.  The "formula", such as (+ wages 100),
can be any scheme expression.  It gets transformed by a #%top which does a
hash-table-get on *field-hash* for any top-level symbol which isn't defined.
So %#top needs to know the enclosing module name (in this case "x") in order
to do the lookup.  I'd like to avoid requiring (+ x.wages 100) if possible
when the reference is to another field in the same template.  When the formula
refers to another template, then it must use the form (+ y.wages 200).

I attempted this using parameters, but this didn't work correctly because
the parameter doesn't get evaluated until run time.  That caused problems
when more than one template was evaluated. 

#%module-begin looks promising, since it includes the enclosing-module-name
syntax property.  However, it seems hazy to me how I can get #%top to see
the property that's only available to #%module-begin.

define-syntax-parameters might work, but I also want to avoid using any plt libs
like stxparam.ss, as the app will be distributed to users who don't have mzscheme
installed (only libmzscheme/libgc, mzscheme will be embedded in the app).

Any ideas on how to define #%top to be able to get the module name at compile time?
If you've made it this far, thanks for your patience on this long post!


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