On Thu, 06 Apr 2000 15:20:32 PDT, the world broke into rejoicing as
Dave Peticolas <[EMAIL PROTECTED]> said:
>
> Right now, reports are represented in guile as a vector
> containing a version, name, option generator, and renderer.
> Some things I'd like to add in the future include a help
> text generator, and report-specific toolbar buttons and
> menu items. To eliminate the need to change each report
> every time we add a new feature, I'd like to move the
> report representation to the "key->value" style scheme
> closure.
>
> Any thoughts?
I'd suggest making it into a Guile "record," in much the way the
budget report uses them.
It is indeed a bad thing to have all the parameters addressed
implicitly by position; I would be a *VERY* happy camper if Guile
offered something equivalent to the Common Lisp idea where you
define a function thus:
(defun complex-function (&rest title version options renderer)
;;; code
)
which would be called thus:
(complex-function :title "Budget" :version 1.5 :renderer #'budrend)
Note that here I didn't bother passing in a value for :options, and
so there is no value...
[CL offers further control over this, allowing a default value to be
defined, but that heads down a pointless road...]
The nearest equivalent in Scheme would be to define the function
thus:
(define (make-report . args)
(let ((report-defn (args-to-defn #f args)))
;;; On to the body...
)
where we'd need, to "parse" the arguments:
(define (args-to-defn input-record arglist)
(let ((inrec (if input-record
input-record
((record-constructor report-record-structure)
#f #f #f #f #f #f #f))))
(if arglist
(let ((id (car arglist))
(value (cadr arglist))
(remainder (cddr arglist)))
((record-modifier report-record-structure id)
inrec value)
(args-to-defn inrec remainder))
inrec)))
I would suppose that to construct a report "record" you'd probably
use the following:
(define budget-report
(args-to-defn #f 'version 2.5 'name "Budget"
'options
(lambda ()) ;;; Some complex function
'renderer
budget-render-function))
If you add another "option" to the report-record-structure, this
means that the existing reports don't use that option; it could
be meaningful to have the function that *reads* out of that record
gripe, in a not-too-unfriendly way, about the slot being left
blank...
[Aside: I find that when I am wondering how to implement something,
it is a *remarkably* useful idea to look to Common Lisp. The designers
hashed through more complex issues with *reasonable* success than just
about any other computer language. If you want to build a date library,
look at the HyperSpec. If you're not sure how to implement a mathematical
function, look at the HyperSpec. They may well explain why the option
that comes to mind first is actually a very BAD idea...]
--
When I die, I'd like to go peacefully in my sleep like my grandfather,
not screaming in terror like his passengers...
[EMAIL PROTECTED] - <http://www.ntlug.org/~cbbrowne/lsf.html>
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