() ri...@happyleptic.org
() Mon, 5 Jul 2010 10:56:36 +0200
Can anyone suggest a better way to do this ?
For "a set of named values", you can use an association list.
If the paren verbosity is off-putting, a common way is to take/show
plists externally (minimal (one) set of parens). So, user sees:
(k1 v1 k2 v2 ...)
which is not so threatening, but you manipulate internally:
((k1 . v1)
(k2 . v2)
...)
This requires a transform, but you do that anyway
(as part of validating the user input), right?
All this presumes that there is no need to specify all keys all the time.
(Re-reading your post, perhaps i am misunderstanding the problem question.)
If the problem really is: how to avoid unwieldy argument lists, the answer
is still "use an association list", but pass to the user a procedure that
encapsulates it. For example:
(define (query-proc alist)
"Encapsulate ALIST; return a procedure to query it."
(lambda (key)
(assoc-ref alist key)))
(define ALIST '((k1 . v1) (k2 . v2)))
(define QUERY (query-proc ALIST))
;; On the user side:
(define (monitor query)
(for-each (lambda (key)
(simple-format #t "k: ~S~%v: ~S~%" key (query key)))
'(k1 k2)))
This example is read-only; if you want ‘monitor’ to be able to munge
you can change ‘query-proc’ to perhaps ‘query/munge-proc’:
(define (query/munge-proc alist)
"Encapsulate ALIST; return a procedure query/munge it."
(lambda (key . newval)
(if (null? newval)
(assoc-ref alist key)
(set! alist (assoc-set! alist key (car newval))))))
(It all depends on how much you trust the users. ;-)
thi
