[plt-scheme] dynamically varying the definitions used by a procedure

In this case, the goal is to parameterize expressions/definitions ( the 
printf here ) over definitions in one and the same program. This is 
what units are for. If David wants to split it over several different 
runs, using modules is okay. -- Matthias



On Sep 30, 2004, at 6:15 AM, Daniel Silva wrote:

> When is it a good idea to use dynamic-require instead of units for
> problems like this one?  The web-server servlet interface (a similar
> problem) uses both, right?
>
> Daniel
>
>
> On Wed, 29 Sep 2004 22:59:44 -0400, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>>   For list-related administrative tasks:
>>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>
>> Here is one way -- Matthias
>>
>> ;; *** start: fxy-sig.ss
>> (define-signature fxy^ (f x y))
>> ;; *** end: fxy-sig.ss
>>
>> ;; *** start: test.ss ****
>> (load "fxy-sig.ss")
>>
>> (define dbms
>>    '((euclidean . "euclidean.ss")
>>      (hamming . "hamming.ss")))
>>
>> (define (execute arequest) (run (lookup arequest)))
>>
>> (define run
>>    (lambda (lfilename)
>>      (invoke-unit/sig
>>       (compound-unit/sig
>>         (import)
>>         (link
>>          [FILE : fxy^ ((load  lfilename))]
>>          [MAIN : () ((unit/sig () (import fxy^)
>>                        (printf "~a~n" (f x y)))
>>                      FILE)])
>>         (export)))))
>>
>> (define lookup
>>    (lambda (arequest)
>>      (cond
>>        [(assq arequest dbms) => cdr]
>>        [else (error (format "request ~a not found~n" arequest))])))
>>
>> (execute 'euclidean)
>> (execute 'hamming)
>> ;; *** end: test.ss ****
>>
>> ;; *** start: hamming.ss ****
>> (unit/sig fxy^
>>    (import)
>>    (define x '(1 0 0))
>>
>>    (define y '(1 0 1))
>>
>>    (define f ;hamming
>>      (lambda (ax ay)
>>        (+  (- (car ax)  (car ay)))
>>        (- (cadr ax)  (cadr ay))
>>        (- (caddr ax)  (caddr ay)))))
>> ;; *** end: hamming.ss ****
>>
>> ;; *** start: euclidean.ss ****
>> (unit/sig fxy^
>>    (import)
>>    (define x '(2 5 7))
>>
>>    (define y '(1 0 2))
>>
>>    (define square
>>      (lambda (ax)
>>        (* ax ax)))
>>
>>    (define f
>>      (lambda (ax ay)
>>        (sqrt
>>         (+ (square (- (car ax)  (car ay)))
>>            (square (- (cadr ax)  (cadr ay)))
>>            (square (- (caddr ax)  (caddr ay))))))))
>> ;; *** end: euclidean.ss ****
>>
>>
>>
>>
>> On Sep 29, 2004, at 7:31 PM, David J. Neu wrote:
>>
>>>
>>> ;; *** start: test.ss ****
>>> (define dbms
>>>   '((euclidean . "euclidean.ss")
>>>     (hamming . "hamming.ss")))
>>>
>>> (define execute
>>>   (lambda (arequest)
>>>     (let ((lfilename (assq arequest dbms)))
>>>       (if lfilename
>>>           (begin
>>>             (load (cdr lfilename))
>>>             (printf "~a~n" (f x y)))
>>>           (error (format "request ~a not found~n" arequest))))))
>>>
>>> (execute 'euclidean)
>>> (execute 'hamming)
>>> ;; *** end: test.ss ****
>>>
>>> ;; *** start: euclidean.ss ****
>>> (define x '(2 5 7))
>>>
>>> (define y '(1 0 2))
>>>
>>> (define square
>>>   (lambda (ax)
>>>     (* ax ax)))
>>>
>>> (define f
>>>   (lambda (ax ay)
>>>     (sqrt
>>>      (+ (square (- (car ax)  (car ay)))
>>>         (square (- (cadr ax)  (cadr ay)))
>>>         (square (- (caddr ax)  (caddr ay)))))))
>>> ;; *** end: euclidean.ss ****
>>>
>>> ;; *** start: hamming.ss ****
>>> (define x '(1 0 0))
>>>
>>> (define y '(1 0 1))
>>>
>>> (define hamming
>>>   (lambda (ax ay)
>>>     (+  (- (car ax)  (car ay)))
>>>     (- (cadr ax)  (cadr ay))
>>>     (- (caddr ax)  (caddr ay))))
>>> ;; *** end: hamming.ss ****
>>
>>