On Monday, 5 April 2021 13:30:21 CEST you wrote:
> Hi,
>
> In dryads-wake I need selection of the element in a list in a macro from
> user-input. Currently I have multiple macros, and the correct one (which
> strips the non-selected choices) is selected in a simple cond:
>
> (define-syntax-rule (Choose resp . choices)
> "Ask questions, apply consequences"
> (cond
> ((equal? resp 1) ;; resp is user-input. It is a natural number.
> (Respond1 choices))
> ((equal? resp 2)
> (Respond2 choices))
> ((equal? resp 3)
> (Respond3 choices))
> (else
> #f)))
>
> For this however I have three syntax-case macros:
>
> (define-syntax Respond1
> (lambda (x)
> (syntax-case x ()
> ((_ ((question consequences ...) choices ...))
> #`(begin
> (respond consequences ...)))
> ((_ (choices ...))
> #`(begin #f)))))
>
> (define-syntax Respond2
> (lambda (x)
> (syntax-case x ()
> ((_ (choice choices ...))
> #`(begin
> (Respond1 (choices ...))))
> ((_ (choices ...))
> #`(begin #f)))))
>
> (define-syntax Respond3
> (lambda (x)
> (syntax-case x ()
> ((_ (a b choices ...))
> #`(Respond1 (choices ...)))
> ((_ (choices ...))
> #`(begin #f)))))
>
>
> I would like to get rid of those three definitions and replace them by
> at most two (one that strips N initial list entries, and Respond1).
>
> I cannot move to procedures, because I have code that must be executed
> only during final processing, and when I evaluate any of the
> consequences (as it happens with procedure-arguments), then the timing
> of the code execution does not match anymore. So I must absolutely do
> this in macros.
>
>
> I’ve tried to get that working, but all my tries failed. Is there a way
> and can you show it to me?
>
> This is a minimal working example. The output should stay the same,
> except for part 4, which needs this change to work (see at the bottom),
> but I would like to:
>
> - replace Respond2 and Respond3 by something recursive, so resp can have
> arbitrary high values (not infinite: max the length of the options) and
> - replace the cond-clause by a call to the recursive macro.
>
> (define-syntax-rule (respond consequence consequence2 ...)
> (begin
> (write consequence)
> (when (not (null? '(consequence2 ...)))
> (write (car (cdr (car `(consequence2 ...))))))))
>
> (define-syntax Respond1
> (lambda (x)
> (syntax-case x ()
> ((_ ((question consequences ...) choices ...))
> #`(begin
> (respond consequences ...)))
> ((_ (choices ...))
> #`(begin #f)))))
>
> (define-syntax Respond2
> (lambda (x)
> (syntax-case x ()
> ((_ (choice choices ...))
> #`(begin
> (Respond1 (choices ...))))
> ((_ (choices ...))
> #`(begin #f)))))
>
> (define-syntax Respond3
> (lambda (x)
> (syntax-case x ()
> ((_ (a b choices ...))
> #`(Respond1 (choices ...)))
> ((_ (choices ...))
> #`(begin #f)))))
>
>
> (define-syntax-rule (Choose resp . choices)
> "Ask questions, apply consequences"
> (cond
> ((equal? resp 1)
> (Respond1 choices))
> ((equal? resp 2)
> (Respond2 choices))
> ((equal? resp 3)
> (Respond3 choices))
> (else
> #f)))
>
>
> (display "Choose 1: should be bar:")
> (Choose 1 (foo 'bar) (foo 'war 'har) (foo 'mar) (foo 'tar))
> (newline)
> (display "Choose 2: should be warhar:")
> (Choose 2 (foo 'bar) (foo 'war 'har) (foo 'mar) (foo 'tar))
> (newline)
> (display "Choose 3: should be mar:")
> (Choose 3 (foo 'bar) (foo 'war 'har) (foo 'mar) (foo 'tar))
> (newline)
> (display "Choose 4: should be tar:")
> (Choose 4 (foo 'bar) (foo 'war 'har) (foo 'mar) (foo 'tar))
> (newline)
> (display "Choose 5: should be #f:")
> (Choose 5 (foo 'bar) (foo 'war 'har) (foo 'mar) (foo 'tar))
> (newline)
>
>
> Best wishes,
> Arne
Hello, Dr. Arne,
would simply transforming the question . response pairs to a list of lists of
responses work?
E.G.
#+begin_src scheme
(define-syntax questions->responses
(syntax-rules ()
((_ (question response ...) choices ...)
(cons (list response ...)
(questions->responses choices ...)))
((_ choices ...)
'())))
#+end_src
Vale,
-Tim
