Ok then, i got problem with this. I wrote a procedure which i called
'make-mutable-selector', which make a mutable selector from quote symbol
like 'mcaar, 'mcadr etc. But i don't know, how i can use this in the code,
what i want to write... i mean a macro with-mcxrs.
(define-macro make-mutable-selector
(lambda (new-selector)
(let ((loop (gensym)))
`(lambda (pair)
(let ,loop ((mutable-selector ,new-selector)
(number 2))
(begin
(if (equal? (car (string->list (substring (symbol->string
mutable-selector) number))) #\r)
(begin
pair)
(cond ((equal? (car (string->list (substring (symbol->string
mutable-selector) number))) #\a)(begin (mcar (,loop mutable-selector (+ 1
number)))))
((equal? (car (string->list (substring (symbol->string
mutable-selector) number))) #\d)(begin (mcdr (,loop mutable-selector (+ 1
number)))))
(else "Error")))))))))
((make-mutable-selector 'mcaar) (mcons (mcons 1 2) '())) ;= 1
((make-mutable-selector 'mcdar) (mcons (mcons 1 2) '())) ;= 2
... etc
(define-macro with-mcxrs
(lambda body
(let ((loop (gensym)))
`(let ,loop ((selectors (quote ,@body)) ) ;;list of selectors
(if (null? selectors)
(,@body)
(let ((new-selector (car selectors)))
(begin (make-mutable-selector (quote
(string->list
(substring
(car new-selector) 2
(- (string-length (car new-selector))1)) )) ,@body))))))))
I don't know, how i can fix this. Please help me.
Patrik
Dne čtvrtek 10. května 2018 5:04:05 UTC+2 David K. Storrs napsal(a):
>
> Hi Patrik,
>
> From what I've seen, people on this list generally don't help with
> homework assignments, especially not when the request is simply
> "please do this for me" as opposed to "please help me figure out this
> one piece that I'm stuck on". You'd probably get better answers if
> you specified:
>
> - Specifically what you don't understand
> - What you've tried
> - What happened and what the error messages were
>
>
>
> On Wed, May 9, 2018 at 6:56 PM, Patrik novak <high...@seznam.cz
> <javascript:>> wrote:
> > Hello,
> > i got really big problem. I study at university for a second year. We
> > programming at scheme, (not racket) and i have two hard quest for exams
> at
> > scheme. My life depends on it. So i please you to help me.
> >
> > First:
> >
> > (with-mcxrs
> > (let ((a (mcons (mcons 1 2) (mcons (mcons 3 4) '()))))
> > (list (mcaar a)
> > (mcdar a)
> > (mcaadr a)
> > (mcdadr a))))
> >
> > --> by using define-macro NOT DEFINE-SYNTAX and we HAVE TO use this
> > procedure for it:
> > symbol?, string-upcase, symbol->string, string-length, string-ref,
> > string->list, substring
> >
> > I know, that were an article about this problem (i think, joah martin
> wrote
> > that), but answers are useless for me :/ how i said, i need it in
> > define-macro by using this small procedures, at school we dont know what
> is
> > "syntax-parse" for example.
> >
> > Second:
> >
> > (define test
> > (make-generator
> > (lambda (collect)
> > (collect 10)
> > (collect 20)
> > (collect 30))))
> >
> > (list (test) (test) (test) (test)) ;; => (10 20 30 #<void>)
> >
> > (define test2
> > (make-generator
> > (lambda (collect)
> > (let x ()
> > (collect (random 100))
> > (x))))) .. ...this piece of code has to work also.
> >
> > Quest: Implement a procedure "Make-generator" one argument, which is
> > procedure one argument, which we called a generated procedure and
> evaluation
> > will we called "collect procedure". Result of aplication is procedure
> > without argument, which we called "a generator". The generator caused
> the
> > generator to apply a procedure that once applied to a brightening
> procedure
> > with some the argument will switch back to the place where it was
> applied
> > generator and its result is that argument. For another application the
> > generator switches the context into the generating procedure in the
> place
> > where the pre-treatment procedure has been applied, etc. Once you have
> > generate the procedure ends without applying the brightening procedure,
> the
> > result the application of the generator is then an undefined value.
> >
> > So please, help me, quickly !
> >
> > --
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