Re: [Chicken-users] Parsing lists from external scheme intepreters

[felix]

Michael Erdmann wrote:
> Now the complicated part starts. FramerD was providing the concept
> of choices in order to represent the contents of result sets.
> The nice thing about it was the following trick:
>
> (define x (choice 1 2 3 4 5) )
>
> (define (inc y)  (+ y 1))
>
> (inc x) -> (choice 2 3 4 5 6)
>
> which means the operation inc was executed on any member in the
> choice. I have not seen this by now in the chicken documentation.
> Does some thing similar exisit some where?

No, chicken doesn't support anything like that (and no other Scheme
system I know, AFAIK). Depending on how desperately you need that,
once could hack around with error-handlers, etc. But I don't
recommend that, unless you *really* need it.

> I guess i can represent a choice as a list of elements where
> the list is somehow marked as a choice.

Or try records, like SRFI-9 (`define-record-type'). That makes
your choice object distinct from other data.


cheers,
felix