Ok, I think I'll add an example with (match (proc obj) (pattern ...))
to the extension section and say something like "there will be a
future srfi using the syntax -> and => and an analogous technique to
accomplish this."

Felix

On Mon, Oct 26, 2020 at 9:58 PM John Cowan <xxxxxx@ccil.org> wrote:
>
>
>
> On Mon, Oct 26, 2020 at 8:35 PM Felix Thibault <xxxxxx@gmail.com> wrote:n
>
>> Wait, is this like (match (view-proc obj) pattern ...)) ?
>
>
> That was my original idea, but now I think it's better to do it differently.  I'm going to stick with -> for now, as I think it helps readability.  Here's an example:
>
> (define-record-type <point>
>   (make-point x y)
>   point?
>   (x point-x)
>   (y point-y))
>
> (define (point-view pt)
>   (if (point? pt)
>    (values (point-x pt) (point-y pt))
>    (values))
>
> (define p (make-point 10 20))
>
> (match p
>   ((-> point? point-view 10 y)
>     (+ y 1))) => 21
>
> (match p
>   ((-> point? point-view x 10)
>    (- x 1))) => error
>
> That allows `match` users to match against any type for which a view-proc can be created  (it need not be a record type), so I don't think we need any of the other bells and whistles.  Note that if view-proc returns zero values, the -> pattern fails.  (That's a usable convention, but not ideal.)
>
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> John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
> There is a Darwinian explanation for the refusal to accept Darwin.
> Given the very pessimistic conclusions about moral purpose to which his
> theory drives us, and given the importance of a sense of moral purpose
> in helping us cope with life, a refusal to believe Darwin's theory may
> have important survival value. --Ian Johnston
>