__brace__ (PEP?)

[Kay Schluehr]

Roy Smith wrote:
> "Kay Schluehr" <kay.schluehr at gmx.net> wrote:
>
> > Roy Smith wrote:
> >
> > > foo->bar ==> foo.__arrrow__(bar)
> > > foo$bar ==> foo.__dollar__(bar)
> > > foo#bar ==> foo.__hash__(bar)
> > > foo::bar ==> foo.__scope__(bar)
> >
> > I'm strongly in favor for the arrow ( but with two "r" only ). The
> > question is simply: for what?
>
> I'm confused.  You're strongly in favor of a piece of punctuation
even
> though you don't have any idea what it might be used for?

Shurely I was joking. I could imagine a few purposes most likely arrows
of some category. That's what You depicted using the "==>" arrow, that
translates some infix operator expression into it's method description.
Arrows are some kind of 2-tuples that express a transition and which
are "left-exact" i.e. there must be at most a right value to some left
value.

Example:

(foo->bar) -> foo.__arrow__(bar)

This is a recursive definition of the arrow which could be further
expanded:

((foo->bar) -> foo.__arrow__(bar)) ->
foo.__arrow__(bar).__arrow__(foo.__arrow__(bar))

etc.

But something intrigues me and that is the prevalence of "foo" above
"bar" i.e. the preimage above the image. I would like to see that one
starts with the binary relation as the primary concept. A relation
should be instantiated by two classes. Let be Rel(A,B) some relation
created from classes A and B. The instances of Rel(A,B) would be arrows
from A to B depicted as arrow diagrams:

   foo->bar -> rel.__arrow__(foo,bar)

There is no absolute meaning of the arrow foo->bar, because it reflects
only the particular relation instance rel.

Besides this I guess Guido wants to use the arrow in the context of
"optional static type declarations" for declaring the return type. I
don't like this optional static stuff but the arrow is playing a role
also in this proposal.

Ciao,
Kay