[plt-scheme] union notation in helpdesk

Technically, that should have been:

  (or/c false/c ...)

which would have made it easier to look up in Help Desk ... fixed now in svn.

Robby

On 9/15/07, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
>
> On Sep 15, 2007, at 4:36 AM, Stephen De Gabrielle wrote:
>
> > Hi,
> >
> > I've been looking at the documentation for the graph.ss library (in
> > MrLib 7.5) and came across some notation that I am not familiar with;
> >
> > (add-links
> >  graph-snip<%>
> >  graph-snip<%>
> >   (union false? (is-a?/c pen%))
> >   (union false? (is-a?/c pen%))
> >   (union false? (is-a?/c brush%))
> >   (union false? (is-a?/c brush%))))       PROCEDURE
>
>
> Try either #f or an instance of a brush%. -- Matthias
>
>
>
> > -- http://download.plt-scheme.org/doc/371/html/mrlib/mrlib-Z-
> > H-55.html#node_sec_7.5
> >
> > I can tell it's asking for things that implement either a class or
> > matching interface,
> >
> > but the use of the 'union false?'
> >
> > Is union the one from the parser tools collection?
> >
> > I'm guessing that it returns #f if the interfce isn't implemented -
> > or do I have this all wrong.
> >
> >
> > Cheers,
> >
> > Stephen
> >
> > _________________________________________________
> >   For list-related administrative tasks:
> >   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
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