Re: Directory/file browser as TreeView

["'A. Pagaltzis'" <pagaltzis gmx de>]

* Ratcliffe, Jeffrey (Peters) <Jeffrey Ratcliffe External eads com> [2006-10-04 15:50]:
> > > 31:  $process->( $pathname, sort +( no_upwards @content ) );
> > >
> > > What's the "+" for?
>
> I, too, had no idea what this was for. Is there another way of
> writing this in one line?

Hmm, there actually is. The following parses the way it needs to:

    sort &no_upwards( @content );

However, I would never be able to remember what special
exceptions apply to the special magic of `sort`. So in order to
be able to read the code when I get back to it in 6 months,
I would still use the plus, which is a construct I am completely
familiar with. Itâs useful in many different contexts and follows
a very simple rule, so itâs easy to commit to memory.

> > Of course in this case you can just as well use curlies to
> > disambiguate. I just prefer this notation for my own
> > (irrelevant
>
> I'm being dumb. How do you can you rewrite this with curlies?

I was talking about `map`. You can write

    %hash = map +( $_ => func( $_ ) ), @list;

as

    %hash = map { $_ => func( $_ ) } @list;

and in fact I know a lot of people *always* write `map` that way
because of the problems with parens.

But it occurs to me that there is a way to write the `sort` with
curlies:

    sort do { no_upwards @content }

That works as it should. Itâs just not obvious why you put the
seemingly pointless `do BLOCK` in there, whereas with the plus
sign, I always immediately know âthis is there because Perl
doesnât disambiguate those parens in the right wayâ by sheer
virtue of what the plus is for.

> > Yes. The prototype lets you write
> >
> >     someutil( sub { ... }, $more, @args );
> >
> > a bit shorter as
> >
> >     someutil { ... } $more, @args;
>
> Do you pass a sub to a sub like this often? I'd not seen this
> before either. I haven't been able to find anything in perldoc
> about it. Is there any documentation anywhere?

Exactly what are you referring to? If youâre asking about whether
I use the `&` protoype much, then no, I donât. youâre asking
about passing anonymous subs in general, then the answer is
absolutely, I do that *loads*. I couldnât live without it. I use
the prototype when the sub in question has characteristics of
a control structure.

The documentation you are looking for is in perlsub, under
Prototypes.

Regards,
-- 
Aristotle Pagaltzis // <http://plasmasturm.org/>