On Sun, 04 Jan 2009 14:19:15 -0500, Uri Guttman wrote:
>>>>>> "m" == moritz <mor...@casella.faui2k3.org> writes:
> m> But I think that a .perl()ification as ("blue", "light", "hayard",) would
> m> make much more sense, because simple thing like
>
> m> @a.push eval(@b.perl)
>
> m> would then DWIM.
>
> for your def of DWIM. i can see wanting an anon array to be pushed onto
> @a building up a structure.
That would be easily achievable if we made the change I'm suggesting, so
that C<@a.perl> emitted round brackets. This is how you would clone an
array, as Moritz wants to do:
m...@edward:~/perl/6$ cat uri1
#!/home/msl/bin/perl6
# Imagine that @b.perl has produced this:
my $p = "('blue', 'light', 'hazard')";
my @a;
@a.push(eval $p);
.say for @a;
m...@edward:~/perl/6$ ./uri1
blue
light
hazard
m...@edward:~/perl/6$
Adding a single backslash before `eval' pushes an anonymous array on to
@b, as you envisage wanting to do:
m...@edward:~/perl/6$ cat uri2
#!/home/msl/bin/perl6
# Imagine that @a.perl has produced this:
my $p = "('blue', 'light', 'hazard')";
my @b;
@b.push(\eval $p);
.say for @b;
m...@edward:~/perl/6$ ./uri2
blue light hazard
m...@edward:~/perl/6$
> a more useful example would be serializing data trees. if you dump @b
> with .perl do you want the current dumper output of a anon array or your
> list of values? when serializing a tree, you must get the ref version so
> that is the common and default usage. your version isn't DWIMmy there at
> all.
I think Perl 6's automatic reference-taking (though we don't call them
references any more) solves that problem for us.
If you say
my @c = eval '(1, 2, 3)';
then @c has three elements. If you say
my $c = eval '(1, 2, 3)';
then Perl constructs (if I've got the Perl 6 lingo right) an Array object
and stores it in $c. So the round brackets DTRT whether you're storing
into an array like @c or into a scalar like $c.
I'd like to use your example of serialising and unserialising to suggest
that the current behaviour is wrong:
m...@edward:~/perl/6$ cat serialise
#!/home/msl/bin/perl6
my @a = <blue light hazard>;
@a.perl.say;
m...@edward:~/perl/6$ cat unserialise
#!/home/msl/bin/perl6
my $p = =$*IN;
my @a = eval $p;
for (@a) { .say }
m...@edward:~/perl/6$ ./serialise | ./unserialise
blue light hazard
m...@edward:~/perl/6$
We serialised an array of three elements; we got back an array containing
just one. Round brackets would have solved that. (Actually, we don't
need any brackets at all, because Perl 6's list constructor is a comma,
not a set of brackets. But round brackets would be no-ops, and they
arguably make the output more human-readable.)
Markus
