Luke --
Hmmm... I haven't been practicing my Perl 6, and its been a while
since the last Apocalyptic refresher, but here goes (I'll don a paper
bag preemptively)...
Thinking of that as the equivalent to:
sort {
my ($ta, $tb) = map { $_.foo('bar').compute } ($^a, $^b);
$ta <=> $tb
} @unsorted;
so if you had a unary <=> that took a two element array (old style
syntax here, sorry):
sub cmp_num { my ($a, $b) = @_; $a <=> $b; }
you could write that as:
sort {
cmp_num map { $_.foo('bar').compute } ($^a, $^b);
} @unsorted;
I'd be a bit afraid of allowing <=> itself to be prefix, although I
admit it would be handy not to need the separate sub definition:
sort {
<=> map { $_.foo('bar').compute } ($^a, $^b);
} @unsorted;
The Schwartzian is the usual way, of course:
map { $_->[1] }
sort { $^a[0] <=> $^b[0] }
map { [ $_.foo('bar').compute, $_ ] }
@unsorted;
But we really aren't being concise here.
(Aside) I wonder if there will be a new Perl 6 idiom to replace this
using properties, something like this:
map { $_.really }
sort : numerically
map { $_.foo('bar').compute but really($_) }
@unsorted;
or:
@unsorted
==> map { $_.foo('bar').compute but really($_) }
==> sort : numerically
==> map { $_.really };
But we *still* aren't concise.
Maybe we should have a two-block sort? The second block gives the
transform to apply to the elements before applying the comparison
block:
sort { $^a <=> $^b } { $_.foo('bar').compute } @unsorted;
Or maybe even something like this:
sort :numerically :as { $^a.foo('bar').compute } @unsorted;
Regards,
-- Gregor
On Wed, 2004-02-11 at 19:11, Luke Palmer wrote:
> I've been thinking about this problem which comes up in my code a lot:
>
> @sorted = sort { $^a.foo('bar').compute <=> $^b.foo('bar').compute }
> @unsorted;
>
> Often the expressions on each side are even longer than that. But one
> thing remains: both sides are exactly the same, substitute a $^b for a
> $^a.
>
> I can see a couple less-than-desirable ways around this redundancy:
>
> @sorted = sort { infix:<=>( *($^a, $^b)».foo('bar').compute ) }
> @unsorted;
>
> Which doesn't work if .compute returns a list... not to mention its
> horrible ugliness. Another is to define a variant of sort (haven't had
> much practice with A6 material recently; here we go!):
>
> multi sub sort (&block($) = { $_ } : [EMAIL PROTECTED]) {
> sort { block($^a) cmp block($^b) } @data;
> }
>
> @sorted = sort { .foo('bar').compute } @unsorted;
>
> Which has the disadvantage of forcing you to use C<cmp> and forcing an
> ascending sort.
>
> Any other ideas? Is a more general solution necessary?
>
> Luke
--
Gregor Purdy [EMAIL PROTECTED]
Focus Research, Inc. http://www.focusresearch.com/
