Hacking Thy Fearful Symmetry

Dancer Goes Megasplat

January 14th, 2013

So the Holidays are gone... But, as usual, leftovers remain. For most people, now that we have reached the middle of January, they probably have dwindled to managable size, like a chunk of ice that was once a majestic iceberg. A few more lunches, and they should be nothing but a (delicious) memory. In the spirit of those microwaved echoes of joyous times, here's a Dancer entry that was submitted to the Perl Advent Calendar, but didn't find its way to publication.

No, Santa Claus' sleigh just didn't have the mother of all reindeer-benders. This entry is rather on the little-known but very useful feature of Dancer known as the megasplat.

So, what's the megasplat? Well, Dancer, being heavily influenced by Ruby's Sinatra, adopted its splat placeholder, which allows to capture elements of a route:

#syntax: perl
use Dancer;

get '/wishlist/*' => sub {
    my( $child ) = splat;

    return NortPole::DB->get_wishlist( $child );

That route will match /wishlist/timmy, and /wishlist/sandy, and the wishlist of every other child in the world. But what if we want to match several path elements? That's where we go mega:

#syntax: perl
use Dancer;

get '/giddy_up/**' => sub {
    my( $reindeers ) = splat;

    my @exclamations = ( 
        'Now', 'On', 'To the top of the porch', 'To the top of the wall' 

    return join '', map { 
        sprintf "%s, %s!\n",
                $exclamations[rand @exclamations], $_ 
    } @$reindeers;


With that, we can hit /giddy_up/Prancer/Dancer/Vixen/Cupid and get back:

Now, Prancer!
To the top of the porch, Dancer!
To the top of the wall, Vixen!
On, Cupid!

Beside that, the megasplat can also be used to mimick Catalyst's chaining behavior:

#syntax: perl
use 5.10.0;

use Dancer;

my( @naughty, @nice, %gift, $child );

any '/child/*/**' => sub {
    ($child) = splat;

prefix = '/child/*';

get '/naughty' => sub { push @naugthy, $child; 'tsk tsk'     };
get '/nice'    => sub { push @nice, $child;    'nicely done' };

put '/gift/*' =>  sub { $gift{$child} = (splat)[1] };

get '/gift' => sub { $child ~~ $naughty ? 'coal' : $gift{$child} };


Which will give Santa a nice little basic web service for his *Nice & Naughty* book keeping:

#syntax: bash
$ curl http://api.toydb.np/child/rjbs/nice
nicely done
$ curl http://api.toydb.np/child/yanick/naughty
tsk tsk
$ curl -X PUT http://api.toydb.np/child/rjbs/gift/pony
$ curl -X PUT http://api.toydb.np/child/yanick/gift/pony
$ curl http://api.toydb.np/child/yanick/gift
$ curl http://api.toydb.np/child/rjbs/gift
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