talkingCode

Perl and JSON: heaven =~ m/made/ ?

If you read the above as ‘Heaven Made’, I’m afraid you lose code Dingbats. Try harder.

Perl is a nice language and JSON is a good way to structure data if you’re about to send over your favourite IPC mechanism. And there are, it seems, many similarities between the way JSON structures data and the way Perl structures data. Unfortunately, I don’t have an awful lot to write on the topic, so as well as briefly introducing the basics of creating JSON in Perl I will, with the irrefutable logic of a professor of philosophy and all the religious sensitivity of a Dan Brown novel, be examining the evidence for Larry Wall being God.

We’re going to start with a motivating example. I want to represent the following JSON object in Perl:

{
  keywords:['cat', 'fish', 'pig'],
  somekey: ’somevalue’,
  someobject: {
    nested: ‘value’,
    another: ‘nestedvalue’,
    a_number: 4
  }
  simple:true
}

I don’t know if you’ve come across JSON before, but it’s basically the way Javascript (ECMAScript) represents objects. Your modelling tools there are strings, numbers and booleans, as you might expect, and some collecting constructs. Specifically, JSON has a way to associate string keys with values - within the ‘{}’, thing on the left of the ‘:’ is the key and the thing on the right is the value, with commas seperating key-value pairs - and a way to create lists of values - inside the ‘[]‘, again seperated by commas.

Now, if you’re familiar with Hashes and Lists (or Arrays), you’ll see that JSON’s collection structures are exactly those. How do we represent those in Perl? Well, we use ‘{}’ for a hash and ‘[]‘ for a list. What’s more, we use commas to separate are values. I know what you’re thinking - “It’s mere coincidence”. The kind of coincidence that sees the Earth just the right temperature to support life, as a function of its being in just the right place in our solar system? Yes. _That_ kind of mere coincidence.

So how, naively, would I go about representing the above in Perl?

my $object = {
  keywords => ['cat', 'fish', 'pig'],
  somekey => ’somevalue’,
  someobject => {
    nested => ‘value’,
    another => ‘nestedvalue’,
    a_number => 4
  }
  simple => true
};

But all I’ve done so far is replace the ‘:’ with ‘=>’. It can’t be that simple, can it? That would be too easy. Almost as though, at the start of the universe, someone had determined that JSON and Perl would have basically the same syntax. Could it be that this synergy is part of God’s great plan? Well, not quite. Turns out you can’t just whack ‘true’ in there for your boolean value. I’ve defined a little function here to return ‘true’:

sub json_true()
{
  return bless ( {value => "true"}, "JSON::NotString" );
}

That’s ugly as sin, I know. (AS SIN! And it’s BLESSED! This conspiracy writes itself.) Anyway. Why would a God, in designing this synergy, allow such evil? Here I distract you by shouting “Look out! Earthquake!”, say “Natural Evil” three times, and we sweep that under the carpet.

The only piece missing from this puzzle are the final bits of fairy dust that’ll actually let you convert JSON to a format suitable for sending over the wire. May I introduce:

use JSON;

my $obj = { test => 'object' };
my $json_string = objToJson($obj);
my $rebuilt_object = jsonToObj($json_string);

Simple as. But… is Larry Wall God? Could anyone but the supreme being have designed this happy coincidence into the starting conditions of the universe? That a humble pre-WWW scripting language would turn out to have approximately similar syntax to one of the high-level interchange protocols powering the modern web? Well, if Larry Wall were God I’d certainly be disappointed, and that’s to say nothing of the fuss that world religions would kick up. And, in fairness, this isn’t a coincidence that has to have been orchestrated from the dawn of the universe. You’d really only need to start thinking about it in… say… 1962.

Maybe Larry isn’t God. Maybe he’s just Al Gore.