From: Intransition <transfire@...>
Date: 2010-09-25T16:49:14+09:00
Subject: Re: Ruby-based data language



On Sep 22, 3:17 pm, Brian Candler <b.cand...@pobox.com> wrote:
> Thomas Sawyer wrote:
> > On Sep 22, 7:20 am, Brian Candler <b.cand...@pobox.com> wrote:
> >> I'd have said most packages use YAML. If you can provide examples which
> >> use method_missing and block-based structure just for conveying static
> >> configuration information, I'd be interested to see them. But then
> >> that's what you asked for in the first place :-)
>
> > I think a Gemfile is a pretty good example
>
> Do you mean a Gemfile from Bundler? e.g.
>
>   source "http://rubygems.org"
>
>   gem "rails", "3.0.0.rc"
>   gem "rack-cache"
>   gem "nokogiri", "~> 1.4.2"
>
> Some attributes have one value, some attributes have more than one
> value, some attributes can be repeated. I guess a generic parser API for
> that would be a call to callback(key, *args), just like method_missing,
> or it could build a linear data structure like
>
>   [[:source,"http://rubygems.org"],
>    [:gem,"rack-cache"],
>    [:gem,"nokogiri","~> 1.4.2"]]
>
> I'm not sure what output you'd want from nested blocks.
>
> > I would expect to get an object that gave me access to the data. What
> > kind of object depends on the parser.
>
> If the parser is generic (not application-specific) then I guess you'd
> just get the structure I've shown above.

That's one way. The parser could just offer a couple of options to
vary how the generic structure is formed.

> > I get what you are saying. But even JSON goes through a parser in
> > Javascript
>
> It *can* go through a parser for security reasons, but the result from
> parsing it is exactly the same as if you read it in as a Javascript
> literal. And there are cases where you intentionally interpret it as
> Javascript code, e.g. JSONP.
>
> > when someone thinks "Ruby-
> > syntax data/config format" they are thinking builder-style, not hash
> > literals.
>
> Perhaps. I think more common would be a Rails-style configuration or a
> gemspec:
>
> Gem::Specification.new do |s|
>   s.name = %q{snailgun}
>   s.version = "1.0.6"
>   ... etc
> end

That's another way to do it, yes. But can it be made a pure data
format?

> Of course, the advantage of having it as real executable code is that
> you can use Ruby to assemble data constructs, and conditional inclusion.
>
>   s.files = [ ...lots of items... ]
>   s.files.concat [ ...more items... ]
>
>   if s.respond_to? :specification_version then
>     s.specification_version = 2
>   end

But there's the disadvantage here too --it's no longer just data.
Depends on what you're trying to achieve.