From: Intransition <transfire@...>
Date: 2010-09-25T17:10:45+09:00
Subject: Re: Ruby-based data language



On Sep 22, 11:37 am, Brian Candler <b.cand...@pobox.com> wrote:
> > If yes: then it looks like you're proposing an alternative syntax for
> > Hash literals - one which isn't widely used. It's Ruby-inspired but not
> > really Ruby, since a simple eval of the above will fail without
> > additional supporting code.
>
> That is, to parse that record using eval I think you need something
> along these lines:
>
> class Parser # < BasicObject ??
>   def self.parse(*args, &blk)
>     o = new
>     o.instance_eval(*args, &blk)
>     o.instance_variable_get(:@value)
>   end
>
>   def initialize
>     @value = {}
>   end
>
>   def method_missing(label, value=:__MISSING__,&blk)
>     if value != :__MISSING__
>       raise "Cannot provide both value and block for #{label}" if
> block_given?
>       @value[label] = value
>     else
>       raise "Must provide value or block for #{label}" unless
> block_given?
>       @value[label] = self.class.parse(&blk)
>     end
>   end
> end
>
> person = Parser.parse <<'EOS'
>   name "Joe Foo"
>   age 33
>   contact do
>     email "j...@joefoo.com"
>     phione "555-555-1234"
>   end
> EOS
> p person
>
> Now, to get the same capabilities as JSON, you also need syntax for
> Arrays. You could do something like the following, although note that
> the parser above doesn't handle this properly:
>
>   people([
>     person do
>       name "Joe"
>       age 33
>     end,
>     person do
>       name "Fred"
>       age 64
>     end,
>   ])
>
> You do need both parentheses and square brackets, unless you replace
> do/end with braces:
>
>   people [
>     person {
>       name "Joe"
>       age 33
>     },
>     person {
>       name "Fred"
>       age 64
>     },
>   ]
>
> Add a few colons and commas and you're back to JSON. Or drop the closing
> braces and brackets and keep the indentation, and you're back to YAML.
>
> You could treat multiple arguments as an array:
>
>   people \
>     person {
>       name "Joe"
>       age 33
>     },
>     person {
>       name "Fred"
>       age 64
>     }
>
> but then if you wanted a one-element array it would have to be a special
> case. Or you could perhaps have a flag to indicate that you want an
> Array:
>
>   people [],
>     person {
>       name "Joe"
>       age 33
>     },
>     person {
>       name "Fred"
>       age 64
>     }

You make a good point about arrays. I'm thinking about configuration
files as the common use case, so complex arrays aren't as common. But,
maybe there are better solutions in anycase:

  people do
    person :name=>"Joe", :age=>33,
    preson :name=>"Fred", :age=> 64
  end

The format is Ruby syntax so it can handle hash arguments. Or,
alternately:

  people ["Joe", 33], ["Fred", 64]

The underlying app would know how to turn this into persons. We might
even do:

  people ['name', 'age'],
              ['Joe',  33],
              ['Fred', 64]