From: Brian Candler <b.candler@...>
Date: 2010-09-23T00:37:14+09:00
Subject: Re: Ruby-based data language

> 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 "joe@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
    }

JSON and YAML may be ugly, but IMO so is this.
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