From: Patrick Li <patrickli_2001@...>
Date: 2008-08-10T08:46:02+09:00
Subject: DSL challenge. Do you guys have any elegant ideas?

Hi,
I'm writing a DSL for some parsing. And would like the following
functionality. I was wondering if there's some metaprogramming experts
in here that can share a bit of wisdom.

Here's the ideal functionality:

string = Farm.create do
  barn do
    animal "dog"
    animal "cat"
  end
  pond do
    animal "whale"
    animal "shark"
  end
end

The string should print:
Farm contains
[
  Barn contains
  [
    dog
    cat
  ]
  Pond contains
  [
    whale
    shark
  ]
]

It would be really really nice to have this also:
Farm.create do
  animal "whale"
end

#throws "IllegalMethodError: method animal() can only be called under
barn()

I currently have a rather inelegant hack using instance_eval, which
messes up a lot of other things.
Thanks a lot for your help.
  -Patrick
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