Yaml, erb, and behavior trees

Hi all,
So, last week, I announced my new behavior tree library. Since them, I've
started trying to apply them to ruby-warrior, for fun, and to improve the
library. I'm quickly realizing that I need an even easier front end for it.
So, I'm thinking something like this would be useful:

select make_empty:


  - empty: <%= lambda {|e| e.empty? } %>
  - sequence:
    - pop: <%= lambda {|e| e.pop? } %>
    - make_empty

Yup, that's YAML, with ERB embedded in it. How hard would it be to take a
structure like this and turn it into a sensible hash/array structure? Would
I be better off just leaving the lambdas as strings, and eval'ing them?