require 'docile'

Family tree node, mother and father are Person values as well

Person = Struct.new(:name, :mother, :father)

Recursive dsl in a mutating builder using Docile

def person(&block) Docile.dsl_eval(PersonBuilder.new, &block).build end

Notice how the builder uses person to recurse

class PersonBuilder def initialize @p = Person.new end

def name(v) @p.name = v end

def mother(&block) @p.mother = person(&block) end

def father(&block) @p.father = person(&block) end

def build @p end end

Example DSL usage

p = person { name 'John Smith' mother { name 'Mary Smith' } father { name 'Tom Smith' mother { name 'Jane Smith' } } }

puts p

Output from this example

#=> #<struct Person name="John Smith",

mother=#<struct Person name="Mary Smith", mother=nil, father=nil>,

father=#<struct Person name="Tom Smith",

mother=#<struct Person name="Jane Smith", mother=nil, father=nil>,

father=nil>>