From: Intransition <transfire@...>
Date: 2011-11-08T05:56:26+09:00
Subject: Re: Tricky DSL, how to do it?

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Check it out:

  class ContextDSL < BasicObject

    def initialize(&block)
      @missing_block = block
    end

    def eval!(&block)
      @context = block.binding.eval("self")
      instance_eval(&block)
    end

    def method_missing(sym, *xargs, &block)
      context = @context
      context_block = ::Proc.new do |*args|
        context.instance_exec(*args, &block)
      end
      @missing_block.call(sym, context_block)
    end

  end

Try it out:

  config = {}

  dsl = ContextDSL.new do |name, block|
    config[name] = block
  end

  dsl.eval! do
    foo do
      puts self
    end
  end

  config[:foo].call  #=> <main>

Now with this general solution in hand, it's really got me asking why Ruby 
just doesn't provide a way to set the context, e.g.

  f = lambda{ self }

  f.context = "Any Object"

  f.call  #=> "Any Object"


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<div>Check it out:</div><div><br></div><div>&nbsp; class ContextDSL &lt; Ba=
sicObject</div><div><br></div><div>&nbsp; &nbsp; def initialize(&amp;block)=
</div><div>&nbsp; &nbsp; &nbsp; @missing_block =3D block</div><div>&nbsp; &=
nbsp; end</div><div><br></div><div>&nbsp; &nbsp; def eval!(&amp;block)</div=
><div>&nbsp; &nbsp; &nbsp; @context =3D block.binding.eval("self")</div><di=
v>&nbsp; &nbsp; &nbsp; instance_eval(&amp;block)</div><div>&nbsp; &nbsp; en=
d</div><div><br></div><div>&nbsp; &nbsp; def method_missing(sym, *xargs, &a=
mp;block)</div><div>&nbsp; &nbsp; &nbsp; context =3D @context</div><div>&nb=
sp; &nbsp; &nbsp; context_block =3D ::Proc.new do |*args|</div><div>&nbsp; =
&nbsp; &nbsp; &nbsp; context.instance_exec(*args, &amp;block)</div><div>&nb=
sp; &nbsp; &nbsp; end</div><div>&nbsp; &nbsp; &nbsp; @missing_block.call(sy=
m, context_block)</div><div>&nbsp; &nbsp; end</div><div><br></div><div>&nbs=
p; end</div><div><br></div><div>Try it out:</div><div><br></div><div>&nbsp;=
 config =3D {}</div><div><br></div><div>&nbsp; dsl =3D ContextDSL.new do |n=
ame, block|</div><div>&nbsp; &nbsp; config[name] =3D block</div><div>&nbsp;=
 end</div><div><br></div><div>&nbsp; dsl.eval! do</div><div>&nbsp; &nbsp; f=
oo do</div><div>&nbsp; &nbsp; &nbsp; puts self</div><div>&nbsp; &nbsp; end<=
/div><div>&nbsp; end</div><div><br></div><div>&nbsp; config[:foo].call &nbs=
p;#=3D&gt; &lt;main&gt;</div><div><br></div><div>Now with this general solu=
tion in hand, it's really got me asking why Ruby just doesn't provide a way=
 to set the context, e.g.</div><div><br></div><div>&nbsp; f =3D lambda{ sel=
f }</div><div><br></div><div>&nbsp; f.context =3D "Any Object"</div><div><b=
r></div><div>&nbsp; f.call &nbsp;#=3D&gt; "Any Object"</div><div><br></div>
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