From: Brian Mitchell <binary42@...>
Date: 2006-05-02T13:29:23+09:00
Subject: Re: from block to code (also: how to get the bindings of a block)

On 5/1/06, chiaro scuro <kiaroskuro@gmail.com> wrote:
> Not sure about the ATs. even if I don't mind them that much... if I unfocus
> my eyes they look like bullet points ;-)
>
> I have got this one working.. see if you can guess how..
>
> recipe "eggs and bacon" do
>   eggs = [2,:big]
>   bacon = 3
> the end
>

If you really want the = look you can capture the binding with the
set_trace_func utility. This has drawbacks right now as there is no
"clean" way to share set_trace_func cooperatively w/o some code (some
small hacking could easily add this though -- sample bellow). So this
will get rid of the ugly "the" but you will need to be careful that
the Kernel stuff is executed before other things that might possibly
want to use the old style tracer:

# Could be cleaned up quite a bit but it should work.
module Kernel
  tracers = []
  legacy_tracer = nil

  set_trace_func lambda {|*args|
    legacy_tracer.call(*args) if legacy_tracer
    tracers.dup.each {|tracer| tracer.call(*args)} unless args[3] == :trace
  }

  define_method(:set_trace_func) {|proc|
    legacy_tracer = proc
    nil
  }

  # Not thread safe but easy to make so.
  define_method(:trace) {|tracer, block|
    tracers << tracer
    result = block.call
    # lambda {} == lambda {} work around just in case.
    tracers.reject! {|x| x.object_id == tracer.object_id}
    result
  }
end

def recipe(name)
  recipe_binding = nil
  trace(
        lambda {|event, file, line, id, binding, classname|
          recipe_binding = binding unless id
        },
        lambda {yield})
  ingrediants = eval("local_variables", recipe_binding)
  puts "To make #{name} you need:"
  ingrediants.each {|i|
    info = eval(i, recipe_binding)
    info = info.join(' ') if Array === info
    puts "  #{info} #{i}"
  }
end

recipe "eggs and bacon" do
  eggs = 2, :big   # Note that ruby has a nicer syntax than explicit [] here.
  bacon = 3
end

I get this output:

To make eggs and bacon you need:
  2 big eggs
  3 bacon

Hope this helps,
Brian.