From: Isaac Sanders <isaacbfsanders@...>
Date: 2011-11-07T21:04:45+09:00
Subject: Re: Tricky DSL, how to do it?

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I really think that we should all take another look at the Ruby Object
Model. Dave Thomas has a great screencast on it. This question would be
answered if the ROM was analyzed closely.

On Mon, Nov 7, 2011 at 6:56 AM, Robert Klemme <shortcutter@googlemail.com>wrote:

> On Sun, Nov 6, 2011 at 11:35 PM, Intransition <transfire@gmail.com> wrote:
> > I'd want to write a DSL such that a surface method_missing catches
> undefined
> > methods and records the blocks that they define e.g.
> >   foo do
> >     puts "foo"
> >   end
> > So I would end up with:
> >   { :foo=>#<Proc ...> }
> > Presently I have something like this:
> >
> >   #
> >   class Evaluator < BasicObject
> >     def initialize(&block)
> >       @__config__ = {}
> >       instance_eval(&block) if block
> >     end
> >     def __config__
> >       @__config__
> >     end
> >     def method_missing(sym, *args, &block)
> >       @__config__[sym] = block
> >     end
> >   end
> > However when I call on a block I want it to evaluate as if in the
> defining
> > context (in this case toplevel), not inside the "DSL" class that
> evaluated
> > via method_missing.
> >   e = Evaluator.new do
> >     foo do
> >       puts "foo"
> >     end
> >   end
> >
> >   e.__config__[:foo].call
> > Instead of what I want, I get a method missing error for #puts.
> > Any ideas?
>
> You can't have both (evaluate with self = Evaluator to trigger
> Evaluator's method missing and invoking the block in the defining
> context) at the same time.
>
> Question is, what happens if a missing method is invoked?  In your
> implementation the block is returned.   I would at least change that
> to return nil to avoid nasty side effects.  But generally execution
> cannot reasonably continue.  What about catching the exception and
> recording it?
>
> 12:54:59 ~$ ./x.rb
> {:foo=>#<Proc:0x101b3554@./x.rb:24>}
> 12:55:02 ~$ cat -n x.rb
>     1  #!/bin/env ruby19
>     2
>     3  class Evaluator < BasicObject
>     4    def initialize(&block)
>     5      @__config__ = {}
>     6
>     7      if block
>     8        begin
>     9          block.call
>    10        rescue ::NoMethodError => e
>    11          @__config__[e.name] = block
>    12          nil
>    13        end
>    14      end
>    15    end
>    16
>    17    def __config__
>    18      @__config__
>    19    end
>    20
>    21  end
>    22
>    23
>    24  e = Evaluator.new do
>    25    foo do
>    26      puts "foo"
>    27    end
>    28  end
>    29
>    30  p e.__config__
>    31
> 12:55:03 ~$
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestpractices.com/
>
>


-- 
Sincerely,

Isaac Sanders
Section C-4B Vice Chief, Order of the Arrow
Vice Chief of Administration, Tecumseh #65
Eagle Scout

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