From: Intransition <transfire@...>
Date: 2010-04-10T00:01:19+09:00
Subject: Re: Is it possible, a fully general Enumerable#recursive ?

On Apr 7, 5:49 pm, Intransition <transf...@gmail.com> wrote:
> For the last couple of days I've been trying to write an Enumerable
> method called #recursive. Rather than create a bunch of methods like
> #recursive_each, #recursive_map, #recursive_sort, etc. I figured that
> it should be possible to create a single #recursive method that
> returned an Enumerator, or barring that a Functor, that would handle
> any enumerable method, e.g. recursive.each, recursive.map,
> recursive.sort, and so on. But I have yet to figure out fully general
> solution.

Working on this more I currently have the method #visit (see the code
below). It almost works, but it has this one issue that makes no sense
to me, and I wonder what is going on under the hood in Enumerator for
it do this. It has the air of a bug to me --or at least a feature
deficiency.

Notice:

  [1, 2, 3, ['a', 'b', 'c'] ].visit{ |x| x.succ }
  => [2, 3, 4, ["b", "c", "d"]]

But using Enumerator:

  [1, 2, 3, ['a', 'b', 'c'] ].visit.map{ |x| x.succ }
  => [2, 3, 4, "b", "c", "d"]

Why is it flattening the result?

Here's the code for #visit:

  module Enumerable

    def visit(&block)
      if block_given?
        map do |e|
          e.visit(&block)
        end
      else
        to_enum(:visit)
      end
    end

  end

  class Object

    def visit(&block)
      block.call(self)
    end

  end

  class String

    # This is needed for Ruby 1.8
    def visit(&block)
      block.call(self)
    end

  end