[ruby-talk:8897] Re: Modules and mixins

"Christoph Rippel" <[e-mail]> wrote:
>
> > -----Original Message-----
> > From: Ben Tilly [mailto:[e-mail]]
> > Sent: Sunday, January 07, 2001 06:25 PM
> > To: ruby-talk ML
> > Subject: [ruby-talk:8803] Re: Modules and mixins
> >
> >
> > Ruby also supports functional techniques. [...]
> >
>Yes, this is a very need solution!
>
>Interestingly enough (basically) the same example came up
>in a very long ``Ruby versus Python'' thread on the python
>list in the middle of November 2000. The proposed Ruby
>solution was something along the line of:
>
>class  MRange
>    def initialize (*a)
>       @len  = a.length/2 -1
>       @lo = a[0..@len]
>       @up = a[@len+1..2*@len+1]
>    end
>    def each
>       __each(0) {|l| yield l }
>    end
>    private
>    def __each(n)
>       if n == @len
>         (@lo[n]..@up[n]).each { |l| yield [l] }
>       else
>          (@lo[n]..@up[n]).each \
>           { |l|  __each(n+1) {|r| yield [l]+ r }}
>       end
>    end
>end
>
>MRange.new(1,'a','A', 2,'c','D').each \
>{|arg| puts arg.join(" ")}
>
>
>The elegance (? probably a matter of taste) of this Ruby
>solution was dismissed since it is pretty easy to calculate
>the index of an element in a ``Multi-Range'' directly.
>(Nobody was public disconcerted that this ``elegant
>solution'' was probably 3 or 4  times as long).

If length is the primary issue (yes, I renamed the method):

    def bind_loops(fn, my_range, *more_args)
      bound_fn = proc { |*args| my_range.each {|arg| fn[arg, *args]} }
      (0 != more_args.length()) ?
        bind_loops(bound_fn, *more_args) :
        bound_fn
    end

    bind_loops(
      proc  {|*arg| puts arg.join(" ")} ,
      1..2, 'a'..'c', 'A'..'D'
    )[]

I should note that this triggers an incorrect warning under -w.
The final [] is most assuredly not useless. :-)

Cheers,
Ben
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