From: Christoph Rippel <crippel@...>
Date: 2001-01-10T07:45:05+09:00
Subject: [ruby-talk:8962] Re: Modules and mixins


> -----Original Message-----
> From: Ben Tilly [mailto:ben_tilly@hotmail.com]
> Sent: Tuesday, January 09, 2001 03:52 AM
> To: ruby-talk ML
> Subject: [ruby-talk:8917] Re: Modules and mixins
...
> Say no more.  Explicit calculations open up room for all
> sorts of potential mistakes.
they are also very inefficient and are either (virtually)
impossible or absurdly complex if you start adding
additional ``if clauses'' etc.  ...
> >
...
> Not much of a trick.  I just intended to use argument
if you know it ....  
> processsing to do what would otherwise be mechanical in
> my original Perl version.
...
> my solution.  I think I like the pattern of this one
> better, just a tad more direct.  However I would
> prefer different names:
On the other hand your solution is more fun and you can
replace the final ``[]'' with the mandatory ``[6,6,6]''. 
Seriously it is probably a good idea to distribute the
argument pre-processing (in both solutions) over two
function calls, lets say  along the lines of

class Array
  def  multi_each  # or each_comb, iter_each  ...
    __e(*self) {|arg| yield arg } unless empty?
  end 
  private    
  def  __e (arg,*more_args)
    (more_args.empty?) ?
       arg.each { |r| yield [r] } :
       arg.each {|l| __e(*more_args) {|r| yield [l]+ r }} 
  end
end

[1...3,'a'..'c', ('A'..'D').to_a].multi_each \
{ |arg|  puts arg.join " " }

[].multi_each \
{ |arg|  puts "nothing"  }

This is sort of complementary to the proposed ``zip'' 
(not that I am suggesting to include this in the Array
interface). 

Christoph