From: Martin DeMello <martindemello@...>
Date: 2006-11-27T17:09:26+09:00
Subject: Re: ruby and list comprehension

On 11/27/06, James Cunningham <jameshcunningham@gmail.com> wrote:
>
> added = new_data.comprehend { |x| x if not old_data.include? x }
> removed = old_data.comprehend { |x| x if not new_data.include? x }
> same = new_data.comprehend { |x| x if old_data.include? x }

I wrote http://zem.novylen.net/ruby/fproduct.rb a while ago to emulate
list comprehensions in ruby - for example:

for x,y,z in product 1..40,
                       1..40, proc {|x,y| x <= y},
                       1..40, proc {|x,y,z| x**2 + y**2 == z**2}
    p [x,y,z]
end

The benefit is that the filters do get applied in order (sorted on
arity), so that it doesn't generate all the combinations first and
then filter.

martin