From: Reimer Behrends <behrends@...>
Date: 2002-09-02T06:59:02+09:00
Subject: Re: Ruby aesthetics

Gavin Sinclair (gsinclair@soyabean.com.au) wrote:
[...]

>  I'll conclude with one (new) feature from Python that makes me green
>  with envy: list comprehensions.  For those who don't know what that
>  means, here's an example:

>   Ruby:  squares_less_than_10 = numbers.find_all{|i| i<10}.map{|i| i^2}
>  
>   Python: squares_less_than_10 = [x^2 for x in numbers if x < 10]

That calls for a functional abstraction (functional abstraction is
essentially a fancy software engineering term for factoring out commonly
occuring code sequences into a procedure, function, or method of its
own) rather than a new language feature. This abstraction is most easily
added to Enumerable:

module Enumerable

  # map all elements through a filtering block, keeping all the results
  # that aren't nil.

  def condmap
    result = []
    each do
      | elem |
      item = yield elem
      result << item unless item.nil?
    end
    result
  end

end

To be used as follows:

    squares_less_than_10 = numbers.condmap{|x| x**2 if x < 10 }

In general, you do not want to expand the language when existing
abstraction mechanisms can already capture the same thing adequately and
with more room for customization.

			Reimer Behrends