From: Michael Neumann <mneumann@...>
Date: 2004-08-27T05:23:18+09:00
Subject: Re: python generators to ruby closures, help

zuzu wrote:
> can anyone help me decode the following python example using
> generators into The Ruby Way using closures?

Okay, here is it ;-)

One problem is, that we can't detect the usage of "break" inside the 
proc, as we're using proc's and not blocks. My workaround is, that a 
return value of nil of a proc.call breaks the generator at this position 
(so make sure to use false and not nil, e.g. "val.nil?" instead just 
"val"!).

Regards,

   Michael


#######
require 'generator'
require 'find'

alias filter lambda

class Generator
   def |(filter)
     self.class.new do |g|
       self.each { |elem|
         val = filter.call(elem)
         break if val.nil?
         g.yield(elem) if val
       }
     end
   end

   def inspect
     to_a.inspect
   end
end

class Proc
   def |(otherProc)
     proc {|*a|
       x, y = self.call(*a), otherProc.call(*a)
       break nil if x.nil? or y.nil?
       x & y
     }
   end
end

def count(n)
   filter {|i|
     break if n == 0
     n -= 1
     i
   }
end

def quit(&block)
   filter {|*a|
     break if block.call(*a)
     true
   }
end

def gen(&block)
   Generator.new(&block)
end

def ints
   gen {|g|
     n = 0
     loop do
       g.yield n
       n += 1
     end
   }
end


##### Test

odd = filter {|x| x % 2 == 1}
notDivBy3 = filter {|x| x % 3 != 0}
oddNotDivBy3 = odd|notDivBy3
firstTen = count(10)
result = ints | firstTen | oddNotDivBy3
p result

oddLowerThanTen = odd | quit {|y| y >= 10}
p3 = ints | oddLowerThanTen | notDivBy3
p p3

isRubyFile = filter {|file| File.extname(file).downcase == '.rb'}
files = gen {|g| Find.find('.') {|file| g.yield file} }
tenRubyFiles =  files | isRubyFile | count(10)
p tenRubyFiles