From: Just Another Victim of the Ambient Morality <ihatespam@...>
Date: 2007-11-28T21:30:01+09:00
Subject: Ruby needs continuations...

Warning:  I don't really know what I'm talking about so if I make any 
mistakes in terminology, please try to correct me...


    I've been doing a lot of Python programming and I've discovered that 
it's actually a very powerful language.  The language, itself, lacks any 
kind of elegance but it has all the power of Ruby and a little more 
performance.  It also has a richer set of libraries, although not in all 
areas, surprisingly.
    One thing that Ruby should take from Python are continuations.  Python 
is moving away from list creation and version 3.0 functions will return 
Python iterators, implemented with continuations, instead of actual lists, 
since they are not used nearly as much as you might think.
    The reason why I say that Ruby needs continuations is because they are 
more versatile than Ruby iterators.  The reason why I say _that_ is because 
you can make Ruby iterators with continuations but you can't make 
continuations with Ruby iterators.  This means that you can implement a 
continuation iterator and Object class can automatically define a Ruby 
iterator based on your continuation iterator.  After all, Ruby iterators are 
nice.  I'm surprised by how annoyed I am that Python for loops don't return 
a value...
    One weakness of Ruby iterators that continuations don't have is parallel 
iteration.  If you have two containers that represent different aspects of 
the same things, it's difficult to iterate over both of them in Ruby.  In 
Python, you can do this:


list1 = [1, 2, 3, 4]
list2 = ['a', 'b', 'c', 'd']

# Okay, Python is more wordy than I'd like
# I could have just used zip() but you rarely need the list!
for num, letter in itertools.izip(list1, list2):
    # Do something with both numbers and letters
    print num, letter
    print


    How would one do this in Ruby?  You can use .each_with_index and index 
the other list but that assumes that the other list is indexable, which only 
happens to be true of arrays but is not true in general.  I've thought about 
implementing some Ruby equivalent of zip() (or preferably izip()) and 
discovered that I can't do so without continuations.
    ...Hence, my post.  I'm actually at odds with Pythonic philosophy.  The 
idea that there should only be one way to do things is ludicrous and a 
constant up hill battle.  One thing that Python does right is that it's not 
afraid to "steal" from other languages and that's the right attitude to 
have.  Adopt whatever is useful!
    Python 3.0 looks like great language.  I'm hoping that Ruby 2.0 will be 
even better 'cause, frankly, Ruby is more fun to program in...
    Thank you...