From: "David A. Black" <dblack@...>
Date: 2004-04-05T21:17:15+09:00
Subject: Re: deciding between ruby and python

Hi --

On Mon, 5 Apr 2004, Charles Comstock wrote:

> > Perhaps some of us like to do our iteration explicitly. I don't think
> > there is any syntactic overhead, and the for loop reads
> > better. Counterexamples welcome.
> > 
> > Obviously we can do #each too:
> > 
> > def L(x):
> >     print x
> >     return x*2
> > 
> > map(L, [1,2,3])
> > 
> (reverse (map (lambda (x) (begin (display x) (* x 2)))
>       (map (lambda (x) (+ x 2)) (list 1 2 3))))
> 
> [1,2,3].each {|x| x+2}.each {|x| print x;return x*2}.reverse

I think you want #map there.  With each, the first block is
essentially a no-op.  Also, return will break through all levels
(including method call):

  def m
    [1,2].each {|x| puts x; return}
  end
  m     # => 1

> or if you prefer
> 
> [1,2,3].each {|x| x+2}.each do |x|
> 	print x
> 	x*2
> end.reverse

Again, with #each rather than #map, you're just throwing away the
results of the calculations (x+2 and x*2).  

[...]

> a = [1,2,3]
> a = for x in a
> 	print x
>          x + 2
>      end.reverse
> 
> In ruby you don't need to choose between map and for if you want the 
> result list, you can do whichever pleases you the most.

for doesn't generate a result list though.  What you've got here will
return [3,2,1], and all the x+2 calculations will be discarded (like
#each).


David

-- 
David A. Black
dblack@wobblini.net