From: Charles Comstock <cc1@...>
Date: 2004-04-05T23:34:21+09:00
Subject: Re: deciding between ruby and python

David A. Black wrote:

> 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):

Whoops, just goes to show what happens when I forget to test the code 
before posting.  I'd forgotten that caveat about each, the commentary on 
map remains true, I find it much easier to read in this order then the 
above functional style.

[1,2,3].map {|x| x+2}.map {|x| print x;x*2}.reverse

[...]

> 
> 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
> 

Hmm I had misunderstood that about each, I encountered it once, but 
promptly forgot about it.  Do we do this to increase efficiency? 
Otherwise I can't see a situation where you wouldn't want to return the 
results of each for iteration.

Charles Comstock