From: "Michael W. Ryder" <_mwryder@...>
Date: 2007-05-25T08:30:08+09:00
Subject: Re: Introducing the "it" keyword

Greg Fodor wrote:
>> Maybe you could do:
>>
>>    return v + 1 if its < 10
>>
>> -- snip
>>
>> return v + 1 if < 10
> 
> Unfortunately this seems much more difficult and ambiguous
> for a number of reasons. First, it is impossible to know
> that our implied "it" should be "v + 1" without making
> assumptions about the intent. (Why don't we include the
> result of the return expression itself? What if it's more
> complex?)
> 
> More importantly, semantics of order of evaluation become
> confusing. Despite v + 1 being evaluated during the
> if conditional, it syntactically appears in the return
> statement. My approach preserves all current ruby semantics
> and is more intentional, I feel. It basically transforms
> this:
> 
> tmp = m(x)
> h(tmp) if g(tmp)
> 
> into just
> 
> h(it) if g(it = m(x))
> 
> The it keyword is essential for one reason and nice for
> a few others. It is essential because of the ruby semantics
> for determining identifiers vs. methods, referenced in my
> original post.
> 
> It is nice because we no longer have to come up with the
> name "tmp,"ruby provides a consistent intentional name.
> It is also nice because it is less code. It is also nice
> because it provides correct scope semantics so it will be
> GCed at the optimal time.
> 
>> No need for it to be such a special built-in construct.
> 
> Depends on what you mean by "need." For an optimal solution,
> I feel it does. "Optimal" means:
> 
> - It only evaluates m(x) once (yours does this)
> - It is the most terse representation of intent (subjective)
> - It introduces the correct scope (yours does not)
> - It releases memory upon GC after the statement (yours doesn't)
> - It avoids side effects (yours changes global space)
> 
> Its hard to think of a solution to this implemented in ruby
> that fits these parameters without introducing a new
> language level construct.
> 

How about something like: return $1 if (v + 1) < 10 if you wanted to 
return v + 1?  If you wanted to return v you could use: return $2 if 
((v) +1) < 10.  Improvements would be using some of the regular 
expression flags to control what $1, $2, etc. refer to.