From: Chad Perrin <perrin@...>
Date: 2007-06-01T03:49:14+09:00
Subject: Re: Introducing the "it" keyword

On Thu, May 31, 2007 at 09:49:49PM +0900, Brian Candler wrote:
> 
> (1)
> 
> with(v+1, x+2) { |a, b|
>   return a if a+b < 10
> }

I think I like this one the most.


> 
> (2)
> 
> a = v+1                  # or: a, b = v+1, x+2
> b = x+2                  #
> return a if a+b < 10
> 
> (3)
> 
> local {
>   a = v+1                # or: a, b = v+1, x+2
>   b = x+2                #
>   return a if a+b < 10
> }
> 
> All these can be implemented without any language changes.

. . . and I like that about all three of them.


> 
> Now, if you could assign default parameters in blocks, you'd have another
> option:
> 
> (4)
> 
> let { |a=v+1, b=x+2|
>   return a if a+b < 10
> }

I understand what you're trying to accomplish here, and I find it an
appealing idea as well -- but I think that diverges enough from standard
Ruby syntax style that it would make things less readable.  If you
really want to use a let statement like that in Ruby, I think I'd prefer
something more like creating a new block construct using let..in..end:

  let a=v+1, b=x+2 in
    return a if a + b < 10
  end


> 
> Having default values for block arguments would be a boon for other reasons,
> including being able to rationalise some of the differences between the
> various flavours of blocks, procs and methods.
> 
> The main difficultly seems to be the ambiguity of '|' as an operator or the
> end of a parameter list.

Notice that a "let block" would avoid that problem nicely.  The one line
version might look something like this:

  let a=v+1, b=x+2 { return a if a + b < 10 }

I also think it has a cleaner look in general than trying to cram the
assignments between pipes at the beginning of the block.  The way
parameters are specified in do..end blocks works great for that, but
once you start performing explicit assignments I don't think it works as
well.

Of course . . . all that aside, I'm not sure I want Ruby to be an OCaml
with dynamic typing, either.  I think connecting with() to a standard
block works quite well enough, and doesn't threaten to turn Ruby into a
different language entirely.

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
McCloctnick the Lucid: "The first rule of magic is simple. Don't waste your
time waving your hands and hopping when a rock or a club will do."