From: dblack@...
Date: 2007-02-06T07:33:20+09:00
Subject: Re: Proc vs lambda vs proc

Hi --

On Tue, 6 Feb 2007, Brian Candler wrote:

> On Tue, Feb 06, 2007 at 04:00:44AM +0900, Pit Capitain wrote:
>> gwtmp01@mac.com schrieb:
>>> (... useful infos about procs ...)
>>
>> Very interesting! Thanks for sharing your experiments.
>
> Yes, it's interesting to be reminded of all this again.
>
> Much as I love Ruby, I hate having multiple versions of essentially the same
> concept which differ in subtle ways. I would find it more aesthetically
> pleasing if a tiny Ruby core could bootstrap the whole language - and it
> might make it easier to port (and understand).
>
> Now, I wonder why you couldn't approach this problem from the other
> direction: instead of having two or more different types of lambda, which
> handle 'return' semantics differently, have a single type of lambda and two
> different return statements. For example:
>
>   return val     # return from enclosing method
>   result val     # return from this block only
>
> Internally, you could implement 'return' semantics using catch and throw:
>
>  def foo
>    ... some code
>  end
>
>  # could be implemented as something like this:
>
>  define_method(:foo) do
>    catch(:return) do
>      ... some code
>    end
>  end
>
>  module Kernel
>    def return(rc=nil)
>      throw(:return, rc)
>    end
>  end
>
> The other difference concerns arity. I don't see why argument checking can't
> be done everywhere, as long as you have the option of explicitly allowing
> variable arguments where you want them:
>
>  p1 = Proc.new { |x=nil,y=nil| ... }   # accept 2 or fewer args
>  p2 = Proc.new { |x, y, *z| ...    }   # accept 2 or more args
>  p3 = Proc.new { |*x| ...          }   # no more single-arg special case!
>
> That is, use the same argument list handling for a 'def' method definition,
> a block, and a Proc/proc/lambda.

I think the reason for there not being default arguments in code
blocks is the ambiguity of the pipe character:

   {| x=1 | 2 | 3 }  # {(x=1) 2 | 3 }  or  {(x=1|2) 3 }  ?

Dave Thomas suggested something at RubyConf 2005 along the lines of:

   def m(a,b,c)    # method
   end

   def (a,b,c)     # anonymous function
   end

I'm not sure what happened to that; I haven't seen it mentioned much
in discussions of this stuff.


David

-- 
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