From: "Ara.T.Howard" <ahoward@...>
Date: 2004-08-06T01:31:28+09:00
Subject: Re: Macros in Ruby

On Fri, 6 Aug 2004, Gavin Sinclair wrote:

> On Friday, August 6, 2004, 12:11:27 AM, Ara.T.Howard wrote:
>
>> perhaps a shorthand:
>
>>    lambda{ puts 'lambda' } => Proc:0xb74041a0
>>    &{ puts 'lambda too' }  => Proc:0xb74041a1
>
>> i'm probably missing something, but i don't think the syntax '&{' occurs
>> anywhere now and '&' is already synomynous with blocks/procs/etc.
>
>
> If you must have a shortcut, I think 'L' makes more sense.
>
>  L { puts 'lambda' }    => Proc:0xb74041a0


but 'L' is a valid identifier:

   ~ > cat a.rb
   L = 42
   L { puts 42 }

   ~ > ruby a.rb
   a.rb:2: undefined method `L' for main:Object (NoMethodError)
           from a.rb:2

problematic.

> My aesthetic sense says that a shortcut is unnecessary because
> creating explicit lambdas is uncommon (because Ruby has blocks, thank
> goodness), and because when you do explicitly create lambdas, they're
> usually so cool and saving so much other effort that I don't begrudge
> them a few characters :)
>
> Gavin

i actually use them quite a bit and would appreciate a shortcut.  i sometimes
prefer to have modifiable Proc attributes of object to parameterize their
behaviour rather than messing with inheritence or dynamic redefinition.  i also
end up writing methods which take options callbacks for debugging/logging, eg:


   def longrunning_database_update arg, opts = {}
     pre, pan, post = opts.values_at 'pre', 'pan', 'post'

     sql = gen_sql arg

     pre.call sql if pre

     res =
       if pan
         t =
           Thread.new(Thread.current) do |c|
             begin
               execute sql
             rescue => e
               c.raise e
             end
           end
         loop do
           break unless t.status
           pan.call(get_state)
           sleep 0.42
         end
         t.join
         t.value
       else
         execute sql
       end

     post.call res if post

     res
   end


now the call looks somewhat like this



   longrunning_database_update 42,
                               'pre' => lambda{|sql| debug{ "sql <#{ sql }>" }},
                               'pan' => lambda{|state| debug{ "state <#{ state }>" }},
                               'post' => lambda{|res| debug{ "res <#{ res }>" }}

i would like say

   longrunning_database_update 42,
                               'pre' =>  &{|sql| debug{ "sql <#{ sql }>" }},
                               'pan' =>  &{|state| debug{ "state <#{ state }>" }},
                               'post' => &{|res| debug{ "res <#{ res }>" }}


of coures this is totally minor - it would be nice IMHO.

-a
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