From: Logan Capaldo <logancapaldo@...>
Date: 2007-09-10T00:47:18+09:00
Subject: Re: Bug in lambda?

On 9/9/07, Bernardo Monteiro Rufino <bermonruf@gmail.com> wrote:
> On 9/9/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
>
> > As far as remember, Guy Decoux and I are the only two people who think
> > that this makes perfect sense, once you learn it, and should not be
> > changed :-)
> >
>
> I think it shouldn't be changed too...
>
I just think it has icky semantics.
a.rb:

fib = lambda do |a|
  if a == 1 or a == 0
    1
  else
    fib[a - 1] + fib[a - 2]
  end
end

p fib.call(10)

C:\Documents and Settings\Logan>ruby a.rb
89

vs.

b.rb:
a = nil
fib = lambda do |a|
  if a == 1 or a == 0
    1
  else
    fib[a - 1] + fib[a - 2]
  end
end

p fib.call(10)


C:\Documents and Settings\Logan>ruby b.rb
b.rb:6: stack level too deep (SystemStackError)
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:6
         ... 633 levels...
        from b.rb:6
        from b.rb:6
        from b.rb:6
        from b.rb:10

Am I the only one who makes use of recursive lambdas? ;) If we keep
assignment semantics for block arguments, I think we should disallow
recursive blocks. I don't want recursive blocks to go away personally.
I think it's reasonable to give block arguments argument semantics
(especially in light of the addition of &block arguments to blocks)
instead of assignment semantics. You don't lose any power, although
you do lose some "expressivity", eg:

a = nil
set_a = lambda { |b| a = b }

instead of
a = nil
set_a = lambda { |a| }

> --
> Bernardo Rufino
>