From: Luke Graham <spoooq@...>
Date: 2005-02-15T09:51:35+09:00
Subject: Re: can anyone verify this code as correct?

On Tue, 15 Feb 2005 00:01:44 +0900, William Morgan
<wmorgan-ruby-talk@masanjin.net> wrote:
> Hi,
> 
> >  foo = choices(1..100)
> >  bar = choices(1..100)
> >  condition(lambda{foo == (bar * 3)})
> >  condition(lambda{bar > 10})
> >  condition(lambda{(bar % 2) == 0})
> 
> Cute! Some comments:
> 
> >   def condition(cond)
> >     return if (self.class == NilClass?)
> >     @@cont.pop.call if !cond.call
> >   end
> 
> More idiomatic usage would be to take a block here, rather than
> requiring an explicit lambda. Then calling it looks like:
> 
>   condition { foo == bar * 3 }

Thusly...

  def condition
    return if (self.class == NilClass)
    @@cont.pop.call if !yield
  end

> Also, you can drop the "class Object" declaration if you like, as
> top-level methods are automatically defined in Object. Or, move
> everything to a new class (even better).

Now that Ive seen the light with the ||= operator, I can indeed drop that class
declaration. Ruby didnt seem to like it the way I had it originally. Maybe
that was when I used attr_accessor, hmm cant remember. At any rate,
the class line can go now. I dont want to move to another class
because that would ruin the simplicity of use :)

> The real problem, though, is here:
> 
> >   class NilClass?
> >    def method_missing(methId, *args)
> >       return false
> >    end
> >  end
> 
> Which has high potential to break existing code, or at least make
> debugging very difficult. I haven't thought this through thoroughly, but
> rather than returning nil, maybe you can jump to another continuation?

I have thought about that too, condition is a possible place to jump back to.
That could have implications though, so I want to be sure of it first.
A manual checkpoint/escape continuation may be necessary.

At the moment Im concentrating more on something like :
condition([bar, foo]) {bar < foo}

The argument tells us what variables affect the outcome of the condition,
so a hash table of results can be created. Then computation can be optimised
by quickly allowing through values that are true and popping continuations that
have no effect on the important input values. Note that the value of bar is good
enough, ie theres no point using :bar, and that the value returned by time()
is a valid and useful argument as well. This is straying into monadic territory
if my understanding of those strange beasts is correct.

> Interesting idea, at any rate. The code is correct, though you have to
> drop the ? in NilClass?.

Yeah, sorry about that, that came from a wiki I posted the code on,
didnt realise till after I sent the mail.

--
spooq