Can anyone verify this code as correct?

ruby-talk
1

Lähettäjä: Luke Graham <spoooq@gmail.com>
Aihe: can anyone verify this code as correct?

class Object
    def choices(choicelist)
  if (!Class.class_variables.include? "@@cont")
    @@cont =
  end

You can use '@@cont ||= '.

  choicelist.each { |choice|
    callcc { |cc|
      @@cont << cc
      return choice
    }
  }
  nil
  end

Continuation returns after the block, either with the value of the
block or the parameter to #call, and it stores its execution context.
Here you're returning in the middle of a loop, so I'm thinking each
#call will cause the remaining 'choicelist' to be iterated over again,
so the actual return value is going to be 'choicelist'.

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

You're attempting to loop until the condition is true? If I'm
understanding correctly you're trying to find the first values that
fill all the conditions set forth?

  class NilClass?
   def method_missing(methId, *args)
      return false
   end
end

foo = choices(1..100)
bar = choices(1..100)

choices() returns nil, no?

condition(lambda{foo == (bar * 3)})
condition(lambda{bar > 10})
condition(lambda{(bar % 2) == 0})
puts foo
puts bar

Thanks for your help.

What are you trying to do, exactly? I'm sure there's an easier way if
you just want to compose conditionals like this; or are you trying to
get a handle on how callcc works? In the former case, you'd probably
want to try something with blocks instead... callcc is really just a
glorified goto.

E

2

> Lähettäjä: Luke Graham <spoooq@gmail.com>
> Aihe: can anyone verify this code as correct?
>
> class Object
> def choices(choicelist)
> if (!Class.class_variables.include? "@@cont")
> @@cont =
> end

You can use '@@cont ||= '.

Thanks, I like that one.

> choicelist.each { |choice|
> callcc { |cc|
> @@cont << cc
> return choice
> }
> }
> nil
> end

Continuation returns after the block, either with the value of the
block or the parameter to #call, and it stores its execution context.
Here you're returning in the middle of a loop, so I'm thinking each
#call will cause the remaining 'choicelist' to be iterated over again,
so the actual return value is going to be 'choicelist'.

I dont understand... the return value is definitely not choicelist, but
a different choice each time. The callcc is -inside- the internal iteration.
After all values have been exhausted, nil is the last thing to be
returned, and effectively marks the limit of choices, as '\0' does for
c-strings. The array could probably stand to be flattened first, just
in case.

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

You're attempting to loop until the condition is true? If I'm
understanding correctly you're trying to find the first values that
fill all the conditions set forth?

Yes, or nil if there are no such values.

> class NilClass?
> def method_missing(methId, *args)
> return false
> end
> end
>
>
> foo = choices(1..100)
> bar = choices(1..100)

choices() returns nil, no?

If all choices are exhausted, it does eventually return nil. However,
in the case of bar, it will once again start returning from the
beginning of the array if foo is unacceptable. Of course, we dont
really know if that value of foo is unacceptable or if its just that
all possible values of bar are unacceptable - that can only be
determined by more computation.

> condition(lambda{foo == (bar * 3)})
> condition(lambda{bar > 10})
> condition(lambda{(bar % 2) == 0})
> puts foo
> puts bar
>
> Thanks for your help.

What are you trying to do, exactly? I'm sure there's an easier way if
you just want to compose conditionals like this; or are you trying to
get a handle on how callcc works? In the former case, you'd probably
want to try something with blocks instead... callcc is really just a
glorified goto.

E

Im just hacking around to see what sort of valid flow control
constructs exist apart from the regular loops and such. The major
problem Ive seen so far with what I have is adding a further set of
choices after the originals, and before the conditions, adds
exponentially to the time required. To be honest, that doesnt worry me
because Im just having fun.

···

On Mon, 14 Feb 2005 17:07:00 +0900, E S <eero.saynatkari@kolumbus.fi> wrote:

3

No.

goto isn't even powerful enough to be called a brain-dead call-with-current-continuation.

(You can't implement branches, loops, exception handling, threading or coroutines with the ease that call/cc lets you do it.)

PGP.sig (186 Bytes)

···

On 14 Feb 2005, at 00:07, E S wrote:

What are you trying to do, exactly? I'm sure there's an easier way if
you just want to compose conditionals like this; or are you trying to
get a handle on how callcc works? In the former case, you'd probably
want to try something with blocks instead... callcc is really just a
glorified goto.

--
Eric Hodel - drbrain@segment7.net - http://segment7.net
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