From: Sam Kong <sam.s.kong@...>
Date: 2006-10-12T09:07:30+09:00
Subject: Re: Question about callcc

Hi Ken,

Ken Bloom wrote:
> On Thu, 12 Oct 2006 01:59:26 +0900, Carlos wrote:
> 
>>> callcc { |c| $label = c }
>>> As I understand it, callcc returns the last expression or return value
>> Try
>>    $label = callcc {|c| c}
>>    $label.call(3)
>> 
>> and
>>    $label = callcc {|c| puts "first call"; c}
>>    $label.call(lambda{puts "second call"})
>> 
>> to understand what's going on.
> 
> This example (run in straight ruby, not irb) should clarify what's going
> on.
> 
> begin
>    $label=nil
>    $label=callcc{|c| c}
>    puts "After the first callcc"
>    $label.call
> rescue StandardError=>e
>    puts e
> end
> 
> begin
>    $label=nil
>    callcc{|c| $label=c}
>    puts "After the second callcc"
>    $label.call
> rescue StandardError=>e
>    puts e
> end
> 
> [bloom@cat-in-the-hat ~]$ ruby callcc.rb | head
> After the first callcc
> After the first callcc
> undefined method `call' for nil:NilClass
> After the second callcc
> After the second callcc
> After the second callcc
> After the second callcc
> After the second callcc
> After the second callcc
> After the second callcc
> (infintie loop)

Although I still don't understand what's going on in the back,
I see the difference.

Thank you very much.

Sam

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