From: Morton Goldberg <m_goldberg@...>
Date: 2007-09-22T09:55:46+09:00
Subject: Re: Break loop by trapping INT

On Sep 21, 2007, at 7:04 PM, Todd A. Jacobs wrote:

> I'm trying to break a loop whenever CTRL-C is pressed, and find that
> this doesn't work:
>
>     trap 'INT', proc {break}; count=0; while count < 10;
>     puts count += 1; sleep 1; end
>
> I'm guessing it's because the loop is somehow out of scope, but I'm  
> not
> sure why.
>
> Some minor syntax changes to trap makes it work, sort of. If I use:
>
>     trap('INT') {break}
>
> instead, then I get a LocalJumpError. So, why does the syntax only  
> work
> one way, and what is the right way to trap the interrupt?

When the trap is triggered, the trap's proc object receives a 'call'  
message. This happens in the scope of top level, not in the scope of  
the while block. To get the result you want, you need to invoke a non- 
local jump mechanism. This can be done with catch and throw.

<code>
trap('INT') { puts "done";  throw :quit }

count = 0
catch :quit do
    while count < 10;
       puts count += 1
       sleep 1
    end
end
</code>

Regards, Morton