From: Robert Klemme <shortcutter@...>
Date: 2008-06-14T18:44:21+09:00
Subject: Re: raise and rescue

On 14.06.2008 00:31, Michael W. Ryder wrote:
> Robert Klemme wrote:

>> There is no way - and for good reason.  An exception is thrown because 
>> execution cannot proceed at that line.
> 
> So how would you do something that requires user intervention, say in 
> putting more paper in a printer?  A lot of my programs require files or 
> other resources that may not always be available and I have programmed 
> them so that an error message is displayed and the operator can fix the 
> problem and continue or abort the program.

That's exactly the case where /retry/ is meant for.  Catch the 
exception, do something and then retry the block of code (see the 
example I posted earlier).

>  A very good example is when 
> a user tries to bring up an account that is in use by another user.  The 
> program states that the record is busy and the operator can wait for the 
> record to be freed and continue or go to another account.
> I can see how to do this in Ruby by using something like a while loop 
> but that requires that the code surround every possible trouble spot 
> rather than having a "generic" exception handling routine like I 
> currently use in Business Basic.

See above.

>> There is however retry, but it will continue from the beginning of the 
>> block:
>>
>> irb(main):001:0> i = 0
>> => 0
>> irb(main):002:0> begin
>> irb(main):003:1* puts 1
>> irb(main):004:1> raise "Foo"
>> irb(main):005:1> rescue Exception
>> irb(main):006:1> puts 2
>> irb(main):007:1> i += 1
>> irb(main):008:1> retry if i < 3
>> irb(main):009:1> end
>> 1
>> 2
>> 1
>> 2
>> 1
>> 2
>> => nil
>> irb(main):010:0>

Cheers

	robert