Re: [Cardinal-dev] Does Ruby require restartable exceptions?

[Erik Bågfors]

On Thu, 2002-05-30 at 19:10, Dan Sugalski wrote:
> At 6:49 PM +0200 5/30/02, Erik Bågfors wrote:
> >On Thu, 2002-05-30 at 18:38, Dan Sugalski wrote:
> >>  Here's a question. Does Ruby require that you be able to catch an
> >>  exception then restart or resume from where the exception was thrown?
> >
> >AFAIK no,
> >
> >What you do in ruby is restart by hand.
> 
> Cool. I was worried you could do something like:
> 
> try {
>     object.method_which_pitches_exception();
> } catch {
>    resume;
> }
> 
> and have the resume jump back into the object's method at the place 
> where it threw the exception. Not having to do that makes life easier.

I've never seen that, but I'm not 100% sure about it.

Another thing you have in ruby is "throw" and "catch".  They have
nothing to do with the try/catch/throw that you have in for example
java.  

It works like this. (example from the pickaxe-book)

The following example uses a throw to terminate interaction with the
user if ``!'' is typed in response to any prompt.


def promptAndGet(prompt)
  print prompt                   
  res = readline.chomp
  throw :quitRequested if res == "!"
  return res
end                                               
                                                  
                                                  
catch :quitRequested do
  name = promptAndGet("Name: ")
  age  = promptAndGet("Age:  ")                   
  sex  = promptAndGet("Sex:  ")                   
  # ..                                     
  # process information                           
end 

What happens here is that when ruby encounters a throw it works it's way
up the call stack until it finds a catch-block with a matching symbol. 
Then it unwinds the stack to that point ant terminates the block (do/end
here is a continuation-block I assume)...

So.. this is not really exceptions but it kindof behaves that way. 


I have no idea how this will affect parrot or if it will in any way.
Perhaps this is already handleable. 

/Erik

-- 
Erik Bågfors               | address@hidden
Supporter of free software | GSM +46 733 279 273
fingerprint: 6666 A85B 95D3 D26B 296B 6C60 4F32 2C0B 693D 6E32