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Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA [message #25168 is a reply to message #25075]

Sat, 19 May 2001 10:20

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

<mankoff@I.HATE.SPAM.lasp.colorado.edu> writes:

> On 18 May 2001, Craig Markwardt wrote:
>> As for continuations, closures, etc., these are computer science
>> jargon for specific language behaviors. IDL has none of them. I
>> understand continuations to be a way for execution contexts to be
>> suspended, saved, and later restored. Perhaps the CATCH error
>> handling technique is a nascent continuation. Alas, this has nothing
>> to do with the CONTINUE reserved word recently added to FOR and WHILE
>> loops.
>
> ok, i get it.
>
> But if you want to "suspend, save, restore" the execution state, wouldn't
> "save, /vars" and "save, /all" simulate this to some extent?

Yes, sort of, but a formal continuation also saves the execution
context, not just the variables. Take a look at CATCH for exception
handling and you will see that CATCH can essentially return *twice*.
Once in the normal program flow, and a second time if an error occurs.

So, internally CATCH saves the execution context so that when an error
happens the execution can resume again within CATCH. To be honest I
don't totally understand formal continuations, but I think CATCH is a
rudimentary example of one.

Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA By: <mankoff[1] on Fri, 18 May 2001 17:17
		Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA By: Craig Markwardt on Fri, 18 May 2001 12:31
		Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA By: John-David T. Smith on Tue, 22 May 2001 13:41
		Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA By: Craig Markwardt on Sat, 19 May 2001 10:20
		Re: IDL interpreter questions - can someone (D.Fanning) explain - TIA By: Mark Rivers on Fri, 18 May 2001 22:28

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