Re: Advantages of RPG

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 24/06/2008, at 4:05 AM, Jon Paris wrote:

> But neither is RPG's form of SELECT either Joe.  In fact it is one of
> the reasons why I don't like the RPG implementation - the languages in
> which I first met SELECT used the case form - and that is where my
> "mental model" was formed I guess.
>
> Subsequently I find I only use SELECT when using simple case
> constructs and use IF/ELSEIF for those cases where the condition
> changes.
>
> In languages where ELSEIF is not supported ELSE followed by IF will
> be.  Not as elegant but ...
>
> I guess we are all somewhat enslaved by our own particular mental
> models.

I think this discussion is missing the major point of difference.

SELECT results in ONE test being selected and then code branches to  
the end of the SELECT.

SWITCH results in a STARTING point being selected and then the code  
falls through all subsequent CASE clauses unless a BREAK or LEAVE is  
encountered.

While there are occasional advantages to the SWITCH form most uses of  
it ALWAYS have a BREAK after the last statement in a CASE thus  
effectively making it a SELECT. Certainly in my teaching I have found  
students grasp the concept of a SELECT much easier than that of SWITCH.

Seems to me that most of you don't really want a SWITCH, you want a  
SELECT with the tested expression specified on the SELECT rather than  
on the WHEN.

Of course PL/1 supported a SELECT with both coding variants. Ahh, if  
only ...

	SELECT ( expr );
		WHEN ( test1 )
		WHEN ( test2 )
		OTHERWISE
	END;

cf:
	SELECT;
		WHEN( expr1 )
		WHEN( expr2 )
		OTHERWISE
	END;

Be nice if RPG supported the former construct. Easy enough to do with  
extended factor 2 and free-form.

Regards,
Simon Coulter.
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