Evaluation of complex conditions

Pete pete at mollysrevenge.com
Wed Oct 5 17:20:39 EDT 2011


Thanks, that's good to know.  I'm looking at using a pretty complex
condition with some of the conditions being trivial but others taking up
significant database access so sounds like I should leave the db access
conditions until last.

Hmmm, now I wonder if nested if statements make any difference to this.
 Probably not.


Pete
Molly's Revenge <http://www.mollysrevenge.com>




On Wed, Oct 5, 2011 at 1:46 PM, Richard Gaskin
<ambassador at fourthworld.com>wrote:

> Pete wrote:
>
>  I'm wondering how LC evaluates If statements with multiple conditions.
>>  Are
>> all conditions evaluated before the overall result is checked for true or
>> false, or does evaluation proceed left to right and stop as soon as a
>> condition is found to be false?  Whichever method is used, is it affected
>> by
>> some conditions being enclosed in parens?
>>
>
> IIRC from discussions with Dr. Raney many years ago, at some point he
> implemented an optimization in which the first part of any multi-condition
> expression that satisfies the expression avoids the need for evaluation of
> other conditions.  This normally follows in left-to-right order, but of
> course using parens can alter the evaluation order.
>
> So in this conditional expression:
>
>  if the short name of this cd is "Pete" and $user <> "pete" then
>
> If the short name of the card <> "Pete" then the engine wouldn't bother
> evaluating $user.
>
> --
>  Richard Gaskin
>  Fourth World
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