Evaluation of complex conditions

[Bob Sneidar]

Yes, if by nested you mean: 
a is true and (b is true or c is true)

The statement in parenthesis gets evaluated first. 

Bob


On Oct 5, 2011, at 2:20 PM, Pete wrote:

> 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
>> LiveCode training and consulting: http://www.fourthworld.com
>> Webzine for LiveCode developers: http://www.LiveCodeJournal.com
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>> 
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