[Mediawiki-l] parserfunctions question: evaluate vs. display?

[Rolf Lampa]

Daniel Barrett skrev:
> In a parserfunctions statement like this:
>
> {{#if:  {{#some-condition:}}  |  {{#some-big-computation:}} }}
>
> if #some-condition is false, which of the following should happen?
>
> 1.	#some-big-computation gets fully evaluated, but results are not
> displayed
> 2.	#some-big-computation is not evaluated at all
>
> Looks like choice #1 is happening in MW 1.12.0, which is bad if
> #some-big-computation has side-effects or is very expensive.  Is this
> correct behavior?
>   

It's absolutely crucial to short circuit  boolen logic at first false 
result - in cases logically equivalent to AND operations.

Your example contains just such a case, the is, your 1:st expression 
should behave equivalent to

{{
if  {{#some-condition1}} and  <--- break here if "false"!
    {{#some-condition2}} and
    {{#some-conditionN}}
then // do this (else nothing)
}}

In for example Delphi the behaviour for boolean expressions is optional. 
Default setting for "complete boolen evaluation" is = False, that is, 
the compiler will produce logic which short circuits at first false 
result. And this short circuit is very powerful for optimizing code 
execution.

Regards,

// Rolf Lampa