What if....

Mike Bonner bonnmike at gmail.com
Sun Jan 27 13:53:14 EST 2013


ifs are evaluated left to right, though there is some leeway using parens.

As to your question though, yes putting slower evals at the end of a string
of ands and ors does save time if the if fails before the slow parts.

Did the following in a button to test. Just change one of the first
conditions to be false and the long myfunc call is never hit.  Placed
parens around the myfunc() to demonstrate that they don't give precedence
in this situation.

*on* mouseUp

   *if* 1 is 1 and 2 is 2 and (myfunc()) *then* *put* "It's all true"

*end* mouseUp


*function* myFunc

   *repeat* 10000 times

      *put* random(10)

   *end* *repeat*

   *if* random(2) is 1 *then*

      *return* true

   *else*

      *return* false

   *end* *if*

*end* myFunc



On Sun, Jan 27, 2013 at 11:39 AM, Peter Haworth <pete at lcsql.com> wrote:

> Musings about complex if statements on this Sunday morning....
>
> Lets say you have a complex if statement with 4 conditions that must all be
> true.  Is there any advantage, other than personal preference/style, to:
>
> if cond1 and cond2 and cond3 and cond4 then.....
>
> or
>
> if cond1 then
>    if cond2 then
>       if cond3 then
>          if cond4 then...
>
> In either case, as soon as a condition evaluates to false, none of the rest
> are evaluated, right?  If so, then always best to put the conditions that
> take the longest to evaluate further down the list, for example perhaps an
> SQL SELECT statement that might take a while to execute?  But then what if
> some of the conditions are in parens, for example:
>
> if cond1 and cond2 and (cond3 and cond4) then....
>
> The manual says the grouping operator (parens) has the highest precedence
> so does this mean (cond3 and cond4) will be evaluated before cond1 and
> cond2?
>
> Just curious.
>
>
> Pete
> lcSQL Software <http://www.lcsql.com>
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