Date:         Fri, 22 Oct 2010 20:09:01 -0400
Reply-To:     Scott Bass <sas_l_739@YAHOO.COM.AU>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Scott Bass <sas_l_739@YAHOO.COM.AU>
Subject:      Function vs. operator: if statement short circuit processing

Hi,

Two questions:

data _null_;
   x=.;
   if (x ne .) then do; * ... ; end;
   if (not missing(x) then do; * ... ; end;
run;

1)  Does anyone know if the SAS compiler is smart enough to generate the
same compiled code for both lines?  Is the first line more performant than
the second?  Does the second line generate a function call for each
observation, or does the compiler transparently convert this to the
equivalent of the first line?

I've been using the 2nd approach a lot, thinking that it's slightly clearer,
and I don't have to think about the data type of the variable.  However,
neither of those are show stoppers; I can easily revert to the first
approach if it performs better.

2)  And I can probably answer my own question #1 via the below code:

data _null_;
   x=.;
   if ((x ne .) and (x + 5 > 7)) then put "YES";
   if ((not missing(x)) and (x + 5 > 7)) then put "YES";
run;

Clearly they must not generate the same code, since the first line
implements "short circuit" if processing, ending statement execution as soon
as the first portion renders the entire statement false.

Anyone know why the second statement results in "Missing values were
generated as a result of performing an operation on missing values."?

So if the answer to #1 is "first line performs better", then my use of the
missing function is going to dramatically decrease.  Perhaps useful in a
macro where the incoming variable data type is unknown, but otherwise...

Thanks for any insights you can share.

Regards,
Scott