Date:         Fri, 4 Jul 2008 14:14:32 -0500
Reply-To:     paul@WUBIOS.WUSTL.EDU
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Paul Thompson <paul@WUBIOS.WUSTL.EDU>
Subject:      Macro behavior in IML and DATA step
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes"; format="flowed"

The macro system behaves a little differently in IML than it does in
other parts of SAS.  In IML, each statement is executed immediately,
rather than waiting until all code is assembled.  This is a bit odd
for those who use macros outside of IML.

Here is a simple example.  First, we see the normal behavior in the
datastep, where the call symput does not affect the value of _i until
after the run:

75   options mprint;
76
77   %let _i=1;
78   data _null_;
79   call symput("_i",'2');
80   put "&_i";
81   run;

1
NOTE: DATA statement used (Total process time):
       real time           0.00 seconds
       cpu time            0.00 seconds


82   %put _i[&_i];
_i[2]

This is all quite what SAS users expect.

In IML, things behave a little differently.  Here is a comparable
example, with the output brought in from the OUTPUT window shown below.

83
84   %let _i=1;
85   proc iml;
NOTE: IML Ready
86   call symput("_i",'2');
87   print "Current value of _i: &_i";
88   quit;
NOTE: Exiting IML.
NOTE: PROCEDURE IML used (Total process time):
       real time           0.03 seconds
       cpu time            0.01 seconds


89   %put _i[&_i];
_i[2]

 From the OUTPUT window:
                               The SAS System           13:58 Friday,
July 4, 2008   6

                                      Current value of _i: 2

I encourage those who have not tried this to do so.

IML is an interesting part of SAS.  Its immediate execution component
is very useful.  It gives the ability of macro code to more tightly
self-modify.

This issue was raised by a post or two earlier today.  I thought it
interesting, so present this small tutorial.