Date:         Wed, 22 Dec 1999 20:33:33 +0000
Reply-To:     roland.rashleigh-berry@virgin.net
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Roland <roland.rashleigh-berry@VIRGIN.NET>
Organization: N/A
Subject:      Re: Return Values in a Macro
Content-Type: text/plain; charset=us-ascii

Walter Smith wrote:
>
> Rolands illustration is exactly on track!! Macro code - even in a data
> step - resolves to text, generally text that is SAS code - data step or
> proc step.
>
> Data step macro example:
>
> <pre>
> %macro boxcox(x,lambda);
>   (%str(&x)**&lambda -1)/&lambda
> %mend;
>
> data a;
>   set b;
>   zz = %boxcox(xx,.7);
> run;
>
> The above would resolve to:
>
> data a;
>   set b;
>   zz = (xx**.7 -1)/.7;
> run;
> </pre>
>
> The resolved text then goes to the compiler to compile the data step
> and the macro processor is out of the picture. While the data step is
> executing (processing observations), the macro processor is NOT active.
>
> Perhaps the most common beginners error in writing macro functions, is
> including SAS statements that the beginner expects to execute before
> the  macro terminates. Any non-macro statements resolve to text.
>
> Rolands example stands as an example of a macro function.
>
> An example of the above error is:
>
> <pre>
> %macro mymacro(parm);
>   options mprint;
>   %if &parm=X %then RED;
>   %if &parm=Y %then BLUE;
> %mend;
>
> %if %mymacro(X)=RED %then %do;
> /*more stuff*/
> %end;
> </pre>
>
> The above macro function would never resolve to the values RED or BLUE
> because the SAS options statement is included in the resolution.
> Instead the above invocation would resolve (in part) as:
>
> %if options mprint; RED=RED %then %do;...%end;
>
> Not what was expected or desired.
>
> Hope this is useful - :)

Yep. Macros reduce themselves to whatever the macro code reduces itself
to. If you want that value from the macro such as

%let word0=%words(&mstring);

then all your %words macro has to do is put the answer you want in a
macro variable and then resolve it right at the end without a ";" after
it. What you get is the text of the answer so you effectively get

%let word0=&answer;

%macro words(string);
  %let blah, blah blah;
  %let num=&answer;
  &num
%mend;

You can write functions that way where the macro substitutes complex SAS
code.

Idiotically simple.

Roland

Pub time, I think.