Date:         Mon, 2 May 2005 10:49:07 -0400
Reply-To:     Dianne Rhodes <RHODESD1@WESTAT.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Dianne Rhodes <RHODESD1@WESTAT.COM>
Subject:      Re: %FACT(or something like that) from SAS 82 Users guide.
Comments: To: "Fehd, Ronald J" <rjf2@CDC.GOV>
Content-Type: text/plain; charset="US-ASCII"

> >
> > Does anyone still have the SAS 82 Users Guide?  I recall an
> interesting
> > macro, %FACT may have been its name, that used recursion to compute
> > factorials.
> >
> > I don't want to compute factorials by I may want to use
> recursion or
> > at least think about it.
> >
> > If anyone has access to this long forgotten text and has
> time to post
> > it here it would be interesting to me.  As I recall it was just few
> > lines.
>

Sure 'nuff,
Page 470 Chapter 15
Example 4
This macro computes the factorial (N!) of the value of macro parameter
N.  It illustrates recursive execution of a macro, that is, a macro
calling itself.

%macro factorl(n);
 %if &n=0 %then 1;
 %else %if &n=1 %then 1 ;
 %else %eval(&n*%factorl(%eval(&n-1))) ;
%mend factorl ;
Here's the log:

1          options mprint symbolgen ;
2
3          %macro factorl(n);
4           %if &n=0 %then 1;
5           %else %if &n=1 %then 1 ;
6           %else %eval(&n*%factorl(%eval(&n-1))) ;
7          %mend factorl ;
8
9          %let number=%factorl(5) ;
SYMBOLGEN:  Macro variable N resolves to 5
SYMBOLGEN:  Macro variable N resolves to 5
SYMBOLGEN:  Macro variable N resolves to 5
SYMBOLGEN:  Macro variable N resolves to 5
SYMBOLGEN:  Macro variable N resolves to 4
SYMBOLGEN:  Macro variable N resolves to 4
SYMBOLGEN:  Macro variable N resolves to 4
SYMBOLGEN:  Macro variable N resolves to 4
SYMBOLGEN:  Macro variable N resolves to 3
SYMBOLGEN:  Macro variable N resolves to 3
SYMBOLGEN:  Macro variable N resolves to 3
 2                                                            The SAS
System                                     10:47 Monday, May 2, 2005

SYMBOLGEN:  Macro variable N resolves to 3
SYMBOLGEN:  Macro variable N resolves to 2
SYMBOLGEN:  Macro variable N resolves to 2
SYMBOLGEN:  Macro variable N resolves to 2
SYMBOLGEN:  Macro variable N resolves to 2
SYMBOLGEN:  Macro variable N resolves to 1
SYMBOLGEN:  Macro variable N resolves to 1
10         %put &number ;
SYMBOLGEN:  Macro variable NUMBER resolves to 120
120
NOTE: SAS Institute Inc., SAS Campus Drive, Cary, NC USA 27513-2414
NOTE: The SAS System used:
      real time           2.15 seconds
     cpu time            0.45 seconds

Dianne Louise Rhodes
Westat