Date:         Mon, 29 Apr 2002 13:07:57 -0400
Reply-To:     bramley.m@PG.COM
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         bramley.m@PG.COM
Subject:      Re: poll: user-defined readonly macro variable
Content-type: text/plain; charset=us-ascii

SAS-L:

Many languages implement "constants" (eg:C++). Why not %Const construct that
allows you to _define_ and _initialize_ a macro variable? This can be thought of
as a superior form of "%Let".

eg: %Const     MyMacroVar = SomeConstantValue ;


Why stop at macro? why not include a "const" statement in the DATASTEP, etc.
with the compiler kicking out a error if you (or a later programmer) tried to
modify that value in the datastep ?

Data NewData ;
...
   Const TestValue "ConstantTestValue" ;
   Const NumValue 2*3.14159 ;
...
Run ;


Hmm, could that open the door to introducing function values in Const/Retain
statements, eg: Retain Const SASFunction(par1,...) ? That would be nice...imho.

Sincerely,

Michael Bramley
Cha Gheill!




 Internet Mail Message
 Received from host:      malibu.cc.uga.edu
 [128.192.1.103]



From: Paul Thompson <paul@WUBIOS.WUSTL.EDU> on 04/29/2002 04:46 PM GMT

           Paul Thompson           To:   SAS-L@LISTSERV.UGA.EDU
 <paul@WUBIOS.WUSTL.EDU>           Cc:    (bcc: Michael Bramley-M/PGI)
                           Subject:      Re: poll: user-defined readonly
                                macro variable
     04/29/2002 12:46 PM
  Please respond to Paul
                Thompson
 <paul@WUBIOS.WUSTL.EDU>






Fehd, Ronald J. wrote:

>From: Shoemaker, Jack [mailto:shoe@statprobetechnologies.com]
>
>>How about another macro declaration
>>to complement %global and %local,
>>say, %readonly?  So, a macro my look like this:
>>%macro sample();
>>%global A_GLOBAL_VALUE;
>>%local A_LOCAL_COUNTER;
>>%readonly A_SPECIAL_TYPE_OF_GLOBAL;
>>%mend sample;
>>
>
>yes! that's a good idea!
>
>That options stuff always gets so complicated
>what with The Options Naming Committee and their Agenda.
>
>- - - - autoexec - - - -
>%LET      A_SPECIAL_TYPE_OF_GLOBAL = some value;
>%readonly A_SPECIAL_TYPE_OF_GLOBAL;
>- - - autoexec end - - - -
>
>Ron Fehd  the macro maven  CDC Atlanta GA USA RJF2@cdc.gov
>
I like the idea.  I use %global variables extensively.  However, what
would be the rule to allow the value to be modified?  Would you need to
set it once, and, once the %readonly condition was applied, it could not
be modified again?

The basic idea is very appealing.