Hi Ian, %length is a very special macro function, it can take ant numbe of comma (,) without any problem. Thus,

%let x = a, b;

%put %length(&x);

will run fine. The result is 3.

Cheers,

Lei

Ian Whitlock wrote: > Subject: Macro quoting essentials > Summary: Short lesson on practical macro quoting > Respondent: Ian Whitlock iw1junk@comcast.net > > After reading the discussion under the subject "%upcase", I think it is > time to look at macro quoting from the practical point of view. > > There are two timing issues with macro quoting. Sometimes a symbol must > be hidden at macro compile time and some times at macro execution time. > Hence there are two important classes of functions. > > 1) compile time quoting - %STR and %NSTR > 2) execution time quoting - %SUPERQ and all other quoting functions > > Symbols hidden at compile time stay hidden at execution time unless > explicitly or implicitly unquoted, so %STR and %NSTR solve most quoting > problems. At compile time the usual problem is hiding a semi-colon, > > %macro q () ; /* version 9.1.2 + */ > %local boundary ; > %let boundary = %str(run ;) ; %* need semi-colon in the value > but %let must not set it at > compile time; > %put &boundary more ; > %mend q ; > > If one is writing messages that involve %-signs and ampersands then %NRSTR > is needed. (NR stands for no-re scan, i.e. evaluation of macro triggers.) > Actually, in a macro there is no need to hide these symbols at compile time > since no resolution or macro execution takes place at compile time. But it > is more convenient to hide these symbols at compile time, and let them stay > hidden at execution time. > > The use of the compile time functions is indicated whenever one is typing a > symbol that must be hidden at some time. This covers the vast majority of > cases. > > Since there is no need to hide most symbols at compile time, it can happen > that a variable's value must be hidden at execution time. The chief reason > is that %EVAL (implicitly called by %IF and in any place where a number is > expected by the system) assumes meaning for arithmetic, logical, and > comparison symbols that may be unwanted in some situation. Such cases can > usually be covered by the use of %SUPERQ, which hides everything and takes > the variable name as its argument instead of the variables value. For > example, %SUPERQ(X), is the quoted value of &X, while %SUPERQ(&X) is the > quoted value of the variable named by &X. > > At execution time there may also be a need to hide commas. For example, > > %let x = a,b ; > > causes no problem, but > > %length(&x) > > will cause a problem at execution time because the %LENGTH function cannot > have two arguments. > > %let x = %str(a,b) ; > > provides the simple compile time solution, and > > %length(%superq(x)) > > provides an execution time solution. > > There is still one more important case. Sometimes one wants to hide a > quote mark so that a macro expression can be evaluated inside single > quotes. Since the symbol is known, as opposed to being in the value of a > variable, one would like to use a compile time function; but %STR and > %NRSTR do not hide quote marks. In this case, the %-sign acts as an escape > character; hence %STR(%') is a hidden quote mark. > > It is important to note that quoting is implicitly removed in the return > value of macro functions that do not begin with a Q. The ones that begin > with a Q apply quoting to the returned value. To prove that Q-functions > apply quoting rather than not removing it, you could execute > > %put %length(%qupcase(a,b)) ; > > and see that it works. To prove that previously applied quoting is removed > by Q-functions you can take advantage that 10 is maximum depth of quoting > and study the execution of > > %macro q ( n ) ; > %local i w ; > %let w = %str(a,b) ; > %do i = 1 %to 20 ; > %let w = %qupcase (&w) ; > %end ; > %put >>>>&w<<< after 20 qupcases ; > %do i = 1 %to &n ; > %let w = %superq (w) ; > %end ; > %put >>>>&w<<< after &n bquotes ; > %mend q ; > %q(9) > %q(10) > > When macro time quoting is applied, it may be necessary to explicitly > remove that quoting at execution time with %UNQUOTE. The most common > example is when single quote marks are needed around the value of a macro > variable. > > %let x = something ; > %put %eval(%unquote(%str(%')&x%str(%'))='something') ; > > The old proverb, "If it looks good but doesn't work apply %UNQUOTE" is > still worth while because there are times when the macro facility leaves > a token in pieces and %UNQUOTE can glue those pieces back together. > I think that the above covers all the important practical facts of macro > quoting. The "other execution time functions %QUOTE, %NRQUOTE, %BQUOTE, > and %NRBQUOTE can be left to those more interested in macro quoting than > writing practical programs. In fact I would suggest that a required use of > these tools is probably an indication that the design is bad or that macro > is the wrong tool for the application. > > I am interested in evidence to the contrary. > > Ian