各位大侠:请教以下程序的详细解释，谢谢！
%macro printall(libname,worklib=work);
  %local num i;
   proc datasets library=&libname memtype=data nodetails;
   contents out=&worklib.. temp1(keep=memname) data=_all_ noprint;
   run;

data _null_;
      set &worklib.. temp1 end=final;
      by memname notsorted;
      if last.memname;
      n+1;
call symput('ds'||left(put(n,8.)),trim(memname));

       if final then call symput('num',put(n,8.));
   run;

    %do i=1 %to #
    proc print data=&libname..&&ds&i noobs;
    title "Data Set &libname..&&ds&i";
    run;
   %end;
%mend printall;

options nodate pageno=1 linesize=70 pagesize=60;
%printall(printlib)