SAS: Recursive macro goes into an infinite loop - sas

Question

Could someone please explain why it is happening?
I'm trying to find objects dependencies tree in a DB.
Let's say view5 is a view sits on top view4 which sits on top view1.
Also,
view3 sits on top view2 sits on top view1.
So,
the when I query the macro for view1, I should get back view4, view5, view2 and view3.
This is the macro:
%macro dependencies(obj=);
%let dependent_objectname =;
proc sql noprint;
select "'"||trim(dependent_objectname)||"'"
into :dependent_objectname separated by ", "
from &_input.
where src_objectname in (&obj.);
quit;
%put &dependent_objectname.;
%let dependent_objectname = (&dependent_objectname.);
%put &dependent_objectname.;
%if %length("&dependent_objectname")>0 %then
%dependencies(obj = &dependent_objectname.);
%mend dependencies;
%let source = 'ditemp.depend_test1';
%put &source.;
%dependencies(obj = &source.);
First iteration works well,
I get the objects sit on top depend_test1
in a form of "('ditemp.depend_test2','ditemp.depend_test3')"
then I'm checking for the length of variable dependent_objectname (greater than zero)
and calling the macro again,
only it never stops...

Answer 1

I see a couple problems.
The statement:
%if %length("&dependent_objectname")>0 %then %do;
will always return true, even if the value of &dependent_objectname is null. Because the quotes are part of the value in the macro language. You probably want:
%if %length(&dependent_objectname)>0 %then %do;
That test for nullness usually works. Or see this paper for better methods. http://support.sas.com/resources/papers/proceedings09/022-2009.pdf
Before that, the statement:
%let dependent_objectname = (&dependent_objectname.);
is adding parentheses to your value. So again, even if &dependent_objectname were null, it would be () after this. It looks like you don't need these parentheses, so I would skip this statement.
I would also add:
%local dependent_objectname ;
to the top of the macro. That way each invocation of the macro will have its own local macro variable, rather than having them all use the macro variable created in the first iteration (or worse yet, all use a global macro variable).
You have sensibly added %PUT statements to help with debugging. I would expect they would show that the value of &dependent_objectname is always non-null as currently written. You could also add:
%put The length is: %length(&dependent_objectname.) ;

Answer 2

Since you are using an SQL query to generate the dependent list you can use the automatic variable SQLOBS in your test to break the recursion.
%if &sqlobs %then %do;
%dependencies(obj = &dependent_objectname.);
%end;
Also do NOT use a comma as the delimiter between the items listed in the OBJ parameter. The IN operator in SAS doesn't need them and they will cause trouble in the macro call.
select * from sashelp.class where name in ('Alfred' 'Alice') ;
So your macro could look like this:
%macro dependencies(object_list);
%local dependent_list ;
proc sql noprint;
select catq('1as',dependent_objectname)
into :dependent_list separated by ' '
from &_input.
where src_objectname in (&object_list)
and dependent_objectname is not null
;
quit;
%put Dependent Objects of (&object_list) = (&dependent_list);
%if &sqlobs %then %dependencies(&dependent_list);
%mend dependencies;
And here is a test case.
%let _input=sample;
data sample;
length src_objectname dependent_objectname $41 ;
input (_all_) (:) ;
cards;
object1 object2
object2 object3
object2 object4
;;;;
%dependencies('object1');