The "double inequality" is sometimes called an "implicit AND" operation.
It is a particular feature of the DATA step language and does not apply
generally to all SAS languages. I am not a macro expert (or Maven), but I
looked at the MACRO evaluation doc
ewer.htm#p18bcfyqilvhc3n12stuo8eafd46.htm, or short url
http://bit.ly/xF98Dh) and didn't see it mentioned.
I do know that the implicit AND operation is not part
of the SAS/IML language, nor is it in PROC SQL, although SQL has the
BETWEEN/AND operator. The implicit AND is also not part of C, C++, R,
MATLAB, or any other language that I routinely use, although I believe it
is valid in Perl 6 (but not Perl 5) and Python.
%if 1 < &parm. le 100 %then %do ;
is always TRUE because it is evaluated from left to right as
%if ( (1 < &parm.) le 100) %then %do ;
Because the first expression is always 0 or 1 (regardless of ¶m), and
because 0 and 1 are both LE 100, the expression is constantly TRUE.
Statistical programming and SAS/IML blog: http://blogs.sas.com/content/iml