When do we need to quote "+" in SAS macro programming?

[Zhanxiong]

I am wondering does there exist a scenario that the "+" operator must be masked by quoting functions such as %STR or %BQUOTE? In SAS documentation, it states that "+" may need to be masked "To prevent it from being treated as an operator in the argument of an %EVAL function".  However, I tested a couple of toy examples and found that directly typing "+" and using "%str(+)" makes no difference. 

For example, both "%let var1 = A+B;"  and "%let var2 = %str(A+B)"  resolve to "A+B" when &var1/&var2 is referenced -- there are no error/warning messages in the log. Therefore, it seems that SAS never misinterprets "+". 

So my question is, could anyone construct a specific example that enclosing the "+" (or similar operators such as "=, -, *") with quoting function is a must? That is, without quoting it, the SAS will issue an error? Thank you very much!

[ChrisNZ]

The help page mentions function %eval, yet you haven't used it.

%put %eval( 2 %str(+) 3 );    will show you the effect of masking the +.

Unsure why you'd ever want to do this.

[Shmuel]

Usually you use the + (plus) sign in mathematical operation,

but sometimes you want to display a formula (to a child) and prompt for a result to check.

Look at next code :

data test;
    no_1 = '2';
    no_2 = '3';
    formula = no_1 || "+" || no_2 || "=?";
    put formula " Enter your answer";
run;

The usage of macro programing is just a tool to generate a code which is finally sas code.

[Zhanxiong]

%put %eval(2 %str(+) 3); will issue an error message, and I know that...

I am asking to construct an example that only after %str(+) is added, the error/warning caused by directly using unmasked "+" can be AVOIDED, not the opposite direction. 

[Astounding · Accepted solution]

An %IF %THEN statement invokes %EVAL.  So try this combination:

%let breakfast = ham + eggs;
%if &breakfast = ham + eggs %then %let fed=yes;

The first statement works just fine.  But the second statement generates an error message.  The implied %EVAL sees the plus sign, and tries to add together ham + eggs.  There are a few ways to get around this, and a quoting function is one of them.

[Zhanxiong]

This is exactly what I want. Thank you!