SAS 9.4 Macro Language, 5th Edition

In the %IF statement, the values of WORD being tested are ambiguous — they could

also be interpreted as the numeric operators AND and OR. Therefore, SAS generates the

following error messages in the log:

ERROR: A character operand was found in the %EVAL function or %IF

condition where a numeric operand is required. The condition

was:word = and or &word = but or &word = or

ERROR: The macro will stop executing.

To fix this problem, use the quoting functions %BQUOTE and %STR, as in the

following corrected program:

%macro conjunct(word= );

%if %bquote(&word) = %str(and) or %bquote(&word) = but or

%bquote(&word) = %str(or) %then

%do %put *** &word is a conjunction. ***;

%else

%do %put *** &word is not a conjunction. ***;

%mend conjunct;

In the corrected program, the %BQUOTE function quotes the result of the macro

variable resolution (in case the user passes in a word containing an unmatched quotation

mark or some other odd value). The %STR function quotes the comparison values AND

and OR at compile time, so they are not ambiguous. You do not need to use %STR on

the value BUT, because it is not ambiguous (not part of the SAS or macro languages).

For more information, see Chapter 7, “Macro Quoting,” on page 81.

Debugging Techniques

Using System Options to Track Problems

The SAS system options MLOGIC, MLOGICNEST, MPRINT, MPRINTNEST, and

SYMBOLGEN can help you track the macro code and SAS code generated by your

macro. Messages generated by these options appear in the SAS log, prefixed by the

name of the option responsible for the message.

Note: Whenever you use the macro facility, use the following macro options: MACRO,

MERROR, and SERROR. SOURCE is a system option that is helpful when using

the macro facility. It is also helpful to use the SOURCE2 system option when using

the %INCLUDE.

Although the following sections discuss each system option separately, you can, of

course, combine them. However, each option can produce a significant amount of

output, and too much information can be as confusing as too little. So, use only those

options that you think you might need and turn them off when you complete the

debugging.

Tracing the Flow of Execution with MLOGIC

The MLOGIC system option traces the flow of execution of your macro, including the

resolution of parameters, the scope of variables (global or local), the conditions of macro

expressions being evaluated, the number of loop iterations, and the beginning and end of

each macro execution. Use the MLOGIC option when you think a bug lies in the

program logic (as opposed to simple syntax errors).

136 Chapter 10 • Macro Facility Error Messages and Debugging

Note: MLOGIC can produce a lot of output, so use it only when necessary, and turn it

off when debugging is finished.

In the following example, the macro FIRST calls the macro SECOND to evaluate an

expression:

%macro second(param);

%let a = %eval(&param); &a

%mend second;

%macro first(exp);

%if (%second(&exp) ge 0) %then

%put **** result >= 0 ****;

%else

%put **** result < 0 ****;

%mend first;

options mlogic;

%first(1+2)

Submitting this example with option MLOGIC shows when each macro starts execution,

the values of passed parameters, and the result of the expression evaluation.

MLOGIC(FIRST): Beginning execution.

MLOGIC(FIRST): Parameter EXP has value 1+2

MLOGIC(SECOND): Beginning execution.

MLOGIC(SECOND): Parameter PARAM has value 1+2

MLOGIC(SECOND): %LET (variable name is A)

MLOGIC(SECOND): Ending execution.

MLOGIC(FIRST): %IF condition (%second(&exp) ge 0) is TRUE

MLOGIC(FIRST): %PUT **** result >= 0 ****

MLOGIC(FIRST): Ending execution.

Nesting Information Generated by MLOGICNEST

MLOGICNEST allows the macro nesting information to be written to the SAS log in the

MLOGIC output. The setting of MLOGICNEST does not imply the setting of MLOGIC.

You must set both MLOGIC and MLOGICNEST in order for output (with nesting

information) to be written to the SAS log.

For more information and an example, see “MLOGICNEST System Option” on page

373.

Examining the Generated SAS Statements with MPRINT

The MPRINT system option writes to the SAS log each SAS statement generated by a

macro. Use the MPRINT option when you suspect your bug lies in code that is generated

in a manner that you did not expect.

For example, the following program generates a simple DATA step:

%macro second(param);

%let a = %eval(&param); &a

%mend second;

%macro first(exp);

data _null_;

var=%second(&exp);

Debugging Techniques 137