Error passing optional parameter to SAS/IML module

[rbettinger]

I have written a SAS/IML module to print a matrix using an optional parameter list. The module is quite simple:

proc iml ;
a={1 2 3, 4 5 6} ;

start print_mat( matrix= ) ;
print 'isSkipped=' (isSkipped( matrix )) ;
print 'isEmpty =' (isEmpty ( matrix )) ;
print 'matrix=' matrix ;
finish ;

run print_mat( a ) ;
run print_mat( matrix=a ) ;
quit ;

and it works for the first invocation of print_mat without the optional parameter syntax, but stumbles for the second invocation where the optional parameter list syntax is used. I do not understand why I get the following error message:

205 run print_mat( matrix=a ) ;

ERROR: (execution) Matrix has not been set to a value.

operation : = at line 205 column 22

operands : matrix, a

matrix 0 row 0 col (type ?, size 0)

a 2 rows 3 cols (numeric)

1 2 3

4 5 6

statement : RUN at line 205 column 1

206 quit ;

Why is 'matrix' considered to be an operand? Why is it considered to be empty?

The error message indicates that the input parameter, matrix, does not point to matrix a. What am I failing to understand about the optional parameter list syntax?

Dr. Wicklin has explained how to use the optional parameter list here: https://blogs.sas.com/content/iml/2015/02/02/detect-empty-module-params.html, and I have modeled my module after his example. Please help my poor neuron to comprehend my error. Thanks!

[Rick_SAS]

Unlike a SAS macro, which supports both positional and keyword syntax, a SAS/IML function only supports positional parameters. You can't call the function by using

run print_mat( matrix=a );

only by using

run print_matrix(a);

When you use that syntax, SAS tries to evaluate the expression "matrix=a", which is a boolean matrix, so that it can pass the appropriate matrix to the function.  However, there is no variable named 'matrix', so the expression "matrix=a" results in an error.  It's the same error you will get if you run

y = (matrix=a);

[rbettinger]

Thank you for an informative reply. I misunderstood the syntax in the example contained in the webpage that I cited and thought that I could use the optionality of a parameter the same way that I can use a SAS/Macro keyword parameter.

[Rick_SAS · Accepted solution]

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