How to pass a value by reference into a macro? Do I used eval-based definition, and if so, how does it work?

[gmagnant]

I wrote a simple macro for a string builder for a full name when passed params for FirstName, MiddleName, and LastName.;  first screenshot - the macro definition 

I can pass the values explicitly to the macro but not by reference from the query that invokes the macro;  second screenshot shows the behavior of the macro both when I explicitly pass the values to it and when I attempt to do so by reference when "Use eval-based definition": is NOT checked.

If I DO check the box for "Use eval-based definition",  I get the following error:
"Error in 'SearchParser': The definition of macro 'CRE_getFullNameTEST(3)' is expected to be an eval expression that returns a string."

What do I have to do to be able to pass the values contained within FirstName, MiddleName, and LastName to my macro?

Thanks for any assistance with this.

Macro definitionSPL that invokes macro

[ITWhisperer]

Try it this way

[gmagnant]

Many thanks for pointing out the syntax for concatenating a string in the macro. 

Works like a charm now. 

Now I can go create my dashboard URL builder macro which will be used to send the URL via Splunk alert into a ticketing application.