EXTRACTING A PART DESCRIPTION "PREFIX" TO USE IN A REPEAT REGION RELATION

I want to automatically set all components in an assembly named with a certain prefix to "REF" for QTY on a drawing BOM.

In the drawing BOM repeat region, is there a way to extract the first part of a part's DESCRIPTION parameter value and use it to change its entry in the QTY column?

Here is the PTC command line I am using to extract: extract(string, position, length)

Here are the code I am using currently, it doesn't give an error, but it doesn't change the QTY column to "REF" like I need it to:

QTY1=rpt_qty
MEM_PRE=extract(asm_mbr_description,1,4)
IF MEM_PRE=="mem-"
QTY1="REF"
ELSE
QTY1=rpt_qty

ENDIF

Thanks in advance!