  Creating user defined functions (UDFs) is a powerful method to improve the
quality of computer applications, in particular spreadsheets. However, the only
direct way to use UDFs in spreadsheets is to switch from the functional and
declarative style of spreadsheet formulas to the imperative VBA, which creates
a high entry barrier even for proficient spreadsheet users. It has been
proposed to extend Excel by UDFs declared by a spreadsheet: user defined
spreadsheet functions (UDSFs). In this paper we present a method to create a
limited form of UDSFs in Excel without any use of VBA. Calls to those UDSFs
utilize what-if data tables to execute the same part of a worksheet several
times, thus turning it into a reusable function definition.
