I had thought about creating a perl script UI to an executable calling a specific function in the Dierckx fitpack. However, many of the routines there require work arrays which contain temporary results, and the function has to be called again with an integer flag changed to have it calculate the final results. Since I am planning on thousands of data points for the function of most interest, the floating point work array would need to be dimensioned at something like 500,000 elements, which would all need to be read in from STDIN. It just didn't look like a workable solution.

FORTRAN has been able have a subroutine/function name as an argument to a subroutine/function for a long time. There are lots of math problems which require this.