I am working on an application which can use part of Dierckx's fitpack implementation at Netlib. The code looks to be old FORTRAN-IV converted minimally converted into FORTRAN-77. Generating a FORTRAN library to call from perl shouldn't be too hard. However, one of the routines requires the user to pass in a reference to a subroutine as an argument to a FORTRAN subroutine. If I implement a perl front end, I would guess this means the user provided subroutine would be in perl? Is this something which is possible, or should I just skip that particular function?