Compiling the Fortran sources with GNU Fortran 77 gave some warnings,
which weren't critical. While working with the mac80 and interp80 sources
I got much more into Fortran again than I thought I ever would. Up until
1984 I got significant work done with Fortran, now I had to relearn a bit
and had to get used to GNU Fortran 77, which is different from what I used
back then. So I fixed the warnings, sources compile clean now. Also
improved the shell driver script for running the PL/M-80 compiler on UNIX

Udo Munk
The real fun is building it and then using it...