what problem are you actually trying to solve? My guess is that Fortran expressions should be quite rare outside a Fortran program, hence f2c.

This guess is unfortunately false. As to the actual problem: ugly old proprietary program at $work that uses Fortran-style expressions in certain contexts needs to be ported to a different framework that required generation of C code.

Real world old code almost always looks ugly and has been hacked into a state where at least parts of it "just works, probably by pure magic". f2c looks quite small, so it should not be that hard to find and understand the relevant parts.

Believe me, I've seen more real world old code than I'd have liked. "I've seen things you humans wouldn't believe" and so on. And luckily, a better, or at least easier, solution appeared in this thread.