is the name of the file being interpreted available?

[Ed Morton]

I just realised that while shell has $0 to hold the name of the file 
containing the script being interpreted, I don't know if that same 
information is available in any builtin variable in awk. Obviously I 
could write:

    awk -v script='/foo/bar/script.awk' -f '/foo/bar/script.awk' input

or similar but is there any way to get that '/foo/bar/script.awk' info 
inside the awk script without any manual intervention so I can just write:

    BEGIN { "we are running", foo }

for some value of `foo` inside the script to output:

    we are running /foo/bar/script.awk

Regards,

    Ed.