#4 Interpreter error reporting is wrong for files using include

[Tom Morris]

If a LL program uses an include statement, any run-time
errors from the interpreter will be reported using the
filename of the most recently parsed file (one of the
includes), rather than the file containing the code in
error.

I'm not sure the information to report this correctly
is currently stored. Each interpreter node has the
line number of the containing line, but no reference to
the original file.