Tips on this lab:

1. Make sure that you have a set of curly braces surrounding the whole program.  If you don't,
your program probably won't work.

2. Some of you are running the program like this:
  ./go < testfile.spl
That is a good idea for testing -- except it doesn't work once WormWorld is connected.
So instead, just run "go" and paste in your SPL code.

3. If your program crashes, and you don't know where, here is what to do:
 a. Start the debugge gdb:
    gdb go
 b. Once gdb starts, start your program:
    run
 c. Your program starts.  Paste in the SPL code.
 d. If your program crashes, enter the "where" command:
    where
 e. gdb will display a stack trace of your program.  From where you can 
    see where it crashed.

4. If your function calls are working properly, then you do *not* need to change
the eval() code for _funcall -- but you do need to add code to eval() for
_builtin.