Dear Mr Caruso,
> I am interested in an NTL interface for Maxima.
> Has anyone ever written such an interface?
>
> Is it easy to link Maxima with some
> external C/C++ library?
the following library is available for Common Lisp programmers:
http://common-lisp.net/project/cffi/
You can install it on Maxima's underlying Lisp system and then write the C
interface in Lisp. It doesn't work on GCL, however, so you will have to
install Maxima with another underlying Lisp system, e.g. SBCL.
On http://common-lisp.net/project/cffi/manual/cffi-manual.html#Tutorial you'll
find a tutorial about interfacing to C programs.
Best regards
Bruno Daniel