If an slisp application is compiled with the xnet module it can be a client to an slisp server. Lisp primitives defined in xnet.c setup a connection to the remote server, and allow control over the delimiters and the timeout. Once the connection has been established an s-expression may be evaluated on the remote server by the function NET-EVAL, which is nearly the same as the ordinary LISP EVAL function. The results of the NET-EVAL function are available within the local slisp process as long as the results don't include pointers to objects in the remote memory space.
The xnet functions are described in the reference part of the info documention for any application compiled with xnet.