SISC is an R5RS Scheme implementation, which includes a full number tower, hygienic macros, proper tail recursion, and first class continuations. SISC is short for Second Interpreter of Scheme Code, in reference to its predecessor LISC, the Lightweight Interpreter of Scheme Code.SISC is free software, dual-licensed under the Mozilla Public License and the GNU General Public License, Version 2. It was developed by Scott G. Miller and Matthias Radestock.