S9fES is a mature, portable, and comprehensible interpreter for the R4RS Scheme programming language. It offers the following features:
support for low-level Unix programming
cursor addressing with Curses
decimal-based real number arithmetics
basic networking procedures
loads of useful library functions
The S9fES code strives to be simple and comprehensible. It is written in ANSI C (C89) mixed with Scheme and runs in many popular environments, including *BSD, Linux, Plan 9, and Windows.
S9fES has been placed in the public domain by its author. Because the author did not host the code for a while in 2011 and may or may not host it at any given time, this mirror has been established. Check out the original site [1] to see the current status.
The internal structure of the interpreter is documented in detail in the book “Scheme 9 from Empty Space” [2]. An obsolete version of the book is available for free at [3].
You can download the S9fES source code from [4].