Subs

Introduction

Subs is a Scheme Lisp interpreter written in C++.

The implementation is incomplete and naive, and is intended mainly to help me understand Scheme and functional programming better. It depends on BOOST (and STL).

I aim to implement enough to be able to run every code sample in Structure and Interpretation of Computer Programs. Versions of Subs are named after the latest chapter of SICP whose code examples work correctly in the interpreter.

Subs is only tested on Linux, but should work on other platforms.

The most glaring limitations are:

performance is likely to be poor due to frivolous use of dynamic memory
no def-syntax
no mutable data (hence the name)
some missing functions

Existing features include:

integer and decimal types (finite precision) and strings
operators such as +, -, *, /
definition of symbols and functions, including via let
lambda functions
if and cond
support for recursive procedures
data structures using cons, car, cdr, list etc.
higher-level procedures e.g. map, filter, for-each
predicates like and, or and not
tail-call optimisation
quoting using ' or (quote ...)

Points of interest:

most built-ins implemented in C++, which might some day provide good performance
written using test-driven development throughout

Examples

 > (define foo 3)
 foo
 > foo
 3

 > (define (square x) (* x x))
 square
 > square
 <<COMPOUND-PROCEDURE square>>

 > (define (factorial n) (if (= n 1) 1 (* n (factorial (- n 1)))))
 factorial
 > (factorial 3)
 6
 > (factorial 4)
 24

 > (load "painter/painter.scm")
 > (define letter-a (segments->painter (list
 .     (make-segment (make-vect 0    0)   (make-vect 0.5  1))
 .     (make-segment (make-vect 0.5  1)   (make-vect 1    0))
 .     (make-segment (make-vect 0.25 0.5) (make-vect 0.75 0.5)))))
 letter-a
 > (svg-document (square-limit letter-a 4))

Download

Install scons, g++, BOOST and (optionally) valgrind:

 sudo apt-get install scons g++ libboost-dev valgrind

Download subs-scheme-x.x.x.tar.gz from https://codeberg.org/andybalaam/subs-scheme/releases .

 tar -xzf subs-scheme-*
 cd subs-scheme-*
 scons
 ./subs

Development

To get the latest code:

 sudo apt-get install scons g++ libboost-dev valgrind

 git clone https://codeberg.org/andybalaam/subs-scheme.git
 cd subs-scheme
 scons
 ./subs

To log a bug:

issues page

Copyright

Subs is Free Software released under the terms of the GNU General Public License version 2 or later.

Subs comes with NO WARRANTY.

See the file COPYING.txt for more information.