Simple Ruby Scheme Intepreter

This is an implementation of a Scheme interpreter written in a single file of Ruby.

It is only 140 lines of code, 53 of which are implementing standard library functions -- like cos to caculate cosine.

Scheme is one of the easiest programming languages to interpret. And Ruby is one of the most expressive and least-terse languages to develop in.

The goal of this repository is to make it as easy as possible to understand how a language intepreter works.

It is not a complete implementation of The R5RS Standard. Notably it is missing pairs and inexact numbers.

How Small/Fast/Complete is this Scheme interpreter?

Small

As mentioned above, the first iteration of this interpreter was 140 lines of code -- 53 of which implemented standard library functions.

Fast

On my machine, it can calculate (fact 1000) 0.00534 seconds. That's fast enough for playing around with, although Ruby can do the same calculation in 0.00038 -- about 15 times faster.

Complete

This interpreter is not very complete. Several missing features include:

Syntax: Missing # literals, derived expression types cond from if and let from lambda, the . list notation, and numerical constants like 3.1415926535F0, 0.6L0, 6/10, 3+4i.
Symatntics: Missing call/cc and tail recursion.
Data Types: Missing characters, ports, pairs, and exact/inexact numbers.
Procedures: Missing several primitive procedures like complex?, real?, rational?, exact?, and inexact?.
Error Recovery: This interpreter has very little error detection, reporting, or error recovery. Good luck [=

Acknowledgements