A Scheme Interpreter in Lua.
Misty has been developed with Lua 5.4.2.
This project is a personal exercise in understanding programming language implementation. The goal was to implement a few major features, therefore, I have not made an attempt to match the semantics of Scheme in detail. As such, Misty can be considered a separate language that derives from Scheme.
lua src/test.lua will evaluate each expression in a file (set to src/test.scm by default) and return the evaluation of the last one. Note that Misty currently has no display method.
Misty exposes two public methods: Misty.run which will evaluate a single expression given as a string, and Misty.run_file which is used in src/test.lua.
On a high-level, Misty supports lexical scoping, higher-order functions, and has tail-call optimization. A full list of primitives can easily be found in src/misty.lua; it is easy to add new primitives there.
One of the main disadvantages of implementing a language using the control-flow of another high-level language is the difficulty in reconciling subtle semantic differences. For instance, which values are falsy for the two languages might be different. A better implementation would be to implement a virtual machine for Scheme.
Moreover, it would be nice to have support for floats, strings, macros, and call/cc.
old-src contains the original implementation of Misty. I wrote it in Jan 2021 but consider it to be very bloated. For e.g., it has a basic notion of types that it doesn't really need. The latest version is rewritten (almost) from scratch.
This project includes a Scheme interpreter for Scheme as well. The code is lifted almost entirely from Chapter 10 of The Little Schemer (see below). I wrote it when I was reading the book, and decided to include it for completeness. Perhaps it will be useful to others as the book never presents the entire implementation together in a single place.
The name should be reminiscent of M-expressions, an early syntax for Lisp (of which Scheme is a dialect).
Rupanshu Soi, Department of Computer Science, BITS Pilani - Hyderabad Campus, India.