# lisp-rs

A simple Lisp interpreter/library in Rust. The interpreter/library was initially developed as a **teaching aid** to explain how [Lisp interpreters work](https://www.amazon.com/dp/B0B1Z48DMT/ref=cm_sw_r_apan_QD16PC5E2EZWMKB1EZMK) and how can they be implemented using the Rust programming language. However the interpreter seems to be taking life of it's own and has been ported to the [web](https://vishpat.github.io/lisp-rs-wasm) using [WASM](https://webassembly.org). The interpreter is available as a [crate](https://crates.io/crates/lisp-rs) and can be used to embed a Lisp interpreter in your Rust projects. The WASM implementation uses the lisp-rs as a library to implement the online interpreter.

## Dialect
The interpreter is based on a modified subset of [Scheme](https://en.wikipedia.org/wiki/Scheme_(programming_language)). Following are the features supported by the interpreter

- Variables and Constants
- Functions (lambdas)
- Functional constructs such as map, filter and reduce
- Closures
- Tail Call Optimization

More information about the dialect can be found at

- [Syntax](https://github.com/vishpat/lisp-rs/wiki/Lisp-Syntax)
- [Sample Programs](https://github.com/vishpat/lisp-rs/wiki/Sample-programs)

## Implementation

The interpreter has been implemented in three phases

- Phase I: Complete interpreter and REPL implementation with support for basic data types (integers and boolean), variables, lambdas, and lambda calls (branch 0.0.1)
- Phase II: Support for advanced data types (string, float, and lists) and functional constructs (branch 0.0.2)
- Phase III: Support for tail call optimization (branch 0.0.3) and closures (branch 0.0.4)


For a detailed code-walkthrough about Phase-I implementation refer to the [docs](https://vishpat.github.io/lisp-rs). For code-walkthrough of all the phases, get the [e-book](https://www.amazon.com/dp/B0B1Z48DMT/ref=cm_sw_r_apan_QD16PC5E2EZWMKB1EZMK).

[![asciicast](https://asciinema.org/a/VVQQfGpp15a4BaoNgnEKIqqrr.svg)](https://asciinema.org/a/VVQQfGpp15a4BaoNgnEKIqqrr)

## REPL
```
cargo run --features="build-binary"
```

## Test
```
cargo test
```

## WASM

The interpreter has also been compiled to WASM so that it can run in a browser and is hosted [here](https://vishpat.github.io/lisp-rs-wasm).