[](https://github.com/PollRobots/scheme/actions/workflows/node.js.yml)
[](https://github.com/PollRobots/scheme/actions/workflows/codeql-analysis.yml)
[](https://app.fossa.com/projects/custom%2B29853%2Fgithub.com%2FPollRobots%2Fscheme?ref=badge_shield)
[](https://github.com/pollrobots/scheme/stargazers)
# scheme.wasm
An R7RS Scheme implemented in WebAssembly
A partial implementation of [r7rs scheme](https://small.r7rs.org/), written
entirely in WebAssembly using the WebAssembly Text format. The only external
imports are for IO (`read`, `write`, and `readFile`), unicode (I have an
import that reads information about 256 code-point blocks to enable case
operations etc.), and process control (`exit`).
You can try it out at [pollrobots.com/scheme/](https://pollrobots.com/scheme/)
## How Complete Is It?
The aim is to write a spec complete version of `r7rs`, although I may skip
some of the optional features.
### What is done so far
- [x] Numerics
- [x] Integers (arbitrary precision)
- [x] Real numbers (double precision)
- [x] Rationals
- [x] Complex Numbers
- [x] Booleans
- [x] Strings
- [x] Characters
- [x] Pairs and Lists
- [x] Vectors
- [x] Bytevectors
- [x] Values
- [x] Records
- [x] Tail call optimization — internally `eval` uses a continuation passing
style, so TCO comes for free.
- [x] `call/cc` and exceptions
- [x] Macros
- [x] `define-syntax`, `syntax-rules`, `syntax-error`
- [x] Hygienic over `let`, `let*`, `letrec`, `letrec*`, and `lambda`
- [ ] `let-syntax`, `letrec-syntax`
- [ ] Modules
- [ ] Ports
- [ ] `dynamic-wind`
- [ ] Everything else
## Credits
Where practical everything has been implemented from scratch, but there
are places where it either wasn't practical, or where I tried and failed
to implement them myself, so credit is due to:
- **xxHash**:
It's probably overkill, but the hashing algorithm used for hashtables,
which are in turn used for environments and interning symbols, is xxHash
translated from the C++ implementation at
[github.com/Cyan4973/xxHash](https://github.com/Cyan4973/xxHash)
- **string->real**:
Strings are converted to real numbers using _Algorithm M_ from
"How to Read Floating Point Numbers Accurately",
[William D Clinger](https://www.khoury.northeastern.edu/people/william-d-clinger/) 1990. Which is conveniently expressed in scheme in the original
[paper](https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.45.4152&rep=rep1&type=pdf)
- **real->string**:
Real numbers are converted to strings using _Grisu 2_ by
[Florian Loitsch](https://florian.loitsch.com/home).
This was translated from C++ found at [github.com/romange/Grisu](https://github.com/romange/Grisu)
Additionally inspiration came from a couple of places
- **Lispy**: [Peter Norvig's](https://norvig.com) article
[(How to Write a (Lisp) Interpreter (in Python))](https://norvig.com/lispy.html)
was a critical source of inspiration.
- **EPLAiP**: Nearly a decade ago a friend gave
me a copy of
[Exploring Programming Language Architecture in Perl](https://billhails.net/EPLAiP.pdf)
by [Bill Hails](https://billhails.net). Definitely worth reading regardless of
your language of choice (I haven't written PERL this millenium).