https://github.com/rotty/poco-scheme

A toy interpreter for a subset of Scheme
https://github.com/rotty/poco-scheme

Last synced: 24 days ago
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A toy interpreter for a subset of Scheme

• Host: GitHub
• URL: https://github.com/rotty/poco-scheme
• Owner: rotty
• License: bsd-3-clause
• Created: 2019-07-25T21:19:43.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2019-08-31T21:35:56.000Z (about 5 years ago)
• Last Synced: 2024-10-10T20:28:31.833Z (about 1 month ago)
• Language: Rust
• Size: 79.1 KB
• Stars: 4
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# An implementation of a tiny Scheme subset

This is an implementation of a (currently miniscule) subset of

R7RS-small. See [the examples directory](./scheme-examples) and the

[smoke tests](./tests/scheme/smoke.scm)for to get an idea of what

already works.

The architecture is currently a fairly basic interpreter, with syntax

analysis phase up-front, which will transform the raw S-expressions

into an AST, which is then evaluated. This code sprang from code

intended as an example for using the [`lexpr`] crate to implement a

simple S-expression calculator, and got a bit out of hand 😀.

The current architecture is insufficient to support several major

language features of Scheme, such as macros or continuations. The plan

is to gradually improve the implementation to make such features

possible, before investing in additional features based on the current

architecture.

The evolution of poco-scheme will probably be largely guided by the

[chibi-scheme] codebase. chibi-scheme is a full implementation of

R7RS-small, written in C, employing a bytecode VM, and using syntactic

closures as the basic macro mechanism.

## Features already present

- Proper tail calls.

- Garbage collection employing the `gc` crate.

- `define`, `lambda`, `if`.

- Fixnums, and some procedures working on numbers.

- A very crude version of `display` and `newline`, both without port arguments.

## Next steps

- Basic cons cell support.

- Implement more syntax in `lexpr`:

  - Quote syntactic shorthand (i.e. `'`).

- Add a transformation of the AST to some kind of bytecode.

[chibi-scheme]: http://synthcode.com/wiki/chibi-scheme

[`lexpr`]: https://crates.io/crates/lexpr