Embedding Scheme in Rust: scheme-rs vs. steel

Sun, 08 Nov 2026 22:30:23 +0100

Steel and scheme-rs are both Rust crates that put a Scheme interpreter inside your process. Steel is the older one: first commit February 2020, 1,213 commits, version 0.8.3, 2,654 GitHub stars, and about 78% of its commits from Matt Paras. scheme-rs started in August 2023, has 263 commits, version 0.2.0, 342 stars, and about 66% from Matt Plant with another 26% from Linus Shoravi.

Steel implements R5RS; scheme-rs implements R6RS.

tl;dr ¶

Steel is R5RS with Racket-like modules, contracts, runtime dylibs, a package manager and an LSP. It has 569 Rust tests and about 421 Scheme assertions.
scheme-rs is R6RS with a full numeric tower, R6RS conditions, records and ports, delimited continuations, a concurrent cycle-collecting GC and Send/Sync async embedding. It has 60 Rust tests, 39 of which belong to the GC.
Steel is the more adopted project. But I couldn’t find its R5RS and R7RS suites in CI.
Neither is 1.0, both are bus-factor-1, and both have real correctness bugs open.
Steel is MIT/Apache-2.0, builds on Linux, macOS and Windows, and its core targets wasm. scheme-rs is MPL-2.0 and tests on Linux.
Pick Steel for a batteries-included scripting layer; pick scheme-rs for a standards-shaped runtime with async and threads.

Two projects, six years apart ¶

Signal	Steel	scheme-rs
First commit	2020-02-20	2023-08-12
Release	0.8.3, August 2026	0.2.0, May 2026
Commits	1,213	263
Top author	~78%, Matt Paras	~66%, Matt Plant
Stars / forks	2,654 / 147	342 / 25
Open / closed issues	72 / 85	23 / 109
crate downloads, last 90 days	24.5k	156
Rust lines	124.8k	37.2k

Steel has the history and the audience. It also nearly died: one commit in 2022, then 298 in 2025 and 148 so far in 2026. scheme-rs is accelerating, with 126 commits in 2026 against 85 in all of 2025, and 47 commits in the last 90 days against Steel’s 25.

Scheme on Simon Shine

Embedding Scheme in Rust: scheme-rs vs. steel

tl;dr ¶

Two projects, six years apart ¶