Self-hosting, to the byte
The compiler is written in the Scheme subset it compiles. The self-hosted build recompiles itself and the output is byte-identical — the fixpoint is checked in CI fashion on every change, and every test runs through both stages.
Native Wasm GC objects
Fixnums are unboxed i31refs, pairs and records are GC structs, eq? is one ref.eq. No shadow heap in JavaScript: the host supplies two byte-stream imports and nothing else.
Hygienic macros
syntax-rules and procedural syntax-case with fenders, nested ellipses and datum->syntax, running in a compile-time interpreter with hygiene by renaming.
Real closures, real tail calls
Typed function references with a fast per-arity entry and a generic entry per closure — variadic procedures and apply are cheap, and every tail call is a return_call. A 100M-iteration loop runs in constant stack, in ~150ms.
call/cc & dynamic-wind
Escape continuations ride the Wasm exception-handling proposal: capture is O(1), the normal path costs one try block, and winders unwind inner-to-outer on the way out.
A reactive web stack
(web sx) templates over fine-grained (web reactive) signals, an (web html) renderer, and a (web js) FFI that reaches straight into the host — this page is built with it.
3D and WebGL
(web three) builds reactive Three.js scenes the way sx builds DOM; (web gl) drives raw WebGL through a command buffer — one bridge call per frame — with shaders written as s-expressions in (web glsl). The title above is exactly this: dot-matrix glyphs, a vertex shader, one draw call.
Scheme-to-Scheme, no codec
When the backend is also Scheme (Igropyr), requests and replies are s-expressions — (rpc "/rpc" '(add 1 2 1/2)) comes back (ok 7/2), the exact ratio intact. (web fetch) makes it direct-style over Wasm JSPI; (web ws) / (web sse) push datum streams; (web json) handles everyone else.
Libraries
R6RS-style (library ...) files with (import (math utils)) resolution, dependencies first; exports are advisory because unused code is pruned anyway.