Kaappi — R7RS Scheme in Zig

conformance

Complete R7RS-small

600+ built-in procedures, 32 syntax forms, all 16 standard libraries — every identifier from Appendix A.

control

First-class continuations

Multi-shot call/cc via stack copying, plus dynamic-wind and call/ec for escapes.

speed

Compile to native code

Compile Scheme to native binaries via LLVM on AArch64 and x86_64 — closures, tail calls, and fixnum arithmetic run at full speed.

batteries

178 SRFIs

Lists, strings, hash tables, vectors, threads, formatting, char-sets — 12 built in, 162 portable.

interop

C FFI with callbacks

Call shared libraries from Scheme, and pass Scheme procedures where C expects a function pointer.

concurrency

OS threads & fibers

Real OS threads via SRFI-18, plus green fibers with channels. Pre-fork and threaded HTTP servers.

recursion

(define (fib n)
  (if (< n 2) n
      (+ (fib (- n 1))
         (fib (- n 2)))))

(fib 30)  ;=> 832040

hygienic macros

(define-syntax my-when
  (syntax-rules ()
    ((_ test body ...)
     (if test
         (begin body ...)))))

(my-when #t
  (display "hello"))

libraries

(define-library (math)
  (export square cube)
  (import (scheme base))
  (begin
    (define (square x)
      (* x x))
    (define (cube x)
      (* x x x))))

The slow brew

Scheme will change how you think about code.

Written for programmers who already know Python, JavaScript or Ruby and nothing about Lisp. It starts at the REPL prompt and builds one runnable example at a time, with exercises at the end of every chapter.

first edition, 2026 337 pages paperback in 9 countries

PART I

Getting Started

Install it, meet the REPL, run your first program.

3 chapters

PART II

The Language

Data types, lists, control flow, functions, bindings, higher-order functions, I/O.

7 chapters

PART III

Going Further

Macros, libraries, records, error handling, continuations.

5 chapters

PART IV

Beyond R7RS

The SRFI library, the C FFI, concurrency.

3 chapters