creme

creme is a small, practical Scheme implementation written in Crystal, following R7RS-small. It's both a standalone CLI/REPL and an embeddable library, with a large, batteries-included extension library and a second, self-hosting C11 VM backend (icecreme) that runs the same bytecode with no Crystal process involved.

(define (fact n) (if (<= n 1) 1 (* n (fact (- n 1)))))
(write (fact 10)) (newline) ; => 3628800

(define (make-counter)
  (let ((n 0))
    (lambda () (set! n (+ n 1)) n)))
(define c (make-counter))
(write (list (c) (c) (c))) (newline) ; => (1 2 3)

(write (map (lambda (x) (* x x)) '(1 2 3 4))) (newline) ; => (1 4 9 16)

(write (/ 1 3)) (newline) ; => 1/3 (exact, not 0.333...)

(define-record-type point (make-point x y) point? (x point-x) (y point-y))
(write (point-x (make-point 3 4))) (newline) ; => 3

(write (guard (e (#t (list 'caught (error-object-message e))))
         (error "boom"))) (newline) ; => (caught "boom")

More in the Language tour, and 50+ runnable programs under examples/.

Features

• A complete R7RS-small language — library system, tail calls, hygienic syntax-rules, define-record-type, a full exception system, multiple values, call/cc (escape continuations), and a numeric tower with exact rationals and complex numbers.
• A batteries-included (creme …) standard library — JSON, YAML, CSV, XML, SQLite, HTTP, crypto (digests, ciphers, PKey, X.509, JOSE), regex, an actor system, Raft consensus, an FFI bridge, and more.
• Two backends: the native Crystal interpreter, and icecreme, a standalone self-hosting C11 bytecode VM.
• Embed it as a Crystal library, or link libcreme.a into a C program.
• Ruby-flavored conveniences: a (dialect ruby) naming layer and a #lang (creme syntax ruby) concrete-syntax dialect.

See the full Features list for everything above in detail, and Known caveats for what's deliberately out of scope (e.g. call/cc is escape-only, not full multi-shot continuations).

Benchmarks

A sample from make bench-md's output — single-threaded wall-clock time in seconds, lower is better. Native-language floors (Crystal, Go) are included for context; see benchmarks/amd64_freebsd.md for the full table (more workloads, more languages), the environment it ran on, and how to regenerate it on your own machine.

| workload | crystal | go | node | luajit | racket | guile | icecreme | creme | ruby | | ------------------------ | ------- | ------- | ------- | ------- | ------- | ------- | -------- | ------- | ------- | | fib(27) | 0.00054 | 0.00060 | 0.00153 | 0.00144 | 0.00085 | 0.00308 | 0.00935 | 0.03069 | 0.01010 | | record-test(500000) | 0.00348 | 0.01011 | 0.00684 | 0.05522 | 0.01180 | 0.01154 | 0.03677 | 0.06148 | 0.09714 | | nqueens(9) | 0.00048 | 0.00051 | 0.00113 | 0.00200 | 0.00078 | 0.00107 | 0.00882 | 0.01323 | 0.01187 | | total (all 9 workloads) | 0.04578 | 0.10587 | 0.07660 | 0.11843 | 0.12980 | 0.13703 | 0.15998 | 0.27220 | 0.32783 |

Quick start

shards install
shards build
./bin/creme path/to/script.scm     # run a script
./bin/creme                        # start the REPL (Ctrl-D or (exit) to quit)

Building requires Crystal ≥ 1.19.0 and the system SQLite3, OpenSSL, and libyaml libraries. See Getting started for prerequisites, building, the REPL, piped input, and running the test suite.

Documentation

• Introduction — what creme is, the two backends, project scope
• Features — the full feature list
• Getting started — build, run, REPL, development
• Language tour — the language by example
• Libraries — the full standard-library surface
• CLI reference — every subcommand and flag
• Embedding — using creme as a Crystal library
• icecreme — the self-hosting C VM
• Repository structure — a map of the codebase
• Known caveats — what's deliberately out of scope

📖 The full documentation index, including maintainer/internals notes, is in doc/README.md.

License

MIT, see LICENSE. © Vincent Landgraf.