# JeffBezanson/femtolisp

a lightweight, robust, scheme-like lisp implementation

Repository: https://github.com/JeffBezanson/femtolisp
Canonical: https://ross.abutalabs.com/products/femtolisp
Language: Scheme
License: BSD-3-Clause
License Family: permissive
Last push: 2020-02-26T09:27:37+00:00

## Health v2 (maintenance only)
Score: 32/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 35, longevity 100
- inputs: {"age_days": 5311, "days_push": 2380, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1721, forks 124 (observed 2026-08-28T04:05:26.824586+00:00)

## What it is
FemtoLisp is a lightweight, self-contained Scheme-like Lisp interpreter written in under 1000 lines of C, featuring a bytecode compiler and VM. It offers a compact yet powerful feature set including proper tail recursion, exceptions, hash tables, a compacting GC, and C FFI support via ctypes-style bindings.

## Use cases
- embed a small scripting language in a C application
- study how a Lisp interpreter and bytecode VM are implemented
- run a fast lightweight Scheme dialect from the command line
- call C functions from a scripting language without heavy dependencies
- learn Lisp with a minimal, readable implementation

## When to choose
- you need a tiny (~150kb), self-contained scripting runtime with minimal dependencies
- you want a fast Scheme-like interpreter that is easy to read and modify
- you need C interop from a lightweight scripting language

## When to avoid
- you need a full R6RS/R7RS-compliant Scheme with a large standard library
- you need native compilation or production-grade concurrency
- you need an actively developed project with frequent releases

## Facets
- artifact type: cli-tool
- maturity: maintenance
- function: interpreter, programming-language
- domain: programming-languages, compilers, developer-tools
- platform: cross-platform, c, cli
- tags: lisp, scheme, small-runtime, bytecode-vm, ctypes-ffi, interpreter

## Member repositories
- JeffBezanson/femtolisp (main) score 32

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:05:26.824586+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T08:32:29.396554+00:00, confidence not recorded.
  - readme: https://github.com/JeffBezanson/femtolisp (fetched 2026-08-28T04:05:26.824586+00:00, sha 7e066c63b9f5)
- Data as of 2026-08-30T08:39:29.467469+00:00.