MicaLang

Mica is a scripting language and its execution engine, built around a single idea: creating a fully isolated, arbitrarily nestable runtime environment should be a cheap, first-class operation in the language itself.

Syntax borrows a subset of Python, but Mica source is compiled into Mica's own instruction stream and executed by the Mica engine — never through exec/eval. Every VM starts with zero capabilities: its own virtual IO, its own in-memory filesystem, and the ability to create child VMs. Everything else (network, host data, whatever you choose) is granted explicitly, layer by layer, through FFI.

中文文档与项目说明

Status

0.1.0 prototype. The engine is a Python reference implementation (codename Mica-PY): zero runtime dependencies, Python ≥ 3.12, 198 regression tests. APIs and semantics may change before 1.0.

Security note. Mica is designed for isolation, but the current prototype runs in the host process and has not been formally audited. Do not rely on it as the only boundary when executing adversarial code. See the security model (中文) for exactly what is and is not guaranteed.

Install

pip install micalang

The distribution is named micalang; the import package is mica.

Quick start

As a CLI:

printf 'print("hello from mica")\n' > hello.mica
micalang hello.mica        # hello from mica

Embedded in Python:

from mica import MicaEngine

engine = MicaEngine()
vm = engine.create_root("""
sub = VM("print('hello from a child VM')")
print(sub.run())
""")
print(vm.run(), end="")

Grant a capability to a VM (FFI):

def double(x):
    return x * 2

vm = engine.create_root("print(double(21))", functions={"double": double})
print(vm.run(), end="")    # 42

What a Mica VM is

A VM is a cheap, self-contained workspace:

• it cannot see its parent's variables, files, or handles, and cannot tell how deep it is nested;
• it has its own empty in-memory filesystem (text only — structurally unable to touch the real disk);
• resource quotas (instructions, memory, output, child VMs, nesting depth, …) can only be tightened, never loosened, and a child's consumption is charged to all its ancestors;
• its parent can preset files, feed input, single-step it statement by statement or instruction by instruction, snapshot its state, or terminate it;
• it can create its own child VMs — isolation is recursive, because untrusted code is.

Documentation

An English documentation set is planned after 0.1.0.

How this project was built

Mica was developed with AI assistance throughout — design discussion, implementation, testing, adversarial review, and documentation drafting. What the AI did, what the author did, and how outputs were verified are documented in AI-assisted development (中文), with selected conversation records alongside.

Roadmap

• List/dict/string methods and more ergonomic syntax
• Performance benchmarks (child-VM creation cost, per-instruction overhead)
• A normative language spec and a conformance test suite, so a future non-Python engine can be validated against them
• Evaluation of a native engine (the package name is language-level on purpose: micalang survives an engine rewrite)

The name

Mica (云母) is a layered mineral: it cleaves into thin sheets, each sheet complete in itself, and it is an insulator — layers do not conduct into each other. That is the shape of a Mica VM tree.

Not related to the Windows "Mica" UI material, the PyPI bioinformatics package MICA, or the (inactive) Rust scripting language named Mica.

License

Apache-2.0 — see NOTICE.