Lemma

Elixir client for the Lemma rules engine, via precompiled NIFs.

Requirements

Elixir >= 1.14

Precompiled NIF binaries are downloaded automatically for macOS (arm64/x86_64), Linux (gnu x86_64 and arm64), and Windows (x86_64).

Development

To compile the NIF from source (contributors), set LEMMA_BUILD_NIF=1 and have Rust stable on PATH:

LEMMA_BUILD_NIF=1 mix compile

Pre-commit check:

LEMMA_BUILD_NIF=1 mix precommit

Installation

Add to mix.exs:

def deps do
  [
    {:lemma_engine, "~> 0.8"}
  ]
end

Or from git:

{:lemma_engine, git: "https://github.com/benrogmans/lemma", sparse: "engine/packages/hex"}

Usage

# Create an engine
{:ok, engine} = Lemma.new()

# Load a spec
:ok = Lemma.load(engine, """
spec pricing
fact quantity: [number]
fact price: 10
rule total: quantity * price
rule discount: 0
  unless quantity >= 10 then 5
  unless quantity >= 50 then 15
""")

# Run with facts
{:ok, response} = Lemma.run(engine, "pricing", facts: %{"quantity" => "25"})

# Introspect
{:ok, specs} = Lemma.list(engine)
{:ok, schema} = Lemma.schema(engine, "pricing")

# Format source code (no engine needed)
{:ok, formatted} = Lemma.format("spec foo\nfact x: 1\nrule y: x + 1")

# Clean up
:ok = Lemma.remove_spec(engine, "pricing", "2025-01-01")

API

Function	Description
`Lemma.new/1`	Create engine (optional limits map)
`Lemma.load/3`	Load spec from string
`Lemma.load_from_paths/2`	Load specs from file paths
`Lemma.list/1`	List loaded specs
`Lemma.schema/3`	Get spec schema (facts, rules, types)
`Lemma.run/3`	Evaluate a spec with facts
`Lemma.remove_spec/3`	Remove a spec from the engine
`Lemma.format/1`	Format Lemma source code (no engine needed)

See Lemma module docs for full typespecs and options.

Engine lifecycle

Each Lemma.new/1 call creates an independent engine. The engine reference is safe to use from a single process. For shared access across processes, wrap it in a GenServer.

License

Apache-2.0