Elixir

lemma_engine provides precompiled NIFs for Elixir (>= 1.14). Erlang and Gleam use the same package.

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

Install

Add to mix.exs:

def deps do
  [{:lemma_engine, "~> 0.9"}]
end

Or from git:

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

Usage

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

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

{:ok, response} = Lemma.run(engine, %{spec: "pricing"}, %{data: %{"quantity" => "25"}})

Introspect loaded Specs:

{:ok, groups} = Lemma.list(engine)
{:ok, show} = Lemma.show(engine, nil, "pricing")
{:ok, workspace_source} = Lemma.source(engine, nil, nil, nil)
{:ok, stdlib} = Lemma.source(engine, "lemma", nil, nil)

Format source code (no engine needed):

{:ok, formatted} = Lemma.format("spec foo\ndata x: 1\nrule y: x + 1")

API

Function	Description
`Lemma.new/1`	Create engine (optional limits map)
`Lemma.limits/1`	Current resource limits
`Lemma.load/2`	Load sources: binary (volatile); map (lexicographic label order) or `[{label, code}, ...]` (caller order)
`Lemma.list/1`	List loaded Specs (includes embedded `lemma` / `spec units`)
`Lemma.source/4`	Formatted Lemma source (`repository`, `spec`, `effective`; omit `spec` for repo-wide)
`Lemma.show/4`	Spec interface + temporal window (`repository`, `spec`, `effective`). `Show.data` values are `Lemma.ShowData`.
`Lemma.run/3`	Evaluate: `target` map (`repo`, `spec`, `effective`), `options` map (`data`, `rules`, `explain`). Each rule result may include `missing_data` (unbound input keys). Non-veto results carry flattened `display` + typed keys (`Lemma.RuleResult`). With `explain: true`, `explanation` matches api.v1.json (`RuleResult.explanation` / `ExplanationNode`). Types and suggestions are on `Lemma.show/4` only.
`Lemma.remove/4`	Remove temporal slice: `repository`, `spec`, `effective`
`Lemma.update/6`	Replace temporal slice (atomic remove + load); optional source `attribute`
`Lemma.quality/1`	Structural quality recommendations across loaded specs (advisory only)
`Lemma.format/1`	Format Lemma source code (no engine needed)

Lemma.Mcp wraps the engine MCP catalog (run, list, show, source, check, guide, resources). run returns Engine Response JSON with explanations always on. Write tools (add_spec, …) are CLI-only (lemma mcp --write).

Lemma.OpenAPI is a separate module (HTTP OpenAPI document helpers via lemma_openapi). It is not part of the core Lemma engine table above.

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.