C# / .NET

Lemmabase.Lemma.Engine embeds the Lemma engine in .NET 8+ via UniFFI. Prebuilt natives ship for macOS (arm64/x86_64), Linux glibc (x86_64/arm64), and Windows (arm64/x86_64). musl / Alpine is unsupported and fails closed at load.

Install

dotnet add package Lemmabase.Lemma.Engine --version 0.10.2

Usage

using Lemmabase.Lemma.Engine;

using var engine = Engine.Create();
engine.Load("""
    spec order
    data quantity: number
    data unit_price: number
    rule total: quantity * unit_price
    """);
Response response = engine.Run(
    RunRequest.Of("order").WithData(new Dictionary<string, object?> {
        ["quantity"] = 3,
        ["unit_price"] = 19.99m,
    }));
decimal total = ((RuleResult.Number)response.Results["total"]).NumberValue;

Introspect loaded specs:

var groups = engine.List();
var show = engine.Show(null, "order");
var workspace = engine.Source(null);

Format source (no engine instance needed):

string formatted = Engine.Format("spec foo\ndata x: 1\nrule y: x + 1");

Install a repository from LemmaBase (download only; then Load). Default transport is HttpClient; pass a client for tests or custom HTTP:

RepositoryInstallResult result = engine.Install("@iso/countries");
engine.Load(new Dictionary<string, string> { [result.Id] = result.Source });

API

Persist and restore without re-parsing:

byte[] bytes = engine.Snapshot();
File.WriteAllBytes("engine.lems", bytes);
using var restored = Engine.FromSnapshot(File.ReadAllBytes("engine.lems"));

Failure modes

• Planning / request errors → LemmaException with EngineError list (serde JSON).
• Evaluation veto → stays inside Response / RuleResult.Veto.
• Bugs / panics across the boundary → LemmaBugException.
• Native load failures → LemmaNativeException.

Thread safety

Engine is thread-safe: every method acquires an internal lock. Prefer one engine per worker for throughput.

Native library loading

The package embeds lemma_dotnet natives (glibc Linux, macOS, Windows; no musl / Alpine). On first use, the SDK extracts the native for the current platform to a content-hashed cache and loads it. Override:

Cache path: ~/.cache/lemma-dotnet/{version}-{triple}/{sha256}/. Override the cache root with LEMMA_DOTNET_CACHE_DIR.