An embeddable C# expression evaluator with
compiler-style binding for your .NET types.

using Alder;
using Alder.Compiled;

// The host owns policy, services, AOT metadata, and compiled reuse.
using var engine = new AlderEngine(options =>
{
    options.UseCompiler();
    options.Security = SecurityOptions.Trusted();
    options.Modules.Register<TaxModule>("tax");
    options.Aot.UseGeneratedContext(RulesAotContext.Default);
});

var totalRule =
    "cart.Subtotal - cart.Discount + cart.Tax";

var sampleCart = new Cart
{
    Subtotal = 120m,
    Discount = 20m,
    Tax = 8m
};

engine.SetVariable<Cart>("cart", sampleCart);

if (!engine.TryValidate(totalRule, out var diagnostics))
    return diagnostics;

var total = engine.Evaluate<decimal>(totalRule, new { cart = sampleCart });

engine.SetVariable<Cart>("cart", sampleCart);
var trace = engine.EvaluateWithTrace(totalRule);
Console.WriteLine(trace.Result);  // 108m

using Alder;
using Alder.Compiled;

// The same cart vocabulary works in Dynamic LINQ pipelines.
using var engine = new AlderEngine(options => options.UseCompiler());

var cartsForReview = await db.Carts
    .WhereDynamic(
        engine,
        "Subtotal - Discount >= @0",
        100m)
    .OrderByDynamic<Cart, int>(engine, "ItemCount")
    .SelectDynamic<Cart, CartReviewRow>(
        engine,
        "new { Id, Subtotal, Discount, ItemCount }")
    .ToListAsync();

// IQueryable<T> sources export expression trees. EF Core translates
// provider-safe shapes to SQL; IEnumerable<T> executes in process.

using Alder;

// Extended mode adds compact rule syntax one operator at a time.

using var engine = new AlderEngine(options =>
    options.LanguageMode = LanguageMode.Extended);

var cart = new Cart
{
    Subtotal = 160m,
    Discount = 20m,
    ItemCount = 3,
    PostalCode = "94107",
    CouponCode = "SHIP-2026",
    Channel = "mobile",
    Region = "bay-area"
};

var couponMatches = engine.Evaluate<bool>(
    """cart.CouponCode =~ "^SHIP-[0-9]{4}$" """,
    new { cart });

var localPostalCode = engine.Evaluate<bool>(
    """cart.PostalCode like "94%" """,
    new { cart });

var normalOrderSize = engine.Evaluate<bool>(
    "cart.ItemCount between 1 and 20",
    new { cart });

var knownChannel = engine.Evaluate<bool>(
    """cart.Channel in new[] { "web", "mobile" }""",
    new { cart });

var safeRegion = engine.Evaluate<bool>(
    """cart.Region not in new[] { "blocked", "manual-review" }""",
    new { cart });

var net = engine.Evaluate<decimal>(
    "let net = cart.Subtotal - cart.Discount in net",
    new { cart });

var oddSquares = engine.Evaluate<int[]>(
    "[x * x for x in 1..=5 if x % 2 == 1]");