Example 7: Real-World App — E-Commerce Business Rules

A complete example that mirrors a real application: business rules for an e-commerce platform are kept in .script files so they can change without recompiling the host application, while the C++ layer handles orchestration, persistence, and infrastructure.

Architecture

scripts/test_files/
├── validation_rules.script  # age / username / email / password validation
├── business_logic.script    # user level, discounts, age-restricted purchases
├── reporting.script         # formatting user profiles & purchase confirmations
└── workflows.script         # registration & purchase workflows tying it together

The C++ host loads all four modules into one ScriptManager, registers external functions (strlen, contains, logging, database access), and drives the workflow by calling procedures.

Business rules, in script

User level based on age and tenure:

int32 calculateUserLevel(int32 age, int32 yearsActive) {
    if (age >= 60 || yearsActive >= 10) {
        return 3; // Premium
    }
    if (age >= 30 || yearsActive >= 5) {
        return 2; // Standard
    }
    return 1; // Basic
}

Discount calculation that combines tiered levels with purchase-size bonuses:

int32 calculateDiscount(int32 userLevel, int32 purchaseAmount) {
    int32 baseDiscount = 0;
    if (userLevel == 3) {
        baseDiscount = 20;
    } else if (userLevel == 2) {
        baseDiscount = 10;
    } else {
        baseDiscount = 5;
    }

    if (purchaseAmount >= 1000) {
        baseDiscount += 5;
    }
    return baseDiscount;
}

Country-specific, age-restricted purchases:

bool canPurchaseAlcohol(int32 age, string country) {
    if (country == "USA") { return age >= 21; }
    if (country == "Japan") { return age >= 20; }
    return age >= 18; // Default
}

Driving it from C++

ScriptManager manager;
std::vector<CompilationError> errors;

manager.loadScriptFile("scripts/test_files/validation_rules.script", errors);
manager.loadScriptFile("scripts/test_files/business_logic.script", errors);
manager.loadScriptFile("scripts/test_files/reporting.script", errors);
manager.loadScriptFile("scripts/test_files/workflows.script", errors);

// Native helpers the scripts rely on
manager.registerExternalFunction("logEvent", [](const std::vector<Value> &args) {
    std::cout << "[log] " << ValueHelper::toString(args[0]) << std::endl;
    return static_cast<int32_t>(0);
});

Value result;
std::string errorMessage;
manager.executeProcedure(
    "registerUser",
    {std::string("alice_smith"), static_cast<int32_t>(28)},
    result, errorMessage);

Sample output

Step 1: User Registration
  Welcome, alice_smith! Your registration was successful.

Step 2: First Purchase (New User)
  Purchase confirmed for alice_smith. Total: $180
  Original: $200, Discount: 10%, Final: $180

Step 4: Large Purchase After 10 Years (Premium Level)
  Purchase confirmed for alice_smith. Total: $2250
  Original: $3000, Discount: 25%, Final: $2250

Why this matters

• Separation of concerns — business rules live in scripts (easy to change), performance-critical code stays in C++.
• Non-programmer friendly — analysts can edit .script files without touching the C++ codebase.
• Testable — the full scenario is covered by tests/test_real_world_app.cpp.

This is the same scenario exercised end-to-end by the project's test suite — run it yourself with:

ctest -R RealWorldApp --output-on-failure