// Enable strict in tsconfig.json
{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true
  }
}

// Discriminated union for AST nodes
type Expr =
  | { type: "NumberLiteral"; value: number }
  | { type: "BinaryExpr"; op: string; left: Expr; right: Expr }
  | { type: "Identifier"; name: string };

// Type guard
function isNumberLiteral(expr: Expr): expr is Extract<Expr, { type: "NumberLiteral" }> {
  return expr.type === "NumberLiteral";
}

// Constrained generics
function map<T, U>(arr: readonly T[], fn: (item: T, index: number) => U): U[] {
  return arr.map(fn);
}

// Conditional types
type Unwrap<T> = T extends Promise<infer U> ? U : T;

// module.d.ts
declare module "lea-lang" {
  export function run(code: string): unknown;
  export function parse(code: string): Program;
}