Example WIT (example.wit)

Same file as docs/example.wit in the repository. The block is WIT; the book applies TypeScript-style highlighting as a rough approximation.

package rib:language-guide@0.1.0;

// Example WIT for docs/language-guide.md (documentation only; not built by default).

interface inventory {
  /// Integer point (record).
  record point {
    x: s32,
    y: s32,
  }

  /// Stock line (record with string + integer).
  record line-item {
    sku: string,
    qty: u32,
  }

  /// Order lifecycle (enum — mutually exclusive named cases).
  enum order-stage {
    draft,
    placed,
    shipped,
  }

  /// Payment outcome (variant — tagged union with different payloads).
  variant payment-info {
    card(string),
    wallet,
    failed(string),
  }

  /// Permission bits (flags — independent booleans).
  flags file-access {
    read,
    write,
    execute,
  }

  /// Manhattan distance from origin: |x| + |y|
  length: func(p: point) -> s32;

  /// True if quantity is under 1000 (example predicate).
  validate-qty: func(qty: u32) -> bool;

  /// Optional product label for an id.
  lookup-sku: func(id: s32) -> option<string>;

  /// Integer division, or an error message.
  ratio: func(a: s32, b: s32) -> result<s32, string>;

  /// Render enum as a short label.
  format-stage: func(stage: order-stage) -> string;

  /// Describe a payment variant as text.
  summarize-payment: func(p: payment-info) -> string;

  /// Construct a line item from parts.
  make-item: func(sku: string, qty: u32) -> line-item;

  /// Toy summary of which flags are set (embedding may return any string).
  describe-access: func(f: file-access) -> string;
}

/// Shopping-cart style **resource** (per-cart state, constructor, methods).
/// Rib: e.g. `let my-instance = instance();` then `let store-main = my-instance.cart("store-main");` → `store-main.add-line` / `line-count` (kebab exports).
interface shopping {
  use inventory.{line-item};

  resource cart {
    /// Host may treat this string as a logical cart key (e.g. store or session id).
    constructor(id: string);

    /// Illustrative counter — embedder returns how many lines were added for this cart.
    line-count: func() -> u32;

    add-line: func(item: line-item);
  }
}

world guide-demo {
  export inventory;
  export shopping;
}