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<meta name="description" content="A named set of integer constants — names for a magic-number space.">
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  <div class="crumbs"><a href="api.html">API Reference</a> <span>›</span> <a href="api.html#structure">Program structure</a> <span>›</span> <span class="here">enum</span></div>
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    <h1 id="top">enum</h1>
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  <code class="sig">enum Name { A, B, C }</code>
  <div class="desc"><p>An <code>enum</code> gives names to a set of related integer values so a magic-number space — a menu selection, a game mode, a machine state — reads as names instead of bare literals. Variants number themselves from <code>0</code> in declaration order, and you access one as <code>Name.Variant</code>, which is a compile-time <code>int</code> usable anywhere an int is: in <code>match</code> patterns, comparisons, and assignments. When every variant is a bare name, an enum value lives in an ordinary <code>int</code> or <code>var</code> and is saved with it, so a plain <code>enum</code> is best understood as a zero-cost naming layer over <code>int</code>.</p><p>## Tagged unions — variants with payloads</p><p>A variant may also carry a **payload**, written as a parenthesized list of types after its name. Doing so turns the whole enum into a *tagged union*: a value is now one of several shapes, each with its own data, and the type remembers which.</p><p>You **construct** a variant by name — <code>Door(3)</code>, <code>Portal(x, y)</code>, or bare <code>Empty</code> for a payload-less one — and store or pass it as a value of the enum's type (<code>let t: Tile = Door(3)</code>). Each value is a small boxed record: a tag naming the variant, plus its payload.</p><p>You take one apart with <code>match</code>, binding the payload names in each arm:</p><p>A tagged <code>match</code> must be **exhaustive**: it either handles every variant or ends with a <code>_</code> catch-all. Leaving a variant out is a compile-time error (<code>match on Tile is not exhaustive: variant Door is unhandled</code>), so adding a new variant surfaces every site that must learn about it. Constructor and pattern arities are checked the same way. A plain (all-bare) enum keeps its compile-time-ordinal <code>Name.Variant</code> form and is unaffected.</p></div>
  
  <div class="examples"><h2>Example</h2><pre data-lang="ludic">enum Tile { Empty, Wall, Door(int), Portal(int, int) }</pre><pre data-lang="ludic">function walk_cost(t: Tile) -&gt; int {
  match t {
    Empty        =&gt; { return 1 }
    Wall         =&gt; { return 0 }
    Door(n)      =&gt; { return 10 + n }   # n is the door's int payload
    Portal(x, y) =&gt; { return x + y }    # both fields bound in this arm
  }
}</pre><pre data-lang="ludic">program BattleMenu {
  enum Action { Attack, Guard, Item, Flee }

  var current_action: int = Action.Attack

  handler ChooseAction phase Input {
    let pressed = Input.key()
    if pressed == 'a' { current_action = Action.Attack }
    if pressed == 'g' { current_action = Action.Guard }
    if pressed == 'f' { current_action = Action.Flee }
  }

  handler DrawWorld phase Render {
    Screen.clear(Color.MidnightBlue)
    match current_action {
      Action.Attack =&gt; Screen.draw_text(x: 8, y: 8, text: "ATTACK", color: Color.Crimson, scale: 2)
      Action.Guard  =&gt; Screen.draw_text(x: 8, y: 8, text: "GUARD", color: Color.White, scale: 2)
      _             =&gt; Screen.draw_text(x: 8, y: 8, text: "FLEE", color: Color.Gold, scale: 2)
    }
    Screen.show()
  }
}</pre></div>
  
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