ludic/kw-let.html
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<title>let — Ludic</title>
<meta name="description" content="An immutable binding — the default choice for a value that never changes.">
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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">let</span></div>
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<span class="kind-badge kind-keyword">keyword</span>
<h1 id="top">let</h1>
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<code class="sig">let name = value</code>
<div class="desc"><p>A <code>let</code> introduces an <b>immutable</b> binding: once set, reassigning it (<code>name = …</code>) is a compile error. Reach for <code>let</code> by default and only switch to <code>var</code> when a value genuinely needs to change — it makes intent obvious and catches accidental writes. Immutability is of the <b>binding</b>, not the object it points at: a <code>let</code> that holds a property record or a slice still lets you mutate through it (<code>node.current = 5</code>), it just cannot be repointed at a different object. Bindings inside a body are locals scoped to their block.</p></div>
<div class="examples"><h2>Example</h2><pre data-lang="ludic">program Damage {
property Health { current: int = 100, maximum: int = 100 }
model Enemy { Health }
handler Boot phase Start {
spawn Grunt { Health { current: 40 } }
}
handler ApplyHit phase Update {
let incoming_damage = 12
for (health) in query [Health, {Enemy}] {
let survivor = health.current - incoming_damage
health.current = survivor
}
}
}</pre></div>
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