d expressions inside the lambda. This is useful when instantiating a branch would trigger a compile-time error; we only want the branch to be instantiated when that branch is selected. Here's how it can be achieved.</p>
<p>For simplicity, we'll use a unary lambda as our unary callable. Our lambda must accept a parameter (usually called <code>_</code>), which can be used to defer the compile-time evaluation of expressions as required. For example, </p><div class="fragment"><div class="line"><span class="keyw