match Is an Expression

`match` Is an Expression

Unlike switch and if/else, match can appear in value position:

(bind message
  (match status
    (200 "ok")
    (404 "not found")
    (_ "unknown")))

const message = (() => {
  const target__gensym0 = status;
  if (target__gensym0 === 200) {
    return "ok";
  }
  if (target__gensym0 === 404) {
    return "not found";
  }
  {
    return "unknown";
  }
})();

The compiler wraps the match in an IIFE (Immediately Invoked Function Expression) when it appears in value position. Each clause body gets a return instead of falling through. The IIFE evaluates immediately and produces the matched value.

Three Contexts, Three Strategies

The compiler picks the most efficient codegen strategy based on where match appears:

Statement position: plain if-chain, no IIFE
Value position: IIFE with returns (as shown above)
Tail position (last expression in a func with :returns): if-chain with return, no IIFE — the enclosing function provides the return context

The reader doesn’t need to think about which strategy the compiler picks. Write match anywhere an expression goes, and the compiler handles the rest.

Why This Matters

JavaScript has no expression-level multi-way dispatch. The ternary operator handles two branches; beyond that, you need if/else statements assigned to a variable. match in value position — (bind x (match ...)) — is genuinely new to most JavaScript developers, and once they have it, the if/else-plus-let pattern feels like a workaround.

Lykn