Lykn

Conditionals: if

The most fundamental control flow form. Lykn’s if is a kernel form that maps directly to JavaScript’s if statement.

Simple if

(if (> temperature 100)
  (console:log "boiling"))

if (temperature > 100) {
  console.log("boiling");
}

if-else

(if (>= age 18)
  (console:log "adult")
  (console:log "minor"))

if (age >= 18) {
  console.log("adult");
} else {
  console.log("minor");
}

The second argument is the then-branch; the third is the else-branch. No else keyword — the structure tells you which is which.

Nested if (and Why You’ll Want match)

(if (= status 200)
  (process-response data)
  (if (= status 404)
    (not-found)
    (server-error status)))

This works but reads poorly. Each nested level adds indentation and cognitive load. Chapter 10 introduces match, which handles multi-way dispatch with exhaustiveness checking:

;; Preview — covered fully in Ch 10
(match status
  (200 (process-response data))
  (404 (not-found))
  (_ (server-error status)))

When you find yourself nesting if more than two levels deep, match is almost certainly the better tool.

No cond, No when

Lykn’s surface language doesn’t provide cond (multi-branch conditional) or when (one-branch conditional without else). For multi-branch, use match. For conditional execution without an else, use if without a third argument. For conditional binding, use if-let or when-let (Chapter 13).