Functions as Values

Functions in JavaScript — and therefore in Lykn — are first-class values. They can be bound to names, passed as arguments, returned from other functions, and stored in data structures.

Binding Functions

(func double
  :args (:number x)
  :returns :number
  :body (* x 2))

;; Bind an existing function to a new name
(bind transform double)
(transform 5)  ;; → 10

;; Bind an anonymous function
(bind increment (fn (:number x) (+ x 1)))
(increment 5)  ;; → 6

Functions in Data Structures

(bind operations (obj
  :add (fn (:number a :number b) (+ a b))
  :sub (fn (:number a :number b) (- a b))
  :mul (fn (:number a :number b) (* a b))))

((get operations :add) 3 4)  ;; → 7
((get operations :mul) 3 4)  ;; → 12

First-class functions are why fn exists as a separate form. If functions couldn’t be values, you’d only ever need func — named, declared, called by name. But functions are values, and that means you need a way to create them inline, without a name, as arguments to other functions. That’s fn.

This is also why the Lisp tradition calls functions “first-class citizens” — they have the same rights as any other value. They can go anywhere a number or string can go. The lambda calculus is built on this principle: everything is a function, and functions can operate on other functions. JavaScript inherited this from Scheme. Lykn inherited it from both.

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