Getting Clojure

Let Over Fn

While the ideas behind let aren’t terribly challenging—it binds names to values in a purely local and temporary way—let does have some hidden superpowers, which only become visible when you combine it with fn. To get a glimpse of these hidden powers, imagine our book discounts are customer-dependent. Somewhere we have a map of the user’s name to the discount that user gets:

(def user-discounts
  {"Nicholas" 0.10 "Jonathan" 0.07 "Felicia" 0.05})

We could certainly add some parameters to compute-discount-amount to deal with this:

(defn compute-discount-amount [amount user-name user-discounts min-charge]
  (let [discount-percent (user-discounts user-name)
        discount (* amount discount-percent)
 discounted-amount (- amount ...