Clojure for the Brave and True - Chapter 7 infix to prefix notation function

infix.clj

(defn expr-arrange [op]
  (fn arrange [expr]
    (cond
      (<= (count expr) 2) expr
      (= (second expr) op)
        (conj (arrange (drop 3 expr))
              (list (second expr) (first expr) (nth expr 2)))
      :else (conj (arrange (rest expr)) (first expr)))))

(def multiply (expr-arrange '*))
(def divide (expr-arrange '/))
(def add (expr-arrange '+))
(def subtract (expr-arrange '-))

(defn infix [expr]
  "Accepts a list containing a valid mathematical expression and returns an evaluatable expression
  conforming to operator prescedence rules."
  (-> expr
      multiply
      divide
      add
      subtract
      first))

; Usage
(infix '(1 + 3 - 4))
(infix '(1 + 3))
(infix '(1))
(infix '(1 + 3 * 4 - 8))