letp.clj

(defmacro letp [expr bindings & body]
  (let [parted
        (partition 3 bindings)
        true-bindings
        (vec (apply concat
                    (map #(take 2 %) parted)))
        false-bindings
        (vec (apply concat
                    (map #(list (first %) (last %)) parted)))]
    `(if ~expr
       (let ~true-bindings ~@body)
       (let ~false-bindings ~@body))))

(letp true
      [x 1 2
       y 3 4]
      [x y])

btw, the above returns [1 3]