1hour-5.clj

(->>
  (let [[h & t] (range 1 10)]
    (reduce
      (fn [l h]
        (mapcat (fn [[a b s]]
                  [[(conj a b) h (str s " + " h)]
                   [(conj a b) (- h) (str s " - " h)]
                   [a (bigint (str b h)) (str s h)]])
                l))
      [[[] h h]]
      t))
  (filter #(= (apply + (second %) (first %)) 100))
  (map #(nth % 2)))

loop

(->>
  (let [[h & l] (range 1 10)]
    (loop [r [[[] h h]]
           [h & t] l]
      (if h
        (recur
          (mapcat (fn [[a b s]]
                    [[(conj a b) h (str s " + " h)]
                     [(conj a b) (- h) (str s " - " h)]
                     [a (bigint (str b h)) (str s h)]])
                  r)
          t)
        r)))
  (filter #(= (apply + (second %) (first %)) 100))
  (map #(nth % 2)))

for

(let [[h & l] (range 1 10)
      r (loop [r [[[] h h]]
               [h & t] l]
          (if h
            (recur
              (mapcat (fn [[a b s]]
                        [[(conj a b) h (str s " + " h)]
                         [(conj a b) (- h) (str s " - " h)]
                         [a (bigint (str b h)) (str s h)]])
                      r)
              t)
            r))]
  (for [[a b c] r :when (= (apply + b a) 100)] c))