I think I have correctly implemented Powerset in Clojure.

(use '(clojure set))

(defn powerset [input result]
  (if (nil? (first input))
    (concat result #{})
    (set (reduce concat
           (for [x input]
             (let [set-of-x #{x}
                   input-no-x (set (remove set-of-x input))
                   next-result (union result (set (list input set-of-x input-no-x)))]
               (powerset input-no-x next-result)))))))

Of course I'm interested in how a library function could make the above a one-liner, but I'm also interested in how the above code could be made more idiomatic.

1. (if (nil? (first input)) feels wrong.
2. Using the let block to replicate imperative calculations. Acceptable?
3. Could I use ->> to make the following line more readable? (union result (set (list input set-of-x input-no-x)))
4. I'm not using recur as I got the "recur must be in the tail position" compiler error.

EDIT Removed (loop) from originally-posted version. - I had erroneously copy-pasted code after I had already commenced attempting to introduce loop/recur (tail recursion). How use loop/recur in this sample?

I think I have correctly implemented Powerset in Clojure.

(use '(clojure set))

(defn powerset [input result]
  (if (nil? (first input))
    (concat result #{})
    (set (reduce concat
           (for [x input]
             (let [set-of-x #{x}
                   input-no-x (set (remove set-of-x input))
                   next-result (union result (set (list input set-of-x input-no-x)))]
               (powerset input-no-x next-result)))))))

Of course I'm interested in how a library function could make the above a one-liner, but I'm also interested in how the above code could be made more idiomatic.

1. (if (nil? (first input)) feels wrong.
2. Using the let block to replicate imperative calculations. Acceptable?
3. Could I use ->> to make the following line more readable? (union result (set (list input set-of-x input-no-x)))
4. I'm not using recur as I got the "recur must be in the tail position" compiler error.

EDIT Removed (loop) from originally-posted version. - I had erroneously copy-pasted code after I had already commenced attempting to introduce loop/recur (tail recursion). How use loop/recur in this function?

I think I have correctly implemented Powerset in Clojure.

(use '(clojure set))

(defn powerset [input result]
  (if (nil? (first input))
    (concat result #{})
    (loop [input result])
      (set (reduce concat
             (for [x input]
               (let [set-of-x #{x}
                     input-no-x (set (remove set-of-x input))
                     next-result (union result (set (list input set-of-x input-no-x)))]
                 (powerset input-no-x next-result)))))))

Of course I'm interested in how a library function could make the above a one-liner, but I'm also interested in how the above code could be made more idiomatic.

1. (if (nil? (first input)) feels wrong.
2. Using the let block to replicate imperative calculations. Acceptable?
3. Could I use ->> to make the following line more readable? (union result (set (list input set-of-x input-no-x)))
4. I'm not using recur as I got the "recur must be in the tail position" compiler error.

I think I have correctly implemented Powerset in Clojure.

(use '(clojure set))

(defn powerset [input result]
  (if (nil? (first input))
    (concat result #{})
    (set (reduce concat
           (for [x input]
             (let [set-of-x #{x}
                   input-no-x (set (remove set-of-x input))
                   next-result (union result (set (list input set-of-x input-no-x)))]
               (powerset input-no-x next-result)))))))

Of course I'm interested in how a library function could make the above a one-liner, but I'm also interested in how the above code could be made more idiomatic.

1. (if (nil? (first input)) feels wrong.
2. Using the let block to replicate imperative calculations. Acceptable?
3. Could I use ->> to make the following line more readable? (union result (set (list input set-of-x input-no-x)))
4. I'm not using recur as I got the "recur must be in the tail position" compiler error.

EDIT Removed (loop) from originally-posted version. - I had erroneously copy-pasted code after I had already commenced attempting to introduce loop/recur (tail recursion). How use loop/recur in this sample?